When one particle of an entangled pair is measured, it forces the state of the other particle. This effect propagates faster than we can measure, certainly faster than light and possibly instantaneously.
Relativistic observers with radically different viewpoints, perhaps travelling near lightspeed in opposite directions, can observe a time reversal in the order of the two measurement events. Thus observer Alice might see measurement A occurring first and therefore determining the outcome of B, while observer Bob might see measurement B occurring first and therefore determining the outcome of A. This despite the fact that Charlie actually set the experiment up so that the result of measurement A physically triggered the measurement of B.
This creates a paradox for Bob as to whether he should take Charlie's experimental setup or his own temporal observations as the correct causal sequence of events. If he accepts Charlie's experimental design then he must accept that temporal causality is broken in his own observations. But, if he accepts his own observations as correctly-ordered, then he must accept that somehow, measurement B triggered A and not the way round that Charlie assumed when they designed their experiment.
One way out of the paradox is to decide that temporal flow and causal flow are not strictly aligned at the quantum level and that entanglement can break their alignment. Are there other ways out?
