Re: Quantum Rebel

From: scerir <>
Date: Thu, 12 Aug 2004 10:06:57 +0200

It seems that Cramer has something to say about
those wires (as diffraction grating).


A number of your readers [New Scientist] have pointed out
that Afshar's grid wires are placed in just the positions that
would form a diffraction grating creating an image of pinhole 1
at the position of the pinhole 2 image. Does this destroy the
purity of Afshar's "which-way" measurement?

I raised the same question with Afshar earlier this year,
and the answer is no. Reason: the wires intercept no light
and so cannot diffract. He has done a variation of his experiment
using ONLY A SINGLE WIRE and recorded all the light in the focal
plane of the pinholes under three conditions: (1)
wire in, one pinhole; (2) wire in, two pinholes; and (3) wire out,
two pinholes. Measurement (1) shows lots of scattering from the
wire away from the image points, indicating that with only one
pinhole open the wire is intercepting and scattering light.
Measurements (2) and (3) show clear images of the pinholes
with nothing in between and are indistinguishable.

Conclusion: no light is scattered or intercepted by the wire in
measurement (2) because the interference pattern is present,
and the wire is at an intensity-zero position of the pattern.
A single wire cannot function as a diffraction grating.
Bohr is still wrong.

John G. Cramer
Professor of Physics
University of Washington
Received on Thu Aug 12 2004 - 04:14:45 PDT

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