Comment Re:This is huge (Score 1) 214
Just some quick comments (that is, in terms of how much time I spent thinking about the reply).
Good that we have cleared things up. I can agree with your characterisation if you are more specific about "common cause": what we have to give up is Reichenbach's common cause principle, which is not the only sort of common cause imaginable. In fact, we know the correlations exist because of the entangled state, so the state is some kind of common cause, just not Reichenbach's.
I think that the seriousness of what is given up here has not been fully appreciated. Yes, the results are correlated, but to maintain locality you need to give up the idea that the cause of that correlation is to be found inside the light cone in the past/present. Note again Werner, in the paper you provided, talking about labs bringing their results together, perhaps centuries later. If you stick to locality, then the common cause must be in the future! That is to say, the correlation occurs when the labs bring their results together. It's not just a matter of giving up on some particular notion of common cause. The reason why you need to give up on common cause is because no local, existing in the past cause can explain the correlation. If you think there is an explanation for the correlation, and you think the world is local, then you need to look in the future. That's how I understand the matter anyway, and it fits with what I've read on the topic and why Werner talks at all about labs bringing results together centuries later.
To put this another way: When you look at Wiseman's paper I linked, and reject Principle 25, you give up on the claim that there is a cause of the correlation for entangled particles. If you want to then claim that there is a reason or cause for the correlation, you need to replace Principle 25 with something else. What will you replace it with? If I understand correctly, you will have to replace it with an in-the-future common cause. E.g., when the labs bring their results together. Anything that lies in the past/present light cone will violate Bell's inequality.
Well, for starters, it is hard to reconcile nonlocality and relativity; it requires the nonlocal influences to be some conspiratorial sort that do not actually lead to any superluminal signalling, and I find this conspiracy distasteful.
The reasons why you cannot communicate using these superluminal signals has to do with epistemic limitations. The reasons are not conspirational, and entirely explicable. Perhaps we will one day discover other superluminal phenomena that won't have the same epistemic limits.
Furthermore, it makes the scientific endeavour very suspect, if not actually impossible. A key hability in science is to isolate some system, control its variables, and see how changing them affect the system. In a nonlocal world, the first step of isolating the system is already impossible, so you're not going to be able to have much control over your system, and this reduces what you can learn about it.
This is not a new problem, but something scientists have been grappling with for centuries. (Almost) every system we experiment on now is not fully isolated from the external world. Suppose you're doing research in thermodynamics -- how easy s it to completely isolate your system from the external world? We might be getting better at it, but the fact that we have not been able to do this perfectly in the past hasn't stopped us from exploring our universe. I don't see how a nonlocal world is going to tip us over the edge from making science "very difficult" to "impossible". So far as I am aware, the only non-local event we have discovered so far is with entangled particles. It doesn't seem particularly common, and hasn't stopped us doing experiments like that which this Slashdot post is about.
Overall, compared to the alternative, accepting that the world is non-local still seems like a no-brainer to me