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Second, non-locality: non-locality is not the same as action at a distance. Action at a distance requires exertion of a FORCE. Nothing in QM is in fact non-local.  The only thing non-local about QM is the Copenhagen interpretation of wavefunction collapse, which is not a part of the equations, but a way of visualizing the effect of observation a QM system.

Second, non-locality: non-locality is not the same as action at a distance. Action at a distance requires exertion of a FORCE. Nothing in QM is in fact non-local.  The only thing non-local about QM is the Copenhagen interpretation of wavefunction collapse, which is not a part of the equations, but a way of visualizing the effect of observation a QM system.

You have mentioned quantum entanglement as a supposed example of non-locality.  Entanglement, and phenomena like quantum teleportation, do not exert FORCES, so they are not actiona at a distance!  Further, quantum entanglement can never be used to transmit information faster than the speed of light.  Hence, there's no contradiction between QM and SR.  Field theory has SR built in.  There is no experiment, in quantum teleportation nor Bell's inequality, that can possibly transmit information FTL. Describe one experiment, just one entanglement experiment, that can supposedly transmit info FTL.  I dare you.  Just one.

You have mentioned quantum entanglement as a supposed example of non-locality.  Entanglement, and phenomena like quantum teleportation, do not exert FORCES, so they are not actiona at a distance!  Further, quantum entanglement can never be used to transmit information faster than the speed of light.  Hence, there's no contradiction between QM and SR.  Field theory has SR built in.  There is no experiment, in quantum teleportation nor EPR paradox, Bell's inequality etc., that can possibly transmit information FTL. Describe one experiment, just one entanglement experiment, that can supposedly transmit info FTL.  I dare you.  Just one.

So what is this supposed "non-locality" then? The Copenhagen interpretation of QM says that the wavefunction should "collapse" (revert to a single eigenfunction) everywhere simultaneously when an observation is made.  If this really happened, it would be a problem for SR, because in SR, simultaneity is relative to the observer. But, two problems. First, this supposed "collapse" can never be observed and can never be used to transmit info FTL.  Second, the Copenhagen interpretation is deeply flawed because it never defined what an "observation" was. It is no longer the most popular interpretation; among physicists, the Many Worlds interpretation is more popular now, because it precisely defines what observation means, in terms of quantum decoherence, so MWI connects better to macroscopic thermodynamics.

So what is this supposed "non-locality" then? The Copenhagen interpretation of QM says that the wavefunction should "collapse" (revert to a single eigenfunction) everywhere simultaneously when an observation is made.  If this really happened, it would be a problem for SR, because in SR, simultaneity is relative to the observer. But, two problems. First, this supposed "collapse" can never be observed and can never be used to transmit info FTL.  Second, the Copenhagen interpretation is deeply flawed because it never defined what an "observation" was. It is no longer the most popular interpretation; among physicists, the Many Worlds interpretation is more popular now, because it precisely defines what observation means, in terms of quantum decoherence, so MWI connects better to macroscopic thermodynamics.