Is this popular description of entanglement correct?

  • #51
PeterDonis
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I don't see how one can talk about Bell's theorem without mentioning hidden variables.
Bell's theorem of course explicitly includes an assumption about hidden variables, so yes, if you want to talk specifically about Bell's theorem, you're going to be talking about hidden variables. (I'll give an explicit example of such talk below.)

However, Bell's theorem, in itself, says nothing whatever about either quantum mechanics, or the results of actual experiments. Of course Bell knew that QM predicts violations of the Bell inequalities (that's why he went to the trouble of publishing his theorem), and we now know that experiments confirm those predictions of QM. But you can talk about QM and experimental results without talking about hidden variables at all. Hidden variable models are not the only possible models. You can even talk about the fact that QM/experimental results violate the Bell inequalities without talking about hidden variable models.

I claimed that one cannot prove, based on Bell's theorem that EM cannot violate them
If you are really unable to see the obvious proof, consider: EM is a local hidden variable model in the sense that Bell's theorem uses that term. (So is classical General Relativity.) Therefore, by Bell's theorem, its predictions must satisfy the Bell inequalities.

There is no other theory of relativity.
If you define "theory of relativity" to only include classical relativity, then you have excluded quantum field theory. In which case your definition of "theory of relativity" is irrelevant to this discussion.

let's assume for the sake of the argument that A caused B.
No, let's define what "A caused B" means in terms of testable predictions. Otherwise it's just meaningless noise as far as physics is concerned. Can you do that?
 
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  • #52
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If you are really unable to see the obvious proof, consider: EM is a local hidden variable model in the sense that Bell's theorem uses that term. (So is classical General Relativity.) Therefore, by Bell's theorem, its predictions must satisfy the Bell inequalities.
Andrei is right about the fact that classical EM can in principle violate Bell's inequality. One just has to fine-tune the initial conditions of the full system accordingly. It's very difficult to write down, but as Bell pointed out in his paper "La nouvelle cuisine," local realism can in principle be saved through freedom of choice loophole, i.e. by violating a certain statistical independence assumption. The debate is not really about whether this is possible, but whether the required amount of fine-tuning is realistic.
 
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  • #53
PeterDonis
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One just has to fine-tune the initial conditions of the full system accordingly.
Ah, yes, I had forgotten about superdeterminism.
 
  • #54
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Andrei is right about the fact that classical EM can in principle violate Bell's inequality. One just has to fine-tune the initial conditions of the full system accordingly.
Ah, yes, I had forgotten about superdeterminism.
Andrei doesn't argue well enough that it would "help" if he defended superdeterminism. Sabine Hossenfelder argues much more subtle, and got many more things right. But even she has trouble to make people see her point(s). Gerard 't Hooft also doesn't argue very convincingly. Tim Palmer seems to argue fine, but he is less "active/vocal/aggressive".
 
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  • #55
DrChinese
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OK, let's assume for the sake of the argument that A caused B. In this case you need to specify an absolute reference frame, to show that A happened first. Since QFT does not specify this frame, it's predictions would be inconsistent (different observers would disagree on how the same experiment happened).

1. Your conclusion is incorrect. QFT does not specify a cause-effect relationship, and so nothing is inconsistent. The error is asserting A causes B in a Bell test. Everyone knows that the relative ordering of Alice/Bob measurements has no observable effect on the outcome.

2. Earlier, you mentioned long range EM effects (which presumably are bound by c). Bell tests have been performed where the measurement settings are changed midflight so that there is no possibility of EM effects between the angle settings of the detection systems. And it is in fact those settings which determine the statistical outcomes in Bell tests.

3. I hate it when Superdeterminism is brought up. There is NO THEORY/INTERPRETATION OF SUPERDETERMINISM that explains Bell test results.

Superdeterminism a general idea, as specific as using the term "God". You can just as easily say God picks the individual outcomes of Bell tests, and that therefore nature can be local deterministic. You aren't explaining anything. An actual theory of Superdeterminism would necessarily have so much baggage, it would be easier to believe in God by way of Occam's Razor. Neither of which would make much sense for a quantum theory.
 
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  • #56
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3. I hate it when Superdeterminism is brought up. There is NO THEORY/INTERPRETATION OF SUPERDETERMINISM that explains Bell test results.
Careful, there is a difference between reproducing the prediction of QM, and violating Bell's inequality. If you create a model and are not careful to properly respect the independence assumption, then you easily can produce a violation. Maybe you believe that you have found some special loophole in Bell's theorem that nobody has discovered before. And Sabine Hossenfelder correctly points out how such "easily overlooked" mistakes could look like. For example, you could have defined a hidden parameter relative to some of the detector settings ("because it seemed to be more convenient for your calculations").
 
  • #57
PeterDonis
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there is a difference between reproducing the prediction of QM, and violating Bell's inequality
@DrChinese was talking about actual experimental results. The experiments in question are deliberately set up to have the measurement settings be independent of the process that produces the particles being measured. Superdeterminism in that context amounts to the claim that it is impossible in principle to set up experiments to actually have those things be independent, no matter how hard you try--even including having the events at which the measurement settings are determined be spacelike separated from the events that produce the particles being measured (as well as the measurement events themselves being spacelike separated). @AndreiB has already said he's okay with that position, but that doesn't make it any less extreme.
 
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  • #58
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@DrChinese was talking about actual experimental results.
Superdeterminism a general idea, as specific as using the term "God". You can just as easily say God picks the individual outcomes of Bell tests, and that therefore nature can be local deterministic. You aren't explaining anything.
To me, that section doesn't sound like talking about actual experimental results.

Superdeterminism in that context amounts to the claim that it is impossible in principle
Well, but superdeterminism is also the name given to a specific class of "loopholes" (or "assumptions") in Bell's theorem. Accidentally producing a model that violates those assumptions has nothing to do with "the claim that it is impossible in principle ..."

That this claim is needed for a "successful" model using superdeterminism is an additional assumption on top of the less controversial role (absence of) superdeterminism plays as a name for a specific assumption in Bell's theorem.
 
  • #59
PeterDonis
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To me, that section doesn't sound like talking about actual experimental results.
Um, what? It says right there in what you quoted: "the individual outcomes of Bell tests".

superdeterminism is also the name given to a specific class of "loopholes" (or "assumptions") in Bell's theorem.
They aren't loopholes in the theorem. The theorem is a mathematical theorem. They are proposed models that violate one of the assumptions of the theorem, while still being deterministic in some sense in which the proposer of the model thinks standard QM isn't.

Accidentally producing a model that violates those assumptions has nothing to do with "the claim that it is impossible in principle ..."
I don't see how this is relevant at all to what I said. I was talking about superdeterministic models as they are proposed by those who argue for superdeterminism, not some accidentally produced model that happens to violate one of the assumptions of Bell's theorem.
 
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  • #60
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3. I hate it when Superdeterminism is brought up. There is NO THEORY/INTERPRETATION OF SUPERDETERMINISM that explains Bell test results.
Well, there is currently no generally satisfactory interpretation of quantum mechanics in the first place. All of them suffer from certain pecularities one way or the other, otherwise we wouldn't have these endless discussions. There has been renewed interest in superdeterminism recently because these discussions were going nowhere. And it's easy in principle to come up with a list of a hundred quadruples ##A,\alpha, B,\beta## that obeys the locality condition, but violates statistical independence.
Superdeterminism a general idea, as specific as using the term "God". You can just as easily say God picks the individual outcomes of Bell tests, and that therefore nature can be local deterministic. You aren't explaining anything. An actual theory of Superdeterminism would necessarily have so much baggage, it would be easier to believe in God by way of Occam's Razor. Neither of which would make much sense for a quantum theory.
I agree that superdeterminism is a peculiar solution to the Bell mystery, but non-locality is no less peculiar. In fact, the knob on Alice's polarizer must, when turned, somehow magically have to capability to modify Bob's particle despite the fact that it was never built specifically to have this capability. Why doesn't it manipulate any other particle in the universe as well? Why doesn't it turn on the TV in the livingroom? What is so specific about Bob's particle that a completely unrelated knob on Alice's device can manipulate its properties? The excess of the speed of light is not even the most peculiar feature in this scenario.

Thus, for me, the lesson of Bell's theorem is not that the world is non-local, but that we need to give up the idea of classical determinism altogether and replace it with something else. Superdeterminism is not the solution either. Maybe we also need to rethink what a causal mechanism is.
 
  • #61
PeterDonis
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the knob on Alice's polarizer must, when turned, somehow magically have to capability to modify Bob's particle
This is only true according to certain interpretations of QM.
 
  • #62
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This is only true according to certain interpretations of QM.
Agreed, but I was specifically talking about non-local interpretations of QM in that post.
 
  • #63
PeterDonis
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I was specifically talking about non-local interpretations of QM in that post.
Which interpretations of QM do you consider "non-local"?
 
  • #64
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Which interpretations of QM do you consider "non-local"?
When I wrote that paragraph, I was specifically thinking about Bohmian mechanics, but I guess it applies to all non-local hidden variable theories.
 
  • #65
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I don't see how this is relevant at all to what I said. I was talking about superdeterminism
You replied to me, and I was talking about how easy it is to accidentally produce a superdeterminsic model. And quoting "the individual outcomes of Bell tests" out of context doesn't make you more right. You simply did not try to understand what I was trying to say.

Bell's theorem is (also) a mathematical theorem, and loading one of its assumptions with connotations can sometimes trigger a mathematician (like me) to protest. What triggered me was the peppering of the connotations with statements like "You can just as easily say God picks the individual outcomes ... You aren't explaining anything."

In the end, I believe nature is non-local in certain ways. So I certainly don't try to fight the conclusions of Bell's theorem. But I do think that Sabine Hossenfelder and Tim Palmer are on a right track to make progress in our understanding of quantum mechanics. Not in the sense of removing counter-intuitive elements of QM, but in the sense of making an additional counter-intuitive element of QM more concrete and "analyzable", just like Bell did with non-locality.
 
  • #66
PeterDonis
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I was talking about how easy it is to accidentally produce a superdeterminsic model.
And I was pointing out that that is irrelevant to this discussion, since, first, @DrChinese was not proposing any model, he was talking about the actual experimental results, and second, those who claim that superdeterminism is a valid explanation of those experimental results are not basing such a claim on models produced "accidentally". They aren't basing the claim on any models at all. Nobody has proposed an actual superdeterministic model that explains the actual experimental results we have on measurements of entangled particles. Which is what @DrChinese said.

What people like Hossenfelder should do, if they want to actually argue for superdeterminism as a valid explanation, is not to complain that other people could "accidentally" produce a superdeterministic model; it is to deliberately produce such a model themselves and show how it explains the experimental results. Then we would have an actual model to evaluate.

And quoting "the individual outcomes of Bell tests" out of context doesn't make you more right.
I didn't quote it out of context. I quoted it directly from what you quoted from @DrChinese; you accompanied that quote with the claim that "that section" (what you quoted) "didn't sound like talking about actual experimental results". I don't know what would sound like that to you if the explicit phrase "the individual outcomes of Bell tests" doesn't.

You simply did not try to understand what I was trying to say.
As the saying goes, the fact that I disagree with you does not mean I don't understand your position.
 
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  • #67
PeterDonis
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loading one of its assumptions with connotations can sometimes trigger a mathematician (like me) to protest.
The fact that you were "triggered" does not automatically make what you are claiming true.
 
  • #68
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As the saying goes, the fact that I disagree with you does not mean I don't understand your position.
But here again you give me the impression that you don't try to understand me. What I wrote was not related to a position. I replied "Careful, there is a difference ..." to a section that read "I hate it when ... NO THEORY/INTERPRETATION OF SUPERDETERMINISM ...".

The fact that you were "triggered" does not automatically make what you are claiming true.
What do I claim from your point of view? I explain why I replied to DrChinese. If you reply to me indicating that you don't get why I replied, or how my reply is related to what DrChinese wrote, it is only natural that I will try to clarify those points.
 
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  • #69
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By the way, it's not true that there exist no superdeterministic models for the Bell correlations. A couple of them are cited in the paper https://arxiv.org/abs/1511.00729 (section 4.2) and the author even argues that they only require a minor violation of statistical independence.
 
  • #70
PeterDonis
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What I wrote was not related to a position. I replied "Careful, there is a difference ..." to a section that read "I hate it when ... NO THEORY/INTERPRETATION OF SUPERDETERMINISM ...".
Yes, and your reply had nothing to do with what @DrChinese actually said. Your reply talked about models and how easy it is to "accidentally" produce a model that violates the independence assumption. @DrChinese was talking about actual experimental results and whether any superdeterministic model could explain them.

For an example of what a substantive reply to what @DrChinese actually said would look like, see post #69 by @Nullstein just now.

What do I claim from your point of view?
You appear to me to be claiming that superdeterminism can provide a valid explanation for the actual experimental results we have on measurements of entangled particles.

I explain why I replied to DrChinese.
You explained that you were "triggered", yes. That explains why you replied, but as I pointed out, it doesn't serve as justification for what you said being true. Or having anything to do with what @DrChinese said, for that matter.

If you reply to me indicating that you don't get why I replied, or how my reply is related to what DrChinese wrote, it is only natural that I will try to clarify those points.
I have already explained, several times now, why your reply was not related to what @DrChinese wrote. Nothing in your responses has addressed anything I said about that.
 
  • #71
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You appear to me to be claiming that superdeterminism can provide a valid explanation for the actual experimental results we have on measurements of entangled particles.
Good to know. I certainly did not intent to claim that. I did try to defend Hossenfelder and Palmer to a certain limited extent, namely that they do understand many important points related to superdeterminism. Not because I want to convince anybody, but simply because it is my honest opinion, and I don't want to lie. But because I have the strong impression that the word "superdeterminism" is heavily loaded with connotations, I also don't want to be drawn into discussions about it. (But I found it valid to reply with "Careful, ..." to a statement that went "I hate ... SOME STATEMENT IN ALL CAPS ...", because it exemplified exactly this loaded state of affairs.)

Nothing in your responses has addressed anything I said about that.
Good to know. Then I will stop here. Thanks for trying to clarify to me what DrChinese really intended to say. Sorry that I have misunderstood his intention because he somehow "triggered" me.
 
  • #72
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Well, there is currently no generally satisfactory interpretation of quantum mechanics in the first place.

I do not think it is a sound scientific practice to state personal opinions as scientific facts. Much better to say there is no generally accepted interpretation of QM everybody agrees on. Some think many interpretations are simply a continuation of discussions about what probability is:
https://math.ucr.edu/home/baez/bayes.html

Yet strangely, interpretations of probability do not seem to generate much discussion. Most that use probability, such as actuaries, do not worry about it at all. Indeed, when I studied it, I was blissfully unaware of the issues. But then again, I did applied math. Pure math guys may go into it more.

Thanks
Bill
 
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  • #73
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let S0 be the microscopic state (position/momenta of charge particles+electric/magnetic fields) of the source at a certain (initial) time before the experiment. Let D10 and D20 be the corresponding microscopic states of the detectors. Since all charged particles interact, the hidden variable, lambda (the polarisations of the emitted EM waves at some later time) would be given by a very complicated function like:

lambda = f(S0,D10,D20).

So, lambda cannot be independent of either D10 or D20, it's a function of them.
Being a function is not in conflict with being independent. A good pseudorandom number generator gives you a pseudorandom number as function u of the seed s and the number of applications of the generator i. In principle it maybe simply defined by a function u(i+1,s) = F(u(i,s)) which gives widely different results even if only a single bit is changed. Nonetheless, for all the usual tests of randomness, these sequences will look like random sequences. In particular ##P(u(i+1,s)|u(i,s)\in[u_0,u_1]) = P(u(i+1,s))## if that part ##[u_0,u_1]## specifies only a minor part of the bits contained in the value ##u(i,s)## itself. So even explicit functions can lead to independence according to all the applicable statistical criteria.
I have no idea what correlations, if any, can be generated in this way.
And I tell you that to destroy remaining correlations is easy, adding a pseudorandom number will do the job. Instead, creating correlations is impossible. Observable correlations require causal explanations.

There is no need to posit any conspiracy. Interacting objects are not independent, this is the only point I am trying to make. Since one premise of Bell's theorem is not fulfilled, the conclusion does not follow. The conclusion might still be true, but not necessarily so.
It is a known property of conspiracy theories that one cannot reject them by pure logic. The basic principles of causality you have to accept too.

As explained, the above argument applies only to interacting systems. Even in a Bell test, the macroscopic settings of the detectors are independent parameters (since the interaction between their constituent particles cannot determine a macroscopic rotation of the device).
No. Microscopic causes can influence macroscopic detector settings and often do it. Without this, no quantum measurements would be possible at all. The experimenters can decide to use microscopic particles by design, say, by using a Geiger counter to decide what to measure. But even if they throw macroscopic dices the results can be influenced by microscopic turbulences which can be caused by even atomar causes.

So, you can assume independence in all experiments where the microscopic arrangement is not relevant, which includes almost everything except Bell tests and a few other quantum experiments.
I disagree. There is no experiment with statistical outcomes where the outcome does not depend on microscopic causes too.

I also think that the importance of the independence assumption is greatly exaggerated. Most experiments do not depend on it.
I disagree. There is no experiment with statistical outcomes which could not be explained away if one cannot make an independence assumption.
It's not about inventing anything. You analyze the situation and determine, based on what we know, what is independent and what is not. It's a scientific, objective criteria.
Using your way of reasoning in the microscopic world the conclusion will be simple - nothing is independent. So, no analysis is really necessary, the result will be all the same.
 
  • #74
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The error is asserting A causes B in a Bell test. Everyone knows that the relative ordering of Alice/Bob measurements has no observable effect on the outcome.
It follows only that as the hypothesis ##A\to B##, as the hypothesis ##B\to A## is viable given the outcome. I don't understand why this would make one of the two possible causal explanations an error.
An actual theory of Superdeterminism would necessarily have so much baggage, it would be easier to believe in God by way of Occam's Razor. Neither of which would make much sense for a quantum theory.
Good point.
 
  • #75
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But you can talk about QM and experimental results without talking about hidden variables at all. Hidden variable models are not the only possible models. You can even talk about the fact that QM/experimental results violate the Bell inequalities without talking about hidden variable models.
The problem is that we have the EPR argument, a form of it being presented in my #7 post. This leaves you with two options: non-locality (in the sense that A causes B even if A and B are space-like) and hidden variables. Rejecting hidden variables necessarily implies non-locality. I am not saying it's wrong but I still think that locality is the most reasonable option, hence hidden variables are the most reasonable option.

If you are really unable to see the obvious proof, consider: EM is a local hidden variable model in the sense that Bell's theorem uses that term. (So is classical General Relativity.) Therefore, by Bell's theorem, its predictions must satisfy the Bell inequalities.
My whole point is that EM has not been shown to obey the statistical independence requirement. Without statistical independence, Bell's conclusion does not follow.

If you define "theory of relativity" to only include classical relativity, then you have excluded quantum field theory. In which case your definition of "theory of relativity" is irrelevant to this discussion.
Relativity is about the space-time structure. There is no quantum theory of space-time. QFT is just an example of physical theory using the SR background in the same way non-relativistic QM uses the Newtonian background.

No, let's define what "A caused B" means in terms of testable predictions. Otherwise it's just meaningless noise as far as physics is concerned. Can you do that?
It's a reductio ad absurdum argument. If you assume, for the sake of the argument that it is the case that A caused B you get into some unpleasant consequences, like the requirement of defining an absolute reference frame. If you don't like those consequences you must deny the premise (A caused B) which, given the EPR argument presented in my #7 post, necessary implies the existence of hidden variables.

I do not think that A causes B, so I take the hidden variable route.
 

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