From: <agrayson2...@gmail.com <mailto:agrayson2...@gmail.com>>
*Does entanglement -- which occurs whenever two systems interact -- imply non-locality? AG*
Not necessarily. If there is a common cause explanation of the correlation, as in classical physics where particles always have definite momenta, then there is no need for a non-local explanation. However, in quantum systems such as the singlet state of entangled spinors, then no common cause or hidden variable explanation is available and we have non-locality.
Actually a similar thing happens in any collision between two quantum particles. If we assume an elastic collision, the outgoing particles will be in the form of outgoing spherical waves -- neither the individual momenta or directions are specified by the collision itself. So observing the direction and/or momentum of one particle determines the direction and momentum of the other remote particle. There is no common cause or hidden variable explanation available for this, especially if the observations are at space-like separations. However, as far as I know there are no Bell-like inequalities that are violated by the statistics in this case, so the non-locality is not always obvious. Interestingly, this forms the basis for an important measurement tool at high energy accelerators. Often the output from experiments will be in the form of a missing mass plot, which is constructed by summing the momenta of the observed particles and determining what is missing. This can then be the basis of a search for undetectable or new particles.
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