Talk:Bell's theorem

EPR on lead

I think Nuretok has a point in the edit that XOR'easter reverted. The sentence is correct, but not helpful. But the more fundamental problem is that the lead is going into detail about a result that inspired Bell. Even if the detail was about Bell's theorem itself it wouldn't belong in the lead. Details about EPR are right out. To compound the issue the lead is already extremely long. Therefore I removed all mentions to EPR from there. It's already discussed in the History section, and that's where it belongs.

This also opens space for mentioning the variations of Bell's theorem that Ianjauslin wanted to include last year. I think that's much more relevant than historical background. Tercer (talk) 07:18, 10 June 2024 (UTC)

I'd been wanting to shorten the lede for a while now, so that seems like a good move. One could maybe make a case that EPR ought to be mentioned up top, but we definitely had too much on it, and I am content with leaving it out as is done presently. XOR'easter (talk) 16:11, 10 June 2024 (UTC)

While I agree that the intro was too long and we don't need all the history jammed in there, EPR->Bell's theorem is one of the most significant historical connections in QM. Per our general guidelines to summarize in the intro, a sentence related to EPR is due. Johnjbarton (talk) 16:42, 10 June 2024 (UTC)

I don't object to mention it, as opposed to explain it, but I'm not going to do it myself.

Encouraged by your comments I went a bit further in shortening the lead, eliminating what I think was just repetition. Tercer (talk) 17:20, 10 June 2024 (UTC)

“Not in doubt”

The intro states:

While the significance of Bell's theorem is not in doubt,

But in fact it is: https://www.degruyter.com/document/doi/10.1515/phys-2017-0088/html

The simulation results are parallel to those obtained in actual optical realizations of the basic Bell-test. The fact that this manifestly classical arrangement leads to a violation of a Bell Inequality must mean either that classical optics also is irreal or nonlocal; or that the significance of Bell’s analysis is misinterpreted, even invalid.

[…]

When this consideration for the most elementary optical version of experimental tests of Bell’s analysis is correctly taken into account, the derivation of a Bell Inequality does not go through. Thus, conclusions drawn from the empirical violation of a Bell Inequality are rendered invalid.

Does this perhaps deserve a mention somewhere? Spidermario (talk) 21:31, 30 September 2024 (UTC)

Not really, no. There's a fringe cottage industry of Bell denialists who churn out screeds that (a) insist all other physicists are wrong, (b) disagree with each other about why, and (c) vanish without trace. (Or they get cited once in someplace like an MDPI journal, which amounts to the same thing.) People who work in the field for any substantial length of time adopt the attitude of patent clerks receiving yet another application for a perpetual-motion machine. XOR'easter (talk) 22:39, 30 September 2024 (UTC)

The reference you linked,

• Kracklauer, A. F.. "Bell’s “Theorem”: loopholes vs. conceptual flaws" Open Physics, vol. 15, no. 1, 2017, pp. 754-761. https://doi.org/10.1515/phys-2017-0088

has one citation, a sign that mainstream physicists don't believe the work with worth mentioning. Johnjbarton (talk) 23:56, 30 September 2024 (UTC)

And that citation is in Entropy, which provides basically no meaningful peer review. XOR'easter (talk) 00:42, 1 October 2024 (UTC)

A possible mistake?

Written by the author - A₀ A₁ + A₀A₃ + A₂A₁ - A₂A₃ . Obviously, the following equality is true: (A₀ + A₂)A₁ + (A₀ - A₂)A₃ etc. But the result of ONE MEASUREMENT can be ONLY 2 parameters. For example, A₀ and A₃ (if they have "heads" by flipping a coin for this ONE measurement). A₂ and A₁ are not determinated in this measure and are INDETERMINATE. Then what is it (A₀ + A₂) and (A₀ - A₂) - is unclear... Further construction is collapsing. Apparently, it would immediately move on to the average values and write a chain of equalities for them? 144.206.128.253 (talk) 18:16, 1 October 2024 (UTC)

In the text, uppercase letters refer to measurement results, while lowercase letters stand for the hidden properties. By assumption, the hidden properties exist whether or not they are measured. So, we can manipulate the lowercase variables by the regular rules of algebra however we like, without worrying about them being "indeterminate". The whole point is to deduce the consequences of that assumption and then show that those consequences conflict with the predictions of quantum mechanics. XOR'easter (talk) 19:00, 1 October 2024 (UTC)

Yes... Clearly.

Thanks. 144.206.128.253 (talk) 13:42, 2 October 2024 (UTC)

Recent review

I was surprised that this review was not cited.

• Wharton, K. B., & Argaman, N. (2020). Colloquium: Bell’s theorem and locally mediated reformulations of quantum mechanics. Reviews of Modern Physics, 92(2), 021002.

Among many topics it mentions Everett's model, the subject of recent edits. Johnjbarton (talk) 17:20, 18 October 2024 (UTC)

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)

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)

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)