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.
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