In a classic interferometer experiment, a half-silvered mirror is placed in the path of a photon, creating two possible paths the photon can follow. When mirrors reconverge the two beam paths, you get interference. According to quantum physics, it’s impossible to say that the photon went down one path or the other, only that there was a 50% probability for each path.
My question: as a thought experiment suppose a fantasticly sensitive mass detector, capable of feeling the gravitational pull of a single photon, was placed by each path. Wouldn’t this contradict the theory? I don’t really expect that you could somehow “catch” the photon going one way the another, but what would happen? I can only think of the following possibilities:
-the detectors collapse the wave function so you don’t get interference. Except that in theory, your mass detector could simply be a torus of material with the light path passing through the center, with the photon being detected by the minuscule tidal distortion it makes on the torus. I don’t see how this could disrupt your interferometer.
-photons don’t have rest mass, so they don’t exert gravitational force? Except that I thought for certain that I’ve read that they do.
-gravity is the odd man out of known forces, and quantum physics can’t account for it.