Depending on who one asks and their interpretation of QM, entanglement seems to be either: a) No problem at all. It's just a matter of information. If you knew one entangled electron was spin up, then the other must have been spin down by inference of the prepared state of the system. b) Potentially "spooky action at a distance." One electron might well be able to tell the other to "flip" its spin instantaneously. Something worth figuring out, but not something we like because that would be non-local. And I've seen some pretty entrenched belief systems based on either way. But couldn't we test this? I would assume we have already? If not, why not some similar scenario as follows... We have a set of points, notated by the following letters, where the distance between each adjacent point is the same as those of any other two adjacent points: A---B---C---D---E---F---G At (D), two entangled electrons are released, electron 1 moving to (A) and electron 2 moving to (G). Both paths are the same in characteristics. At point (C) the spin of electron 1 is measured as "up," thereby we "know" that of 2 is "down" at (E). At point (B) (or even we could say immediately at the measurement on point C), electron 1 is hit and its spin changed from "up" to "down". As both particles reach their endpoints, electron 2 is measured at (G). If electron 2 is shown as "up," then would we not know that electron 1 somehow told electron 2 to flip sometime after (C-E)? Would this not support then that entanglement is not merely inference of information from the system, but rather an actual effect of one particle upon the other (even if it is non-local)? Surely something like this experiment has already been done? thanks all.