““And, though it doesn’t seem possible, it gets spookier still. If we now let photon y hit the slits and the measuring screen first, and a split second later measure its twin far away, we should have fooled the quantum laws. The first photon already ran its course before we troubled its distant twin. We should therefore be able to learn both photons’ polarization and been treated to an interference pattern. Right? Wrong. When this experiment is performed, we get a non-interference pattern. The y-photon stops taking paths through both slits retroactively; the interference is gone. Apparently, photon y somehow knew that we would eventually find out its polarization, even though its twin had not yet encountered our polarization-detection apparatus. What””
