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

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