Quantum nonlocality and "spooky action at a distance"

[DrChinese]

[Moderator's note: Thread spun off from previous discussion due to topic/subforum change.]

1. But when you analyze the results, they look as if the state of each particle pair was decided from the beginning.

2. One is tempted to think in terms of a "spooky action at a distance," that when photon A reaches the polarizer, it affects the state of photon B. But in actuality, our observation of results is post-facto, after all interactions are finished and we can analyze the results of all detectors jointly.

3. The "weirdness" of QM comes from the fact that while everything looks like it was decided from the beginning (my "or" scenario), we know that it is not the case because we can make measurement choices after the particles have been sent on their way that show that they had to be in a superposition of states and entangled with each other.

4. I have feeling that you simply need to convince yourself that there is no actual "spooky action at a distance."

@DrClaude,

Respectfully, I am not meaning to disagree with you specifically. I see comments regularly more or less with the same perspective as you have presented above. However, I am going to challenge some of these statements, as they are not be supported by current generally accepted science.

----------------------

1. I agree with this. It is a useful perspective to think in terms of "as if". And you even get the right answer!2. By implication, you diminish evidence of "spooky action at a distance" by saying that evidence only appears "post-facto".

I don't know of any generally accepted scientific principle which changes the results of a scientific experiment based on when all of the results are fully available. And specifically, I challenge the idea that there is any difference in the scientific conclusion based on whether the results must be analyzed "post-facto" or not. Events under scientifically controlled experimental conditions are valid regardless of when the data is collated. The events recorded are the events that occurred regardless of distance and time of collation, and nothing less.

And those events lead to valid scientific conclusions. If anyone can produce a PF suitable reference that says otherwise, I would appreciate it.

I will point out that many experiments require data to be collated post-facto, and there is no less value attributed to those experiments for that. An obvious example is the LIGO experiment, which relies on the distance of the separated laboratories for its analysis. The distant data must be transmitted at light speed to a common location. This is no different than occurs with entanglement experiments (including swapping types) where results must also be transmitted at light speed to be understood. Here is a specific reference to a highly regarded experiment in which there is violation of strict Einsteinian locality, and the results are collated after the fact by signals limited to c:

Violation of Bell's inequality under strict Einstein locality conditions

I hope you can see that dismissing evidence of quantum nonlocality (a/k/a Einstein's "spooky action at a distance") because you cannot transmit signals faster than light is a circular argument. You are assuming that which you seek to prove. (Or more accurately, you are dismissing that with which proves something you may disagree with.)

Bell's Theorem - generally accepted science - requires abandonment of locality and/or realism. When we use the "as if" argument (as you did, and I do as well), we are tacitly abandoning locality. But regardless: the measurement settings for A and B - and those alone - determine the statistical predictions of QM, even when A and B are distant from each other as are changes in the measurement settings. From Bell: we know that somehow or another, there must be some method whereby there is rapport between them. They are not in a Product State and therefore they are not independent regardless of distance.3. I agree with this.4. The generally accepted term for this is "quantum nonlocality" (or sometimes "Bell nonlocality" or even just "nonlocality"), which is itself generally accepted. There are thousands of papers demonstrating quantum nonlocality, this being merely one example (from Zeilinger et al):

Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping

An ARXIV, "Nonlocal/nonlocality" shows up over 5000 times in the title of papers. It shows up over 11,000 times in abstracts. It is generally accepted that quantum nonlocality also encompasses the concept of quantum causality, in other words: that causal order is not an observable factor in these type of experiments.

---------------------

If discussion around this challenge would be better off in a separate thread, please feel free to split it off. [Moderator's note: This is that spin-off thread.] Please note that when discussing this, I am not taking the position of any particular interpretation. Just talking about generally accepted science, not personal opinion. I believe it is manifestly unfair to allow folks to speak as if quantum nonlocality does not exist and should be denied in the Quantum Physics forum. If you dislike the term "spooky action at a distance", fine, I understand that. But "Quantum Nonlocality" is generally accepted and should therefore be promoted here - and not in any way diminished as happens too often.

Respectfully,

-DrC

 

[PeterDonis]

I believe it is manifestly unfair to allow folks to speak as if quantum nonlocality does not exist and should be denied in the Quantum Physics forum.

"Quantum nonlocality" as far as this [Edit--the regular QM] forum (as opposed to the QM interpretations forum) is concerned has to be defined very carefully in order to not make any interpretation-dependent claims. Basically that definition comes down to just pointing to the experimental facts, such as violations of the Bell inequalities, and stopping there.

 

[DrChinese]

"Quantum nonlocality" as far as this forum (as opposed to the QM interpretations forum) is concerned has to be defined very carefully in order to not make any interpretation-dependent claims. Basically that definition comes down to just pointing to the experimental facts, such as violations of the Bell inequalities, and stopping there.

And violating a Bell inequality means local noncontextual theories are ruled out. There is nothing to debate about this point, it’s been standard science for nearly a half century.

Why would we try to convince people to reject the very thing Einstein called “spooky action at a distance”? He knew full well what that meant, and that if the EPR argument was wrong (as Bell later proved) that would be what we would be left with.

So why wouldn’t we simply point folks to the preferred PF term? Rather than persuading them that nothing is going on, when obviously something is. Either: the quantum context is nonlocal; or there is nonlocal action. That’s Bell, plain and simple. And that what Quantum Nonlocality is.

I provided references saying exactly this. No one can provide a single reference to the contrary. Weihs et al 1998, Violation of Bell’s Inequality Under Strict Einsteinian Locality Conditions… and so on. There’s nothing to interpret on this point.

It seems to me that in reality: for many here, their preferred interpretation actually denies the Bell result, I.e. that they actually believe we live in a local realistic world. It’s that point of view that should be called out clearly - instead of trying to talk posters into denial of the extremely sophisticated experiments being performed that show that Einsteinian locality is not respected. Again, hundreds of papers back up that position. And none say otherwise. If we call ourselves scientists, why back away from published conclusions?

 

[PeterDonis]

violating a Bell inequality means local noncontextual theories are ruled out.

Yes, but such theories do not include QM--the actual theory we are discussing. Pointing out that theories nobody uses anyway are ruled out doesn't seem to me like it helps the discussion any.

It seems to me that in reality: for many here, their preferred interpretation actually denies the Bell result

This is intepretation discussion and belongs in the interpretations subforum [edit: and has now been moved there], not here.

 

[PeterDonis]

If we call ourselves scientists, why back away from published conclusions?

I don't see anyone in this thread denying published experimental results.

"Conclusions", again, implies interpretation [edit: and hence discussion of this has been moved to the interpretations subforum], and is off topic here.

 

[DrChinese]

"Conclusions", again, implies interpretation, and is off topic here.

Please tell me how anyone could consider these top scientists' conclusions (verbatim from their abstracts) to be "interpretations".

1. Violation of Bell's inequality under strict Einstein locality conditions
Gregor Weihs, Thomas Jennewein, Christoph Simon, Harald Weinfurter, Anton Zeilinger (1998)
We observe strong violation of Bell's inequality... [and] for the first time fully enforce the condition of locality...

2. Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping (2002-2008)
Thomas Jennewein, Gregor Weihs, Jian-Wei Pan, Anton Zeilinger
The nonlocality is confirmed by observing a violation of Bell's inequality by 4.5 standard deviations. Thus, by demonstrating quantum nonlocality for photons...

3. Bell nonlocality (2013)
Brunner, Calvacanti et al
We review the main concepts and tools which have been developed to describe and study the nonlocality of quantum theory...

4. Experimental test of quantum nonlocality in three-photon Greenberger–Horne–Zeilinger entanglement (2000)

Are they not as enlightened as us, or are they simply loose with their language? Call it for what it is.

Orthodox quantum theory is nonlocal. You know that because nonlocal measurement settings (and nothing else) define the quantum expectation value for experimental coincidence of particles that have never existed in a common light cone. Again, this is the math (cos^2 for distant photons), and no interpretation is necessary.

I personally call it "quantum nonlocal" in order to specify that only quantum effects are nonlocal, because there is strict signal locality (as agreed by all of us). In PF, we should use the same language as is generally accepted. There is no need to qualify generally accepted scientific terminology - used in thousands of peer reviewed papers (as I have pointed out repeatedly) - as an "interpretation".

 

[PeterDonis]

Please tell me how anyone could consider these top scientists' conclusions (verbatim from their abstracts) to be "interpretations".

All of these papers are using the term "quantum nonlocality" to describe experimentally verified violations of the Bell inequalities. But "quantum nonlocality" is just words. The experimentally verified physics is that the Bell inequalities are violated. If some people don't like to use the term "quantum nonlocality" to describe that experimentally verified physics, there is no way you can prove they are wrong. You can state your own preference for what words to use, but you can't declare by fiat that it is the only correct way of describing the experimentally described physics. Physics is not words. And if you keep insisting that everyone use your particular preferred words, when nobody is questioning the experimentally verified physics, then that is getting into "interpretation" territory, because "interpretation" is the only possible ground you can have for continuing to object when some people don't use the words "quantum nonlocality" when you think they should.

 

[DrChinese]

All of these papers are using the term "quantum nonlocality" to describe experimentally verified violations of the Bell inequalities. But "quantum nonlocality" is just words. The experimentally verified physics is that the Bell inequalities are violated. If some people don't like to use the term "quantum nonlocality" to describe that experimentally verified physics, there is no way you can prove they are wrong. You can state your own preference for what words to use, but you can't declare by fiat that it is the only correct way of describing the experimentally described physics. Physics is not words. And if you keep insisting that everyone use your particular preferred words, when nobody is questioning the experimentally verified physics, then that is getting into "interpretation" territory, because "interpretation" is the only possible ground you can have for continuing to object when some people don't use the words "quantum nonlocality" when you think they should.

You have completely turned around my point. This isn't about my choice of words at all, and it never has been. It's about an idea. And yes, I can prove them wrong if they deny peer reviewed published experiments. Please, anyone, show me an experiment where entanglement effects cease at an Einsteinian light cone. There is no interpretational element to the experiments I cite. If the experiments of Nobel winners is not to be considered generally accepted science at PF, we have a serious problem.

----------

@DrClaude said a poster should disavow the idea of spooky action at a distance. That was his choice of words, and he said it as if denying "spooky action at a distance" is generally accepted physics. He may as well have said we should deny "quantum locality". That's flat out wrong! We (at PF) should embrace some form of nonlocality, as that is generally accepted science today. Call it what you like, "nonlocality" or "quantum nonlocality" or "Bell nonlocality" or even the dreaded "spooky action at a distance". I am not pushing a particular phrase, you can call it what you like. And I am not pushing an interpretation. And I am certainly not pushing my own view, I have no more idea how things work than anyone else. I am merely stating what should be obvious to every single scientist reading this: experiments prove there is nonlocality of some type. And as loophole after loophole has been closed, all doubts should evaporate for even the most diehard old schooler out there who longs for the good ol' days. (PS I include myself in that group, so don't take offense...)

I have cited plenty of watershed experiments. I have shown you the verbatim conclusions presented in those experiments' abstracts. None of this is about my personal views. We are all supposed to be adults here, to the extent that we can acknowledge what these important and definitive experiments point to. Bell correlations (i.e. violations of Bell inequalities) between photon pairs that have never been in each others' light cones, and under conditions of strict Einsteinian locality, are proof of nonlocality. Certainly that conclusion is warranted with our current knowledge.

I am shocked that in 2023, the standard of proof for the existence of nonlocality is apparently - in PhysicsForums at least - higher than the standard of proof for any other physical concept I am aware of. And yet, each of my cited experimental proofs are merely in keeping with orthodox quantum theory as it has existed for nearly 100 years. Where's the surprise here? The math says: a nonlocal context (the measurement settings for distant Alice and Bob) is the sole determinant for the quantum expectation value. And yet there are folks that 100 years later... post Bell, post Aspect, post Zeilinger, post Wineland, post entanglement swapping, post GHZ and so forth... can't spit out these few basic words?

Nonlocality is an established element of quantum theory.

And you want to say the official position of PF is: that's an interpretation? Wow. And yet there is not the slightest evidence of any kind to the contrary. Next you'll be saying the concept of an expanding universe can only be discussed in an interpretations subforum. Every element of every physical theory is always subject to later advancement or even disproof. Why take a special stance on nonlocality?

 

[PeterDonis]

Nonlocality is an established element of quantum theory.

As I have already said, that depends on how you define "nonlocality".

If you define "nonlocality" to mean "violations of the Bell inequalties", then your statement is correct. But nobody has denied the correctness of that statement, so your continued complaints about people somehow not accepting nonlocality make no sense with this definition.

Any other definition of "nonlocality" is an interpretation, since it must draw a distinction between the experimentally confirmed QM prediction of Bell inequality violations and whatever "nonlocality" is.

And you want to say the official position of PF is: that's an interpretation?

See above.

 

[PeterDonis]

You have completely turned around my point. This isn't about my choice of words at all. It's an idea.

I disagree. See my post #9 just now.

If you think there is a definition of "nonlocality" that is somehow (a) not the same as "violation of the Bell inequalities" and also (b) not an interpretation (i.e., not dependent on adopting some particular QM interpretation or class of interpretations), then the burden is on you to give that definition and back it up with references. If you think your past posts on this topic have done so, you are mistaken.

My usual practice when a term becomes problematic for discussion because of people talking past each other is to taboo the term: stop using it altogether, and instead state what you mean without it. If you mean "violations of the Bell inequalities", then say that. If you mean something else, then say that. I think that is what you need to do with the term "nonlocality": you need to taboo it, at least for this discussion, and say what you mean without using it. That way I and others will know exactly what you are talking about, without having to argue about terminology.

 

[PeterDonis]

@DrClaude said a poster should disavow the idea of spooky action at a distance.

And my statements about clarifying exactly what the term means apply to him too. It might well turn out that "spooky action at a distance" is also an interpretation, as is the claim that one should disavow it.

 

[PeterDonis]

Bell correlations (i.e. violations of Bell inequalities) between photon pairs that have never been in each others' light cones, and under conditions of strict Einsteinian locality, are proof of nonlocality.

This statement is evidence that you are not using the definition of "nonlocality" as being Bell inequality violations. So what definition are you using? And why do you think experiments that show Bell inequality violations are "proof"? How can these experiments "prove" anything except that the QM prediction of Bell inequality violations is correct? How is any claim beyond that not an interpretation?

 

[DrChinese]

If you define "nonlocality" to mean "violations of the Bell inequalties", then your statement is correct.

This statement is evidence that you are not using the definition of "nonlocality" as being Bell inequality violations.

There are many nonlocality proofs via experiment. So no, they are NOT the same thing (Bell violations are but one example of nonlocality). An important example is GHZ. A single run of a GHZ experiment is sufficient to disprove locality. No Bell inequality needed. Please note that these authors (as cited above and here) evidently didn't agree with you in 2000.

Experimental test of quantum nonlocality in three-photon Greenberger–Horne–Zeilinger entanglement (2000)

You are stretching the norms of both language and science to say that locality is the standard and nonlocality requires interpretation. There is no version of orthodox QM in which the quantum expectation value can be determined without reference to a context which is nonlocal. Again, no interpretation required. There are probably dozens if not hundreds of papers today that demonstrate that local contextual theories are not viable for a variety of reasons, including the failure of factorizability . It doesn't matter if they are or are not - those objections to nonlocality are not standard.

You are sticking to your entrenched position, and ignoring the weight of peer-reviewed published papers. Again, I challenge anyone to present a paper supporting the idea that quantum nonlocality is still yet to be demonstrated satisfactorily.

Sometimes I think I am discussing this with the local realist society, and not PF experts. (That's a joke, by the way.) Get with it, it's 2023. Nonlocality (or whatever phrase you prefer) is here, and it's here to stay.

 

[PeterDonis]

There are many nonlocality proofs via experiment.

You're not answering my question.

You are stretching the norms of both language and science to say that locality is the standard and nonlocality requires interpretation.

You're not answering my question.

Can you please stop inundating me with irrelevancies and answer my question? What is the definition of nonlocality you are using?

 

[PeterDonis]

You are sticking to your entrenched position, and ignoring the weight of peer-reviewed published papers.

You're still not answering my question. I am not asking you what experiments have been done. I am not asking you what predictions QM makes and whether experiments match them. I am asking you what definition of nonlocality you are using. Why do you keep not answering a simple question?

 

[PeterDonis]

local contextual theories

Are, as I said in the other thread, irrelevant, since QM is not one and QM is the theory we are discussing. Why do you keep harping on irrelevancies?

 

[PeterDonis]

@DrChinese, if I sound frustrated in my previous posts, it's because I am. You appear to think that whatever meaning you are assigning to the term "nonlocality" is so obvious that you don't even need to state it. It's not. It's not obvious to me, and it's evidently not obvious to all the other people who have had the same experience as I have with you in discussions of this topic. If it's really so obvious, you should be able to give the obvious meaning of "nonlocality" and point us to a reference that expounds that meaning. But you keep not doing that and peppering your posts with boldface as though shouting louder will somehow make us understand. It's not working.

 

[PeterDonis]

An important example is GHZ. A single run of a GHZ experiment is sufficient to disprove locality. No Bell inequality needed. Please note that these authors (as cited above and here) evidently didn't agree with you in 2000.

From what I can gather, the definition of "nonlocality" used in this paper is "not local realistic", i.e., the same as Bell's definition. It is true that there are ways of testing for violations of local realism other than testing for Bell inequality violations (and Bell did not mention those other ways in his original papers, because he didn't know of them), and the GHZ experiment has the advantage of not requiring statistics--you have a result which literally cannot occur at all under "local realism" but which does occur in experiments and which QM predicts will occur.

So do I understand, then, that your definition of "nonlocality" is "not local realistic"? If so, the same comments that I made before apply: as a definition, this is fine, but also tells us nothing helpful, since everyone already knows that QM is not local realistic, and nobody, certainly not @DrClaude, was denying this. @DrClaude was advocating for not adopting "spooky action at a distance" as a viewpoint, but that is not the same as denying violations of local realism.

 

[Morbert]

We (at PF) should embrace some form of nonlocality, as that is generally accepted science today. Call it what you like, "nonlocality" or "quantum nonlocality" or "Bell nonlocality" or even the dreaded "spooky action at a distance".

The problem is these terms have subtle distinctions that should not be papered over when trying to decide some practical convention. In particular, "spooky action at a distance" heavily implies a violation of relativistic causality, and there is no agreement that entanglement implies a violation of relativistic causality.

 

[DrChinese]

@DrChinese, if I sound frustrated in my previous posts, it's because I am. You appear to think that whatever meaning you are assigning to the term "nonlocality" is so obvious that you don't even need to state it. It's not. It's not obvious to me, and it's evidently not obvious to all the other people who have had the same experience as I have with you in discussions of this topic. If it's really so obvious, you should be able to give the obvious meaning of "nonlocality" and point us to a reference that expounds that meaning. But you keep not doing that and peppering your posts with boldface as though shouting louder will somehow make us understand. It's not working.

I'm frustrated too. As I have said repeatedly, what is commonly called "quantum nonlocality" (and sometimes "Bell nonlocality" or just "nonlocality") is precisely what is demonstrated in the experiments I have cited, and hundreds/thousands more. They use that language. And... it precisely matches orthodox quantum theory to a tee. They describe that mapping in their papers, showing that QM is being confirmed. So it's not my definition, it's the definition of the scientific community that is writing the papers we all read. Maybe we should take that up with Zeilinger, Pan, Weihs, Gisin, Franson, Kwiat, Brunner, Calvacanti, Wiseman and so forth. Because apparently they feel the term "quantum nonlocality" should be sufficiently understood by the reader. And if folks at PF want to describe how and why "quantum nonlocality" should be qualified as a phrase, that up to each writer.

And... I am quite aware that what they call "quantum nonlocality" may or may not be a strict proof that there is "action at a distance" occurring. I'm not claiming otherwise here. And yes, one can refer to quantum nonlocality as you seem to prefer: "violation of Bell inequalities" or "not local realistic". But none of that matters, for these two reasons:

a) Since that's how the scientific minds writing the papers use the term, we should too. No interpretation is presented or implied with their usage of the term.
b) Quantum theory explicitly features nonlocal contextuality in determining expectation values. Again, no interpretation involved in that statement.

IMHO, the most useful language to present at PF is that matching the papers we cite. And when they discuss their proofs of quantum nonlocality, they don't reference quantum interpretations at all. But... I am not asking anyone to change how they refer to this element of QM. Use whatever language to describe things you like. What I am asking for is two things: a) Don't banish the term "quantum nonlocality" to the interpretations subforum unless it is used in context of an interpretation; b) Don't try to talk people out of believing in the quantum nonlocality that is part and parcel of both quantum experiments and quantum theory. When @DrClaude (and again I mean this with respect) says that there is no "action at a distance" or similar, he is stating a personal opinion or a preferred interpretation that belongs in the interpretations subforum.

As for the boldface: I use that to make a point stand out relative to other points. I am sorry if you interpret as shouting. (I prefer to use all caps and exclamation marks when I shout. )

 

[GarberMoisha]

I'm frustrated too. As I have said repeatedly, what is commonly called "quantum nonlocality" (and sometimes "Bell nonlocality" or just "nonlocality") is precisely what is demonstrated in the experiments I have cited, and hundreds/thousands more. They use that language. And... it precisely matches orthodox quantum theory to a tee. They describe that mapping in their papers, showing that QM is being confirmed. So it's not my definition, it's the definition of the scientific community that is writing the papers we all read. Maybe we should take that up with Zeilinger, Pan, Weihs, Gisin, Franson, Kwiat, Brunner, Calvacanti, Wiseman and so forth. Because apparently they feel the term "quantum nonlocality" should be sufficiently understood by the reader. And if folks at PF want to describe how and why "quantum nonlocality" should be qualified as a phrase, that up to each writer.

And... I am quite aware that what they call "quantum nonlocality" may or may not be a strict proof that there is "action at a distance" occurring. I'm not claiming otherwise here. And yes, one can refer to quantum nonlocality as you seem to prefer: "violation of Bell inequalities" or "not local realistic". But none of that matters, for these two reasons:

a) Since that's how the scientific minds writing the papers use the term, we should too. No interpretation is presented or implied with their usage of the term.
b) Quantum theory explicitly features nonlocal contextuality in determining expectation values. Again, no interpretation involved in that statement.

IMHO, the most useful language to present at PF is that matching the papers we cite. And when they discuss their proofs of quantum nonlocality, they don't reference quantum interpretations at all. But... I am not asking anyone to change how they refer to this element of QM. Use whatever language to describe things you like. What I am asking for is two things: a) Don't banish the term "quantum nonlocality" to the interpretations subforum unless it is used in context of an interpretation; b) Don't try to talk people out of believing in the quantum nonlocality that is part and parcel of both quantum experiments and quantum theory. When @DrClaude (and again I mean this with respect) says that there is no "action at a distance" or similar, he is stating a personal opinion or a preferred interpretation that belongs in the interpretations subforum.

As for the boldface: I use that to make a point stand out relative to other points. I am sorry if you interpret as shouting. (I prefer to use all caps and exclamation marks when I shout. )

Classical thinking... little marble balls and interpreting everything as existing classically. Interpreting as in interpretation. You are using one. Nobel prize winners do too. For some reason.

In QM nothing is realistic. Hence your futile battle with unicorns. There is no nonlocality in the absence of realism. If you can't handle that, stay on the safe side with classical ideas.

 

[PeterDonis]

what is commonly called "quantum nonlocality" (and sometimes "Bell nonlocality" or just "nonlocality") is precisely what is demonstrated in the experiments I have cited, and hundreds/thousands more.

And what is demonstrated in experiments is violations of the Bell inequalities, or the GHZ condition, i.e., violations of "local realism". So if that's the definition of "quantum nonlocality" that you are using, why not just say so? Why do you keep harping on things that everyone already knows? We already know that the experiments show violations of "local realism". Nobody is disputing that.

it precisely matches orthodox quantum theory to a tee.

Everybody already knows that too. Nobody is disputing that the experimental results match the QM predictions. So why do you keep harping on it? You keep talking as if you are giving us valuable new information by saying these things. You're not. You're just belaboring beyond all reason what everyone already knows.

I am quite aware that what they call "quantum nonlocality" may or may not be a strict proof that there is "action at a distance" occurring.

Exactly. And that is what @DrClaude was saying: the fact that "local realism" is violated is not the same as "action at a distance" (with or without the adjective "spooky" tacked on). So why were you objecting to what he said? What he said was perfectly consistent with what you are saying. And with what everyone already knows. Yet you're talking as though PF is somehow destroying science by letting him say it. What the heck is going on?

none of that matters

It most certainly does matter if you are accusing @DrClaude and other PF Mentors and SAs of going against established science, just on the basis of a statement that "spooky action at a distance" is not experimentally established.

Don't banish the term "quantum nonlocality" to the interpretations subforum unless it is used in context of an interpretation

And now that you have given a definition of quantum nonlocality that is not interpretation dependent, that's fine: with that definition (quantum nonlocality = violations of "local realism" as shown by violations of Bell inequalities, the GHZ condition, etc.), quantum nonlocality is not interpretation dependent. But I asked you for that definition in what was originally the other thread, a couple of days ago, before this thread even got spun off. Why couldn't you have just given me that definition? Or at least just clarified that when you use the term "quantum nonlocality", you mean that definition?

If you ask why I even needed you to clarify it, that's because, as I've already said, and as I pointed out in the previous thread before this one even got spun off, your criticisms of @DrClaude's statement about "spooky action at a distance" not being established made no sense if that was the definition of "quantum nonlocality" you were using. You have now confirmed that by saying (I quoted you above saying it) that the experiments showing quantum nonlocality do not establish that "action at a distance" is occurring. And yet, as I said above, you accused PF of going against established science by allowing statements like @DrClaude's. So I thought you must be using some other definition of "quantum nonlocality", one which does imply "action at a distance". And so I asked you to clarify that point by telling me what definition you were using.

In short: I could not believe that you would (1) agree that the experiments do not establish that "action at a distance" is occurring, and that "quantum nonlocality" does not mean that, yet also (2) accuse PF of going against established science by allowing @DrClaude to make precisely that statement. But now it appears that yes, that is what you were doing. Now that we've cleared that up, my only request is to please stop accusing PF of something that, by your own admission, we are not doing.

 

[PeterDonis]

When @DrClaude (and again I mean this with respect) says that there is no "action at a distance" or similar, he is stating a personal opinion or a preferred interpretation that belongs in the interpretations subforum.

This is a valid point, and we might need to have a brief moderator discussion about how best to deal with that in the previous thread, which was not in the interpretations subforum.

 

[GarberMoisha]

Nonlocality is not an established fact. It is a way of interpreting the entanglement experiments.

 

[PeterDonis]

Quantum theory explicitly features nonlocal contextuality in determining expectation values.

This is a separate topic that might be worth an Insights article (I don't think we currently have one that addresses this topic, which is fairly subtle and is not discussed in many QM textbooks). Would you be interested in writing one?

 

[PeterDonis]

Nonlocality is not an established fact. It is a way of interpreting the entanglement experiments.

This is matter of definition, as I have already said. @DrChinese has now given a definition of "nonlocality" which basically makes it equivalent to the observed results of entanglement experiments. The papers he has referenced appear to be using a similar definition. By that definition, nonlocality is an established fact; what is not is "action at a distance".

 

[martinbn]

Quantum theory explicitly features nonlocal contextuality in determining expectation values.

This is a separate topic that might be worth an Insights article (I don't think we currently have one that addresses this topic, which is fairly subtle and is not discussed in many QM textbooks). Would you be interested in writing one?

Is it possible to say what this refers to without a whole new thread?

 

[DrChinese]

Is it possible to say what this refers to without a whole new thread?

Yes [referring to nonlocal contextuality]. The formula for polarization matches of a stream of entangled photon pairs (for example) is cos^2(Alice-Bob), depending on entanglement type as correlated or anti-correlated. Alice meaning a measurement setting chosen by one observer, Bob being a setting chosen by another.

Note that those settings are the only variables, and the distance between them is not relevant. That allows the context to be nonlocal, if you so desire. I don't think there is any significant debate about this particular point, which relates to what @PeterDonis was referring to in one of his comments.

Keep in mind that the actual outcomes themselves are completely random as far as is known, but in principle there could be elements/variables that determine the individual outcomes that are currently unknown. That is something that arouses debate, as you know.

 

[DrChinese]

Classical thinking... little marble balls and interpreting everything as existing classically. Interpreting as in interpretation. You are using one. Nobel prize winners do too. For some reason.

In QM nothing is realistic. Hence your futile battle with unicorns. There is no nonlocality in the absence of realism. If you can't handle that, stay on the safe side with classical ideas.

You are placing me in a classical school? That's a laugh. Not that it matters to this discussion, but I am certainly not a realist.

What does matter is that one can deny *both* realism and locality, and still follow Bell. In other words: there is no logical substance to your statement "there is no nonlocality in the absence of realism"...

 

[DrChinese]

1. And what is demonstrated in experiments is violations of the Bell inequalities, or the GHZ condition, i.e., violations of "local realism". So if that's the definition of "quantum nonlocality" that you are using, why not just say so? Why do you keep harping on things that everyone already knows? We already know that the experiments show violations of "local realism". Nobody is disputing that. ... Nobody is disputing that the experimental results match the QM predictions. So why do you keep harping on it?2. And that is what @DrClaude was saying: the fact that "local realism" is violated is not the same as "action at a distance" (with or without the adjective "spooky" tacked on). So why were you objecting to what he said? What he said was perfectly consistent with what you are saying. And with what everyone already knows. Yet you're talking as though PF is somehow destroying science by letting him say it. What the heck is going on? ... It most certainly does matter if you are accusing @DrClaude and other PF Mentors and SAs of going against established science, just on the basis of a statement that "spooky action at a distance" is not experimentally established.3. And now that you have given a definition of quantum nonlocality that is not interpretation dependent, that's fine: with that definition (quantum nonlocality = violations of "local realism" as shown by violations of Bell inequalities, the GHZ condition, etc.), quantum nonlocality is not interpretation dependent. But I asked you for that definition in what was originally the other thread, a couple of days ago, before this thread even got spun off. Why couldn't you have just given me that definition? Or at least just clarified that when you use the term "quantum nonlocality", you mean that definition?

1. OK, then we both agree, and we agree with standard usage of the terminology in papers on the subject. Good to know.2. What I am saying is not really a knock on anything @DrClaude has said, even though you might read it that way. My issue is more along the lines of how we discuss things in the Quantum Physics forum. I get chastised for a) using terminology that is common is the literature ("QM is quantum nonlocal") but someone else can say b) there is no "action at a distance" with impunity. When we discuss QM with those who are relatively new to the subject, it makes sense to allow a) and then qualify the statement if necessary if the discussion gets deeper. In fact, I often bring up the subject of the Interpretations/Foundations subforum quickly to insure that the reader is aware of its existence. That allows for an easy segue if the discussion goes in that direction, but allows the reader to walk away with some basic understanding if the discussion ends there.

I recognize that my next statements will be met with some passionate disagreement, but I think this opinion is well justified. In 1947, Einstein told Born he did not believe in the orthodox ("statistical") view of QM, in part because it implied "spooky action at a distance" (the nonlocal contextuality mentioned above in this thread, which was already evident from the 1935 EPR paper). Einstein died before Bell (1964) and Aspect (1981), but he was certainly capable of amending his beliefs upon good evidence. Bell's Theorem, coupled with Bell tests with settings changed midflight, would certainly have forced Einstein to substantially revise his opinion.

So...Is there action at a distance? I can't really say what nonlocal mechanism might be at work, whether there is "action" or "influence" or "mutual rapport" or whatever might be used to describe it. But since there is nonlocal agreement when distant measurement settings are set midflight to be the same, leading to perfect correlations: I wouldn't rule it out.

But I also would agree with @DrClaude (or anyone) if he said "action at a distance" has not been demonstrated conclusively. But that wasn't what he said. He flat out said it doesn't exist. It should be obvious that some kind of "action at a distance" is in fact consistent with the experimental evidence.3. I thought I did do just that. I quoted example after example. If the authors I cited use "quantum nonlocality" and "nonlocality" in similar contexts, I would hope that anyone would see that this is common usage and there is no need to provide definitions upon using.

On the other hand: You are probably right that I could have done a better job of explaining things. I will continue to try to be clearer, more effective, and maybe even seek more... brevity. PS After writing the above, I did my usual daily search on new papers on entanglement. The first sentence of the first one I encountered started as follows: "Quantum entanglement manifests quantum nonlocality...". The paper then goes on to demonstrate "quantum nonlocality without entanglement." (Not citing this paper for the accuracy of their conclusions, as it is not peer reviewed. Just mentioning to show how common the usage of "quantum nonlocality" is, no definitions are provided as the authors assume the reader knows what they mean.)

https://arxiv.org/abs/2309.16907 (29 Sept 2023)

 

[GarberMoisha]

You are placing me in a classical school? That's a laugh. Not that it matters to this discussion, but I am certainly not a realist.

What does matter is that one can deny *both* realism and locality, and still follow Bell. In other words: there is no logical substance to your statement "there is no nonlocality in the absence of realism"...

That's a new one after you failed to explain what you mean by 'nonlocal'. What is "to follow Bell"?
If by nonlocal you mean faster than light influences propagating through space, you are mistaken. Bell's theorem doesn't say what is true locality or realism. It merely states that the world cannot be both local and real at the same time. QM is unrealistic and is probably local in the practical sense where no ftl signals can propagate. I.e. nonlocality in this sense is a misnomer.

 

[GarberMoisha]

People use 'nonlocal' when they refer with a pedestrian worldview in mind to the entanglement correlations(where everything is solid and predictable). After all, how else(they would say) except through nonlocal ftl influences can it be so? Still, it doesn't make it true.

 

[Haborix]

That's a new one after you failed to explain what you mean by 'nonlocal'. What is "to follow Bell"?
If by nonlocal you mean faster than light influences propagating through space, you are mistaken. Bell's theorem doesn't say what is true locality or realism. It merely states that the world cannot be both local and real at the same time. QM is unrealistic and is probably local in the practical sense where no ftl signals can propagate. I.e. nonlocality in this sense is a misnomer.

@DrChinese can speak for himself, but your comments seem to suggest you just dislike a definition of non-local that isn't your own. That's fine but you shouldn't confuse your choice of words with reality. Follow Bell almost certainly means rejecting at least one of locality or realism, and DrChinese simply observes that this can be satisfied by rejecting both.

 

[GarberMoisha]

@DrChinese can speak for himself, but your comments seem to suggest you just dislike a definition of non-local that isn't your own. That's fine but you shouldn't confuse your choice of words with reality. Follow Bell almost certainly means rejecting at least one of locality or realism, and DrChinese simply observes that this can be satisfied by rejecting both.

I didn't get the impression he was rejecting both. In which post did he do so?

 

[timmdeeg]

Keep in mind that the actual outcomes themselves are completely random as far as is known, but in principle there could be elements/variables that determine the individual outcomes that are currently unknown.

Sorry for a layman question in between:

If not "completely random" do we think that the outcomes - in principle - are determined by microscopic states of the detector or by yet unknown "elements/variables" before measurement?