I'm guessing the answer is no ;) but figured I'd ask anyway. Suppose I have one partner in an entangled pair and my friend on Alpha C has the other. I measure an observable (spin?) and the wave function collapses to a single eigenvalue. Does this cause the wave function for that observable to collapse for the remote partner, and if so, can the wave function collapse event itself be used as a superluminal signal? I assume the answer is no simply because he can't tell if the wave function has collapsed without making a measurement . . . which would cause the wave function to collapse. The whole idea falls apart if wave function collapse per se is not something that can be observed directly but is only inferred from measurement, I suppose.
In the 2 slit experimentsuppose Bob is located at hole 2 with a mechanism that can instantly close the hole or open it. Sue is located on the screen plane a large distance, D , from the slits and at the position of the first interference fringe towards hole 1, where the probability of particle detection is zero when both holes are open. Bob closes hole 2, so the probability distribution for detecting a particle at Sue’s position changes from p1*p1 +p2*p2 +2p1*p2(=0) to p1*p1 > 0 . Does this change occur instantly? or does the effect propagate from Bob to Sue with the velocity of the particles? taking a time equal to the time of flight t = mD/p where m= particle mass, p= particle momentum?
If the change in probability distribution at Sue’s location is instantaneous ( as delayed choice experiments confirm that it is) can Bob use this to instantly modulate the number of particles per second received by Sue and hence send a signal faster than light? Why not?