Marty Tysanner wrote:
While I may understand their rationale, it still dismays me that so many people have thrown locality “under the bus” (so to speak). Locality isn’t like the 19th century ether that was invented to explain certain physical phenomena; it’s at the core of relativity, electromagnetism, classical mechanics, and even QM evolution up to the time of measurement. I can’t think of anywhere else in all of fundamental physics – outside QM entanglement – where locality is in question. Moreover, there are obvious conceptual issues with non-local influences/communication between entangled particles at space-like separation: How do the particles “find” each other within the entire universe, so they can “communicate” (other than tautalogically or some other version of “it just happens; don’t ask how”); and why don’t we see nonlocality in other contexts if it’s a truly fundamental aspect of nature? ...That part of Tysanner's comment is correct. Locality is at the core of nearly all of Physics, including quantum field theory (QFT). If it were false, we would expect to see some convincing evidence, and then do some radical rethinking of out theories.
Given the centrality of locality in physics, I think we should “fight to the death” to preserve it in a fundamental theory.
We do see the Bell test experiments, but they only negate the combination of locality and counterfactual definiteness. You can preserve locality by rejecting counterfactual definiteness. That is what mainstream physicists have done for 90 years.
Tim Maudlin disagrees with Woit and writes:
You do experiments in two (or three: GHZ) labs. You get results of those experiments. Those results display correlations that no local theory (in the precise sense defined by Bell) can predict. Ergo, no local theory can be the correct theory of the actual universe. I.e. actual physics is not local (in Bell’s sense).Bell defined a local theory as a classical theory of local hidden variables. In later papers, he called them beables, and gave some philosophical arguments for believing in them, but the definition of locality is the same.
Quantum mechanics uses non-commuting observables. By the uncertainty principle, they cannot have simultaneous values. That remains true if you call them beables instead of observables. If you create a model in which they do have simultaneous, but maybe unknown values, then you get predictions that contradict experiment. That is what Bell and his followers have shown.
The only conclusion is the null result: No reason to reject quantum mechanics. Any other conclusion is an error.
Update: Lubos Motl completely agrees with me about Bell. Bell proved a nice little theorem in 1964 that supports locally causal quantum mechanics. Then he wrote some later papers that did nothing but confuse people who refuse to accept quantum mechanics:
In this later paper, Bell coined the new terms "local beables" and "local causality" which have turned his writing into complete mess combining outright wrong statements with totally illogical definitions. He also tried to retroactively rewrite what he did in 1964. While in 1964, as I said, he was rather clear that he made two main assumptions about the theory, namely that it is local and it is classical (although he wasn't a sufficiently clearly thinking physicist to actually use the word "classical"), in the 1976 paper, he already tried to claim that he had only made one assumption, "local causality". ...This is correct. The term "beables" is just a goofy term for local hidden variables in a classical theory. Talking about them is just expressing a religious objection to quantum mechanics.
There only exists one physically meaningful notion of locality or local causality – and it's what holds whenever the special theory of relativity (or its Lorentz invariance) is correct. The probabilities of measurements done purely in region A are determined by the prehistory of A – and don't depend on further data in the region B although it may contain objects previously in contact with the objects in A. There may exist correlations between measurements in A and B but all of those are calculable from the conditions in the past when A,B were a part of a single system AB. What's important is that people's decisions (e.g. what to measure), nuclear explosions, and other random events in region B don't cause changes to the system A. ...
The claim by Bell, Eric Cavalcanti, and this whole stupid cult that quantum mechanical theories cannot be "Bell locally causal" is wrong ...
People who talk about "beables" in quantum mechanics are doing an equally silly mistake as a molecular geneticist who builds his science on the seven days of creation.