I have a question I havnt been able to figure out by reading or googling: If we have an entangled pair of particles, and we measure one, thus collapsing its wavefunction, 'when' does the other particle collapse? 'Instantly' begs the question of 'in which reference frame?' For instance, 'instantly' as seen from their combined center of mass. Is this experimentally measurable? Or is this an altogether meaningless question? That is, all that matters and all you ever know is that the particles have consistent histories? Im tending towards the latter conclusion, but Im not sure.