Dear generous and helpful physicists, A number of threads here contemplate strategies for transmitting information faster than light by observing an entangled particle in one place, allegedly causing the wave function of its entangled twin to instantly collapse in another, far away place. Leaving aside the question of whether it is possible to devise a way of using this to transmit information faster than light, I am interested in whether the suggestion that the wave function of particle B collapses the instant its entangled twin A is observed is * part of the generally accepted principles of quantum mechanics, * a point of controversy, or perhaps * just a matter of interpretation, with no practical implications. Further, is it possible to even tell that particle B's wave function has collapsed without observing it? Of course the wave function of B collapses when you observe it, but how can you know whether it has collapsed just then because of the observation you made, or earlier, when the observation of A was made? If it's not possible to tell does that mean that my initial question is just a moot point - a matter of metaphysics rather than physics?