Re: Quantum Rebel

From: Russell Standish <>
Date: Thu, 12 Aug 2004 15:32:08 +1000

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
> 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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A/Prof Russell Standish            	 Director
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Received on Thu Aug 12 2004 - 01:36:54 PDT

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