Official Afshar Experiment Blog Questions 1

Dear professor Afshar,

I was fascinated by the recent experiment made recently by you. Afshar and by its controversial interpretation. I would like to comment that for me there are two fundamental problems in this
experiment. The first problem concerns the use made by you of the Bohr complementarity principle and the second the definition of what we call generally a ''which path experiment'' in quantum
physics.

Let me first explain what is the meaning of the Bohr principle. Quantum mechanics is a statistical theory and by
definition this theory can only give us informations about averages and probabilities obtained by experiments made on many identical systems. In classical physics we can build such models easily for example if we play with a dice. However in classical physics we know that in principle we could describe exactly the motion of the system studied (the dice). In quantum physics we have no such fundamental theory and we must only consider statistical predictions. The problem is that these probabilities are connected to a wave function introducing a strong dualism in the formalism. How indeed to justify the double slit experiment made by Young with particle going to only one slit? It seems that the particle knows magically the presence of the second slit. Bohr and Heisenberg realized that if you would like to build such a theory of what happen in the slits region you would need observations which would disturb or destroy your original system prohibiting then any positive conclusions. Imagine now a photon crossing a double slit you can naturally put a detector just after the slits to see the photon but you will then absorb it and you
will not be able to use it again. Oppositely you can detect the particle on a screen after a lens and observe after statistical accumulation of identical event the famous fringes. You have then a choice between measuring the distribution of particle in the slit screen or to observe the distribution of particle in the fringes plane. But this two choices exclude each others. This is the idea of the principle of complementarity : with a same
particle you can not extract sufficiently of information to reconstruct in a statistical way all the predictions potentially contained in a same wave function. Einstein didn't like very much dices (he prefered cats) and imagined experimental protocols to use two time the same photon and to break down the principle of Bohr. Unfortunately for him and for us all of them failed. The fundamental reason for that is that a quantum system is very fragile by nature and will be immediately disturbed by the measuring apparatus. Now considering the experiment of Afshar we
see that we can observe after the lens two separated spots A' and B' which are images of the two pinholes A and B. Naturally neglecting some losses if you count the number of particle in A' you will know how many particles crossed A and similarly for B' and B. But do you know something about fringes before the lens? Clearly it is not the case. If you want to know something about them you would have to introduce a fringes detector which will disturb the system. Now the wires introduced by you are located at the minimum of the fringes so that the perturbation is very
weak. But in counterpart the information that these wire give us is very small. Imagine that your photon survive to the wire and that it is detected in A' or B' you will be able, as previously, to say by a statistical accumulation of similar events how many particles came from A and B. The spots however will be slightly modified by the wires and the distribution of particle in the slits plane will be slightly uncertain. But now with the same surviving particles you can not reconstruct completely the fringes you will just know that if your particles survive to the wire it it is for sure that the density of particle at the minimum of the fringes is closed to zero. As you see you can not have completely the two informations and the more you know one the less you know the other. This is contained in the principle of Bohr and far to be a counter example your experiment is just one other
proof of its general validity.

The second problem concerns the concept of potential trajectory followed by a photon between the pinholes and the imaging plane. Indeed you not only claimed that he can disprove the complementarity principle but the added that he can effectively determine the path followed by the particle. Following here a old assumption originally enounced by Bohr, Heisenberg and Wheeler,you accepted that even with the two pinholes open a photon trajectory (if trajectory there is) will necessarily connect a pinhole to its optical image as it is if the other pinhole would be closed. However, as is was realized by numerous physicists as de Broglie, Bohm, Bell and Scully, this is a free metaphysical
assumption which depends of our model of reality and which can not in general be experimentally tested [read for example " Surrealistic Bohm trajectories", Englert et al in Z. Naturforsch. Vol 47a , p 1175.]. Effectively nothing in your experiment forbids a photon coming from one pinhole to go in the 'wrong' detector for the second pinhole. This is the case for example in the d eBroglie-Bohm's theory which is an alternative conception of
quantum mechanics.

My conclusion is that in the experiment made by you and presented in New scientist not only the principle of complementarity is still valid but it is not necessary a which path experiment.

Prof. Afshar,
Congratulations on coming up with such an elegant experiment that challenges long accepted concepts in physics.

My question is somewhat similar (I think) to the second question in the 1st comment(although I can't put it in so technical terms :)). how can one prove that the photon coming from one pin hole will definitely end up at the corresponding detector. Is it possible that it gets scattered at the wires and end up at the opposite detector? The absolute dark region of the interference pattern has zero width, so one can not put a wire precisely at that point without blocking some light. There will be some light at the vicinity of the absolute dark point bouncing off the wire. What happens to this light? does this introduce an uncertainty into the detection scheme?
- Mehrdad

Dear Prof. Afshar:
I am in awe of the simplicity of your experiemnt. And, I am very enthusiastic about your results! It has changed my thinking entirely about quantum physics!

Question:
Was the experiment repeated with a single-photon source? If so was the result the same?

Thank you for any information....Kristian

Dear everybody,

Please take a look at my preprint:

http://www.irims.org/quant-ph/030503/

It answers many of your questions. But generally speaking let me provide you with my starting assumptions and some comments:

1) Quantum-Mechanical formalism is completely valid, and should be used to make the calculations for the the amplitudes, as well as the observables in any experiment.

2) According to QM, an image produced by a lens contains the "which-way" information. More correctly, in a double-slit type of experiment, the images of the slits contain the "which-slit" information, given the images are well-resolved and have virtually no overlap. This is based on a long list of literature starting with the original "Heisenberg's Microscope" proof of the Uncertainty Principle, in which the image prodoced by the lens provides the information on the spatial origin of the photon. Wheeler specifically uses this method in his delayed-choice experiment. See the above preprint for more references and detailed argument.

3) The visibility of an interference pattern is defined as : V= (I_max - I_min)/(I_max + I_Min). Notice that when I_min = 0, the V==1; (== means "is identical to"). That means if you find directly, or indirectly that I_min=0, you NEED NOT measure I_max. As long as you know that there is light passing through the wire grid region, and its total flux is not affected by the wires, you have the NECESSARY AND SUFFICIENT criteria for establishing a perfect interference. (See the above preprint for detailed QM analysis).

4) Having establshed that V=1, Bohr's Complementarity demands that K=0 [1], that is the which-way information must be completely lost. For an imaging system like the lens, it means that the images of the two pinholes must overlap completely due to diffraction and scattering caused by the wires. If we were to obtain such a result, Complementarity would have survived, beacuase we could no longer tell which of the two slits the photons are coming from. The actual experimental result is the same as the case in which both pinholes are open and there are no wires: Two crisp images.

5) Some have argued that the wires destroy the which-way information and somehow conspire to produce the same two well-resolved images. As I have indicated in my talks at Harvard, Princeton, TAMU, and elsewhere, I would award a $1000 prize to the first person who can show that the wavfunction of EACH image in the image plane in the case that both pinholes are open, and the wires are present, is a 50/50 mixture of the two wavefucntions emerging from EACH pinhole. I claim that it is impossible to achieve this feat using QM formalism.

6) Please notice that I do not claim that the which-way information in the last case is still 100%, just that it is not 0% as Bohr claims. Mehrdad is correct in that a risidual amount of light hits the wires and is scattered into the wrong image, even when we have a perfectly visible intereference pattern. This is due to the finite thickness of the wires. However, the reduction in the which-way information is quite small (so that which-way information is about 99.99% or better)comapred to the case when only one pinhole is open and the wires are present, simply beacuse in that case the incident flux on the wires is relatively large, and thus the scattering caused by the wires is also considerable. At any event, Complementarity demands that for the case where V=1, the which-way information is 0%. This is clearly not the case in my experiment.

7) Finally, the single-photon experiment has produced the same exact result as my original one.

Best regards.

Shahriar S Afshar

[1] Englert et al in Z. Naturforsch Vol 47a , p 1175. (among many other ref.s listed in my preprint).

Dear Professor Afshar,
I would like to comment your precedent vision.
First I would like to thank you for the online preprint. I Neverthelles remark that the date of this preprint is 2003 in may... Does it means that this article was not accepted or that he was resubmitted??? in addition the name seems to be connected to the los alamos preprint web page. However I can not find it on it.....

Concerning the different points of your comment:

I agree with 1) which is obvious in the context but I desagree completely with 2).
It is not because Heisenberg and Wheeler or even God used this old argument concerning trajectories that it is a good one ...
This idea was criticized by Scully and other as I told you already.

Concerning 3)I desagree too. You think as it will be possible to construct fringes without observing them. With the same kind of reasonning I can prove in basic geometry that by one point only one line goes. Such postulate is obviously false because we need at least a second point. You say that you dont need the complete recording supposing that fringes are here even when you can can not observe them . But your reasoning is circular because it is just what you want to prove.

Naturally I desagree with 4) too because your visibilty is close to zero not to one as you claimed.

I agree with 5) even if it is sad for the 1000 dollars. Obvioulsy I can not prove that 1+1=3.... perhaps it is a good sign for me.

The point 6) is simply wrong because as I said before V=0 (practically). In addition you use the relation of duality introduced by greenberger but I want to mention that
on a quantitative point of view this relation is not sufficiently general to be applied here . D and V refere to a particular class of experiments which seems not to contain your experiment. indeed your knowlege concerning the interference is so weak that the visibility V can not be experimentally defined. Similarly the modification of the spots is not so trivial that the one used in the Greenberger relation. Prudently I will consequently reformulate my sentence : The point 6) is simply wrong because as I said before we know practically nothing about the fringes. (The same remark concerns naturally my discussion of the point 4)....


The point 7 is quite nice for an experimentalist as me. What was the set up?


with best regards

your best reader Aurelien

Dear Aurelien,

The paper was finalized in 2003. However, it was submitted to AJP late September 2004. Since the subject matter is highly controversial, it was necessary to ensure that a few high-ranking experts read, understand and approve of the content of the paper before making it publicly available. I hope you take a deep look into its contents, and respond as rigorously.

Further, the paper is posted on an internal irims.org archive, and not the lanl or arXiv. If you wish to refer to this paper, please make sure you add www.irims.org/quant-ph/xxxxxx

1) Now, are you saying that the wires do not establish V=1?
2) Am I correct in saying that you believe V=0 at the wires?
3) If so, why aren't the wires blocking the decoherent distribution of light at the wire grid?

Regards.
Shahriar S Afshar

Dear Shahriar,

thank you very much for your informations
perhaps i will write a reply but i need at least a reference to your paper so I will probably wait.... I will see

In fact I considered seriously your article before to write my last comment.

There is some point in the text that i could criticized as for example the axiomatic structure based on theorems 1 ,2 and 3 and the fact that this seems not to be connected with the rest of the text but this is for me a detail that the referee will probably see and I hope that he will not refuse the paper for this aspect.

I think that the essential point of conflict between us come from the fact that you believe that there is fringes in front of lens and that you dont need to observe them to prove their existence. I know that you believe in a 'all is wave ' model (me too in fact: funny isn't it ? ) and in this context it is clear that fringes must be here even if I don't observe them. But here we speak about experimental fact and not metaphysical structures. the unical way to see fringes in your experiment is to construct them using a lot of photons as you did in the first experiment. but if you don't put the screen and use your lens with the grid you dont see the fringes and you have not sufficiently of experimental information to conclude that these fringes exist.

A last comment but why did you choose AJP??? this journal is cetainly a very good one but your experiment show something of new or controversial and this is not really the politic of this journal.
(naturally there is a lot of exeptions).

whatever your answer good luck for your article.

best regards
Aurelien

Dear Aurelien,

You can use http://www.irims.org/quant-ph/030503/ as a permanent reference for my manuscript. There are other manuscripts under peer-review right now, but I prefer this one, due to the fact that it is written in a pedagogical sense (hence the submission to AJP.) There maybe some redundancies in this paper, but they are aimed at clarifying experimental and theoretical facts. The theorems are trivial, but one is amazed on how many notable physicists forget to recall them during the discussion of this experiment.

I do not have any particular fondness of the "all is wave" model, but that SEEMS to be the best way to explain the nature of light at this moment. I have designed a series of new experiments, which will directly probe this question... Let Nature reveal herself!

Best wishes.
Shahriar S Afshar

Dear Shahriar Afshar
Thanks for your time,
I would like to know how you can justify the old experiment made by Grangier et al. [1] on the basis of a ''all is wave '' model . by such model I mean a theory where a photon is a continuous and macroscopical train wave which can have a coherence length of several meters (and I dont speak about radio waves). The old semiclassical model of Lamb can not indeed explain all. In particular he fails to justify the coincidence experiment of Grangier. Scully(who worked with lamb as you know) says directly in his book [2] that a semiclassical model fails to justify entanglement. If i detect a photon here this means that the rest of the wave desapears instantaneously .... this old paradox was already pointed out by Einstein.

Personally(because I am old fashioned) I guess that we need at least something as a singularity in the wave to justify all ....


For the rest I think that you are right, I can use your preprint as a reference.

With best regards from Aurelien Drezet

[1] P.Grangier G.Roger A.Aspect europhysics letters 1 pp 173-179 1986.
[2]Quantum optics but you know this reference .....

Your recent experiment is presumed to violate the principle of complementarity by observing both interference and non-interference simultaneously in the same experiment. This contention rests on the belief that there are locations of zero intensity because an interference pattern is present.

We construct an 'Afshar-like' experiment for which this premise is false.

Consider the double slit experiment with circular polarizers covering each slit. Photons passing through slit 1 are now right circularly polarized and photons passing through slit 2 are left circularly polarized.
Each position state is now entangled with a polarization state that acts like a tag attached to each photon. We now know, in principle, which slit the photon passed through. There is no interference.

We now place an x-polarizer, immediately in front of the photon detector. Now, every photon passing through the apparatus is x-polarized before detection. There is no way to determine which slit a photon went through, and we see interference in the angular distribution of scattered photons. The polarization tags have been "erased" by the presence of the x-polarizer.

We now place eraser-detectors at the minima of this interference pattern and no particles are ever detected, as long as the erasers are in place. But, none of the photons passing through the slits ever passes through any of the erasers and no photon tags are ever erased. The position states of these unerased, undetected photons are still entangled with polarization and, when detected, they do not exhibit any interference. This is confirmed when these previously undetected photons impinge on a detector screen.

We now have the essential elements of the Afshar experiment:
a) non-interference at a detector screen and
b) no photons detected at the previously measured positions of an interference minima.

There are locations of zero intensity because the erasers are in place, not because an interference pattern is present. If an interference pattern were present, we would be able to see it on the observation screen. But, we don't; no interference pattern is ever observed anywhere. Your (and Cramer's) claim that if there are locations of zero intensity then there must be an interference pattern present is disproved.

We emphasize that quantum mechanics does not describe the behavior of undetected photons. It only gives us the probability of getting through the apparatus and into the detector. As John Archibald Wheeler has said, "-------, we have no right to say what the photon is doing in all its long course from point of entry to point of detection".

The existence of points of zero intensity does not constitute an observation of an interference pattern for the photons that pass by the wires undetected. Only the actual detection of an ensemble of these previously undetected photons can do that. No experiment can tell us anything about the probability distribution for undetected photons, and quantum mechanics doesn't tell us anything either.

It is meaningless to ascribe an interference pattern to undetected photons.

You can detect both interference and non-interference only if you do two different experiments. In the first experiment, place the observation screen in front of the lens and you will, indeed, observe an interference pattern. But, of course, you are now unable to see non-interference because all photons are intercepted by the screen. In the second experiment the detection screen is placed behind the lens. Here, there is no interference, but now you have no knowledge of what the undetected photons in front of the lens are doing. You cannot perform both experiments simultaneously. Complementarity remains intact.



thomas_marcella@uml.edu

Dear Aurelien,

The "all is wave" approach used in the semi-classical electrodynamics is rather different from my approach. For the past 18 years I have been developing a Theory of Everything in which elementary particles are nothing but "sources" of electromagnetic radiation and thus their dynamics is described by wave mechanics . This is a highly speculative theoretical work and it is not my intention to advertise it here, but it is quite successful in providing the correct relativistic results in calculating the inertial mass of such particles, resolving the dark matter/energy mystery in cosmology, etc. For a primer on this theory of mine, take a look at this link to the abstract

https://commerce.aip.org/jsp/Lookup.jsp?item=APCPCS000458000001001033000001&src=PFtop

I will be posting this paper on my archive shortly.

The main point of my “which-way” experiment has been to shed doubt on the validity of Complementarity and show that insisting on Einstein's definition of photons leads to contradictions in an experiment like mine. What it ultimately means as to the true nature of light, we just simply have to wait for the next set of experiments.

Regards.

Dear Thomas,

As the name implies, the Principle of Complementarity is supposed to be universally valid, i.e. there can be no exceptions where the Principle fails. The experiment proposed by Unruh and (perhaps yours) are two examples of the great many experiments in which Complementarity does survive. It would be very helpful if instead of suggesting your own version of the "Afshar Experiment" and then defeating it, you simply address my arguments in the real "Afshar Experiment," which to my knowledge, is the only one thus far in which Complementarity clearly fails. To be fair, I wish to better understand your thought experiment and perhaps you could kindly e-mail me a short paper with a few equations, and the schematics of your experimental setup. Meanwhile I would appreciate if you could take a look at my preprint and let me know exactly where I have erred:

http://www.irims.org/quant-ph/030503/

In the above manuscript, I clearly mention that "perturbative" means of measurement in which "tagging" and direct destructive detections are made (such as your scheme,) are certainly in agreement with Bohr's Complementarity. It seems however, that Bohr and his colleagues did not recognize that ensemble properties such as the interference pattern can be measured nondestructively. Using nondestructive measurement schemes, one can indeed demonstrate a failure of Complementarity Principle as delineated in my paper.

Regards.

I would like to comment your last message concerning the experiment of Marcella. I agree completely with his last part when he says that we can just speak about what we effectivelly detect. It was what I was saying to you when I was speaking about the problem of the visibility. If you observe your photon in the interference plane you will find fringes with V=1 but of course you dont see the images. If you see the spots you can say nothing about the fringes and V=0 ON an experimental point of view (but ok as i said already it is perhaps nor a good way to speak). It is only when you do the two different experiments that you can controle the relation D^2+V^2 =1 (of course to apply such relation you need to have the right to do it : It is however a good approximation if the wire are not to thick) .

Concerning his proper gedanken experiment I have two remark . First (and this remark is applied to your experiment too) you can not speak of which path without reference to a particular model of reality. In the Bohm model it is not a which path experiment and for this reason I contest the generaltiy of such name (but I will use it now not to confuse you).
Secondly, I dont think that in thisexperiment it is just to tell that there is no fringes at all. There is fringes in this experiment but there are not observed completely. Clearly you see a minimum when you project your state on |R>+|L> or a maximum if you project on |R>-|L>. However this is a proof that it is the eraser interacting with the incoming wave which produce fringes and not as it is claimed that there is no fringes at all. You just select one result or the other by changing of detector. Of course for the photons ouside of the eraser the fringes are not here but it is normal ....

This experiment is then a mixture beween a measurment of the fringes and of the so called which path measurment. For a particular photon you will made one or the other experiment depending in which location it is detected on the screen: mimimum or maximum= fringes and for the rest of the screen =''which path''.

In the Afshar experiment too you need two experiment too in order to have all the interference or the nice spots. But if you put absorbing wires you will have the same situation that in the marcella experiment: photon absorbed = fringes , photon no absorbed = images (''which path'').

These two experiments are then equivalent and both satisfy complementarity. consequently none of them can be used to refute the interpretation of the other.



with best regards
Aurelien

Oh!!! a last thing . what do you think about the experiment propsed by Agarwal [1,2]?
this experimend pretended toot to see something concerning the wave nature and on the particle nature which seem forbidden by complementarity . However as in your experiment thex can just see these two behavior in 2 differents experiments. you see the wave in the bema splitter if you loofk what is happening inside or you see the path if you look oustide but one exclude the other. for you it is the same : you see fringes or you see 2 spots : the rest is metaphysical.

aurelien (bis repetita)

Oh I forgot

[1] Physics letter A 168, 95 (1992)
[2]Physics letter A 328, 313 (2004)



aurelien (again me)

Dear Aurelien,

You haven't really read my manuscript have you? If you had, you would have noticed that I have mentioned Home/Agarwal experiment. Please take a look at paragraph 3, page3, on the Home/Agarwal experiments, and also read Ref. [20] papers on the topic. Their experiment does not measure Complementary wave-particle measurements. Complementary measurements have non-commuting projection operators, i.e. one measurement rules out the other. Interference and which-way are two such measurements, but tunneling and subsequent detection of the photon imply each other not negate one another, which is the requirement of Complementarity. Thus their experiment does not test Complementarity, and is not in the same category as mine.

Please also, read section 3. "Measurement revisited" of my manuscript and critique that. http://www.irims.org/quant-ph/030503/
Regards.

Dr. Afshar,

I know that your currently available paper does not cover intermediate conditions, where V and or K take values between zero and one. I was wondering: What have you found when you do address these conditions? Do any of your other submitted papers deal with this issue?

Regards,

David Strayhorn, MD, PhD
Dept of Neurology
Wash U School of Medicine
Saint Louis, MO

Dear Dr. Afshar.
In your interesting paper you state (p. 2), in logical terms, the complementary principle, for 'sharp' complementarity observables. I think this principle - as stated - must be reformulated, since it is well known that you can get interference, on the screen of a Young two-slit set-up, even when the quantum passed - for sure - through 'only one' of the slits. See the references below.
- L. Janossy, and K. Nagy, Annalen der Physik, 17, (1956), p. 115-121;
- Leonard Mandel, J. Opt. Soc. Amer., 49, (1959), p. 931;
- R.M. Sillitto and Catherine Wykes, Physics Letters, 39-A-4, (1972), p. 333, who performed the Janossy and Nagy experiment and found a good interference when just one photon was present in their interferometer, at a time, and when an electro-optic shutter was switched several times during the time travel of each photon, closing one of the two slits, and then the other (but reopening the first), so that it was sure that the photon went through 'only one' slit.
In terms of photons the condition for interference was that the two paths lead to the same cell of phase space, so that the path of each photon was intrinsically indeterminate. Of course, if you close one slit, and then the other (and the first reopens), the shutter must be switched in a time which is less than the
uncertainty in the time arrival of the photon at the screen.
I'm inclined to think that the principle of complementarity (for 'sharp' observables) must be reformulated in a more general way, in terms of 'indistinguishability' of paths.
I have many more questions to ask but, for now, I thank you very much.
Regards,
Serafino Cerulli-Irelli (Rome)

dear Shahriar,

I read your paper but i didint watch all the references. in addtion I wrote my letter at midnight (I have not a lot of time to consider your experiment ) so please : mea culpa.

However this doesnt change any thing and I just give the Home/Agarwal experiment to point out some similitudes. first I agree that their definition of what they call complementarity is wrong : they see a wave going through a beam splitter and they deduce that there is an evanescent wave. for me it is not in contradiction with Bohr because the wave particlwe duality is a characterist of ALL experiments. In this sense they confuse wave particle duality and complementarity .
However we can analyse the complementarity with this experiment too

Indeed the key point is that they never observe this evanescent wave as. If they want to observe this wave they will change the experiment drastically . I recall you that the transmission of the beam splitter increase when the two prisms are closer . you change then at the same time the reflection. This prove that the two surface constituiting the gap are fundamental and that there is a superposition of different ''counter propagative''waves in the cavity (in the sense of evanescent waves). Consequently your argument is wrong : the two projector of the wave in the cavity and ouside doesnt commute at all ...

the rest of my argumentation is still true : you can not see a photon without eyes and the rest is theology

regards
aurelien

Is Serafino Cerulli-Irelli saying that we can see interference with only one wave ? Can we hear the clap of one hand too ? I have some doubt.... but science is funny .

If you want to see interference you need a contribution from each apertures a think that this is clear .... I hope

Because Mandel was a solid physicist perhaps I forgot something but what .....

aurelien

Yes, I'm saying exactly that. Of course here the 'indistinguishability' is (perhaps) related to the time-dependent Schroedinger equation. So it is a sort of time-energy 'indistinguishability'. Please read - if you can - those papers by Mandel, and Sillitto and Wykes. I read those papers years ago, and my memory is a bit chaotic! (Janossy & Nagy old paper was just a gedanken experiment, pointing out that if we use a random macroscopic shutter/opener, or something like this, we could be aware of the 'welcher weg', standing outside the set-up, thus our 'consciousness' should collapse the superposition ...).
Regards,
s.

Sorry. I forgot to say that, in principle, it is not so different from the 'one single photon - emitted by two different sources' interference, in which you combine two amplitudes (giving interference) one related to a source, and the other related to the other source. Here (Sillitto and Wykes exp.) there is just one source, but the shutter/opener, moving very fast, gives a similar effect: 'indistinguishability'.
s.

Dear David,

I am working on a theoretical paper to address the intermediate stages in V and K. I'll post it here as soon as it is finished (in a couple of months.)

Regards.

Dear Serafino,

QM is weird, but not that weird! It is impossible to produce interference effects for a photon the wavefunction of which does not receive-at least partially- a contribution from both slits/paths. So, I am positive you have misunderstood the papers' conclusion. I'll try to take a look though...

Regards.

Dear Aurelien,

I am starting to feel like I am in a Seminary! Your "mea culpa", "you can not see a photon without eyes and the rest is theology" and Serafino's "thus our 'consciousness' should collapse the superposition"!!!

But seriously, I certainly agree that if one does not detect a photon, talking about its behavior is simply beyond what physics allows, however, I do detect all the photons in my experiment in the image plane. Once you detect a photon, it's past behavior can be discussed within the limits allowed by the laws of physics as we understand.

All the photons arrive at the two images having passed the wire grid region. So physically-speaking, we know that (i) they could not have come from any other region, and (ii) there was no significant reduction in the total flux. The only way such an attenuation-free passage is possible is to say that there where no photons incident on the wires (physics demands that if photons were incident on the wires, they should be blocked). The only way to achieve no incident flux on the wires, is to use QM and figure out a process by which it can happen. That process is interference and no other process exists to explain it. In fact if there is another means by which the photons can avoid hitting the wires, then we would have a discovery on out hands, something our known laws of physics do not allow!!! But I highly doubt that: Interference happens before the lens, and Fourier does his magic with the lens to give us which-way information, all within the known laws of physics. We are forced to wake up and face the fact: the only bit of discrepancy and "theology" (or even the occult) here is Complementarity and it needs to go back where it came from: a Buddhist monastery.

Regards.

Dear Shahriar ,
It is true that the quantum physics comunauty looks very similar to a sect but I dont want to enter in this debate here.

The problem in your argumentation seems to be again connected with the fact that you know that a wave function is necessary to explain all evolution of the probability in space in time and that neverthelles you dont observe these fringes. I think that you are more religious that Bohr on this point :

YOU believe that fringes are Here even when we dont observe them and then YOU believe that we don't need to measure them ( a minima of absorbtion at the wire position is in fact a partial measurement of the intrterference fringes). This is the exact opposite of the point of view of Bohr.
Following Bohr the wave is hereas a tool but not effectivelly realized (i.e it is just a potentiality) and the the unical way to transform potentiality into a fact is to detect your photon. The rest is really metaphysic theology or science fiction.....

Dont think however that I like Bohr so much ( I prefer Einstein and deBroglie) but I just defend his point of view effectivelly because I dont believe in it (in order to clarify my proper conceptions I mean).



alea jacta est

aurelien

5) Some have argued that the wires destroy the which-way information and somehow conspire to produce the same two well-resolved images. As I have indicated in my
talks at Harvard, Princeton, TAMU, and elsewhere, I would award a $1000 prize to the first person who can show that the wavfunction of EACH image in the image plane in the case that both pinholes are open, and the wires are present, is a 50/50 mixture of the two wavefucntions emerging from EACH pinhole. I claim that it is impossible to achieve this feat using QM formalism.

I believe there is a very simple argument which provides the proof required.

The wavefunction at the lens is a sum of the wavefunctions originating from each pinhole. Under certain assumptions (which apply in the case of your experiment) the two wavefunctions can be said to have the same amplitude at each point in the plane of the lens (although the amplitude varies in this plane). The only difference between the two wavefunctions is the way the phases vary in the plane. In some places the phases are such that the total amplitude is zero (where you place your wires), and in other places the phases are the same giving maxima in the interference pattern. As the amplitudes from the two pinholes are the same, the total amplitude at any point can be said to be a 50/50 mixture of amplitudes orignating from the two pinholes.

So far so obvious. Now, the Schrodinger equation is a wave equation and therefore obeys Huygens Principle: The amplitude of a wave at any point in space can be treated as a new source of a wave. Therefore the plane at the lens can be treated as a new source of waves. It is clear that the total amplitude at every point in this plane has a 50/50 contribution from each pinhole and so, when we propagate it forwards, any future amplitude will be made up of a 50/50 mixture from the two pinholes. Therefore when a photon is detected at one of the two detectors it can be said to be made up of a 50/50 combination of photons from each pinhole.

The complementarity principle is an attempt to describe the behaviour of the quantum formalism. If the complementarity principle says something which disagrees with the quantum formalism then the complementarity principle is an incorrect statement and needs to be amended or discarded. In this case the complementarity principle says that, since you can indirectly detect the interference pattern you cannot know any which way information about the photon. The above argument shows the complementarity principle still holds.

Please reply to my e-mail address and we can sort out the transfer of the $1000.

Dear Dr. Afshar.

"It is impossible to produce interference effects for a photon the
wavefunction of which does not receive -at least partially- a contribution
from both slits/paths."

I agree with that, of course. The trick is to get two different paths having
just one slit opened for a very short time, and then the other for a very
short time. Now imagine a *single* photon entering this peculiar
'interferometer'. The condition for having the interference (tested also in
case of *single* photons) is that the two possible and different paths
(first slit closed, second opened + second slit opened, first closed) can
lead to the same point of phase space. This occurs if the shutter operates
its switching in a time (Heisenberg's delta t) which is *less* than the arrival
time of the photon at the screen. In this case the 'which path' the photon
took is uncertain (like in the usual two-slit) but it is also evident that
the photon passed through 'only one' slit, because only one slit was opened.

Regards,
s.

Correction, of course!

The condition for having the interference (tested also in
case of *single* photons) is that the two possible and different paths
(first slit closed, second opened + second slit CLOSED, first OPENED) can
lead to the same point of phase space. This occurs if the shutter operates
its switching in a time WHICH IS LESS THAN THE UNCERTAINTY of the arrival time of the photon at the screen (Heisenber's uncertainty).

s.

Dear Aurelien,

Am I right in saying that according to your view, there is negligible flux on the wires? If yes:

1) Then we have no choice but to declare that the cause of this lack of incident flux is destructive interference. There simply is no other process by which a certain regions of space (wires) do not receive flux, while we KNOW that regions close to the wires do (we see all the photons at the image plane).

2) If you dont agree with (1), then please tell me how you can use QM to show a particular region CONTINUALLY receives no flux, without assuming interference as the cause.

Regards.

Dear Morgan,

"The only difference between the two wavefunctions is the way the phases vary in the plane. "

Bzzzzz... Wrong answer!

The two wavefunction also have an ANGULAR separation due to the fact that they are coming from two distinct spatial locations. The wavefunction is (at least) a 3D VECTOR entity and not a vector in certain dimensions (so you can have interference) and a scalar in the other. As any good advanced physical optics textbook can demonstrate, a lens operates as an ANGULAR discriminator, and the linearity of the Fourier transform ensures that a suitably placed lens can resolve two sources of certain minimum angular separation. That minimum ANGULAR separation is the lens' resolving power. If you doubt this, then you must boldly announce that Heisenberg’s Microscope proof of the Uncertainty Principle is also wrong, because he uses the lens to obtain the “which-way” information for the photon that scatters off an electron, and the spatial resolving power of the lens enters the delta_P . delta_x >h relation as delta_x…

Sorry, NO $1000 prize for you!!!

Regards.

Regards.

Dear Serafino,

I'll get back to you after I read the papers you mentioned.

Regards

Several people have claimed that your experiment falsifies the many-worlds interpretation, but I falied to find any statement to that effect in your paper. Have you made this claim, or is it just others?

Dear Jim,

I claim that my experiment rules out Complementarity as a “Principle” that has no exceptions.
Generally, I am not very fond of "Interpretations", but from my limited exposure to MWI, it does not even qualify as a viable theory because it seems to violate conservation of linear momentum in interference experiments, as I have pointed out to David Deutsch in the past. One does not need my experiment to question the validity of MWI, but if others think my experiment rules it out, I have no quarrel with that!

Regards.

On Aurelien's theological/metaphysical point of the need to validate fringes, can you replace the wires by optical fibres (they may need to be roughened to transmit through their walls) and tap at least some proportion of photons which may impinge (when not destructively interfered away)?

Regards.

Dear Tom,

Yes, you can. Better still, you can plcae a thin array of photodetectors that form a line not thicker than 1/10 of the peak to peak distance of the fringes. I predict that the results WILL BE identical to mine.

Regards.

Dear Shahriar,

I am a little confused by your response, and I don't think you have discredited my proof.

"The wavefunction is a 3D VECTOR entity and not a vector in certain dimensions (so you can have interference) and a scalar in the other."

No it isn't, and I'm not sure how you got this from my previous post. The wavefunction is a complex scalar field, which means at each point in space there is a complex number. This complex number has an amplitude and a phase.

Perhaps I can clarify some of the words used in my proof. Wherever I say "the plane", "this plane", or "the plane of the lens" I am referring to the physical plane parallel to your sigma1 plane which goes through the lens. The argument is just as valid for your sigma1 plane too, however. Wherever I say "amplitude" I am refering to the magnitude of the wavefunction. So wherever I talk about amplitudes or phases varying in the plane I am referring to the magnitude and the phase of the wavefunction being different at different points in space(specifically in the specified plane).

"As any good advanced physical optics textbook can demonstrate, a lens
operates as an ANGULAR discriminator, and the linearity of the Fourier transform ensure that a suitably placed lens can resolve two sources of certain minimum angular
separation. That minimum ANGULAR separation is the lens' resolving power."

I agree with this entirely, and so Heisenberg's Microscope proof is safe!

Coming back to the statement that you disputed,

"The only difference between the two wavefunctions is the way the phases vary in the plane. "

The wavefunctions from the two pinholes can be calculated explicitly, but it really isn't necessary for the argument I provide. These two wavefunctions are identical except that their centres are separated by the distance between the two pinholes. This separation persists as we get further from the pinholes and the two wavefunctions start to overlap significantly. By the time we reach the lens we can see that the radii of the Airy discs from the the two pinholes are much larger than the separation of their centres (using numbers from your paper about 20mm compared to 2mm). Therefore the magnitudes of the wavefunctions from each slit are always roughly the same, and the approximation that they are the same gets better the further the lens is placed from the pinholes.

Also the distance between neighbouring maxima in your interference pattern is much smaller than the total size of the Airy disc because the phases from each of the two pinholes are varying faster than the amplitudes as you move around the plane of the lens.

Since the amplitudes from the two pinholes are approximately the same at each point in the plane of the lens, the natural conclusion of my argument using Huygens principle is that approximately half the photons coming from each pinhole end up at each detector.

I still think I am due the $1000.

Morgan

Dear Morgan,

"These two wavefunctions are identical except that their centres are separated by the distance between the two pinholes."

No! The two wavefunctions are NOT identical (regardless of their spatial separations.) Crucially, they have a different ANGLE of INCIDENCE. That angular separation is what allows the lens to form two distinct images of the sources. The purpose of this blog is not to teach Physical Optics. I suggest that you formally study the subject [1] or ask an expert in the field to explain coherent imaging theory for you. But to quickly remind you of why you are wrong, think of two distant stars with a small angular separation. The physical lateral separation of the stars may be many hundreds of light years, but the lens could care less about that spatial separation, because all it does is to separate the two sources based on the slight difference in the angles of incidence of the two beams. To think otherwise simply demonstrates lack of knowledge in the field.

"I agree with this entirely, and so Heisenberg's Microscope proof is safe!"

Well if the imaging theory used in Heisenberg's proof is safe, so is mine, which is exactly the same argument. If you reflect on your statement a little, you would realize that your above statement undermines your original claim.

I am sorry for the emphatic tone in my response, but this experiment is far too important to be dismissed by patently erroneous arguments. Simply repeating a false claim does not make it true!

Regards.

[1] For starters, please take a look at the Fourier Optics section (p. 512) of Hecht’s book called Optics (3rd Edition).

Dear Prof. Afshar!

Will You agree that standard quantum theory brings formal procedures to calculate probabilities of elementary processes only. Quantum mechanics does not supply an EXPLAINING MODEL of "weird" behaviour of quantum objects, does it? And this is what distinguishes QM from ALL the other scientific traditions. Science should provide EXPLAINING MODEL (underlying picture, in John Cramer's words).

I have read John Cramer's paper, saying Your experiment seems to verify his transactional interpretation of QM (TIQM). I believe that TIQM is one step to pecome a MODEL, not simple an INTERPRETATION. You can view the MODEL I propose via the reference I supply.

I would be happy to know Your (and anybody's else) criticism. Please email me: kurakin.pavel@gmail.com. Thank You.


-----------
P.S. For those who are interested.

I proposed a conjecture that Cramer's transactions can happen in HIDDEN TIME, not equivalent to physical time. One may treat hidden time as true physical entity or as a mathematical object (like wave functions) only, I don't care. I only proposed an formal algorithm, how hidden time must relate to physical time ("sewing procedure").

I unmodestly think that "transactions in hidden time" concept is the only serious PHYSICAL hypothesis of last decades. Not an overcomplicated mathematical trics, which govern quantum physics for last decades, but a PHYSICAL idea. Three basic ideas bring a radically new concept in quantum physics:

1) Feynman's many-path formulation of QM
2) John Cramer's TIQM
3) When amplified by HIDDEN TIME, (1) + (2) make a new PHYSICAL MODEL of quantum phenomena (NOT an interpretation).

Dear Dr Afshar,

I am very interested in interpretations of QM. As soon as I heard about the availability of your preprint, I downloaded it.

I am having difficulties understanding the aim of your experiment. Only your Figure 1 shows a classical interference setup between the two pinholes, and the scan of the field intensity, essentially at infinity, is the classical interference pattern.

In Figs 2 and 7, the scans of field intensity are not taken at infinity, but the other side of a lens, in the plane of the image of the two pinholes. Hence a full-blown classical interference pattern with pronounced minima is not to be expected.

In media reports of your work, emphasis has been placed on the lack of difference between Figures 2 and 7. Your wire grid is well clear of the plane of the pinholes or of the image, so it is totally out of focus, and it would not be expected to lead to large differences in the shape of the profile in the two cases. However, on close examination, there are differences in the shoulders of the images of the two pinholes. You are working close to the diffraction limit, and I would expect that the wires would lead to increased oscillatory behavior of the sidelobes of the resolving function. This is quite consistent with what you have observed.

In fact you appear to agree that your results are in perfect accord with the quantum formalism. This is just what I might expect. The analysis of your set-up is a lot simpler than the calculation of the Lamb-Rutherford splitting or of the g-factor of the electron.

Bohr is now dead; he set the quantum revolution in motion but was not totally omniscient. His simplistic version of quantum theory is now just of historical interest. By all accounts he was a bit of a mystic and enjoyed the blockage of thought his complementarity principle led to. The sound of one hand clapping. Now, half a century later, even though we still don't understand completely what QM means, we have a lot more experimental results to draw on. Bohr thought that single atoms were not "things" and could not be directly observed, but now we have a number of techniques at our disposal that allow us to do just that. It seems to me that you are setting up a straw man and knocking it down. Is there anyone out there who seriously supports the narrow interpretation of Bohr's which-way argument? Any serious physicist would do the calculations and predict the result which you have observed. There are much more important aspects of the Copenhagen interpretation to be clarified, in particular the existence of wavefunction collapse, and the questions of non-locality and causality.

Cheers,

Zigoteau.

Dear Pavel,

The primary goal of Science is the discovery and categorization of Natural phenamena, discovery of interconnectedness of such phenomena, and testing of hypotheses that predict a certain relationship between these phenomena. Therefore, as long as a theory is successful in providing the correct answer for a given initial condition, the theory is a successful model. Modern physical theories have mathematical structures, and are precise within the confines of the mathematical limits. As to why a certain set of mathematical relations happens to have a physical manifestation, one has to resort to philosophy, or even metaphysics. As an example, Newton's law of gravity was a perfect solution to the apparent backward motion of planets in the line of site of observers on earth, but so were the Ptolemaic epicycles. Newton's ideas were accepted because it explained a lot of other seemingly disparate phenomena like the tides, the orbit of the Moon, falling of an apple, (as well as established evidence for the heliocentric worldview such as the moons of Jupiter and the phases of Venus, etc.) But when ultimately Newton was forced to give an answer as to what lies behind his theory, and what "causes" gravitation, he avoided that question and said "I propose laws, and cannot be bothered with hypotheses." Einstein answered that question partially, and we ended up with a powerful new model the GR.

So, as an experimentalist, I only wish to test validity of most commonly agreed upon theories and concepts to advance science. As a theoretician with a philosophical bent, I enjoy trying to answer question like why is there inertia (e.g. see my paper: https://commerce.aip.org/jsp/Lookup.jsp?item=APCPCS000458000001001033000001&src=PFtop ), or why does QM work. As more and more phenomena are explained better and better, the role of physicists as Natural Philosophers becomes critical in finding out the answers to these "hidden" mechanisms, and I wish to do my little part in that realm as well.

I will visit your site and get back to you soon.

Regards.

Dear Zigoteau,

"...you are setting up a straw man and knocking it down."

This "straw man" has scared generations of physicists away from asking some of the most fundamental questions about QM long before I was even born, so I can hardly be blamed for his appearance. Bohr's Complementarity is the rite of passage for new initiates, and almost all textbooks on QM mention it. Therefore, it was essential that an experiment like mine clearly demonstrate that Complementarity is not a part of the QM formalism and is in fact incorrect. My experiment validates the QM formalism and invalidates Bohr's Complementarity.

The question of wavefunction collapse will be investigated in the next set of experiments I am currently preparing.

Regards.

Dear Shahriar,

Thanks for your response. The relevance of what you have achieved in your experiment is now sinking in gradually.

In a way, it is related to Hund's paradox, to which I have given a certain amount of thought recently. That's the Hund of Hund's rule for the spin occupation of degenerate orbitals, amongst others. Anyway Hund pointed out way back in the 1920s (I think) that a chiral molecule cannot possibly be an eigenstate of the Hamiltonian, which essentially commutes with reflection in any plane (coupling via the weak interaction with nuclear spins is negligible for organic compounds and does not invalidate the paradox). The true eigenstate must be a superposition of the two enantiomers, so that according to CI, observation of chirality should lead to immediate racemization. Experimentally, it does not.

Good luck and best regards,

Zigoteau.

Dear Prof. Afshar!

Thank You so much for Your reply.

1) I would be happy to get aquainted with Your electromagnetic theory of inertia, because I believe that in SOME SENSE such theories must be valid. As A. Polyakov, a distinguished specialist in superstrings pointed, "any untrivial idea is valid in some sense."

But unfortunately, Your paper on is not free-- and online-- accessible at the URL You pointed.

2) Yes, I do agree that laws of physics are laws of physics, regardless how easily they are viewed and conceived. And laws (equations) are not obliged to seem "explaining" and easily imaginable. As Heisenberg once noticed, for ancient Egyptians a river flowing NOT in meridianal direction was unimaginable.

Still the science, I believe, does move to more and more clarity, simplicity and visuality in its formulations. Say, Feynman's many-paths formulation of QM is VERY visual and conceivable, compared to Heiseberg's formulation in matrices.

Please note, that A. Einstein's parer "Zur elektrodynamik bewegter korper" DID NOT provide "pridictions, distinguishable from current knowledge" and thus today's "Physical Review" would NOT accept that paper for publishing.

What Einstein's classical paper DID supply, was a new kind of logical ordering of previous knowledge, and nothing more. So, logical unity and clarity (including, if possible, visuality), I believe, has scientific validity in its own.

3) Dear Prof. Afshar, please do believe I imagine a huge busyness of a scientist like You. I kindly ask You not to be too polite. If You are not interested in a new model, take it easy.

But if You do move towards my proposal, I wanna move towards too, and I wanna propose You significantly shorter paper I proposed at first:

http://time2050.narod.ru/texts/dettime.html

It is the heart of our approach, currently developed at Keldysh Institute of Applied Mathematics, Russian Academy of Sciences.

Thank You for Your attention and sorry for trouble.

Dear Dr. Afshar,

Thank you for your reply regarding intermediate values of V and K. I suppose I'll go ahead and post my thoughts on the issue that prompted my question. I have been contemplating how V and K might vary as functions of the thickness t of the wires: V(t), K(t). If t = 0, then this is basically the same as no wires at all, so V(0) = 0 and K(0) = 1. Following the reasoning of your paper, if we set t to some arbitrarily small but nonzero value, then K(t) remains (approximately?) 1, whereas V(t) jumps from 0 to 1. This change in V(t) from 0 to 1 appears to indicate a discontinuity in V(t) at t = 0. Do you agree with this line of reasoning? Do you think there is a theoretical lower limit to the size of the wires? What if they are no thicker than an atom? If you think there is no lower bound, then how would you justify this sudden "jump" in V(t)?

One further thought. On page 9 you make the argument that "all we need to establish perfect visibility is to determine I_min = 0." Are you arguing that it is sufficient to show that I_min is less than some very small value epsilon, or -- alternatively -- does your argument rely on showing that I_min equals zero *exactly*? (I suppose that the former is sufficient, *if* it is possible to calculate a lower bound on I_max based on the total flux at the detector, in which case all you need to observe is that epsilon in which all you need to observe is that epsilon is much much less than the lower bound of I_max, therefore (by eqn 2 of your paper) V is very close to 1.

Regards,

David Strayhorn

Dear David,

You are correct. The physical limit is that the wires must be “opaque”, i.e. their thickness must be at least ~5 lambdas. Also, note that there are no real zeros in experimental physics, and the "epsilon" you mentioned depends on the margin of error (MOE) of your photo-detection process (for a given wire thickness, the higher the signal/noise ratio, the lower the epsilon). So essentially, the upper bound for the thickness is determined by the MOE, and the lower bound is determined by the opacity requirements.

Regards.

Dear Pavel,

Please give me a couple of months for things to slow down a bit. By then I will have had a chance to think about your approach. But I genrally agree with you that ultimately the TOE will be a readily visualizable theory, so obvious that most people will understand its foundational concept(s).

Regards.

Dear Shahriar ,
So many comments during this week end!!!
(who is this zigoteau ???? I like his name a lot probably french I suppose )
I will just concentrate on our discussion.

You justify your point of view in such a way that I can only agree with you: the unical known quantum process which can explain the presence of zero on the wires is fringes. This is clear and I never claimed that the formalism is wrong. If you put your detector in the interference plane you will see for sure these fringes there is no doubt . But Bohr was the most prudent physicist of his time and he prefered to say that when you close your ''eyes'' you are sure of nothing in particular in quantum mechanic. It was for him the unical way to solve the wave particle duality. I like particulary this sentence of him:

''since it is only the circumstance that we are presented with a choice of either tracing the path of a particle or observing interference effects, which allows us to escape from the paradoxical necessity of concluding that the behaviour of an electron or a photon should depend on the presence of a slit in the diaphragm through which it could be proved not to pass. We have here to do with a typical example of how the complementary phenomena appear under mutually exclusive experimental arrangements and are just faced with the impossibility, in the analysis of quantum effects, of drawing any sharp separation between an independent behaviour of atomic objects and their interaction with the measuring instruments which serve to define the conditions under which the phenomena occur.''
Bohr [1949]

On this point he was unfortunatelly wrong because hidden variable models exist which predict with succes all the effect of the quantum universe (see de Broglie and Bohm with some problems for the relativistic model , and the many world model of everett that i interprettas a hidden variabel theory where the the the dynamical value of the system ar just the observables of the formalism) and in particular the wave particle duality. However his point of view concerning complementarity is absolutely non refutable as well that we accept the validity of quantum mechanic.

You can said that there is fringes or that there is 2 spots but YOU will never be able to USE THE SAME PHOTON in the two experiments.

You never effecvelly reconstruct experimentally the fringes point per point ( your prefer to deduce them on the basis of the theory )so i am right when I say that your fringes are metaphysical and that the unical part of the firnges which is experimentaly real is the one absorbed by the wires ..... and i am right when i said that your reasoning is circular.


with best regards


Aurelien Drezet

Dear Shahriar,

"this experiment is far too important to be dismissed by patently erroneous arguments. Simply repeating a false claim
does not make it true!"

I agree. One can't use forcefulness in a scientific argument. One has to address the issues with clarity and an open mind.

"No! The two wavefunctions are NOT identical (regardless of their spatial separations.) Crucially, they have a different ANGLE of INCIDENCE. That angular separation is
what allows the lens to form two distinct images of the sources."

I don't need to read an optics text book, thanks. The optics I learnt at high school is sufficient for this problem: Regardless of the presence or absence of an angular difference between the two wavefunctions, the lens will focus the light from each pinhole to a separate point. That's what lenses do, map one point onto another.

"But to quickly remind you of why you are wrong, think of two distant stars with a small angular separation.
The physical lateral separation of the stars may be many hundreds of light years, but the lens could care less about that spatial separation, because all it does is to separate
the two sources based on the slight difference in the angles of incidence of the two beams. To think otherwise simply demonstrates lack of knowledge in the field."

I think I see the point of confusion. The lens discriminates the angular separation of the stars. The angle in question being defined by star1--centre of lens--star2. In your experiment the angle is pinhole1--centre of lens--pinhole2. The only difference between the two cases is that a star is (usually) an isotropic emitter of radiation whereas a pinhole is not. A pinhole emits more strongly in some directions than others: it is not these directions that the lens is discriminating. I believe that when a pinhole in a plane is illuminated from behind, most of the light is emitted perpendicular to the plane in something called an Airy disc (there are also higher order diffraction rings at other angles). Hence my assertion that the wavefunctions from the pinholes should be identical apart from a lateral translation.

As I read your paper you have a plane wave impinging upon a pair of pinholes in a flat barrier. The wavefunction from one will be identical to the other, apart from a translation. Perhaps you have curved the barrier such that the two wavefunctions come out at different angles, but this is not stated in the paper. Also, it seems unlikely because eq 7 in your paper can only have been obtained by making the assumption that the two wavefunctions are essentially the same (ie same amplitudes but different phases). This is the exact same assumption that you have been disputing.

Anyway, the presence or absence of an angular difference is also entirely irrelevant to my argument which you still have not addressed.

Morgan.

Hi! I'll respond as soon as I have the time. Meanwhile, please feel free to talk amongst yourselves...--S

Aurelien Drezet writes:
'You can said that there is fringes or that there is 2 spots
but YOU will never be able to USE THE SAME PHOTON
in the two experiments. '

I would say that it is possible that a photon is a carrier of a limited amount
of information, say 1 quantum of information, say 1 bit. So it is difficult
indeed to get from a photon (= a quantum of information) information
about *both* non-commuting (sharp) observables, since this information
is expected to require more than 1 bit. It is, of course, possible to get, from
a photon, information about *both* non-commuting observables, but this
information is a probabilistic one (Greenberger, YaSin, Englert, Zeilinger,
Wootters, Zurek, etc.).

Now there are two points.

Afshar's 'little wires' give us direct information about the absence (nearly) of photons, in those points. This is not a *direct* information of the presence ('visibility') of 'fringes' elsewhere. Nevertheless it is *indeed* information. More or less, it appears like the 'negative measurement' information gained by Renninger in his gedanken experiment. (Does a 'negative measurement'
collapse, according to the orthodox QM, a superposition of states?).

The second (naive!) point is this. What would happen if we use, instead of photons, entangled photons (bi-photons)? A bi-photon, because of non-separability, appears to be - according to orthodox QM - a single, unique quantum system (with a different de Broglie wavelenght I can imagine). But it is difficult, for me, to believe that also a bi-photon is a carrier of such a limited information (= 1 bit). Thus, it seems to me that *in principle* a bi-photon
(or a multi-photon!) could provide *more* information about *both* non-commuting (sharp) observables. (I'm not thinking here necessarily that it is possible to measure 'fringes' with one entangled photon and 'which way' with the other, since I know there is a strict correlation of of both momenta, in entangled pairs).

But it is too late now. And I've written enough stupidities.

Au revoire,
- serafino

Dear Morgan , I imagine that S. Afshar will give you an other argument but it seems that I can explain in ''few ''worlds why your are wrong. This just come from the linearity of the wave equations and it doesn't realy matter that you think with electromagnetic wave or with scalar wave .

When you close one pinhole (say 2) practically all the light goes to 1' . Except that you have some few percent of light diffracted by the wires but this is far of 50 percent. Similarly if you open 2 and close 1 you will see 2'. Now the linearity of the theory tell you that if you open the 2 holes you will have a linear superposition of the wave at every point of space. You like the Huygens-Fresnel principle so think that in reality you can apply this principle to the total wave by summing the cases of the two single pinhole experiment. Then clearly the surface integral made on the sum can be decomposed in two part which separate completely the evolution of the two waves.

Now if you look in the detail: if you want to treat rigourously the problem of the lens you need at least the Fresnel approximation this means that all will come from the difference in the phase taking into account not only plane waves but parabolic waves too . The amplitude supposed constant will play no role in the paraxial approximation and all the separation of the two waves will comes naturally from an integration of the phase factor (I ensure I made the calculation).

in other terms you can not mathematically says that only because the amplitude is constant that the law ''50/50'' is valid (an integration of a phase factor can generate all the effect).

The real problem is not when you think into wave but when you think into particle. A simple model of photon can be constructed by imagining that the photon follow the line of energy flow . The photon path will depend of the densitiy of energy which means on the square of the field (more exactly the square of his norm) . then the principle of supperüpostion is broken for the trajectory of the photon: The photons coming from 1 will go to 2' and the ones coming from 2 will go to 1'.

I t is not a good idea to create a cocktail with the two representationsof the phenomena....


with best regards

(PS:as you ''few'' is a relative notion)
Aurelien

To serafino ( i am tired too : probably we hare crazy in Europa)
Your argument concerning information is pertinent and I never say that we have no information at all. If the wire are absorbing the surviving photon plus the absorbed one will give us the initial flow . However even in the Renninger or in the Dicke experiment we can not violate complementarity : the information on the total number of particle will not give you an information on the shape of the wave function. To have such information you need a precise measurment which in the configuration of afshar is not compatible with the detection of the two images.

Anton Zeilinger (and others) wrote a lot concerning this problem and a lot too concerning the entanglement problem : You can not have all the information with entanglement too and the complementarity will be still respected for sharp or not so sharp measurements.


Ok tomorrow is another day


Tchao

Aurelien

Dr Afshar,

I was wondering if you have any views on how your experiments sit with David Bohm's hidden variables/implicate order theory?

Please be "gentle" - I'm a quantum outsider (i.e. non-physicist)

kind regards and congratulations - a wondrous and important debate rages.

Peter FYFE
Playwright
Sydney, Australia

Mr Afshar

Congratulations on creating such a stir on the philosophy and interpretation of QM. I have been following this field for 15 years now and although we allmust have read about the double slit (and variations) experiment 100 times in 100 different books I have only seen one other experiment that shows waves and particle behaviour at the same time. The other experiment is described in John Gribbins (the laymans best friend in QM) book entitled "in search of schrdingers kittens" which describes a experiment by which particles at the start of the experiement are subsequantly seem exhibiting wave like behaviour (quantum tunneling effect as only waves can tunnel or so I have been told) through a xystal placed in one of the which way paths with a narrow air gap between them. No one knows what the implications are for quantum phyics but I agree that the Copanhagen interpretation is and always was on shaky ground.

Let us hope that your paper is peer reviewed successfully and no flaw in your arguments is found.

"Simon Hopkins" wrote in message news:...
> Ok I'm an amateur just beginning to train myself in QMs so what I am about
> to say is probably going to sound quite dumb. Surely Afshar's experiment is
> simply measuring properties of different photons at each stage of the
> experiment - those that pass prior to the lens, those after the lens and
> those ejected from atoms in the mirror. So in this sense Afshar is not
> really measuring complementarity of the same "object". Only if probability
> functions on the same photon pass though the lens can true complementarity
> be assured.
>
> I have a crude thought experiment to answer this question. We place a lens
> between the slits and the detector and pass photons one at a time through
> the experiment. The closer the lens is placed to the slits the smaller will
> be the overlap of the two wavefunctions. If the probability functions are
> truely refracted then we would expect an interference pattern no matter how
> close to the slits we place the lens. However, I expect that the photon
> would be we absorbed by an atom in the lens. At this stage the multiple path
> info would be lost (wavefunctions collapse and new ones are created). Thus a
> photon emerging from the lens would not"know" about the slit arrangement so
> no intereference pattern would be seen (instead we see two clusters).
> Simon.

Contrary to stereotyped physical interpretation of an interference
phenomenon of a light on two slots:

The experimental fact of existence of a "virtual interference"
in VLBI basically excludes ANY POSSIBILITY of simultaneous
passing of a photon through both slots (separate magnetic tape
for each antenna/slot). There is no ANY POSSIBILITY
in VLBI for a photon to pass simultaneously through both
slots/antennas at all!!!

============
The events happening on _slots of an interferometer have
primary significance, all _other _events happening in an
interferometer have the status secondary.
============

In a case of VLBI an interferometer, we have:

The absence of influence of a state of an electromagnetic field
in space of one slot (antenna) on a state in other one becomes
perfect obvious, since a limit of a distance between slots
(antennas) experimentally is not reached, and this distance can be
made _physically vast_ on a comparison with a wavelength.
(Earth diametr or many more)

See additional INFO:
http://groups.google.com/groups?selm=e16a4a22.0409210207.2c8d0f34%40posting.google.com

The events happening on _slots of an interferometer have
primary significance, all _other _events happening in an
interferometer have the status secondary.
The experimental fact of existence of a "virtual interference"
in VLBI refutes physical interpretation of an interference on two
slots of "particle - photon", which one you have described ABOVE!!!

The experimental fact of existence of a "virtual interference"
in VLBI basically excludes ANY POSSIBILITY of simultaneous
passing of a photon through both slots (separate magnetic tape
for each antenna/slot). There is no ANY POSSIBILITY
in VLBI for a photon to pass simultaneously through both
slots/antennas at all!!!

The VLBI interferometer is an interferometer
with independent registration of signals in shoulders and the
process of summation of signals is carried out in the computer.
The phrase " process of summation of signals is carried out in
the computer " allows clearly to seize essence " concepts of an
interference pattern " and source of an origin of this concept.
In the given type of an interferometer there is some
arbitrariness in choice by us of the law of summation of signals
from the right and left shoulders.

Then in any time, convenient for us, we input the information from
these macroscopic magnetic tapes in the computer and mathematically
on any required (demanded) algorithm (which can be changed at any
time) we obtain an interference in representation, necessary for us,
it is so called "virtual interference".

At use of the given method the "interference pattern" represents the
pure abstract information, then this information the macroscopic
computer can transform to the form accessible for the analysis by
a macroscopic system - by the person:

http://groups.google.com/groups?selm=e16a4a22.0204040251.53e4b391%40posting.google.com

http://groups.google.com/groups?selm=e16a4a22.0410150149.29a4b6f2%40posting.google.com


> "Quantum Mirror" wrote in message
> news:7b043f08.0410191148.2338e6f5@posting.google.com...
> > Shahriar S. Afshar has found a experiment that will open a discussion
> > on the Bohr complementarity principle.Coherent laser light is passed
> > through a dual pinhole and allowed to go through a converging lens,
> > which forms well resolved images of the respective pinholes, providing
> > complete path knowledge. A series of thin wires are then placed at
> > previously measured positions corresponding to the dark fringes of the
> > interference pattern upstream of the lens. No reduction in the
> > resolution and total radiant flux of either image is found in direct
> > disagreement with the predictions of the principle of complementarity.
> >
> > He also has made this offer: I would award a $1000 prize to the first
> > person who can show that the wavfunction of EACH image in the image
> > plane in the case that both pinholes are open, and the wires are
> > present, is a 50/50 mixture of the two wavefucntions emerging from
> > EACH pinhole. I claim that it is impossible to achieve this feat using
> > QM formalism.
> >
> >
> > At last there is a preprint ! The preprint is PDF
> >
> > http://www.irims.org/quant-ph/030503/

Dear Shariar,

Hi again.

While pondering whether there is the support for the Copenhagen interpretation that you say, I came across the following website which is good for a laugh, at least:

http://higgo.com/quantum/laymans.htm

I'm sure there will always be reactionaries in physics, as in all subjects. It takes all types to make a world, and it would be no good at all if everyone was a rebel. It would be total chaos. The reactionaries ensure that new ideas are thoroughly proved, not adopted lightly like the latest fashion.

There is a sense of "complementarity" in which gamma rays look very much like classical particles, while radio waves look very much like classical waves. I don't think you have disproved complementarity in that sense, which will be with us for a very long time to come. What you have disproved is one of the siller things that Bohr claimed about complementarity. Certainly it is a very useful thing to have done. However, although I can understand your frustrations, I'm not sure that the coverage of your paper in New Scientist was a very good idea. The journalists at NS were away from school the day they did quantum mechanics, and claimed more for your experiment than is really justified. I still think that 99% of competent physicists would analyze your experimental setup correctly, and predict the results which you actually observed.

Bell's work, particularly, has done much to show that Bohr's prohibition on thinking certain thoughts was unfounded and pernicious. For me, also, it was significant that Bohr said you could not observe individual atoms, but this is now done on a routine basis. Perhaps you should do a survey of professional physicists, asking how many believe the various interpretations of QM, and publish the result.

Best regards,

Zigoteau.

Dear quantumenforcer,

Funny you should mention Prof. John Gribbin. I have a great deal of respect for him and his efforts to popularize QM and physics in general. He did raise that issue shortly after The Independent aticle, and I gave him a response, that seems to have satisfied him. Here's the exchange of 3 e-mails you might find helpful in this regard:

-------------------------------------------------------------------

John Gribbin
07/10/04 08:24 am

To: letters@independent.co.uk
cc: mafb5@sussex.ac.uk
Subject: quantum leap

Sir,
The work by Shahriar Afshar showing that quantum entities are both
particle and wave at the same time (Science page, Wednesday) is
indeed imortant and interesting, but this us not the first time the
dual nature of photons has been observed directly. In an
experiment devised by Dipankar Home, of the Bose Institute in
Calcutta, and carried out by Yutaka Mizobuchi and Yoshiyuki Ohtake, of
Hamamatsu Photonics in Hamakita, in the early 1990s single photons
were "caught" behaving as both wave and particle at the same time.

Dr John Gribbin
Astromy Group
University of Sussex
j.r.gribbin@sussex.ac.uk

-------------------------------------------------------------------

From: "Shahriar Afshar"
To: j.r.gribbin@sussex.ac.uk
Date: Tuesday - October 12, 2004 11:34 AM
Subject: Re: Fw: quantum leap

Dear Prof. Gribbin,

It is a great pleasure for me to read your comments regarding my recent
experiment. You are truly one of my heroes, in that your popular-level
books were instrumental in bringing a starry-eyed teenager in awe of
Quantum Mechanics, to realize that "all is not well with QM!"

I am quite aware of the theoretical work done by Prof. Home, and enacted
by Mizobuchi et al. at Hamamatsu. In fact I got in touch with Prof.
Home, and the Hamamatsu team's liaison person in Boston, to better
understand their work.

Please take a look at the preprint of my paper (which I shared with
Prof. Home) here:
http://irims.org/quant-ph/030503/

The last paragraph on page 3 briefly addresses Home's work. As discussed
in papers mentioned in Ref. [20] in my manuscript, the criterion for
complementary wave-particle properties is the mutually exclusive nature
of the logical inferences of the two different measurement. For example
in the Bohr-Einstein debates, the fact that one could provide the
which-way information for a photon, and establish that the same photon
had participated in an interference pattern leads to such inconsistent
logical inference: i.e., the which-way information tells us the photon
acted as a particle and came through only one of the slits, while the
interference pattern dictates that the SAME photon acted as a wave and
came through both slits. These two wave-like and particle-like
measurements are logically-inconsistent and thus are considered by Bohr
to be complementary.

Now, in the work of Home and his colleagues, the wave-particle behaviors
are not complementary, since the act of tunneling (the wave-like
behavior) and the detection by the detector in front of the beamsplitter
(the particle-like behavior) are not mutually-exclusive. Rather the act
of tunneling IMPLIES the detection of the photon by that detector and
vice versa. These two phenomena do not NEGATE each other, and are
therefore not considered to be subject to Bohr's complementarity
principle.

Indeed, if just any wave-like and particle-like behavior were considered
to be complementary, then the mere build up of an interference pattern
by single photons would have been sufficient to declare a violation of
the Principle of Complemetarity. However, a quick review of the original
Bohr-Einstein debate on the which-way experiments clearly indicates that
the two esteemed physicists considered this question and BOTH rejected
the idea as inconsequential. It is only when we talk about the
"which-way" vs. "interference phenomena" for the same particle, that we
are addressing the Principle of Complementarity. This is a view shared
by the eminent historian of physics Prof. Gerald Holton of Harvard
University who had the distinct honor of being a participant in some of
discussions between Bohr and Einstein. Since my experiment shows clear
evidence of both interference and which-way information in the same
experiment for the first time since the inception of quantum physics, I
believe it deserves to be recognized as the first solid experimental
critique of the Copenhagen school of thought.

Looking forward to hearing from you soon.

Most humbly yours
Shahriar S. Afshar

-------------------------------------------------------------------

From: John Gribbin
To: ROWANDOM.GWIA."afshar@rowan.edu"
Date: Tuesday - October 12, 2004 5:45 PM
Subject: Re: Fw: quantum leap

The report in the Indy obviously did not do justice to your work!

John

Shahriar S. Afshar

Thanks for replying to my post it is greatly appreciated. I also noticed that John Gribbin is a advocate (well he was in 1994) of John Cramers transactional interpretation of QM and that in the NS article Mr Cramer (his daughters blog was where I got this site from) seems to be implying that your possible violation of Complementarity assits with the vindication of his theory where waves travel a temporally (non locally) in time in a retarded and advanced wave handshake which appears to thus resolve the paradoxes of QM.

What would be your (philosophically fun) assessment of such a idea ? It is really wild and out there to be thinking like this or as John Gribbins 1994 books states is it the best interpretation of our time ?

Is it possible that advanced and retarded a temporal waves can solve such issues as Machs principal (the origin of inertia etc).

Thanks again

Thanks for your comments Aurelien. To aid clarity (at least for me, if not for others) I want to describe the two ways of looking at this.

The way you describe involves observing that wave equations are linear and that therefore you can add two independent solutions and obtain another solution. With pinhole 2 closed all the light from pinhole 1 gets to detector 1 and vice versa. With both pinholes open it is natural to conclude that in the superposition of the two solutions we can make the same deduction (with or without the wires present). The light emitted from pinhole 1 all reaches pinhole 2. If we are allowed this deduction then Shahriar Afshar's argument holds and complementarity, as Afshar has stated it, is history.

The way I have presented is also framed in terms of a wavelike picture. We are all familiar with the idea that each point on a wavefront can be considered a new source of waves. This is true of all linear wave equations of which the Schrodinger equation is an example. Now we are led to the idea that in places of the phase space which are accessed by light from both pinholes (I.e. any position in the interference pattern) the value of the wavefunction is a sum of the contribution from each pinhole. The question is how much of the resulting sum came from each pinhole? The answer is that it is clearly indeterminate; we don't know which bits of the sum came from where. The origin of the photon is not a question that the quantum formalism can answer. If at this point in the phase space we cannot be sure, then at all future points we cannot be sure either since the future evolution depends only on the value of the wavefunction at the earlier point. Hence the conclusion that, by the time the photon reaches the detectors, the question "Where did this photon come from?" is indeterminate and we do not have complete which way information.

It is worth noting that both these ways of looking at it provide results identical with the quantum formalism and with Afshar's experiment. One of them (the first) contains an unnecessary assumption which is not present in the quantum formalism. It assumes that when the photon is split between the two pinholes some piece of information is attached to it telling us where it came from. This really doesn't happen. When it reoccupies the same space there is no way we can distinguish the two bits, they are the same particle.

I have thought further about the approximate argument I gave a few posts ago and I believe that, using a simple idea, I can show that the amount of which way information you obtain is precisely zero. Consequently you would expect the photons measured at each detector to be just as likely to have come from one pinhole as the other. Assuming just that there is a plane of reflection in the problem and that when only one pinhole is open all the light crosses this plane and reaches one detector, it is necessary than the which way information is completely lost.

Morgan Harvey

Oops, in the second paragraph the sentence "The light emitted from pinhole 1 all reaches pinhole 2." should of course read "The light emitted from pinhole 1 all reaches detector 1".

Dear Morgan,
I agree ... and I desagree with your reasonning (dont be affraid I am not drunk .... for the moment).

You i) first accept that the two waves propagate independently and after you say that this is true then Shahriar Afshar is right. And after ii) because this conclusion seems for you impossible you precize that in fact because the two wave are mixed in the interference zone we know nothing about the motion of the photon (please dont care about my english ).
The problem is that if ii) is true as I explained different times before i) is false. There is no contradiction: the fact is that the reasonning using waves can not be teleported for particles. The result imposing that the two waves move independently is correct in classical optics but you have to remember that already in such theory the energy will not follow simply the trajectory connecting the pinhole 1 (respectively 2) to its image 1'(respectively 2') . If you imagine (this is just a possibility ) that the photon follow the energy flow you will have a situation which is not simply the sum of the two independent problem for one single pinhole ( as it should be with the old newtonian particles).

Finally if you forget this 1000 $ ( if you can prove that the axiom of Afshar is wrong I accept to eat my hat..... but i need to buy a hat before) your opinion is now very close of mine but you made a assumption when you say that that the photon can have 50/50 probability to go in the wrong image. This depends of you choice for a model of reality. In the de Broglie-Bohm model (my choice here) a photon follows a deterministic trajectory defined by the energy flow of the guiding wave. Then if you observe a photon in 1' you know for sure that it comes from 2 (probability =1 and not 0.5) but you can imagine other models naturally (I am not here to speak about hypothertical model that could explain something that nobody can control experimentally ).

The central point of all my messages was to show 2 things:
1 ) the Afshar experiment can not be called a which path exeperiment without reference to a particular model of reality (on this point you agree know with me i believe )
and 2) that the complementartiy principle is not in danger (see my precedents messages) because a photon can not be used to plot at the same time an interference pattern and to participate to one of the images (you can see a photon only one time by absorbing him). If you change the experiment introducing some entanglement tricks the result will be the same but this is well known.

for these two reasons the conclusions of afshar are wrong....


.... but a wave coming from 1 (2) always goes in 1' (2') .... this depends on your definition of ''to go''.

I hope it is clear

aurelien

Aurelien wrote:
"In the de Broglie-Bohm model (my choice here) a photon follows a deterministic trajectory defined by the energy flow of the guiding wave."

This is a good point. But Afshar (and Heisenberg, von Weizsaecker, Zeilinger, etc.) say something similar, using 'ray optics' between each slit and each detector. I find interesting what Basil Hiley writes here about real (and surreal) Bohmian trajectories http://www.arxiv.org/abs/quant-ph/0010020 . See figures 2 and 3 in example. (If, as I suppose, Bohmian mechanics and Schroedinger wave mechanics are both time-symmetrical, what does it happen if we place mirrors instead of detectors, in Afshar's set-up?)
Saluti,
-serafino

Carl Friedrich Freiherr von Weizsaecker:

'Classical physics has been superseded by
quantum theory. Quantum theory is verified
by experiments. Experiments must be described
in terms of classical physics.'

'Nature is earlier than man,
but man is earlier than natural science.'

Dear Serafino,
You say ''But Afshar (and Heisenberg, , etc.) say something similar, using 'ray optics' between each slit and each detector. '' This is wrong Heisenbergvon, Weizsaecker, Zeilinger and Bohr used different times the fact that the trajectory given by the geometrical path connecting a pinhole can not explain interference to insist on the paradox of the wave particle duality and to convince people about the necessity to renunce to any causal dynamic of the photon.

What de Broglie and Bohm and other as Scully and Hiley shown it is that Heisenberg is wrong : we can have trajectory able to justify fringes but there are less intuitive .

Now if you put mirrors (say in the image plane) in such a way that the wave will return back(ommiting diffraction of course) the result will be naturally that the photon will return in his original pinhole because the photon can nver cross the symetry plane. the important point is that you will never know that because you have not observe the photon in the image plane.


A last point concerning the experiment made by Home-Agarwal . I think that there is strong parallel betwwen this experiment and the one made by Afshar : in the two you observe your photon after the lens or after the beam splitter, in the two you can infer that they must be a wave to explain the result. And in the two case you dont observe this wave in the region where the interference occur. In the two case the principle of complementarity is then still true and even never judged.



Aurelien

This is how John Gribbin and John Cramer explain QM from a phisosophical perspective taking into account the physics of QM.

But a giant leap in what might be called quantum philosophy has recently been taken by the American physicist John Cramer. He has taken a new look at the wave equations of quantum mechanics -- the famous Schrdinger equation, and the equations describing the probability waves, which travel, like photons, at the speed of light. What Cramer has pointed out is that the equations actually have two sets of solutions, one equivalent to a positive wave flowing into the future (a "retarded" wave), and the other describing a negative wave flowing into the past (an "advanced" wave). As all physicists learn at university (and most promptly forget) the full version of the wave equation has two sets of solutions -- one corresponding to the familiar simple Schrdinger equation, and the other to a kind of mirror image Schrdinger equation describing the flow of negative energy into the past.

I wonder if this could be possible.

Dear Aurelien,

Your english is fine, it's the complexity of the issue that causes any problems.

You talk about different models of reality and how that will affect which of i) and ii) is the correct way of looking at things. I agree that it depends on the definition of "to go", which varies with the model of reality. While this is very interesting it is not relevant to my claim for Shahriar's $1000. He wrote:

"As I have indicated in my talks at Harvard, Princeton, TAMU, and elsewhere, I would award a $1000 prize to the first person who can show that the wavfunction of EACH image in the image plane in the case that both pinholes are open, and the wires are present, is a 50/50 mixture of the two wavefucntions emerging from EACH pinhole. I claim that it is impossible to achieve this feat using QM formalism."

So, even if a de-Broglie-Bohm type model is relevant in reality, it will not endanger the $1000. My argument shows that, in the quantum formalism, all which way information is lost and hence I am claiming the $1000 (and would also like to see you eat your imaginary hat!).

The QM formalism in this case consists of just the Schrodinger wave equation propagating the photon from the two pinholes to the two detectors and the plotting of the intensities at the detectors. I presented two ways of looking at what is going on in the Afshar experiment: i) where we use the linearity of the wave equation to argue that pinhole 1 all goes to detector 1 and ii) where we think in terms of propagating waves and Huygens principle which demonstrates that the which way information is lost. As you point out one (or both) of these is incorrect. Afshar explicitly uses i) in his argument. If it is wrong his argument is flawed.

You seem to think that I am confusing particle and wave pictures, but I assure you I am not. I am thinking entirely in the wave picture because we are using the Schrodinger wave equation. When thinking like this we can immediately see that i) is false (or at least contains an extra assumption) because when two waves interfere we cannot tell which part of the wave came from where. This is well understood from the standard two slit experiment. At any point in the measured interference pattern we have no which way knowledge. This is simply a property of the wavefunction being made up of contributions from both slits. For i) to be true something needs to be attached to the part of the photon which came from pinhole 1 such that when it occupies the same phase space point as a contribution from pinhole 2 we can tell which bit is which and propagate them on to the relevant detectors. We know that this does not happen. ii) contains no extra assumption because we can mathematically map the schrodinger equation into a propagator form and therefore the mathematics of the quantum formalism behaves exactly as described in ii).

I can rigorously show that in the quantum formalism using the propagator form of the schrodinger equation that in the Afshar experiment all which way information is lost, regardless of whether or not the wires are present. I am very interested to hear Shahriar's response to this.

Morgan Harvey

Morgan--Are you saying that in a simple imaging experiment (no wires) the images do not provide which-way information?--S

According to the argument I have given, yes.

M-Then essentially according to your argument, is Heisenberg's Microscope proof of Uncertainty (which depends on the premise that the images provide which-way information) wrong? I think not! Sorry...-S

Morgan,

I consider again this long sentenceof Afshar,
"As I have indicated in my talks at Harvard, Princeton, TAMU, and elsewhere, I would award a $1000 prize to the first person who can show that the wavefunction of EACH image in the image plane in the case that both pinholes are open, and the wires are present, is a 50/50 mixture of the two wavefucntions emerging from EACH pinhole. I claim that it is impossible to achieve this feat using QM formalism."
1000 $ is a nice sum but nevertheless you can forget them ( and my hat too: I dont like hats in fact).

in this sentence Afshar precized '' wavefunction of EACH image''. WAVE FUNCTION implies superpostion principle and such principle implies that the two waves propagates independently.

you can not violate this principle and then you will not prove that your wave ''is a 50/50 mixture of the two wavefunctions emerging from EACH pinhole''.
I confirm that you confuse the wave point of view , the energy point of view (in a classical sense) and the particles point of view .

I agree that the subject is complex and perhaps it is difficult to be clear but think to this sentence of bohr:

clarity and truth are complementary

HAHAHAurelien

I'm not convinced that Heisenberg's microscope proof would be invalidated by this. I shall think about it. Perhaps you could spare a few moments to explain more details of why it would?

Morgan

M-The Heisenberg's microscope proof is based on the imaging theory of a lens, in which the resolution limit of the lens directly enters the uncertainty relation as delta_x, the uncertainty in position. See Physical Principles of the Quantum Theory by Heisenberg (Dover paperback), or any other textbook on QM for that matter.-S

Dear all.
Trying to make a point here, a logical point, or a pseudo-logical one!

Imagine a Young two-slit interferometer with its screen, where we can see the interference pattern, with its minima and maxima of interference (given a certain number photon passing through). And imagine now we ‘reduce’ that screen to those little wires only, located at minima of interference, as in Afshar experiment. I would say that the interference pattern is still there, even if I cannot see it any more. Why can I say that? Because of statements [1] or [2] below, at choice.

[1] *If* we can PREDICT with CERTAINTY the result of a measurement of a physical quantity, then there exist an element of reality corresponding to this physical quantity, and having a value equal to that PREDICTED measurement result.

[2] *If* we can PREDICT with a certain PROBABILITY DISTRIBUTION the result of a measurement of a physical quantity, then there exist an element of reality corresponding to this physical quantity, and having a value coherent with that PROBABILITY DISTRIBUTION..

Before I go on writing the second (brilliant) part of this pseudo-logical argument: is the above correct ? Does it make some sense?

s.

dear serafino Have you read the EPR paper before to write this mail?

Einstein podolsky and Rosen wrote in 1935:

If without in any way disturbing a system, we can predict with certainty (i.e. with probability equal tzo unity ) the value of a physical quntity then there exists an element of physical reality corresponding to this physcial quantity.



EPR found a famous example but this example was alredy refuted by Bohr on the basis that we can not spaek about not measured things :
if you change the experimental conditions you can not be sure that the thing will be here really and nothing prohibit the existence of ''un malin genie '' [in french see Descartes] which can play wtih our nerf in order to create an illusion .

This is the key point in the philosophy of Bohr i think annd unfortunatelly because of the structure of quntum mechanics we can not speak about fringes without directly observing them


If quantum mechanic is true i think that the real is definitly masked experimentally.

But I dont care about that in fact and I continue to imagine that a dynamic model can explain all .

If we can justify masses and charges and all the others properties (9perhaps even the planck constant this will be a proof that such model can be usefull to understand the real . Probably we have to be more modest than our ancestors . Eistein progressively realized that and I think that he was one of the first to accept this fact contrarly to some false ideas.

Aurelien

Dear Aurelien.

Yes I've read the paper by EPR. And there is a fresh historical paper here http://www.arxiv.org/abs/quant-ph/0408105 . Readhead tried to change that
"if we can predict with certainty ..." in "if we can predict or infer with certainty ...".

Btw, this EPR 'realism' criterion applies perfectly to theories like ... MWI,
where you can indeed predict, with certainty, which and what are the sharp
non commuting observables, since they are in a different universe.

Anyway I’m supposing the EPR ‘realism’ criterion is valid after all
(if we avoid the entanglement case because, in this case, there is no possible
*prediction* to be made, it is just possible to make a *conditional* probability
statement or a *conditional* inference, which is much different from a
*prediction*).

We, in our lives, think the moon *is* there, even if the sky is foggy,
or if we do not look at it. I'm aware there are things like K&S theorem
or the contextuality or the nonseparability or the 'operational' meaning of modern physics (both SR and QM, according to Bridgman, and Heisenberg,
and Einstein himself but not always).

But I'm assuming here the moon *is* there (the interference is there, at those littlle wires) even if/when we do not look at it. This is (imo) a necessity. Because if we do not assume it, we cannot *even* show that this very assumption is wrong.

Saluti,
s.

Since Prof. Afshar once was very kindl to allow to use this forum to talk "amongst ourselves",
I would be very happy to address, if possible, to Dr. Kathryn Cramer, and indirectly to her father Prof. John Cramer.

I think I am DIRECT folower of TIQM in my developent of hidden time concept (HTC -- see the URL). I kindly asked prof. Cramer to criticize the concept, still he stays silent.

Well, OK, I don't mind his caution. No one is obliged to answer some "crazy revolutioneers" like me.

Still I've got an idea of an experiment. It can be stupid due to my elementary ignorance, and thus I don't mind if anyone points me my ignorance.

=====

I suppose that putting clock into ANY strong field -- let it be enormously charged condensor, let it be intensive laser radiation (from 2 sides -- to make accelerating force zero!), or let it even be enormous pressure, DO slow clocks like gravity or acceleration.

An explanation, in the frames of hidden time concept (HTC), is qualitatively very simple. HTC suggests that a charge (say, an electron) scatters photons NOT LINEARLY, i.e. - independently. The charge puts coming photons in the que. Stricly speaking, in FIFO (first in -- first out).

In a mob of very many charges, photons wait very much in the que :)

If it's right, one need not exactly gravity or acceleration. Just ANY huge amount of scattering events should slow down the clock :)

I am on my way to make appropriate estimations. It can be my mistake. Still I am not afraid of mitakes :)

=====

I can quite be elementary ignorant! :) Please let me know anybody if there WERE already performed experiments with putting clock into strong static electric field or anything like this.

In addition to my previous message
-----------------------------------------------

Please let me remind that the 1st model of turbulence was L.D. Landau's model of coupled non-linear oscillators (1944). It happened to be wrong, and IT IS EXACTLY WHY that model was of high validity!

It is VERY serious and VERY important to consider simple (and maybe stupid) models before making complicated models.

So, I insist, when seeking for SIMPLE (and may be stupid! :)) experiments I proposed above, and when seeking a SIMPLE decoding of TIQM like hidden time concept (HTC), I do a VERY serious and VERY important deed.

Dear Shahriar S. Afshar

I want to attract your attention to physical principles of operation of VLBI (Very Long Baseline Interferometry). Conceptually VLBI is rest on usage of an abstract mathematical interference, which one in physical essence differs from a real (actual) physical interference. I want to note that, your interpretation of your experiments is very close to the physical concepts of VLBI.
The most remarkable physical fact is that in VLBI the self-interference of a photon is impossible basically. To my severe regret, this fact obstinately is ignored by orthodox science.

Best regards
Aleksandr Timofeev

This is my opinion, not the official opinion of Space Research Institute Russian Academy of Sciences

Dear Prof. Afshar and Prof. Timofeev!

here's a paper by A. Zeilinger from Arxiv, with a reference to an experiment where two sources (atoms) interfere to emit 1 (single!) photon:

http://bellstheorem.narod.ru/texts/time_reversed_EPR.pdf

Perhaps it deals to what Prof. Timofeev means in previous posting.

Dear Shahriar,

There is a fine distinction here. The resolving power of the lens tells you the limit for forming discernable images. This resolving power comes into the Heisenberg Microscope proof as it tells you the uncertainty in the position of the scattering event based on the position of the image. In your experiment I would expect that the resolving power was easily good enough to form two separate images of the two pinholes, but this does not affect my argument in the slightest.

For both the Heisenberg microscope proof and your experiment, both i) the superposition of independent waves and ii) the Huygens principle ideas predict exactly the same experimental consequences. For the Heisenberg Microscope proof the uncertainty in the position of the scattering event is precisely the same both ways. For your experiment they both predict the formation of two discernable images (assuming the resolving power is good enough). In i) we infer that the image at detector 1 came from pinhole 1 and in ii) we cannot make that inference. I have argued that ii) is the correct way of looking at it. I really think you need to address this directly rather than introducing further confusion.

Morgan Harvey

Dear Aurelien,

With reagrd to Afshar's offer of $1000 you said

"in this sentence Afshar precized '' wavefunction of EACH image''. WAVE FUNCTION implies superpostion principle and such principle implies that the two waves propagates independently. "

I agree wavefunction and schrodinger equation imply that the superposition principle holds (and I emphatically agree that it does apply in the quantum formalism) but I do not agree that it implies the two waves propagate independently. They propagate as if they were independent sure, but when they occupy the same phase space notions such as "this part of the wave came from over there" lose their meaning.

The superposition principle says that the sum of two solutions to a wave equation is also a solution to that wave equation, it does not say anything else whatsoever.

Morgan

Dear Morgan,

FYI: Huygens principle is an outdated and INCORRECT approximation, so I would not pin my hopes on it. There is no possibility of mutual scattering of wavefunctions from EACH hole simply due to spatial overlapping before the lens. Please do ask some of your Prof.s who know about physical and Fourier optics to explain the meaning of the linearity of the process. I encourage you to write a rigorous paper on your approach as it would help clarify your error. I would certainly consider such a paper if you e-mail it to me, but short of that I'm afraid your further posting would fall outside the scope of this Weblog.

Good luck!

"Eistein progressively realized that and I think that he was one
of the first to accept this fact contrarly to some false ideas."
- Aurelien

I'm inclined to agree with that. But he hated non-locality
(rectius: non-separability of entangled systems) till the
end. He did not publish his 'hidden variables' model just
because it implied non-locality.

Being in historical mood let me post here something
by P.A.M. Dirac, which - in general - is not well known.
(I've heard a similar speech, by Dirac himself, in Rome,
many years ago.)

"This statistical interpretation is now universally accepted as
the best possible interpretation for quantum mechanics, even
though many people are unhappy with it. People had got used
to the determinism of the last century, where the present
determines the future completely, and they now have to get used
to a different situation in which the present only gives one
information of a statistical nature about the future.
A good many people find this unpleasant; Einstein has always
objected to it. The way he expressed it was: 'The good God does
not play with dice'. Schroedinger also did not like the statistical
interpretation and tried for many years to find an interpretation
involving determinism for his waves. But it was not successful
as a general method. I must say that I also do not like indeterminism.
I have to accept it because it is certainly the best that we can do
with our present knowledge. One can always hope that there will
be future developments which will lead to a drastically different
theory from the present quantum mechanics and for which
there may be a partial return of determinism. However, so long
as one keeps to the present formalism, one has to have this
indeterminism".
- P.A.M. Dirac, "The Development Of Quantum Mechanics -
Conferenza Tenuta il 14 Aprile 1972, in Roma, Accademia
Nazionale dei Lincei", 1974, 11 pages, [taken from page 6].

Cari Saluti,
- serafino

'The question of whether the waves are something
"real" or a function to describe and predict phenomena
in a convenient way is a matter of taste. I personally like
to regard a probability wave, even in 3N-dimensional space,
as a real thing, certainly as more than a tool for
mathematical calculations ... Quite generally, how could
we rely on probability predictions if by this notion we
do not refer to something real and objective?'
- Max Born, Dover publ., 1964, "Natural Philosophy
of Cause and Chance", p. 107

Let us put it in this context - as soon as you in any gather any knowledge or information about which way the particle went the wave function collpases and you destroy the interference pattern. According to classical QM you cannot know the wave aspects and the particle aspects of light or atoms at the same time. No known experiment until recently had ever shown this and as such QM has been proved right for seventy years

Afshar appears to have contradicted this by devising an experiment that simultaneously shows both wave and partical aspects of light or atoms (in theory). Does the mathematics of QM show that this is not possible ? Has Prof Ashar violated QM in some way ?

What does it mean for QM tha wave and particles are shown to coexist in the same experiment ?

Dear Professor Afshar,

I have been thinking hard about your experiment and would like to know what you think would happen in the following extension to it.

In your experiment you place wires in a plane just in front of the lens along lines where the interference pattern has minima (in fact zeroes). You can imagine many planes parallel to this one where the minima lines were in slightly different positions. The set of these lines would then describe surfaces in the space in front of the lens where the interference pattern was zero.

Lets say you placed thin sheets of material along these surfaces and performed the experiment as before (obviously this is a thought experiment!). Would you expect the same behaviour as with just the wires? Would this be a second experiment which contradicted the Complementarity Principle (although really it is only a minor extension of yours)?

According to my quick calculations the separation of minima in the interference pattern decreases as you move the screen further away. You could imagine making these surfaces long enough such that no classical light ray could travel from either pinhole to the lens. Would this make any difference? Is this mutual scattering of the wavefunctions allowing the propagation down the channel?

Also you could imagine closing off the ends of the gaps between the sheets and look at these channels just one at a time. What would happen then?

Chris.

Dear CTN Hoigns
As you can imagine, Professor Afshar is having the busiest year of his life. I hope you do not mind if I answer for him. The experiment you are asking about would be extremely hard to line the sheets up perfectly. The result would provide you with the same information as the present experiment. It would be more trouble than it was worth.
Please read the paper carefully before you start forming questions. The pinholes must be within a specific distance from the lens to provide which way information. This is what the whole experiment is about!

Dear quantumenforcer,

The QM formalism is not violated by my experimental results; in fact it is fully confirmed. It is Bohr's Principle of Complementarity that is ruled out. The theory of measurement also needs revamping in order to include non-perturbative schemes. There is a lot of work to be done, and the jury is currently out on whether the particle picture is still valid or not. However, in my opinion, Einstein's conception of photons as "rain drops" with linear trajectories is certainly falsified.

Regards.

Dear CTN Hoigns,

You may wish to take a look at this paper: W. Wooters and W. Zurek, Phys. Rev. D. 19 (1979) 473, if you have access to old volumes of PRD. They talk about an idea similar to yours, but without the lens, and they find that Complementarity is upheld. Can you e-mail me a short paper with the schematics of what you have in mind? I'll try my best to address your questions more directly after I read it.

Regards.

Dear Morgan :
I agree that you can not be sure of the path followed by a particle but accepting that imply necessarily that you dont think in term of wave but in term of energy or in term of flow of particles. The (continuous ) wave coming from the pinhole A goes to the image A' and the same is true for B and B' this is just a mathematical definition. But the particle or the energy can follow a different path that A-->A' Such path is not described UNIVOCALLY by the quantum formalism ( there is no well defined trajectories in the present formalism) .

But I repeat you agree in fact with me for practicallly all.
Forget the 1000 $ and we will be friend .

Dear Shahriar , If you refuse the principle of Huygens-Fresnel you refuse optics. By such principle I mean : Fresnel=Kirchoff = propagator=evolution operator .....


Aurelien (tired )

Dear Aurelien,

I am glad you agree that the wave(function) propagation through the lens does map silt 1 (2) to image 1' (2') through the use of accepted QM formalism. I do not refuse Huygens, I just want to make it clear that the Huygens principle in itself is not strictly valid and leads to incorrect results if one is not aware of the subsequent 300 years of development in the field. This is clearly reflected in your comment above where you use "principle of Huygens-Fresnel" instead of Huygens alone. Fresnel corrected the ideas of Huygens by introducing the DIRECTIONALITY of the wave (CRITICAL IN CORRECT ANALYSIS OF MY EXPERIMENT), as well as taking advantage of LINEAR superposition of secondary AMPLITUDES. Plain Huygens principle is useful as an approximation, but in subtle cases like my experiment, it is perilous to rely on approximations. Physical optics is the correct process of analysis which is also implicit in QM formalism.

Just to quote a real expert, in his excellent book "Principles of Electrodynamics", the 1988 Physics Nobel Laureate Melvin Schwartz wrote: "Huygens' principle tells us to consider each point on a wavefront as a new source of radiation and add the "radiation" from all of the new "sources" together. Physically this makes no sense at all. Light does not EMIT light; only accelerating charges emit light. Thus we will begin by throwing out Huygens' principle completely; later we will see that it actually does give the right answer for the WRONG reasons."

As I stated before, this Blog is not an optics history or tutorial site. If Morgan e-mails me a rigorous paper on his ideas, I will certainly consider and share it with others here. Alternatively, if others suggest similar arguments, demonstrating a general misunderstanding among the participants, then although I am severely pressed for time, I will spend some time to clearly delineate the correct application of Huygens-Fresnel principle in my set-up in a separate paper which I'll post on the IRIMS archive.

Regards.

Dear Shahriar,
We are not effectivelly here to speak about history of optics but about history of quantum mechanics ( where past and present are mixed in anon local way ). Because the two domains are connected I insist on the importance to use correctly optics and the good terminology. You say ''I am glad you agree that the wave(function) propagation through the lens does map slitt 1 (2) to image 1' (2') through the use of accepted QM formalism.'' It seems that this is an essential point of misunderstanding between us. As i say it already N times or more a wave effectivelly goes from one pinhole; say A, to its image A'. However to extrapolate that this is NECESSARILY true for a photon is just a free metaphysical senseless and unbelievable religious idea (associated with some elements of crazyness without rational basis) .

I think that you need really to consider the theory of Bohm as a counterexample (you dont need to really believe in such theory). if you dont read the work of Bohm I think that you will never see your mistake.
You can read [1] for informations if you want .

[1] Englert et al in Z. Naturforsch. Vol 47a , p 1175.]
NB: dont confuse it with Englert PRL 77, p2154 (1996) as the last time.



Aurelien Drezet

an other reference

Bohm nature vol 315 (1985) p 294

Aurelien

Dear all,

Three little (and naive) points.

1. Am I right in saying that in orthodox QM there are no physical waves at all, just particles and wavefunctions and amplitudes? As far as I remember in matrix mechanics there are no physical waves indeed.

2. In the experiment there is that lens and that couple of detectors. Their purpose is just to show the 'welcher weg'. (Ok, there are conceptual or theory laden problems here, but let us go on). What if we remove that lens and those dectectors and we get the information about the 'welcher weg' elsewhere? In example, we could shoot the photons targeting more the slit A than the slit B. In this case we could get (see Zurek and Wootters, 1979) the information that a photon passed through slit A with a probability of, say, 95% (even 100% if you like). Am I wrong in saying that, in this case, the 'virtual' interference pattern at those little wires vanishes almost completely (or completely)?

3. Now can we - in principle - shoot photons targeting exactly slit A *or* slit B, in such a manner that: a) we can be sure that a photon goes through slit A *or* slit B; b) we cannot know - in principle, because of uncertainty in time, or diffraction in time - *which* slit the photon went through?

Sorry if I wrote nonsenses!
-serafino

C. Brukner, A. Zeilinger
Diffraction of Matter Waves in Space and in Time
Phys. Rev. A, 56 (1997) 3804.

Dear Professor Ashtar

Congratulations on getting to the heart of the matter. This is a definitive leap past the excellent experiment of Y. Mizobuchi and Y Ohtake.

Your experiment seems obvious in hindsight. Why do you think it wasn't done before?

Do you believe the results of your experiment leave the Transactional Interpretation of Quantum Mechanics (TI) as the only viable interpretation left standing?

I have authored a paper approved for publication in Physics Essays vol.16 no. 3 . Entitled “Velocity Correlation derived from the Transactional Interpretation of Quantum Mechanics.” In it I argue that TI allows for an improved model of special relativity and provides a connection between Special Relativity and Quantum Mechanics. This has been lacking up till now.

When is the next colloquia or demonstration of this experiment?

So by showing wave particle duality simultaneously you have proved complentarity wrong and entanglement right ? I read somewhere recently that after a long review of the EPR paradox and FTL (non locality) most physicists agreed that bohr's arguments were based on a strange coincidence between the measurements from experiments and the uncertainty principle were in fact were incorrect and that entanglement is in fact the reason for non local behaviour and hence the explanation for EPR behaviour.

"So by showing wave particle duality simultaneously you have proved complentarity wrong and entanglement right ? "
- quantumforcer

In the paper http://www.arxiv.org/abs/quant-ph/9903047 Scully (et al.) claim that their "experimental results demonstrated the possibility of simultaneously observing both particle-like and wave-like behavior of a quantum via quantum entanglement". I think this responds to your question, at least partially.
-serafino

So by showing wave particle duality simultaneously you have proved complentarity wrong and entanglement right ?
- quantumforcer

In the paper below Scully (et al.) claim that their experimental results demonstrated the possibility of simultaneously observing both particle-like and wave-like behavior of a quantum via quantum entanglement. I think this responds to your question, at least partially.
-serafino

http://www.arxiv.org/abs/quant-ph/9903047

Thanks Serafino Cerulli-Irelli,

I believe that this document points out that under certain circumstances complementarity is not held to be true and that Bohr did appear to assign his argument to the uncertainty principle which apears to have been more of a historical scientific coincidence than actual fact.

It does indeed appear that Entanglement is reason for quantum behaviour in the main.

Dear quantumenforcer, and Serafino,

My experiment does not address entanglement, because the effects observed are the result of single-photon states. Entanglement involves at least two particles, which have entangled states, be it the spin, energy, etc. The work of Scully et al. DOES NOT violate Complementarity, and they have made NO such claim (he kindly invited me to give a talk on my experiment to his group at TAMU, where we discussed his team's work as well.) What Scully et al. suggested and was later tested by Rempe et al. was that the causal origin of Complementarity is not ALWAYS the uncertainty principle, and I fully agree with him on that. No one, up until my work, has had a legitimate claim that their experiment violates Bohr's Complementarity, that includes Home et al. (as per personal communication), and Mizobuchi et al.

Entanglement is an extremely important phenomenon and fairly soon, I will embark on a series of experiments that involve entangled states.

Regards.

Dear Aurelien,

As you well know, in QM, once you have an amplitude from a particular origin, then the observable of that amplitude can be attributed to that origin (in our case to the particular slit) in order to uphold a relevant conservation law (e.g. linear momentum, spin, etc.) This is clearly manifested in the Heisenberg's Microscope: the amplitudes from the scattering of a photon by the electron are summed up to produce the "image" of the electron. The wavefunction is NOT a "physical" wave (in the sense of classical wave mechanics), but travels and interacts with boundary conditions exactly as regular waves do (at least for the first order effects).

Bohm has a different formalism for QM and postulates the existence of "empty waves" similar to deBroglie’s "pilot waves". Until and unless the traditional QM formalism fails in predicting an experimental outcome, like most other physicists, I would avoid using the language of Bohm. Once we observe a failure of current QM, then other alternatives, like Bohm's theory can be legitimately tested, and either accepted as the new paradigm, or rejected as a failed (but most admirable) attempt.

Regards.

"The work of Scully et al. DOES NOT violate Complementarity, and they have made NO such claim."

Dr. Afshar,
I may agree with that ('does not violate Complementarity'). After all with entangled particles we have a second/fourth order interference. But for sure they made that specific claim I wrote in my message, in that paper http://www.arxiv.org/abs/quant-ph/9903047. I quote from the abstract "The experimental results demonstrated the possibility of simultaneously observing both particle-like and wave-like behavior of a quantum via quantum entanglement". I quote again from the paper "The experimental results demonstrate the possibility of observing both particle-like and wave-like behavior of a light quantum via quantum mechanical entanglement".

The problem I also see is that the meaning of "Complementarity" is not well fixed. (And of course You are trying to fix it!). There is the implementation due to Greenberger, YaSin, Englert, etc. in terms of "visibility" of fringes vs. knowledge of "welcher weg". But there are also the more general statements by Bohr: "This [quantum] postulate implies a renunciation as regards the causal space-time co-ordination of atomic processes" or "Conversely, any conclusion, based in an unambiguous manner upon the strict conservation of energy and momentum, with regard to the dynamical behaviour of the individual units obviously necessitates a complete renunciation of following their course in space and time".

Now - apparently, and paradoxically - Your experiment *seems* *to me* to confirm this "renunciation of following the course in space and time", unless we introduce time-reversals, retrocausations, Feynman zig-zags in space-time, etc. Which (according to Wootters & Zurek, Wim Rietdijk, etc.) is also a good possibility.

Regards,
-serafino

I was hoping that this experiment that shows wave and particle behaviour of light simultaneously may shed some light on the central mystery of QM. Many authors are still talking about "Conscious" observers being required etc. Philisophically speaking now, we want to devise a theory whereby QM is objective and the reality that is perceived by QM in experiments is explained by objective means and not by invoking subjective observers, or many worlds, many universes etc.

QM appears to violate causality as it is non local (indeed even if QM is wrong nature appears to be non local) and this appears to be due to entanglement. If we accept non locality then surely the central mystery of QM disappears as we are accepting that somehow some form "spookyness" is possible.

I have even read recently that the virtual particle sea interacts with real particles and this is why entanglement is seen as the reason for everything QM and not the uncertainty principle.

There was a artcicle in new scientist around two years ago called Entanglement rules OK which put simply stated that the Uncertainty principle argument used by Bohr to argie with Einstein may have won the day but it was simply incorrect and that after a exhaustive review of QM Entanglement was the cause of all strange QM behaviour in the main.

Dear Dr. Afshar,

http://groups.google.com/groups?selm=3B2834CE.12A292B0%40lycos.com

"It is fundamental to understanding the concept

of generalizing the observant variables in theoretical physics.

Timofeev is conceptualizing the basis for the Copenhagen Interpretation.
His point is revolutionary. Why does Minkowski Space Exist? It is answered by the
posting, explaining INFORMATION reconstruction in an interference system
where the causality ENDED at the SLOTS.

Douglas Eagleson
llef@lycos.com "

Douglas Eagleson:

"A Note to Quantum Mechanicist's:


What follow this set of paragraphs is an example of the interpretation
of Quantum Mechanics by someone willing to consider the photon a
logically abstract object. The system of describing physics is simply
elegent when the Copenhagen Probability of Interaction concept is seen to be
a result of the Principle of Relativity's need for a generalized
observer. Our eyes are on example of such an observer.

Please think it to be the same problem. How do our eyes detect and
transform the quanta to information? They are one in the same
questions. You must answer this to study Quantum Mechanics, otherwise
you lose perspective of real proofs of the below system.

After Treeforv's reposting below there follows a logic to implement the
reconstruction of Information obtained from Minkowski Space.
This space is the only place photon's exist, and is only inferred.
There is a little translation problem in Treeforv's posting that
you are not taking account of. When photons do not exist, he means
photons are inferred in his Interpretation of Quantum Mechanics.
Copenhagen does not even address this simple logical beginning
of an intepretation's complete statement.


************************************************************************
The following was posted by Aleksandr Treeforv
on the sci.physic group

************************************************************************
You can play with a virtual radio interferometer.

If you will manage to explain a principle of operation of this type
of interferometer from the photon point of view, then:

I shall believe in existence of photons, and I shall eat my tie or hat.
---------------------------------------

I think, that your navel will be untied, but you can not explain
----------------------------------------------------------------
a principle of operation of a virtual interferometer from a photon
point of view!


Give an evaluation to the size of a photon if the photon has
a wavelength 3.5 cm. and if the distance between antennas is equal
to diameter of globe. :O) !

Any attempts to explain the principle of operation of the given
type of the radio interferometer from a photon point of view
will suffer a fall.



The radio interferometer with independent writing of signals on
"slots" is a direct proof of a non-existence of photons in a nature.

By my former scientific chief Matveenko Leonid Ivanovich (he works
at the Space Research Institute RAS till now) in 1963 was invented
the absolutely new kind of the radio interferometer.

Main ideas of this type of the radio interferometer were:
1. A simultaneous independent recording of signals on each
separate antenna ("slot") on magnetic tapes;
2. " The interference picture " is received in the computer
as an outcome _ mathematical _ addings of signals recorded on
magnetic tapes;
3. The distance between antennas ("slots ") of a radio
interferometer can exceed diameter of the Earth. (For definit
wave length limiting distances between antennas, at which the
interference picture disappears, is not known until now!)

There are no problems for explanation of a principle of operation
of the radio interferometer with simultaneous independent writing
of signals from a wave point of view.

---------------------
Here for the first time clearly emerges, that for a hypothetical
particle of a photon there is no necessity to pass simultaneously
through both slots (antennas), since the virtual interference
abstractly or mathematically will be realized in the computer at
any convenient time hereafter. !!! It is the experimental fact!!!

How the admirers of a hypothesis of photons now will explain
an interference?
---------------------

But any attempts to explain a principle of operation of the given
type of the radio interferometer from a photon point of view will
suffer a fall for the following reasons:

1. In this case there is no real physical process of an
interference - interference will be realized abstractly
mathematically in the computer;
2. Give an evaluation to the size of a photon if the photon has
a wavelength 3.5 cm. and if the distance between antennas is equal
to diameter of globe. Average on space density of energy impresses,
the delay of time in all processes impress too.


The quantum microsystems can absorb energy only by quantum
portions. This energy is absorbed as electromagnetic waves by
quantum microsystems at random coincidence of orientation of a
spatial dynamic configuration of a quantum microsystem with
orientation of an electromagnetic wave. Analogy between a quantum
microsystem and directional antenna here is conducted in an
obvious kind.

"

Dear Serafino,

"To be sure the interference pattern disappears when which-path information is obtained."
Scully et al. in http://www.arxiv.org/abs/quant-ph/9903047

This clearly shows that they did NOT claim violation of Bohr's original assertion that interference and which-way information are Complementary, i.e. mutually exclusive in any given experimental setup.

It is true that Bohr overextended the philosophy of complementarity to many diverse fields, from physics to psychology etc. But in the context of Bohr-Einstein debates in physics, it is absolutely clear that in a welcher Weg experiment the Complementary observables are interference pattern and which-way information. Just a quick look at the ref.s in my paper would suffice to illuminate this point. Many physicists who have been frustrated by Bohr's ideas call his assertions vague, and evasive. While it is correct that Bohr enjoyed speaking in such covoluted terms, he is uncharacteristically clear where it comes to Complementarity in "which-way" experiments, i.e. what Englert calls the “Interferometric Duality.” I have sited over 16 ref.s in my paper (not to mention hundreds of textbooks on QM including Feynman's lectures) that discuss this point and make it clear. Therefore I could hardly be blamed for "trying to fix" the meaning of Complementarity in “which-way” experiments, Bohr himself took care of that.

Wave-particle aspects are not always Complementary and can be observed simultaneously in a given experiment. The mere fact that an interference pattern builds up from individual clicks of photon absorption on a photographic plate is sufficient to see simultaneous wave and particle aspects in an experiment. But they are not forbidden by Complementarity as both Bohr and Einstein agreed. Complementary observables are mutually-exclusive and are forbidden by Bohr's Principle of Complementarity becasue accepting both leads to logical inconsistencies. Any other definition of Complementarity in welcher Weg experiments is just factually incorrect. Every notable physicist I have discussed the issue of the definition of Complementarity in welcher-weg experiments agrees with me: Prof.s Gerald Holton, John Cramer, Halperin, Feldman, Home, Zubairym, Marshal, Griffiths ...

Regards.

Afshar

If they are as you say mutually exclusive and you have shown the logical inconsistency of complementarity with the only experiement so far that shows this then surely this does not as yet scientifically make complemtarity worng does it? if we have 100 experiements that show complementarity not to be violated and 1 that violates it, does that make it wrong ? Surely we need more evidence of complementarities weakness before we rewrite the quantum rule book ?

Would you agree ?

I personally have never been comfortable with complementarity as it appeared to be too subjective for my liking invoking conscious observers etc. Still it is the standard interpretation and science will not dismiss it on the basis of a single experiment.

Dear quantumenforcer,

Bohr called Complementarity a "Principle" (and everybody in the Orthodox physics community accepted it as such.) As soon as an exception is found to a Principle, it loses its stature as a Principle, and that is what my experiment does. The Ptolemaic (Geocentric) theory was successful in explaining hundreds of phenomena. But as soon as Galileo found an exception to it (e.g. moons of Jupiter) the stature of Ptolemaic worldview was reduced overnight. Of course, it is essential to follow up on the tantalizing suggestions a new finding brings about to shore up one's position, and that is exactly what I intend to do.

Science is not a democracy as some might think. Truth could care less about the opinions of mere mortals. In my view, as harch as it sounds to modern man, Science is the dictatorchip of Truth and Reason, and as Galileo said:

"In questions of science the authority of a thousand is not worth the humble reasoning of a single individual"

That is not to say persuading your colleagues is not an essential and noble task, but it is secondary to pursuit and discovery of Truth.
Regards.

Can you explain a bit more regarding simultaneously showing wave and particle behaviour and it not violating Bohrs complementarity. I thought that no experiment had managed to show wave and particle behaviour simultaneously. I thought that many had tried but none had suceeded as it had collapsed the wave function everytime they have tried.

I thought that yours was the one and only to show wave particle duality without collapsing the wave function. Is this the case ?

Dear quantumenforcer

Consider the build up of an interference pattern. As one-photon after another is registered, each making particle-like clicks in only one point at a time, we start to see an interference pattern emerge, which is a wave-like property. Both the particle and wave properties are present in an interference pattern. But this is not a violation of Complementarity, and is absolutely allowed.

It is only when the particle and wave properties give contradictory logical inferences that Complementarity gears into action by forbidding it to happen. For example, if you obtain the "which-way" information for a photon, then you can tell it came through a particular pinhole. But as soon as you make this inference, then this photon could not participate in the build up of an interference pattern, because it must "go" through both pinholes to do that. One photon cannot do both, and that is why Complementarity forbids it. The fact that we see exactly this kind of contradiction in my experiment, leads us to either (i) abandon use of human logic in describing the experiment, or (ii) look for alternative explanations beyond the commonly accepted ones. I for one, would opt for (ii)!

Regards.

Dear Professor Afshar,

How does you experiment relate to the Rempe/Dürr and others experiments (based on Scully-Englert-Walther Inequality?) where Complementarity is rather taken as a uncertainty relation than full exclusion? I see that you state that 99.99% of the WWI is sustained, but how much of the wave-like info is? If you can reach almost 100% info from both behaviors, this would clearly indicate that an inequality to extend complementarity is also incorrect.

Regards,
André.

(PS: I'm still reading the paper carefully, I'm still a beginner and have some mathematical difficulties, so I'll take a time to finish it)

Dear Prof. Afshar,

Thanks for the answer!

"To be sure the interference pattern disappears when which-path information is obtained". And reappears when the information is erased. No doubt that when they - Scully et al. in http://www.arxiv.org/abs/quant-ph/9903047 - say "The experimental results demonstrated the possibility of simultaneously observing both particle-like and wave-like behavior of a quantum via quantum entanglement" they say too much. (Simultaneously is a dangerous term in SR but also in QM).

Just a lucid dream here. Is it possible to take a part of that 'virtual' - let me say so - interference pattern (I mean the interference pattern 'existent' before the lens) and take it to another place, without perturbing it too much? I mean by means of a half silvered mirrors or something else? (Ok the dream is not so lucid, indeed, but it might be interesting anyway).

Saluti,
s.

Dear Shahriar just two things :

1) Bohm mecha.doesn't use an other QM formalism but use this formalism in a different way. the formalism is sufficient ot justify all but the concept of particel is not well introduce in the theroy of Bohm. We need certainly to modify the model to explain the existence of the particle. Remark: Bohm speaks about ontology and Bohr about experimental fact and there is no conflict between the two conceptions.
2) However the Bohm theory is highly non local as proven by Bohm and Bell . In the experiment of the Heisenberg microscope this nonlocality will be present and will falsify your result . I dont want to introduce math. here but it is trivial to observe that the entanglement between the photon and the emiting atom will depend on the moment where the effect is observed . If you detect the photon in the vicinity of the slits you know for sure the which path. but if you detect the phtotn with a microscope the photon come from the wrong pinhole and you have no really a which path experiment.

3) As I say it several+1 times you must separate the problem of the path followed by the photon (if such path exists ) from the complementarity principle. The first is connected to a precize model of the photon (which doesnt exist in a univocal way presently ) and must certainly other theoretical elements to be consistent . The second is strictly connected to the formalism and to its statistical meaning and will never be false if you interpret it correctly (see all my precedents comments ).


Aurelien

Dear Prof Afshar

But surely the contradiction is that a photon acting as a particle and as a wave at the same time does not make sense from a classical standpoint. Therefore you attempt to resolve the issue inferring that as you are seeing the wave properties of a particle then the particle needs to go both ways (entanglement with itself ? ie a special case of it) in order to create interference. And from a classical standpoint you cannot understand how this is. From a quantum standpoint as you have observed wave particle behaviour at the same time then you could accept the fact that light is what you are seeing it to be.

A direct or indirect measurement, absense or gaining of any knowledge or information pertaining to which way (route) information collapses the wave function and reveals which way the photon went.

You now say otherwise as you have measured, gained the which way knowledge/information but the wave function has not collapsed ! True ?

Dear Shahriar , I would like to discuss about the D.Home experiment with D.Home him self. It is extremelly difficult to find his email adress on the web. If you have something can you sent it to me via email ( you have my adress I think?)


thanks in advance


Aurelien

Dear Aurelien,

1) In Bohmian mechanics we have the Guiding Equation: dQ_k/dt = (h_bar/m_k) Im [ψ*∂_kψ/ ψ*ψ] (Q1,...,QN). There is no such equation in ordinary QM, let alone the concept of "guidance" for a single particle in the interference pattern. By-the-way, I have never seen Bohmians explain single photon interference, only electrons. If you know of a ref. where light is discussed I would appreciate it.

2) In my experiment I never talk about the "path" a particular photon takes, only the fact that it's origin can be assigned to a particular pinhole. This is an important distinction. In Bohr-Einstein debates, when they talked about "which-way" information they actually meant "which-slit" for the double slit type of experiments. The "which-path" is only relevant to Mach-Zehnder type of interference experiments. It is a very long story, which I will talk about in the book I am currently writing.

3) I am trying to contact Prof. Home to ask his permission to give you the e-mail address.

Regards.

Dear quantumenforcer,

In QM, entanglement can only be defined as between (at least) two particles. A single particle cannot entangle with itself! The collapse of the wavefunction is also a very thorny problem. I am writing a popular level book right now, and I will attempt to explain this concept in general, and in light of my experimental findings.

Regards.

I went through many of the posts above, and was struck by the that way many speak of the solutions obtained by using otpical calculations (Read Maxwell's equations) as though they are "quantum wavefunctions".

Maxwell's equations are not identical to the "psi"functions of QM. It appears to me that there is an underlying assumption within these conversations that collapses the two togehter. Just because both allow us to calculate "probability amplitudes" that does not mean that they are equivalent.

Surely one of the questions one could raise about QM is: Are the interference effects that photons exhibit governed by the same mechanisms as the ones that operate when particles of matter experience interference.

Your experiment may allow us to break that equivalence. Could you envision a version of your experiment that we could do with say electrons, atoms or bucky balls?

As an aside, some posts raise the issue on non-detection. Surely your experiment should also work in the inverse. That is, if two black disks are placed in a beam then their shadows should interfere and you could image them with the same lens and mirror setup. This time, you could place the wires at the interference maxima without altering the "darkness" of the disk images.

Regards. JM

Dear Prof Afshar

In the two slit experiment when a single photon is used we see a interference pattern and hence this possibly means that the photon went both ways or am I just thinking about this experiment from a classical perspective ?

Most textbooks on the subject explain it this way but I guess that they to are thinking in either/or terms. It can be a wave or it can be a particle. From a quantum perspective a quantum entity is a wave and a particle and as such can only be defined in terms of probabilities. This quantumness has no classical counterpart and I guess it is this that causes all of the fuss in qm.

Still it has not stopped people from trying to find out which path the photon want but then theydestroy the quantumness and end up with a classical answer and hence again it looks like quantumness appears to be very fragile in nature. I presume that as you have manged to infer which way the photon has gone and preserved the quantumness of the experiment you have ruled out the act of observation as the cause of the collapsing wave function.

Dear Prof Afshar

This is posted on John gribbins website in the "quantum mysteries section"

Common sense tells us that the first atom cannot be excited until a finite time after the second atom decays -- until there has been time for radiation travelling at the speed of light to cross the gap. That is the result Fermi found. But it now turns out that he made a mistake in his calculation. Probably because the mistaken conclusion matched common sense, it took a long time for this to come to light. But Hegerfeldt's correct version of the calculation now makes it clear that there is a small chance that the first atom will be excited as soon as the second atom decays (Physical Review Letters, vol 72 p 596). As with all such quantum puzzles, this is only the beginning of the story; now, the experts have to explain what this mathematical result means. The best interpretation of the evidence so far seems to be that we should not think of any object, not even a single atom, as an "isolated system".

Are you sure that a single photon cannot interfere or entangle with istelf ?

regards

Dear Murphy,

Maxwell's equations give the exact same result for first order effects if you translate irradiance -> probability distribution. Since all observed effects are of first order in my experiment, one can use the QM and physical optics language to get the right answers. The only problem is the collapse issue at destructive detection events at the detector that needs to be treated with care. I am currently working on a paper discussing that issue.

Regards.

Dear quantumenforcer,

A single photon almost always interferes with itself, given alternate routes to the same spatial location. A single photon cannot entangle with itself! It takes (at least) two to Tango,... (i.e. entangle)!

What John Gribbin is talking about is that a single atom is almost never an isolated system: it is constantly interacting with its environment such as other atoms, free particles, em field, gravitational field, etc. Many of these interactions can lead to decoherence depending on the severity of the perturbation they impart. This is a very long story, but one that is not directly related to my experiment. I will be covering decoherence in my book as well, in case you are interested.

Regards.

Dear Prof Afshar

It seems strange to me that if the central mystery of qm is realised in single photon experiments and entanglement is not a factor here due to the fact that that there needs to be two in order to entangle then that must mean that single photon experiemts are a special case in qm. Everything else appears to be driven by entanglement ! I actually though that there was no such thing as a isolated systems due to the virtual particle sea.

Was complementarity dreamed up in single photon times only ?

Dear Shahriar,
first thanks for your question to D.Home.

concider now our problem:

The Bohm mecha. in term of point like particle dynamics is effectively defined for the non relativistic case (and for dirac field ) only. Because your reasoning with the lens is general it can be apllied with electrons too and your argument fails.

The problem for relativistic particle is complicated because in general we can not easily define a time like probability current .
A method is however possible if we consider the 4 tensor T^{i,j} of energy and momentum [1] and consider the quantity T^{i,j}a_{i} where a_{i} is a time like 4 vector. This method applied to the photon is independent of a_{i} for a plane wave but in th general it is not the case. becaue I speak only about possibilities this is not for me a problem here and we can use it a good basis in the discussion. However i insist on the faxt that this covariant choice is for me arbitrary if we can not justify it on a physical principle.

I submitted recently something using this idea in a comment . I can not for this reason give you for the moment this paper (which is not directly conneted to the present problem).

The most interesting point is when you distinguish between path and origine of a path . what do you mean by assigned to a pinhole?
I f you mean that a detector just after the slit will see the photon I agree with you but dont use in this case the term which path or which way without precision in your futur work : way = trajectory .

there is a lot of ambiguity on this concept and if your paper(s) is (are) accepted i will submit a short comment on this direction

In any way my argument is still completely correct:

1) Which path implies a model and such path can be counter intuitive= the model can lie to us ( this is a dramatic consequence of the quantum formalism).
2) The complementarity principle can not be jugded and is still valids.


aurelien

[1] Holland the quantum theory of motion , cambridge university press 1993.

Dear Prof Afshar

Thank you for considering my point. The intensities that are calculated from Maxwell's equations exactly match probability distributions (when counts of individual photons are taken) in space/time.

In contrast, quantum theory appears to be very different. The equations operate in Hilbert space, and do not play out in "physical" space-time.

I am not sure what you mean by "first order effects". QM exactly predicts the far field pattern in experiments such as the two slit experiment. The momentum distribution in the pattern is the Fourier transform of the hole pattern in the screen scaled by Planck's constant.

The difficulty occurs because the formalism doesn't provide the intermediate information as to how the pattern is formed. One takes the initial spatial distribution (the transverse slit pattern), performs one mathematical operation and bingo! you get the final (the transverse momentum) pattern.

If one takes the step of assuming that the probability patterns must to be "explained" by some sort of propagating wave-function, then one is led to consider such notions as collapse and complimentarity in order to get the idea to work.

However, after all this time, there still seems to be a lack of solutions that are consistent with the propagating wave-function idea. Notably, De Broglie failed to obtain his "pilot" wave solution and there has never been an explicit model of "collapse".

Surely, the whole question of complimentarity and collapse is a result of taking that one step of assuming that the mechanism at play is one in which particles (photons/electrons/atoms etc.) are governed by a common propagating wave mechanism that is somehow related to the mathematics of Schrodinger's equations.

It could simply be that current QM formalism just cannot provide the "intermediate" solutions, says little about the mechanisms involved, and is not related to some propagating wave function in space/time.

Anyway, I still beg to differ and re-state that one cannot just take probabilities obtained from Maxwell's equations and assume that they reveal the behaviour of some underlying "propagating wave-function" for which we do not have an explicit model.

Regards.

Dear Aurelien,

Therefore according to your arguemnt, the only way one can save Bohr's Complementarity is to accept Bohmian mechanics (Anti-Bohr!!!) and forgo the generally accepted quantum formalism. Well, that really does sound like throwing out the baby with the bathwater! My experiment shows that something has to give, but at this time I am not ready to convert to Bohmian mechanics just yet, (like most other physicists.) As you well know, Bohm put forward his theory to circumvent the Copenhagen Interpretation. He will turn in his grave to learn that his theory is being used to defend Bohr’s Copenhagen school of thought!!!!

Best regards.

Dear Shahriar
I dont forget the quantum formalism because Bohm is based on the quantum formalism it self. I will never used Bohm for practical calculation naturally because only average can be observed. I present just this dynamic as a counterexample to the intuition ''if a saw a photon in A' then for sure he came from A''.
Heisenberg , Bohr Wheeler and you used this intuition and dont consider that in quntum mechnics the dynamic of a particel could be completely different.

Now when you say
'As you well know, Bohm put forward his theory to circumvent the Copenhagen Interpretation. He will turn in his grave to learn that his theory is being used to defend Bohr’s Copenhagen school of thought!'' you believe that my argument is only based on bohm dynamic.
however this is not my idea :
Different times I explained indeed that you never observed really the fringes but just deduced them from your complete conviction that waves are here even when we can not see them .

The Bohm argument is a second point more general but less important here because applicable to any so called which path experiment. This second point is in fact a problem of semantic which is not connected to the problem of the complementarity.

I think that I confused you with this two argument used in parallel....

please excuse me for that

Aurelien

Dear Aurelien,

I am not in the least bit confused about your arguments (I am not sure about you though!) You use two different and completely unrelated arguments: Bohmian mechanics, and no "observation of interference pattern". As for Bohm, you know where I stand from the previous post. The "no observation" argument is just simply false if QM is correct. I accept QM formalism as an axiom, therefore I use it to get a prediction as to what we expect to observe (or not to observe for that matter.) It tells us that if light is incident on the wires, and we don't observe light blocked by the wires, we MUST assume an interference pattern. There simply is no other explanation within QM. So again, I choose to accept QM formalism, rather than Bohr's philosophical bent.

Regards.

concerning Bohm it is your personal choice to like or not Bohm dynamic and this is the problem. You can ot refute and I can not prove Bohm's theory. But one thing is clear If you follow this consistent model then your trajectories for the photon are Fuzzy.

I insisted too much on this dynamic because you asked me some details on it. However it was just an example . And this example prove that the term which path that you use depend of the hidden variable model considered. In a class of hidden variable (The Bohm's class) the photon come from the wrong pinhole. consequently this is sufficient to eliminate the term which path of you experiment (after you use it in your title).


Ok now concerning complementarity :

Consider just the Young experiment . You see fringes with visibility V=1 on a screen. consequently wave optics tell you that there is necessary two pinholes emitting the same amount of light in phase (if the maximum is in x=0 the difference between the phase of the wave in the two pinhole must be equal to zero) .
Did you effectively observe this pinhole ? no
Did you know where this photon come from ? no
if you want to know you have to see the photon. To see mean absorbtion and destruction CQFD .
If you use entanglement it is more complicated but the result is the same: after statistical accumulation your photon participate to a interference pattern or to the information ''how many photons would be in A or B if I measured them directly in such place''.

the Young experiment (as your experiment) can not construct the the two distributions with the same photons: this is bohr's complementarity.

Remark :I didnt used the term which path because this term is ambiguous as proved before and this conclude my reasonning


aurelien

Dear Prof. Afshar,
Dear Aurelien Drezet,
Dear John Murphy,
Dear quantumenforcer,
Dear Quantum Mirror,
Dear Pavel Kurakin,

From: a_n_timofeev@my-deja.com (Aleksandr Timofeev)
Newsgroups: sci.physics,sci.physics.relativity,sci.astro
Subject: Re: Quantum Paradox of a Self-Interference of a Photon in VLBI
Date: 10 Nov 2004 09:12:10 -0800

selftrans@yandex.ru (Sergey Karavashkin) wrote in message news:...
> Dear Aleksandr, my search have led me to your discussion. As far as I
> can understand, you are discussing, whether the photon can interfere
> with itself in your VLBI. Why so complicated. I many times asked
> respectable supporters of photon conception to explain the
> interference of light at the edge of screen. There is no signal
> transformation which takes place in VLBI. There things are ultimately
> simple. We have a source of light, a screen and its edge. A laser can
> serve as a source of light. What can be simpler?

THE PERFECT EXAMPLE.

Here you describe actual physical process of an AUTOCORRELATION.

> Two photons cannot
> interfere at the edge of screen, but we have an interference; if
> someone doubts, I can refer to not one but several photos from
> different sources. Well, when Quantum Mirror explains you the
> phenomenology of this phenomenon, he will be allowed to oppose you in
> the rest issues. ;-)

Dear colleagues you have caught themselves in a trap of a faulty
logic vicious circle! The conventional approach to physical
interpretation of principles of operation of an interferometer
contains a _key_ physical error.

Till now you can not understand the prime physical device (interferometer),
which one consists of TWO INDEPENDENT BASIC PARTS:

1. THE SELECTOR of streams or stream of an electromagnetic radiation.

2. A CORRELATOR. THE CORRELATOR is the Device integrant streams of
an electromagnetic radiation shifted from each other on set of time
delays.

The correlation can be of two grades:

a) an actual physical correlation between streams of an
electromagnetic radiation.

b) a Computer correlation between streams of an experimental
digital data for actual streams of an electromagnetic radiation.

I have two problems for you:

1. What is a CORRELATION of streams of an electromagnetic radiation?

2. What devices can supply the mechanism of a CORRELATION of streams
of an electromagnetic radiation from a source(radiant) of the given
radiation?

What is a CORRELATION from a mathematical point of view?

Best regards,
Aleksandr Timofeev

This is my opinion, not the official opinion of Space Research Institute Russian Academy of Sciences

PS The term a CORRELATION is a synonym for the term an INTERFERENCE.

Dear Aleksandr Timofeev
I have been working in the field of GPS interferometry, which works by mixing signals from two separated antenna into a correlator. The signal from one antenna is fed through a (periodic) phase shifter and the "signal" is the variation in the intensity of the correlator output.

In a sense, the interference that is measured is the interference between the modulated signals rather than that between the underlying photons. The GPS signals are below the noise threshold and are indistinguishable from noise without the "magic" of the correlator. The raw summed signals that come out of the mixer appear to be just "noise". The amplitude of the correlator output varies in step with the cycles of the phase shifter.

This is quite different from the Young's type of photon experiments because it requires a signal modulated onto a stream of coherent photons. GPS correlators work by correlating a received signal with a local signal using a-priori information. My concept of correlation is that it is a statistical measure of the temporal similarity of two signals, autocorrelation refers to a signal's temporal variation with itself and can be used to distinguish information from noise. I'm not sure if this helps, but most descriptions of GPS systems will give you a pretty good idea about correlation and it's applications.

I'm not quite sure about your questions, but here goes...

1) correlations between "streams" of radiation looks at the temporal relationship between the patterns of received signal, often modulated onto the streams.

2) Mathematically it is done by convolving signals (sets of successive measurements) and if done in real-time is usuually over a fixed time apeture.

Regards

Dear Prof Afshar

The posts by Aleksandr Timofeev are inappropriate for this discussion and can be deleted if they bother you. He is a crank of the highest order and everyone on usenet has tried to explain to him that telescope interferometers do not involve self interference of photons. I pointed out in a recent thread in the simplest terms I could think of that he had confused physics and astronomy's terms for interference. He has been posting this same drivel over and over for three years and will never listen to the truth. I could never phrase it as well as John Murphy just did in his last message.

Dear John Murphy

Aleksandr Timofeev is not asking questions. Believe me when I tell you, he will try to involve you in a long circular discussion, where he can tell you about photons self interfering in a telescope and what this means to physics. This is his great discovery and no one will convince him otherwise! :)

Dear Aleksandr,

There really is such a thing called a two-photon interference, and it is a second-order (or higher) effect, so all interference effects are not single photon self-interference. While there is still some controversy over the interpretations of correlated flux measurements in VLBI within the context of QM, it is not directly related to the experiment I have conducted. I wish to use this Blog to answer questions related to my work, and would appreciate if you limit your question/comments to the scopes of this page.

Best regards.

of the allowable pathways (those that link points of non zero probabilities of finding a photon) your experiment excludes none, since your wires are placed at a point where the probability of finding a photon is zero. Since your experiment does not reduce the number of allowable pathways the 'which way' information is not changed by your placement of wires.

Dear Dr. Afshar:

Thank you very much for your comment to my message.

You can be acquainted with methods of VLBI in the magnificent book:

INTERFEROMETRY AND SYNTHESIS IN RADIO ASTRONOMY
second edition
A. Richard Thompson National Radio Astronomy Observatory
James M. Moran Harvard-Smithsonian Center for Astroohysics
George W. Swenson, Jr. University of Illinois at Urbana-Champaign

ISBN 0-471-25492-4 INGLISH John Wiley & Sons, Inc., 2001

The principles of operation of a VLBI CORRELATOR will help to you to look at your experiment in considerably diverse physical interpretation or from completely other point of view of an ABSTRACT MATHEMATICAL INTERFERENCE, which one is possible ONLY in VLBI. The revolutionary methodology and the technologies VLBI more than for 60 years anticipate methods, which one you have used now.

Best regards,
Aleksandr Timofeev

Dear Mr Timofeev
On reflection, I have realized that both GPS and VLBI interferometry do not employ interference effects at all. This whole VLBI thing is a red herring.

The object of interferometry is to form an image of the source by calculating the direction of the incoming rays (all "classical", no Planck's constant or expectation values required).

In contrast, with the optical interference, one observes the pattern thrown up on a (disant) screen by a coherent source.

The interferometers employ correlators which match up signal patterns to get the time delay between reception of signals so that the direction of propagation can be determined via a bit of determined trigonometry.

The Fourier transformations are performed to facilitate convolution of the two signal patterns. The algorithms perform sophisticated pattern matching to pick up shifts between similar signals. The outputs are precise time delays.

It doesn't matter how the signals arrived or are propagated. The signals could come via intergalactic carrier pidgeons and it would still work (provided they all flew in straight lines at the same speed). I can do it, I wrote real-time software to do exactly that job, and there is no obvious parallel here.

And now Prof Ashfahar

Back to Bohr....

It seems to be difficult to define what it is that we are arguing because complimentarity can be correct whether or not there is some particular mechanism involved. Even if one takes a trajectory approach, (say like Bohm) the principle is obeyed because QM predicts that the trajectories are sufficiently "delicate" for direct observation to destroy the pattern.

Comlimentarity could be fundamental or it could just be a shorthand way of expressing the limits of knowledge embodied in Heiseberg's uncertainty principle. So far, there is no way to tell, and it would seem to me that your experiment doesn't provide a way to resolve this.

At the very least, it does however indicate that putting sensors in locations that we know "a priori" that the particle will "not be" does not constitute an "observation" in the strict Copenhagen sense.

In logic theory, there are two kinds of negation. Boolean style (A is Not B) and "denial" (familair in speech, e.g. the statement "It is not raining" tells me little about the weather).

It seems to me that your experiment is of the latter type, "the particle did not go there".

If so, then this would indicate that the information gained from an experiment that produces denial type of result does not constitute a "measurement".

Regards John

Dear John Murphy,

If "the information gained from an experiment that produces denial type of result does not constitute a 'measurement'" as you suggest, then this seems quite exciting to me.

To my layman's understanding, it would seem that this opens up a whole new way to probe quantum phenomena and especially the boundary between quantum and classical physics.

I think it would be especially interesting to see just how much " denial type" probing a quantum wave could take, and how much information could be extracted, before it collapsed. As a blind guess, I suspect that it will degrade gradually, rather than an either/or collapse, which would open up all sorts of interesting possibilities.

Maybe Professor Shahriar Afshar has stumbled on a much more powerful tool than he realizes. And maybe, the way an open Internet discussion can allow have many minds probe the same question from many angles may be a new way to do, or at least test, some sorts of science.

Regards
Stephen Heyer

Dear Shahriar,
More I analyze your article less I see how you can even think to break down the principle of Bohr wich such system.

You see no fringes and you would like nevertheless to convinces your self that there are here. Naturally I understand that you are right to say that : the wave formalism imply that you need fringes in front of the lens . The problem is that to observe this interference pattern you need different photons that the ones used to construct the two spots 1'and 2'. Dont forget this fundamental part of the Bohr principle:
2 complementary information can not be extracted from the SAME PHOTON . You need unfortunately 2 experiments excluding each other to manage that.

Aurelien

Dear Stephen Heyer,
The "Denial" type of logic is inherent in Quantum formalism. I have a paper by Dr Rachel Garden that goes into it in mathematical detail.

Polarization measurements are an example of a denial measurement. If a photon passes a polarizer set at orientation "A" all you can say about its original polarization is that it was not linearly polarized at exactly at 90 degrees to "A" (and therefore always be absorbed or deflected away). Dr Garden points out that this type of logic allows Bell inequalities to be broken without the need for drastic assumptions regarding non-locality and FTL collapse.

This type of information is actually quite limited, because the measurement destroys the original state and only says that the polarization state was definitely not "one thing" amongst an infinite set of possible "other" things.

By the way, how do you know that what we are probing, is in fact, a quantum wave? Bohr's philosophical work looks to be a bit like Freud's work, leading everyone into a theoretical edifice based on a narrow foundation of assumptions about the nature of what is being examined. If we uncritically use the language of Bohr's paradigm we automatically prevent ourselves from being able to think outside that paradigm.

Regards, John

Dear John Murphy,
Dear Prof Ashfahar,


I did comment for you at URL :
http://groups.google.com/groups?selm=e16a4a22.0411120701.26587111%40posting.google.com

Best regards
Aleksandr Timofeev

PS It was deleted from BLOG

Dear John Murphy,
I don't know. As I understand it, Professor Shahriar Afshar first tests (yes, via a "denial measurement") for the presence of an interference pattern, THEN tests for and finds "which-way" information.

By first and then I mean of course along the path of the photons, not in different experiments.

Incidentally, it occurs to me that the order in which the experiment is carried out - first test for wave, then for particle - may be as important as testing by using a denial method.

Anyway, the test does seem to not only establish that an interference pattern exists prior to testing for which way information, but also partially map it. It seems to me that if you could use this method to fully map all the dark fringes of the interference pattern you would, by default, also know exactly where the bright fringes where: You would have mapped the complete interference pattern, THEN established full which way information.

The way to do this would be of course to place wires, or some other suitable obstruction, in all the dark fringes (as established by previous tests or by calculation) then see how much light was blocked and how much which way information was preserved.

As I wrote in my first post, I have a gut feeling (and that is all it is) that as the interference pattern is probed, the which way information will progressively degrade.

However, and this is a very big however, it should still be possible to gain quite a lot of information about both the interference pattern and the which way information at the same time (just not complete information). Certainly, however, enough information to do some very interesting things, and blow a sizable hole through part of quantum theory, or at least our current interpretation of it.

In fact, I think Professor Afshar has already demonstrated this in principle.

As for the " quantum wave" reference, well, I used that description because it seems to be the generally accepted one. I am aware that others exist.

Regards
Stephen Heyer

"complementary information can not be
extracted from the same photon"

Dear Aurelien,
Of course you mean information about 'sharp' complementary observables.
But is it possible to extract *part* of that 'virtual', 'potential' interference
pattern that 'might' be before the lens? I mean a half silvered mirror,
or something like that, which could carry *part* of that 'virtual', 'potential' interference pattern to a different location, i.e. a screen or a detector
array, to test if there is a 'real' interference pattern? (I'm not saying here
that we could extract, this way, 'complementary information' from
a single photon, I'm just saying that we could prove that the interference
pattern before the lens is not a 'ghost').
A bien tot,
-serafino

Dear Friends,

It seems that a few points are still not clear to all:

1) "denial measurements" are indeed measurements. John says that the statement A: "It is NOT raining" tells me little about the weather". This is true, but this same statement tells you all you need to know about the following statement B: "It IS SUPPOSED to be raining". Evidence that A is true, invalidates B immediately.
2) In my experiment all photons either end up in detector 1' or detector 2' placed at the location of the images. IF we accept the QM formalism, then there is no ambiguity about which pinhole each photon has come through. (IF you have a problem with this statement, then either you have not calculated the quantum-mechanical outcome of the experimental setup, or you happen to believe in Bohmian mechanics, or some other hidden-variable theory which is not universally accepted by most physicists.) Since we have the which-way information, therefore, NO photon is allowed to have behaved in a coherent manner according to Complementarity. That means NO photon is SUPPOSED to participate in the BUILD UP of an interference pattern.
3) If none of the photons are participating in an interference pattern, then some of the photons MUST be incident on the wires and thus cannot make it to the images. We observe that all INDIVIDUAL photons arrive either at detector 1', or detector 2', none is missing. From this observation we conclude that the statement dictated by Complementarity, i.e.: "some of the photons MUST be incident on the wires" is thus FALSE.
4) The only known mechanism by which these photons can avoid hitting the wires is interference. Read section 3 in my preprint to follow the reasoning behind this conclusion.
5) Thus we establish that which-way information for all photons is obtained (K=0.999), and interference takes place before the lens (V=0.99). This is a violation of Complementarity.
6) Now on the idea that C: "complementary information can not be extracted from the same photon." I wish people would read and reflect on my preprint before making such claims. While I agree that if you use perturbative measurement schemes (see the preprint), statement C is true, however, if we use a non-perturbaitve scheme as with the wires, C is found to be false. The most important distiction between my experiment and all others thus far, is this: YOU NEED NOT DESTROY OR EVEN PERTURB A SINGLE PHOTON TO EXTRACT ENSEMBLE PEOPERTIES SUCH AS THE INTERFERENCE PATTERN. This is the crux of my work, and if you do not agree with this, then I can explain why I make this categorical claim. But I strongly suggest that you read my preprint very carefully, because the explanation is already discussed there.
7) In my experiment C is found to be false on the SINGLE-PHOTON level.

Regards.

"YOU NEED NOT DESTROY OR EVEN PERTURB A SINGLE PHOTON TO EXTRACT ENSEMBLE PEOPERTIES SUCH AS THE INTERFERENCE PATTERN."

Dear prof. Afshar,
I understand the above perfectly. The question a physicist (I'm not a Bohrian, I'm not a Bohmian, I'm not a ManyWorlder, and I'm not a real physicist) must ask is the following. How can we define, in your experiment, 'V', the 'Visibility' of fringes?
That is - I suppose - the question Aurelien (real physicist) and myself (amateur physicist) are asking themselves. Can we re-define that 'V'?
Regards,
-serafino

Dear Serafino,

My explanation concerning visibility of interference pattern is clearly delineated in the preprint, which is simply using QM to describe the state of affairs in the experimental configuration. However, if you (or anybody else) can explain the lack of incident photons on the wires without invoking interference I would be eager to hear about it, since it would mean that I have discovered a new phenomenon, capable of producing regions where photons avoid, without destructive interference as the explanation. That would be a phenomenon not currently described by QM (and I highly doubt it would be accepted by anyone, as the loci of avoidance coincide exactly with the dark fringe regions predicted by QM, or even physical optics)!

Regards.

Dear Shahriar, dear Serafino

1) The question ''where this photon come from'' is a metaphysical question whcihc can not be answered by any experiment because we can not distinguish between Bohm yand the intuition ' a photon in A' come from A as in newtonian dynamic' (idea very old that I attribute to Heisenberg Bohr and wheeeler but I can be wrong: I am not historian put physicist). For this reason If you or any one use the term which path experiment I become nervous...

2) Complementarity is a statistical statement independent of 1 .
Considering one photon you can use it in a interference pattern or in a image pattern . These two statistical behavior, observed EXPERIMENTALLY, exclude each other.

You dont observe experimentally fringes then you can say nothing about complementarity.
3)
an other point .

In your experiment you see the spots images unchanged and symetrical : this means D=0.
You have V=1 but to observe the fringes you need to put a detector in the fringes plane . You dont do it so you can not jugde complementarity.
You made Half of the work : you see spots. If you can see fringes nevertheless with the same photon you are a wizard.
You can be in addition tempted to say that D=1 if you concentrate only one one image. This will suppose V=0. However if you look in the fringes plane you see V=1? This is not a paradox because you can not be sure that the photon observed in the fringes plane will be the good one because as I said before it will be necessary a different photon that the one detected in A'. You have no experimental criteria to define such correlation (no entanglement) so this definition is not physical .

In your set up you have then really D=0


4) Concerning the effect of the wires you said: ''some of the photons MUST be incident on the wires" is thus FALSE''. you are right you have then extracted a information on the probability of presence at the wire positions but that 's all . The rest of the fringes pattern is not seen and again the principle of Bohr is saved.


voila a bientot

aurelien

Dear Aurelien,

''where this photon come from'' is a metaphysical question

1) This is your personal opinion and I respect that. However, Neither Bohr, nor Heisenberg (nor anybody else as far as I know) have ever disputed the fact that AFTER a photon is detected, it is legitimate to ask the question about where it originated. What they may have considered as metaphysical was talking about a photon's origin BEFORE it was detected. In fact before the photon is detected, one cannot even say that it existed, if no other a priori knowledge is accessible. THIS IS A VERY IMPORTANT DISTINCTION.

"Complementarity is a statistical statement independent of 1"

2) Complementarity is not independent of (1), at least in welcher Weg experiments. Indeed one leg of the complementary observables is the answer to "where this photon came from" and the other is the interference phenomena. What is your justification, or even a reference for such an assertion?!

"You dont observe experimentally fringes then you can say nothing about complementarity"

3) I certainly observe the Dark fringes experimentally. Yes, I do not observe the bright fringes directly, but that is not necessary for the purposes of the experiment since it is necessary and sufficient to prove interference with observation of Dark fringes, as described in my preprint. If you have a problem with that poof, or any of the theorems therein, please feel free to critique it. Otherwise, as I said in the previous post, if you can explain the lack of incident photons on the wires without invoking interference I would be eager to hear about it. Simply put, can you tell me why the wires are not receiving flux?

Let's make it as easy as it can be: Bohr says if you have complete which-way information, then your photons CANNOT have interfered. This is Complementarity in welcher Weg experiments. According to QM, the two images give us the full which way information for ALL of the photons. Therefore NONE of them could have interfered. Thus SOME (~6%) of the photons must have hit the wires. But none of the photons are missing at the image plane. Thus Bohr's assertion that there must have been a decoherent distribution before the lens is found to be false. However, this result is in complete agreement with the presence of interference at the wires, too much of a coincidnce don't you think?!

"you are right you have then extracted a information on the probability of presence at the wire positions but that 's all"

4) Well, thank you! That is all one NEEDS to prove Bohr wrong, because he predicts some incident flux at the wires, and we see none.

Looking forward to hearing your rigorous answeres to the above, especially to my challenge in (3). The response must be in QM formalism (not Bohm etc.) as I have shown in my paper. Any other explanation, simply highlights the fact that Complementarity and QM formalism have very little overlap!

Regards.

the topology of the space beyond the slits is a function of the slits. the surface of a torus is different than a the surface of a sphere! it is like a mechanical quincunx.

Dear Prof Afshar,

You observe interference at the wires (since there is no 6% reduction) therefore the photon which passes the wires must have gone through both pinholes. You later detect a photon which, since it is the same photon, must also have come from both pinholes. There is no which way information. I can't see any escape from this.
Also, the notion that you can use the principle of superposition to determine which pinhole a photon went through is actually invalidated by your experiment.
The wavefunction with both pinholes open and the wires in place is not the same as the sum of the two wavefunctions with only one pinhole open and the wires in place. The 6% reduction in intensity tells you this.

Chris.

Dear Chris,

I don't have much time, so very briefly:
1) Please read previous posts on this issue, especially the challenge for which I have offered a $1000 prize; it is impossible (using QM formalism) to show that which-way information is destroyed.
2) Principle of superposition deals with superposition of AMPLITUDES (ψ) not INTENSITIES (|ψ|^2). Therefore, when you superpose two wavefunctions from each pinhole, ignoring normalization, you have ψ _12= ψ _1 + ψ _2, and this is how the interference minima (as well as maxima) appear. Your MISTAKE is in thinking that |ψ_12|^2=|ψ _1|^2 + |ψ _2|^2. This is certainly incorrect! Please take a quick look at an introductory QM book like Feynman's Lectures on Physics...
3) The situation with both pinholes open and wires present at the minima, is essentially equivalent to the situation where both pinholes are open and no wires are present. Please read my preprint for more details.

Regards.

Dear Prof Afshar,

I don't think you have answered the first part of my post. Interference implies the photon went through both pinholes, hence no which way information can later be gleaned.

In answer to your three points

1) I have. You state that it is impossible, but you have not proved it. As far as I can see the only way you can be certain that a particular photon came from one pinhole is if all possible quantum mechanical trajectories came from that pinhole. With one pinhole open this is necessarily true, with two the QM formalism does not allow you to determine it with certainty. Lack of certainty implies lack of which way knowledge.

2) Why do you think I was confusing amplitudes and intensities? What I said was true when the wires are in place: if you calculate the two wavefunctions with one pinhole open and add them together you do NOT get the wavefunction with both pinholes open. However, if you do it with no wires then you DO get the same wavefunction. Please tell me you don't disagree on this point.

3) I agree. Hence, if you cannot use the principle of superposition to determine the origin of the photon with the wires in place, then you also cannot when they are not present.

Chris

Dear Chris,

1) Could you please reiterate what my challenge entails?
2) Are you saying in (3) that the images in front of the lens do not provide which-way information, even if there are no wires? Then, you should show us (using QM formalism) how it is possible NOT to have which-way information in the case when there are no wires, and two well-resolved images are obtained. Please do the claculations and e-mail me the paper.

(I would like to remind you that Heisenberg used the which-way information obtained by imaging techniques in his famous Heisenberg's Microscope proof of the Uncertainty Principle.)

Regards.

Dear Prof afshar,

1) Ok, if you insist.

"As I have indicated in my talks at Harvard, Princeton, TAMU, and elsewhere, I would award a $1000 prize to the first person who can show that the wavfunction of EACH image in the image plane in the case that both pinholes are open, and the wires are present, is a 50/50 mixture of the two wavefucntions emerging from EACH pinhole. I claim that it is impossible to achieve this feat using QM formalism."

You didn't say whether you agreed or disagreed with 2). Are you going to?

Re your 2) Yes, I said I agreed that the wires make no difference when both pinholes are open.

There is no need for a paper with explicit calculations, my point is physically obvious:
In the total wavefunction in the plane of the wires there are zeros and maxima. The maxima come about when the contributions from the two pinholes add in phase; we essentially get psi=1+1=2. Now, the crucial question is which part of that 2 is the first 1 and which is the second? Hmmm? Even worse than this, what about the zeroes, psi=1-1=0. How does it know that its not 2-2 or 100-100? The answer is that it doesn't know! The contributions from the two pinholes have interfered with each other, and the wavefunction at every point in the plane of the wires is a 50/50 mixture of the two pinholes. Once they have interfered we cannot separate them again and know for certain that this bit came from there. The QM formalism does not allow it.

In the QM formalism a calculation proceeds by starting with a separated 50/50 mixture of the two pinholes, propagating it forward in time, interfering the two contributions together and then separating them out with the lens. You WILL produce two well defined images which correspond to the two pinholes, but all you can say is that a photon measured at either detector came from an initial state which was a 50/50 mixture of the two pinholes.

Chris.

Dear Chris,

Each image receives amplitudes from only one pinhole, even when the wires are there. If you can prove that the final amplitude at EACH image is a 50/50 mixture of the TWO wavefucntions emerging from EACH pinhole, then it would be possible to show that when a photon is detected at an image, it's origin is not known. This is impossible to do. Remember, there is only one photon at a time, and you cannot (for example) use "photon-photon" scattering at the interfernce plane to arrive at the conclusion that which-way info. is lost.

Just curious, do you know how a lens works? If you do, you would realize that it dosen't matter if the light is coherent or not, the lens separates incoming wavefunctions based on their ANGULAR separation. The only difference between the coherent and incoherent/decoherent light is that for the coherent light the wires are inconsequential, but not so for the latter.

Regards.

Chris,
tThere is a good paper by Zeilinger
http://www.physik.fu-berlin.de/~simons/Publikationen/RevModPhys99.pdf
discussing an 'experiment' performed in Austria.
It is similar to Heisenberg's experiment.
If you can (I do not because of the language)
read the original paper by Dopfer here
http://www.quantum.univie.ac.at/publications/thesis/
Regards,
serafino

Dear prof. Afshar,
Imagine we have, instead of those two detectors at the image plane, two mirrors. And imagine those two mirrors, at the image plane, send each photon back, I mean from right to left, through the lens, and then through those little wires. Do you expect that this time (travelling from right to left) photons should be scattered by those little wires? I'm asking this because this time photons, travelling from right to left, might (might!) carry some information about the welcher weg. Or not?
Regards,
s.

Dear Shahriar,
you said '' I would award a $1000 prize to the first person who can show that the wavfunction of EACH image in the image plane in the case that both pinholes are open, and the wires are present, is a 50/50 mixture'' why 50/50 ? why not 51/49 for example. Of course I joke because for me this is not the essential argument.

The essential is that your use of the formalism is correct but that you dont know well the articles of Bohr (I guess you just read some sentences of him). You dont understand complementarityas I think I do. This is sad but but I am too tired to explain you again my argumentation.

You said :'' Complementarity is not independent of (1) [thequestion concerning whre this particle come from], at least in welcher Weg experiments. Indeed one leg of the complementary observables is the answer to "where this photon came from" and the other is the interference phenomena.''

This is the popular account (completely wrong as usual) Bohr considered trajectory as metaphysical (whihc mean not the subject of physics) the unical thing that we can be sure is the click on the detector. The term welcher weg was used by Him, Heisenberg and his colleagues against Einstein to show the contradiction existing if you use such classical concept. Their error(even if bohr him self was usuallly more prudent ) was to confuse with von neuman and Landau what is accessible to the theory (the statistical predictions) and what is not a part of the model (the dynamic of the individual system ). A trajectory can be then completely different of what you expect as I explained already. Consequently IN YOUR EXPERIMENT YOU HAVE NO WAY TO GIVE EXPERIMENTALLY AN ANSWER TO THE QUESTION ''BUT WHERE THIS STUPID PHOTON COME FROM????'' However the complementatiry of the statisitics will be rigourously observed and with a same photon you will never answer all the questions .

Your experiment is nice and well done but you interpretation is wrong. I think that this will be usefull for students to learn a interesting error

A lot of author realized that the definition of Bohr was not perfect Einstein , de broglie, bohm Schrodinger , Bell ..... even Dirac
If you dont know these references it would be good for the consistency of the argumentation to read them .

Complementarity is a subtle notion and if you want a good definition in a reference I will introduce it in my futur papers with my colleagues from Vienna but there is a lot of good work already in the original publications of Bohr and friends.
Now to finish this hopeless discussion with you you asked me to send you some mathematical justification of my arguments concerning complementarity . I explained you several times already in simple terms what is my point of view (what is the truth I should say in fact). The mathematics is so trivial that even a beginner can do such calculation. In order to be more precise I even calculated the diffraction at the fresnel approximation to reproduce your oscillation in the spots patterns (what for I dont know in fact ) but this is just basic optics no really quantum mechanics. Only if you introduce thec single photon experiment QM will be used but the calculation wil be the same As I told you your problem concern interpretation and the definition of the complementarity principle and this can be expressed without a lot of mathematics and in a consistent and rigourous way ( as I managed).

The formalism is nothing if you dont know what is its meaning.


aurelien for the last time.

Dear Prof Afshar,

"Each image receives amplitudes from only one pinhole, even when the wires are there. ". You give no justification for this statement.

"If you can prove that the final amplitude at EACH image is a 50/50 mixture of the TWO wavefucntions emerging from EACH pinhole,". I just did, tell me why what I said is wrong.

" then it would be possible to show that when a photon is
detected at an image, it's origin is not known.". Close, but this statement needs to be more accurate. It would be (and is) possible to show that the photon could have come from any known sources (i.e. the two pinholes) which are mutually interfering with each other before a photon is subsequently detected. In the propagator formalism of Schrodinger it is just obvious.

" This is impossible to do.". Another unjustified statement.

I agree with the rest of your post and I do understand how a lens works, thanks.

Incidentally the Heisenberg microscope is not relevant because it is fundamentally different. In that case the photon is scattered from a region about the size of the photons wavelength in the vicinity of a single electron. There is only one source. In Prof Afshar's experiment there are two interfering sources.

Again, rather than just telling me I am wrong, please tell me why I am wrong.

Chris

Dear Aurelien

"Bohr considered trajectory as metaphysical"


Here's what Bohr actually says in a famous published lecture:
“…we are presented with a choice of either tracing the PATH of the particle, or observing interference effects…we have to do with a typical example of how the complementary phenomena appear under mutually exclusive experimental arrangements.” [1]

The above (and many equivalent remarks by Bohr) is the basis of the Complementarity in welcher-weg experiments, still in use in modern literature. I am certainly not a historian of physics, and have not read all of Bohr's writings (which include metaphysical discussions, epistemological investigations, and linguistics etc.) but those who have (e.g. Prof. Gerald Holton, the eminent historian of science at Harvard) concur with me that the above statement by Bohr is indeed what he meant by Complementarity in welcher-weg experiments. Interestingly enough, Bohr actually does mention "tracing the PATH of the particle" which clearly shows your assertion above is factually incorrect!


"A lot of author realized that the definition of Bohr was not perfect Einstein , de broglie, bohm Schrodinger , Bell ..... even Dirac. If you dont know these references it would be good for the consistency of the argumentation to read them."


Thanks for the kind offer, but I am all too aware of the unsuccessful efforts of the past luminaries, and have learned a great deal from their failures.

Looking forward to continuing this discussion in the professional literature.

Regards.


[1] N. Bohr, in: Albert Einstein: Philosopher-Scientist, P. A. Schlipp, Ed. (Library of Living Philosophers, Evanston, Illinois, 1949).

Dear Chris,

Just so I can better understand your argument,

1) Are you saying that simply because the two wavefunctions from each pinhole spatially overlap before the lens, we can no longer obtain which-way information?
2) If we place a detector in front of one of the pinholes (before the two wavefunctions overlap), do you consider the detection of a photon in that detector to provide you with the which-way information for that photon?

Regards.

Dear Prof Afshar,

Yes, I am saying that when the two wavefunctions interfere they lose their individual identities. They must be treated as a whole. Sometimes this whole can be understood in terms of a superposition of independent wavefunctions on the same experimental equipment (as in your experiment without the wires) and sometimes they cannot (with the wires). However it is always true that this whole can be understood in terms of the propagator solution of the Schrodinger equation.

Your second question is very pertinent to the view I have presented. It must be true that detection of a photon right in front of a pinhole almost guarantees that it came from that pinhole, but there is a small chance that it did actually come from the other. Only a small amount of the which-way information is lost. Therefore, according to the principle of complementarity, it should be very difficult to observe interference effects before this detection takes place. This is clearly true because the magnitudes of the waves from the two pinholes are now vastly different. In this case, it would be impossible to perfectly map out an interference pattern using a non-destructive approach as in your experiment.

This seems to me a very nice illustration of the complementarity principle.

Chris.

"A lot of author realized that the definition of Bohr was not perfect, Einstein , de Broglie, Bohm, Schrodinger , Bell ..... even Dirac."

Dear Aurelien,
In 1956-57 Vladimir A. Fock discussed, with Bohr, the interpretation
of QM, in Russia if I remember correctly. Fock wrote a paper titled
"My answers to Professor Niels Bohr", published in 1964. This paper
contained 4 major objections to Bohr's ideas on the foundations of QM.
1. The wavefunction represents something "real", as it allows one predict the evolution of probabilities.
2. Only Laplacian determinism was broken down by QM.
3. Complementarity principle expresses limitation (imposed
by Heisenberg's principle) only on the "classical" description of
phenomena.
4. There is no "uncontrollable" interaction between
classical apparata and quantum objects.
According to many authors, which read the original papers in Russian, after reading that paper by Fock (still unpublished when Bohr read it) Bohr changed his views about QM. Difficult to find some good information about all that in the books by Faye, Folse, etc. Aage Bohr wrote something but not definite.
-serafino

Dear Shahriar,
the complete sentence is

This point is of great logical consequence, since it is only the circumstance that we are presented with a choice of either tracing the path of a particle or observing interference effects, which allows us to escape from the paradoxical necessity of concluding that the behaviour of an electron or a photon should depend on the presence of a slit in the diaphragm through which it could be proved not to pass. We have here to do with a typical example of how the complementary phenomena appear under mutually exclusive experimental arrangements and are just faced with the impossibility, in the analysis of quantum effects, of drawing any sharp separation between an independent behaviour of atomic objects and their interaction with the measuring instruments which serve to define the conditions under which the phenomena occur.

The meaning is clear: if you use trajectory you can not expalin fringes then : paradox. but the experiment protect us and we can not decide . the question is then for Bohr metaphysical as I said.

an other example in the same text :
The extent to which renunciation of the visualisation of atomic phenomena is imposed upon us by the impossibility of their subdivision is strikingly illustrated by the following example to which Einstein very early called attention and often has reverted. If a semi-reflecting mirror is placed in the way of a photon, leaving two possibilities for its direction of propagation, the photon may either be recorded on one, and only one, of two photographic plates situated at great distances in the two directions in question, or else we may, by replacing the plates by mirrors, observe effects exhibiting an interference between the two reflected wave-trains. In any attempt of a pictorial representation of the behaviour of the photon we would, thus, meet with the difficulty: to be obliged to say, on the one hand, that the photon always chooses one of the two ways and, on the other hand, that it behaves as if it had passed both ways. It is just arguments of this kind which recall the impossibility of subdividing quantum phenomena and reveal the ambiguity in ascribing customary physical attributes to atomic objects.

Same conclusion . Remark that Heisenberg defended this idea too ignoring the fact that de broglie propseod in 1927 in front of him a model proving that his assumption is too strong ......

I am sad to stop this conversation now but we can not progress and I guess that you and me will stay in our positions.......

So finally I tell you sincerely good luck for your paper(s) even if dont believe in the content and perhaps we will meet one day in a scientifical context .

Aurelien Drezet

Dear Lubos Motl
This is at the top of this blog.

3) Please read the above preprint, before posting a question. You may find your answer there.
4) This Blog is intended to address well-thought/researched questions related to my experiment. This is not an educational site! If you are not an expert in quantum mechanics (at least through QED) and physical/experimental optics, please ask an expert to take a look at your argument first, and if it is found to be technically rigorous, then by all means submit your question/comment.
5) Scientific objectivity is the direct opposite of irrational emotional ranting.

From the above I would conclude that you have not read the preprint. I don't believe your arguments are well thought out or researched. From your weblog it seems as though most of your information came from commercial science articles. Most of what you have to say sounds like irrational emotional ranting. Show us your brilliance by preparing a scientific argument in response to the actual preprint.

Dear Lubos

In your Blog, you say that I have insulted people here. I would never insult anyone, nor would I engage in name-calling, it is not in my nature, and it certainly goes against my principles to be belligerent. Would you kindly show me where I have insulted anyone on my Blog, so I can apologize to that individual? My work is not about one-upmanship; it is about the pursuit of truth through scientific methodology! As for my "numbers", they are in the manuscript.

The interference pattern is NOT a single particle phenomenon and CAN be observed non-perturbatively. I never said you can measure V with infinitesimally thin wire (or detector). As you can find in my preprint, I have said a thin wire (not infinitesimally thin) would block a much larger amount of light for decoherent distribution as opposed to the coherent one. There is a world of difference between this and what you say. Again, if you can explain lack of flux on the wires by invoking anything other interference, using QM formalism, I could accept your arguments about V.

On the other hand. single-particle properties like the kinetic energy of a neutron can ONLY be measured by perturbaitve schemes, be it in a scintillator, or by means of QND.

Your comment on my "ordinary 19th century" experiment is irrelevant. The concept of purturbation-free measurement of ensemble phenomena (e.g. the interference pattern) has not been discussed anywhere else before. I intentionally made the experiment as simple as it can be so that the discussion revolves around the concepts rather than technological marvels. My experiment is all about a better definition of “measurement”, the rest is details.

Regards.
Shahriar S. Afshar

P.S.- I'll have a new post on my Blog soon which might interest you.

Dear Lubos

[I don't believe your "arguments" are well thought out or researched.]

No mention of a question.

[Most of what you have to say sounds like irrational emotional ranting.]

There is no place in science for emotion although heated scientific arguments are its mainstay. You are very emotional.

I do not know or represent Shahriar. I think this is a very ingenious experiment that will challenge everyone to explain it. Please do not associate my arguments with him.

[If Shahiar Afshar decides that only questions and compliments belong here]

Come on now! How shallow is your reasoning and your intellect that you must resort to junior high school accusations?

[Show us your brilliance by preparing a scientific argument in response to the actual preprint.]

This answer is your brilliant reply?

Quote from the abstract of the paper:

"Coherent laser light is passed through a dual pinhole and allowed to go through a converging lens, which forms well-resolved images of the respective pinholes, providing complete path knowledge. A series of thin wires are then placed at previously measured positions corresponding to the dark fringes of the interference pattern upstream of the lens. No reduction in the resolution and total radiant flux of either image is found in direct disagreement with the predictions of the principle of complementarity."

Actually, the resolution and total radiant flux would be predicted to be the same by regular QM. For simplicity, consider a system governed by Hamiltonian
H = p^2/2m + V(x)
with stationary states psi_n
H |psi_n> = E_n | psi_n>

Now consider a particular state psi_M. Suppose this wavefunction is zero at
some set of points y_1, y_2, ...

Let us construct the potential U(x) = delta(x - y_1) + delta( x - y_2) + ....,
where delta() is the Dirac delta
and the new Hamiltonian

H' = H + U

Then, trivially,

H' |psi_M> = (H+U)|psi_M> = E_M |psi_M>

i.e., modifying the potential at the nodes of a particular wavefunction leaves that wavefunction a stationary state of the modified system.

So "No reduction in the resolution and total radiant flux of either image is found" is not at all a surprise.

However, for n != M, in general, |psi_n> is not a stationary state of H'.

The next claim to examine is that in the Afshar experiment, H' violates the principle of complementarity.

Afshar's H is such that all particles from the upper pinhole are received at the lower detector, and all particles from the lower pinhole are received at the upper detector. That is why we say that we have "complete path knowledge". I like to think of it as H preserving two independent channels. Afshar's H' does not have this property. Particles from the upper pinhole are received at the upper detector as well. While H' shares a common stationary state with H, states of H', (even the one shared with H), cannot be interpreted as having this channel preservation.

That is, the set of initial states of the Afshar system separate into two subspaces, the upper pinhole states U and the lower pinhole states L which H propagates to the lower detector LD states and upper detector UD states respectively.

H' is constructed using a particular state u + l, a superposition from the two subspaces, finding the nodes of that state, and modifying the potential only at the nodes. As noted, H' propagates the state u + l identically to H. However, H' does not preserve U -> LD or L -> UD. In particular, we know (experimentally, too) that H' does not propagate u identically to H, nor does H' propagate l identically to H. If particle propagation under H' does not have channel preservation then u + l cannot be interpreted as having channel preservation. We lose info. of "which-way".

Dear Quantum Mirror,

I met with Lubos over a nice dinner, and found him to be quite intelligent and fairly objective. I understand he was upset about the various claims people have made about my work, and I fully understand that. I would have been angry too if I were in his shoes, and in fact I was quite upset about my experimental results at the beginning (way back in 2001)!!! But we both realize now that our difference of opinion is in accepting that my non-perturbative measurement of the interference pattern is legitimate or not. He suggested that he will write a rigorous analysis of his views on the relation between the total number of photons n, and V.

Let me make it clear to all: As I have stated in my preprint, if we define measurement only as a perturbative process (such as when we place a CCD directly in front of the interference patter, or when we use a which-way marker such as polarization for the photons), then Complementarity holds, BUT if we use the non-perturbative process I have employed for the measurement of the interference pattern, then Complementarity fails. One may argue that Complementarity should not be discussed for the type of measurement I make at the wires, but that simply implies that Complementarity, while helpful in certain conditions, cannot be called a Principle, as there are situations where it does not apply. In short, if you agree with section 3 of my preprint, then Complementarity fails, otherwise one should show why my analysis there is incorrect. For me, QM formalism is the axiom, and the rest (including Complementarity) need to be tested against that QM model. I also believe that Complementarity does not fully overlap with QM, so that if it gets nullified, QM is still fully valid.

The only way forward is to take a deep breath, remain objective and see the other side’s point of view. In all these things, the most important element (in my opinion, even above the scientific argument) is mutual respect, because at the end of the day we are all in the same boat...

Regards.

"The question of wavefunction collapse will be investigated in the next set of experiments I am currently preparing."

Hi Prof. Afshar,
I was wondering what the time frame will be for these upcoming experiments?

Thanks

The next question that needs to be addressed is whether Afshar's H' (obtained by the placing of wires in the nodes of a wavefunction) constitutes a non-destructive measurement of a "perfectly visible interference pattern". We've previously seen that the K (denoting knowledge of which way) is less than unity. How about Interference Pattern Visibility V? Has Afshar measured it? Is V anything other than 0?

If V is considered to be measured at the detectors, then V is clearly 0, because there is no contrast between the results of H and H'. Clearly, the measurement, if any, is considered to be in the placements of the wires.

Does locating the zero amplitude points of a wavefunction constitute a measurement?

The reason that I hesitate to call this a measurement is because in any quantum system, a measurement is always a measurement of some superposition of basis states, which constitutes perfect interference. That is, if there was not perfect interference there would be no quantum systems, period.

Think of it like a game of battleships and cruisers. You move around a tiny-in-extent potential peak within some region through which a wave is propagating, and if the presence of the dot makes no difference, you've located a zero amplitude point.

Another caution is because I can use this measurement to possibly violate the uncertainty principle, and not just the principle of complementarity. If the eigenstates of an operator A are distinguished by the number of zeroes of the wavefunction, then I can "measure" A by my battleships and cruisers game, and this does not change A, and then I can measure precisely an operator complementary to A.

More to come.

Dear Andrew,

The next set of experiment will begin in January 2005 and results would be available sometime in March, with a paper submitted in May, if all goes as planned.

Regards.

Dear Chris, (Aurelien, and Morgan would find this interesting too)

You said: "when the two wavefunctions interfere they lose their individual identities"

Sorry about the long delay to respond to your comment on 11/23/04 @ 07:15. Please take a look at Fig.1 which is John Wheeler's original delayed-choice experiment. We are not concerned with the delayed-choice aspect, and will only discuss the Complementary pair of observables one at Sigma_1 (perfect interference), and the other at Sigma_2 (perfect which-way information). I would have used this setup instead of the one I did use, were it not technologically more difficult. As you can see the interference region is quite small, and that entailed I had to use extremely thin wires, which would pose very difficult positioning problems, and lead to unreliable results. But I did arrange the optical setup as shown, and one can observe a highly visible (though spatially tiny) interference pattern at Sigma_1, and further down, as the two wavefunctions no longer overlapped, two distinct beams are observed at Sigma_2. So this is indeed a real experiment and not Gedanken! The good thing about this setup is that there is no lens and we don't have to be bugged down with imaging theory etc.

Now consider the application of your statement above to this set up. Say I run the experiment in the single photon regime, and observe a click in the D1 detector. According to your argument, then simply because the two wavefunctions had interfered earlier on at Sigma_1, there is a 50% chance that the photon came from Pinhole 2. But in order for it to have come from pinhole 2, it must have changed its momentum from P2 to P1 as shown in Fig.1. We know that the photon could not have exchanged momentum with anything along its path to detector D1, and in order for a photon originating from Pinhole 2, it must change its linear momentum by Delta P. This is impossible, unless we are ready to forgo the law of conservation of linear momentum, which I am not!

Therefore, simply because the two wavefunctions had interfered earlier on, they DO NOT lose their identity if they no longer overlap spatially (that is ensured in fact by the linearity of Schrödinger equation).

Regards.

P.S. Exactly the same line of reasoning is used for the case when a lens gives us the which-way information, though it is much more complicated beacuse of the coherent imaging analysis.

Dear Prof Afshar,

Thanks for your response, and the insight into how you arrived at your experiment.

The issue of conservation of momentum and wavefunction collapse is a confusing one. I'm really not convinced that you can apply conservation of momentum in the way you propose for a couple of reasons.

Firstly your response seems to imply that when you measure the location of the photon at one of the detectors that you can then infer a classical trajectory linking a pinhole and the detector. This is obviously nonsense.

Also, is it not the case that the standard analysis of double-slit-like problems requires that the wavefunctions are standing waves? If this is the case then talk of conservation of momentum is irrelevant.

Chris



Chris.

Dear Chris,

This discussion of linear momentum actually goes back to Heisenberg's proof of the uncertainty principle, in which he uses a slit illuminated by collimated coherent light to show that if one measures the position of the photons within an accuracy of delta_x (width of the slit), then the momentum of the photons after slit will have a spread of the order of delta_p, where delta_p . delat_x =h_bar. This is indeed observed experimentally and is seen every time particle colliders spit out data. Without this argument, the Compton effect cannot be described, and all the physics based on high energy particle collisions would be wrong! Both Einstein and Bohr (and any other physicist since) agree on the fact that photons do carry a momentum that can be traced back to either an atomic or a charged particle source. If you wish I can further elaborate on this point, but you can find a discussion of Heisenberg's proof in any introductory QM book. If you are an advanced reader, I suggest the excellent book "Quantum Measurement" by Braginsky and Khalili--although some of its contents need to be updated to incorporate my results...

Discussion of double-slit experiments does NOT require standing waves at all. Standing waves only exist in cavities, i.e. where there are well-defined boundaries for the wavefunction to bounce off the walls and interfere with itself within the travel time of the cavity for the entire wavefunction. Wavefunctions actually do move (they are not physical waves, but they do move at the group velocity in space). A wavefunction emerges from each pinhole and moves according to Shrödinger equation and the Hamiltonian of the quantum system (which incorporates the conservation laws etc.)

Regards.

I am not a QM expert (I am an electrical engineer), so my terminology below may not be exactly correct, but I think you will understand my intent.

I have read the entire blog up to this point, and it seems to me that fundamentally most of the critics seem to disagree with one (or both) of the following two assertions:
1) The results of the experiment indicate a wave interference pattern at the plane of the wires.
2) The experiment is a which-path experiment.

I have a few comments/questions below on 1, but will leave 2 to the experts.

With respect to 1 above, the critics seem to be arguing that the results at the detector do not indicate a wave interference pattern at the plane of the wires. They seem to be arguing that you can only prove a wave interference pattern at the plane of the wires by an observation at the plane of the wires. I wonder if they would also claim that the interference pattern at the screen in the classical double slit experiment does not indicate that the wave passed through both slits? I wonder if they would argue that the only way to prove the wave passed through both slits in the classic double slit experiment is to make a measurement at both slits? It seems to me that the results at the detector in this experiment are evidence for a wave interference pattern at the plane of the wires. It seems to me if one disagrees with this, then one would also have to disagree that the interference pattern on the screen in the classic double slit experiment indicates anything about what is happening in the vicinity of the two slits. Many of the critics seem to be arguing for the Copenhagen interpretation. Is their argument consistent with the Copenhagen interpretation?

Would it be of any value to run multiple trials of this experiment with the wires placed in various positions? Assuming a wave interference pattern at the plane of the wires, would the results at the detector vary based on the characteristics of the interference pattern at the point of placement of the wires? Assuming the answer to the preceding questions is yes, if the results of all of these trials for all placements of the wires were consistent with the predictions based on the characteristics of an interference pattern at the plane of the wire, would the critics still remain unconvinced of the existence of a wave interference pattern at the plane of the wires?

It seems to me if one agrees the results of this experiment indicate a wave interference pattern at the plane of the wires, one is forced to make one of the following two conclusions:
A) The principle of complementarity is not valid
B) A lens does not provide which path information.

I gather that conclusion A would be more significant than conclusion B, but even conclusion B would be significant since it would invalidate several earlier QM experiments.

So, I can hold you to the following,

"Discussion of double-slit experiments does NOT require standing waves at all. "

Chris.

Dear Chris,

Yes!

Regards.

Dear Clark,

I agree with all your conclusions!

No physicist would argue that in a regular double slit experiment with direct observation of the interference pattern, the wavefunation did not sample both pinholes (i.e. is not a superposition of wavefunctions from each pinhole). Even Bohr himself asserts as much...

Regards.

Dear Afshar,

In my original posting on 12/3/2004, I indicated that I thought the results of the experiment indicated a wave interference pattern in the plane of the wires. Unfortunately after thinking about the experiment some more, I have refined my opinion. I now believe that the results of the experiment indicate a wave interference pattern at the location of the wires, but not necessarily in the entire plane of the wires. I will attempt to explain my refined position.

The detectors detect all photons that are passed through the two holes that do not impinge on the wires. The photons that impinge on the wires pass through both holes, and thus can be predicted by the wave interference pattern at the point of the wires. The photons that are detected at the detectors pass through only one hole, and thus do not exhibit any wave interference pattern in the vicinity of the plane of the wires. Therefore this experiment does not prove that complementarity is violated, nor does it prove that lenses do not provide which-path information. So all is well with the Copenhagen complementarity principle and with lenses providing which-path information.

Sorry for the bad news. I think that perhaps I have earned that $1,000 even though perhaps I did not prove exactly what you requested. :)

Regards,
Steve Clark.

Dear Clark,

The real bad news is that it seems you have not read all the above Q&As (or my preprint) after all! Please do a calculation for the following:

1) The 6.6% of the photons that were supposed to be incident on the wires: (i) how do they make it to the detectors?, (ii) do they land on the wrong detectors?, (iii) If you believe for this group which has V=1 (at the wires), and K=0 (at the image plane), what leads to their arrival at the wrong image, knowing that they do not have a chance to be scattered by the wires?

2) The 93.4% that make it to the right detector, thus have a V=0, which means there is no fringe system, dark or bright. (iv) How is it that 6.6% of this 93.4% is not blocked by the wires, since the decoherent distribution must be a random one? (v) Is it possible for a decoherent distribution to have a minimum within its spatial distribution (i.e. can decoherent photons avoid a particular region persistently)? (vi) Is there a QM description for such a behavior or is it outside the realm of QM formalism?

A quantitative analysis of the above two subensembles will clarify the error in your last conclusion. I especially recommend that you read section 3 in my preprint, and if you don't agree with it write a rigorous critique of it.

Regards.

Dear Shahriar the 11/30/04 you explained that I could be interested by your argumentation concerning momentum. I am effectivelly interested but only becaue it confirm one more time a classical fatal error . Your conception is in my opinion dangerous because you use some semiclassical description of the momentum and you applied this to quantum mechanics. This mistake is very usual Heisemberg and Bohr him self were victims of their classical scientific background (wheeler too....) so finally you are not so bad 73 years latter.

As I explained to you( so many times that my key board becames depressed) this geometrical conception of gran pa newton is not necessary (see Bohm de broglie and my 10000 last messages....). Then the concept of which path is fallacious in your case and your argumentation with momentum is too classical to be honest. Concerning complementarity: if you want to refute Bohr you have to consider 2 points : 1) quantum mechanics speaks only about statistical behavior 2) Complementarity means complementarity of statistical patterns.

In your case this means you can not use the same photons to build two statistical graph needing obviously two different analyze planes (fringes or spots planes). If you see the spots the interferogram is hypothetical even if you guess that it should be here. (you guess to much my dear Watson)

Shahriar since the beginning you dont play the game of Bohr and in conclusion you can not then refute his principle . It is elementary and I need probabaly a psy to be so patient with you

However I agree with you that the argument of chris is wrong : there is no mixture of the schrodinger waves . But perhaps he thinks (as me ) that the trajectory of a photon can be completely different .... ???? As you he makes some confusions in the vocabulary but we can excuse him : 1) he is no trying to prove that Bohr is silly but try to clarify his conception...... you should try that too and 2) his english is much better that minde and I have always the feelling to be a guy of an other planet when I try to comunicate with you.


Ok you are practically a friend now so you will not be ofended :) humor and science constitutes a good couple if we dont want to look too serious.

Aurelien

PS: Serafino ; I dont think that bohr never changed his point of view but if you can send me a copy of the paper I will be please

Dear Aurelien,

I am afraid we are talking past each other now! You agree with me that Bohr made an error, but the error you have in mind is the radiator-emitter connection by means of the conservation laws, which I have never heard anyone refuting, (and if you have a solid argument, let’s hear it.) If you believe such a connection is wrong, then you deny the validity of the conservation laws, which is simply unimaginable to a physicist, as it has been proven at every single experiment we know of. Bohr never changed his views on PC and as far as I know, no one has effectively challenged his ideas until my work. I am truly amazed that you willing to forgo the conservation laws just to uphold Bohr's outdated philosophy...

As you know, we are facing very serious crises in physics today, the Higgs hasn’t been found, the dark matter seems to dominate the gravitational potential in galaxies, the mysterious dark energy of cosmology is 10^120 times smaller than the QM vacuum energy,… We have so many divergent interpretations and theories that we are starting to look like philosophers, everyone starting a cult and then bringing in followers that happen to LIKE that kind of philosophy. I am fed up with these things, and am asking our colleagues to get back to the basics where the real problems lie, rather than blindly believe the dogma, and continue on this foolish path. We need experiments, and we need real solid phenomenological theories that lead to no logical inconsistencies, no more, no less. Yes, technologically we have advanced beyond measure, but fundamentally, I am ashamed to say that we don’t even understand light!

I have no problem with humor as a lubricant in a discussion, but when it is used to dismiss important issues upon which the very foundations of physics rely, I have very little patience for chit-chat!

From planet Erath!
Regards.

Dear Afshar,
My response is several pages, and it appears to be too big for a single post, so I will post the remainder of my response in multiple pieces. If you send me your e-mail, I will send you the entire post in a single message. This post picks up with where my previous post left off.

Here is part 2.

Your discussion of coherent behavior in section 3.3 starts out talking about taking a measurement in the plane somewhere in front of the wire (immediately in front of the wire?), and ends up talking about taking a measurement somewhere behind the wire (but before the lens). I believe for the measurement in front of the wire V=1 and K=0, but for the measurement behind the wire 0

Dear Steve,

My e-mail address is: afshar@rowan.edu.

Looking forward to reading your response.

Regards.

Dear Afshar,
From my second attempt, I conclude it wasn't a size problem, but the fact that I am using the "less than" character in my response. Apparently this character is being used to denote the beginning of an XHTML tag. I have replaced the "less than" characters in my response and will try another attempt to post my entire response.

Dear Afshar,
Thank you for considering and responding to my earlier two posts.

I was joking about the $1,000 in my previous post, but my rationale for why I thought I deserved it was NOT that I had proved your challenge, but that I had identified the flaw in your interpretation of the results of your experiment. Things now seemed so obvious to me that I thought after reading my response you would reach the same conclusions. In hindsight, I should NOT have expected you to immediately understand or agree with my conclusions. I spent quite a bit of time thinking about this problem between the time I formed my original opinion and the time that I refined my opinion, but I only provided a very brief explanation in my previous post. Also, I imagine it was much easier for me to change my opinion than it will be for you, as it is probably much more entrenched in your mind than it was in mine. I had only formed my original opinion a few hours before I refined it, and you have spent the last month defending your opinion on your web blog. You are probably getting weary of defending your position against all of the skeptics at this point, but in an experiment where you make such a controversial claim, you have to expect a lot of scrutiny.

With respect to your $1,000 challenge, at this point I am more interested in understanding the results of your experiment and the implication of these results than in proving your challenge. Besides, if I prove you wrong in the end, you will be probably be feeling a bit let down, and I wouldn’t want to make you feel any worse by making you fork over your $1,000. But I might like to see Aurelien eat his fictitious hat.

I did read the entire blog before my previous post, but I admit I did NOT understand all of the details of all of the arguments. I had also read a few other articles on the web about your experiment, but these tended to high-level oversimplified explanations of your experiment. I had also taken a quick scan of your preprint. In this first scan I had focused more on the early portions of your paper and your diagrams and their explanations at the end of the paper, since the later portions of your paper seemed less accessible to me due to their more complicated mathematics

After your latest reply, I went back and took a more detailed look at your paper and waded my way through more of the mathematics. I now have a more detailed understanding of your experiment at this point, but this understanding is still consistent with my refined position. This more detailed review of your paper did help to clarify a few points to me that I was confused about in your web blog.

I am NOT disputing any of your calculations or measurements (though I would like to see a few more calculations/measurements that I mention below). I am only questioning how you apply some of these calculations, whether the conclusions you draw from your calculations and measurements are self-consistent and correct, and whether another set of conclusions can be drawn that are self-consistent, consistent with the QM Principle of Complementarity, and consistent your calculations/measurements. I am still trying to understand your assumptions and the rationale that led to your conclusions.

I would first like to give you some comments on your paper. Then I will respond directly to the questions that you raised in your response to my most recent post (where I refined my position). Finally I have a few questions for you that are intended to help clarify for me your assumptions and rationale.

Preface – I disagree with your conclusions for reasons that I will state later.

Section 1 - In (III), I think you could provide a more precise definition of “single experimental setup”. However you provided some clarification of this issue earlier in the blog, and I believe I understand your intent.

In the last paragraph, I disagree that your experiment investigates “sharp complementary wave and particle behaviors explicitly forbidden by PC in the same experiment” for reasons that I will give you later.

In the last paragraph, I understand from the earlier portion of the web blog and other web sources that the single-photon source version of your experiment has been performed and confirms your results.

Section 2.1 - I think you could give a more precise definition of “particular experimental arrangement”. But again, you provided some clarification of this issue earlier in the blog, and I believe I understand your intent.

Section 2.3 – In the last paragraph you talk about IP being lost at an earlier stage (before the lens) in a non-local manner. In the case where you are taking a measurement behind a lens, was IP really lost anywhere? Did it ever exist (since all photons behave like particles in the vicinity of the holes and pass through only one hole)? I am NOT sure I fully understand the implications of the last paragraph (it certainly is a mystery).

Section 3.1 – Here you state “However, as we shall demonstrate in the next section the measurement of a multi-particle or ensemble property need not be destructive”. I am not totally satisfied at this point that you have demonstrated this anywhere, but you definitely don’t demonstrate it in the next section (section 3.2). I believe you should be referencing section 3.3 here instead of the next section (section 3.2).

Section 3.3 – I don’t agree that you can assume Imax is NOT zero just because Imin is zero and the total radiant flux of the dual pinhole output is nonzero. I believe you need to put these statements into the context of an experiment and where you are taking a measurement in order for them to make any sense. For example, if you take your measurement at a position behind a lens (after the photons pass through the lens) and find there are no photons at this position, you would assume an interference pattern behind the lens?

Your discussion of coherent behavior in section 3.3 starts out talking about taking a measurement in the plane somewhere in front of the wire (immediately in front of the wire?), and ends up talking about taking a measurement somewhere behind the wire (but before the lens). I believe for the measurement in front of the wire V=1 and K=0, but for the measurement behind the wire V is greater than 0 but less than 1, and K=0. I think V would be less than 1 because the presence of the wire would degrade the interference pattern at the measurement plane.

It is NOT clear how this discussion of coherent behavior measured in front of the lens relates to your experiment, since you do NOT take any measurements in front of the lens in your experiment (except possibly an indirect measurement at the wires). In your experiment, you only take a measurement after the lens, which leads to loss of all IP information. I think V=0 and K is greater than 0 but less than 1 for a measurement behind the lens. V=0 since no IP is present behind the lens. I think K would be less than 1 because the presence of the wire in front of the lens would degrade the path information detected behind the lens. I believe it is impossible to obtain path information on any of the photons incident on the wire that are reflected by the wire and make it to the detectors behind the lens.

I assume for the decoherent state discussion you are talking about a measurement with one of the holes covered.

In the last paragraph of section 3.3, you talk about a coherent state in the context of flux entering the lens. This makes no sense in the context of a measurement behind the lens, since as you have stated in the last paragraph of section 2.3, IP is lost before the lens in a non-local matter.

Section 3.4 – You state that in your simulation the obstacle is assumed to be a perfect mirror. What are your assumptions about the wires in your actual experiment?

Section 4.1 - I would have liked to have also seen a control run with one pinhole open and the wire grid not present.

Section 4.2 – I disagree that V=1 anywhere but at the wires, and that there is an interference pattern anywhere but at the wires. See my responses to your questions below for further explanation.

Section 5 – Again, I disagree with your conclusions for reasons I provide below in the answers to your questions.

I will now attempt to answer your questions, but we now have two very different perspectives on this experiment, and some of your questions don’t make much sense from my perspective, and consequently some of my answers may NOT make much sense from your perspective.

1) The 6.6% of the photons that were supposed to be incident on the wires:

Why do you think 6.6% of the photons are supposed to be incident on the wires with both holes open? I think we both agree that a much smaller percent will be incident on the wires with both holes open because the photons that are incident on the wires exhibit an interference pattern and the wires are placed at the maximum point of destructive interference. So your questions (i), (ii), and (iii) don’t make a lot of sense to me in this context, but nevertheless I will attempt to answer them as best as I can. I think you are really asking about the extra 6% of photons that make it to the detector with both holes open.

(i) how do they make it to the detectors?

They make it to the detectors the same way all other photons make it to the detectors: through the lens and mirror apparatus. But I think you are really asking about the path distribution before the lens. Why do you think it looks any different than your Figure 4e? If you consider the y-axis as probability, the area under the curve is 1. If you consider the y-axis as number of photons, the area under the curve is simply 6% larger. Whoops, I think I just proved your $1,000 challenge, and I’ll bet the proof was much simpler than you imagined. Now about that fictitious hat… Actually, I have only proven that the results at your detectors can be explained with a coherent source at the holes (with 6% larger output). This does NOT explain the reduction in photons incident on the wires. This reduction can only be explained with wave behavior in the vicinity of the holes. So your $1,000 is safe after all, and we will NOT get the pleasure of viewing the spectacle of Aurelien choking down his fictitious hat.

(ii) do they land on the wrong detectors?

All photons NOT incident on the wires land at the right detectors including the extra 6%. There are simply 6% more of them.

In the case of the much smaller percent that are incident on the wires, I am NOT sure I understand all of your assumptions about the wires, but in my previous response, I assumed that none of the photons incident on the wires make it to the detectors. I suppose some of them could make it to the detectors by being reflected off the wires, but in this case there is no right or wrong detector, since the photons incident on the wires exhibit wave behavior in the vicinity of the holes. This would result in a degradation of K at the detectors.

(iii) If you believe for this group which has V=1 (at the wires), and K=0 (at the image plane), what leads to their arrival at the wrong image, knowing that they do NOT have a chance to be scattered by the wires?

The extra 6% that arrive at the detectors do NOT have V=1 at the wires since they are NOT incident on the wires. They follow other paths as I explained above. They do NOT have K=0 at the detectors, they have K=1 at the detectors. They do NOT arrive at the wrong image.

2) The 93.4% that make it to the right detector, thus have a V=0, which means there is no fringe system, dark or bright.

As I said before, 100% of the photons NOT incident on the wires arrive at the right detector. I agree there is no fringe system at the detectors. I also agree there is no fringe system at the plane of the wires except at the wires themselves. Are we agreeing here about the location of fringe systems?

(iv) How is it that 6.6% of this 93.4% is NOT blocked by the wires, since the decoherent distribution must be a random one?

Did you really mean “6.6% of this 93.4%”, or did you mean “100%- 93.4% = 6.6%”?

As I said before, the extra 6% that are NOT blocked by the wires follow similar paths as the remainder of the photons. There are simply more of them following each path.

I do NOT agree the decoherent distribution is a random one. My response to (v) and (vi) below provides further clarification on this issue.

(v) Is it possible for a decoherent distribution to have a minimum within its spatial distribution (i.e. can decoherent photons avoid a particular region persistently)? (vi) Is there a QM description for such a behavior or is it outside the realm of QM formalism?

I think the answer to this question is quantum weirdness (seriously). My interpretation of your questions is that you are really asking me to explain the fundamental quantum mystery. Consider the classic double slit experiment, but remove the right half of the screen. I think we would both agree that an interference pattern would still be present on the left half of the screen with V=1 on the left half of the screen. Now place an apparatus designed to distinguish path information in the right half where the screen was removed with the lens slightly behind the plane of the screen. Assume this apparatus consists of a lens, mirrors, and detectors as in your experiment. I think we would both agree we could detect path information (V=0 and K=1) on decoherent photons incident on the lens in the right half, while the interference pattern remains for the coherent photons incident on the left half where the screen is still present (V=1 and K=0). Now we have decoherent photons striking the lens in the right half, but we only have coherent photons striking the screen in the left half. I think your questions (v and vi) are equivalent to the question: “Why don’t any decoherent photons strike the screen in the left half”? There certainly is a large target in the left half for decoherent photons to strike, and we can imagine a path from one (or the other) of the two slits to the left half of the screen. So, why don’t any decoherent photons take the path we imagine? The answer is the fundamental quantum mystery. The behavior of photons (whether they passed through one slit or both slits) that we observe at a measurement point is based on the type of measurement we are making at this point.

I would like to expand on my thought experiment because it is conceptually simpler than your experiment. If I accept the reasoning you used to reach your conclusions in your experiment, I could apply the same reasoning to my thought experiment and conclude a similar result. You claim that observation of an interference pattern in part of a plane means the interference pattern extends across the entire plane. In my experiment, an interference pattern is observed in the left half where the screen is present, and therefore using your reasoning this interference pattern must also be present at the right half where the lens is present. Therefore there is an interference pattern in front of the lens, but I resolve the path of the photons after the lens. Therefore I have demonstrated both interference and path information for the photons that arrive at the detectors behind the lens. And I have achieved this without relying on magic like nondestructive measurement of an interference pattern. I didn’t need to pull any tricks with careful placement of thin wires at points of maximum destructive interference, or make any complicated calculations about the incident particles on these wires. I didn’t need to get bogged down in issues like whether the wires were thick enough and what happens to the missing 6.6% of photons. And I didn’t need to make any claims about having V=1 without measuring Imax. Clearly I can measure Imax as well as Imin at the screen on the left side of my experiment.

I think the source of a lot of confusion in your experiment is that you are making two complementary measurements at different measurement points similar to my thought experiment, and you are insisting that the photons at both measurement points behave in a similar manner (all coherent or all decoherent).

I realize you were probably trained to treat the two holes as an emitter of coherent or decoherent photons to make your calculations, but this is NOT an accurate description of physical reality. The two holes are NOT emitters of coherent or decoherent photons. They do NOT push coherent or decoherent photons to all regions of space. In reality, the particle versus wave behavior of each individual photon at the two holes depends on the measurements being made on that individual photon. You would be better off thinking of a pull model where each measurement point pulls the appropriate type of photons from the two holes based on the type of measurement being made at the measurement point.

Treating the two holes as an emitter of coherent (or decoherent) photons will work for experiments in which you are only making one measurement, and also for multiple measurement experiments where you are making the same type of measurement at all measurement points. But you need to be careful in multiple measurement experiments where you are making complementary measurements at different measurement points. In this last case, you can still treat the two holes as an emitter of coherent (or decoherent) photons when making the calculations at a particular measurement point so long as you select the correct photon emitter for the type of measurement you are making at the measurement point. But you must realize that the holes are NOT really emitting the selected type of photons to all regions of space.

I have given you a logical self-consistent explanation for your experimental results that is consistent with the Principle of Complementarity. I have also identified the errors in your assumptions and reasoning process that led you to your incorrect conclusions. If you have fully understood my response up to this point and you are NOT beginning to have any doubts about your conclusions and claimed results, I am afraid there is little hope of me ever convincing you to change your mind.

Now I have a few questions for you intended to help clarify your assumptions and the rationale that led you to your conclusions.

1) How do the photons that are incident on the wires behave at the holes? Do they behave as particles or waves?

2) What are your assumptions about the wire? Does it reflect all photons as a perfect mirror? Does it absorb all photons? Are some photons reflected and some photons absorbed? If any photons are reflected, do any of these make it to your detectors? If some photons are reflected and some of the reflected photons make it to your detector, do you think you can obtain path information for these photons at your detectors?

3) How do the photons that are NOT incident on the wires behave at the holes? Do they behave as particles or waves? If they behave as particles at the holes, how do you justify your inconsistent claim of a coherent state at the plane of the wires across the entire plane of the wires? If they behave as waves at the holes (i.e. they pass through both holes), how do you justify your inconsistent claim of being able to resolve path information on these photons at the collector?

4) You claim that a coherent state at the plane of the wires exists across the entire plane of the wires. This could only be achieved if all photons pass through both holes. Yet you claim to resolve path information for these photons at your detectors. How do you explain this inconsistency in your conclusions?

5) Please identify exactly the photons in your experiment for which you have both path information and visibility information. Do you claim to have this information for the photons that are incident on the wires? Do you claim to have this information for the photons that are NOT incident on the wires? Or do you claim to have this information for all photons?

6) Are you claiming that measurement of an interference pattern in part of a plane indicates the interference pattern extends across the entire plane?

7) Are you claiming that measurement of decoherent photons in part of a plane indicates the presence of decoherent photons in the entire plane?

8) Are you claiming that all photons in an experiment must exhibit similar behavior (they all pass through only one hole or they all pass through both holes)? If so, even when multiple complementary measurements are being made in an experiment (on different photons at different points in space)?

9) Do you disagree that the behavior of the particles that one observes at a measurement point depends on the type of measurement being made at that measurement point?

I think I have given you enough things to think about for now. I hope I have succeeded in clarifying my assumptions, rationale, and conclusions. Please consider the explanations I provide above for my viewpoint and let me know if you have any other questions that would help to further clarify my viewpoint to you. If you disagree with any of the assumptions, rationale, or conclusions I have provided above please let me know the specific points of contention. Also I would appreciate it if you would provide answers to my questions above to help clarify your viewpoint to me.

I have proven the conclusions you reached from your experimental results are incorrect, but I still consider this a very interesting and thought provoking experiment. I had never before considered an experiment where complementary measurements are taken at different points in space, and this experiment has helped me to clarify my understanding of QM behavior in this type of an experiment. I would really like to have seen the calculation and measurement results for another trial with the wires placed at the points of maximum constructive interference (versus the points of maximum destructive interference).

Thanks,
Steve Clark.

Dear Afshar,
After removing all of the "less than" characters from my response, I was successful in posting my entire response on the third attempt, so I guess there is no longer any need for me to send you my entire response in an e-mail.

Please delete my first two attempts that terminated at the "less than" character from the blog.

I am looking forward to seeing your reply to my response.

Regards,
Steve Clark.

Dear Steve

The wires in this experiment can be thought of as interference indicators. If the wires could talk they would be saying: interference is present or I would be sparkling. Interference is present or I would be blocking 6.6% of the light. Interference is present, there is no way around it or both of these would be true! So much for a talking wire to say.

With the wires present the photons reach their proper destination according to QM formalism and have complete which-way information. The question to address from this experiment is how we have interference at the wires and which-way information at the same time. I think you have complicated this issue exponentially in the above chapter or book, although I must admit I did not read all of it. :)

"This could only be achieved if all photons pass through both holes. Yet you claim to resolve path information for these photons at your detectors. How do you explain this inconsistency in your conclusions?"

This is your best question and the answer is they must do both. This is again the central mystery of Quantum mechanics. They must go through both, interfere and then decide which path they took. This is the perplexing question that this experiment demonstrates.

Dear Steve,

Thanks for taking the time to write the long elaboration of your views and comments. I am afraid I completely agree with Quantum Mirror's above post. I am in a bit of a hurry right now, but quickly:

1) In answering your Q3 and Q4, if we assume a wave-like behavior for light (which we should if we believe in QM formalism), we know that waves CAN do both, produce an interference at the wires, and at each image carry the full which-way information for the subensemble that reaches that image. It is ONLY when we use the particle picture that we bump into logical problems. The issue at the core of all this, is that we have to use the particle picture at the detector, because we only have one click at a time, either in 1', or 2', never at both. Any wave mechanics that fails to account for this particle-like, singular detection at the detectors needs to be revised so that this singular MEASUREMENT problem is fully accounted for in the formalism. This is the famous Collapse of the wavefunction problem in QM, which is not formally part of the formalism itself, it belongs to the Mesurement Theory. My experiment seems to suggest that there is no collapse!

2) In response to Q6, the answer is yes! Under the constraints of my experimental setup(and this is extremely important as discussed in the Preprint Appendix), if the wires do not register a flux, then there must be an interference pattern, simply because QM allows no other process for avoidance of wires for a prolonged period of time. Let's put it this way, if we set up an experiment, in which you see the pattern after the wires, and the only information you give me is the (i) position of the wires, (ii) the fact that the wires block no light, and (iii) the total amount of radiant flux (not its spatial distribution), I can predict exactly what type of distribution you are seeing, without actually seeing it!
In my experiment, (i) is provided from the initial direct observation of the interference pattern. (ii) is provided by the final tally (though it could be directly provided if the wires are photo-detectors), and (iii) is provided by the sum of radiant flux at the image plane.

3) Now, I know you have not formally studied QM, which frankly would go a long way in helping me explain things, but let me just point out a few things:
Decoherent distribution: It is basically the same as incoherent distribution, but the difference here is that you initially prepare you quantum system in a coherent state, but then something (like direct interaction with the light, or passage of a bunch of scattering electrons across the coherent beam, or as Bohr would have us believe the mere fact that one can gain the which-way information), leads to the loss of coherence, so things like the interference patter disappear.
Dephasing: The actual process that leads to decoherence. This is also an important topic, currently being feverishly investigated experimentally, which you can look in literature on Mesoscopic quantum mechanical phenomena.
Ensembles: This is an important concept in QM. Please look it up, as I will soon be posting a detailed analysis of why V=1 at the wires based on formal QM, using this concept.

If you are not satisfied with the above, I can respond to all your comments one-by-one, as you have kindly gone through the trouble of writing a qualitative paper on my preprint, but it may be a few days before I can get around to doing this.

On the personal side of things, I am never frustrated when it comes to explaining my arguments to unbiased and objective participants. It is only when someone confuses his/her opinions with facts, and insists on holding such views, that I first try to politely reach out to the individual, and if it fails, I simply ignore them. That is because I am confident that Truth has a way of getting itself established, sooner or later, with or without the opposition...

Regards.

Dear Quantum Mirror,

I agree there is an interference pattern at the wires, but I disagree that there is an interference pattern anywhere except at the wires. This was in my response, but perhaps you did not see it since you did not read all of it.

I realize that my response was rather lengthy, but Afshar asked for a rigorous critique of his conclusions, and a rigorous justification for my conclusions. I will give you a high-level summary of my argument in one paragraph, but if you really want to understand the details of my argument, you will need to read the portion of the post where I provide answers to Afshar's questions. I would be particularly interested in your viewpoint on my thought experiment, which is conceptually much simpler than Afshar's experiment.

I agree that there are two complementary measurements being made, but they are NOT being made on the same photons, and thus the principle of complementarity is NOT violated. To keep things simple, lets stick to the single-photon version of this experiment. Each photon either passes through one hole as a particle, or it passes through both holes as a wave and interferes with itself. The photons can be divided into two groups: Group A photons that are incident on the wires (admittedly very few in this experiment), and Group B photons that are not incident on the wires. Group A photons pass through both holes as a wave and exhibit an interference pattern on the wires. Note we have no path information for Group A photons. Group B photons pass through only one hole, and are resolved at the detectors. Note that we have no visibility information for Group B photons. There is not a single photon in this experiment for which we have both path information and visibility information, and therefore the principle of complementarity is not violated.

Afshar and you are both hypothesizing visibility information of Group B photons based on visibility information of Group A photons, but you have not actually measured visibility information of Group B photons. If you were to actually measure visibility information of Group B photons, you would no longer be able to determine path information for Group B photons.

Regards,
Steve Clark.

Dear Steve

"I agree there is an interference pattern at the wires, but I disagree that there is an interference pattern anywhere except at the wires."

The wires are placed at the point calculations say that interference minima should appear. Where else in the experiment would you expect to find interference? This is the only place that interference should appear and is carefully calculated by the distance between the center of the pinholes, the diameter of the pinholes, the distance between the dual pinholes and the wavelength of the laser.

"The photons can be divided into two groups: Group A photons that are incident on the wires (admittedly very few in this experiment), and Group B photons that are not incident on the wires. Group A photons pass through both holes as a wave and exhibit an interference pattern on the wires. Note we have no path information for Group A photons. Group B photons pass through only one hole, and are resolved at the detectors. Note that we have no visibility information for Group B photons. There is not a single photon in this experiment for which we have both path information and visibility information, and therefore the principle of complementarity is not violated."

I think what you are not understanding in this experiment is the use of the lens. It is also calculated to be within a specific distance from the pinholes so that photons from each pinhole can only end up at their specific detector. This provides the which way information.

Dear Shahriar,
The famous connection pinholes images used by you was clearly accepted by Heisemberg in differents books and by Bohr . Do You remember the beautifull sentence :

''This point is of great logical consequence, since it is only the circumstance that we are presented with a choice of either tracing the path of a particle or observing interference effects, which allows us to escape from the paradoxical necessity of concluding that the behaviour of an electron or a photon should depend on the presence of a slit in the diaphragm through which it could be proved not to pass. We have here to do with a typical example of how the complementary phenomena appear under mutually exclusive experimental arrangements and are just faced with the impossibility, in the analysis of quantum effects, of drawing any sharp separation between an independent behaviour of atomic objects and their interaction with the measuring instruments which serve to define the conditions under which the phenomena occur. ''

Bohr 1949

Here the hypothesis is clearly ennounced and Bohr deduce that such classical picture is not appropriate to describe the photonin a dynmical way. . Now if you ask me to give you a reference concerning the conservation of momentum in quantum mechanics it will be good for you to decide waht is a momentum: the definition used by you consider the momentum of a PLANE WAVE this defintion is senseless if we dont expand a wave packet in plane waves. de Broglie used a different definition : P= the grad of the phase/ hbar (and other definitions in the relativistic cases) . This defintion is in perfect agreement with tthe conservation of energy impulsion if you consider the quantum potential which exist even without external potential . In this model the motion is completely deterministic but the particle follow obviously some strange and non intuitive trajectories which can for example connect the pinhole A to B' . to explain this you must consider the quntum potentila in the interference region as a source of distirubance i.e. a kinf of self force..... There is no paradox If you want to unify wave and particle you must include a modification of the naive pictures......

As you see following my analysis bohr was right to see paradox in the use of the classical picture but he was to pessimistic ...

aurelien

Dear Prof Afshar,

I have though about how the Wheeler Delayed Choice(WDC) setup that you posted
compares to your setup and it is all clear to me now. Standing wave versus
single photon IS an issue.

In the WDC setup the difference in distance from the pinhole to the top and the
bottom of the interference pattern is much larger than in your original setup
(In fact it is approx. (pinhole separation)/(pinhole diameter) wavelengths in
both cases). So, while in your original setup you can claim that the wave train
of a single photon simultaneously passes the whole plane of the wires, and hence
an interference pattern is measured, this is not necessarily true of the WDC
setup. If the single photon wave train is too short the contributions from the
two pinholes will not simultaneously occupy the whole area covered by the wires;
this will only occur in a smaller region in the center of the area with the
wires. Hence the visibility of the interference pattern will be reduced from the
perfect value of 1.

Similarly the which way information obtained by applying conservation of linear
momentum is not perfect either. The uncertainties in the momentum of the photon
at the pinholes and at the detectors ensure that, while some which way
information is available, this is not a perfect way of measuring which pinhole
it came from.

It is quite clear that as the visibility of the interference pattern is
increased (by making the wavetrain longer say) the which way information is
reduced (the momentum becomes less well defined for more standing wave like
behaviour). Alternatively you could try to make the which way information better
by widening the pinholes (achieving a lower uncertainty in momentum) but this
then reduces the number of zeroes in the interference pattern making the
visibility worse.

Complementarity anyone? I can continue playing Bohr to your Einstein if you
want, but we both know who wins in the end.

Chris

Quantum Mirror,
This post is in response to your post dated 12/06/04 @ 18:39. I have enclosed your comments in quotes below, and my responses immediately follow each of your comments.

“The wires are placed at the point calculations say that interference minima should appear. Where else in the experiment would you expect to find interference? This is the only place that interference should appear and is carefully calculated by the distance between the center of the pinholes, the diameter of the pinholes, the distance between the dual pinholes and the wavelength of the laser.”

I agree that the wires are placed at the point of maximum destructive interference. But this is not the only place the wires can be placed to observe interference. For example, the wires can be placed at the point of maximum constructive interference. In this case, we would expect to see the greatest reduction in the number of photons incident on the detectors behind the mirrors.

“I think what you are not understanding in this experiment is the use of the lens. It is also calculated to be within a specific distance from the pinholes so that photons from each pinhole can only end up at their specific detector. This provides the which way information.”

I don’t think you understood my original paragraph you are commenting on here. In my original paragraph, I indicated that Group B photons are resolved at the detectors (i.e. we have path information), but we have no visibility information on Group B photons (i.e. we have no evidence of an interference pattern).

Regards,
Steve Clark.

"I agree that the wires are placed at the point of maximum destructive interference. But this is not the only place the wires can be placed to observe interference. For example, the wires can be placed at the point of maximum constructive interference. In this case, we would expect to see the greatest reduction in the number of photons incident on the detectors behind the mirrors."

If you place the wires at the point of maximum interference you will see the photons hitting the wires and a garbled picture the same as in B on page 33 of the preprint. What information can you get from seeing the loss of resolution of the image? With the wires in the minima you are able to say yes there is interference and compare the attenuation
of the radiant flux with with the original A.

"Group A photons pass through both holes as a wave and exhibit an interference pattern on the wires. Note we have no path information for Group A photons. Group B photons pass through only one hole, and are resolved at the detectors. Note that we have no visibility information for Group B photons. There is not a single photon in this experiment for which we have both path information and visibility information, and therefore the principle of complementarity is not violated."

Yes I read this very carefully and decided you could not understand how which way information was being observed in this experiment. If photons are not interfering 6.6% will be incident on the wires. If they are interfering only 0.1% will be incident on the wires. You must explain this difference to make the designation of Group A and group B have any meaning.

Quantum Mirror,

“If you place the wires at the point of maximum interference you will see the photons hitting the wires and a garbled picture the same as in B on page 33 of the preprint. What information can you get from seeing the loss of resolution of the image? With the wires in the minima you are able to say yes there is interference and compare the attenuation of the radiant flux with the original A.”

Do we care about the garbling of the picture, or do we only care about the amount of radiant flux at the detectors? My point was that with the wires at the point of maximum constructive interference, we would get a reduction in radiant flux at the detectors much greater than the 6.6%. Therefore we have exhibited constructive interference at the wires.

”Yes I read this very carefully and decided you could not understand how which way information was being observed in this experiment. If photons are not interfering 6.6% will be incident on the wires. If they are interfering only 0.1% will be incident on the wires. You must explain this difference to make the designation of Group A and group B have any meaning.”

I still don’t think we understand each other.

Group A photons are the .1% of photons incident on the wires. I am assuming that these photons don’t reach the path detectors. Even if they were reflected off the wires and somehow made it through the lens to the path detectors, we would not be able to resolve path information on them (since they passed through both holes). Therefore we have observed interference information on Group A photons, but have no path information on Group A photons.

Group B photons are the other 99.9% of photons that are not incident on the wires. Group B photons pass through the lens and are resolved at the detectors. Therefore we have path information on Group B photons (i.e. which hole they went through), but we have observed no interference information on Group B photons. Afshar is hypothesizing interference information on Group B photons based on the observation of interference information on Group A photons. But Group B photons cannot exhibit interference since they only passed through one hole.

Therefore we have interference information on Group A photons and path information on Group B photons. But they are not the same photons, and therefore the principle of complementarity is not violated.

Regards,
Steve Clark.

Dear Afshar,
This post is in response to your post dated 12/06/04 @ 13:01.

Please do respond to my questions one-by-one at the end of my (rather lengthy) post dated 12/06/04 @ 08:41. Also, please let me know specifically where you disagree with my assumptions, rationale, and conclusions for the results of your experiment.

1) There is one point that is unclear to me. Are you saying the coherent distribution is caused by the wires, or are you saying the coherent distribution is merely demonstrated by the wires, and exists even in the absence of the wires?

2) I disagree with your conclusions, but do you agree that if one accepts your conclusions, then one must also accept that my thought experiment also violates complementarity?

3) I agree that V=1 on the wires, but not anywhere else.

If we cannot resolve which set of conclusions is correct by logic, perhaps we can resolve the truth by further experimentation. You are hypothesizing a coherent path distribution in front of the mirror. Is it possible to use a smaller lens to examine the intensity in the vicinity of a peak or valley in your hypothetical coherent distribution? The results should be different than what would be expected for a decoherent path distribution.

Regards,
Steve Clark.

Dear Steve
Once again you must explain:

How have the photons taken this bizarre trip around the wires without interference? This will be an amazing new discovery in Physics and the result will be you with a Nobel prize. If you can only explain!

Maybe Shahriar has found a entryway into one of the many worlds of Everett! :)

If photons are not interfering 6.6% will be incident on the wires. If they are interfering only 0.1% will be incident on the wires.

Quantum Mirror,

"How have the photons taken this bizarre trip around the wires without interference? This will be an amazing new discovery in Physics and the result will be you with a Nobel prize. If you can only explain!"

Now I think I finally understand your point of contention. I think this is also one of Afshar’s primary points of contention with my conclusions. I address this issue in detail in my (rather lengthy) post dated 12/06/04 @ 08:41. The explanation is rather lengthy, and so I won’t duplicate it here. See the part of the post where I provided my responses to Afshar’s questions.

Steve Clark.

Dear Steve,

After reading your lengthy critique several times, I can only say that I always try to make everything as simple as it possibly can be. The only conclusion that I can make is that you do not really understand the experiment. You keep getting sidetracked by questions that have no bearing on the actual outcome of the experiment. Such as putting the wires in the maxima. This would serve no purpose. You try to divide the photons into two groups that have no actual association with the experiment. You ask questions such as:

6) Are you claiming that measurement of an interference pattern in part of a plane indicates the interference pattern extends across the entire plane?

The interference pattern has been completely and rigorously worked out so that we know exactly where every minima and maxima will occur.

There are many such errors in your critique. You should go back through the experiment and make it as simple as possible. Visualize the photons going through every part of the experiment, See the wires as only interference indicators, and ask yourself how could the photons could miss the wires without interference. If you can explain this then you have a real contention to the experiment.

Here is a good refresher on wave particle duality.

http://arxiv.org/pdf/physics/0302062

Quantum Mirror,

”I can only say that I always try to make everything as simple as it possibly can be.”

I agree my explanation seems more complicated than accepting an interference pattern everywhere. But I believe my explanation is consistent with the Copenhagen interpretation.

“The only conclusion that I can make is that you do not really understand the experiment. You keep getting sidetracked by questions that have no bearing on the actual outcome of the experiment. Such as putting the wires in the maxima. This would serve no purpose.”

You claimed that interference could only be shown at the point of maximum destructive interference. My only point here was that you are wrong. I used the point of maximum constructive interference as an example. In fact, there is only one point where interference cannot be shown, which is at the point of intersection of the coherent and decoherent distribution curves (where the two are equal).

“You try to divide the photons into two groups that have no actual association with the experiment. You ask questions such as:

6) Are you claiming that measurement of an interference pattern in part of a plane indicates the interference pattern extends across the entire plane?

The interference pattern has been completely and rigorously worked out so that we know exactly where every minima and maxima will occur.”

It is true the interference pattern has been completely worked out and we know exactly where every minima and maxima will occur. But the Copenhagen interpretation indicates that this interference pattern only exists in regions where we are measuring visibility information, and does not exist in regions where we are measuring path information.

”There are many such errors in your critique. You should go back through the experiment and make it as simple as possible. Visualize the photons going through every part of the experiment, See the wires as only interference indicators, and ask yourself how could the photons could miss the wires without interference. If you can explain this then you have a real contention to the experiment.”

I agree that my explanation may seem more complicated than Afshar’s explanation, but it is logically self-consistent, consistent with the Copenhagen interpretation, and preserves the principal of complementarity. Afshar’s explanation that the coherent interference exists everywhere may seem simpler, but his argument is not logically self-consistent. He claims that the photons go though both holes, and yet he resolves path information. He concludes the principal of complementarity is proven invalid. I refuse to give up the principle of complementarity so easily based on an argument that is not logically self-consistent, even if some aspects of his explanation seem simpler than mine. I will provide further clarification on my explanation in a future post.

Regards,
Steve Clark.

Aurelien wrote:
PS: Serafino, I dont think that bohr never changed his point of view but if you can send me a copy of the paper I will be pleased.

As far as I remember, those late papers (end of '50s, '60s) by Fock and Bohr were translated fron Russian to Italian by Silvano Tagliagambe. He also published a book about all that, in the '70s. Since I have that book I can read it and (if there is something interesting) translate it from Italian into English!
A presto,
serafino

Dear Steve,

You said: "my explanation may seem more complicated than Afshar’s explanation, but it is logically self-consistent, [and] consistent with the Copenhagen interpretation"

It is certainly NECESSARY for an idea to be logically self-consistent, but it is not SUFFICIENT to make it a PHYSICAL principle.

This reminds of the evil mind tricks my elder sister used to torment me with. Let me call one such scheme the Bogeyman Principle, and here’s how it goes: There is always a Bogeyman behind you. No matter which way you turn your head you will never see it, because he moves in such a way that he is always behind your head. I would constantly try to come up with ways of catching this monster. After a while, I discovered a way to circumvent the logic of co-movement of the monster with my head. I confronted my sister confidently, my face beaming with pride: the Boogeyman is not real, because I looked at the back of my head with a mirror, and there is nothing there! She laughed a devilish laugh and dismissively said: Of course you can't see him silly, he is INVISBLE to boys!!!

This Boogeyman Principle (BP) is indeed “logically-self-consistent” and fully “consistent” with the existence of the Boogeyman. Alas, we adults are not too fond of such imaginary things. More specifically, we physicists look for TESTABLE, positive predictions, and then we run experiments to VALIDATE such predictions. I am not going to give you a lecture on why it is futile to search for a negative prediction, but suffice it to say that for example a claim that "there are no flying pigs anywhere in the universe" is an empty prediction, since the whole universe cannot be searched... Logic is a very rigorous yet tricky discipline, and it is very easy to fall in love with a logical fallacy! We need both necessity and sufficiency in an idea that is to be called a physical Principle.

So, coming back to our main discourse, let me tell you clearly that my starting point is the QM formalism, and anything that happens to disagree with that formalism, I dismiss as a BP, not worthy of being called a physical Principle.

You argue in your long response that everywhere else, other than the wires, there is a decoherent distribution. Now, my challenge to you (and Luboš) is the following:

I will believe you if you can write an explicit wavefucntion (complete with all the bells and whistles) that is capable of producing regions with zero amplitude WHITIN itself, without using at least two interfering coherent wavefunctions. If you can do that, then I would agree that PC is not a BP. ONLY then, you would have shown PC’s full consistency with the QM formalism.... Why stop, there, I would personally nominate you for the physics Nobel prize, (not to mention the Fields medal) on top of mine of course!

And by-the-way, MAGIC is not a physical concept, it belongs to the Occult practices in which I am not a participant, though I must admit, I have never been able to shake off my sister’s Boogeyman story!!!

Good luck, and best regards.

Dear Steve

"I used the point of maximum constructive interference as an example. In fact, there is only one point where interference cannot be shown, which is at the point of intersection of the coherent and decoherent distribution curves (where the two are equal)."

This again has no reason or logic in association with this experiment. With every reply you prove that you have no understanding of the concepts involved in experimental physics. Please before you complicate Shahriar's life with such trivial misconceptions, take your critique to an expert in quantum mechanics and physical/experimental optics, and ask him look at your arguments first. He is having a very busy year as you can imagine and does not need to be instructing you in physics.

Once again you must explain:

How have the photons taken this bizarre trip around the wires without interference?

Your Nobel awaits you!

Dear Serafino, thanks for the information and your erudition , perhaps it will be possible to find something in my side but i dont know where to search. I am
waiting for the details concerning Bohr and Fock. If you can give me some sentence of the book it will be fine for my culture.

Dear Shahriar ,

your reasoning using momentum is completely wrong. in quantum mechanics a momentum is associated with a plane wave. such plane waveis infinetelly extended and if you measure the momentum you can no be sure that the photon come from the good pinhole. In fact it is so trivial that I am a little bite surprised by your conviction . the wave coming from A and the wave coming from B interfere only because they possess a contribution for the same value of the momentum. if you say the opposite then no fringes....

secondly your conception of the momentum is classical. Such conception is only possible if you use a model in which the photon exist a point like structure moving in a well defined way (strict causality and determinism are here even not necessary ). A simple model is the one of de Broglie Bohm . the momentum is the gradient o the phase divided by hbar. this is the same formula that in classical mechanic if the action S is equal to the phase X hbar. The rest is the Hamilton-Jabobi dynamic with such definition and with an extra potential coming from the wave function. this
potential deform the naive trajectories and finally the particle coming from A goes into B' and not A'. However you will never know that because the only thing that you can see is a click on your detector in B' or A' and nothing concerning the intermediate stages. This is to finish I hope with this debate on the the 'which path ' in your experiment. I explained you that the complementarity principle doesn't need to use the term of which path which is generally senseless in QM. there is some exceptions:

one consist into detect the particle just after the slits . this means as well know destruction of the particle and you can not use the same particel to build fringes. and other way is to create an entanglement with an other system says an atom in the vicinity of the slit A or B and to detect the state of this atom before that the photon interfere (this is not easy but I know how to do it). If you don't do that strange things can happen conected to the non locality in QM. I dont want here to enter into the details but again the photon will come from the bad pinhole as in your configuration (see the famous Hardy paradox for information).

Whatever the so called ''which path experiment'' you have nevertheless a test of the principle of complementarity saying: that with a same photon you can not by statistical repetition and accumulation re-build the interference pattern and the distribution in the aperture plane. What you called which path information is here replaced by distribution in the aperture plane. All is statistical and the concept of trajectories is even not mentioned. I think that I am one of the first to define correctly the principle of Bohr. My definition is much more modern that the one used by Bohr him self because I don't introduce other concepts that the statistical ones contained in QM.

To finish i would like to confirm that for Bohr and Heisenberg the concept of trajectory was classical and thenr necessary limited ot a class of experiment. I dont subscribe to this strange vision as you but I dont believe in the impossible. The futur is open but not infinite..... I am convinced that one day me or an other will find a good theory for the particles accepting the QM duality as a fact but without neglecting the dynamical structure of the universe. I am already on the good way for the photon whihc is probably the simpler QM object possible.

au revoir et a bientot

Aurelien,

Quantum Mirror,

“"I used the point of maximum constructive interference as an example. In fact, there is only one point where interference cannot be shown, which is at the point of intersection of the coherent and decoherent distribution curves (where the two are equal)."”

“This again has no reason or logic in association with this experiment. With every reply you prove that you have no understanding of the concepts involved in experimental physics. Please before you complicate Shahriar's life with such trivial misconceptions, take your critique to an expert in quantum mechanics and physical/experimental optics, and ask him look at your arguments first. He is having a very busy year as you can imagine and does not need to be instructing you in physics.”

I apologize if I have insulted you by pointing out your error. I was only trying to point out that there is no magic associated with the point of maximum deconstructive interference. I think this whole notion of using non-destructive interference to illustrate visibility information is just confusing the real issues. One does not need to use non-destructive interference to illustrate both visibility and path discrimination in the same experiment. This is illustrated in my much simpler thought experiment where we have a screen on the left side illustrating the visibility of the interference pattern and a lens on the right side resolving path information.

” Once again you must explain:

How have the photons taken this bizarre trip around the wires without interference?

Your Nobel awaits you!”

The Copenhagen Interpretation predicts interference is present at the wires, but no interference is present in front of the lens. In a future post, I will attempt to clarify Afshar’s results further in the context of the Copenhagen Interpretation. But my interpretation of your question is that in order for you to accept the Copenhagen Interpretation, I must explain the fundamental mystery of how an observation at a measurement point affects behavior at the holes and path distribution between the holes and the measurement point in a non-local manner. Obviously I cannot explain the fundamental mystery, and I agree I would deserve a Nobel Prize if I could. So I will never convince you that the Copenhagen interpretation is correct. My hope has not necessarily been to convince you that it is correct, but only that it has not been disproved by Afshar’s experiment.

Steve Clark.

Dear Steve,

"I apologize if I have insulted you by pointing out your error."

I made no error, you keep embarrassing yourself with your awkward, overblown delusions of competency in physics! Please take a course in Physics 101 at your local city college! I would suggest some math first!

"Obviously I cannot explain the fundamental mystery"

If you will look back at my post on 12/06/04 @ 11:32
You will see what I tried to explain to you that your line of reasoning was constrained by the fundamental mystery.

Good day to you!

Dear Steve, Dear quantum mirror, dear Shahriar,
I try to understand your meta-magico-physical discussion sponsorized by the Boogeyman.
Are you saying that there is no fringes in front of the lens? but what do you mean by that . Fringes is a statisticasl concept in QM. To see them you need to see them .... It is clear I guess: if you put a detector in this plane with or without wires you will see fringes no doubt about that, now if you are saying that even without putting the detector the fringes are here or not here this is another problem because the definiton of the fringes is different. Clearly you need the wave eqution to expalen the propagation and the shape of the spots at the end of the experiment. You dont need to observe the phtotn to be sure of the validity of this principle you just observe the pertinence of this use by the agreeemmnt with the experiment. And of coures if you consider others photon detected in the fringes pnae you will see the pertinence one more time of your affirmation. all is then coherent. The uniqual point that you can not discuss is the nature of the wave and the real shaope of it around the particle. In other term the lawfor the individual system are not know and you just have statistical laws.

dont concentrate to much on this discussion . it is very similar to the discussion between me and Afsahr concenring the term which path. Stay close of the facts and you will clarify you thought.
The real point concern the complementarity principle which is a statistical statement which can be difined in the following way:
A same photon (or electron, or...) can not participate to build two statistical pattern exlucde experimentally by their complementary nature.
Here we speak about the fringes pattern and the distribution of particles in the 2 pinholes plane.
Never Shahriar observed (rebuilded) this two patterns simulteanously so never he questionned complementarity. That 's it and that' s all friends.


aurelien

Afshar,
With respect to my post dated 12/07/04 @ 09:19 where I suggested using a smaller lens to measure the peaks and valleys, I now realize this will not prove anything. I now realize that if you conduct this experiment you will indeed find the peaks and valleys of a coherent path distribution, but this will still not prove a coherent path distribution exists across the face of the smaller lens. I was starting to go down the same track of thinking that you are on, and I admit it is hard sometimes not to go down this track.

Doesn’t the lens and mirror apparatus map different points at the plane of the wires where you are claiming interference to different points at the image plane at your detectors? If a coherent distribution is present at the plane of the wires, shouldn’t the interference pattern be visible at the image plane of your detectors?

Perhaps this could be more clearly illustrated with a couple of simulations. I am assuming two simulations both with the same physical configuration. Close one of the holes and get rid of the wires in front of the lens. Run one simulation assuming a decoherent path distribution function sourced at the hole and the second simulation assuming a coherent path distribution function sourced at the hole. The results at the image plane of the detector should clearly illustrate the differences in a coherent path distribution versus a decoherent path distribution.

I agree with Aurelien that your argument for interference in front of the wires is a “Boogyman” argument. I think I have clearly illustrated above that the Copenhagen interpretation is not a “Boogyman” argument.

Steve Clark.

Dear Steve, (Aurelien may also be interested)

It is now clear to me that you do not understand the basics of physical optics. A smaller lens would not be able to resolve the images due to smaller aperture, and you would lose which-way information! The moral of my Bogeyman story was to show you that you can have an absurd idea that is logically self-consistent with itself, but that cannot be taken seriously from a physical point of view. SO IF I MUST SPELL IT OUT: the Bogeyman is the Complementarity Principle which fails in experiments employing non-perturbative measurements for ensemble properties such as the interference pattern.

Complementary measurements MUST be made on the SAME photons (and you miss this simple point in your thought experiment). In my experiments all photons reach the image plane through the wire grid region. Since the images are not affected by the wires, they all carry perfect which-way information, but these very same photons have passed the wire plane in a manner that cannot be explained in any way other than an interference if we assume validity of QM formalism, which I do. If you don't, that is your problem not mine.

I delineated the challenge that you would have to meet to be to taken seriously back in 12/08/04 @ 07:44, so short of that no further posts please! I really don't have the time to provide you with free physics lessons...

Finally, my arguments with the wires is certainly not a Bogeyman argument (and Aurelien does not suggest that it is) because the physical reality of the wires cannot be doubted: just carry a very small current through the wires during the experiment!!!

Regards.

Dear Afshar,
This is my final post.

“A smaller lens would not be able to resolve the images due to smaller aperture, and you would lose which-way information!”

I agree with what you are saying. My thought was to create a smaller lens by masking parts of your lens.

“Complementary measurements MUST be made on the SAME photons (and you miss this simple point in your thought experiment).”

This is exactly what I have been trying to point out to you for the last week. My experiment is no different than yours. You measure visibility on the photons incident on the wires, but path information on photons that are NOT incident on the wires.

“Finally, my arguments with the wires is certainly not a Bogeyman argument (and Aurelien does not suggest that it is) because the physical reality of the wires cannot be doubted: just carry a very small current through the wires during the experiment!!!”

Your argument is a "Boogeyman" argument because you claim an interference pattern that is not visible. If there were a coherent distribution at the face of the lens, it would manifest itself in an interference pattern at the detectors. How do you explain the lack of an interference pattern at your detectors? If you don’t believe me, I suggest you run the simulations that I have suggested.

Regards,
Steve Clark.

Dear Steve,

"How do you explain the lack of an interference pattern at your detectors?"

It is very simple really, the two wavefunctions do not overlap spatially, so one cannot see a spatial interference pattern! It is exactly the same reson as to why one does not see an interference pattern immediately after the dual pinhole (in the near-field regime).

"If there were a coherent distribution at the face of the lens, it would manifest itself in an interference pattern at the detectors."

This statement is so ridiculous that I don't think I should even dignify it with a response! The lens Fourier separates the wavefunctions based on their angular partition, regardless of the existence of an interference pattern at the lens or not! See the previous paragraph for an explanation as to why there is no interference at the detectors.

My question to you is: Do you know what a Decoherent distribution looks like? There are no minima in a decoherent distribution, thus ANY subensemble that is supposed to be decoherent has a 6.6% blockage, no matter what the NORM of the subensemble. Then again I think it is useless to talk about these technical details to a person not versed in QM.

My challenge to you still stands. After you learn the QM formalism please do take a shot at it. It will teach you a lesson or two on what my experiment is all about!

Regards.

Dear Steve, (and naturally always Shahriar the master of this place)
ones more time, I think you have to concentrate more on the experiment and on the quantum nature of the reality.
When you think about wave it is visible that you think in classical term which means elctromagnetic wave . Such waves are made of several photons and can not be used for your reasonning with this half lens to prove anything . If you have classical waves then effectively what you do have a sens but only if you want to test the validity of optics.... however nobody doubt about optics i guess.
A photon is a kind of paradox in the context of wave theory and I think that you have not sufficiently concentrate on this point . A photon will appear as a local click in one point and not as a wave : never . It is only the accumulation of such events which produce fringes or spots (with shapes given too by wave optics naturally). It is only the STATISTICAL accumulation which produce the wave duality and similarly the principle of complementarity. If you are interested in the dynamic of one photon then you can not apply the quantum formalism which is statistical .

Don't forget this basic fact : you can see a single photon only one time but to see the wave you need many photons.....


with best regards.


Aurelien
Ah!! I will keep my virtual hat for you but i guess this hat will have a long 'life' in front of him ......hihihi

dear Shahriar I would like to have your point of view concerning the following remarks:

In an ideal Young double slit experiment we must have D=0 and V=1 this means that the two spots in the aperture plane have the same intensityI_A=I_B----> D=|I_A-I_B|/(I_A+I_B)=0 similarly
V=2|sqrt[I_A*I_B]|/(I_A+I_B)=1. In your experiment you see the spots then for me D=0 and V=1 too as it can be observed directly from your data.
Now if we concentrate on one spot ( say A') we have D=1 because we can draw the distribution for the hole A. The problem is that now we can not be sure that the photon in the fringes plane will really goes to A' then we can not say that V=0. We can not test complementarity in this way.


Aurelien

I am sorry a part was cut:

you must in your case then accept V=1 and D=0. This is of course differnt if you close one pinhole because you now for sure where come from the photon and where he will goe.

In every case the complementarity principle is a statistical statement. and you need always to choose if you want that your phtotn participate in the building of a interference pattern or of a double spots image.

Dear Aurelien and All.
I've read the original paper by Fock. And some pages from the 1959 paper by Bohr, as response. In the next post (not in this one) I will quote from these papers, as they are interesting. Actually Bohr changed his interpretations a bit, or perhaps much (according to Fock).

About Bohr - Fock debate (Copenhagen and Moscow, 1957 - 1959)

Let us start from what Bohr says about complementarity.

‘This point is of great logical consequence, since it is only the circumstance that we are presented with a choice of either tracing the path of a particle or observing interference effects, which allows us to escape from the paradoxical necessity of concluding that the behaviour of an electron or a photon should depend on the presence of a slit in the diaphragm through which it could be proved not to pass. We have here to do with a typical example of how the complementary phenomena appear under mutually exclusive experimental arrangements and are just faced with the impossibility, in the analysis of quantum effects, of drawing any sharp separation between an independent behaviour of atomic objects and their interaction with the measuring instruments which serve to define the conditions under which the phenomena occur.’

'However, since the discovery of the quantum of action, we know that the classical ideal cannot be attained in the description of atomic phenomena. In particular, any attempt at an ordering in space-time leads to a break in the causal chain, since such an attempt is bound up with an essential exchange of momentum and energy between the individuals and the measuring rods and clocks used for observation; and just this exchange cannot be taken into account if the measuring instruments are to fulfil their purpose. Conversely, any conclusion, based in an unambiguous manner upon the strict conservation of energy and momentum, with regard to the dynamical behaviour of the individual units obviously necessitates a complete renunciation of following their course in space and time'.

Thus, from the quotes above, we get concepts, dogmas and principles: about: 1 the uncontrollable interaction (and the nonseparability) between the quantum system and the measurement apparatus; 2 the necessity of mutually exclusive experimental arrangements; 3 the break down of causality; 4 the impossibility of ordering in space-time, or the impossibility of following the course of quanta in space-time.

In the next post (after the flu I've got) we'll (perhaps) see that Bohr, after the debate, changes his mind about points 1 and 3, and perhaps also about 2. But not much about point 4, given the statistical nature of quantum description.

serafino

Would someone be so kind as to explain for a non-scientist what the implications for all of this are? Does this experiment imply anything about the uncertainty principal? Dr. Afshar can you send me to a page anywhere where I might read of your own TOE.

Dear Afshar,

I was wondering about your thoughts on Quantum erasure in relation to your experiment? As we can see from the following as does happen a lot in Physics, you can't always believe everything you read. I think your experiment may "erase" a few papers.

Also I would like to read your TOE.

This is a excerpt from: http://arxiv.org/pdf/physics/0302062

Two clarifications of their quantum erasure and quantum optical tests of
complementarity need to be made. Both in this paper,13 and in a recent popularized
version in Scientific American,14 unless one reads these articles very carefully one is left
with the impression that these experiments have already been done. Reading their
prior papers,15-19 one finds that these experiments have yet to be done. Even with
careful reading of these papers,13, 14 not the least hint is given of a number of scientific
papers with opposing views, and one is left with the impression that their views on
complementarity and quantum erasure are completely accepted by the scientific
community. As we shall see in the next and other following sections, they have been
challenged by their colleagues on the simpler claim that complementarity is an independent pillar of quantum mechanics, rather than merely a consequence of the
uncertainty principle. Quantum erasure may also be challenged.

13. M.O. Scully, B.-G. Englert, and H. Walther, Nature 351, 111 (1991).
14. B.-G. Englert, M.O. Scully, and H. Walther, Scientific American 271, 86 ( Dec. 1994).
15. B.-G. Englert, and M.O. Scully in New Frontiers in Quantum Electrodyanamics and
Quantum Optics (edited by A. O Barut, Plenum, NY 1990).
16. B.-G. Englert, J. Schwinger, and M.O. Scully in New Frontiers in Quantum
Electrodyanamics and Quantum Optics (edited by A. O Barut, Plenum, NY 1990).
17. M.O. Scully, and H. Walther, Phys. Rev. A 39, 5229 (1989).
18. M.O. Scully, B.-G. Englert, and J. Schwinger, Phys. Rev. A 40, 1775 (1989).
19. M.O. Scully, and K. Druhl, Phys. Rev. A 25, 2208 (1982).

Sorry - reposted with paragraph breaks that "fell out" on first attempt.

Dr. Afshar,

I read about your experiment, and comments by John Cramer that your results are consistent with his transactional interpretation of QM, and probably not with the Everett or Copenhagen views. I also noted that you are interested in interpretations of QM that might further the search for a TOE. I would like to call to your attention what seems to me to be a fascinating possibility that your experiment apparently strengthens, that when you take the work of Carlo Rovelli regarding atemporality and incorporate it into Cramer/Feyneman’s wave theories, you have an incredibly rich atemporal model of the universe that fits your results. Before proceeding I should add the disclaimer that neither Carlo nor Dr. Cramer (nor for that matter Julian Barbour – author of “The End of Time”) are enthused by the idea. Briefly -

Rovelli argues that there is no fundamental observable temporal variable “T”ime, rather there is a temporal variable “t”ime that is derived from relative motion. In his recent book (pre-print http://www.cpt.univ-mrs.fr/~rovelli/book.pdf), Quantum Gravity (given a terrible – I think biased - review by your colleague Lubos Motl http://schwinger.harvard.edu/~motl/rovelli.html), summarizes his thoughts on temporality and the potential for loop quantum gravity theory. Earlier in his career he was more concise about his views on temporality - http://fr.arxiv.org/abs/gr-qc/9903045 and a LaTex file http://www.ws5.com/copy/time.tex. Essentially, he notes that Einstein’s field equations can be solved without any reference to a variable “T” and that QM can also be formulated without “T” when using Heisenberg states – “In the absence of a normal notion of time evolution, the Heisenberg picture remains viable, the Shrodinger picture becomes meaningless.” Rovelli concludes that “we should accept what general relativity is telling us”… “At the fundamental level, we should, simply, forget time.”

Rovelli recognizes that pre-symplectic mechanics allows for motion in a fully atemporal universe. In such a universe the variable “t”ime is derived from that relative motion. I would suggest that this means that tensed words like “before” and “after” lose all temporal meaning, and have meaning only as descriptors of the sequence of events in a pre-symplectic manifold. In other words event 1 occurs “before” event 2 and event 3 occurs “after” event 2, without any sense of the passage of a fundamental time. The immediate knee jerk reaction is that this model does not resemble space-time, and is therefore wrong, however that is not the case. As far as I can tell there is absolutely nothing in a fully atemporal model that requires any changes in GR or the Heisenberg formulation of QM.

Now the interesting part. If you combine the idea of an atemporal universe with Cramer/Feynman waves, you have no problem understanding waves that project into the “past” and “future” because the waves are essentially moving “forward” and “backward” in a spatial sense. Again this brings protests that GR/SR is violated, however those who are able to overcome the psychological barriers against atemporality can at least accept the possibility that nothing at all is violated. What we are left with is a bounded area of “space-time” where atemporal waves are free to interact without regard to the passage of time. It is only matter that finds itself a slave to a derived time, and then only as the result of the ordered nature of all sets of events wherein matter changes its relative position to other matter. We are provided with an atemporal “present” that is focused at one space-time event (or perhaps a set of events), yet that interacts with what in a temporal model is called the recent past and near future. This view fully allows for the observed symmetry of the arrow of time, while providing a strict asymmetric pre-symplectic model of causality (in my opinion allowing for Penrose’s orchestrated state vector reduction).

Whether or not a photon is ever truly a particle, the advanced and retarded waves would engage in an atemporal ballet that builds a pre-symplectic stage on which the photon performs as both particle and wave, as observed in your experiment. While it may be wrong, the atemporal model offers so many possible answers to difficult questions that it deserves serious consideration.

Sincerely, Paul Snyder

Dear all , I found in the web the interesting web page:
http://en.wikipedia.org/wiki/Double-slit_experiment
and
http://en.wikipedia.org/wiki/Principle_of_Complementarity
concerning the double slit experiment . A section has been added concerning Afshar and I added this morning something in comment.

My commnet is the following:
However the interpretation is not trivial and it could be that the experiment made by Afshar is based on a misundertanding of the principle of Bohr. This principle tell us (as explained before) that if one of a pair of complementary properties of a quantum object is know for sure, then information about the second complementary is lost. This complementarity can be then expressed as a kind of duality between different representations of the reality associated with different experimental arrangements. In the case of the experiment made by Afshar, based on a variant of the double slit experiment, the two spots in the image plane of the lens give us a information about the distribution of particles in the aperture plane (see the publications cited before). However in counterpart the information about the fringes is very weak. Indeed, due to their particular spatial locations, the wires used by Afshar only tell us that there are some minimum in the fringes and nothing more. Unfortunately, this is not sufficient to reconstruct completely and simultaneously the distribution of particles in the aperture plane and the interference pattern. Finally, it seems that, as pointed out originally by Bohr, we can not use information associated with a same photon event to reconstruct in a statistical way (i.e. by an accumulation of such events) the two complementary distributions of photons in the aperture plane and in the interference plane.

Aurelien

PS: thanks Serafino asnd good luck with your virus.

Aurelien,

Please stop posting your personal comments on the main Wikipedia pages. There is a "discussion" page where you can make your statements, and bring forward arguments. You MUST however, provide your name in the discussion page. The main pages require a higher standard of language and verification than the discussion page. If you keep posting on the main pages without having gone through the discussion page first, the moderators can blacklist you form Wikipeida. This is considered Vandalism.

I WILL SHARE YOUR NAME WITH WIKIPEDIA MODERATORS IF YOU CONTINUE ARBITRARILY CHANGING THE MAIN PAGE CONTENTS.

Dear Shahriar,

While the wikipedias ability to change quickly with changing current knowledge is a good thing, there should still be some rigidity to it. Perhaps it would be sensible for the comments concerning your experiment to be removed, at least until your research gets published in an scientific journal. By the way, how is that going?

Chris

Dear Chris,

I have been asked by Wikipedia to write a description of my experiment, and what it means. They are confident it can be discussed in public domain since it has been published in a number of high caliber popular science outlets (in contrast to the views of the opposition). It is NOT required that a work be published in a peer-reviewed journal for it to be covered by Wiki, and I am not going to remove the references to my work as it is absolutely solid.

As for the peer-review argument, I actually believe that there is not a single “published” paper out there that has received anywhere near the amount of scrutiny and peer-review as my work has already gone through, and yet it stands unchallenged. BTW- the journal peer-reviewers are still considering the experiment and my arguments. Sooner or later the other shoe will have to drop!

Regards.

P.S. While I encourage feedback from experts, I must say I am very disappointed with Aurelien's unprofessional conduct vis-à-vis Wikipedia. He has vandalized comments on Wikipedia and made disgraceful statements which I will not quote here. IT IS VERY UNBECOMING...

Dear Quantum Mirror,

Most quantum erasure experiments involve entangled photons, and thus are not addressed by my current experiment. However, it is safe to say that "delayed-choice" experiments are also falsified by my results, as there seems to be no real choice to be made. I will shortly embark on experiments directly addressing entanglement and related topics.

Regards.

Dear Freinds,

I have recently been commissioned to write a book about my physics research during the past 18 years (which will also cover some of my TOE ideas). This, in addition to the upcoming experiments and other academic duties, would entail very limited free time to work on this Blog. If anybody wishes that I discuss a particular issue in the book, please let me know here. But otherwise I already apologies for my anticipated inability to respond to all comments and questions on this page. I thank you all for sharing your thoughts and ideas here, and wish you all the best.

With warmest seasonal greetings!

Best regards.
Shahriar S. Afshar

"If anybody wishes that I discuss a particular issue in the book, please let me know here."

If you choose to discuss the transactional interpretation as it applies to your experiment, you may want to explain how the confirmation wave does or does not interact with the wires. There is only one final confirmation wave (from the detector that detects), which propagates backward in time to the source. Therefore, there is no interference for the advanced wave, and no canceling at the wire locations. Are your results consistent with that?

Thanks.

salam bar shahriar aziz....
az didane maghalat kheili khoshhal shodam...( har chand ma ke in kare nistim ) , omidvaram zodtar be natije berese... ke hatman mirese...movagh bashi... va montazere shenidan akhbare khob baraye to hastam...
ghorbonet
30na

Dear Prof. Afshar,

" The first, completely _classical_ derivation of Planck's law, replete
with the perspective of the thermodynamics of computation pioneered by
Landauer and Bennett at the IBM Watson lab where I had the honour of
working for some years, is at

http://www.columbia.edu/~vg96/papers/planck.pdf

It establishes that
the Planck's constant h is really just the Fourier transform of the
Boltzmann constant k - to be precise, it serves the same role for the
spectral domain as k does for the ordinary (un-Fourier transformed)
time domain. About the only part I'm not totally happy about is the
derivation of the Boltzmann distribution (in appendix), but this does
not diminish the main contention of the paper in sections IV (the
derivation) and V (applications to boson statistics, zero-point
energy/field and entanglement)."
V. Guruprasad

Please, your comment on paper:

http://www.columbia.edu/~vg96/papers/planck.pdf


Best regards,
Aleksandr Timofeev

Dear Shahriar

The following is a story in Physics Today about the difficult task of understanding physics better than your predecessors and how with time you will overcome.

"Beware ye, all those bold of spirit who want to suggest new ideas."

Good luck to you in all your endeavors.

http://www.physicstoday.org/pt/vol-54/iss-7/p46.html

Dear Prof. Afshar,

I read your preprint with interest, although I believe the subject matter belongs to the realm of philosophy or science history rather than physics. For a physicist, any interpretation is fine as long as the theory predicts the experimental result correctly. And your experiment yields expected results according both to classical optics and quantum mechanics.

You argue that a detection of a photon at 2' is equivalent to "tracking the path of the photon" through slit 2. But how do you know the photon didn't happen to pass through slit 1 if both slits were open? In support of your argument, you cite some prior work by Wheeler and others, but this is the key point of the paper, and I would like to see it discussed in more detail. I doubt that a "common sense" argument based on the fact that the geometrical image of slit 2 is located at 2' will work well. One could equally make the following "common sense" argument: if the detector at 2' only detects photons passing through slit 2, the measurements at 2' should not depend on whether slit 1 is open or closed, because if nothing passes through it, then it does not interact with light at all. But you show that measurements at 2' do change when one closes slit 1! BTW I don't think this latter argument is particularly elegant either, but the bottom line is that in order to "track the path" of a photon trough slit 2 one needs to put a detector in slit 2, and I don't see a good way around it!

Not being an expert in interpretations of quantum mechanics, I believe that according to the standard interpretation(whichever it's called), the photon passes through both slits 1 and 2, forms an interference pattern at sigma1 and ends up at sigma2 in a superposition state with equal amplitudes of being at detectors 1' and 2'. A measurement made at 2' detects the photon with 50% probability. Thus I don't see any contradiction between the results of the experiment and the standard interpretation, but, again, as long as everybody agrees that the formalism of quantum mechanics predicts the experimental results correctly, the whole issue of the interpretation is of rather didactical and historical interest.

Alex
The lens Fourier is a measured distance from the slits so that photons from each hit it at the precise angle so they can only reach the correct detector. This provides which way information. Interference does not mean that the wavefunctions are split into Two, 1/2 photons. You must read the preprint very carefully to understand all the mechanics of the experiment. I hope this makes sense, its 4:30 AM and I am barely awake.

Dear Quantum Mirror,

One needs to accurately define the meaning of the statement "photon passes through slit 2". If we have a detector at slit 2 (or any physical process that can detect a photon), then it's clear. But if there's no detector how can one say that "the photon passed through slit 2"? I would assume that if the wavefunction has amplitude 1 at slit 2, then the photon passes through this slit. If the wavefunction has an amplitude 1/sqrt(2) at slit 2 and 1/sqrt(2) at slit 1, then one cannot say through which slit it passes - it simply doesn't have a trajectory. Alternatively, you can say that the photon passes through slit 2 if its path constructed according to geometrical optics passes through slit 2. With the former definition Afshar's conclusions are incorrect, with the latter one they are correct. So it's just a matter of semantics.

The lens is shaped like this (). The photons from one slit can only hit it on the side of the curved lens so the angle will only allow it to arrive at the proper detector. The photon must make a decision after interference as to which path it has taken. THIS is what makes this experiment unique. If it was as simple as you stated, we would not be discussing it at all.

What you describe is geometrical optics. This description implies that a photon follows a certain path (BTW how do you explain that closing slit 1 changes the photon count at 2' ??). But if you don't make this assumption, then, if both slits are open, you cannot establish that a photon passes through 2 unless there's a detector at 2.

Alex
"What you describe is geometrical optics"

I was trying to make it simple as I did not know your level of expertise.

I will assume you are looking at the illustrations on page 33 of the preprint. In A both slits (pinholes) are open. You can set your CCD at either D1 or D2 it makes no difference.

In B the pinhole witch "corresponds" to the CCD is left open, (It makes no difference whichever side you prefer) and the wires are added. A measurement is taken at the CCD of the amount of light that is lost.

The other pinhole is opened with the wires still in place and produces C. This is compared to A and B. The only explanation for the lack of attenuated and diffracted light is interference.

" BTW how do you explain that closing slit 1 changes the photon count at 2'"

The wires are added to the experiment which block some of the light.

Dear Quantum Mirror,

Of course there's interference at the sigma1 plane. I was just saying that you were using geometrical optics to support the statement that a detection of a photon at 2' is equivalent to "tracing the path" of the photon through 2.

>"BTW how do you explain that closing slit 1 changes the photon count at 2'"
>The wires are added to the experiment which block some of the light.

The wires are there whether slit 1 is open or not. You're saying that all photons detected at 2' have "passed" through slit 2, i.e. they didn't have any interaction with slit 1 at all. Then closing or opening slit 1 should have no effect on those photons. Then how come the photon count at 2' decreases when slit 1 is closed?

Alex
"The wires are there whether slit 1 is open or not."

Please look carefully at the experiment! There are no wires in A on page 33!!!

"they didn't have any interaction with slit 1 at all"

Where did I say this???????

"Then how come the photon count at 2' decreases when slit 1 is closed"

Once again: Interference has points of minima and maximum. The wires are placed at the point of minima. When one pinhole is open there can be no interference. The photons hit the wires and are blocked from the CCD. When both are open there is interference so no light is blocked!!!

If you do not put more thought into your next inquiry, I will not respond.

>>You're saying that all photons detected at 2' >>have "passed" through slit 2, i.e. they didn't >>have any interaction with slit 1 at all.

>Where did I say this???????

Very good! Then you agree that the photons detected at 2' did interact with slit 1? (of course they did because, as you correctly point out, their count at 2' is affected by the interference). How can one say then that the photons "passed" through slit 2? Wouldn't you agree that each photon interacts with both slit 1 and slit 2? Then there's no such thing as the "path" of a photon through a certain slit. Please feel free not to respond :-)

Alex
Are you saying that because the photon must go through both slits and interfere with itself that it can't then have a path? This is the central mystery of quantum physics. It has you talking in circles and me trying to explain in circles.

This is what I meant by this experiment being unique and we would not be discussing it if was simple.

If you want to explain that the path is indeterminate you must invalidate quantum mechanics formalism. Are you ready to give up on QM?
If not you must explain how the photons got around the wires without interference.
The third choice is to invalidate complimentary.

In the QM formalism a photon does not have a path. One can measure the position of a photon, but not the full path. In Afshar's experiment, CCD arrays measure the coordinate of a photon in the sigma2 plane. At the plane with the slits, however, the photon does not have a coordinate. It is described by a wavefunction with equal amplitudes at slits 1 and 2.

Afshar's experiment is indeed trivial (so perhaps we should not be discussing it :).

Alex

This is Shahriar's answer to the same reasoning earlier:

If you take a look at fig.1 Fig.1 which is John Wheeler's original delayed-choice experiment. We are not concerned with the delayed-choice aspect, and will only discuss the Complementary pair of observables one at Sigma_1 (perfect interference), and the other at Sigma_2 (perfect which-way information). I would have used this setup instead of the one I did use, were it not technologically more difficult. As you can see the interference region is quite small, and that entailed I had to use extremely thin wires, which would pose very difficult positioning problems, and lead to unreliable results. But I did arrange the optical setup as shown, and one can observe a highly visible (though spatially tiny) interference pattern at Sigma_1, and further down, as the two wavefunctions no longer overlapped, two distinct beams are observed at Sigma_2. So this is indeed a real experiment and not Gedanken! The good thing about this setup is that there is no lens and we don't have to be bugged down with imaging theory etc.

Now consider the application of your statement above to this set up. Say I run the experiment in the single photon regime, and observe a click in the D1 detector. According to your argument, then simply because the two wavefunctions had interfered earlier on at Sigma_1, there is a 50% chance that the photon came from Pinhole 2. But in order for it to have come from pinhole 2, it must have changed its momentum from P2 to P1 as shown in Fig.1. We know that the photon could not have exchanged momentum with anything along its path to detector D1, and in order for a photon originating from Pinhole 2, it must change its linear momentum by Delta P. This is impossible, unless we are ready to forgo the law of conservation of linear momentum, which I am not!

Therefore, simply because the two wavefunctions had interfered earlier on, they DO NOT lose their identity if they no longer overlap spatially (that is ensured in fact by the linearity of Schrödinger equation).

Dear Alex,

I see you are confusing "Which-Way Information" (WWI) in 2 different types of welcher weg experiments:
1) In welcher weg experiments involving AMPLITUDE splitting (Mach-Zehnder type interferometers), the WWI is in fact a "path" or "Trajectroy" determination, thus the WWI is called the "which-path information".

2) In welcher weg experiments invoving WAVEFRONT splitting (double-slit interferometers), the WWI is not a trajectory determination, but "which slit" or in my experiment "which pinhole" information.

In my experiment, it is impossible to discuss a single path for a particular photon, but it is absolutely possible to discuss "which pinhole" its wavefunction eminates from. Thus WWI of the 2nd type can be obtained with high accuracy.

Regards.

Dear Quantum Mirror,

Coordinate and momentum of a photon cannot be determined simultaneously. In the figure Shahriar is discussing, coordinate of a photon is measured at the Sigma_2 plane. Consequently, the photon does not posess a momentum at Sigma_2 (I mean the vertical coordinate and the corresponding momentum component), and it's hard to see how the momentum conservation argument can be made.


Dear Shahriar,

Indeed, the key point of you paper is the statement that measuring the coordinate of a photon at the image plane tells us through which slit the photon has passed. This statement appears to be very believable from the "common sense" point of view, and I agree that a number of verbal arguments can be made to support it (I gave an example of an opposing argument: if all photons detected at 2' passed through slit 2, then why is their count at 2" changed by opening or closing slit 1?). Verbal arguments aside, however, it's hard to see how one can establish that a photon passed through slit 2 without putting a detector at slit 2.

As far as the photon wavefunction, I hope you agree that it has equal amplitudes at slits 1 and 2. Therefore I don't quite see what you mean by saying that the wavefunction "emanates" from a certain slit.

Es tut mir leid dass Ihre Messung doch keine "welcher Weg" Information zu liefern scheint :)

Dear Quantum Mirror,

Let me be more precise: if one wants to demonstrate the violation of the momentum conservation law, one should clearly define what the initial and the final states of the photon are, considering the complete experiment, and demonstrate that the photon posessed a definite momentum value in both initial and final states. The arguments "if the photon came from hole 2 then the momentum conservation would be violated, therefore it must have come from hole 1" doesn't make much sense because it implies that these are the only two choices. If the photon was in a superposition state with e.g. equal amplitudes at holes 1 and 2, then it's momentum was not defined and, consequently, momentum conservation does not apply.

Dear Alex,

"As far as the photon wavefunction, I hope you agree that it has equal amplitudes at slits 1 and 2. "

I do agree with the above. But it means that there are two correlated wavefucntions with equal amplitudes, but at TWO DISTICNT spatial coordinates, which associates each one with a particular pinhole via the Unitary Time Evolution.

Regards.

I don't understand why such an important experiment, showing wave properties and path information simultaneously for single photons, should be sent for publication in the American Journal of Physics, basically a periodic addressed to teachers, with pedagogical aims, and not specialized in original research. In my opinion you should send this result to the Physical Review Letters or another high impact physics journal. Just my two cents.

Dear Stephen,

It has also been sent to PRL, and is still under peer-review! The difficulty with short papers is that all technical detail cannot be covered, and hence a longer more pedagogical paper was submitted to AJP. There are other longer papers on measurement theory in the works...

Regards.

Dear Prof. Afshar, I would like to suggest you to send a preprint of your PRL submission to ArXiv. It is common practice and will not harm the peer review process. I even think that it would protect the content of your research. Best Regards, Stephen.

New Interesting preprint on Complementarity:


http://arxiv.org/PS_cache/quant-ph/pdf/0412/0412180.pdf

Dear Prof. Afshar,

I have found in the Internet the pictures of the NewScientist article. Here is my opinion.

The which-way determination in your experiment depends on the following inference chain: if the photon reaches the upper detector you are allowed to infer that it followed one of the two yellow paths in the figure; so you can infer that the photon came from pinhole 2. The same is valid, mutatis mutandis, for pinhole 1.

If you have just one open pinhole, this inference chain cannot produce a logical contradiction.

Now, in the case of two open pinholes the inference chain can be proved to contradict the experience. Take for example the yellow paths. In this experimental arrangement they intersect many dark zones, where no photon could ever be found. So, when both pinholes are open, it is absurd to infer, for example, that any photon reaching the upper detector came by one the yellow paths, and so it is also absurd to infer that it is a pinhole 2 photon. To prove that in this case the necessary paths are not actually followed by any photon you can put thin wires in the many intersections between dark zones and the respective paths, and, despite this partial blocking of the paths, I believe, there will be no significant change in the detectors.

I agree that by putting thin wires in the dark zones before the lens you have determined in a clever and "null" way -- I have no problems with this -- that there is an interference pattern in your experimental arrangement. But in my opinion it is not true that you have determined any which-way information in this case. The inference chain: detector -> paths -> pinhole is not valid when both pinholes are open.

Best Regards,

Stephen

Dear Steven
If you inferred all of that from the pictures, you could do wonders with the preprint.

http://www.irims.org/quant-ph/030503/

" To prove that in this case the necessary paths are not actually followed by any photon you can put thin wires in the many intersections between dark zones and the respective paths, and, despite this partial blocking of the paths, I believe, there will be no significant change in the detectors."

But there was a significant difference. See the preprint for details.

Dear Quantum Mirror,

Thanks for the preprint link! I will read it right now. Are you sure there was a significant difference with both pinholes open? Notice that I am proposing new thin wires which would block the yellow and orange paths, and not the original ones use by Afshar near the lens. The location for this wires will be the points of intersection between the yellow and orange paths and the destructive interference dark zones.

Regards,

Stephen.

I am not sure which picture you are looking at with yellow and orange paths. Maybe you could give me a link or tell me which page in the preprint you are referring.

This picture:

http://wiz.cath.vt.edu/exper/kcramer/blogpix/Ashargraphic.jpg

I'm reading the preprint carefully and after that I will post a comment.

Merry Xmas.

Dear Prof. Afshar, I have a simple question:

When BOTH PINHOLES ARE OPEN how do you know that EVERY photon detected by detector 1 came from pinhole 1?

I'm using the notation of figure 2, page 27 of your preprint.

Thanks.

Zweistein.

I think that you are reasoning this way: if you detected a photon at 1 it must have followed one of the dashed paths of figure 2, so it came from pinhole 1.

But that reasoning is wrong! WHEN BOTH PINHOLES ARE OPEN you cannot say that ANY, not even a single one, photon followed the dashed paths!

To prove that experimentally you can simply put wires ALONG the dashed paths in those points where we have destructive interference. And there is more than one wire position which satisfy this simple condition. Since no photon will be blocked in this case how can you say that ANY photon followed the dashed paths? You cannot. And so you cannot also determine the which-way of the photons detected at 1.

Of course, everything I said above is valid for the other pinhole, paths and detector.

Let me say it again: WITH BOTH PINHOLES OPEN block the dashed paths with wires localized in those points where we have destructive interference -- the so called dark zones. No single photon will be blocked, and so no single photon can be said to have followed the dashed paths, since they this paths are now blocked. And so you have not determined the which-way information for the photons detected at 1.

Again, I'm using the notation of figure 2, page 27 of your preprint.

Thank you!

Zweistein.

Dear Zweistein,

Talk of "paths" or trajectories in my experiment is meaningless: all amplitudes within the wavefunction contribute to the final observable (at either image). Sorry, but a robust knowledge of physical optics and QM is a prerequisite for following the arguments presented in my preprint, and I am unable to simplify it any further. You may find my comments on 12/22/04 @ 15:20, as well as some earlier discussions to be helpful.

Regards.

Dear Prof. Afshar, thank you for your answer.

Yes, I am trying to put my objection in the most elementary way, in order to get at the essence of the problem.

I maintain that you don't have any good reason to infer that, when both pinholes are open, a photon detected at detector 1 (2) came from pinhole 1 (2). And we don't need the formalism of QM to see this. The simple argument sketched above shows it in elementary terms.

If the paths are really meaningless, there is no which-way determination anyway.

Best Regards,

Zweistein.

If the paths are meaningless why do you draw them? Why do you use them to establish your lens geometry? Why do you use them to position each part of your equipment?

JUST ONE OPEN PINHOLE: you can infer the paths in a simple way and determine the which-way information.

TWO OPEN PINHOLES: you cannot infer the paths from the detector and there is no real which-way determination. You detected the photon at detector 1? You will never know if it came from pinhole 1 or 2. If you could we would never need any amplitudes and there would be a simple system of probabilities to understand the phenomena, which displays interference, as you determined.

Dear Zweistein,

The lines you see in the diagrams, are the boundaries of the wavefunctions as they unitarily evolve in time, not actual paths.

To demonstrate your error, consider your own statement:
"JUST ONE OPEN PINHOLE: you can infer the paths in a simple way and determine the which-way information."

When a single pinhole is open, once a photon is detected by a detector, its trajectory (which is supposed to be a series of connected lines from the image, through the lens back to the pinhole) is not a unique one. There are in fact infinitely many such paths possible with various separations from each other. Thus it is useless to talk about a single "path". However, it is completely legitimate to talk about a single origin, which is the open pinhole. Take a look at Feynman's Lecture on Physics where he discusses the lens to understand how the amplitudes add to produce an image.

As for the case when both pinholes are open, you need to browse the entire Blog, especially my posts in response to Chris.

Good luck!

Of course talking about one or two paths for each pinhole is just a way to simplify things and to get what is essential in the argument. It seems that you like Feynman. In many other subjects of the Feynman lectures he did exactly this kind of simplification in order to see behind the details.

Choose some paths which you expect to be related to photons coming from pinhole 1 and block them by the method I have proposed: put new wires in the many dark zones which intersect the choosen paths. Do a drawing; you will see what I am talking about. Nothing will be changed in the detectors. So it is wrong to infer that a particular photon came from pinhole 1 just because it was detected by detector 1. This is "the only mistery" of quantum phenomena operating in your experiment.

The which-way information is not determined in your experiment when you have both pinholes open.

Cheers.

Just and addition. Refering again to you figure 2, page 27 of the preprint: Would it be wrong to say that when just pinhole 1 is open the dashed paths are the most probable paths to be followed by the photons? If so, those paths are anything but meaningless.

I forgot this one!

As you say in your post above that "Talk of "paths" or trajectories in my experiment is meaningless", you should change the abstract of your preprint, since there we can read "Coherent laser light is passed through a
dual pinhole and allowed to go through a converging lens, which forms well-resolved
images of the respective pinholes, providing complete path knowledge.". So you get complete knowledge abou a meaningless thing?

Dear Prof Afshar

I have been studying your experiement and it is indeed ingenious. When the pattern is restored by opening the other slit and the diffraction pattern disappears you are indeed infering wave like behavious due to this very effect. The lens and experiemental setup indeed guarantees that photons from slit one and two hit their respective detector.

The diffractiion grating works equally well for either slit alone and not at all for both. Brilliant !!

So according to quantum lore any which 'way information' gained will collapse the wave function and destroy one aspect of the experiment, either wave or particle. So are you sure that you have a 'which way' experiment here ?

Single photon experiements state that due to the interference pattern being produced by a single photon (which is classically unexplainable) then any attempt at knowing which way the photon want causes the wave property of the photon to disappear (wave pattern) and for us to know the direction it went (particle trajectory).

You appear to have violated this concept and if quantum lore states that the interference pattern must disappear then surely you have results that contradict quantum physics ? Is this not the case ?

Regards

Dear Quantum Enforcer,

You said: "The lens and experimental setup indeed guarantees that photons from slit one and two hit their respective detector."

This is only true when just one pinhole is open, say number 1, and so the most probable paths for the photons are the dashed ones at figure 2, page 27 of the preprint. Just in this case you can infer the coming pinhole from the detector trigged by the photons.

When you open both pinholes this is no longer true. No photon could have followed those most probable paths since they cross many dark zones of destructive interference where no single photon can ever be found. It is an illusion that you have determined which-way information in this case.

I agree that Prof. Afshar have determined the occurence of interference in an elegant way. But I think that he has not determined the which-way information simultanously.

All my best,

Zweistein.

The Lens is setup in such a way that photons entering point one goto detector 2 and vice verse for photons entering point two. If this part of the experimental setup is true before the diffraction grating in put in place then why is it not true after ? I presume that the photon detectors are detecting photons in perfect coincidence at first. In other words block off point one and no photons will reach detector two and block off point two and no photons will reach detector one I presume ? This shows that only photons from point one reach detector two and vice versa.

The diffration grating does not change that does it ?

Dear quantum enforcer,

With zero amplitudes at the wires, their presence does not change the dynamics of the system at all--given both pinholes are open.

You may also wish to take a look at:

http://www.newscientist.com/article.ns?id=mg18324614.100 (From John Cramer's response to criticism in New Scientist letters).
and
http://www.physics.ohio-state.edu/~perry/p631/articles/afshar_Slide3.GIF (From my seminar at Harvard.)

Regards.

"The Lens is setup in such a way that photons entering point one goto detector 2 and vice verse for photons entering point two. If this part of the experimental setup is true before the diffraction grating in put in place then why is it not true after ? I presume that the photon detectors are detecting photons in perfect coincidence at first. In other words block off point one and no photons will reach detector two and block off point two and no photons will reach detector one I presume ? This shows that only photons from point one reach detector two and vice versa. The diffration grating does not change that does it?"

Dear Quantum Enforcer,

My objection has nothing to do with the diffraction grating. Please, read my posts again.

I'm arguing that when both pinholes are open we can't know for sure that a photon detected at detector 1 (2) came from pinhole 1 (2).

My proposal to show this experimentally is simple: with both pinholes open find a few points of destructive interference which lie on the most probable paths for photons coming from pinhole 1 (2). Put some blockers on those points. You will not see any difference in the detectors!

Another proposal: with both pinholes open find a few points of constructive interference which lie on the most probable paths for photons coming from pinhole 1. Put blockers on those points. You will see a difference on detector 2!

After that, can you still believe that we are determining which-way the photons go in this experiment when both pinholes are open? I'm sorry, but I can't!

Forget the diffraction grating. It is fine and clever. What I'm trying to point out has nothing to do with the grating.

Regards,

Zweistein.

Ah yes I see, because Afshar has only concentrated on where the interference is not influencing the experiment and not where it is potentially influencing it his answers may not be all that they appear to be. However he has demonstrated that wave and particle knowledge appear to be in coexistance without collapsing the wave function simply by using a clever inference argument.

You've got it, Mr. Quantum Enforcer! The point is that we can give an operational meaning to the concept "which pinhole the photon came from".

"Ah yes I see, because Afshar has only concentrated on where the interference is not influencing the experiment and not where it is potentially influencing it his answers may not be all that they appear to be."

I couldn't say it better!

"However he has demonstrated that wave and particle knowledge appear to be in coexistence without collapsing the wave function simply by using a clever inference argument."

But any observed particle aspects are far from disclosing both interference and which-way information in the same setup, as claimed in the abstract of the preprint.

Regards,

Zweistein.

By the way, which particle aspects are disclosed with both pinholes open? The photons coming in "lumps" at the detectors? Well, that is pretty trivial and expected, isn't it?

If, in the case of both pinholes open, we don't have the which-way information for the photons, no surprising particle aspects are revealed by the experiment.

Regards,

Zweistein.

>I do agree with the above. But it means that there are two correlated wavefucntions with equal amplitudes, but at TWO DISTICNT spatial coordinates, which associates each one with a particular pinhole via the Unitary Time Evolution.

Dear Shahriar,

I don't see what is your point here. If the photon wavefunction has equal amplitudes at pinholes 1 and 2 this means that the photon does not posess a definite coordinate, and it's impossible to tell whether it passes through pinhole 1 or pinhole 2.

You argument is based on the conjecture that if you measure the photon coordinate at the image plane this tells you what the photon coordinate was at the object plane. I don't think this conjecture agrees with the QM formalism. An observable has a definite value only if the photon is in the eigenstate of the corresponding operator. If it is in the superposition state, then the observable does not have a definite value until the measurement is made. For any measurement, be it of the photon position, momentum or polarization, one cannot establish, in general, what was the value of the observable before the measurement.

Let me present an example making this point clear in application to your experiment. Suppose we remove the screen with pinholes, and let's say a collimated beam (i.e. a plane wave) is incident on the lens from the left. A photon in the "plane wave" state posesses a definite momentum, but does not posess a definite coordinate. After passing through the lens, the beam is focused at the distance x=F from the lens and then diverges again. Let's say you have a CCD array at x=2F and it detects a photon at a coordinate y=Y0. Then would you agrue that the photon had the coordinate y=-Y0 at the plane x=-2F before the lens? But before the lens the photon was a plane wave, it did not posess any coordinate!

Dear Alex,

"Your argument is based on the conjecture that if you measure the photon coordinate at the image plane this tells you what the photon coordinate was at the object plane. I don't think this conjecture agrees with the QM formalism."

I strongly believe that you are right. This inference, or, as you say it, the conjecture that detector image => pinhole isn't true when both pinholes are open. I have tried to show this by the elementary arguments above.

Regards,

Zweistein.

Let us see if Prof Afshar can answer the charge of only setting up the experiment for a special case of so called wave particle duality where it is bound to work. Should it not also work if we place the wires in the area of maxiumum intensity when both slits are open.

Let us return to basics. Consider the archetypal two slit experiment whereby a source emits something (light is the best example) and it hits a barrier with two vertical slits in it. These two slits act as secondary sources of light and this light is transmitted to a detector of some kind that records the effect. The effect recorded is a pattern that you see if light is travelling as a wave with bright and dark fringes of a interference pattern. Now as we know the trick is too reduce the emitting source down to the intensity of one. In the last 10 years lasers have come to dominate here as the emitting source, as in Prof Afshars experiement as they emit monochromatic light of a well defined wavelength and enegy. This single source is called a photon and it is here where the issues of quantum physics begin. Put simply in the two slit experiment described what is recored at the detectors is a interference pattern. It takes time to build it up but it is there. What this appears to mean is that a particle of light acted as a wave (classically impossible) and somehow interfers with itself to produce the interference pattern. The concept of particles comes originally from Planck and added to by by Einstien in the photoelectric effect. Any attempt to infer via direct or indirect means the path of the quantum entity collapses the so called wave function of the quantum entity instantly and hence we get the principle of Complementarity which states that any experiement that attempts to measure simultaneously both wave and particle aspects of a quantum entity will not work as they are mutually exclusive states of a quantum entity. In fact we now move our emphasis over to the act of measurement itself as we are told that a quantum entity is actually in all possible states (wave and particle) until measured but we cannot see it in action as any attempt to do so will result in knowing it to be a wave or a particle.

Prof Afshar sets up his experiment with a additional ingredient, that of a Lens which he uses to focus the quantum entities onto a mirror and onto detectors. The reflective angle of the lens is known to prof afshar so he is able to focus the photons from either one of the two sources onto one of two detectors. He can prove this by shutting of one of the sources and measuring all of the photons hitting each of the detectors. Source one will all hit detector one and source two detector two when the other source is shut off proving this point. Now when he opens both sources at the same time what he gets is which way information as it is a particle experiment. Due to this you cannot measure any wave property of light here. What is happenning when you shut off one of the other slits and place the wires in the way is nothing because you already have which way information so you cannot measure waves because you are already measuring particles. You are not allowing the experiemnt to be in a superposition of all possible states are you ?

Dear Alex, Zweistein,

This issue has already been addressed. Please see my 11/30/04 @ 06:10 post in this Blog. Brifely, the law of conservation of linear momentum forces us to accept which-way information.

Regards.

sorry the last part of my last post is incorrect. Setting up the experiment for particles but then also showing the wave nature of light as well is sheer genius.

Regards

An interesting aspect of Afshar's experiment is that it appears to work only if the pinholes 1 and 2 are identical in shape and size. If the pinholes are different, then the optical intensity at the wires at sigma1 won't be equal to zero.

One possible "common sense" argument in support of the statement that the experiment provides the "which way" information is the following: "since we have an image of pinhole 2 at the CCD camera at 2', then the photons detected at 2' carry information about pinhole 2, hence they came from pinhole 2". However, this argument only works if the images of pinholes 1 and 2 are different and in this case the experiment will not really work!

Now let's say one wants to transmit data from 2 to 2' by changing the shape of pinhole 2. A simple way of doing this would be e.g. to move the pinhole 2 up or down, causing the corresponding displacement of the image at the CCD camera at 2'. But in this case the minima of the interference pattern will also move and, again, the experiment won't work.

Let me propose the following conjecture: it is impossible to transmit information from 2 to 2' AND simultaneously maintain the optical intensity at zero at a given point at sigma1 plane.

Interference is a wave property pure and simple no matter how you look at the experiment. Photons being blocked and then not been when the slit is opened again. Photon cound returns to pre wire state. Inference is that waves are causing the effect seen.

Dear Shahriar,

I'm afraid the momentum conservation argument doesn't quite work here. Please see my comment of 12/23/04 @9:26

Dear quantum enforcer, Of course there's interference at the sigma1 plane. The point I've been trying to make is that the experiment does not provide "which way" information.

does it provide which way information before the wires are introduced ?

>does it provide which way information before the wires are introduced ?

I'm afraid not.

The experiment is setup to measure particles and what is more to record which way particle information from how I understand it to be. So why do you say otherwise, what is your reasoning ?

Dear quantum enforcer,

If both slits 1 and 2 are open, how can one definitely establish that the photon passed through slit 2 without putting a detector at slit 2?
Also see my comments of 12/23/04 @ 07:24

by how the lens focuses the light in line with the law of refraction. The only difference between this and any other which way experiment is the lens which is wel understood optically. Setup the apparatus so that when either slit is closed all of the particles goto a given detector.

Dear quantum enforcer,

Yes, when either slit is closed, all particles go to a given detector. However, this doesn't have to be true when both slits are open. Indeed, a conjecture that this is true looks very believable, and a lot of "common sense" arguments can be made to support it (you gave one - laws of refraction - but note that laws of refraction is a quasiclassical approximation assuming that particles follow certain "trajectories" which doesn't provide an accurate description for quantum particles). Now let me give you an opposing "common sense" argument: the experiment demonstrates that the particle count at 2' is changing depending on whether slit 1 is open or closed. Would you agree then that the particles detected at 2' somehow interact with slit 1? But then how can you say they "passed" through slit 2? I'm not trying to argue that this argument is better than the other, but the bottom line is this: if both slits are open, you cannot establish experimentally that the photon passed through a given slit without putting a detector in the slit. You can try to infer it based on various assumptions (e.g. an assumption that single photons follow the laws of refraction) but note that in physics a statement only makes sense when it's experimentally verifiable (at least in principle).

OK Alex, when both slits are open in a two slit experiment you generally cannot tell which way a photon has gone. This means that in Afshars experiment if you cannot tell which way the photon has gone then you can still exploit the wave property of the quantum system. You are trying to disprove the very core of his argument regarding wave/particle duality. Prof Afshar is telling us that even though the wave function has collapsed via which way information he can still infer the wave nature of light in a particle experiment.

The Lens is the crucial peice of the puzzle here, does it give which way information ?

Dear Quantum Rebels!

Our leader Afshar said: "According to QM, an image produced by a lens contains the "which-way" information... Wheeler specifically uses this method in his delayed-choice experiment.".

But compare the figure for the Wheeler which-way experiment with the setup described in the Afshar preprint.

In the Wheeler case, because of the converging lens placed so close to the slits, the paths which go from each slit to the respective detector do not cross any destructive interference zone (at least in my drawings!). In the Afshar case we have this problem (at least in my drawings!).

Are you all sure that putting the lens so far way from the slits, Afshar is not fooling himself with respect to the which-way determination in his experiment?

Can we do an additional simple test to check if the which-way information is really ok?

Bye! Feimen.

Dear Feimen,

The setup in Fig. 1, is ESSENTIALLY equivalent to the one I have used in my experiment, just analytically simpler, because we don't have to talk about the lens’ Fourier transforms etc. My setup is indeed discussed by Wheeler, and he uses the lens in exactly the same manner as I have, in a setup he discusses in a paper mentioned in my preprint. Please read my preprint and you will also find a ref. to Heisenberg, where he uses a lens to obtain which-way information. You may also wish to take a look at this paper by Zeilinger: http://www.physik.fu-berlin.de/~simons/Publikationen/RevModPhys99.pdf

Regards.

Dear quantum enforcer,

Anyone that wishes to prove that the lens does not provide the which-way information must meet the challenge mentioned in my posting of 11/22/04 @ 08:01.

Regards.

Dear Alex,

Let me ask you a question: Assume that both pinholes are open, and immediately after the pinholes --in the near field regime i.e. before the two wavefunctions emerging from each pinhole overlap spatially--we place a detector in front of one of the pinholes. We know that BEFORE a photon is detected, both wavefunctions have equal amplitudes (but at two different locations). Now let's further assume that our detector detects a photon. Now AFTER this detection, it is impossible to assign the origin of this photon to the other pinhole, because doing so would lead to a violation of the law of conservation of linear momentum.

Do you disagree with the above? If you do disagree, then you have not understood QM, and I suggest you do the necessary calculations.

Regards.

Dear Prof Afshar

I am not even going to attempt falsifying the experiment as I believe it to be correct and very ingenious. My personal opinion is that you have setup the experiment to measure particles of light but you then manage to infer waves too adding in wires that scatter the light when only one slit is open but when both are, the scattering stops. This shows that it must be interference that is in evidence here and that is only a wave property.

So you have demonstrated wave/particle duality simultaneously and potentiallty debunked complementarity, one of the cornerstones of QM.

I am not more interested in what it means for QM itself as I was under the impression that QM states that the gaining of any which way information will collapse the wave function and give either particles. You experiment has a so called collapsed wave function from the start as you are measuring which way the photons have gone. The fact that you also appear to be able to demonstrate the wave properties of a particle experiment is almost too good to be true even when the wavefunction is already collapsed.

So this now adds to the questions of QM and all the experiments before it regardng the collpase of the wave function and wave/duality.

Dear Afshar,

If you and the physics community are sure that the use of the lens provide which-way information when both pinholes are open I have no further objections to the experiment, since I do believe that the gratting placed at the dark zones which does not absorb any photon is indeed a proof that we have interference in the same setup.

My last word is that you should take Wheeler's words with as great care as you did for Bohr. He made great mistakes. The most famous is the fallacy of "charge without charge" where he "proved" that a topological aspect of space would be the cause for the field aspects of a single charge. Of course he was wrong, because the proof applied the Stokes Theorem to a region which does not satisfy the conditions of the theorem.

Vive felice!

Feimen.

Dear quantum enforcer,

"So you have demonstrated wave/particle duality simultaneously and potentially debunked complementarity, one of the cornerstones of QM"

Contrary to the accepted dogma, it is crucial to understand that Complementarity is NOT a cornerstone of QM. The QM developed quite independently of Bohr's philosophical bent, and as soon as he realized that he can uphold his philosophical views using an accepted QM principle (namely Heisenberg's Uncertainty Principle), he did his best to inject his philosophy of Complementarity into the mainstream QM language. Those who are experts in this field know that what I just said is absolutely correct. In fact Heisenberg himself recounts a story about a meeting between him (then only 25) and Bohr, during which the latter forced the young genius to include his Complementarity argument in his paper...

At any rate, the goal of my experiment has been to clarify the above, i.e. the fact that Complementarity and QM formalism have very little overlap, if at all. Beyond Heisenberg's uncertainty principle, which is fully derived from the properties of the Fourier transform, there is nothing in QM that looks startling. But that said, it is quite evident that the Uncertainty Principle certainly is NOT MAGICAL. Complementarity demanded Magic, an irrational process beyond any explanation and quite outside the reach of QM formalism.

The other important implication of my experiment is a necessity for the revision of the Measurement Theory, to include measurements that do NOT cause a collapse of the wavefunction. I am currently working on a paper that attempts to address this pivotal aspect. It is a very long story, and I will talk about it in my book as well. So stay tuned!

Regards.

Dear Feimen,

Let me assure you that my reverence for Wheeler has in no way blinded me to a critical review of his reasoning, which goes back to Heisenberg himself. Wheeler's prodigious mind spit out so many novel ideas that he can be fully excused if on rare occasions he actually erred. IMHO he should have won two Nobel prizes in physics, and another one just for his generous and gentlemanly manners!

Regards.

" ... there is nothing in QM that looks startling ... "

How about quantum erasure, delayed-choice and entanglement?

Cheers,

Feimen.

Dear Shahriar,

In your example, BEFORE the measurement the photon did not posess a coordinate. AFTER the measuremetn you can of course assign the photon to the corresponding pinhole. However, I'd object to the statement that it's possible to assign the "origin" of the photon, because the word "origin" implies that you know what was the coordinate of the photon BEFORE the measurement.
Let me ask you this: if there's a plane wave incident on the CCD and you detected a photon at a certain coordinate Y, what was the photon's coordinate immediately before the measurement? Would you agree that in this example the photon did not posess a coordinate before the measurement?

Dear Feimen,

I'll address those issues in my next experiments, but delayed-choice is already falsified by my current experiment, as it shows there is really no "choice" to be delayed!

Regards.

Dear Alex,

All measurements in physics are "after the fact", i.e. before something happens we have no right to talk about it. This is also true in classical statistical mechanics, where we have classical uncertainties due to huge degrees of freedom in multi-particle systems. So to answer your question, it is meaningless to talk about the coordinates of a photon in a collimated beam BEFORE it is detected. However, for beams that are either divergent (e.g. the diffracted beam after a collimated beam passes through a slit) or convergent (as in a focused beam), there are certain boundaries within which photons can be found and certain regions where there are no photons. Using QM, these regions can be accurately PREDICTED even before an actual measuement is made. Later direct measurements have always confirmed these predidctions...

Regards.

Dear Shahriar

After much thought and careful deliberation, I have found only one possible argument against your experiment.

In this paper:

Dear Shahriar,

You couldn't put it better. So in your experiment, indeed, QM accurately predicts that the photon will be detected, with equal probability, in the region 1' or in the region 2'. Whether you detect the photon at 2' or at 1', BEFORE the measurement it was in the SAME STATE described by a wavefunction with equal amplitudes at 1' and 2'. Therefore, it is meaningless to say that the photon had passed through pinhole 1 or pinhole 2 depending on whether it was detected at 1' or 2'.
Let me give you another example very familiar to everybody. Consider a particle in a potential well with discrete energy levels E1, E2, etc. and corresponding eigenstates Psi1, Psi2, etc. Let's say the particle is in the superposition state Psi=(1/sqrt(2))(Psi1+Psi2). If we measure the energy of the particle, then of course we get, with equal probability, either E1 or E2.
Now let's say we measured the energy and it's equal to E1. How would you like the following argument: "because of the conservation of energy, the energy of the particle before the measurement was also E1, and, consequently, the particle was in the Psi1 state. And if the measured energy is E2, the particle has been in the Psi2 state". I hope you agree that this argument doesn't make any sense. But this is exactly the same kind of argument (with momentum conservation etc.) as you use when you argue that the photon detected at 2' has passed through pinhole 2.

Dear afshar

The above was about 200 words but all was lost due to some HTML I tried to include for links. Here is a paper by Anton Zeilinger:

http://arxiv.org/PS_cache/quant-ph/pdf/0201/0201026.pdf

"It is argued here that quantum interference is a consequence
of the finiteness of information. The observer has
the choice whether that information manifests itself as path
information or in the interference pattern or in both partially
to the extent defined by the finiteness of information."

"The possible choice between path information and the
observability of interference patterns is one of the most
basic manifestations of quantum complementarity, as introduced
by Niels Bohr. Following our discussion, it is
clear that it is the experimentalist who decides which observable
to measure. He can decide, for example, whether
to put a detector into the interfering paths or not."

It could be argued that in the concept of information, the wires do not disturb any photons. This would mean the interference is not directly measured only inferred by a non-perturbative fashion. If there is no disturbance to the actual physical process no information is extracted.

Oh Well, I had this written much better in the first post. This has been bothering me for a while and I would like to hear your views. Thank You!

Afshar: "I'll address those issues in my next experiments, but delayed-choice is already falsified by my current experiment, as it shows there is really no "choice" to be delayed!".

Fine. Maybe the quantum erasure concept could be falsified too. Have you tried to polarize the photons and observe the presence of the interference minimuns in your non-interactive way?

Cheers, Feimen.

Dear Feimen

I asked about this same issue and here was his reply to me:

Most quantum erasure experiments involve entangled photons, and thus are not addressed by my current experiment. However, it is safe to say that "delayed-choice" experiments are also falsified by my results, as there seems to be no real choice to be made. I will shortly embark on experiments directly addressing entanglement and related topics.

"... it is safe to say that "delayed-choice" experiments are also falsified by my results ..."

The interesting results of Prof. Afshar does not prove this to be true. Since he is not claiming that complementarity does not hold in general -- there are many experiments where it does hold, and I think he would agree with this -- in those situations where complementarity holds delayed-choice is a meaningfull issue.

Dear Feimen

I think this is pretty strong language against complementarity calling it a philosophy.

"he did his best to inject his philosophy of Complementarity into the mainstream QM language"

I believe that prof. afshar would find other reasons where it does hold up such as uncertainty, decoherence and the finiteness of information. Here is what Einstein had to say about it:

"Despite the expenditure of much effort, I have been unable to obtain a clear
understanding of Bohr’s principle of complementarity"

Dear afshar and everyone:


Here is a great new preprint that I think everyone should read:

http://arxiv.org/PS_cache/quant-ph/pdf/0412/0412195.pdf

Prof. Afshar,

In your preprint you accept and use the standard definition of the visibility V of the interference pattern:

V = (I_max - I_min) / (I_max + I_min)

where I_min is the minimum radiant flux at a dark fringe and I_max is the maximum radiant flux at a bright fringe.

In section 3.3 you argue that in order to determine V it is enough to measure I_min, since for an almost perfectly visible interference pattern I_min ≈ 0, and therefore the visibility V ≈ I_max / I_max = 1, "regardless of the actual value of I_max".

This reasoning from the definition of V above is so simple that it is hard to believe that it could be wrong from a mathematical point of view. But, from the point of view of experimental physics, it is so fallacious that it is hard to believe that anyone could have ever accepted it as true.

The fallacy is simple: since you pretend to be determining V from your experimental data you must provide the experimental error σ_V of your determination of the visibility. Standard error theory gives the estimate for σ_V in terms of the errors of I_min and I_max as:

σ_V² = (∂ V/∂ I_min)² σ_Imin² + (∂ V/∂ I_max)² σ_Imax²

Now, even if you have determined I_min to be very small with great precision, so that σ_Imin is also very small, in your experiment you can't have any idea about the value of I_max and its error. Therefore, the only reasonable way to express your knowledge about I_max and σ_Imax in your experiment is to say that I_max may have any finite value and that σ_Imax is infinity!

Using the formula above for σ_V, the only possible conclusion is that in your experiment you have determined that the visibility of the interference pattern is V = 1 ± 1.

Best Regards,

John Friend.

Dear Friend,

You have made a trivial mistake. I'm sure you'll catch it if you redo your analysis. (Hint, if σ_Imax -> infinity, then V->1 ...)

Also, even if we hypothetically accept your argument, then we can still clearly rule out V=0 due to the absence of the incident flux on the wires (which is the necessary and sufficient condition to rule out Complementarity).

Regards.

Dear Quantum Mirror, and Feiman

In QM formalism, the wavelike evolution of the wavefunction is always true, regardless of the conditions, therefore, there is really no place for the particle-like picture (such as trajectories) prior to measurement at all. In a sense there is really no duality, since there is only a wavelike behavior--up until the moment of detection of the quantum in a singular event. As far as this singular event is concerned, I personally do not believe that this particle-like detection means a particle-like history, and tend to tilt more towards stochastic QED for an explanation of wavefunction collapse. However, the collapse of the wavefunction is such a thorny theoretical issue, that I have given up on its complete resolution through purely theoretical investigations. That is why the next set of experiments are so crucial.

As for Anton's paper discussing complementarity in terms of informatics, he has made the same error as Bohr. The fact is, contrary to the orthodox view, we do not need to perturb the wavefucntion of a quantum particle in order to gain INFORMATION about the ensemble to which it belongs. This is the most crucial aspect of my experiment, and one that has been ignored by all other investigators including our illustrious friend Zeilinger. I will discuss these issues at length in my upcoming book.

Now, Saunders’ philosophical paper is a good one--given one assumes that he has not heard of my experiment. He struggles as usual to explain Bohr’s intentions, and agrees with Scheibe that “there is no single formulation of quantum mechanics based entirely and consistently on the principles proposed by Bohr.” In physics, as soon as you make a statement that is not backed by formal equations, you enter the realm of philosophy, and hence become the subject of philosophical papers like Saunder’s. (Not that I have anything against philosophy!!!)

I must say though, I completely agree with Saunders on the fact that Bohr “was dogmatic about the impossibility of a classically visualizable interpretation of quantum phenomena”, yet he equally dogmatically believed that “however far the phenomena transcend the scope of classical physical explanation, the account of all evidence must be expressed in classical terms.” It is precisely this dogmatism which logically leads to the paradox posed by my results. IMHO, we should all abandon the classical particle picture when it comes to QM phenomena involving coherent states; but the ultimate statement must be made by Nature herself to merit universal acceptance.

Regards.

Dear Alex,

This is in response to your posting of 12/29/04 @ 04:14.

There are numerous technical details about my experiment that I have not discussed here. One of them is the fact that we can introduce asymmetries to it. For example, we can move only one of the pinholes relative to the lab's frame of reference, and observe the corresponding image to entirely co-move with it (of course the wires must also be adjusted simultaneously). The asymmetric positions of the pinhole and its image relative to the optical axis of the lens, provide a spatial correlation between the position of the pinhole and its image regardless of the intervening region where they overlapped (with or without the wires). This type of asymmetry cannot be applied to the example you have mentioned, and thus your argument is not applicable to my experiment.

Regards.

Prof. Afshar,

The above error analysis was just a sketch. I can do a detailed calculation if needed.

Please, you have determined the visibility in your experiment, right? Should you post in this blog the experimental value of V and its error?

About your "hint", it seems that your are confusing the experimental value of I_max with its error... Hint: evaluate the partial derivative and you will see.

Regards,

John.

Dear John,

Please go ahead and e-mail me your detailed error analysis to afshar@rowan.edu. I will be happy to discuss it with you as my time constraints permit.

It is meaningless to talk about measurement errors for an INDIRECTLY inferred parameter, and a pedagogical paper on an experiment is not the right place to talk about the intricacies of error analysis. A direct measurement of the visibility yields V=0.98± 0.1, but since for the which-way determination we were unable to use the direct measurement of the interference pattern, instead of V, another parameter R (the normalized reduction in the total radiant flux for pinhole 2) was directly measured and thus has a real MOE. From this observation, the other conclusions are reached, namely that V=0 at the wires is ruled out. All that matters experimentally to prove Complementarity wrong, is to show that there are real dark fringes, which in turn can only be explained quantum mechanically by interfering wavefunctions.

Regards.

Dear Shariar,

I think that at some point the referees of your paper will point something analogous to my objection. May I suggest you to talk with any bayesian guy who does data analysis in a regular basis. It seems to me that you can do a very elegant data analysis of your indirect determination of V treating I_max as a nuisance parameter (so you can integrate it out) and plugging some suitable prior.

Best regards,

John.

"It is meaningless to talk about measurement errors for an INDIRECTLY inferred parameter ..."

Dear Shariar, reading your posts I see that you love saying this or that concept to be meaningless in your experiment. You are completely wrong in this case. Geophysicists are always doing "indirect" inferences and estimating the errors of such inferences. Even if you have infered the visibility indirectly it is mandatory to present some estimate of the error in this inference.

"All that matters experimentally to prove Complementarity wrong, is to show that there are real dark fringes, which in turn can only be explained quantum mechanically by interfering wavefunctions."

Maybe you are right. But then all the talk about visibility is unnecessary.

Dear afshar

"The fact is, contrary to the orthodox view, we do not need to perturb the wavefucntion of a quantum particle in order to gain INFORMATION about the ensemble to which it belongs. This is the most crucial aspect of my experiment, and one that has been ignored by all other investigators"

Great answer! This is exactly what I have been thinking but was having trouble putting into words. There are many forms of deduction that involve something that is not found. This is confusing in the context of all is information concepts.

Dear Prof Ahshar

In your experiment could you remove the photon detectors and add your lense into a laser based classical two slit experiement where it is waves that are measured. Not just any waves but interfered with waves that are focused by the lens to provide which way wave information You lens would focus interfered with waves into a photosensitive plate that would also record which way information. I believe your lens when fed single photons should provide which way information via the lens when the experiemnt is setup for wave or particles should it not ?

Gentlemen

Richard Feynman said that the two slit experiment is the only issue in quantum mechanics. If we setup the experient for waves and not particles (in classical quantum physics terms) and the lens provides which way wave information instead of a detector of some kind placed in the actual path of one of the possible routes (as in experiments up until now have) then we should be able to show the same effect.

When the wires placed in front of the lens diffract a one slit Ashar experiment and then do not in a two slit version it is difficult to not infer anything but waves regardless of them being in the so called zero interference region.

Dear quantum enforcer

"In your experiment could you remove the photon detectors and add your lense into a laser based classical two slit experiement where it is waves that are measured. Not just any waves but interfered with waves that are focused by the lens to provide which way wave information You lens would focus interfered with waves into a photosensitive plate that would also record which way information."

The lens Fourier separates the wavefunctions based on their angular partition, regardless of the existence of an interference pattern at the lens.

Dear Quantum Mirror

In the Afshar experiment what is it that gives which way information in the particle sense ? I thought that it was to do with the laws of refraction or light in a lens ? What do you mean by angular partition ? the engle at which the light hits the lens ?

Regards

Dear quantum enforcer

In the experiment we know the wavelength of the laser, pinhole center-to-center distance,
pinhole diameters, distance to the lens, and the focal ratio and distance of the lens. We can then figure out exact pinhole origin of the wave function. we can't say anything about the particle sense until it is destructively registered by the CCD. This provides the "which way" information.

I don't think particles have any sense, or else they wouldn't be so hard to figure out. ;)

Dear John,

From your last two posts, it is now clear to me that you are a Bayesian, which for geophysicists is the rational choice of statistics. Unfortunately, when it comes to QM, most physicists are Frequentists, simply because they do not like to talk about inferred phenomena; only observed phenomena are discussed. Due to the enormous size of the action relative to Planck's constant h, geophysicists can confidently talk about the physical reality of Tsunami waves before they actually produce evidence of their existence, sadly by devastating the shorelines of a continent; however, the same stance is not applicable to QM. A wavefucntion does not physically exist even after it has been destructively measured by a particle-like detection. All the 80 years of hoopla over wavefunction collapse and its reality centers around the fact that prior to its measurement it is indeed meaningless to talk about how it had evolved… Alas, unless you are familiar with the long history of this debate, my experiment would not make much sense! That said though, I am still interested to see your analysis. Who knows, maybe one of the lessons of my experiments is that we should start considering Bayesian ideas in QM as well...

Regards.

So quantum mirror as in all classical two slit experiments all of what you say is also known also but until now you could not do the following, show which path the photon took to it's destination without destroying the interference pattern. As Afshars experiment appears to allow for which path knowledge without wavefunction collapse it is attributed to the lens which focuses the light to which path photon detectors. It is not a wave based experiemnt but a particle one at first. I am stating that we should be able to setup the experiment to look at wave behaviour and then extract the particle behaviour collapsing the wave function either.

All of the quantum experiments I have read about until now have used lasers (last 10 years anyway and down converters, mirrors and detectors to create equivilent particle based two slit experiments which according to all the literature I have read until NS last year could not determine which path information without destroying the interference pattern no matter how complicated the experiment was setup and how many beam splitters and mirrors were used.

So why is this one different ?

Dear John,

If the power of the laser used in the experiment is known, then you know the total photon flux, and measuring I_max and I_min separately is not necessary: you can just measure I_min and get I_max as follows: I_max=2I_average - I_min

Dear Shahriar,

All I wanted to say is that the statement "if a photon is detected at 2', it must have come from pinhole 2" has no basis in the QM formalism. BEFORE the photon position is measured by a CCD, the photon is in a superposition state with equal amplitudes of being at 1' and 2', and it's meaningless to say that it "came" or "emanated" from a particular pinhole.

Dear quantum enforcer

" I am stating that we should be able to setup the experiment to look at wave behavior and then extract the particle behavior collapsing the wave function either."

That is exactly what this experiment has already accomplished. The way it does this is with a non-invasive probe of the dark fringes, showing that interference is definitely there and we can still collect the particle information. I think the main thing that we can say from the results of this experiment is there is no Voodoo or occult situations that are involved in quantum mechanics. No spooky action is causing the wave function to collapse! Just say no to complementarity!

I am happy to wave goodbye to complementarity personally and Prof Afshar in his last post to me states the same thing. I am just concerned that one two slit experiment amongst many carried out in the last twenty years has yielded such a result. Are we now going to revisit these experiments and see why they have not managed to also lay to rest complementarity.

best wishes

Dear Prof Afshar

Looking at the experiment again I believe that people are confused by the way things are explained by physicists in explaining the concepts of quantum physics. For instance if we are talking about particles then the wires should stop some of the particles reaching the detectors even in two slit mode but because they are also waves (or travel as waves) then interference also plays a part and we get full photon count detection at the detectors the same as before the wires were put in place. What this appears to mean is that although the mathematics of quantum physics is fine the interpretation into human language is not as we have no method of describing a phyical barrier (wires) not blocking particles when a second slit of light of shone over the existing slit as for some reason interference is obtained which cannot be explained by using the metaphor of particle, we have to introduce waves to explain the issue away.

It is like saying that a car travels through a tunnel which merges with another tunnel and another car. Not only do the cars merge and interfere with each other but this allows the merged cars to miss the barrier (wires) in place. Quite rediculous eh unless you accept the concept of waves for cars.

Surely it's about time physicists came up with another name for the concept of wave particle duality and stop using meatphors from classical physics ?

Dear Prof Afshar

I have been looking at the experiemnt over and over in an attempt to find issue with it and eventually it dawned on me that you need a conincidence counter to measure the respective rate of photon detection relative to each other when the wires are in place don't you ?

Dear A Neale

"it dawned on me that you need a conincidence counter to measure the respective rate of photon detection relative to each other when the wires are in place don't you ?"

Have you found the preprint? The link is below. If you will look closely at the preprint you will see that he only has one CCD. This is so he can compareA, B and C on page 33 of the preprint. and show the difference in the two with and without interference.

link to preprint

The experiment has D1 and D2 does it not. I thought that as it is a interference experiement that it photons from both detectors were important and not just one even if the diffraction pattern does disappear.

Dear A Neale,

In the experiment conducted at Rowan university we did the single-photon version, in which D1 and D2 demonstrated perfect anticoincidence as expected.

Regards.

Dear Prof Afshar

That settles it then for me.

Dear Prof Afshar

So are you saying that in a single photon Afshar experiment the following happens:

1. that the wavefunction of the photon does not collapse even though you know which slit the photon went ?

due to the fact that

2. That you revealed the wave nature of light in this particle based Afshar experiment.

kind regards

Dear mr Afshar, I am coming late in the discussion now but it seems that your experiment contains a fatal misinterpretation which was already pointed by several other visitors.
Indeed to see fringes you need several photons and not only one. The same is true to see the two images of the apertures giving us statistical information on the number of photons that we would observe directly just after the holes.

However with a single photon you can only done one of these two choices :
A) the photon will be used to created a a statistical distribution in the fringes plane
B) the photon will be detected in the image plane and will participate to find how many particles were in one or the other pinholes.
However one choie exclude the other (complementarity of information).
This is not only clear from the fact that a photon detection is destructive but can be justified similarly in any which path experiments using entanglement with one other system.

In you case you have no entanglement so the analysis is easier: with your wires you can not construct the interferogram without making assumptions on the shape of the distribution in front of the lens: you first see the fringes with several photons and after you suppose already that fringes are present when you detect other photons in the image plane with the wire in place: the reasonning is circular and trivially false.


AZ

Dear AZ,

"I am coming late in the discussion"

Yes, you are certainly late in this discussion! Please read my preprint to understand my arguments...

"However one choice excludes the other (complementarity of information). "

This is the Anton Zeilinger’s approach which is also ruled out by my experiment. See my posting on 12/31/04 @ 22:21.

"with your wires you can not construct the interferogram"

While it is true that the ENTIRE Interferogram cannot be constructed from the direct observations, it is crucial to understand that INTERFERENCE can indeed be proved. I do directly observe, with a very small margin of error, the presence of dark fringes (established by lack of blocking by the wires.) Then assuming QM formalism to be correct, I prove in section 3 of my paper that the only way such dark regions are possible is to appeal to interference. If you can disprove those arguments, I would agree with you.

"you first see the fringes with several photons and after you suppose already that fringes are present"

Wrong! If I had made such an erroneous assumption, then I would not have even used the wires!!! The initial direct observation of the interference pattern is carried out to measure the exact POSITIONS of the dark fringes, which are then used to place the wires precisely at the minima. IT IS NOT NECESSARY TO ESTABLISH PRESENCE OF THE BRIGHT FRINGES. COMPLEMENTARITY FORBIDS THAT PHOTONS LANDING ON THE TWO IMAGES COULD HAVE INTERFERED. THEY ALL ARRIVE WITHOUT BEING AFFECTED BY THE WIRES. THE ONLY ALLOWED PROCESS BY QM FOR SUCH AVOIDANCE OF THE WIRES IS INTERFERENCE.

"reasonning is circular and trivially false"

You should blame Bohr's Complementarity for such circularity in argument. I have only demonstrated this logical paradox by my experiment...

Regards.

Dear AZ,

"I am coming late in the discussion"

Yes, you are certainly late in this discussion! Please read my preprint to understand my arguments...

"However one choice excludes the other (complementarity of information). "

This is the Anton Zeilinger’s approach which is also ruled out by my experiment. See my posting on 12/31/04 @ 22:21.

"with your wires you can not construct the interferogram"

While it is true that the ENTIRE Interferogram cannot be constructed from the direct observations, it is crucial to understand that INTERFERENCE can indeed be proved. I do directly observe, with a very small margin of error, the presence of dark fringes (established by lack of blocking by the wires.) Then assuming QM formalism to be correct, I prove in section 3 of my paper that the only way such dark regions are possible is to appeal to interference. If you could disprove those arguments, then I would agree with you.

"you first see the fringes with several photons and after you suppose already that fringes are present"

Wrong! If I had made such an erroneous assumption, then I would not have even used the wires!!! The initial direct observation of the interference pattern is carried out in order to measure the exact POSITIONS of the dark fringes, which is then used to place the wires precisely at the minima. IT IS NOT NECESSARY TO ESTABLISH PRESENCE OF THE BRIGHT FRINGES. COMPLEMENTARITY FORBIDS THAT PHOTONS LANDING ON THE TWO IMAGES COULD HAVE INTERFERED. THEY ALL ARRIVE WITHOUT BEING AFFECTED BY THE WIRES. THE ONLY ALLOWED PROCESS BY QM FOR SUCH AVOIDANCE OF THE WIRES IS INTERFERENCE.

"the reasonning is circular and trivially false"

You should blame Bohr's Complementarity for such circularity in argument. I have only demonstrated its logical inconsistency by my experiment. As for triviality, it is a matter of personal perspective.

Regards.

dear mr. Afshar,
you said : ''Then assuming QM formalism to be correct, I prove in section 3 of my paper that the only way such dark regions are possible is to appeal to interference. If you can disprove those arguments, I would agree with you. ''
This is exactly what I claimed that you did when I told you ''you first see the fringes with several photons and after you suppose already that fringes are present'' and this is the problem . Indeed you supposed (see your preprint analyzed by me before my first message) that we have a fringes pattern with a visibility V= (I_max-I_min)/(I_max +I_min) this is clear from the direct experiment consisting into observing fringes with a detector but in the other case it is an theoretical assumption .

I summarize :
1) you observe fringes in the palne before the lens you could certainly do the same experiment when the wire are in place ( in order to check the consistency ).

2) You use the hypothesis that there is a wave then you suppose the validity of V= (I_max-I_min)/(I_max +I_min).

3) You see no change in the signal with or without wire in the image plane and then you deduce that necessarily I_min =0 and V=1.

But to do that you need to accept the formula for V i.e. that you accepted that fringes are here. You can tell me: OK can you find an other explanation? can you explained the shape of the distribution in the image plane withoust supposing wave optics? Of course I could not. But I dont need to do that and this is the conclusion of Bohr and Zeilinger: you need waves all the time to explain the unitary evolution and to calculate the distribution of probabilities but if you want to observe such thing without making any assumption you need differents photons.

I will give you an other example: omit the lens and observe fringes. You see a pattern with V=1 and from optic you know that this implies that the two holes emiited in phase the same number of photon and of course you could control that directly . Would you say that you break complementarity in that case ? I dont think so : as in the young double slit experiment described here you did two experiments with differents photon and then you never test the principle of Bohr. Such test requires the same photon for the two statistics.

A final remark in your experiment you have V=1 (if you measure directly the fringes ) but D=0 ( if you measure directly the image as you did) because the two spots in the image plane are indentical . If you consider ony one spot you can claim that D=1 and this following the duality relation mean V=0 !! however this V=0 is obtained experimentaly with half of the particles :you see V=1 because you consider ALL the particles then there is no contradiction at all . In other term in term of hidden variable you can not be sure that the photon detected in the fringes plane would go to the image 1' or 2' . This can only be analyzed by a particular model which unfortunately, I guess, will never be testable .

friendly,
AZ

A last thing , Einstein said you much always explain things in the simplest way possible.... but not more that that .


My explanatiion is that a photon follow a well defined path but that this path is nod defined by quantum mechanics in the present form . You can only speak about statistics and complementarity need only that the rest is metaphysical ( or more precisely meta experimental : this is not exactly the same ).


AZ

Dear AZ,

The same photons that end up in the images must have passed the wire grid region. They cannot possibly pass that region without having interfered, and MAGIC is not an acceptable physical process. They are then refocused by the lens and which way information is obtained for each photon.

"because the two spots in the image plane are indentical "

Wrong! They are not identical, since they are angularly and spatially non-overlapping, which makes them clearly distinguishable. Furthermore, an asymmetry can be introduced in their positions. Please see my posting of 12/31/04 @ 22:37.

"My explanatiion is that a photon follow a well defined path is nod defined by quantum mechanics in the present form "

That's absolutely false! A simple QED analysis of the double-slit experiment can demonstrate that (e.g. see Feynman Lectures on Physics!!!) In fact, as much was known at the time of Bohr-Einstein debate in 1927. As for your comment on the inadequacy of current formulation of QM: if you can present it in a better "form" please go ahead and enlighten us, otherwise I suggest that you correct your views in accordance with the currently accepted QM formalism.

Regards.

http://physicsweb.org/articles/news/8/2/9/1

Looks like Afshars experiment will take some time to become there norm if it proves to be accurate. Still cannot help thinking about all of the experiments that have not shown wave particle duality simultaneously. Decoherence appears to be the new thing in QM.

Dear mr. Afshar I explained you my point of view and you and in spite of what you say now it is still valid and even not really correctly criticized by you (you omit the essential ) . I want just comment some of your sentences:
you said:

1)''The same photons that end up in the images must have passed the wire grid region. They cannot possibly pass that region without having interfered, and MAGIC is not an acceptable physical process. They are then refocused by the lens and which way information is obtained for each photon.''
Reply :
I agree i am not a magician, but I agree only if you speak in the language of Einstein (realist) not in the one of Bohr (positivist). Consider again the classical double slit experiment without lens and wires: I see fringes but I have only two pinholes so my photon must come from one place . But from which place that is the question ? You can not solve that question experimentally and your experiment is not better . I t was was I was twelling to you by :'' Would you say that you break complementarity in that case ? I dont think so : as in the young double slit experiment described here you did two experiments with differents photon and then you never test the principle of Bohr. Such test requires the same photon for the two statistics.''

..... THE SAME PHOTON FOR THE TWO STATISTICS!!!!!

2) I said "because the two spots in the image plane are indentical "
and you said :
''Wrong! They are not identical, since they are angularly and spatially non-overlapping, which makes them clearly distinguishable. Furthermore, an asymmetry can be introduced in their positions.''

Reply:
By identical I mean symetric and just translated : it is the current defintion for example in the double slit experiment and in the image plane it is still valid since you neglect modification of the pattern by the wires ( sharp complementarity ).

3)I said "My explanatiion is that a photon follow a well defined path which is not defined by quantum mechanics in the present form "
and you said:

''That's absolutely false! A simple QED analysis of the double-slit experiment can demonstrate that (e.g. see Feynman Lectures on Physics!!!) In fact, as much was known at the time of Bohr-Einstein debate in 1927. As for your comment on the inadequacy of current formulation of QM: if you can present it in a better "form" please go ahead and enlighten us, otherwise I suggest that you correct your views in accordance with the currently accepted QM formalism.''

Reply : I am not here to enlight you with a new hidden variable model which can not be tested. It is well know since the time of Einstein Bohr and de Broglie that such models are not falsifiable.
For de Broglie (whihc is the uniqual self consistent example that i know) the particle follow a path but this path is complicated and very fragile: if you try to isolate a path you collapse the wave function and fringes are washed out. This should be the same for every model since we want to always reproduce QM. Feynman never pretended that the photon follow a path but just insisted ( as it was done by Bohr before ) that such concept is not observable without modification of the system : fringes OR ''paths''. Latter it was observed by Scully that what you described in a so called which path experiment is not necessary a path: the complementarity is NOT COMPLEMENTARITY BETWEEN PATH AND FRINGES BUT BETWEEN NUMBER OF PARTICLES IN EACH PINHOLES AND FRINGES.

do you see the differences? or not?



friendly AZ

Dear AZ

I have a couple of questions that will help to clarify your point of view:

You say: "as in the young double slit experiment described here you did two experiments with differents photon and then you never test the principle of Bohr."

Where or when was this experiment divided into two?

"Such test requires the same photon for the two statistics.''

Why do we need a principle that says anything that is destroyed by observation is no longer observable?

Is this what you think complementarity really says?

How did the photons make it around the wire?

Thank you in advance.

Dear Mr or Ms Quantum mirror ,
I think that your questions will not clarify my point of view ( all is clear for me concerning this experiment).
I will give a short answer to your questions.

you asked :
''Where or when was this experiment divided into two?'' Reply:
what is an experiment? if you consider two optical experiments grouped in one you have now just one experiment OK ? but here I speak about complementarity . Complementarity speak about the statistics obtained with particle . Normally if you observed fringes you need some particles and if you observe images you need other particles because the detection is a destructive process an because a single photon can not be absorbed twice. Now the question of bohr is the following : could you build up the two statistics using the same photons ? Clearly in the preceding example it is not the case. Einstein imagined to considered the recoil of the slit to record the missing information but unfortunatelly doing that create a new wave function (collapse + entanglement...) then you modify the result and no fringes . The result is general and the two statistic can not be builded with the same photons.

Do you think that it is different in the experiment of Afshar? NO AFSHAR ONLY OBSERVED IMAGES AND NEVER CONSTRUCTED FRINGES WITH THE SAME PHOTONS: HE JUST DEDUCED THEIR EXISTENCE FROM AN ASSUMPTION THAT FRINGE EXIST AND THAT THE VISIBILITY FORMULA IS CORRECT: OBSERVING THAT THE PINHOLES IMAGES ARE NOT MO)DIFIED NATURALLY GIVE HIM V=1 BUT THE REASONNING IS CIRCULAR AND NOT HONEST.

Conclusion :"Such test requires the same photon for the two statistics.''


friendly
AZ

Dear AZ

Hear is what Einstein had to say:

"Despite the expenditure of much effort, I have been unable to obtain a clear
understanding of Bohr’s principle of complementarity"

When a mind logical and well trained to work out problems in physics looks at a problem it asks:

What kind of force, reaction, law or mathematical relation is responsible for the problem?

I can find the answer to none of these for Complementarity and neither could Einstein.

I see no reason for Complementarity! Why have a principle that says something observed is destroyed therefore you can't observe it and still have it? It is a circular argument and I think it gave Bohr some attention.! The problem is drilled into physics students until it has become real only in their minds and yours!

Complementarity is invulnerable in your evaluation and the rules you set to remove it. It will be a part of physics forever without reason or function and can never be destroyed

dear quantum mirror
you said:
''Complementarity is invulnerable in your evaluation and the rules you set to remove it. It will be a part of physics forever without reason or function and can never be destroyed''


perhaps??? probably ??? certainly???


human think naively that he can not only understand all but observe all . In classical mechanics every elements of reality of a model are in principle testabel at the same time even if it is very difficult : example you want to see a bird which is very intelligent and is a singer but this bird is very timid too and he sing only during the night when no people can see him. question : how to see the bird singing? the way is to use for example infrared light that the bird can not detect but with molecules and photons this argument is wrong ......


this doesnt mean that the complete reality existing without us is not hre but only that we can not see it : the word could be deterministic but not determinable .


personally I accept the complementarity but not the pessimistic vision of Bohr : It is not because you can not see the moon when you close you eyes that the moon is not here.....
friendly
Az

Happy New Year for all!

The following questions relate to professor Afshar's experiment with both slits open.

1) Is it possible to calculate in detail the evolution of the wave function: plane wave before the slits -> superposition of circular waves after the slits and before the lens -> something in the lens region (what?) -> non-unitary colapse at one of the detectors?

2) Using 1) is it possible to calculate: the probability of a photon to have passed through a particular slit? the probability of a photon to be found at a particular detector at a later time?

3) Finally, is it possible to calculate, using 2), the conditional probability that a photon coming from slit 1 arrives at detector 2? Is this probability really zero if we calculate with the standard quantum recipes? May we say that we have perfectly determined which-way information even if this probability is not equal to zero?

Best wishes for all,

Student.

Dear Student,

1) Yes.
2) Yes. The lens acts as a positional phase shifter, i.e. it changes the phase of the incident parts of wavefucntion according to the thickness through which it passes.
3) Yes. The probability of a photon ending up in the "wrong" image is the same as in the case in which there are no wires, which is of the order of 10^-9.
You can do the calculations with QED analysis, using a large number of paths (at least 1000, and more for certain high fluctuation parts of the image.) You can also use a quantum mechanics simulation package, but they tend to require a supercomputer for large scale setups like that used in my experiment.

Regards.

Dr. Afshar - Simon Saunders –a philosophy/physica professor at Oxford - asked if and why the results of your experiment should be viewed as inconsistent with Everett models? My thought was that if non-locality is eliminated there is no longer a need for a multiverse approach. Is there a more fundamental reason that your experiment would disprove Everett?
Thanks, Paul Snyder

Dear professor Afshar,

Thank you for your answers. Is it possible for you to provide your basic biographic data? My friends here at the university are really curious. I must say that we are all really wishing that your paper is published and the results of the experiment accepted. The prevailing dogmatic stance of the Copenhagen guys turn us all sick: "you can do this, you can't do that, and it is not right to try to understand why things should be that way, it is naive to ask why". But we are not naive, and we want to try! Lets the theory and the experiment say what we can really know.

Cheers,

Student.

Dear Student

Here is a link with some biograpical material links. Some of the information on this page is dated as I don't think Prof. Asfhar has been at Rowan to update in a while.

http://users.rowan.edu/~afshar/

Looking again at the experiment it still appears to me that light arrives and leaves as particles but travels as waves. Quite fascinating what Prof Afshar has achieved here with his experimental setup.

Dear Paul Snyder

Prof. afshar must be having a very busy weekend.
I remembered the answer to this question before on this blog and found it for you:

Q: Several people have claimed that your experiment falsifies the many-worlds interpretation, but I falied to find any statement to that effect in your paper. Have you made this claim, or is it just others?

A: I claim that my experiment rules out Complementarity as a “Principle” that has no exceptions.
Generally, I am not very fond of "Interpretations", but from my limited exposure to MWI, it does not even qualify as a viable theory because it seems to violate conservation of linear momentum in interference experiments, as I have pointed out to David Deutsch in the past. One does not need my experiment to question the validity of MWI, but if others think my experiment rules it out, I have no quarrel with that!

I thought that interpretations of QM where required back when the role of the conscious observer was deemed to be necessary as when Schrodingers cat was unleashed on the world to provide a clue as to the absurdity of complementarity. Everyone knows that complementarity is absurd but could not provide evidence to disprove it until now that is.

QM still has it's issues including FTL (entanglement and tunneling) and decoherence amongst them but not any more the measurement problem and consciousness I believe.

Dear mr. afshar

You didn't treply to my critics so I will explain my problem again (perhaps I Was not clear ).
there is two points and I will only present you one now and I will giv you the second one later on

point of divergence 1) :

Suppose N photons crossing the interfererence plane before the lens (these N photons must be ideally inserted one after the others) . If n>>>1 I will detect N/2 photons at each image spots. The distinguishability K can be defined as K= |N_A-N_B|/(N_A+N_B) so K=0 if you consider the whole pattern. But if you watch only A then N'_A=N_A et N'_B=0 then K'=1 the relation
K^2+V^2=1 [1]
(for a pure state) implies then V'=0 et V=1. You compare V and K' which are constructed using a different number of particles (statistical ensemble differents) then you can not conclude to a violation of the duality relation [1]. In other terms you must use the correct formula V=1 and K=0 because the other choice not use the same number of particles since you have no way to distinguish a photon going to A or B lookiing them in the fringe plane.

AZ

point of divergence 2)

I suppose that you use the good definition V=1 K=0.
now we must define the principle of complementarity:

consider one photon used in an experimental set up to see the spots (K=0) or the fringes (V=1). The principle say that the same photon can not be used in the two experiments :

the photon will participate to a statistical pattern for K or for V and that we can not imagine an experiment which can give us the two number using the same photons (statistical accumulation).

Your experiment fails to disproof this principle since your photons are only seen in the pattern for K=0. The pattern for V=1 being obtained with different particles. You deduce that V=1 not form a direct observation but from an extrapolation based on the fact that you must have fringes using law of optics. but this law can only be justified experimentally using others photons: consequently the reasoning is circular.

AZ

point of divergence 3) (bonus)

what is a trajectory for a photon? if you claim that a photon come from one hole I can agree but if you claim that a photon coming from A must goes to A' i desagree on the basis that this is a metaexperimental assumption...... see bohm and [1] (this argument has been already used by others against your point of view ).

AZ

[1]" Surrealistic Bohm trajectories", Englert et al in Z. Naturforsch. Vol 47a , p 1175.

Dear AZ

This is the logical process that this experiment entails:

Set up with double pinholes and photosensitive surface. Turn on laser and mark destructive interference bands and establish K=0 and V=1, laser off. Remove photosensitive surface and install lens and CCD detectors at D1 and D2. Turn on laser with both holes open and record photon count and pattern at CCD's. Establish welcher weg information. close 1 pinhole and record count and pattern at CCD which corresponds to open pinhole. Laser off and install wire in dark fringes. Laser on and "oh no" we can see laser light hitting the wires and the CCD pattern is garbled. Laser off and open the pinhole that is closed. Laser on and "huh"? what has happened? No laser light on the wires and the CCD pattern has cleared up. Thus:

We must explain how the light has missed the wires. Interference is the only answer anyone can come up with, So:

Eq.(1)In any particular experimental arrangement,
(i) If V=1, then K=0.
(ii) If K=1, then V=0.

It is clear from CPC (i) that in any welcher weg experiment, obtaining full visibility for
the IP should lead to a complete loss of the WWI for the quanta.
Therefore, since no diffraction takes place, no reduction in K is possible. Thus it is
established that in the same experiment, sharp complementary wave and particle
behaviours can coexist so that V^2+K^2 =2 >1 violating Eq. (1) and the PC.

Hope this helps. If not you must wait for Prof. afshar to answer.

dear quantum mirror and dear mr afshar ,

Sorry but every thing claimed by you is wrong:

1) I never desagree with the fact that reasonning as you did with classical waveallow you to describe all without contradiction. But a photon is a discrete entity and you can not see him twice.

Complementarity is a statement about the number of information that you can extract from every single event ( single photon event here ) in order to build statistics associated with differents observables. if such observables doesnt not comute you can not say all [1]

you said in particular ''We must explain how the light has missed the wires. Interference is the only answer anyone can come up with'' this is not a scientifical answer: if you can not test what you say with the same photon your reasoning will be necessary circular (naturally with a classical wave i.e. with a large amount of photon or in a statitistical way every thing is self consistent but you dont test complementarity ). Did you really read Bohr? if not I doubt that you can really understand the principle of complementarity. But dont worry you are not the first one see for example the experiment of D. Home and G.S. Agarwal with a prism the errors is different but an error stays an error.

[1] Anton Zeilinger: http://www.quantum.univie.ac.at/zeilinger/foundations.pdf

with best regards
AZ

AZ

"this is not a scientifical answer"

This is not intended to be. If you can understand the paper the scientifical answers are there.

I was trying to get you to explain HOW the light missed the wires. You seem to avoid this at all costs!

"if you can not test what you say with the same photon your reasoning will be necessary circular (naturally with a classical wave i.e. with a large amount of photon or in a statitistical way every thing is self consistent but you dont test complementarity ). Did you really read Bohr?"

Once again your reasoning is circular. You are saying that because a photon is destroyed when we observe it, there is no information that can be extracted from it. The photons that are bringing the words off this page to your eyes are destroyed and yet the words remain on the page and in your memory with a lot of information included. All the visual information you have accumulated in your life has been brought to you by photons.

What is your explanation for how the light made the bizarre dance around the wire???

Dear Quantum mirror I guess that I understand the paper of mr. Afshar better than afshar him self the scientifical answer is not here anymore.

my reasoning is not ciruclar you confuse the different level of definition and you feel mysteriously chocked by the result of mr.Afshar after that you wonder why ?


your conclusion is contained in your reply ''This is not entended to be [a scientifical answer] '' but here it is a scientifical discussion so you argument is a non sense.


you asked:
What is your explanation for how the light made the bizarre dance around the wire???

the good question should be here
What is your explanation for how the light made the bizarre dance around the wire EXPERIMENTALLY TESTABLE ???

There is no way to test then no way to speak about that fuzzy path of a virtual trajectory .

To use the words of Pauli if you can not speak about something shut up.

AZ said: "To use the words of Pauli if you cannot speak about something shut up."

Men, this sentence is so agressive that now I am sure that the experiment touched something deep within those traditionalists as Mr. AZ. They are shocked. The complementarity magic vaporized.

This experiment claims to establish in the same setup: 1) the which-way information for each single photon; and 2) that there is interfence, otherwise the photons could not pass the wires without being absorbed.

It is as simple as that. If someone claims that there is an error in the experiment or in its interpretation he or she must present a convincing argument that 1) or 2) or both are false.

If he or she can't present that argument the only thing to do is to shut up.

Student.

AZ

Again you did not answer any question only made some statements. CAN YOU NOT ANSWER QUESTIONS? I said this is not meant to be scientifical because YOU DO NOT SEEM TO BE ABLE TO UNDERSTAND scientific arguments. The math and reasoning are clear in the paper!!! I am so sorry for the loss of your dear friend complementarity. You and it are so close to fossilization you need to be in a museum.

What is your argument?" if you can not test what you say with the same photon your reasoning will be necessary circular".

How convenient for you and Bohr to have this moronic untestable test! That is my definition of circular!!!!

If you want to tell me to shut up don't beat around the bush you metaphysical imbecile!

Dear student you said

''this sentence is so agressive that now I am sure that the experiment touched something deep within those traditionalists''

you are not completely right what is touched here is the scientific methodology . Mr quantum is not a good mirror since he can not think seriously without beeing agressive. My sentence was not an invention however the author is not Pauli as claimed by me before but the philosopher Wittgenstein (but pauli or Bohr or others perhaps used it too).

Concerning the last words of quantum mirror I will just ask where is the imbecile : it is the one which proposes an interesting experiment as mr. Afshar (even badly interpreted) or the imbecile who follows the imbecile without thinking because he needs naively to believe that science is made with revolutions every day ? Personnaly I know quantum mechanics and I know that it is dangerous to speak seriously about it after drinking too much of coffee or other things as mr QM did visibly.


My conclusion for student : if you want to study physics only read the authors never the text books but be prudent with the authors it is very difficult for the beginner to distinguish a genious from an imbecile.

best reguards
Az

I want to conclude with mr QM with the following rule defined by Afshar


5)Scientific objectivity is the direct opposite of irrational emotional ranting. In the interest of scientific methodology, I reserve the right to remove any inappropriate posting.

It would be good if mr Qm mirror could used other terms in his discussion such as imbecile for example

AZ said: "My conclusion for student : if you want to study physics only read the authors never the textbooks but be prudent with the authors it is very difficult for the beginner to distinguish a genious from an imbecile.".

Dear AZ, you are supposing many wrong things here. I believe that the experiment made by Afshar is indeed showing which-way information and interference effects in the same setup. But, with that said, I don't think that this result makes him a genius.

By the way, does AZ = Anton Zeilinger?

Regards,

Student.

Dear AZ (AKA Tatiana Karmanova, Aurelien Drezet!),

I see you have made so many erroneous remarks in my absence that it is quite pointless to discuss them. I too agree with Pauli, and I highly doubt you have the necessary qualifications to make even a "wrong" comment. And please no more underhanded and rude gestures...

I have one simple question for you (which you have constantly avoided answering): Why is there no light incident on the wires?

Regards.

dear mr. afshar
to be nice with you i reply to your question.
you asked
''Why is there no light incident on the wires?''

answer: because there is fringes naturally as it can be seen by scanning the interference plane.
I never doubt of that point . if you put instead of wires counting detector you will see indeed a very small number of particles.

in the same vain if you consider the young double slit experiment you can deduce that you have two pinhole open from the fact that fringes are here. where is complementarity in danger here?

please define complementarity and you will see your mistake.
The problem is when you detect photons in the images plane one after the others at X (X ideally two valued ) and try to calculate how many particles was at every position x in front of the lens. you can not do that without assuming that fringes are here. in other term you can not define a joint probability P(x,X) experimentally observable.

complementarity is a quantitative statement concerning probabilities . if you can ot define a joint probability P(x,X) then you can not judge Bohr.

What you do is just classical optics no quntum optics : from the statistical distribution in the image plane you deduce with few assumption the distribuion in front of the lens unfortunatelly no P(x,X) here

with best regards
AZ

Dear AZ,

Finally (!) in your response to my question "Why is there no light incident on the wires?" you have admitted interference:

"because there is fringes naturally"

Now, consider the fact that the same photons that interfered at the wires, go through the lens and produce images which give us the which way information. THIS IS A VIOLATION OF COMPLEMENTARITY!

By-the-way, your earlier argument about K=0 (posting 01/10/05 @ 10:58)is simply wrong, because in the analysis where K is defined as K= |N_A-N_B|/(N_A+N_B) sadly, you have abused the definition of K due to your lack of knowledge in the subject (probably because a shorthand version of the equation is used in the literature, which assumes familiarity of the reader with the details of the formalism). The correct equation is K(x,y)= |N_1(x,y)-N_2(x,y)|/[N_1(x,y)+N_2(x,y)], i.e. all parameters are functions of (x, y) the coordinates of the point where the detector is placed in the image plane. Since the two images are well-resolved, they do not overlap in the image plane, and thus at two separate points (x1, y1) and (x2, y2) corresponding to the peak of the airy disk of each image, they have equal flux. While it is true that N_1(x1, y1) = N_2 (x2, y2), in order to calculate K(x1, y1) you must use values for that particular coordinate. Therefore, since N_2 (x1, y1)=10^-9=0, K(x1, y1)=1.

And NO, what I did is ABSOLUTELY quantum optics! You may wish to see page S290 in http://www.physik.fuberlin.de/~simons/Publikationen/RevModPhys99.pdf where Zeilinger uses what he calls the Heisenberg lens in to get which-way information in the imaging plane in exactly the same sense in which I have used a lens in my experiment. This is also discussed more explicitly in a recently (2004) published book titled "Science and Ultimate Reality" (pp. 204-209).

Regards.

Prof. Afshar,

You have written many times in this blog that the which-slit determination by the converging lens in your experiment is based on exactly the same mechanism used in the Heisenberg microscope. Please, this is not true: in Heisenberg's microscope there is only one scattering event and not two distinct "alternatives" (open slits) as in your experiment!

Zeca Pagodinho.
Prof. of Physics
Brahma Institute.

Dear Prof. Pagodinho,

It is certainly true that the lens produces which-way information in the same sense the Heisenberg's microscope does. It does not matter how many secondary sources are present, as long as the lens can resolve them we have which-way information. Please take a look at the ref.s in the above post. In fact Zeilinger calls it the Heisenberg lens and uses it in a double-slit experiment! John Wheeler has also used the lens in a similar setup, and no serious physicist has disputed this fact...

Regards.

Dear mr. Afshar the discussion becomes more interesting

I comment to you different statements:

1]
''Finally (!) in your response to my question "Why is there no light incident on the wires?" you have admitted interference:

"because there is fringes naturally"

Now, consider the fact that the same photons that interfered at the wires, go through the lens and produce images which give us the which way information. THIS IS A VIOLATION OF COMPLEMENTARITY!
''

reply: first I only admitted that you can see fringes if you observe them directly (a fact which is evident) with your wires you have not such information and they are useless to test complementarity . Now you say ''consider the fact that the same photons that interfered at the wires, go through the lens and produce images'' ?? but mr afshar if this photon goes to the image plane it is the proof that I have not see him in front of the lens since in other case it will be absorbed .
I didn't claimed that the photon was not in the interference plane and that he can not participate to a interferogramme; I claimed that if you detect the photon in the image plane at x you dont know from which point X of the interference plane he comes so that you can not define P(x,X) where x is ideally two valued: x= +/- R (with 2R= distance between the 2 spots). this probability would be essential to rebuild fringes : your interferogram is deduced from information coming for from others photons and the reasoning is then circular as I continue to claim.

2] you claimed that i dont know my subject ? I noted the distinguishability
K= |N_A-N_B|/(N_A+N_B)
i.e.
K= |N_A'-N_B'|/(N_A'+N_B')
because N_A =N_A' and N_B=N_B'. I reasoned in the ideal approximation to simplify the discussion where the two spots are sufficiently well resolved to neglect overlap (by the way you did the same in your paper !! ) if the overlap is so small thay you claimed my approximation more than legitimitate .
Now there is your formula K(x1, y1)=1.:
which is my formula for K' =1 . you should realize that this formula suppose that you ues only half of the total probality space i.e. half of the number of photon touching the interference plane.
you have V'=1 with such definition but this V' is not associated to an experiment in your set up. you should introduce entanglement to see that.

3] Concerning the paper of Anton Zeilinger I would like to precise that his student at that time used entanglemt to realize a which path experiment . in this case the joint probability missing in your work is clearly defined.


Az

Dear professor student :
So every one used a pseudo in this blog? ok

I agree with mr afshar (this is very rare !!!!) entanglement atom-photon create a distinguishability and the Heisenberg microscope is done to see that .

you claimed before ''I believe that the experiment made by Afshar is indeed showing which-way information and interference effects in the same setup. '' what is a set up ? a set up for an amount of photons or the sum of two set up to break complementarity with one photon . the last one doesnt exist sorry!!!

AZ

Dear AZ,

I hope we are not talking across each other.

Do we, or don't we have which-way information for each photon in my experiment? (Remember there is only one photon in the system at any time between detections).

Regards.

P.S. Changing pseudonyms in the middle of a debate is not an ethical conduct worthy of a genuine scientist. It is OK if you change your mind, just make your point, and move on!

Dear mr afshar

Your definition of K(x,y)= |N_1(x,y)-N_2(x,y)|/[N_1(x,y)+N_2(x,y)]
is associated to a visibility V(x,y)= 2sqrt[N_1(x,y)*N_2(x,y)]/[N_1(x,y)+N_2(x,y)]. This visibility is not associated with your experiment which use my definition
V= 2sqrt[N_1*N_2]/[N_1+N_2]
where N_1 is the integral of N_1(x,y) this value can be measured by closing pinhole 2 (without wires of course ). your definition is mathematically nice but its physical meaning is no so trivial . at least at the center of the pinhole image K=1 and V=0 because there is no overlap in your case. In this case your defintion is associted with the experiment with one pinhole but in the general case it has to be defined which experiment can measure V (if it is possible) or if this is not just a mathematical definition.

AZ

dear mr.Afshar

reply to : ''Do we, or don't we have which-way information for each photon in my experiment? (Remember there is only one photon in the system at any time between detections).''

Answer :
for a photon alone nobody knows it . the photon could come from the wrong pinhole . However if you wait sufficiently and collect a statistical diagram then the number of impact in the image A' will be a direct measure of the number of photon crossing A . This is true even if these photons are not necessary the same because every one can goes in the wrong image (try to prove me the opposite ).

whatever the dynamic of the photon (hidden by definition) complementarity is a statistical statement:

you collect one after the other photons in the image plane and you observe the two symetric images imposing K=0 (no distinguishability) because N_A=N_B. The which way used in the definition of complementarity is obtained when N_B =0 or when you introduce an other degree of freedom in order to have entanglement with two orhtogonal states |left> and |right> of an other system .


if you choose to consider only the N'_A=N_A photon in A' (N'_B=0 )you have not the right to use the number N_A +N_B = 2N_A inthe interference plane .


AZ

Dear AZ,

Please answer with a simple yes or no:

1)Does a lens provide which-way information at the image plane without the wires present? Forget visibility for now.

You said: "for a photon alone nobody knows it. the photon could come from the wrong pinhole"

2) What is the magnitude of the probablity of a single photon landing in the wrong image? Is it 50%?

"you collect one after the other photons in the image plane and you observe the two symetric images imposing K=0 (no distinguishability) because N_A=N_B."

3) This is wrong! The photons are distinguishable precisely because they land in two spatially separated regions.

Regards

Prof. Afshar,

I'm a high school physics teacher. My question is:

Is there any experimental way to support the assertion that with both slits open, and without the destruction of the interference pattern, there are no photons coming from 1 detected at 2?

I see that you can argue from the quantum wave functions, sum the amplitudes for a huge number of Feynman paths, or some sort of semi classical reasoning involving momentum conservation, ray optics of the converging lens, etc.

But is there any known way to verify the assertion experimentally?

Best Regards,

Nu Bor.

Dear Mr. Nu Bor, (if it is a real name!)

YES! There is an experimental methods to verify that there is a one-to-one relation between the images and the pinholes without closing one of them:

Slowly move one of the pinholes away from the optical axis of the lens, and simultaneously reposition the wires in a smooth manner. One would observe that 100% of one of the images (the one corresponding to the displaced pinhole) co-moves away from the optical axis of the lens. There is no way to explain this phenomenon without attributing it to the fact that 100% of the wavefunction ending up in that image originates in the corresponding pinhole.

Regards.

Dear Mr. Afshar,

Thank you for your answer. I understand your reasoning.

Maybe you are not interested in the de Broglie-Bohm theory, but let me point out that an adept of that theory would say that there are bohmian paths going from 1 to 2 and that when you rearrange the setup moving one of the pinholes there is a "co-redetermination" of those paths by the new quantum potential, and so there are new bohmian paths still going from 1 to 2 as before.

Thank you again,

Nu Bor.

Dear Nu Bor,

In the next set of experiments we will be testing some of the alternative theories such as Bohm's.

Regards.

dear mr afshar
I am not a cpmputer and binary answer are difficult in physics

however
question 1) Does a lens provide which-way information at the image plane without the wires present? Forget visibility for now.
answer: yes but you consider only half of the photons present in front of the lens (probability =0.5 neglecting losses) and the visibility V=1 is associated with the whole ensemble (probability =1 neglecting losses).


question 2) What is the magnitude of the probablity of a single photon landing in the wrong image? Is it 50%?
answer nobody knows it . in the bohm dynamic the probability is 100% but other model are certainly possible.

question or remark 3):
"you collect one after the other photons in the image plane and you observe the two symetric images imposing K=0 (no distinguishability) because N_A=N_B."

you said : This is wrong! The photons are distinguishable precisely because they land in two spatially separated regions.


answer: see question 1 K=0 for the whole ensemble corresponding to V=1 and K=1 for the half ensemble with V=0 . in this last case the V=0 value can be obtained closing one pinhole.


it is not completely binary but your questions were not binary

I have a question for you : what is your definition of complementarity?


Regards

mr afshar you said

''Dear Mr. Nu Bor, (if it is a real name!)

YES! There is an experimental methods to verify that there is a one-to-one relation between the images and the pinholes without closing one of them:

Slowly move one of the pinholes away from the optical axis of the lens, and simultaneously reposition the wires in a smooth manner. One would observe that 100% of one of the images (the one corresponding to the displaced pinhole) co-moves away from the optical axis of the lens. There is no way to explain this phenomenon without attributing it to the fact that 100% of the wavefunction ending up in that image originates in the corresponding pinhole.''


Wrong ! in bohm dynami if you change th allignement of one the element the empty wave (quantum potential) modify the result. for example if you move one pinhole apart for the rest of the set up you find again the one pinhole case and the trajectory are obviousyl different: they connect A and B' (B and A')before that you move the pinhole and A to A' after.....

AZ

Dear Shahriar,

"Slowly move one of the pinholes away from the optical axis of the lens, and simultaneously reposition the wires in a smooth manner. One would observe that 100% of one of the images (the one corresponding to the displaced pinhole) co-moves away from the optical axis of the lens. There is no way to explain this phenomenon without attributing it to the fact that 100% of the wavefunction ending up in that image originates in the corresponding pinhole."

Indeed this demonstrates that the image at 2' is affected by the position of the pinhole 2. However, if you move the pinhole 1 (this time WITHOUT moving the wires) you will also see that the image at 2' is affected (the photon count will be reduced). It's hard to see how you conclude from this that all photons detected at 2' "came" from pinhole 2.

Dear AZ and Nu Bor,

At this point in time, like the majority of other physicists I do not believe Bohm's theory is correct (for a large number of reasons), therefore I will refrain from using it as a model to explain what happens in my experiment. As you know, I have talked about this at length previously. I can only use the generally ACCEPTED quantum formalism in my discussions of the experiment.

For a definition of Complementarity in the context of welcher weg experiments take a look at my preprint.

Regards.

Dear Alex,

You must also adjust the wires along with the movement of either pinhole to maintain the dynamics of the experiment smoothly, i.e. keep the total detected flux (which is the main observable) unchanged.

Regards.

''For a definition of Complementarity in the context of welcher weg experiments take a look at my preprint.''

I have you prepreprint but the definition is not complete you wrote


if K=1 V=0 and if K=0 V=1
and more generally K^2 +V^2

this is the dualtiy relation and the meaning is clearly defined when you considered 1) classical field or 2) statistical amount of particle
for classical field the two quntitiy can be measured in the same experiment there is no problem because every is continuous and there is no limitation in the precision.

however the principle of complementarity speak about the exclusivity of complementary measurements for particles whihc are localized events. This means as you know that if you detect a photon one time you must choose in which statistic you want to see him : in the one for fringes (V is then defined ) or in the one for spots (K is defined ) . it is with this two experiment that you can verify the duality relation.
in your experiment you have two experiment and you measure K=0 or K=1 (depending if you just concentrate on two or 1 pinhole). but you measure only V=1. Then you can verify the relation 0+1 =1. Naturally you nedd two experiments to do that and when you introduce the wire you dont plot the fringes. your argumentation is really curious ???

Az

PS : if you dont like Bohm and hidden varibles dont speak about trajectories which is an hidden concept in qwuntum mechanic it is in every text book.

Dear Shahriar,

If one wants to study the effect of a parameter, one should change just this one parameter without changing anything else in the experiment. If you move both the pinhole and the wires you're studying the combined effect which cannot be ascribed to the position of the pinhole alone.

At any rate, your argument basically is that the photons detected at 2' "carry information" about pinhole 2, from which you deduce that they "emanated" from pinhole 2. But the photons detected at 2' "carry information" about pinhole 1 as well! (because if you close pinhole 1, or change its size or shape or position, the photon count at 2' will change).

Sharp images of the pinholes by no means indicate particle-like behavior - wouldn't you agree that your results are in agreement with classical optics which only deals with waves?

Dear AZ,

Definition of Complementarity outlined by Bohr himself is mentioned in the last paragraph on page 2 of the preprint: "we are presented with a choice of either tracing the path of a particle or observing interference effects". [Ref.1 in the preprint]. So, according to Bohr which-way information and interference "effects" are not allowed to exist in the same experiment, plain and simple!

You said: "if you dont like Bohm and hidden varibles dont speak about trajectories which is an hidden concept in qwuntum mechanic it is in every text book."

This is utter nonsense, which clearly puts your earlier erroneous remarks in the proper context! The trajectory is NOT a “hidden concept” as that used in Bohm’s theory. If the concept of a trajectory was “exclusively” a Bohmian idea, then Bohr would not have talked about it in his publications as sited above, (See also Heisenberg's "The Physical Principles of the Quantum Theory", p. 21, 65, and his discussions on Compton scattering). It is not a matter of my liking or disliking Bohm's ideas, but as you may know, hidden variable theories are at best a minority view among physicists, and therefore I cannot use it in my arguments until it becomes the predominant theory. NAME ONE TEXTBOOK that says the trajectory is a "hidden variable" concept...

To see how patently your argument about the trajectory is wrong, just take a look at any high-energy particle physics data output in which gamma rays are traced back on a definite trajectory from particle(s) annihilation to particle(s) creation. Particle physicists don't use Bohm's theory, they use the standard relativistic QM, and they happily talk about a trajectory for a gamma ray photon, without talking about "hidden" anything, just using plain old conservation laws.

Regards.

Dr Prof Afshar

Surely it must be possible to resolve this argument with your detractors here ? When is peer review completed ? Surely then this experiment will then reside on a much stronger foundation and you will no longer have to answer silly posts on this forum.

Dear quantum enforcer,

In my personal experience, I have found that it is impossible to change a mind that's already made up, and sadly, human nature guarantees that. The peer review is out of my hands and their "process" still continues, as unprecedented as it may seem it's already been about 6 months. I highly doubt that even a peer-reviewed publication would put the controversy to rest, and that is why more experiments are essential. Only history can judge the current drama objectively enough, as it has done so in the past. To that end, this Blog can stand as a good witness in the court of time, surely to the embarrassment of some. History has a way of repeating itself!

Regards.

Dear quantum enforcer,

There's no disagreement regarding experimentally verifiable things - everybody agrees that Afshar's experiment yielded expected results. The discussion is about "interpretations", and I doubt it can be put to rest by peer review. It would be indeed interesting to see the reviewers' comments - perhaps Prof. Afshar could post them here if the paper has already gone through the first round of reviews.

Dear Alex,

The paper has already gone through the first round, in which one of the referees recommends publication (and interestingly believes that the textbooks would have to be quickly corrected to include my results) and the other raises some trivial objections (like the ones covered in Opinion Letters in New Sciensitst after the publication of the initial article, which I subsequently answered.) That said, I do not think that it is appropriate to post the referees' comments here before a final decision is made, as it might be seen as public interference in the peer-review process. However, if this situation "drags along" a few more months, I may reconsider my decision regarding the public disclosure of the reviews.

Regards.

NAME ONE TEXTBOOK that says the trajectory is a "hidden variable" concept...

Landau, von Neumann for example but the book of Bohr and Heisenberg are good too even if this is less explicit


The example of the path in a particle chamber was used by Heisemberg before that he found the heisenberg principle and that Bohr found complementarity after that the situation changed : for Bohr as for Heisenberg the concept of trajectory is useful (particle chamber, single slit experiment ) in certain situation and in other not because not logical (double slit).

More precisely Heisenberg used in his books ( as the one that you consider ) the example of a double slit experiment to show the apparent stupidity of this concept here : if a particle choose a path how it can be influenced by the presence of a hole in which it never enter ?? Bohr used the same sentence when he says: ''since it is only the circumstance that we are presented with a choice of either tracing the path of a particle or observing interference effects, which allows us to escape from the paradoxical necessity of concluding that the behaviour of an electron or a photon should depend on the presence of a slit in the diaphragm through which it could be proved not to pass.''


however this is not consistent because de Broglie-Bohm dynamic exists mathematically then the path can be defined even in the double slit because of the quantum potential.

the meaning of trajectory is then completely different for Bohm and Bohr .
for Bohm it is a real property
for Bohr just a tool usefull based on macroscopical analogies.
unfortunately the postion of Bohr is as much arbirtrary than the one of Bohm.
I eliminate all this metaphysical elements of my definition of complementarity in order to consider only the essential .
We have to kinds of statistic that s it and we dont need to consider the trajectory but just the experimental clicks . If a photon click in the image plane in orderto participte to one of the two spots he can not clicks in the the interference plane to participate to fringes. I dont care about the real path of the photon to speak about complementarity (but i dont doubt that this path exist)


with best regards

Aurelien Drezet

dear quantum enforcer
you said: ''you will no longer have to answer silly posts on this forum.''

You are not objectif . there is certainly good and bad critics cocnernig the work of afshar but to be an aficionado dont help science. I critic and i progress if you dont critic no science at all ...

feynman said that science begin when you stop to believe in your master . I think he is right but it is even worst if the master had different students because then a student can doubt about the claim of another one.


AZ or Drezet or what you want

Dear AZ, (AKA Aurelien Drezet), (AKA Tatiana Karmanova)...

I am glad that you finally admitted to your apparent identity crisis in the last post. Interestingly your different IDs have diagonally opposite views, as anyone who can read the previous postings by you can clearly see. Disappointedly, I do not think that you are either sincere or objective. As a final remark on your post, there is not a single mention in Landau's book that says assigning a trajectory to a particle (when its particle-like properties are demonstrated) is to be considered a hidden variable property. It is quite telling that you do not provide a page for such an assertion. FYI, Heisenberg's book was originally published in 1949, well after Bohr's introduction of Principle of Complementarity in 1928 (ibid pp.62-65, and the original ref. to Bohr’s 1928 Nature paper on Complementarity.)

Dear Asfhar,

I think that your experiment does even more than violating Bohr's Complementarity Principle.

There is another way to look at your apparatus: when you have 100% percent of the flux at the detectors with both slits open you can say that you have measured the position of the wires without changing their momenta.

If you adjust the geometry of the apparatus in order to have just one interference minimum at the wires region you will have a sort of "fringe microscope" which in principle can determine the position of a particle without disturbing its momentum.

There are many details to be checked, and the whole idea needs elaboration, but I believe that the essential point has been revealed: it is possible to use this non-disturbing measurement technique to violate Heisenberg's Uncertainty Principle.

Best Regards,

P. Marques

Sao Paulo - SP - Brazil

AZ aka Complementarity Priest

"I know quantum mechanics and I know that it is dangerous to speak seriously about it after drinking too much of coffee or other things"

May we pray quietly after a month of fasting?

If you will get off your knees and unclasp your hands you will see that physics is not exactly as you BELIEVE it to be. It is the way that experiments tell us through physical interpretation. Your bully pulpit will not work here. I think you have expressed your views in every possible way under many names and no one is buying your religion. Go find you a flock elsewhere preacher!

Dear P. Marques,

Yes, if a particle is in one of the interference minima it will not interact with light. But if the particle has a definite momentum, then its wavefunction is a plane wave, and it will interact with light. In fact, experiments of this kind have been done, see e.g. Oberthaler et al., "Dynamical diffraction of atomic matter waves by crystals of light", Phys. Rev. A., 60, 456 (1999).

Dear Alex,

Suppose that you prepare the particle with very small momentum. In this case the wave-function says that we have little knowledge about the particle's position. But this wave-function does not forbid that when you turn the lasers on the particle will be exactly at one of the interference minima, and so you will see no flux reduction at the detectors. If this happens, what can we say about the particle's momentum after this "non-disturbing measurement"? Should we collapse the wave-function as usual to one of the interference minima, so that we will have no knowledge about the particle's momentum? Does this standard collapse recipe applies here? If so, could you explain the physical mechanism -- not magic, please -- which changes the particle's momentum?

Best Regards,

P. Marques.

Dr. Afshar - sorry to bother you but I wanted to reply to Prof. Saunders this weekend if possible in regard to why the results of your experiment should be viewed as inconsistent with Everett models? Is there a fundamental reason that your results are incompatible with Everett?
Thanks, Paul Snyder

Dear Paul Snyder

I remembered the answer to this question before on this blog and found it for you:

Q: Several people have claimed that your experiment falsifies the many-worlds interpretation, but I falied to find any statement to that effect in your paper. Have you made this claim, or is it just others?

A: I claim that my experiment rules out Complementarity as a “Principle” that has no exceptions.
Generally, I am not very fond of "Interpretations", but from my limited exposure to MWI, it does not even qualify as a viable theory because it seems to violate conservation of linear momentum in interference experiments, as I have pointed out to David Deutsch in the past. One does not need my experiment to question the validity of MWI, but if others think my experiment rules it out, I have no quarrel with that!

Dear Everyone

What concerns me here is that it appears that the same argument is being used over and over in an attempt to discredit the experiment which seems futile to me as only peer review by other quantum physicists will judge Prof Afshars experiment valid of not. If you were arguing only about interpretations of QM then fine but that is not what I appear to be reading.

I would also imagine that as science requires a process of verification that other physicists would attempt to recreate Prof Afshars experimental setup and results in a manner consistent with the Scientific method. Surely other physicists who have been trying for decades to reveal wave particle duality simultaneously in a two slit experiment would be speaking with Prof Afshar and attempting to recreate and understand his experiement.

Thanks again Prof Afshar for your reply to me. As a interested lay person in QM who has been following it since around 1990 and looking for the correct interpretation to come to light I believe that you have lifted a lot of the fog on this one.

Thanks for the update on the peer review status.

Dear Paul Snyder

I was wondering if you had seen my post to you above. I wanted to make it clear that this is Prof. afshar answering this question.

If this has answered your question please let us know.

Thanks - I had overlooked the reply. Paul

Dear P. Marques,

Let's say we have a screen with a pinhole and we're measuring particles hitting the screen (e.g. we can detect generated heat, or cover the screen with a CCD array etc). If the particle is NOT detected, this means that it passed through the pinhole and thus we measured its position. Following your line of thought, this might seem to be a nondestructive measurement, since it appears that the particle passing through the pinhole does not interact with the measurement device. However, if a particle initially had a definite momentum, you'll find that after it passes the pinhole it will no longer have a definite momentum (a well-known phenomenon called diffraction - the pinhole should be of course small enough, e.g. less than a micron for visible range photons). The point is that if the particle is in a state with a definite momentum (i.e. a "plane wave" state), it's not only that we have little knowledge of it's position, it simply does not have a position. Therefore it always interacts with the whole screen. As a result of this interaction, it either gets absorbed by the screen, or passes through the pinhole (now it will have a definite position, but no definite momentum).

"If the particle is NOT detected, this means that it passed through the pinhole and thus we measured its position. Following your line of thought, this might seem to be a nondestructive measurement, since it appears that the particle passing through the pinhole does not interact with the measurement device."

Wait a minute, Alex. You are not following my line of thought. Your critic is like Unruh's objection on Afshar's experiment: you take a different experiment and see a problem in the original one.

The problem with your example is obvious: when a particle passes through a pinhole it can exchange momentum with the screen -- to check this you could measure the screen recoil, for instance -- so the "measurement" you describe is not a "non-disturbing" one.

Read the well-known papers related to the Einstein-Bohr dialogue, and their discussion about the double-slit experiment.

About the rest of your comment, you are taking for granted that the wave-function has a strict ontological meaning. We see these words in many of the quantum mechanics textbooks, but when we go beyond this textbook level the question is still open.

Dear All,

Here are my final words about my post above on the possibility of "non-disturbing measurements".

As I said before, there are many issues which need clarification: a new design with just one minimum interference spot; the dependence of "resolution" on the laser parameters; the statistical character of this new kind of "measurement"; the epistemological / ontological aspects of the wave-function in this situation; concerns about realism; an appropriate extension of the quantum rules to account for this new type of "measurement"; etc.

In the original Heisenberg's microscope, if you try to improve the localization of the particle using light of a shorter wavelength, you disturb its momentum more and more. Here we have exactly the opposite situation: the more a particle is at the position of the interference minimum, the less we disturb its momentum.

These considerations are of course semi-classical and heuristic, but I think they deserve a detailed investigation.

Finally, we are posting in Afshar's blog, a public forum dedicated to discuss his experiment. My original post was just intended to point out one aspect that I think is important to understand a possible implication of his experiment: it suggests a careful analysis of a new class of "non-disturbing measurements" which can have a non-trivial content. This is not the right place to detail these issues, and I will not do it here.

Best Regards and good luck for all,

P. Marques.

"One does not need my experiment to question the validity of MWI, but if others think my experiment rules it out, I have no quarrel with that!"

I'm sorry, but could someone please explain how this experiment rules out the MWI. The above quote does not make the claim; it only refuses to quarrel with those who do. Thanks

Dear Michael Bacon,

Here’s how Prof. Cramer explains it:

"We are led by the Copenhagen Interpretation to expect that the positions of the interference minima should have no particular significance, and that the wires should intercept 6% of the light they do for uniform illumination. Similarly, the usual form of the Many Worlds Interpretation of quantum mechanics leads us to expect 6% interception and no interference, since a photon detected at image #1 is in one universe while the same photon detected at image #2 is in another universe, and since the two "worlds" are distinguished by different physical outcomes, they should not interfere."
Source: http://www.analogsf.com/0410/altview2.shtml

Regards.

FWIW, here is what an unabashed many-worlder has to say:

"There is always an understandable temptation for proponents of any particular quantum interpretation to see stronger evidence for it than a particular experiment provides. For example, shortly before this book went to press, an ingenious experiment by Shahriar Afshar was claimed to have "disproved" both the Copenhagen and the many-worlds interpretations. In fact, it is exactly consistent with the modern many-worlds view, specifically the idea that interference effects from "other-wordly" photons continue up to the point where a measurement is made. Afshar's experiment demonstrates wavelike behavior followed by particle-like detection, just like our bomb detectors."
Ref.: Schrodinger's Rabbits by Colin Bruce, p.230

Dear Prof Afshar,

I see it has been very busy here. I was interested to hear about your referees' comments. It sounds very much like you will be able to get this published, you just need to keep pushing them. I still disagree with you though, and I would like to post my most clarified thoughts.

The issue I want to address is whether, in your experiment without the wires, the quantum formalism demands that photons measured at detector 1 always come from pinhole 1, and photons measured at detector 2 always come from pinhole 2. You say emphatically yes, I say emphatically no. I feel it must be possible to resolve this disagreement.

When you fire a pulse of light at the barrier with the pinholes, the resulting wavepacket that is emitted can be labelled Psi_1(x,t), Psi_2(x,t), or Psi_12(x,t) for the cases where pinhole 1, pinhole 2, or both pinholes are open. In the quantum formalism, it is unarguable that (as long as there are no wires for the photons to interact with, and not worrying about normalisation) Psi_12=Psi_1+Psi_2 because of the superposition principle for wave equations.

The physical picture we have is of two waves being emitted from the two pinholes. These waves are spatially separated in the vicinity of the pinholes and can therefore be distinguished from each other. Later, at the lens, the two wavefunctions are interfering with each other and measurements cannot distinguish whether a photon came from one or the other pinhole. Even later, in your experiment, the wavefunctions get separated out and are again spatially separated, and hence distinguishable.

The question is, "Can the two separated parts of the wavefunction after the lens be independently traced back to the two separated parts of the wavefunction at the pinholes?". I do not see that the superposition principle on its own is sufficient to make this inference. Regardless of how I think about this problem in terms of the quantum formalism (waves, path integral sum over histories, whatever) I do not see that it says anything whatsoever on the matter. The quantum formalism does not require it to be true that a photon detected at 1 came from pinhole 1 and so there is no reason to suppose that it did. The answer to the question "What fraction of the image at detector 1 in the image plane came from detector 1 and how much from detector 2?" is not 100%:0% or 50/50 but "I don't know".

Regards,

Chris

Ah! It was going so well till the last sentence...

"What fraction of the image at detector 1 in the image plane came from PINHOLE 1 and how much from PINHOLE 2?"

Chris

Dear CTN Hoigns

I believe that Prof Afshar speaks of the conservation of linear momentum in this regard as he has state in many of his posts here. You just have to run through the arguments that have already been posted on the Pinhole 1 slit 1, pinhole2 slit 2 arguments.

Dear Joseph Kahr, and Paul Snyder

The primary goal of my experiment has been to refute Complementarity, and I think this goal has been achieved (as evidently Colin Bruce seems not to reject Copenhagen's failure vis. a vis. my results). It is indeed a secondary to discus the Many Worlds Interpretation, but now that I am being pressed for an opinion on it, you may find the following ideas relavant, (it is an excerpt from a letter I wrote to a colleague back in May of 2004):
--------------------------------
I must confess that MWI looks like the ultimate revenge of my elder sister’s imaginary friends, taunting me as a child! All joking aside, it is a clever and quite liberating paradigm, allowing one to imaginatively explore many possibilities—very useful if one happens to be a science-fiction writer. But upon closer inspection, it seems to break down as a rigorous and viable candidate either as a theory on its own merits, or as an interpretation of Quantum Mechanics. I had never looked into MWI in the past, and my exposure at this time is only limited to what I can glean out of David Deutsch’s book “The Fabric of Reality”. Therefore, with the above caveats, I have the following comments:

I assume that based on MWI:

1) All photons are like rain drops or billiard balls with a well-defined trajectory in each universe. (p. 35)
2) Real photons are the ones that we observe directly in our experiments. (pp. 42-43)
3) Real photons can pass through each other without an exchange of momentum. (p. 41)
4) Shadow photons belong to parallel universes, and are “Real” in the corresponding universes and not the universe in which the “current” observer resides. (pp. 44-45)
5) Interference Pattern (IP) is produced by the interaction of Real photons with Shadow photons.
6) In order to produce the IP, the Real photon must be “deflected”, so there is an exchange of momentum between the Real and Shadow photons. (p. 49)
7) Any effect of the Real photon that can provide “which-path” or “which-way” information must destroy interference, i.e. Complementarity is upheld by MWI) (p.50).

Comments:
I) I find it interesting that David does not even bring up the possibility of describing the IP as a result of interference of waves. As I mentioned in the past, Willis Lamb and Leonard Mandel as well as many others in the Stochastic Quantum Electrodynamics community have shown that one can explian the Photoelectric effect (as well as Compton scattering, etc.) by using a classical electromagnetic field (waves) interacting with quantized matter. In other words between the emission and absorption of photons, light can be described perfectly using Maxwell’s equations. There is absolutely no evidence for (1); every attempt to demonstrate photon trajectories, invariably bumps into the wave nature of light.

II) Why is it that Real photons do not exchange momentum with each other, but Real and Shadow photons do?

III) What is the mechanism for the exchange of momentum between the Real and Shadow photon? What is the coupling process, and is momentum conserved in this process?

IV) From the perspective of a Real observer, we must say that the Real photon one observes in an interference pattern was deflected on its path, such that it avoids the dark fringe. This necessitates a violation of Real momentum in our universe (world), unless the Shadow momentum from the Shadow photon can become Real in the process. This is an amazing statement: momentum can be created in our universe without it ever having a history here. This is a clear violation of the Law of Conservation of Momentum and Energy, and has NEVER been observed in any experiment.
--------------------------------

I have a lot more to say, but it would be nice if a Many Worlder could respond to my comments above.

Regards.

Dear Prof Afshar

Seeing as how you are feeling philisophical today do you then have a issue with John Gribbins "answer for our times" when he postulates John Cramers "Transaction Interpretation" of QM ? I mean does the thought of advanced and retarded waves maving atemporally in time and space sound plausable.

Dear quantumenforcer,

Conservation of momentum is not violated in Afshar's experiment. He tried to refute my argument using an alternative experiment, which led to some confusion. I'm sure Prof afshar,
would like to kee[ this clear and limit discussion to his experiemnt, and what it says.

Chris

That is what I am stating. He is stating that the conservation of momentum and energy is what allows him to know which particle hits which detector. He has as I say mentioned it in many posts in this thread.

Regards

QE.

Dear qe,

Afshar is not saying that conservation of momentum allows him to know which particle hits which detector in his experiment. He said that alternative expeirments are possible where such considerations could be discussed.

As far as I can see, complementarity is a clear consequence of the evolution of the wavefunction using the schrodinger wave equation. The quantum formalism implies complementarity, it only appears not to when you get confused about particles and waves. Reading Afshar's comments on MW makes me wonder.

Chris

Dear Chris

So you are refuting what Prof Afshar is saying then ? Even though Schrodinger came up with the cat paradox to debunk complementarity in the first place.

Qe.

I'm not sure I understand for this experiment the simultaneous measurement of particle and wave properties. I think I understand an interference pattern is formed just prior to the lense, and also substituting the lense for an image plane measuring by photosensitivity, and that which-way information can't be obtained at that plane, anywhere within the interference pattern with both pinholes open.
Then, past the lense to either detector I understand each image corresponds to each pinhole without question, but no interference pattern is not detected at either detector's image (with or without the wires).

Well, maybe I'm not clearly understanding, and having the wires does actually cause some interference pattern? I hope I'm not confusing the issue. Anyhow I am to understand there is which-way information at each detector (image) without interference, so this isn't simultaneously having particle behaviour and wave-behaviour. Is that a valid conclusion?

Is the valid conclusion to consider the detectors' image each at one distance along a photon-path and the inteference pattern earlier (in time, and distance) along the photon-path (prior to the lense) to be a "simultaneous" measurement of particle and wave behaviour in one experiment?

I thought being simultaneous meant the time and distance differences are the same, so at the plane prior to the lense (where the wires are located) there must be "which-way" and "interference" properties known together (in violation of the Principle of Complementarity) and also at the detectors, having the which-way information for each slit (particle-behaviour) and the interference-pattern (wave-behaviour).

If a detector's image, imaged when both pinholes are open for photon-passage, is showing particle-behaviour by having a path is there also wave-behaviour by having an interference pattern on the detector? The contribution to the upper detector is effectively only from the lower pin-hole, so I am not sure about an interference pattern being present (at the image) therefore I am also unsure about a V=1 measurement at the detector with K=1 (which I am sure of). If everywhere along the path a simultaneous measurement of V and K holds V^2 + K^2 1 being concluded must a detector and the image-plane be considered one simultaneous measurement, spread over distance and time? If so I am not sure the involvement of uncertainty, how numbers calculated are within or beyond error bounds.

If 1 photon enters the both pin-holes and the interference pattern is produced and the image at each detector is resolved, does this actually mean particle-behaviour has been observed?

If 300 photons enter both pin-holes and form an interference pattern upstream of the wire-grid and each image at each detector is resolved almost completely (assuming the wire-grid reflects, diffracts, absorbs almost no incident light), how can an image at a detector be said to be particle-behaviour of any photon, having a path to just one predicted slit and never the other, but also be part of an interference pattern upstream of the lense? Is the photon-path at L known for any given photon since the interference pattern is known? If K=0 (or is almost 0) at L (at the plane upstream of the wire-grid, or some parallel-plane within the interference pattern) and V=1, how can K increase again later? K is lost then is restored? V is maintained at 1 for the entire photon path for all photons at the same time K becomes 0 then raises to 1 again?

Dear Prof. Afshar!

A couple of months before You were very kind to answer me. If You are still interested, let me introduce our last non-technical introducing paper on development of transactional interpretation by John Cramer, where we mention Your experiment.

Our collegues from French society of artifical intelligence were very kind to place this paper at their on-line magazine:

http://www.admiroutes.asso.fr/larevue/2005/61/pavel.htm

Hi Prof, is it not the outcome that the Uncertainty of Position and similtaineous Momentum, is by fact that particle-wave uncertainty is no different than saying:You cannot be certain of Paticle's or Waves?

If one actually knows that a 'Particle', exists for sure, then one can be certain about a number of paramiters attributed to such a certainty?

Dear all

I found a very interesting preprint which seems to explain the wave particle duality problem more effectively than any I have ever read. It also could explain the results of this experiment. Prof. afshar I would like to hear your opinion. Here are the last two paragraphs, the rest is at:

http://arxiv.org/PS_cache/quant-ph/pdf/0501/0501148.pdf

"As seen above, a particle can be described as a non-spreading wave packet satisfying
a linear equation within the framework of special relativity and interference experiments
can be explained with the hypothesis that there is a coupling interaction between
the peaked and non-peaked pieces of the wave packet. The off-peak part of the wave
packet plays a dramatic role in the quantum world. It seems that this article has solved
the wave-particle duality problem and answered the question “How can a particle pass
through both slits simultaneously and interfere with itself?′′. This explanation of the
interference experiments provides a realistic interpretation of quantum mechanics. The
interpretation implies that there is physical reality of particles and no wave function
collapse. It also implies that neither classical mechanics nor current quantum mechanics
is a complete theory for describing physical reality. This conclusion answers the
question raised by Einstein and coworkers [15]: “Can quantum-mechanical description
of physical reality be considered complete?′′ Thus, the experimental violation of
the inequalities [14] with the Bell-type hidden variables can not disprove the EPR argument.
This violation simply signifies that the quantum probability is different from
the classical-like probability.
The present realistic interpretation of quantum mechanics is consistent with the
physical aspects of the Copenhagen interpretation, such as, the superposition principle,
Heisenberg’s uncertainty principle and Born’s probability interpretation, but does not favor its philosophical aspects, such as, non-reality, non-objectivity, non-causality and
the complementary principle."

In the year 2000 a low temperature helium physicist called Humphrey Morris believed that he had found that electrons can be split in half or fragmented. I have not heard of this before but this paper I believe dicusses such results and QM in general.

http://www.blacklightpower.com/pdf/technical/E_Helium.pdf

It appears to be very interesting as it regards QM as being incomplete and possibly flawed.

Dear quantumenforcer

Yes I have been closely following the results of H.J. Maris and his experiments. Most are published in the Journal of Low Temperature Physics and I don't have access without paying for them. I must read about them in commercial journals. Makes it seem like the wave packet is a physical object without any particles. Strange indeed! The question is what happens to the charge? One mystery just leads to another! LOL

All of the web related information on Maris' experiments say nothing regarding it after the year 2000. Shame really as his results initially were potentially earth shattering.

The inquiring mind of our physicists should be lauded and thank you for making this topic so exciting and bringing it to the laymen. Many young minds are in overdrive now, due to Prof. Afshar.

This said, I think you would want to hear AZ Drezet - after all I believe he is from Innsbruck, where I am pretty sure Wittgenstein did vacation.

Dear Prof Afshar,

I am a supporter of the Transactional Interpretation. Your experiment using non-destructive testing of wave structure IP is incontravertalble. When is the next demonstration /colloquia of your experiment ? I have not been able to find out from the website or the blog.

Regards
Peter Tanguay

I don't really see how this is supposed to violate wavefunction collapse. Perhaps you can try to clarify. As I see it, the photon travels through the two slits, interferes, the interference pattern travels through the carefully arranged dark-fringe wires, and then the photon collapses upon being detected at one of the detectors. Now, obviously if the wavefunction collapse occurred at the time of measurement, then that photon has reached that detector and so possibility of it having been stopped by the wires is erased. It seems that the argument is being made that because the path of the photon is being determined, that somehow it should go back in time and reestablish a chance to collide with the wire. But this does not seem to logically follow. In a standard delayed choice (http://www.bottomlayer.com/bottom/basic_delayed_choice.htm) experiment, the path the photon took is selectively determined after the photon has already passed through the slits, but this at no point goes back in time and arranges something inconsistent with the measurement that was made. So since in order for collapse to occur, the photon has to strike the detector, that collapse already rules out the possibility that it struck the wire. The interference pattern at the detector is only determined by the past of the photon, not the future, because just like in the delayed choice experiment, the detector arrangement could be replaced by a screen.

New preprint about the implications of this experiment. It is called:
The Afshar Two-Slit Experiment and Complementarity

http://arxiv.org/PS_cache/quant-ph/pdf/0502/0502021.pdf

Dear Prof. Afshar,

I would like to ask about a possible reduction exercise. As a computer science major, I regrettably didn't take enough physics courses at the university (to be exact, just two: 8.001 and 8.002). So your patience is requested if my understanding of quantum phenomena is incomplete and/or erroneous.

I wonder if it is possible to reduce the Afshar experiment to a simpler one that obviates the need for a lens.

Assume we remove the lens (and the wires). The two propagating probability wave functions are now intersecting and continue past the region of interference. To make the experiment more definitive, lets say we narrow the wave functions so that it become a narrow cone, emanating from the pinhole and going towards each other, like two fixed light beams, and then continue to diverge past the region of intersection. This can be done by inserting a diaphragm in front of each pinhole, in a cockeyed geometry, to narrow and direct the PWF (which naturally will also result in some loss).

The two PWF "cones" intersect and produce an interference pattern, just as in the standard two pinhole experiment. This ascertains the wave behaviour. If we put a detector screen at the far end past the region of intersection, one for each PWF, we will see a circular spot where the PWF intersects the screen. There will be no interference pattern on either of these two images, and thus this ascertains the particle behaviour (a photon array detector can confirm this if necessary). Would this not be wave and particle duality in the same experiment with the same photon?

Now if the requirement is to ascertain particle-wave simultaneity in the same-photon experiment, then we can put Prof. Afshar's brilliant idea of the wire grid at the interference minima, and if it is made of photoelectric material, measure the current, which should be next to none. This would assure simultaneity.

Would it be fair to say that this experiment is isometric to the Afshar experiment and also does away with the lens? What is missing in this reduction, and what logical component has been unduely jettisoned in this reduction? Many thanks in advance.

After having read the archive suggested by Quantum Mirror, I have some questions for the CI advocates.

http://arxiv.org/PS_cache/quant-ph/pdf/0502/0502021.pdf


1) The preprint maintains that one still cannot simultaneously observe a photon and observe the wave as opposed to simultaneously in a single experiment.

2) The Afshar experiment does demonstrate non-destructive observation of a wave without a photon at the wires. You cannot observe a photon at the wires non destructively, if the photon does not exist there. Why stop at a photon? Logically nothing can be observed simultaneously with the wave if it does not exist. This is not the logical equivalent to saying one cannot observe one without the other as in the Heisenberg principle.

3) If at the wires, one can observe the wave without a photon, what therefore, is the reason for the principle of complimentarity? The burden is on the advocates of CI to now show the necessity of PC.

4) Related to PC in CI is that the state vector is not a real physical quantity, but is a mathematical quantity that has no reality until destructively observed. The non destructive observation of the wave at the wires would imply the TI version of QM using a real physical wave, as opposed to CI in which the state vector represents our knowledge of the system. To the CI advocates I ask “Cannot you define physics with something physical? Why would that not be preferable? One can make up anything non physical rule and say it is the reason for any observed physical system. Non-physical entities are hard to disprove, when they don’t have an experiment to prove them in the first place.

Dear Unconscious Observer

I hope you soon recover from your coma. Oh I guess you mean not informed instead of asleep. LOL

The lens operates as an angular discriminator, and the linearity of the Fourier transform ensures that a suitably placed lens can resolve two sources of minimum angular separation. That minimum angular separation is the lens' resolving power. Without the lens the common interference bands of Youngs double slit experiment will spread out to any distance and you will never get any circular spots.

A Follow up to the preprint by Kastner

The preprint by Kastner maintains that the Afshar experiment has shown that a wave and particle have been observed simultaneously in the same experiment, but not simultaneously. Thus the principle of complimentarity remains in tact.

It may remain technically in tact, but its implications are now questionable. The implication that light must have simultaneous Wave/Particle duality is now no longer necessary. Since light has now been viewed as a particle and a wave simultaneously in the same experiment, going to the extreme of violating the logical consistency argument is no longer necessary to explain phenomena. (see Afshar preprint pg. 1) In fact what we see is exactly the description of TI; a photon at emission through which way information, a wave in transmission at the point of the wires, and a photon at the point of absorption /detection.

It is important to note that not viewing a wave and particle simultaneously is in agreement with TI. It is however, just a statement that could be made on the side. TI does get bogged down with all the metaphysical problems that develop from the Copenhagen Interpretation.

Dear Peter Tanguay,

Dr. Kastner is WRONG on the issue of simultaneity of wave and particle aspects of light in my experiment, and therefore Complementarity is NOT technically intact! Briefly, while it is true that the two types of measurements are carried out at two separate spacetime coordinates, (wave property earlier at the wires, and the complementary particle property later at the image plane,) however, both these measurements tell us something about what took place in a single spacetime region, namely the slits while the photon passed through. Therefore, both measurements retrodict their logical inferences to the same place and time, which is the relativistically correct definition of simultaneity. To put it simply, one measurement implies the photon passed through both slits, while the other implies the same photon passed through only one of the slits.

I am writing a rebuttal to her arguments, one of which is the old "Complementarity is too vaguely defined" apology. Fortunately (or perhaps unfortunately) Bohr himself spelled it out in his Nature paper, and his definition is currently being used in physics journals, not to mention hundreds of text books!

Regards.

Dear professor Afshar

Good to hear from you again!!!! I hope everything is going good for you. Is your paper still in preprint? I thought I would mention this preprint with a citation to this paper. You are allready collecting a number of citations. It is time for them to print your paper!!! IMHO

http://arxiv.org/PS_cache/quant-ph/pdf/0409/0409197.pdf

Dear Quantum Mirror,

All is well on this side! I have been too busy with work lately, but things are shaping up OK. I'll be giving a talk at Ohio State University on Feb. 23rd (open to public), and another one at the American Physical Society March meeting in LA (members only). Also, a conference in Sweden is scheduled for July. I'll update this information with links as they become available online. The PRL review is going well; that is to say they are catching up with the rest of the world. They receive so many conventional manuscripts that it's difficult for them to readjust their frame of mind to think about my paper, and as they complain, it has "confused" the editorial baord somewhat! One can only hope that they don't deprive the rest of the physics community from the pleasure of this "confusion"...

Regards.

Dear Professor Afshar,

Thank you for the clarification. I should emphasize my statements as opinion.
My rebuttal was not meant to be a scientific rebuttal, as I leave that to you. It was intended to be similar to a lawyer with a hostile witness using the Socratic method.

In my opinion, the mistake Einstein, Schrodinger, and others made in trying to disprove the Copenhagen Interpretation, is that they believed they were involved in a scientific debate, and not a political one.

After all, the CI advocates rejected logic, as in the LCA. They politically spun the Schrodinger’s cat paradox around to say, “If you don’t believe Copenhagen then you are either not smart enough, or open minded enough, to accept new ideas.” It is inferred that any scientist, who disagrees with this interpretation, is the equivalent of a creationist vs. a Darwinist.

Today CI advocates enjoy hegemony, and so they equate nonbelievers with being fringe scientists, attacking their credibility. Now the debate will be fierce, as many a career and ego is at stake.

It is my opinion that Bohr survives in textbooks today, not because he was the definitive scientist, but because he was the craftier politician. Even physicists are people.

In the future, I will make sure that my comments/rebuttals are noted as opinion. A small correction in my rebuttal: The last line should have read. TI does NOT get bogged down with metaphysical problems….


Regards,

Peter Tanguay

Dear Prof Afshar

full steam ahead then regarding the simultaneous measurement and wave and particle behaviour in a two slit experiment ?

During peer review has no respected quantum physicist rebutted your claim that the principle of complementarity is currently on shaky ground (If I can say that)?

If so then congratulations on your work. Still can you explain which way the photon went is it goes both ways (wave) and one way (particle) simultaneously?Oh yer of course particles do not necessarily exist do they as everything can be explained in wave terms instead ?

Dear Quantum Mirror and Prof. Afshar

Further to the reduction exercise proposed on 2/9/05-17:25 - A picture is worth a thousand words. Pls. view the diagram at:

http://www.geocities.com/zekise/unoba1.jpg

Question - does this capture the logical essence of Prof. Afshar's experiment, and as it does away with the lens, if so would this not be a simpler (as per Occam) thought experiment?

======

QM - and LOL, the name Unconscious is a pun intended on the subjectivists (e.g. postmoderns and solipsists) that deny objective reality and claim reality can and will be altered by conscious subjectivity. The term refers to "being unaware of itself" - e.g. a cat (neither asleep nor in coma). See the Sokal Hoax - http://en.wikipedia.org/wiki/Sokal_affair

======

Dear Peter Tanguay - IMO the debate between Einstein et al and Bohr et al at that time was a metaphysical and not a political debate. To apply the metaphor of political dialectics to that of a scientific or even philosophic one is inappropriate and in some ways negativist and anti-empiricist. To accuse Bohr of indulging in petty politics to get his way does not serve the scientific community nor does service to those who take issue with the Principle of Complementarity. Scientists make a conscious effort to be above such pettiness.

You say "even physicists are people" - meaning that if they have a chance they will not hesitate to employ underhanded methods to get their way, no matter what the truth of the matter is. And unlike what you say, I dont think there are too many scientists betting their careers and egos on the "hegemony" of the Principle of Complementarity. Quantum Mechanics is complete and does not rest on this principle.

The intention of this discourse here is not to bring down Bohr or other individuals or counter their dominance. The intention is to delve into the nature of the universe for the purpose of enlightenment.

This world-view that the scientific method is subject to power politics, and Bohr and PC is accepted because he was a craftier politician, is very disturbing - it is an attack on science itself - that the scientific method is a social construction whereby power relationships (politics) and ideology plays a determining role in scientific inquiry. This reduces science to a "meta-narrative" of the postmodern project - a decidedly anti-enlightenment and conscious project loaded with ideology to hack away at positive empiricism. Please review the Sokal Affair linked above.

The scientific method of inquiry stands on its own. It is inherently non-ideological and objective. Power relationships do not enter into the equation, unless forced in from the outside, which it will consciously reject - and any cynical effort to reduce it down to a power relationship will be rejected equally. Science occupies the high and lofty grounds and remains unchallenged from the anti-enlightenment currents currently in vogue.

Dear Unconscious Observer

I believe that John Bell found a very large mistake in Von Neumans work when he looked into hidden variable theories and the fact that as Von Neuman had disproved them mathematically they were not worth looking at. However it turned out that Von Neuman had made a trivial mathermatical error that no one for 40 years had picked up on. It can be seen quite clearly that scientists are human and politics, prejudice and hero worship all play a part in defining Science. I personally can well believe that often in science the correct science does not always win out. In fact recent work done in regard to the EPR paradox hows that both Bohr and Einstein were incorrect I believe.

Dear Quantumenforcer and unconscious observer

"politics, prejudice and hero worship all play a part in defining Science"

We all wish that science could be perfect and based only on observable results of experiments. That is not enough to explain everything that results have indicated. When we get into theory and interpretation, this is where science will and has gone wrong. There are now so many unanswered questions that are waiting for the results of experiments and data to lead the way I would look for anything to be possible.

"The scientific method of inquiry stands on its own. It is inherently non-ideological and objective. Power relationships do not enter into the equation, unless forced in from the outside, which it will consciously reject - and any cynical effort to reduce it down to a power relationship will be rejected equally. Science occupies the high and lofty grounds and remains unchallenged from the anti-enlightenment currents currently in vogue."

If only this were true it would be wonderful and science would advance faster because of it. To be outside of the Vogue in this modern structure is career, academic and public suicide!

Professor Afshar,

I understand that the purpose of your paper is to refute sharp PC, by showing WWI and IP in the same experiment, and through the LCA demonstrate wave and particle behavior at the point of the slit. Which I agree was accomplished.

According to the Transactional Interpretation, there is a four-vector standing wave at the slits of your experiment when both determining WWI and the IP. Therefore, it is not true that WWI => presence of photon. I understand that you would not include this, as it is not the direct purpose of your paper, and would have further confused an already confused review board. Would you comment?

Regards,
Peter Tanguay

Dear quantum mirror, Unconscious observer and quantum enforcer,

I agree with quantum mirror in his last entry. I also believe the best experiments are those who divorce themselves from politics as the Afshar experiment has done. I am, however, a little cynical that with all the careers dependent on CI, the Afshar experiment will judged strictly on its scientific merit.

Revised and much more critical preprint entitled: Why the Afshar Experiment Does Not Refute Complementarity by R. E. Kastner has appeared on Arxiv. Not a very well researched or enlightened writing in my humble opinion.

http://arxiv.org/PS_cache/quant-ph/pdf/0502/0502021.pdf

Dear professor Afshar

In reading the preprint by Kastner I was surprised by all the talk about spin? I thought we were trying to show sharp wave and particle in the same experiment? It seems that all the spin talk is used as a smokescreen to hide the fact that Kastner has no real argument to refute the experiment.

"Note that in this spin experiment, even though we allow that finding result
“U,” or “up along z” at t2 is accurate in that it does describe the particle’s spin
state at t2, we don’t typically use that result to assert that “from the time of
preparation in state ‘S’ (or ‘up along x’), the particle really was ‘U’ or ‘up along
z’.” If we do try to make the above kind of retrodiction, we run into a paradox,
because we can also make a prediction that the particle should “really” be “up
along x” during the same interval of time. So we obtain two mathematically
correct inferences that such a particle is simultaneously in eigenstates of
different complementary observables."

Huh? what does that have to do with this experiment?

"Because we are used to thinking of that measurement as
a “which-way” measurement allowing us to infer which slit the photon “really”
went through. But, in view of the interference pattern detected by the grid, we
know that would be nonsense—the photon was clearly in a superposition of slits
at t1, so it couldn’t have gone through only one or the other slit."

Kastner seems to be arguing that the photons after interference can't have a individual identity. There must be some kind of division and recombination of pieces of a photon. Does anyone know of such a experimental result or theory?

Dear Prof Afshar

This experiment appears to demonstrate a two slit experiment in time rather than space and again obtaining which way/path/whatever information leads to the collapse of the wave function, ie only one type of behaviour is observed.

http://physicsweb.org/articles/news/9/3/1/1

Quite brilliant it would seem and quite as traditional quantum theory would tell us. You cannot demonstarte when able to know which way information both waves and particle behaviour at the same time.

I am having a lot of trouble finding out anything about this experiment. A search of the web, Google scholar and all major journal index has nothing. There is the principles web site: http://faculty.physics.tamu.edu/ggp/

This says nothing about interference, only the research in high output laser:

[Now one might adopt two different point of views: The phase-dependent spectra can be considered as a measure of the absolute phase. Measuring the absolute phase is an extremely important issue because the absolute phase determines the temporal evolution of the electric field of the laser pulses. The laser field in turn governs the manifold of phenomena which can be induced.
One the other side, we could control the absolute phase and thus the direction to which electrons are emitted. This is a new type of coherent control, admittedly a particular simple one. Nevertheless, the imagination to control electron emission by changing subtle properties of a laser pulse is fascinating and great fun. On top of that, it takes little imagination to predict that this new type of coherent control (possibly extended by control of time-dependent laser polarization) will have profund impact on what is known as quantum computing, laser chemistry, etc.]

I am having a lot of trouble believing the main part of this story:

[Paulus and co-workers focused a train of pulses from a Ti:sapphire laser into a chamber containing a gas of argon atoms. The pulses were so short – just 5 femtoseconds – that each one contained just a few cycles of the electric field.

The team was able to control the output of the laser so that all the pulses were identical. The researchers could, for example, ensure that each pulse contained two maxima of the electric field (thatis, two peaks with large positive values) and one minimum (a peak with a large negative value). There was a small probability that an atom would be ionized by one or other of the maxima, which therefore played the role of the slits, with the resulting electron being accelerated towards a detector. If the atom was ionized by the minimum, the electron travelled in the opposite direction towards a second detector.]

[The team registered the arrival times of the electrons at both detectors and then plotted the number of electrons as a function of energy. The researchers observed interference fringes at the first detector because it was impossible to know if an electron counted by the detector was produced during the first or second maximum.]

How did they know this was the reason?

There was no interference pattern at the second detector because all the electrons were produced at the same time at the minimum. However,when the phase of the laser was changed so that there was one maximum and two minima, interference fringes were seen at the second detector but not at the first.

[ “We have complete which-way information and no which-way information at the same time for the same electron,” says Paulus. "It just depends on the direction from which we look at it."]

For the same electron, one electron. Paulus is a assistant professor at Texas A&M. Perhaps we should put as much credence in this as we did Lubos Motl's assessment of this experiment.

What concerns me is that it would appear that this is another vindication of standard quantum theory (or maybe just the principle of complementarity) in that which way information leads in a two slit experiment leads to wave function collpase it would seem.

Only one experiemnt so far appears to show how it is possible that wave and particles can co exist in the same two slit experiment simultaneously and I would prefer it is moe reputable quantum scientists took a serious look at Prof Afshars work in order to :

a, refute or accept it
b, understand why if the results are accepted it differs from all other which way experiements.

The whole thing looks to me like another pat each other on the back for coming up with such a brilliant quantum deduction. Only there is more deducting than there is de-getting their ducks in a row. I am speaking before seeing the paper since I cant find any such paper. PhysicsWeb is still just a commercial news journal and the editors could have misinterpreted the experiment. High energy laser experiments are Paulus' area and his web page never mentions quantum anything. I wish to see a paper as these news journals are notorious for completely missing the science.

I found some of the work here:

http://www.mpq.mpg.de/krausz/publications/115a_UFOlindner.pdf

Note that the measurement is fast, since many electrons per laser shot
can be detected (more than 50 in each direction in these experiments).

Dear Unconscious Observer,

Please take a look at my 12/27/04 @ 15:41 entry. Fig. 1 is essentially the same as your suggested setup (see the discusion). It is much more difficult to actually perform though, due to the small size of the interfrence region.

Regards.

Dear Prof Afshar

Your whole experiment appears to rest upon the conservation of linear momentum. Even quantum physics obeys this law to a high degree of probability always or nearly all of the time ? I ask because when it comes to the uncertainty principle and precise measurments in QM I thought that you got a probability wave and hence it was possible if not likely than one photon in a million would be found doing exactly that.

regards

Dear Quantum Mirror, and quantumenforcer

Dr. Kastner's paper is rather disorganized as far as its logical structure is concerned, and I do not see much refinement in the second version. She like many others uses a completely different experiment in which a certain aspect is erroneously ASSUMED to be fully analogous to mine and then tries to render my conclusions irrelevant. Here’s what I mean: For example, an asymmetry can be introduced in my experiment by moving only one of the pinholes and observing the corresponding image to co-move with it, however, the same type of asymmetry cannot be applied to the spin argument she presents, in which the pre- and post- overlap regions are entirely symmetric for the up and down spins. Since such an asymmetry cannot be introduced to her setup, therefore her conclusions have no logical bearing on mine. I'll explain it more clearly in the Wikipedia page soon.

While the double "slit" experiment in time is nifty, it is in no way a breakthrough in our understanding of QM and simply confirms the known formalism and interpretation. Besides, we already knew from Special Relativity that space and time are in fact aspects of the same manifold namely the spacetime, and phenomena seen in one extreme can be extended to the other as well as shown in many quantum beat experiments.

Finally in response to the issue on violations of the conservation laws, there is virtually no observable effect due to HUP in my experimental setup which is quite macroscopic in both in space and in time. Virtually no photon is allowed to spontaneously change its momentum in my experiment.

Regards.

Dear professor afshar

"it is in no way a breakthrough in our understanding of QM and simply confirms the known formalism and interpretation."

I assume the time must be much shorter than the wavelength of the light for self interference to happen. They say the reason for interference in these experiments is because we can't know which of two peaks created the electron which then self interfered. I think they are reaching a bit too far here. I may be completely off base since I can't read the paper but could this also be explained as the two peaks created two electrons which interfered with each other? The single peak could only produce one. This sounds more reasonable than we can't know which peak created the electron so complementarity is put into action. Is there a QM reason this is not possible?

Dear Prof Afshar

It is intruiging though that only one two slit experiment has ever claimed to show wave and particle behaviour of a quantum entity simultaneously and hence I wish that in the crusade to understand the ultimate nature of quantum reality other sincere quantum physicists would take a objective look at this experiement and comment about on it.

It is such a important experiement for quantum physics.

New and interesting preprint stating that complementarity is based on entanglement, has just arrived on Arxiv:

http://arxiv.org/PS_cache/quant-ph/pdf/0503/0503073.pdf

"Understanding that it is not the
uncertainty principle, but rather quantum entanglement
responsible for complementarity is an enormous step, presumably
in the right direction. Quantum entanglement
is at the heart of the modern theory of quantum measurement.
We have learned that it is the act of measurement
itself, and not the quantum uncertainty” involved with
the measurement that is responsible for the complementarity
principle. This may seem like a subtle point, but
it is one that has caused many physicists to sleep more soundly at night.

This paper still states that even when measuring non complemantary values, interference and which path inforamtion are not available at the same time. Hence complementarity is a consequence of entanglement in certain situations. However we are still in the either/or debate and not the both at the same time one.

Can Entanglement explain Prof Afshars result as when I stated in this forum that Entanglement was the deeper process I was told by Prof Afhar that Entanglement does not happen in single photon experiments. Particles cannot entangle with themselves. Parametic down conversion is used in these experiements to generate two entangled photons.

NOt sure if this article helps us at all in the verification of Prof Afshars results.

Professor Afshar,

Your experiment has been criticized for not observing wave and particle behaviors simultaneously, as opposed to simultaneously in the same experiment. I believe it is possible that at the wire position, you can.

In your experiment, if you add one wire at a time, and as you do so, take a radiant flux measurement at the detectors, you would gain wave IP knowledge with each wire added by identifying a minimum. You would also gain photon position knowledge, as the photon could not pass the thickness of each wire. This would show simultaneous violation of complimentarity and Heisenberg at the position of the wires.

Can you explain?

Peter Tanguay

dear quantumenforcer

I did not mean to imply that this has any bearing on this paper. I thought it was interesting and wanted everyone to be aware of it. I to was puzzled by the self entanglement aspect, so much so that I emailed the author and sent him a link to this weblog asking how he could explain self entanglement. His paper states though that the

"Entanglement enforces the complementarity principle by coupling the
photons path to different polarizations which are completely distinguishable from each other."

I can find no explanation for this in the paper and have not received a reply from the author in 2 days. I would like to know why he never mentions how self entanglement is possible.

Dear Quantum Mirror

It is a very interesting paper, however using parametric down conversion to generate two entangled photons of which one if passed through a classic two slit experiement is not the same as what Prof Afshar has done.

Prof Afshars experiment is much simplier and hence a lot harder to falsify. Entanglement is not (apparantly) the reason for wave particle duality in single photon experiments as he is measuring complemtary values at the same time.

I am personally astounded that Prof Afshars work is not recieving scrutiny by the quantum community as it demonstrating what has never been demonstrated before. I presume that by now most physicists have heard of this experiment.

Dear Quantumenforcer

" am personally astounded that Prof Afshars work is not recieving scrutiny by the quantum community as it demonstrating what has never been demonstrated before. I presume that by now most physicists have heard of this experiment."

I think the preprints by R. E. Kastner show that the community is very much aware of this experiment. You will notice that the only public voice has been in opposition to the paper and the outcome. Once the paper is published you will see a lot more activity. If you look through the archives you will see about 1 out of 20 papers on quantum physics involves complementary. This is a large background and a lot of work based on complementarity. To say that it is baseless and inconsistent will take years to accomplish. This would be like trying to remove a virus from someone that has been infected for years. They will still be arguing this many years from now!


" It is a very interesting paper, however using parametric down conversion to generate two entangled photons of which one if passed through a classic two slit experiment is not the same as what Prof Afshar has done. "

No one that I know is even comparing the two. I will stop giving reference to interesting papers on complementarity if it does not interest anyone. I thought with Prof afshar so busy he might not have time to pour over the literature and find papers such as these. It might save him some time and everyone else who is interested in the latest developments of complimentarity would enjoy them.

Dear Prof. afshar

Can we please have a page two? It takes a while for my browser to download this page now. I will do the work if you give me access to the layout html. :)

"I am personally astounded that Prof Afshars work is not recieving scrutiny by the quantum community as it demonstrating what has never been demonstrated before. I presume that by now most physicists have heard of this experiment. "

The general response to this experiment is "so what?". It does preciesly what any quantum physicist worth his salt would expect. It definitely does not rule out any modern interpretation of quantum mechanics (which ARE necessarily equivalent to the quantum formalism). The biggest impact it can have is a more careful wording of the complementarity principle which, after all, is just a description of the behaviour of the quantum formalism. Quantum mechanics carries on exactly as it did.

Chris

Also, if Prof Afshar wishes to discredit the copenhagen interpretation he should do so theoretically rather than expeirmentally. All he needs to do is show that the copenhagen interpretation makes a different prediction from the quantum formalism. An application of the Copenhagen interpretation to his experimental setup gives the results observed. Any difficulties are just in the wording, and hence uninteresting to the scientific community.

Sorry for the three messages in a row, but I just had an idea which would help make concrete progress here.

Since Afshar's choice of experimental setup is partly based on practical considerations which have the potential to occlude what is fundamentally going on, Afshar (and anyone else who is thinking about this) should try to come up with the simplest possible thought experiment which demonstrates a violation of the principle of complementarity. In this way we should be able to isolate the problem exactly and see whether it is a serious flaw in the copenhagen interpretation, whether it is a verbal distinction which can easily be fixed, or whether it is absolutely no problem at all.

I hope someone accepts this challenge,

Chris.

Quantum Mirror

Do not misunderstand me, please post all relevant quantum related material. I enjoy reading it personally.

In quanatum physics I have been reading for years that all experiments without exception cannot and do not show waves and particles simultaneously until now. If quantum physics predicts results no different than Prof Afshars experiement shows then fine. But how is it that quantum physics verfies experiments that do not show wave particle duality and also the one that does. Surely Prof Ahshars experiment must faslisfy part of the quantum physics formalism itself ?

Dear CTN Hoigns

" if Prof Afshar wishes to discredit the copenhagen interpretation he should do so theoretically rather than expeirmentally. All he needs to do is show that the copenhagen interpretation makes a different prediction from the quantum formalism. An application of the Copenhagen interpretation to his experimental setup gives the results observed. Any difficulties are just in the wording, and hence uninteresting to the scientific community."

I don't know of one instance where Prof. afshar said he had discredited the copenhagen interpretation. Where did you get that idea? I think it is revealing that you put more credibility in theory than experiment. Theories are just wording applied to experimental
outcome.

" should try to come up with the simplest possible thought experiment which demonstrates a violation of the principle of complementarity. In this way we should be able to isolate the problem exactly and see whether it is a serious flaw in the copenhagen interpretation, whether it is a verbal distinction which can easily be fixed, or whether it is absolutely no problem at all."

Huh? Prof. afshar has come up with a real experiment which is very simple and demonstrates a violation of the principle of complementarity. Why would you put more stock in a thought experiment? Again you are trying to tie together the principle of complementarity and the copenhagen interpretation. The only flaw that has been mentioned here is complementarity. You say this experiment is uninteresting. I can see why, you are confused about which principle, interpretation, formalism or mechanics it has violated.