How do you know that no information is transferred between them? Without this information transfer, how does a correlation remain in place? Isn’t information transferred in Bohmian Mechanics? Why isn’t entanglement taken as evidence for superluminal communication?

@ArthurOfNavases The experimental results on one part of the entangled system are random, you cannot chose them. Thus the later observed correlation cannot be used to send a signal. Bell has shown that there is no local hidden variable theory (which could give a causal explanation) that explains the results. As far as I know, the Bohmian theory is an explicitly nonlocal (hidden variable) theory which yields the same results as quantum mechanics and doesn't allow transfer of information either. Experiments and QM theory show that entanglement doesn't allow superluminal signal transfer.

@freecharly There is non local causal connection between the measurements of entangled objects. If we reject that we have to accept the many worlds approach or the pilot wave theory (which is non local) or the shut up and calculate approach. You are right that this effect cannot be used to communicate non random information superluminally.

@KDP Thank you for your comment. I wonder whether the observed nonlocal correlation falls under the usual definition of causality. Even in classical science correlation is usually no proof of causality. A would appreciate, if you coiuld give an expert reference for that.

You are confusing signal transfer with non local influences. What matters is whether the particles’s properties are influenced by another in any way, not whether one can use entanglement results to send signals. Lastly, the No signalling theorem is a circular argument since it assumes the non existence of superluminal influences

I cannot provide a reference, because there is no officially recognised philosophical explanation for the mechanics of how the correlation is achieved. Bell said "If [a hidden-variable theory] is local it will not agree with quantum mechanics, and if it agrees with quantum mechanics it will not be local." Ref en.wikipedia.org/wiki/Bell%27s_theorem In other words the correlations are non local. As I said before, alternative explanations are many worlds or a pilot wave that has non local properties.

@freecharly is simply incorrect. The no signalling theorem does not rule out non local causal influences that may be superluminal. Whether one can or can’t take advantage of this for signalling purposes later on is irrelevant

@freecharly Consider this thought experiment. A magic genie gives a 1000 identical devices. They each have a switch with two positions labelled 1 or 0. They also each have two lights which are red and blue. They cannot be switched on or off and one of the lights come on randomly. If both switches of two devices are in the same position, then whatever colour lights up on one device then the same colour lights up on the other device. If the switches are opposite positions, then different colours light up simultaneously on both devices. This happens, no matter how far apart the two boxes are. .

If millions of scientists carry out millions of tests and the boxes have this consistent behaviour all the time, would you agree that appears to be a causal link between the devices? Would you also agree that it would be impossible to send meaningful information superluminally using these devices?

@KDP This is a very interesting discussion! I have to leave now and will continue tomorrow. Thank you!

@ArthurOfNavases The no-communication theorem of quantum information theory states that measurements on one quantum mechanical (qm) subsystem cannot be used to transmit information to another subsystem, in particular, by the non-local correlations in entangled subsystems. It follows that no superluminal communication is possible by these correlations. Indeed, no superluminal information transmission has ever been found experimentally. All experiments are explained by standard QM. Thus there is no need for a "more complete“ theory. Research on theories (e.g, unification of GE & QM) continues.

@KDP Very vivid thought experiment! It corresponds to the Bell experiment measuring the two spins (or photon polarizations) in parallel directions. This parallel detectors case, as opposed to certain inclined ones, could still be explained by local hidden variables or angular momentum conservation and thus be causal. The problem with the causality of non-local correlations measured faster than light is that the SR time order of events can be reversed from a suitable reference frame. The usual definition of causality requires that the time order of events is the same for all reference frames.

There is no experiment that tells you which measurement outcome will occur. Hence, by definition, it is not complete. Secondly, no signalling does not mean no influences as has been pointed out many times. Bohmian mechanics explicitly makes use of non local superluminal influences between particles. Until you can rule these kinds of theories out, there is nothing in physics that says no information is exchanged between particles. @freecharly

See this answer: physics.stackexchange.com/questions/343071/…

@ArthurOfNavases "There is no experiment that tells you which measurement outcome will occur". Thats just typical QM! By whose definition is this "not complete"? QM has shown very successfully that this is how nature works. The observed measured non-local correlation effects, can be "superluminal", but the sequence of events can be reversed depending on the reference frame. This is contrary to the commonly accepted concept of causality in physics. Bohms theory seems to be causal, but introduces exactly the same random effects by "unknown" initial random variables.

@ArthurOfNavases Re "...there is nothing in physics that says no information is exchanged between particles." Information is exchanged between observers, not particles. Bohms theory is interesting, has the same results as QM, introduces this nonlocal pilot field, but has problems with relativistic extension.

Well if there was no correlation observed, perhaps you could say there’s no evidence it’s incomplete. But the fact that there is a correlation strongly suggests influences even if we haven’t discovered it yet. Suppose that I flipped a dice and you flipped a dice on the other side of the world. Suppose we kept getting the same results, and yet each result seemed to be just as random. Suppose we then couldn’t figure out a way how this is happening and to the best of our theories, there is no way. Would you accept that, or would you suspect there’s something more to be known? @freecharly

@ArthurOfNavases Our first natural instinct would be, of course, to look for a causal explanation. This guides us successfully in our usual environment. But it seems that there are objects with non-local connections in the microscopic world that are part of nature we have to accept, We have the theories to describe them. Thats usually the goal of physics.

@freecharly “non-local connections” that’s the point. Most physicists deny these. They say there are no connections but rather that there are correlations only

@KDP Being able to know the probabilistic distribution of certain measurements in controlled experiments does not tell you how the world works. We do not know how the world works. QM doesn’t tell you what’s happening before measurement. Hence it is incomplete. The universe isn’t.

@ArthurOfNavases Your dice example is interesting. The results could be simulated by special dice. These dice have a little processor inside and a seed number. Each time the dice are thrown, they add one to the seed number and calculate the corresponding digit of Pi for that number and output that digit modulo six plus one. If the other similar dice has the same seed number, it will duplicate the results of its twin. This is something like the super-deterministic explanation of QM. Its predictable if you known the hidden the variable (the seed number).