Talk:Bell's theorem

	Mathematics portal This article is within the scope of WikiProject Mathematics, a collaborative effort to improve the coverage of mathematics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.MathematicsWikipedia:WikiProject MathematicsTemplate:WikiProject Mathematicsmathematics
Mid	This article has been rated as Mid-priority on the project's priority scale.

Physics High‑importance

	Physics portal This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics
High	This article has been rated as High-importance on the project's importance scale.

Archives

Index

Archive 1	Archive 2	Archive 3
Archive 4	Archive 5	Archive 6
Archive 7	Archive 8	Archive 9
Archive 10

This page has archives. Sections older than 90 days may be automatically archived by when more than 1 section is present.

Article is self contradictory re locality

Intro says experimental results are incompatible with local hidden variable theories, but Manyworlds section says Bell's doesn't apply and it is a dynamically local theory. This is clearly inconsistent with the intro. Suggest intro be changed to "*most* local hidden variable theories" Joncolvin (talk) 16:48, 31 October 2024 (UTC)[reply]

No. Hidden worlds don't seem to count as "hidden variables". So all local hidden variables are incompatible. Johnjbarton (talk) 17:16, 31 October 2024 (UTC)[reply]

The MWI (or rather, all the various versions of it proposed over the years) is not a hidden-variable model. In a hidden-variable model, either a wavefunction is a probability distribution over the true physical states, or the hidden variables exist in addition to the wavefunction. In MWI, the wavefunction is physical reality. XOR'easter (talk) 22:15, 31 October 2024 (UTC)[reply]

Clarification of the mathematical hypotheses of Bell's theorem

Bell's work started from an in-depth analysis of the logic underlying EPR's reasoning, as he himself explained. This fact must be clearly highlighted. Furthermore, the only two mathematical hypotheses present in the theorem must be listed clearly, which are the locality hypothesis and the statistical independence hypothesis.

The proposed changes are there: https://en.wikipedia.org/w/index.php?diff=1275703974 Mr.Data0101 (talk) 18:42, 14 February 2025 (UTC)[reply]

Your proposed changes do not accomplish the goals you outline and they are not supported by references. Johnjbarton (talk) 18:52, 14 February 2025 (UTC)[reply]

These changes DO accomplish the goals I outlined and DO add the references.

https://en.wikipedia.org/w/index.php?title=Bell%27s_theorem&diff=next&oldid=1275703974 Mr.Data0101 (talk) 18:54, 14 February 2025 (UTC)[reply]

As far as I can tell you added historical primary references. To build a case for your changes you need reliable secondary sources. Please see WP:PSTS. Your addition makes the assertion that the probability hypothesis is related to free choice, but you give no source for that claim.

Later your addition say "We note...", which is an editorial comment. In its place we need a reliably source comment. Johnjbarton (talk) 20:23, 14 February 2025 (UTC)[reply]

Bad ending to the section on Bell's 1964 paper.

The section on Bell's paper now ends with

In other words, Bell's 1964 paper uses the EPR criterion to argue that local hidden variables exist, and then demonstrates that local hidden variables are incompatible with quantum mechanics.

This is not good. Bell is our hero in this article. Here he argues "that local hidden variables exist". That is not what Bell says. If we claim that it is what he said, we need a secondary reference for that claim. I tried a simple fix but @XOR'easter reverted it.

Also what is a " probability-1 prediction "? The reference says nothing like that. Johnjbarton (talk) 01:50, 15 February 2025 (UTC)[reply]

It's just paraphrasing the beginning of Bell's section 2: Since we can predict in advance the result of measuring any chosen component of

{\vec {\sigma }}_{2}

, by previously measuring the same component of

{\vec {\sigma }}_{1}

, it follows that the result of any such measurement must actually be predetermined. Since the initial quantum mechanical wave function does not determine the result of an individual measurement, this predetermination implies the possibility of a more complete specification of the state. Perfect correlation, predicting with probability 1, it's all in there. (The EPR criterion takes "certainty" and "probability equal to unity" as synonymous.) Bell argues from the EPR criterion, a form of locality, and the perfect (anti)correlations of the spin singlet state that a local hidden variable

\lambda

would have to exist, and then he shows that the predictions based on the assumption of

\lambda

existing are inconsistent with quantum physics. XOR'easter (talk) 02:59, 15 February 2025 (UTC)[reply]

The section of Bell you quote starts out: "the EPR argument is the following". So it is EPR that argues that local hidden variables exist, not Bell. Bell demonstrated this is inconsistent with QM. Thus EPR was wrong. That is the take-away we should leave the reader. Johnjbarton (talk) 03:41, 15 February 2025 (UTC)[reply]

I changed "probability-1" to "completely certain" (I know I've read both in the literature, but the latter might be less jargon-y) and have made various other phrasing adjustments. XOR'easter (talk) 05:14, 15 February 2025 (UTC)[reply]