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> Wherein the authors show, using previously untested correlations between two entangled photons, that maintaining realist interpretations of quantum mechanics (such as pilot-wave theory) as a fundamental concept require the introduction of locality-defying 'action at a distance' actions.

Not sure what the big revelation is supposed to be here. Everyone knows that Bohmian mechanics is non-local, that's exactly the point!

> The double slit experiment has been used in various forms to, over time, eliminate these channels. I'm not a physicist, but the language that they are using quite a few papers leads me to believe that these channels have been closed, and the realists are out of remaining options for maintaining realism.

No, no and no.

Why do you think this disproves pilot wave theory?

> Physicists also compulsorily reject Bohm’s construction because it explicitly builds nonlocality into its framework—even though violations of Bell’s inequality have conclusively shown that the stage of our universe is nonlocal. This is perplexing. Nonlocality is unavoidable in any theory that recovers the predictions of quantum theory. Therefore, any criticism of a theory that displays Nature’s nonlocal feature in an obvious way is both unfounded and counterproductive. Despite this, Bohm’s inherent explication of nonlocality continues to be obnoxiously mistaken as a strike against it instead of for it.

> even though violations of Bell’s inequality have conclusively shown that the stage of our universe is nonlocal

They have not. What they have shown is that the universe cannot be local and deterministic at the same time.

Bell's theorem rules out locality even for non-deterministic theories as well. Don't get determinism and realism confused...

I might not be using the same definitions as you are or maybe I'm getting something mixed up, so I'd be glad if you could elaborate on what exactly you mean by "determinism", "realism" and especially "locality".

(In my book, the Copenhagen interpretation is a non-realistic(∆), non-deterministic and local theory, which would contradict your statement.)

(∆) Assuming, of course, that the wave function is not an object of reality, as I think is standard.

Many would argue that Copenhagen is not local, but its very hard to even define locality if you are genuinely non-realist about everything.

Regardless, if it was possible to be "local + non-deterministic" many of us would be fine with that. But its not - Bell rules out "locality + realism", regardless of whether the realistic theory is deterministic or non-deterministic.

> Many would argue that Copenhagen is not local

Who? I believe the point of view that the Copenhagen interpretation is local is the standard one.[1]

> but its very hard to even define locality

How so? There are various definitions of locality—in terms of no faster-than-light transmission of information, in terms of commutators of field operators at spacelike distances vanishing as well as in terms of C* algebras—and the Copenhagen interpretation fulfills them all.

> if you are genuinely non-realist about everything

I'm being non-realist only about things whose existence we can't prove, e.g. the wave function.

> Regardless, if it was possible to be "local + non-deterministic" many of us would be fine with that. But its not - Bell rules out "locality + realism"

I don't see how this disproves anything of what I said. While I think you're right[2] about the fact that the violation of Bell's inequality rules out local realism—irrespective of determinism—, I already said that, in my book, Copenhagen is not a realistic theory because the wave function is not an object of reality.

[1]: https://en.wikipedia.org/wiki/Principle_of_locality#Copenhag...

[2]: "However, Fine's theorem shows that, this deterministic assignment of properties is not required to prove Bell's theorem. This is because the set of statistical distributions for measurements on two parties, once locality has been assumed, are independent of whether or not determinism is also assumed." (https://en.wikipedia.org/wiki/Principle_of_locality#Local_re...)

s/realistic/realist, sorry for the typo.

Don't throw out realism so easily. Ending the quest for answers by invoking mysticism is very easy for people to do but its never the right answer. https://www.lesswrong.com/s/5uZQHpecjn7955faL/p/6i3zToomS86o...

Where did I invoke mysticism? And where did I end the quest for answers?

I said "in my book" for a reason. You might of course argue that the wave function is real, which would make the Copenhagen interpretation a realistic, albeit non-local theory (as the collapse of the wave function would happen instantaneously everywhere). I'd be very happy to discuss this but please bear in mind that this was not what the discussion was about.

Because pilot wave theory assumes realism and determinism[1], and the authors of the first paper I listed conclude that their result "suggests that giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned."

Their conclusions could be wrong, of course, but if they are not, according to the authors' interpretation physicists should abandon realist theories like pilot-wave theory.

[1] https://en.wikipedia.org/wiki/Pilot_wave_theory#Principles

It would help if these weren't all from the same single source: Zeilinger's Vienna group and friends.

On the other hand formalism works seamlessly mathematically, which cannot be said of standard quantum mechanics. Even this year's Fields medalist Figalli has a paper on how good things are in Bohmian land.

Fine, here's another from Ronald Hensen at Delft:

Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km 2015 https://arxiv.org/abs/1508.05949v1

"...This result rules out large classes of local realist theories, and paves the way for implementing device-independent quantum-secure communication and randomness certification. "

This isn't relevant because Bohm's theory isn't local. There are much stronger results like PBR ruling out a large class of non-local realist theories, but that also doesn't include pilot wave theory.

No known experiment can rule it out because it's predictions equal those of Copenhagen.

This is something different. Zeilinger paints himself disproving realism alone and has a well known philosophical stance/bias here. Local realism testing here however is about being both local and realist, and pilot waves aren't local to begin with.

Yeah, that makes sense. Do you have an example of Zeilinger's writing where he discusses his philosophical stance?

Is a philosophical stance something you believe that a physicist shouldn't have?

Isn't special relativity a serious mathematical problem for Bohmian mechanics?

Relativistic extensions aren't pleasant in standard QM either.

Bohmian formalism would require something perhaps no less aesthetically repulsive, but surely more alien: a preferred foliation of spacetime to avoid a preferred reference frame. Turns out it wouldn't have to be an artificial choice, as it can be derived from the wave function itself https://arxiv.org/abs/1307.1714 (that would also mean this preference existing within QM irrespective of any interpretation).

Sadly this seems to be an issue that is shrouded in a lot turf war within the physics community. As someone who is mostly interested in the history of it from my armchair, I think it's important to put out there:

The assertion that Bell's inequality shut down Bohemian Mechanics is absolutely false. This claim has been floating around since the the 60s. The biggest disagreement came from ... J.S. Bell himself. He was a proponent of Bohemian Mechanics and didn't agree that he had dismantled it.

==== The criticism ====

> Recently, however, physicists more commonly cite the Kochen-Specker Theorem and, more frequently, Bell’s inequality in support of the contention that a deterministic completion of quantum theory is impossible. We still find, a quarter of a century after the rediscovery of Bohmian mechanics in 1952, statements such as these:

> The proof he [von Neumann] published …, though it was made much more convincing later on by Kochen and Specker (1967), still uses assumptions which, in my opinion, can quite reasonably be questioned. … In my opinion, the most convincing argument against the theory of hidden variables was presented by J.S. Bell (1964). (Wigner [1976] 1983: 291)

==== Bell's Take ====

> There was, however, one physicist who wrote on this subject with even greater clarity and insight than Wigner himself: the very J. S. Bell whom Wigner praises for demonstrating the impossibility of a deterministic completion of quantum theory such as Bohmian mechanics. Here’s how Bell himself reacted to Bohm’s discovery:

> But in 1952 I saw the impossible done. It was in papers by David Bohm. Bohm showed explicitly how parameters could indeed be introduced, into nonrelativistic wave mechanics, with the help of which the indeterministic description could be transformed into a deterministic one. More importantly, in my opinion, the subjectivity of the orthodox version, the necessary reference to the “observer”, could be eliminated. …

> But why then had Born not told me of this “pilot wave”? If only to point out what was wrong with it? Why did von Neumann not consider it? More extraordinarily, why did people go on producing “impossibility” proofs, after 1952, and as recently as 1978? … Why is the pilot wave picture ignored in text books? Should it not be taught, not as the only way, but as an antidote to the prevailing complacency? To show us that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice? (Bell 1982, reprinted in 1987c: 160)

> Wigner to the contrary notwithstanding, Bell did not establish the impossibility of a deterministic reformulation of quantum theory, nor did he ever claim to have done so. On the contrary, until his untimely death in 1990, Bell was the prime proponent, and for much of this period almost the sole proponent, of the very theory, Bohmian mechanics, that he supposedly demolished.

https://plato.stanford.edu/entries/qm-bohm/