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As John Bell stated,

I cannot say that action at a distance is required in physics. But I can say that you cannot get away with no action at a distance.

Regardless of whichever interpretation of quantum mechanics is true, one thing remains true: particles at a large distance from each other have observed to be correlated in the case of entanglement, and only appear to be as such after measurement of their states.

Non local hidden variable theories, such as Bohmian mechanics, are often considered fringe and implausible due to the idea that the velocity of any one Bohm particle proposed depends on the value of a guiding equation, which depends on the configuration of all the particles under consideration. Thus, it is non-local. It is also criticized for proposing the existence of Bohm particles which are considered superfluous entities.

But how are they superfluous if they otherwise help make the theory be more in line with everything else that we’ve seen in the world?

Given that non local correlations have already been observed, and everything else within the universe seems to be determined and caused in an efficient manner, it seems to postulate no “new” phenomenons. Deterministic behavior and non locality both have been observed. Sure, Bohmian mechanics may propose the idea of new kinds of particle configurations that we haven’t observed, but this is nothing new in science. We have had past encounters in science where we proposed particles or configurations of them only to observe them later on.

On the other hand, we have never observed anything that is truly uncaused, until, supposedly the collapse of the wave function. Keep in mind that the nature of collapse and the nature of a measurement is still debated upon and yet we somehow, with confidence, can say that the exact time of a radioactive atom decaying is truly uncaused.

Everything in line with our experience of the world, for good reason, suggests that things occur in lawful manners and have causes. It is the very foundation of the scientific enterprise to seek these causes.

Isn’t it thus more likely that a deterministic (something that we already see in our macro world) non local (the only thing that can’t be questioned given the results of correlated particle states) account is true rather than a purely indeterministic one?

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  • Personally, I dont know much about the majority opinions of scientists, so I'm not even sure if physicists see it as less probable, or if it's more an issue of it being less practical given our current understanding. I think that is worth considering if you haven't already.
    – JMac
    Nov 9, 2023 at 17:36
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    As written this is an open ended question about physics/physicists. It lacks connection to philosophy.
    – Dave
    Nov 9, 2023 at 17:40
  • Two points. We have no candidate for what a non-local variable would be, so it would be an entirely ad hoc assumption. Secondly, if there were any way to interact with a non-local quantity of this kind, it would violate special relativity.
    – Bumble
    Nov 9, 2023 at 19:15
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    Hats off to TM- given that I seem to remember you saying that you weren't a physicist, you've done an impressive job of assimilating and summarising key issues in relation to QM. Nov 9, 2023 at 20:29
  • Everything else seems to be determined? To whom? Nothing "seems" to be determined except in toy models. Bohmian mechanics is considered fringe not just because of non-locality, but also because it has Bohmian particles that are absolutely undetectable, like Lorentz's aether once was. And the "non-locality" is just an artifact of these added apparitions, quantum mechanics itself is perfectly consistent with the speed of light as the limiting speed. Quantum field theory is even explicitly based on it.
    – Conifold
    Nov 9, 2023 at 20:54

4 Answers 4

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Physics is undetermined, as explained in this answer: Deterministic or stochastic universe?

Math and logic are also undetermined, as explained in this answer: Is the Münchhausen trilemma really a trilemma?

Some people WANT the world to be definitive and predictable, and that appears to be your motivation, based upon this untrue assumption in your question: "everything else within the universe seems to be determined and caused in an efficient manner".

Our world is not deterministic and predictable. As noted for classical physics -- there are multiple solutions to the equations. For logic and math -- there are multiple logically coherent formulations. For knowledge -- our justification for epistemologies do not close, and the efforts to try to close them are well known logical fallacies.

Socrates' key insight was to teach us to question the assumptions we want to believe so much that we hide them from ourselves. Philosophy and knowledge do not close, and we HAVE to learn to live with uncertainty, and judgement.

Relative to Bohmian mechanics vs. QM, quoting the linked answer on stoichiometry in physics:

The results of test cases to date, have been strongly trending against Bohm and in favor of Copenhagen; http://settheory.net/Bohm https://www.physicsforums.com/threads/back-pedaling-on-bohm.905194/. Bohm -- has not been widely considered refuted yet -- but these observations and test cases have drastically dampened enthusiasm for Bohm's theory.

The history of the last 200 years of philosophy, logic and science has been one where determinism and the "wish it were so" desire for certainties, have repeatedly lost when going head-to head with intrinsic uncertainties. Your citation of a trend line from "what we have been able to show" should lead you to abandon Bohm and determinism, not QM and indeterminacy.

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  • very inspiring! Nov 10, 2023 at 21:01
  • I think you are confusing subjective uncertainty with objective uncertainty even if your point about questioning assumptions stands. Of course there is no objective way to reason as per the dilemma you pointed out. But there is an objective matter about things, assuming realism. Joe was killed by Jack or not. This is a necessarily binary outcome regardless of whether we can prove this in a deductive way or not. The only place that has been shown to contain mind independent randomness is quantum mechanics but that is still an ongoing issue
    – user62907
    Nov 10, 2023 at 21:21
  • @thinkingman -- you can of course continue with a faith-based belief in certainties. Me, I am a fan of Sam Harris's "The End of Faith" approach of drawing legitimate inferences in cases of incomplete information and intrinsic uncertainty. There is a reasonable inference we can make that "objectivity" is an impossible standard, and all our thinking has to embrace subjectivity and judgement as core features. You may wish this were not so, but that is just wishing.
    – Dcleve
    Nov 10, 2023 at 21:39
  • @Dcleve You misunderstood what I said. How we feel or think about a proposition does not change the fact that it is either true or false. It doesn’t matter if we’re certain or uncertain. The reality that is out there is objective, atleast under realism.
    – user62907
    Nov 11, 2023 at 2:06
  • @thinkingman -- you assert, as unquestionably so for "realism", the LEM. This is NOT "unquestionable", as loads of logics are not just two-state. You also presume that the states of the world MUST be true and false, AND that A=A for realism (A=/=A for almost all physical objects over time). None of this is actually unquestionable.
    – Dcleve
    Nov 13, 2023 at 18:58
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Relativity unifies space and time, and in the process also a lot of other seemingly separate concepts: energy and momentum, electricity and magnetism, and so on. Quantum mechanics unifies classical particle and wave mechanics, which no one had ever even conjectured might be possible before its discovery.

Bohmian mechanics undoes all of that. Its underlying reality is separate particles and waves with entirely distinct natures in a quasi-Newtonian world with absolute time. The mathematics has to be carefully tuned to hide that reality from us; if the rules were a little different then we would be able to see it, and there's no apparent reason why the rules shouldn't be a little different.

It's not impossible, but does seem implausible, that seemingly different things are really aspects of the same thing at a deeper level, but then at an even deeper level they're different again. I think that's the strongest argument against any model resembling Bohmian mechanics.


I think the argument for determinism from cause and effect is weak also, because it's difficult to work out what cause and effect even means in a deterministic world. To believe that the flap of a butterfly's wing can cause a hurricane, you'd have to believe that everything after the flap is an inevitable consequence of what came before, but the flap itself is not; otherwise you might as well identify something else entirely as the cause. In a nondeterministic classical model where the flap is uncaused, it's still difficult to assign credit/blame unless it's the only uncaused event in the past light cone of the hurricane.

Quantum mechanics manages to avoid that problem. Because of the non-clonability of quantum information, you can trace the violation of Bell's inequality uniquely back to the generation of the Bell pair.

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  • Your determinism spiel makes no sense. Everything after the flap is an inevitable consequence of what came Bedford, and this includes the flap until the beginning of the universe. On the other hand, in QM, you have some necessary conditions mixed in with magic to efficiently cause something. The necessary conditions only determine possibilities and probabilities. The actual thing that happens occurs for no reason. If the actual thing happens for a reason, why are there probability distributions in the first place? Why not pure chaos
    – user62907
    Nov 10, 2023 at 3:57
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My instinct is always to remind myself that QM is just a model. It's one that has been phenomenally successful in allowing calculations that agree precisely with experimental results, but it's still just a model, and it's full of conceptual holes. For example, the Schrodinger equation itself is a mongrel mix of classical and quantum, in that it typically treats a quantum particle, such as an electron, as moving against a classical background potential, when in reality that potential field is the cumulative effect of other quantum particles. The theory behind a typical two slits experiment is that the screen in which the slits are formed acts as an impenetrable classical barrier to the wave function everywhere but at the slits themselves. Really??? How is that meant to work? Given all that, I suspect that QM will be replaced by something that is on more sound conceptual foundations, and who knows, maybe some kind of non-local effects will play a part in it.

I get the impression that the reason why physicists aren't rushing to embrace non-local effects is that the direction of travel for more than a century has been consistently away from a belief in action at a distance, so there's a kind of communal intellectual inertia at work.

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    I wonder that as a physicist you have to remind yourself that QM is a model. Because each theory in physics is a model. And each model is an idealization, incorporating some properties while dismissing other properties of the world. Textbooks normally advance from Schroedinger equation to Dirac equation and to QED. Successively incorporating spin, relativistic effects, electron-electron/positron scattering etc. – Why is the idealization of the impenetrable barrier problematic? Taking into account the tunnel effect would it change the characteristics of the double slit experiment? (1/2)
    – Jo Wehler
    Nov 9, 2023 at 22:15
  • – What is your reason to consider non-locality in order to base QM on more sound conceptional foundations? Do you consider entanglement a conceptual breakthrough for foundational questions? (2/2)
    – Jo Wehler
    Nov 9, 2023 at 22:16
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    @JoWehler many thanks. I'm very doubtful that I can adequately address your questions in comments, so might you consider posting them on Physics SE? The reason I stress that QM is a model is that I think that some of the issues that arise may be artefacts of the model, and that sometimes gets overlooked. Nov 10, 2023 at 6:51
  • @JoWehler the idealisation of the barrier is problematic to me because there is no physical explanation of how it is a barrier. The experiment works regardless of the material from which the barrier is made or the nature of the particles being studied. As for non-locality, I said maybe it will figure in whatever replaces QM- I have an open mind about it. Nov 10, 2023 at 6:57
  • @JoWehler if you want to know why I don't rule out the possibility of non locality playing a role, it is because we don't currently have an accepted theory that explains entanglement without it. Nov 10, 2023 at 7:00
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I take it nonlocal deterministic means nonlocal hidden variables theories.

There is a lot of history on nonlocal hidden variables that I can only jesture at:

For many decades von Neumann had an incorrect proof nonlocal hidden variables couldn't exist, even though Grete Hermann disproved it within a few years (that wasn't widely known for various reason). Then in the 50's Bohm's Theory was formalized, "once Bohm’s pilot wave paper came out it was obvious that von Neumann had to be wrong". The theory really took till Bell a little later to really hammer home how wrong von Neumann was. Also Bohr was very captivating apparently. And Einstein was not on board, even if he saw through von Neumann's error as he was strongly opposed to nonlocality. He had some strong reasons to be against it, but perhaps too strong/non-purely scientifically motivated. He read lot of philosophy, hence there are philosophical/philosophy of science reasons, such as how would science even be possible if nonlocality exists. But we can now see through science many ways it can. So, that's several reasons and lot of big names against it for decades.

This is all loosely paraphrased largely from Tim Maudlin's work such as What Bell Did. https://iopscience.iop.org/article/10.1088/1751-8113/47/42/424010

Maudlin is a founder of the John Bell Institute which specifically aims to further develop Bohmian Mechanics. It's by no means unanimous these types of theories are less plausible.

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