The debate is very strange. First of all, these two guys are extremely smart, and are two of the world's experts on quantum mechanics. And yet they disagree so much on the basics, that Maudlin accuses 'tHooft of not understanding Bell's theorem, and 'tHooft accuses Maudlin of sounding like a crackpot.
Bell's theorem is fairly elementary. I don't know how experts can get it wrong.
Maudlin says Bell proved that the quantum world is nonlocal. 'tHooft says that Bell proved that the world is either indeterministic or superdeterministic. They are both wrong.
I agree with Maudlin that believing in superdeterminism is like believing that we live in a simulation. Yes, it is a logical possibility, but it is very hard to take the idea seriously.
First of all, Bell's theorem is only about local hidden variable theories being incompatible with quantum mechanics. It doesn't say anything about the real world, except to reject local hidden variable theories. It is not even particular important or significant, unless you have some sort of belief or fondness for hidden variable theories. If you don't, then Bell's theorem is just an obscure theorem about a class of theories that do not work. If you only care about what does work, then forget Bell.
I explained here that Bell certainly did not prove nonlocality. He only showed that a hidden variable theory would have to be nonlocal.
Sometimes people claim that Bell should have gotten a Nobel prize when experiments confirmed his work. If Bell were right about nonlocality, and if the experiments confirmed nonlocality, then I would agree. But Bell was wrong about nonlocality, and it is highly likely that the Nobel committee recognized that.
At most, Bell proved that if you want to keep locality, then you have to reject counterfactual definiteness. This should be no problem, as mainstream physicists have rejected it since about 1930.
I am baffled as to how these sharp guys could have such fundamental disagreement on such foundational matters. This is textbook knowledge. If we can't get a consensus on this, then how can we get a consensus on global warming or anything else?
Update: Lubos Motl piles on:
Like the millions of his fellow dimwits, Maudlin is obsessed with Bell and his theorem although they have no implications within quantum mechanics. Indeed, Bell's inequality starts by assuming that the laws of physics are classical and local and derives some inequality for a function of some correlations. But our world is not classical, so the conclusion of Bell's proof is inapplicable to our world, and indeed, unsurprisingly, it's invalid in our world. What a big deal. The people who are obsessed with Bell's theorem haven't made the mental transformation past the year 1925 yet. They haven't even begun to think about actual quantum mechanics. They're still in the stage of denial that a new theory is needed at all.I agree with this. Bell's theorem says nothing about quantum mechanics, except that it helps explain why QM cannot be replaced with a classical theory.
Free will (e.g. free will of a human brain) has a very clear technical, rational meaning: When it exists, it means that the behavior affected by the human brain cannot be determined even with the perfect or maximum knowledge of everything that exists outside this brain. So the human brain does something that isn't dictated by the external data. For an example of this definition, let me say that if a human brain has been brainwashed or equivalently washed by the external environment, its behavior in a given situation may become completely predictable, and that's the point at which the human loses his free will.I agree with this also. No one can have perfect or maximum knowledge, so free will is not really a scientific concept, but it clearly exists on a practical level, except for brainwashed ppl.
With this definition, free will simply exists, at least at a practical level. According to quantum mechanics, it exists even at the fundamental level, in principle, because the brain's decisions are partly constructed by "random numbers" created as the random numbers in outcomes of quantum mechanical measurements.
But I don't agree with his conclusion:
Maudlin ends up being more intelligent in these exchanges than the Nobel prize winner. But much of their discussion is a lame pissing contest in the kindergarten, anyway. There are no discussions of the actual quantum mechanics with its complex (unreal) numbers used as probability amplitudes etc.No, 'tHooft's position is philosophically goofy but technically correct. Maudlin accepts fallacious arguments given by Bell, when he says:
Bell was concerned not with determinism but with locality. He knew, having read Bohm, that it was indeed possible to retain determinism and get all the predictions of standard non-Relativistic quantum theory. But Bohm's theory was manifestly non-local, so what he set about to investigate was whether the non-locality of the theory could be somehow avoided. He does not *presume* determinism in his proof, he rather *derives* determinism from locality and the EPR correlations. Indeed, he thinks that this step is so obvious, and so obviously what EPR did, that he hardly comments on it. Unfortunately his conciseness and reliance on the reader's intelligence have had some bad effects.No, Bell and Maudlin are just wrong about this. All of that argument also assumes a hidden variable theory, and therefore has no applicability to quantum mechanics, as QM (and all of physics since 1930) is not a hidden variable theory. If Bell and Maudlin were correct about this, then Bell (along with Clauser and Aspect) would have gotten the Nobel prize for proving nonlocality. 'tHooft is correct in accepting locality, and denying that Bell proved nonlocality.
So having *assumed* locality and *derived* determinism, he then asks whether any local (and hence deterministic) theory can recover not merely the strict EPR correlations but also the additional correlations mentioned in his theorem. And he finds they cannot. So it is not *determinism* that has to be abandoned, but *locality*. And once you give up on locality, it is perfectly possible to have a completely deterministic theory, as Bohm's theory illustrates.
The only logically possible escape from this conclusion, as Bell recognized, is superdeterminism: the claim that the polarizer settings and the original state of the particles when they were created (which may be millions of years ago) are always correlated so the apparatus setting chosen always corresponds—in some completely inexplicable way—to the state the particles happen to have been created in far away and millions of years ago.