Suppose one prepares two particles in an entangled state (at point S) and that one has detectors (say A and B) at opposite equidistant positions, separated by a large distance from S. Now, if one makes a measurement of the spin at A, the spin at B should SIMULTANEOUSLY change to the opposite spin as A. These kind of spooky actions are by now a well established fact. Now, as we all know, according to special relativity, there is no such thing as absolute simultaneous events. What is simultaneous for one observer is not simultaneous for another one moving at constant speed relative to the positions of both events. This means that if one measures the spin at A, such that the spin changes at B, a fast moving observer can see the observation of the spin at B BEFORE the measurement is made at A ! So, this observer will see the effect before the cause ! Since both quantum physics and the special relativity are valid, one would expect that such a situation can really occur. This in turn would imply that one is dealing with signals which go back in time.(adsbygoogle = window.adsbygoogle || []).push({});

I thought to be the first one who thought of this, but this was unfortunately not true . One can find more on internet about this but I could not find or uderstand the solution to this apparant paradox. Has anyone figured out how to solve this ?

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# Entanglement and special relativity : a paradox

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