Consider a fully entangled pair of polarized photons, A and B, fired at two detectors with polarisation filters in front of them. I have to get a little philosophical to understand the way the interpretations of this experiment play out. My knowledge is still very basic but I'm working on it. I'm curious though. When does the polarisation get determined? I have several different ways of looking at this: Collapse. A reaches the filter and 'collapses' into a parallel or perpendicular polarisation. At this very point B takes on this direction of polarisation also. However, in a different reference frame B could be the one that collapses. So there this interpretation seems have a kind of arbitrarity in it. Determinism. A reaches the filter and we interpret that its path was entirely deterministic, so that its polarisation can be traced 'back in time' to the creation of A, thereby fixing the polarisation direction of B. This is a kind of retrocausality. However, this interpretation has the same arbitrarity as (1), for which photon first reaches its filter depends on the reference frame. However, B's path is in this view as deterministic as A's. Uncertainty. There is no way to determine when the polarisation got determined. The state of the pair is fully mixed, and no knowledge is available about either photon state with respect to their polarisation until observed. And if this is true, then there is no need to further try to define or investigate it, for it is all we know. Now, firstly, admin, I want to stress I am not putting forward any theory of my own. I just don't know how to phrase the question other than this. Is (3) closest to the truth?