Mermin (1985) quotes an unnamed physicist as saying:

Anybody who's not bothered by Bell's theorem has to have rocks in his head.

This seemed like a pretty dire indictment, so I decided I had better look once again at this sort of thing in hopes that this time I would become disturbed. I read Mermin (1985), Greenberger (1990), and Mermin (1990). (There is also a well known lecture by Sidney Coleman, "Quantum mechanics in your face," but I'm impatient with videos, so I just gleaned the other three references from one of the slides in his talk.) Most of these are about GHZM experiments, which are advertised as similar to experiments that violate Bell's inequality, but more pedagogically direct -- which renewed my hope of being able to make myself bothered.

The following is what I came away with. Is this wrong?

Local realism seems to me to be more or less the statement that entanglement can't exist. What Bell and GHZM tell us is that we can't avoid entanglement using hidden variable theories.

When people say you should be disturbed by Bell and GHZM, I think what they have in mind is that you should be disturbed by entanglement. The only relevance of Bell and GHZM would be if you had in mind some idea of banishing entanglement using hidden variables.

I do find entanglement disturbing, but I have never seen any particular reason to seek escape in hidden variable theories. Am I guilty of having rocks in my head? Have I misunderstood something crucial?

Related: Why is quantum entanglement considered to be an active link between particles?

References, with handy copyright-violating pdf links

Mermin, "Is the moon really there when nobody looks?," Physics Today, April 1985,

Greenberger, Horne, Shimony, and Zeilinger, "Bell's theorem without inequalities"

Mermin, "Quantum mysteries revisited," Am J Phys 58 (1990) 731

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    $\begingroup$ You say "I do find entanglement disturbing, but I have never seen any particular reason to seek escape in hidden variable theories." How else would explain the correlations measured in microscopic systems? It seems to me that entanglement and hidden variables are the only two naively possible explanations for the weird non-deterministic (or at least not-obviously-deterministic) behavior of the micro world, so rejecting hidden variables is basically equivalent to accepting entanglement, which you admit is disturbing. $\endgroup$ – tparker Jan 7 '18 at 23:13
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    $\begingroup$ @tparker: Finding something disturbing isn't the same as seeking to deny it or explain it away. I find it disturbing that Trump is president of the US, but I don't waste my time denying that he was elected. Hidden variable theories were old and musty before I was born, and nothing interesting has ever come out of them. $\endgroup$ – user4552 Jan 7 '18 at 23:21
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    $\begingroup$ Ben, you're a respected poster, but this is really more a discussion question than a straight Q&A thing. I'd suggest you open a chat on this topic, rather than asking as a question. $\endgroup$ – StephenG Jan 7 '18 at 23:22
  • $\begingroup$ In QFT is the whole business of creation and annihilation of quanta not a spread-out instantaneous effect? Accepted but not understood yet somewhat disturbing. Still entanglement follows naturally from it if I'm right. Just as wave form collapse in QM. Or should one say that these are open questions in physics and that not necessarily anything nonlocal is going on? $\endgroup$ – Jan Bos Jan 7 '18 at 23:28
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    $\begingroup$ I don't understand what your question is - would you mind reformulating it? I think you're correct that Mermin's quote basically means "Everyone should be bothered by entanglement." And you admit that you are bothered by entanglement. So what's the problem? $\endgroup$ – tparker Jan 7 '18 at 23:43

I think you're in good shape. This kind of "are you troubled by it" statements are only because our intuition is trained in classical fashion where the phenomenon under consideration doesn't exist. For example, are you troubled by:

  1. The twin paradox?
  2. The probabilistic nature of QM?
  3. Schrodinger's cat?
  4. The speed of light in a vacuum being constant for all observers (i.e. breakdown of Galilean relativity)?

These are all things that would've shocked physicists before the 20th century. Bell's theorem is similar.

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    $\begingroup$ "Bell's theorem is similar." --- This is a purely opinion-based statement. $\endgroup$ – Norbert Schuch Jan 8 '18 at 0:10