Re: Quantum Rebel

From: George Levy <glevy.domain.name.hidden>
Date: Wed, 11 Aug 2004 10:56:43 -0700

Hi Russel

I just came back from vacation and am catching up with the list.

Are you claiming that photon particles are redirected to the detectors
by diffraction around the wires? If so your objection to Afshar's
experiment is not valid because you presupposes that the photons are
waves obeying diffraction rules. Quantum mechanics does predicts
Afshar's experiment when it is applied inconsistenly. Afshar's
experiment highlights these inconsistencies.

George

Russell Standish wrote:

>I just read the New Scientist article "Quantum Rebel" last night about
>Shariar Afshar's work on the double slit experiment. Ingenious as the
>experiment is, I really don't think it says anything about different
>interpretations of QM. Indeed, the outcome of the experiment is just
>what I'd expect from quantum theory, regardless of which
>interpretation is used.
>
>OK - so the claim is that Bohr's complementarity principle (CP) is tested
>by this experiment and found wanting. I decided to go back to the two
>text books I learnt quantum mechanics from - Leonard Schiff's book
>which is the older and more traditional of the two, and Rammamurti
>Shankar's book which has the more modern approach, but which I found
>explained things better. Shankar doesn't mention the CP at all, and
>for Schiff, the CP is basically a restatement of the Heisenberg
>uncertainty principle, a principle not tested by Afshar's experiment.
>
>In the double slit experiment, how I understand the CP to work is that
>one cannot measure which slit a photon passes through, and retain an
>interference pattern. Assuming it is possible to do this, one could
>divide the measures data into those photons that passed through slit A,
>and those that passed through slit B. The resulting distribution of
>photons arriving at the screen of
>the two slit experiment is then the sum of the distributions of the
>two subsets of data. However, the two sub distributions do not have
>inteference patterns so how can the sum have an interference
>pattern. Hence any such measurement of which slit the photon passes
>through must affect the photons so as to destroy the intereference
>pattern.
>
>Now in the article, Afshar claims to have measured which slit the
>photon passed through and verified the existence of an interference
>pattern. However, this is not the case - without the wires in
>place to detect the presence of the interference pattern, photons
>arriving at detector A have passed through slit A, and vice-versa with
>detector B and slit B. However, with the wires in place, some photons
>are scattered, indeed some photons which passed through slit A will
>arrive at detector B. With both slits open, and the wire placed
>exactly at a null point of the interference pattern, the photons
>passing through slit A and arriving at detector B exactly counteracts
>the photons passing thoguh slit B that have been lost through
>scattering. The mathematics of quantum mechanics assures this,
>coincidental this may seem.
>
>It may be a question of "interpretations of interpretations of QM",
>however on the basis of the New Scientist article, I don't believe
>Afshar have shown a problem with the complementarity principle.
>
> Cheers
>
>
>
Received on Wed Aug 11 2004 - 14:09:04 PDT