How much time should not elapse between measurements of e- and e+ spin computed at a distance ot 1km to not detect effects of the entanglement? There should be a finite speed? Maybe greater than $c$?
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By the 'effects of the entanglement' I assume you mean the correlations between the measurement outcomes: in particular, the overall pattern of the correlations when the experiment is repeated for a variety of measurement angles.
To rule out the possibility that the correlations were caused by movement of information from one spin to the other, each pair of measurements should be spacelike-separated. That means there should not be enough time for a signal travelling at the speed of light, setting off from the start of one measurement, to arrive at the other measurement before it is completed.
Andrew Steane
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Entanglement does not have a speed. It occurs at the point where particles interact, and becomes a property of their joint wavefunction. when the correlation is measured is not relevant, unless either of the particles undergoes interactions with other particles, thereby "diluting" or "spreading out" the correlation via entanglement with the other particles.
Note that my statement about the point at which entanglement starts is not quite correct: it can start earlier than that.
S. McGrew
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