Morbert said:
Brun and Griffiths read QM as a realistic theory, but introduce a restriction on the construction of logical propositions about quantum systems. They argue that this restriction eliminates the need to infer nonlocal influence.
https://arxiv.org/abs/0908.2914
Note that none of these approaches premise "no nonlocal influence" on coincident pasts of subsystems. As such, papers like the one referenced by
@DrChinese in post #45 don't pose a novel challenge to these approaches.
I both agree and disagree with the Griffiths citation in various manners.
1. First, I criticize him for specifically ignoring GHZ, swapping and other theorems/experiments. "
In an article of modest length it is impossible to deal with all published arguments claiming that quantum theory is beset with nonlocal influences and in conflict with special relativity. In particular we do not discuss those based upon the GHZ [60, 61] or Hardy [62] paradoxes, nor Stapp’s counterfactual arguments." So basically, he passes on addressing the difficult situations. On the other hand, this paper was written in 2009 and some of the newer works were not as well known as today.
2. On the other hand, he says: "
Similarly, entangled states of two spin-half ions in a trap, or two photons traveling away from a crystal where they were produced by down conversion, can properly be said to be nonlocal." Yes, this is the situation in which an entangled system has spatial extent. Many authors agree that an entangled systems are not separable and have physical extent in space. And as you say, from that we can make the leap to spatiotemporal extent (distance in space and/or time) and presumably to entanglement between particles with no common past.
So I am quite comfortable with that description of nonlocality in QM, but I point out that going from there to "Quantum Locality" (the paper's title) seems a bridge too far.
3. And this statement was a shocker: "
This [definition of classical realism] renders the Bell-CHSH inequality invalid for drawing conclusions about the real (quantum)world, in particular its locality or lack thereof." Hand-waving.
Griffiths has repeatedly maintained a position that he calls "local realism", such as
here: "...quantum theory itself is both local and realistic when properly interpreted using a quantum Hilbert space...". That paper is objecting to the famous, well-accepted and well-cited (3367) "loophole-free" experiment of
Hensen et al. (2015). Griffiths' objecting paper is cited by 1 author. Science does not rest on number of citations. But I might at least point out his "Consistent Histories" approach (interpretation) was originally developed in 1984, prior to the work I refer to as "modern".