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- TL;DR Summary
- You can't do FTL message sending via entanglement, but can you tell whether you have measured an entangled particle without being told?
Suppose you make a measurement of some particle. If you know it is entangled, you may have conditional knowledge of measurements that might be made at a spacelike distance (if the other observer does/has done x, they will/did get result y). Note, I am using local in the sense of special relativity - a small volume of spacetime in which some measurement has been made, not in the sense of Bell.
So my question is: If you know someone is setting up a series of identical preparations, but you don't know whether the setup entangles two particles or not (whichever it is, it is the same for all cases - they are identical preparations), can you tell whether the particles are entangled by a series of local measurements with no communication outside of your small world tube? This is not the same as getting information FTL, just knowing whether you have measured an entangled pair member without being told.
So my question is: If you know someone is setting up a series of identical preparations, but you don't know whether the setup entangles two particles or not (whichever it is, it is the same for all cases - they are identical preparations), can you tell whether the particles are entangled by a series of local measurements with no communication outside of your small world tube? This is not the same as getting information FTL, just knowing whether you have measured an entangled pair member without being told.