On Thu, Aug 12, 2004 at 01:08:36AM -0400, Jesse Mazer wrote:
> Also notice that in the analysis of Afshar's experiment by W. Unruh at 
> http://axion.physics.ubc.ca/rebel.html which scerir linked to, Unruh does 
> not dispute Afshar's claim that all the photons from the each pinhole end 
> up in a single detector. In fact, he offers a "simpler version of the 
> experiment" involving a multiple pass interferometer, depicted in figure 2, 
> and says that in this experiment you do know which path a photon took by 
> looking at which detector it hits: "By measuring which detector they 
> triggered, 5 or 6, one measures which of the beams, 1 or 2, the photon 
> traveled along". Since the experiment in figure 2 is just supposed to be a 
> "simpler version" of Afshar's experiment, it's pretty clear that Unruh 
> would not disagree that the lens insures that knowing which detector 
> absorbed a photon is enough to tell you which path the photon must have 
> taken through the pinholes. Unruh is a fairly big-name physicist and his 
> explanation of what's wrong with Afshar's conclusions about complementarity 
> are pretty detailed, while I don't know anything about Basil Hiley and his 
> criticisms are more vague.

After looking at Unruh's explanation, I can only say that he puts in a
very persuasive manner, the substance of my post to this list: namely
that the insertion of a diffraction grating (equiv. Unruh's path 4
absorber) destroys the "which-way" information.

So Unruh does not claim that the lens suffices to tell you which path
the photon takes in the presence of the diffraction grating.

*PS: A number of people ask me about the attachment to my email, which
is of type "application/pgp-signature". Don't worry, it is not a
virus. It is an electronic signature, that may be used to verify this
email came from me if you have PGP or GPG installed. Otherwise, you
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A/Prof Russell Standish                  Director
High Performance Computing Support Unit, Phone 9385 6967, 8308 3119 (mobile)
UNSW SYDNEY 2052                         Fax   9385 6965, 0425 253119 (")
Australia                                [EMAIL PROTECTED]             
Room 2075, Red Centre                    http://parallel.hpc.unsw.edu.au/rks
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