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