afshar experiment

JoeB-

Hi
I was reading up on quantum theory and all that and came across Afshars 'which way' experiment from 2004. It is claimed that his results show that the Copenhagen interpretation and the 'many worlds' interpretation are essentially 'wrong' while my favorite, the transactional interpretation' is ok. (It's only my favorite because I'm a fan of Cramers writing and story telling, not because I understand the subtleties of the theories). It would appear that this result also has implications for Heisenbergs uncertainty principle as well.

I know his experiment hasn't been submitted to peer review but it does seem to be taken seriously. Isn't this huge news? Why haven't we heard more about it so?

link to article on Wikipedia http://en.wikipedia.org/wiki/Afshar_experiment

Any comments on this?

Son Goku

This is going to seem like a really lame answer, but unfortunately Afshar has never given a detailed description of the experiment so it is very hard to comment on it. To be honest though I find it weird that an experiment can claim to refute any of the interpretations, considering they're all interpretations of the same theory and it's only the theory itself which can be tested.

Some people think he claims to have found the point which marks the "Heisenberg cut", but again no details so it's very hard to say anything.

Professor_Fink

The bottom of the wikipedia article you linked to lists specific criticisms of the experiment from some very big names. It might be worth checking out some of the counter arguements.

The comment about lenses and semi-silvered mirrors (beam splitters)preserving and destroying information respectively is rubbish. I'd like to think that this is a problem with the understanding of quantum optics of whoever updated the wikipedia article, and not Afshar.

In quantum optics both perform unitary operations on the photon, and so neither can "destroy" or extract information.

JoeB-

Son Goku wrote:

To be honest though I find it weird that an experiment can claim to refute any of the interpretations, considering they're all interpretations of the same theory and it's only the theory itself which can be tested.

Great point! John Cramer addresses it as follows... (in a discussion on the following URL. Cramer on Afshar experiment)

John Cramer wrote:

Many (including me) have declared, with almost the certainty of a mathematical theorem, that it is impossible to distinguish between quantum interpretations with experimental tests. Reason: all interpretations describe the same mathematical formalism, and it is the formalism that makes the experimentally testable predictions. As it turns out, while this "theorem" is not wrong, it does contain a significant loophole. If an interpretation is not completely consistent with the mathematical formalism, it can be tested and indeed falsified.

I didn't realise that full details weren't available on the experiment, sounds fishy if so. There is a page which contains a 33 page PDF document, 569Kb in size, which claims to describe the experiment, I haven't looked at it as I wouldn't understand it but I thought it might be the full technical details... (URL... http://www.irims.org/quant-ph/030503/ )

Thanks for the replies...
Cheers
Joe

Son Goku

JoeBallantine wrote:

Great point! John Cramer addresses it as follows... (in a discussion on the following URL. Cramer on Afshar experiment)

Sorry, that arguement slipped my mind. I think most of the interpretations don't contradict the mathematics. Although, I'd imagine showing that that is true would be quite difficult.

Similar thing happened to GR back in the 1960s (maybe 70s), there was a problem called the "hole arguement" which showed that the standard interpretation of GR might not match the mathematics entirely.

Afshar

FYI: The details of the experiment are fully discussed in the 33 page paper mentioned above (see the ref.s in the Wikipeia article for more details.) Also a refereed paper has passed peer-review and will be published soon. Please read these papers to ensure your comments are up-to-date. Best regards.-- Prof. Afshar

Son Goku

Afshar wrote:

FYI: The details of the experiment are fully discussed in the 33 page paper mentioned above (see the ref.s in the Wikipeia article for more details.) Also a refereed paper has passed peer-review and will be published soon. Please read these papers to ensure your comments are up-to-date. Best regards.-- Prof. Afshar

I'll definitely read the peer review paper, looking forward to it. (I had a good deal of interest in the experiment when it first went public.)
Thanks for keeping us updated.

Professor_Fink

Do you mind me asking what journal it has been accepted for?

tabish

There is glorious flaw in Afshar's interpretation of his experiment. The existence of interference in his experiment is correct, but the two detectors do not give any which-way information.
The two part of the state (call it a superposition of two wave-packets) are initially orthogonal, but when they cross each other, they interfere. In the interference, a part of each cancels out with a part of the other - that is what gives the dark fringes. The parts of the wave-packets which are left, are no longer orthogonal - so they can't give any which way information.
Infact, it can be rigorously shown that if there is interference, each slit contributes to BOTH the detectors. Or each detector gets a contribution from both the slits, and hence, no which-way information.
Thus complementarity principle is not violated, and cannot be violated.
For details, see
http://arxiv.org/abs/quant-ph/0701109