Timeline for answer to Is This Video on Bell's Theorem Wrong? by rob
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| 18 hours ago | comment | added | Mark Foskey | "I don't have a lot of confidence that everyone involved in a discussion will come to the table using all of these technical terms the same way." - This line by itself is enough for a +1. | |
| 19 hours ago | comment | added | schtandard | @Obie2.0 "Granted, I have never heard anyone say that how QM "says" it works is obviously pilot wave theory." I have. Well, maybe not in the sense that it is "obviously correct", but certainly in the sense that it is an "obvious completion": If a plane wave features a probability current predicting where particles are found, isn't it obvious that this should represent an actual particle current? You get the guiding equations from there. (Your point stands, of course.) | |
| 19 hours ago | comment | added | rob♦ | Muller has also been up-front about YouTube's perverse incentives re engagement, where making controversial videos which generate lots of responses can generate extra short-term revenue at the cost of reputation. The incident you describe was in 2021; I think the research and production team has grown since then. | |
| 19 hours ago | comment | added | rob♦ | @Cleonis I was actually thinking specifically about Muller's Poynting vector/ transmission line video when I wrote that top paragraph. I personally didn't internalize the way that fields carry energy in transmission lines until I had a particular problem as a postdoc, and I had to remind several highly-qualified people about transmission-line physics in order to spend a few thousand dollars on some unusual reflection-swallowing terminators. With that context I found the first video perfectly clear, but I also found many of the skeptical responses unsurprising. Everybody whiffs one. | |
| 20 hours ago | comment | added | Nilay Ghosh | Certainly, too long for a comment. +1 ;) | |
| yesterday | comment | added | Cleonis | About Derek Muller: my two cents: Derek Muller used to be good, but somewhere along the way he lost the quality/mindset that made him good. Over the past years a recurring theme has been that he takes on a subtle issue, and then approaches it with a sledge hammer. Example: how is electric energy transmitted? Derek came out with a provocatively titled video, and then other youtube channels such as AlphaPhoenix had to step in and get the physics right. A little time later Derek made a follow-up video, taking cues from AlphaPhoenix etc., acknowledging how he should have presented the subject. | |
| yesterday | comment | added | rob♦ | @tparker Thanks for your comments (and for your parallel answer). | |
| yesterday | comment | added | tparker | But either way, I would say that the specific form of the Schrodinger equation is not the root of the issues around locality in QM. Those issues mostly has to do with the nonlocal nature of measurement, which is largely orthogonal to the details of the Schrodinger equation and can already be understand in a situation where the Hamiltonian is trivial. | |
| yesterday | comment | added | tparker | And that most people in that camp use the term "Schrodinger's equation" to mean the general equation $i \hbar \frac{d|\psi\rangle}{dt} = \hat{H} |\psi\rangle$, where $\hat{H}$ could be a nonrelativistic Hamiltonian of the form $\frac{\hat{p}^2}{2m} + V(\hat{x})$, but it could also be the integral over spacetime of a local Hamiltonian density for a relativistic quantum field theory. (As the zeroth component of the energy-momentum four-vector, it is not Lorentz invariant, but it is (non-manifestly) Lorentz covariant.) | |
| yesterday | comment | added | tparker | @rob I think this is an outstanding answer (+1), but I would quibble a bit with your claim that most people use the term "quantum mechanics" to refer to the nonrelativistic version. There's definitely inconsistent usage in the community, but I would guess than the (slight) majority usage these days is probably that most people use the term "quantum mechanics" to also encompass relativistic quantum field theory, and use the phrase "nonrelativistic quantum mechanics" to restrict to the "$\frac{\hat{p}^2}{2m} + V(x)$" version. | |
| yesterday | comment | added | tparker | @Obie2.0 Perhaps the granddaddy of all interpretations of QM that are "local realist" (under some plausible definition of that phrase) but are still fully compatible with the Bell inequality experiments goes by the name of "superdeterminism". But be warned: the mere mention of superdeterminism can be pretty violently triggering to some quantum physicists, and some (but certainly not all) will yell that it doesn't even qualify as a possible scientific theory. That topic is even more of a Pandora's box than the box that holds Schrodinger's cat. | |
| yesterday | comment | added | rob♦ | @Obie2.0 Search for literature about what loopholes were and weren't closed by the 2015 experiments. You might ask a follow-up question. | |
| yesterday | comment | added | Obie 2.0 | @rob - You write "Other proposals remain, but my understanding is that they make some assumptions which the community finds more improbable than the simpler idea that quantum mechanics works how it says it works. " Could you elaborate? I have heard knowledgeable people say that how quantum mechanics "says" it works is obviously some kind of many-worlds interpretation (see one of the other answers), or obviously some kind of non-deterministic/Copenhagen-style theory. Granted, I have never heard anyone say that how QM "says" it works is obviously pilot wave theory. | |
| yesterday | comment | added | rob♦ | @RobertFurber Very interesting. Thanks! | |
| yesterday | comment | added | Robert Furber | "The theorem is that the quantum-mechanical superposition gives the largest possible correlations." Absolutely not. Bell's inequality can be violated more severely than is possible with quantum mechanics, as shown by Popescu and Rohrlich. This is often called a "PR-box". | |
| yesterday | comment | added | rob♦ | @schtandard No, I don't have a good reference for that comment. Perhaps I have misremembered. The toy model in Bell's paper is the "local variables" model that people are referring to when they say things like "local variables predict an anticorrelation of 1/3 while quantum entanglement predicts an anticorrelation of 1/4," as described at length in the video and in most other expositions of the problem. | |
| yesterday | comment | added | schtandard | "Bohm's "pilot wave" model was ruled out in 2015" Do you have a reference for this? As far as I know, the experimental statistics predicted by Bohmian mechanics are identical to those of Copenhagen QM, so I don't see how it could be ruled out. (I'm not familiar with Aspect or Bell's toy model you refer to, so maybe I'm missing your point.) | |
| yesterday | comment | added | schtandard | I think @Ruffolo has a point in the sense that Bell's theorem does rule out local models that are compatible with QM. Of course, it is the experiment that rules out local models as a description for reality. | |
| 2 days ago | comment | added | rob♦ | @Ruffolo In the spirit of my remarks about a journey of understanding: I disagree with you, but I'm not yet done thinking about your remarks. | |
| 2 days ago | comment | added | Ruffolo | We could say that the theorem does not end the question by itself, but to say that it just defines the question is again, too much. If you rely on the quantum postulates and the prediction power of it, the result of the theorem is a theoretical answer for the question. Of course Physics is an experimental science, so theoretical answers are not enough, but they are answers as well | |
| 2 days ago | comment | added | rob♦ | @Ruffolo You have misread what I wrote (which I understood was also of the points in the video). Bell's theorem defines a question. We draw conclusions about the question based on experimental evidence, not based on a mathematical theorem. If I remember correctly, the toy model in Bell's 1964 paper was ruled out by Aspect in the 1980s; Bohm's "pilot wave" model was ruled out in 2015. Other proposals remain, but my understanding is that they make some assumptions which the community finds more improbable than the simpler idea that quantum mechanics works how it says it works. | |
| 2 days ago | comment | added | Ruffolo | I think that to say "Bell's theorem doesn't rule out anything" is a bit too much. It is a no-go theorem, so it indeed says that a particular situation is physically impossible. The situation is of a local model, satisfying all the constraints that we could imagine for a realistic description of the physical systems, reproducing all possible quantum correlations in a Bell test. | |
| 2 days ago | comment | added | rob♦ | postscript: my fruit bowl had two apples in it. | |
| 2 days ago | comment | added | rob♦ | I have poor self-control about figuring things out. | |
| 2 days ago | comment | added | naturallyInconsistent | +1 lol you start out saying that you are just writing a long comment, and then actually ended up with a proper full answer including watching the whole video. | |
| 2 days ago | history | edited | rob♦ | CC BY-SA 4.0 |
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| 2 days ago | history | edited | rob♦ | CC BY-SA 4.0 |
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| 2 days ago | history | edited | hft | CC BY-SA 4.0 |
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| 2 days ago | history | answered | rob♦ | CC BY-SA 4.0 |