Difference Between Non-Seperability and Non-Locality?

[mach567]

I am taking a philosophy of quantum mechanics class and my teacher told me that if we believe in non-separability than locality is true. However, I do not see how this is possible. Non-separability and non-locality appear to be the same thing. Non-seperability is the fact that events disconnected by physical means can affect each other...which is the same as non-locality. Any insight into what my professor actually meant?

thanks,
mach

 

[Demystifier]

We already had a thread with a similar subject:
https://www.physicsforums.com/showthread.php?t=344165

 

[ThomasT]

@ mach567

There are different meanings for the terms nonseparability and nonlocality. Your professor might have been talking about quantum entanglement and the fact that the nonlocality of standard QM isn't in conflict with the locality of SR.

The locality of SR refers to the principle of local causality in 3D classical space. The nonlocality of standard QM refers to the fact that an entangled system can be described more completely than any of its subsystems. This nonlocality is a consequence of the parameter (not ontological) nonseparability of entangled systems and their experimental analysis, which is reflected in the QM formalism.

It would be wrong to say that if we believe in (quantum) nonseparability, then (3D classical) locality (that is, the assumption that nature is evolving exclusively in correspondence with the principle of local causality) is true. It's just that the assumption of 3D classical locality isn't at odds with quantum nonseparability. Nor is SR, which sets a greater than zero, and finite, limit on causal action in 3D classical space. There's no empirical evidence contradicting the assumption that nature is entirely and exclusively local, but that doesn't mean that it is.