Due to my lack of time to maintain this weblog, it will only be accessible as an archive until further notice. In the meantime, I can be reached through my e-mail afshar[at]rowan.edu.

Thank you for your cooperation and understanding.

Best regards.

Shahriar S. Afshar

1) It would be helpful if you reproduce Fenyman’s statement on page 81.

2) I don’t believe Prof. Afshar has carried out his experiment with matter waves. The outcome should not be different.

3) I wholeheartedly agree with your assessment. A meme had befallen the physics community and some mystical followers for a few decades that, based on the Schroedinger Cat thought experiment, claimed that reality does not exist without “conscious” observers. That there is no planet on “51 Cygni” until somebody on earth 45 light years away discovers it, and then all of a sudden it gets formed. In the past 2 decades, the advent of Decoherence theory (Zeh, Zurek) has put to rest such irrational notions of self-centricity and solipsism.

It is not an observation or measurement that results in collapse. According to decoherence, as I understand it, it is simply an interaction that results in loss of coherence, which precipitates collapse. This usually is simply a photon hitting an object with many degrees of freedom. The issue is not whether there is an observer or not. The issue is whether the information “is there in principle” or not.

4) Multiple collimated photons do produce interference. Also for entanglement, you need multiple particles - however it can be argued that in full entanglement, the multiple particles are in reality a single particle. So yes, quantum phenomena do appear across multiple unrelated particles. Any (?) interaction between two (coherent) particles will produce a quantum phenomena.

5) I think you are pinpointing the central mystery to QM. If there is a second aperture open, the trajectory is affected by that, even though the trajectory does not go through the second aperture. If one insists in viewing this phenomena in particle and trajectory terms, indeed such mystery will arise. Under this interpretation, we have a paradox. That is why the wave interpretation of light has been proposed, and the wavefunction model can explain away this mystery (but produces another mystery, namely collapse and the interpretation of the wavefunction).

6) Perturbations are not limited to electrons and photons. Any system will do. What is important is the “degrees of freedom". An electron/photon interaction with the self-interfering object produces an entanglement that will kill the self-interference, through the production of the anti-fringe. So you raise a very good question.

Assume we have a matterwave interferometer. The massive molecule has passed a double slit and would produce an interference pattern if it hits the screen. But before it hits the screen, we shoot a photon at it that bounces off, and is now entangled with the molecule. So we will lose the self-interference (without correlation selection). We now break the entanglement by absorbing the photon by a system with large degrees of freedom.

Question is: would the self-interference pattern reappear, or is it irrevocably lost? I understand that Scully has shown that the self-interference is irrevocably lost (i.e. cannot be recovered without correlation selection). Therefore, there is no “reset” effect, and you are correct that self-interference will not preserve across an interaction.

I appreciate receiving feedback from Prof. Afshar and others.

Regards

]]>I have just read of your experiment and viewed your November 2005 presentation. Although not a physicist, I venture the following comments/questions:

1. Your experiment contradicts a statement in Richard Feynman’s book “QED: The Strange Theory of Light and Matter”, page 81. Consequently the single particle experiments he refers to and any subsequent ones must have a flaw, which I presume is the issue of perturbation of the particle as it is measured passing through the aperture.

2. Has your experiment yet been carried out for particles with mass, as you have suggested should be done?

3. Presumably one of the crucial points to draw from the experimental results is that quantum measurement (or indeed the possibility of measurement) does not necessarily change/make reality, and consequently the concept of reality as existing separate to an observer, and without requiring one, can be restored?

Speculative questions:

4. Does the totality of experimental physical evidence indicate that quantum particle interference might never be related to having more than one particle (i.e. it is always single particle interference), or are there plenty of examples of definite multiple particle quantum interference?

5. I guess from your comments that you would disagree with the following statement:

The results of single particle self-interference experiments are -

• A single particle sent to a single aperture goes through as everybody would expect (with a single real trajectory seemingly randomly selected according to the appropriate single aperture wave function);

• A single particle sent to a double aperture also goes through one aperture only, but after exiting that aperture follows a modified single real trajectory (for some yet to be explained reason) but this time seemingly randomly selected from the two aperture wave function.

Why is the above wrong?

6. Coming back to perturbation during measurement. Is the only perturbation possible electron/photon interaction? Do you think that this then must/may reset the particle’s self-interfering capability? That is particle self-interference is only possible between interaction events and not across them.

]]>I see the problem in any case should be addressed to detection of singnals from sorces. Could everyone in world measure with precise mathematical value which will not be changed by repetition of the further the same experiment for example what we call in optic significant physical characteristic is photocurrent. It s clear that we would like to say that some value has fluctuation and we should apply some approximation model.The argument is that we live in reality with there time developing natural laws. The detector will give us only some approximated by our model the answer on what happens with source.

Sincerely yours,

Estimator

]]>

To the extent that the question in Afshar’s experiment is not “which detector” (future tense), but given a detection, “which pinhole” (past tense), one must perform an interpretation, insofar as such questions (in terms of QM) don’t make sense - literally.

The “particle” of which way questions, when translated into QM terms, could have been the probability of a particle, at the nominated junture (pinhole). But given the detection, this probability no longer exists. The probability of where the photon might be found or otherwise theorised - at an earlier time - would be everywhere zero, insofar as the photon detection is already given.

Since a which way question is asking something of the past, (rather than the future) we can construct a wave function from the downstream data, and propagate it backwards through the apparatus, in order to reconstruct what might be a suitable answer to a which way question.

To be consistent with the principles that saw each detection as the result of a wave distributed to both detectors, we must, therefore, use detections from both detectors to reconstruct the which way answer.

We will see (of course) that two pinholes are reconstructed - not one.

If we limit our downstream data to that produced in one detector our reconstruction will be, accordingly, just one pinhole. It is the choice of detector which determines which pin hole is reconstructed. Not the wave function. The wave function is constructed from data in both detectors.

The reconstruction of just one pin hole should tell us something is amiss. Where is the other pin hole?

It was edited out, insofar as the data that would have otherwise reconstructed it, was edited out.

Since the reconstruction of one pin hole, rather than two, is not based on the wave function but a decision regarding which data to use, the corresponding result does not constitute the identification of which way the wave/particle went. The result just tells us which detector was chosen to otherwise represent/imagine which way the wave/particle went.

Neo-classical reconstructivism.

Carl Looper

22 January 2006

]]>

The following either answers the challenge, or says the challenge can’t be answered. I leave that up to you.

The wave function used to predict the interference patterns in each detector (or the probability of where a particle might be found in each detector) is computed across both detectors.

This is consistent with conventional applications of quantum theory.

The computed wave function defines an equal probability of finding a particle in one detector as it does the other. This probability is not affected by the introduction of the pinholes. The two waves emerging though the pinholes are the same wave function. Wavelets. That we can direct one wavelet to one detector, and the other wavelet, to the other detector, by means of the same lens (or different lenses) still doesn’t change this, or the probabilitys.

Until the photon is measured, it still has an equal probability of being measured in one detector as it does the other. Again, this is consistent with conventional quantum theory.

That we find a particle in one detector, and not the other, does not mean the wave (otherwise used to predict that particle’s location) came only through one pinhole. The same wave also went through the other pin hole, to the other detector.

The same wave.

Now the 50/50 probability of a particle being found in one detector vs the other is not defined by the wave per se, but the question - which detector? Each detector has been prepared with equal access to the same wave so the probability - in terms of the question - is 50/50.

Carl Looper

21 January 2006

To the extent that Afshar’s experiment is positioned as a violation of Copenhagen principle(s) we should provisionally set aside the math otherwise used to represent such principles. For example, the math that otherwise embodys Relativity Theory can’t be used to prove Newton incorrect anymore than the statement 2+2=4 can.

But through careful experiments, theoretical arguments, philosophical debates, a day in the art gallery, and the math, we can allow ourselves to adjust Newton’s equations to match those of Einstein’s. Otherwise we could just use Newton’s equations and say: see Einstein’s done the math wrong, he is therefore wrong.

Afshar’s experiment is a “which way” experiment. Such experiments already violate Copenhagen principles before they’ve even been performed. To follow Afshar’s experiment/argument is to (if only provisionally) employ a violation of the principle in preparing the experiment.

We should, against our better judgement, allow this.

The most famous “which way” experiment of all time is EPR. It begins as a violation of Bohr’s principle, before it is even performed. And it demonstrates (itself as) a violation.

Bohr’s comeback is to show how a correlation of the remote measurements, required to complete the demonstration, can not be performed without relocalising the remote measurements, ie. bringing them together. In the interim period, the information that would otherwise demonstrate the violation (through localisation) has yet to occur. The violation, in a sense, has yet to be demonstrated. It is in “waiting” so to speak.

Are we allowed to use this future event (localisation) to say what is taking place prior to such? Why not. We can just imagine ourselves in two places at once, performing the correlation, and thus predicting the conclusion which is otherwise demonstrated when done locally.

Bohr is in a good position here. He knows (to the extent that we can grant him such insight) that such a superpositioned observer can’t be localised any earlier than the measurements. The information otherwise held by our imaginary observer is as inaccessible (and therefore not information) as the remote measurements.

But insofar as we are allowed to imagine the violation, albeit retrospectively, we can imagine we’ve violated the Copenhagen principle.

And that is all that seems to matter in “which way” experiments.

But if a “which way” experiment could physically demonstrate a violation of Copenhagen principles, ie. before they could physically do so, only then would the principle be actually violated.

Obviously, if only by definition, this is impossible.

If, on the other hand, we read Bohr as advocating some limit on what we might imagine, or otherwise theorise as “there” prior to the demonstrated correlation, we could argue that Bohr is wrong.

We can, obviously, imagine anything.

But any serious analysis of Copenhagen (Bohr, Heisenberg, et al) would not see it as imposing any limits on our imagination per se. Afterall, the probability wave is an imaginary wave and forms the basis for predicting interference patterns.

‘Which way” measurements are at cross purposes to the principles of Copenhagen. Copenhagen is about what can, in fact, be measured. “Which way” measurements are about what could have been measured if it wasn’t for those pesky Copenhagen principles.

Carl Looper

21 January 2006.

http://www.geocities.com/zekise/rochester-mandel.htm

I believe this faithfully reproduces the experiment conducted by Mandel at Rochester. C1 and C2 are spontaneous parametric down converters. A1 and B1 are entangled. So are A2 and B2. A1 and A2 are coherent. So are B1 and B2. (Pls. note the use of the term coherent here is slightly different from Afshar’s usage in the preprint.)

I understand that in this experiment Mandel observed no IP at D0 (a CCD array). Thus V = 0 and D1 or D2 provides us WWI, hence K = 1.

He then removed D1 and D2, and with the help of mirrors combined B1 and B2 together and decohered the combination so that WWI was lost. As a result, he observed an IP at D0, hence V = 1 and K = 0.

My question is, what happens if we instead move both D1 and D2 far off to a distance, so that the length of the B paths are much longer than the A paths. Will we see V = 1 restored while maintaining K = 1 (after a short delay) and thus produce a violation of PC?

If not, then what if we remove D1 and D2 altogether so that B1 and B2 never decohere, even though they are not combined? Will we get V = 1 (as K = 0)?

I wonder if such entanglement can be used to confirm the Afshar experiment? I would appreciate your opinion on this thought experiment.

]]>