Before reading this page, you may care to look at Nigel Snoad's essay which very neatly summarises the problem and the views which any unbiassed reasonable person might hold.
Let's get it straight: everyone agrees that communication between two human beings separated by a spacelike interval is impossible. If it were possible, it would be the end-of-physics-as-we-know-it.
Also impossible is superluminal communication between two devices which stand proxy for human beings, such as computers or various measuring devices.
Nevertheless, we cannot rule out the possibility of something like a natural Vernam cipher at work in quantum mechanics. This could give us John Bell's over-correlation, but would be useless for superluminal communication between human beings.
The trick is to devise your theory of superluminal activity, and then to explain why that theory is useless for superluminal communication. This might suggest that you take an anthropocentric or anthropomorphic view of nature, but that doesn't matter.
You may still have a problem with causality or the relativity of simultaneity. One way out of that one is to latch on to the Big Bang as establishing a preferred frame of reference in this universe, which is after all the only known universe. This preferred frame of reference, now marked by the Cosmic Microwave Background Radiation, is the one to choose when talking about causality. Quantum mechanics is a theory of matter, which was created in the Big Bang, so this is not unreasonable.
Just the same, we might prefer not to latch on to the Big Bang, though the grounds for this are purely aesthetic ones. This is an open question. The aesthetic view is presumably the conventional view, and the author will do his best to stick with this view for the time being. Latching on to the Big Bang is giving a hostage to fortune: it looks permissible now but we don't know about future developments.
An alternative view is to say that the phenomena we are dealing with are uncontrollable random collective phenomena in which there is spontaneous symmetry-breaking. Our concept of cause-and-effect is derived from the study of controllable deterministic simple phenomena, and the attempt to extrapolate this concept to uncontrollable random collective phenomena is going to lead to difficulties. The sequence of cause and effect is easy to reverse in the superluminal world, but this is nothing to worry about when we are looking at random collective behaviour over which we have no control.
To put it another way, there are two classes of phenomena in this universe, Protean phenomena and non-Protean phenomena (here we have 'something new under the sun'). Most phenomena are non-Protean, and from these we get our ideas about cause-and-effect: grab hold of one end of a stick, and the other end waves in response. The phenomena of quantum mechanics are nonlocal and Protean and different rules apply. The word 'Protean' is of course derived from Proteus, the sea-god of Greek mythology who could evade capture by continually changing his form, until Heracles managed to pin him down using his great strength. The analogous feat is impossible in nature. This identification of Protean phenomena is inconsequential until we start looking at the joint correlations which we find in quantum mechanics.
Perhaps there are people who will disagree with this alternative view. If you want to argue it out, then please pay close attention to the simulation of the Von Karman vortex street to be found elsewhere on this website. You ought to know all about this public-domain simulation anyway as part of your general education. Please run it a few times until you are familiar with it. Then you may return to the argument.
Now we ask you: in the computer simulation of the Von Karman vortex street there is a symmetry-breaking signal of some sort. Which way does the signal go?
The author's view is that this is merely a matter of convention: it always goes from the 'past' to the 'future'. If you swap 'past' and 'future' around, as you can easily do with nonlocal phenomena, there is no case to answer in any question you raise about 'causality'. Note that this argument only applies to a rare and special type of phenomenon, the random collective phenomenon of which the formation of the Von Karman vortex street is a prototype. It does not apply to the usual run of deterministic phenomena. We are not trying to upset several thousand years' worth of thinking about cause and effect. Instead we are pointing out that there are 'Protean' phenomena of an unusual type of which the reader almost certainly has no previous experience. Get some experience by running the vortex street program!
The argument about the Big Bang providing a special frame of reference may be found in Bohm and Hiley (1). The argument about random collective phenomena is new, but has a precursor in Hugh Everett's 'relative state formulation' which we are regarding as a commentary and not as an interpretation. The word 'Protean' is a neologism in this context.
There is another problem. Suppose the reader concedes everything said so far. Well, quantum nonlocality allows particles to group together as pseudo-particles, and Baugh (2) argues that the quantum many-particle problem will require an exponential-time algorithm for its computer simulation. There's no answer to that one, but it does not stop us from dealing with nonlocality in simple cases.
That gives us three potential problems with quantum nonlocality, which is one more than most people would have thought of. In the author's opinion, the first two problems are paper tigers. The only real problem concerns the matter of exponential-time algorithms, and that problem has no solution.
Here we are telling it like it is. Nonlocality is not the problem that some people may have thought it was, but there is another problem with exponential time. The idea that 'nothing can travel faster than light' is a simple-minded one. We may certainly have problems devising our superluminal theory, but that theory surely exists for simple systems. We might exclaim after Einstein