DrChinese said:
Observation causes collapse (whatever that is) based on the observation. According to EPR, that makes Bob's reality dependent on Alice's decision.
Or, we can assume that the correlated events at A and B have a local common cause. And, standard qm is not incompatible with that assumption.
DrChinese said:
Now, both EPR and Bell realized there were 2 possibilities: either QM is complete (no realism possible) or there is spooky action at a distance (locality not respected).
EPR said that either qm is INcomplete (local realism possible) or there is spooky action at a distance (local realism impossible -- a detection at one end is instantaneously determining the reality at the other end -- in which case locality would be out the window). Qm is obviously incomplete as a physical description of the underlying reality. All you have to do is look at the individual results, wrt which, by the way, qm isn't incompatible with an lhv account of, to ascertain that. (But that doesn't entail that a viable lhv account of entanglement is possible.) The reason that the qm treatment is a 'complete', in a certain sense, account of the joint entangled situation is because the information necessary to predict individual detection SEQUENCES isn't necessary to predict joint detection RATES. But, again obviously, qm isn't, in the fullest sense, a complete account of the joint entangled context either, because it can't predict the order, the sequences, of the coincidental results. It can only predict the coincidence RATE, and for that all that's needed is |a - b| and the assumption that whatever |a - b| is analyzing is the same at both ends for any given coincidence window -- and that relationship, that sameness, is compatible with the assumption of a local common cause (even if qm doesn't explicitly say that, but, as I've mentioned, the emission model(s) can be interpreted that way).
DrChinese said:
But either way, the superposition means there is something different going on than a classical mixed state.
I agree. We infer that the superposition (via the preparation) has been experimentally realized when we observe that the entangled state stats have been produced -- which differ from the classical mixed state stats. But this has nothing to do with the argument(s) presented in this thread.
DrChinese said:
A local realist denies this, saying that there is no superluminal influence and that QM is incomplete because a greater specification of the system is possible.
I think we agree that lhv theories of entangled states are ruled out. We just differ as to why they're ruled out. But it's an important difference, and one worth discussing. I don't think that a greater specification of the system, beyond what qm offers, is possible. But I also think that it's important to understand why this doesn't imply nonlocality or ftl info transmission.
I do very much appreciate your comments and questions as they spur me to refine how I might communicate what I intuitively see.
DrChinese said:
But Bell shows that QM, if incomplete, is simply wrong. That's a big pill to swallow, given 10,000 experiments (or whatever) that say it isn't.
Qm, like any theory, can be an incomplete description of the underlying physical reality without being just simply wrong. I think Bell showed just what he said he showed, that a viable specification of the entangled state (ie., the statistical predictions of qm) is incompatible with separable predetermination. However, in showing that, he didn't show that separable predetermination is impossible in Nature, but only that the hidden variables which would determine individual detection SEQUENCES are not relevant wrt determining joint detection RATES. A subtle, but important, distinction.
Regarding billschnieder's argument, I'm not sure that what he's saying is equivalent to what I'm saying, but it seems to accomplish the same thing wrt Bell's ansatz, which is that it can't correctly model entanglement setups. (billschnieder might hold the position, with eg. 't hooft et al., that some other representation of local reality might be possible which would violate BIs, or that could be the basis for a new quantitative test which qm and results wouldn't violate. That isn't my position. I agree with Bell, you et al. who think that Bell's ansatz is the only form that an explicit lhv theory of entanglement can take, but since this form can't possibly model the situation it's being applied to, independent of the tacit assumption of locality, then lhv theories of entanglement are ruled out independent of the tacit assumption of locality. We simply can't explicate that tacit assumption wrt the joint context because that would require us to express the joint results in terms of variables which don't determine the joint results.)
Anyway, it seems that we can dispense with considerations of the minimum and maximum propagation rates of entangled particle 'communications' and, hopefully, focus instead on the real causes of the observed correlations. Quantum entanglement is a real phenomenon, and it's certainly reasonable to suppose that it's a result of the dynamical laws which govern any and all waves in any and all media. That is, it's reasonable to suppose that there are fundamental wave dynamics which apply to any and all scales of behavior.
After all, why is qm so successful? Could it be because wave behavior in undetectable media underlying quantum instrumental phenomena isn't essentially different than wave behavior in media that we can see?
With apologies to billschnieder for my ramblings, and returning the focus of this thread to billschnieder's argument, I think that he's demonstrated the inapplicability of Bell's ansatz to the joint entangled situation. And, since P(B|H)/=P(B|AH) holds without implying ftl info transmission, then the inapplicability of P(AB|H)=P(A|H)P(B|H) doesn't imply ftl info transmission.
Beyond this, the question of whether ANY lhv theory of entanglement is possible might be considered an open question. My answer is no based on the following consideration: All disproofs of lhv theories, including those not based directly on Bell's anstatz, involve limitations on the range of entanglement predictions due to explicitly local hidden variables a la EPR. But it's been shown that these variables are mooted in the joint (entangled) situation and explicit lhv formulations of entanglement bring us back to Bell's ansatz or some variation of it. So, lhv theories (of the sort conforming to EPR's notion of local reality anyway) seem to be definitively ruled out.