Russell Standish wrote:
The presence or absence of the absorber on path 4 changes the wavefunctions involved, even though the amplitude of the wavefunction along path 4 is zero.
How exactly does it change the wavefunctions involved? If the outcome of the experiment is exactly the same, the amplitude-squared of the wavefunction must be unchanged at all points, so is it just a phase shift? Have you actually done a calculation to see how the wavefunction is changed?
The same is true with Afshar's experiment. This may seem nonsensical, but its exactly what QM says happens, and this sort of thing has been seen often in quantum experiments. The Aharanov-Bohm effect comes to mind.
In the Aharonov-Bohm setup, would the charged particle's wavefunction actually have an amplitude of zero inside the solenoid containing the magnetic field, or is their some nonzero probability that you will observe it inside the solenoid? If the latter, this isn't really analogous to Afshar's experiment or Unruh's variation on it.