Hidden Assumptions in Bell's Theorem?

[kurt101]

You think it means something physical is happening to [1&4] when Victor does his measurement, but you are wrong. These experiments disprove such an idea, especially the delayed-choice one which I already quoted.

But in the case where Victor (2 & 3) measurement is done before measurement of 1 & 4, would you say something physically is happening? At least in the context of reality where we have time ordered cause and effect, doing the measurement 2 & 3 does something to the 1 & 4 measurement. I am not sure if this would qualify under your definition of physical given that the cause and effect is non-local.

I read through some of your previous comments on this thread and it was not clear to me that you were distinguishing between the two cases in your arguments. But if you are taking some kind of realist viewpoint of this experiment where cause and effect matter, I don't see how you can deny that 1 & 4 do not directly affect each other in the case where the BSM test is done before the measurement of 1 & 4 since you could change their angles of their measurement well you after you obtained the knowledge that these pairs are entangled at Victor (2 & 3) (same logic you used in one of your arguments for the opposite case) and you would get the correct statistics which could not happen if this was some post selection phenomena. If 1 & 4 are not truly entangled (i.e. not a post selection phenomena) in this case, you would not get the right statistics for some angles of measurement you decided to use at the very last moments before measurement of 1 & 4 no matter what the BSM had previously told you you about 1 & 4.

 

[kurt101]

1. Wow, this is a treasure trove for me! LOL... from the reference:

"ENTANGLEMENT AS A CAUSE OF CORRELATION...
Quantum physics predicts the existence of a totally new kind of correlation that will never have any kind of mechanical explanation. And experiments confirm this: Nature is able to produce the same randomness at several locations, possibly space-like separated. The standard explanation is ”entanglement”, but this is just a word, with a precise technical definition. ... Quantum correlations simply happen, as other things happen (fire burns, hitting a wall hurts, etc). Entanglement appears at the same conceptual level as local causes and effects. It is a primitive concept, not reducible to local causes and effects. ... In other worlds, a quantum correlation is not a correlation between 2 events, but a single event that manifests itself at 2 locations."

By "mechanical explanation" does the author mean "local causes and effects" and not non-local causes and effects. In other words is the author ruling out mechanical explanations but not mechanistic explanations? It is hard to tell what he means because he throws in randomness which is not mechanistic, but he uses "a single event that manifests itself at 2 locations" which does sound mechanistic. And by randomness it is not clear if he means fundamental randomness or apparent randomness (because we can't see what the starting state is). So to me his statement is as clear as mud.

 

[Cthugha]

2. Of course Victor's future action changes the past. That's the entire point, my friend! Quantum mechanics does NOT respect Einsteinian causality, even in direction of causality. Victor's action to entangle the distant pair can be done anytime and anywhere, as experiments actually demonstrate. It could be in the past, present or future. It could be near or distant. Is this paradoxical? Yes! Is it consistent with QM? Yes! To reference the late great Asher Peres (see [4]):

Per the Zeilinger team here, page 5:
"A seemingly paradoxical situation arises — as suggested by Peres [4] — when Alice’s Bellstate analysis is delayed long after Bob’s measurements. This seems paradoxical, because Alice’s measurement projects photons 0 and 3 into an entangled state after they have been measured. Nevertheless, quantum mechanics predicts the same correlations. Remarkably, Alice is even free to choose the kind of measurement she wants to perform on photons 1 and 2. Instead of a Bell-state measurement she could also measure the polarizations of these photons individually. Thus depending on Alice’s later measurement, Bob’s earlier results either indicate that photons 0 and 3 were entangled or photons 0 and 1 and photons 2 and 3. This means that the physical interpretation of his results depends on Alice’s later decision. Such a delayed-choice experiment was performed by including two 10 m optical fiber delays for both outputs of the BSA. In this case photons 1 and 2 hit the detectors delayed by about 50 ns. As shown in Fig. 3, the observed fidelity of the entanglement of photon 0 and photon 3 matches the fidelity in the non-delayed case within experimental errors. Therefore, this result indicate that the time ordering of the detection events has no influence on the results and strengthens the argument of A. Peres [4]: this paradox does not arise if the correctness of quantum mechanics is firmly believed."

I do not intend to enter into discussions of interpretations, but I would like to comment on the state of the community. I had the pleasure of cohosting Gregor Weihs last week in the colloquium of our department and besides funny/tragic stories about what discussions with Joy Christian are like, he also speaks quite clearly about Zeilinger's take on interpretations and Zeilinger's view is a modern information-theoretic version of Copenhagen which is heavily on the update-of-information side (https://arxiv.org/abs/quant-ph/0005084 and follow-up papers). It goes by the name Brukner-Zeilinger interpretation and a (non-Shannon) information vector is fundamental. The idea of finiteness of information is a golden thread through much of Zeilinger's work.

Quoting Zeilinger in support of a statement claiming that a future action changes the past in entanglement swapping experiments misrepresents Zeilinger's point of view. This becomes clear when reading Zeilinger's own papers on delayed choice entanglement swapping (https://arxiv.org/abs/1203.4834).

He closes stating:
" If one views the quantum state as a real physical object, one could get the seemingly paradoxical situation that future actions appear as having an influence on past and already irrevocably recorded events. However, there is never a paradox if the quantum state is viewed as to be no more than a “catalogue of our knowledge”. Then the state is a probability list for all possible measurement outcomes, the relative temporal order of the three observer’s events is irrelevant and no physical interactions whatsoever between these events, especially into the past, are necessary to explain the delayed-choice entanglement swapping."

and goes on to explain:
"What, however, is important is to relate the lists of Alice, Bob and Victor’s measurement results. On the basis of Victor’s measurement settings and results, Alice and Bob can group their earlier and locally totally random results into subsets which each have a different meaning and interpretation. This formation of subsets is independent of the temporal order of the measurements. According to Wheeler, Bohr said: “No elementary phenomenon is a phenomenon until it is a registered
phenomenon.”We would like to extend this by saying: “Some registered phenomena do not have a meaning unless they are put in relationship with other registered phenomena.”"

Whether or not one considers this convincing is everone's own decision. However, quoting Zeilinger to support interpretations where the future influences the past is going against Zeilinger's views and intentions.

 

[PeterDonis]

The microcausality condition rules out causal connections between space-like separated events

For experiments that test the Bell inequalities or entanglement swapping, this is actually a red herring, because the results of the experiments are actually the same regardless of whether the individual measurement events are spacelike, null, or timelike separated!

 

[lodbrok]

But in the case where Victor (2 & 3) measurement is done before measurement of 1 & 4, would you say something physically is happening? At least in the context of reality where we have time ordered cause and effect, doing the measurement 2 & 3 does something to the 1 & 4 measurement. I am not sure if this would qualify under your definition of physical given that the cause and effect is non-local.

In these experiments, time ordering makes no difference. Nothing that happens to particles (2&3) physically affects anything that happens to particles (1&4). It doesn't matter whether it is done before or after. It's all about how experimental results are handled after the experiments are long complete.

Chtugha's quote from Zeilinger himself says it more clearly:

"What, however, is important is to relate the lists of Alice, Bob and Victor’s measurement results. On the basis of Victor’s measurement settings and results, Alice and Bob can group their earlier and locally totally random results into subsets which each have a different meaning and interpretation. This formation of subsets is independent of the temporal order of the measurements."

 

[kurt101]

In these experiments, time ordering makes no difference.

Nobody on this forum is disputing the order makes any difference to the statistical results.

Nothing that happens to particles (2&3) physically affects anything that happens to particles (1&4). It doesn't matter whether it is done before or after. It's all about how experimental results are handled after the experiments are long complete.

That is your opinion based on some non-realistic interpretation that lacks cause and effect that you have chosen. If you choose a realistic interpretation with cause and effect then what happens at (2&3) does affect (1&4), but only in the case where (2&3) is done first. To the best of my knowledge nobody has come up with an experiment that disproves realism with cause and effect. The delayed choice experiments are no different.

 

[PeterDonis]

If you choose a realistic interpretation with cause and effect then what happens at (2&3) does affect (1&4), but only in the case where (2&3) is done first.

This doesn't make sense, though, given the fact that the actual results are the same regardless of the spacetime relationship between the measurements. Since the results are the same, whatever is going on "underneath" should be the same as well. But your claim here says that's not true; that whatever is going on "underneath" has to be different depending on the spacetime relationship between the measurements.

To my knowledge nobody in the QM community has proposed any such interpretation.

 

[kurt101]

Since the results are the same, whatever is going on "underneath" should be the same as well.

And that is your potential error. I am not saying that you are wrong, but it is possible that you are wrong. In other words what is going on underneath does need to be the same in both cases. That may seem strange, but I don't think it is strange at all. After all I wrote a simulation that tells me it is not really strange at all. I have tried to explain it in words and maybe I will try again, but once you understand it it is just symmetry.

To my knowledge nobody in the QM community has proposed any such interpretation.

I am just assuming a generic realistic cause and effect interpretation. Didn't Einstein, Bell, and others use such an interpretation to make progress in understanding quantum mechanics?

 

[PeterDonis]

In other words what is going on underneath does need to be the same in both cases. That may seem strange, but I don't think it is strange at all.

I don't think you'll find many people who share your opinion. In particular, if there is anyone in the QM community who has published a claim along these lines, you should reference it. I doubt that there is, but you are welcome to post a reference if you have one.

After all I wrote a simulation that tells me it is not really strange at all.

As you have already been told multiple times, your simulation is off topic here. If you mention it again you will receive a warning.

I am just assuming a generic realistic cause and effect interpretation.

I'm not sure what you mean by this; certainly, given the extensive debate in the literature, you can't just help yourself to this term as though its meaning were self-evident. You need to give a specific reference that describes the interpretation you are using.

Didn't Einstein, Bell, and others use such an interpretation to make progress in understanding quantum mechanics?

Einstein believed that such an interpretation that would preserve locality as well as realism was possible, but Einstein didn't know about Bell's Theorem.

Bell himself was well aware that his theorem ruled out any interpretation along the lines Einstein was looking for. In at least one of his papers (collected in Speakable and Unspeakable in Quantum Mechanics), he notes that the Bohmian interpretation is an obvious, simple interpretation that accounts for violations of the Bell inequalities by being a nonlocal hidden variable model--and then remarks that this is the sort of resolution that Einstein would have liked least.

 

[kurt101]

I don't think you'll find many people who share your opinion. In particular, if there is anyone in the QM community who has published a claim along these lines, you should reference it. I doubt that there is, but you are welcome to post a reference if you have one.

I don't have any reference. I can explain it in the language of cause and effect and realism. I will never understand why such language would be off limits since that is the basis we all come from and is the common language we used to understand each other. When something does not seem to follow realism and cause and effect we explain how it differs from this basis of understanding.

Bell himself was well aware that his theorem ruled out any interpretation along the lines Einstein was looking for. In at least one of his papers (collected in Speakable and Unspeakable in Quantum Mechanics), he notes that the Bohmian interpretation is an obvious, simple interpretation that accounts for violations of the Bell inequalities by being a nonlocal hidden variable model--and then remarks that this is the sort of resolution that Einstein would have liked least.

Bell also discussed interpretations in the generic sense. He clearly did not rule out realistic non-local interpretations in general. And while Einstein might not have been an advocate for non-locality he definitely discussed it in the context of reality.

 

[PeterDonis]

I don't have any reference.

Then I would strongly suggest reviewing the literature to see if you can find one. We allow somewhat more latitude in this forum, but even here, the kinds of claims you are making should be supported by references. If you claims are really as obvious as you seem to think, you should have no trouble finding them discussed in the literature.

I can explain it in the language of cause and effect and realism. I will never understand why such language would be off limits

Because such language makes assumptions that we know nature violates. The standard "language of cause and effect and realism" leads to models that satisfy the assumptions of Bell's theorem and therefore cannot explain violations of the Bell inequalities. That was one of Bell's main reasons for deriving the theorem.

He clearly did not rule out realistic non-local interpretations in general.

Of course not: the Bohmian interpretation itself is an example of one.

However, Bell to my knowledge never claimed that such interpretations could be described unproblematically using "the language of cause and effect and realism". He recognized that the nonlocality aspect is highly significant. His example of the Bohmian interpretation was meant to illustrate just what one has to commit to if one is going to take a realistic (but nonlocal) view of QM.

 

[kurt101]

Then I would strongly suggest reviewing the literature to see if you can find one. We allow somewhat more latitude in this forum, but even here, the kinds of claims you are making should be supported by references. If you claims are really as obvious as you seem to think, you should have no trouble finding them discussed in the literature.

Ok, I will look harder. And if I can't find one, maybe I will try contacting the authors of the paper https://link.springer.com/article/10.1007/s10701-021-00511-3#Sec21 and see what they think on why what I think is obvious has not been published.

And I think some extra leeway should be allowed in this case if you are going to allow Dr. Chinese to claim that the entanglement swapping disproves cause and effect interpretations. It is hard to refute him with tied hands.

Because such language makes assumptions that we know nature violates. The standard "language of cause and effect and realism" leads to models that satisfy the assumptions of Bell's theorem and therefore cannot explain violations of the Bell inequalities. That was one of Bell's main reasons for deriving the theorem.

but we don't know that "cause and effect" and "realism" violates nature. We know either "realism" or "non-locality" is violated. If we are having conversations in the context of realism, then we should be holding non-localism sacred. That seems like a combination that should be allowed to discuss on this forum as it is very narrow and familiar to everyone and can easily be moderated. And if we deny realism, then you can say anything, but that is clearly absurd to allow for discussion on this forum and so forcing people to use credible references definitely makes sense. Anyways that is my opinion for whatever it is worth.

However, Bell to my knowledge never claimed that such interpretations could be described unproblematically using "the language of cause and effect and realism". He recognized that the nonlocality aspect is highly significant. His example of the Bohmian interpretation was meant to illustrate just what one has to commit to if one is going to take a realistic (but nonlocal) view of QM.

Maybe a good question to ask is how entanglement swapping is handled in the Bohmian interpretation since in this interpretation the photon has a definite position. In particular the case where the BSM is done after the measurement of 1 & 4 might be interested to understand.

 

[DrChinese]

I do not intend to enter into discussions of interpretations, but I would like to comment on the state of the community. I had the pleasure of cohosting Gregor Weihs last week in the colloquium of our department and besides funny/tragic stories about what discussions with Joy Christian are like, he also speaks quite clearly about Zeilinger's take on interpretations and Zeilinger's view is a modern information-theoretic version of Copenhagen which is heavily on the update-of-information side (https://arxiv.org/abs/quant-ph/0005084 and follow-up papers). It goes by the name Brukner-Zeilinger interpretation and a (non-Shannon) information vector is fundamental. The idea of finiteness of information is a golden thread through much of Zeilinger's work.

Quoting Zeilinger in support of a statement claiming that a future action changes the past in entanglement swapping experiments misrepresents Zeilinger's point of view. This becomes clear when reading Zeilinger's own papers on delayed choice entanglement swapping (https://arxiv.org/abs/1203.4834).

He closes stating:
" If one views the quantum state as a real physical object, one could get the seemingly paradoxical situation that future actions appear as having an influence on past and already irrevocably recorded events. However, there is never a paradox if the quantum state is viewed as to be no more than a “catalogue of our knowledge”. Then the state is a probability list for all possible measurement outcomes, the relative temporal order of the three observer’s events is irrelevant and no physical interactions whatsoever between these events, especially into the past, are necessary to explain the delayed-choice entanglement swapping."

Whether or not one considers this convincing is everyone's own decision.

That is a great anecdote about Weihs and Christian (whom I think is off the rails). I can imagine those discussions... so thanks for sharing. And thanks for the Brukner/Zeilinger reference, I had not seen that.

Yes, I get that Zeilinger might say one thing in one place and yet another in the... same... place. "Whether these two particles are entangled or separable has been decided after they have been measured." Which is basically exactly the opposite of the next few sentences.

I found the text following (what you provided) interesting because it is oddly identical to an earlier quote I provided. I guess it might indicate some evolution in his thinking over time.

• Zeilinger et al 2002: ... this paradox does not arise if the correctness of quantum mechanics is firmly believed.
• Zeilinger et al 2012: ...there is never a paradox if the quantum state is viewed as to be no more than a “catalogue of our knowledge”.

I personally don't see how "a catalogue of knowledge" has anything to do with Quantum Mechanics. (Ditto for interpretations where the "agent" is the key.) The experiments are real, and the results objective. We all agree: "the time ordering of the detection events has no influence on the results". Obviously, we agree distance doesn't influence the results either.

But hey, as you say, to each their own.

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

I will repeat an argument I made earlier: Photons [1 & 2] are initially maximally entangled. Photons [3 & 4] are initially maximally entangled. In these states, neither [1] nor [4] can be entangled with anything else, and certainly not with each other. That's because of monogamy of entanglement (see proof). At a later time, [1 & 4] are maximally entangled (as demonstrated by experiment), clearly an objectively different state than their initial state. I see only 2 options to explain the "DrChinese paradox":

1. Is monogamy of entanglement a flatly incorrect principle? Maybe the proof is wrong, and then my argument fails. If so, a few textbooks may need updating.
2. Or does the entanglement swap executed at [2 & 3] objectively change the state of distant [1 & 4]? (This is of course entirely consistent with every known experiment.)

 

[PeterDonis]

think some extra leeway should be allowed in this case if you are going to allow Dr. Chinese to claim that the entanglement swapping disproves cause and effect interpretations

He has given a number of references to relevant papers.

 

[PeterDonis]

we don't know that "cause and effect" and "realism" violates nature. We know either "realism" or "non-locality" is violated.

These kinds of discussions really can't be done with vague ordinary language. Different people mean different things by "realism" and "locality". (I assume you mean "locality" is violated in the last part of what is quoted above.)

Bell gave a precise definition of "locality" in his papers on Bell's theorem: that the joint probability for measurements on a pair of quantum systems should factorize in a particular way. To my knowledge nobody has produced a model that satisfies that assumption but violates some other assumption of Bell's theorem in order to explain experimental results that violate the Bell inequalities. I think that is why most workers in the field have accepted that non-locality, in the sense of Bell inequalities being violated and that being due to non-factorizability of the joint probability, is unavoidable. If you are going to argue for a position that denies "realism" (and you would need to then point at the specific assumption behind Bell's theorem that you mean by "realism") while preserving "locality" in the sense of the factorizability assumption, you will need to find something in the literature that argues for that position.

Maybe a good question to ask is how entanglement swapping is handled in the Bohmian interpretation since in this interpretation the photon has a definite position.

In the Bohmian interpretation, while the particles have definite positions, those positions are not observable. But those positions determine measurement results, heuristically, by determining
which particular piece of, say, a beam splitter the particle passes through, which in turn determines which output arm the particle ends up in. Since in the Bohmian interpretation effects can propagate instantaneously, the particles can influence each other faster than light and that kind of influence can be used to explain their Bell inequality-violating correlations.

The main limitation I'm aware of with the Bohmian interpretation is that there is no generally accepted relativistic version of it.

 

[kurt101]

He has given a number of references to relevant papers.

Can you post one of the papers that proves the entanglement swapping experiment disproves non-local cause and effect interpretations?

 

[PeterDonis]

Can you post one of the papers that proves the entanglement swapping experiment disproves non-local cause and effect interpretations?

Please read through the thread. (As far as "non-local cause and effect interpretations", I'm not sure there are any other than Bohmian, in which "cause and effect" can be instantaneous.)

 

[kurt101]

The main limitation I'm aware of with the Bohmian interpretation is that there is no generally accepted relativistic version of it.

So how would the entanglement swapping experiment be handled by the Bohmian mechanics interpretation for the case where the BSM test is done after measuring 1 & 4?

The only thing I can think of to explain it is if 2 & 3 are affected by the 1 & 4 measurement in such a way where randomly once in a while 2 & 3 happen to end up in the same state when they enter the BSM. And by argument of symmetry when 2 & 3 end up in the same state 1 & 4 end up in the state required for entanglement if the experiment was run in the opposite order (BSM test first). And this is the argument that I think refutes Dr. Chinese claim that the entanglement swapping experiment disproves cause and effect. @Demystifier is this the correct explanation?

 

[PeterDonis]

how would the entanglement swapping experiment be handled by the Bohmian mechanics interpretation for the case where the BSM test is done after measuring 1 & 4?

That is one of the things I would expect a relativistic version of Bohmian mechanics to address. The non-relativistic version could treat the "cause and effect" between the BSM test and the 1 & 4 measurements as symmetric, i.e., not having a particular direction from one to the other, but I have not seen that kind of thing discussed in what literature I have read on the Bohmian interpretation. (A relativistic version, if it were based on something like quantum field theory, would naturally incorporate such a symmetry, since the operators corresponding to the measurements all commute.)

 

[DrChinese]

Can you post one of the papers that proves the entanglement swapping experiment disproves non-local cause and effect interpretations?

One of us is seriously confused. I say that swapping demonstrates nonlocal action and violates Einsteinian causality. I don’t know anything that matches what you describe.

Bohmian mechanics is nonlocal and realistic, although it is also contextual. Is that what you refer to? If so, I am not arguing for or against.

Hmmm, references to nonlocality? I think I have mentioned there are 5000+ papers with this in the title. Gisin, a top author, wrote a paper simply concluding: “Nature is nonlocal.” He adds that no relativistic theory can fully explain quantum mechanical behavior, and essentially vice versa. (Note this is not in any way a rebuttal to QFT or relativistic QM.)
https://arxiv.org/abs/0912.1475

https://arxiv.org/abs/1401.0419
In this reference, he argues any nonrealistic theory must include some nonlocal components.

I can do these quotes all night long. What I miss is you providing an actual suitable quote supporting your position from someone other than yourself.

 

[martinbn]

I will repeat an argument I made earlier: Photons [1 & 2] are initially maximally entangled. Photons [3 & 4] are initially maximally entangled. In these states, neither [1] nor [4] can be entangled with anything else, and certainly not with each other. That's because of monogamy of entanglement (see proof). At a later time, [1 & 4] are maximally entangled (as demonstrated by experiment), clearly an objectively different state than their initial state. I see only 2 options to explain the "DrChinese paradox":

1. Is monogamy of entanglement a flatly incorrect principle? Maybe the proof is wrong, and then my argument fails. If so, a few textbooks may need updating.
2. Or does the entanglement swap executed at [2 & 3] objectively change the state of distant [1 & 4]? (This is of course entirely consistent with every known experiment.)

You say that the state of 14 is objectively different. But you also agreed that measurements on 14 alone cannot tell the difference if 23 were measured or not. These are incompetible. The problem is that you omitt something important. That after the many trials you need to select a subset of the pairs 14, not the full set. Here is my chalange to you. If the state of 14 is objectively different after the measurement of 23, write it down. Show us what it was and what it became. Also explain how a system can be in different states but have the same outcomes on mearements.

 

[Demystifier]

So how would the entanglement swapping experiment be handled by the Bohmian mechanics interpretation for the case where the BSM test is done after measuring 1 & 4?

The only thing I can think of to explain it is if 2 & 3 are affected by the 1 & 4 measurement in such a way where randomly once in a while 2 & 3 happen to end up in the same state when they enter the BSM. And by argument of symmetry when 2 & 3 end up in the same state 1 & 4 end up in the state required for entanglement if the experiment was run in the opposite order (BSM test first). And this is the argument that I think refutes Dr. Chinese claim that the entanglement swapping experiment disproves cause and effect. @Demystifier is this the correct explanation?

I see nothing Bohmian in your explanation.

 

[martinbn]

I see nothing Bohmian in your explanation.

What is the BM explanation? Is it just a combination of the usual delayed choice plus entangelment explanations?

 

[Demystifier]

What is the BM explanation? Is it just a combination of the usual delayed choice plus entangelment explanations?

It's standard explanation, including the entanglement with the measuring apparatus (a'la von Neumann), minus collapse (a'la many worlds), plus Bohmian ontology (particles, fields, or whatever).

 

[martinbn]

It's standard explanation, including the entanglement with the measuring apparatus (a'la von Neumann), minus collapse (a'la many worlds), plus Bohmian ontology (particles, fields, or whatever).

Ah, I see, by the method of rigorous handwaving.

 

[Simple question]

You say that the state of 14 is objectively different.

No. QM say that if one can swap entanglement, the state 14 can be objectively different. So when a theory make predictions, scientific minded people that prefer hard science and not quibbling about philosophy, meanings of words or interpretations, and that are also ready to challenge their long held intuition/beliefs about NATURE .... build some experiment

But you also agreed that measurements on 14 alone cannot tell the difference if 23 were measured or not.

Correct, that is what QM says.

These are incompetible.

It does not follow. This is a beleif not logic.

The problem is that you omitt something important. That after the many trials you need to select a subset of the pairs 14, not the full set.

The problem is that you think it is omitted, while it actually is very important, and in plain sight.

If the state of 14 is objectively different after the measurement of 23

First mistake... the causal ordering is irrelevant.

, write it down.

... partially entangled

Show us what it was

Completely non-entangled

and what it became.

... partially entangled

Also explain how a system can be in different states but have the same outcomes on mearements.

Second mistake... in QM the initial system is unique. So only people using interpretation about causality and locality would think that 1&4 is in "more than one state".

Furthermore, the explaining needs to be done by people making the widest claims, like "everything is local and causal". QM is not, Bell's showed that in theory, and this was confirmed by experiment.
And if you think "un-realism" solved that issue, then fine. "whatever happens happens", may be a fine way to explains things. But none of that is in contradiction with DrChinese reporting (not interpretation) of standard QM results.

You will not be able to get rid of that paradox in your thinking, unless you drop one of those assumptions in Bell's theorem.

I myself equate Non-realism with incompleteness, you do that too, but unknowingly.

Meanwhile other people bet on non-locality. A significant bet, because they'll use teleportation or swapping, to physically protect information handling, and they want it to be real, to be secured... 100%

 

[Fra]

Below isnt a "claim" just painting a picture for balance and motivate the information or agent interpretation. Some you may convert to radical qbism ;)

Yes, I get that Zeilinger might say one thing in one place and yet another in the... same... place. "Whether these two particles are entangled or separable has been decided after they have been measured." Which is basically exactly the opposite of the next few sentences.

I found the text following (what you provided) interesting because it is oddly identical to an earlier quote I provided. I guess it might indicate some evolution in his thinking over time.

• Zeilinger et al 2002: ... this paradox does not arise if the correctness of quantum mechanics is firmly believed.
• Zeilinger et al 2012: ...there is never a paradox if the quantum state is viewed as to be no more than a “catalogue of our knowledge”.

I personally don't see how "a catalogue of knowledge" has anything to do with Quantum Mechanics. (Ditto for interpretations where the "agent" is the key.) The experiments are real, and the results objective.

If the information update is localized to the agent/observer (and as an agent/observer is just made of matter so it must be encoded there), then any information update from any observation of spatially separated events are always local by construction. All the paradoxes typically start when freely mixing up information acquired by different observers, ignoring the physics of communication between agents. Even to define "objectivity" operationally requires nothing less than agent-agent communication. How else can you speak meaningfully objectivity?

Any any interaction between information processing agents are by construction also constrained by communication. An agent cant process information it does not have and thus does not respond to it (for example non-clonable HV). And if the agent is a lump of matter I expect the same to hold for matter-matter interactions.

Of course there are cans of worms all over here, but its a picture at least. The dark side isnt that bad!

/Fredrik

 

[gentzen]

No. QM say that if one can swap entanglement, the state 14 can be objectively different. So when a theory make predictions, scientific minded people that prefer hard science and not quibbling about philosophy, meanings of words or interpretations, and that are also ready to challenge their long held intuition/beliefs about NATURE .... build some experiment

Correct, that is what QM says.

It does not follow. This is a beleif not logic.The problem is that you think it is omitted, while it actually is very important, and in plain sight.First mistake... the causal ordering is irrelevant.... partially entangledCompletely non-entangled... partially entangledSecond mistake... in QM the initial system is unique. So only people using interpretation about causality and locality would think that 1&4 is in "more than one state".

Furthermore, the explaining needs to be done by people making the widest claims, like "everything is local and causal". QM is not, Bell's showed that in theory, and this was confirmed by experiment.
And if you think "un-realism" solved that issue, then fine. "whatever happens happens", may be a fine way to explains things. But none of that is in contradiction with DrChinese reporting (not interpretation) of standard QM results.

You will not be able to get rid of that paradox in your thinking, unless you drop one of those assumptions in Bell's theorem.

I myself equate Non-realism with incompleteness, you do that too, but unknowingly.

Meanwhile other people bet on non-locality. A significant bet, because they'll use teleportation or swapping, to physically protect information handling, and they want it to be real, to be secured... 100%

I have no idea what you mean by this; it seems like word salad to me.

 

[kurt101]

I see nothing Bohmian in your explanation.

My explanation assumes:
The photons have a definite position at all times. That is Bohmian, right?
That cause and effect are preserved (i.e. no retrocausality). That is Bohmian, right?
That the photons have a state. That is Bohmian, right?

So maybe all that is lacking is how the mechanism of entanglement actually works or is described. I don't know how that is done in Bohmian mechanics, but I don't believe it matters to my argument.

I am just trying to understand how Bohmian mechanics can explain the ordering of photons and their states in entanglement swapping, in the case where the BSM test with photons 2 & 3 are done well after the measurement of photons 1 & 4. Bohmian mechanics needs to explain how the entanglement between 1 & 4 is established without resorting to an explanation involving retrocausality. Bohmian mechanics can't look into the future and see what will happen with photons 2 & 3, right?

 

[kurt101]

One of us is seriously confused. I say that swapping demonstrates nonlocal action and violates Einsteinian causality. I don’t know anything that matches what you describe.

That is very possible, but I have given you many opportunities to explain what exactly you mean and often you just ignore my questions about clarity. For example I asked what you meant by violating "Einsteinian causality". And you never gave me an answer. I will ask it again, is this what is your definition of Einsteinian causality? Is this your definition?:
(posted from google search):
In both Einstein's theory of special and general relativity, causality means that an effect cannot occur from a cause that is not in the back (past) light cone of that event.

Furthermore I have stated many times my position on non-locality and this experiment in many ways. It should be very clear to you what my position is by now. Here it is again:

1) In the case where the BSM test is done in the absolute past, I agree with you, this demonstrates non-locality.
2) In the case where the BSM test is done in the absolute future, I disagree with you (at least I think I do) that this demonstrates non-locality.

I can't prove for certain 2 is correct, but I don't think you can prove that it is wrong. That is my disagreement with you. I don't know how I can state it any clearer than that.

Bohmian mechanics is nonlocal and realistic, although it is also contextual. Is that what you refer to? If so, I am not arguing for or against.

And maybe we just have a misunderstanding, but if that is the case, I find your statements very misleading (and I will dig them out of history if you want me to explain more). They are misleading to me because you seem to imply that the entanglement swapping experiment excludes cause and effect interpretations, when that is not true. It only eliminates local interpretations (or realism), something Bell already proved to us a long time ago.

Hmmm, references to nonlocality? I think I have mentioned there are 5000+ papers with this in the title. Gisin, a top author, wrote a paper simply concluding: “Nature is nonlocal.” He adds that no relativistic theory can fully explain quantum mechanical behavior, and essentially vice versa. (Note this is not in any way a rebuttal to QFT or relativistic QM.)
https://arxiv.org/abs/0912.1475

https://arxiv.org/abs/1401.0419
In this reference, he argues any nonrealistic theory must include some nonlocal components.

I can do these quotes all night long. What I miss is you providing an actual suitable quote supporting your position from someone other than yourself.

Again, I agree with non-locality and I have stated that like every other time I post. So I don't know why you are bringing this up.

 

[Demystifier]

The photons have a definite position at all times. That is Bohmian, right?

It is Bohmian within non-relativistic QM. But here some photons are destroyed, after which they don't have definite positions. That's why you need to reformulate Bohmian mechanics in relativistic QFT.

As I said before, the simplest way to reformulate it is to forget about ontological particle positions and postulate the ontological fields having definite values at all times. Even when the photons are destroyed, the fields have some values $\phi({\bf x},t)$. The "velocity" $\dot{\phi}({\bf x},t)$ at any spatial point ${\bf x}$ nonlocally depends on $\phi$ at all points at the same time $t$. This dependence on time is not Lorentz covariant, but $\phi({\bf x},t)$ is a "hidden variable", i.e. not measurable in practice. The measurable quantities are Lorentz invariant. If you wonder how Lorentz non-covariant dynamics of "hidden variables" may lead to Lorentz invariant measurable predictions, see my https://arxiv.org/abs/2205.05986

In this language, you don't longer talk about entanglement between particles. Instead, you talk about entanglement between fields at different positions. The so called "particles" are no longer simple pointlike objects, but complicated configurations of fields.

 

[Demystifier]

That cause and effect are preserved (i.e. no retrocausality). That is Bohmian, right?

I suspect you are confused about the notion of cause and effect. For simplicity, consider classical mechanics without dissipation. For example, billiard balls without friction. How do you distinguish the cause from the effect?

The point is that, at the microscopic level, not only that the the future can be determined from the past, but also the past can be determined from the future. It's only on the emergent macroscopic level that the latter cannot be done. The absence of retrocausality is emergent at the macroscopic level. The hidden variable theory is, however, a microscopic theory in which retrocausality is possible. This should resolve your issues.

 

[Demystifier]

I am just trying to understand how Bohmian mechanics can explain the ordering of photons and their states in entanglement swapping, in the case where the BSM test with photons 2 & 3 are done well after the measurement of photons 1 & 4. Bohmian mechanics needs to explain how the entanglement between 1 & 4 is established without resorting to an explanation involving retrocausality. Bohmian mechanics can't look into the future and see what will happen with photons 2 & 3, right?

At the microscopic level, the state at any time $t$ determines both the future and the past from $t$. So in a sense, yes, Bohmian mechanics can "look" into both the future and the past, in the same sense in which classical mechanics can do that.

The above is just a consequence of determinism. But it should be distinguished from superdeterminism, which is, roughly speaking, determinism plus fine tuning of initial conditions. Classical and Bohmian mechanics are deterministic, but not superdeterministic. With superdeterminism one might, in principle, avoid quantum non-locality. Bohmian mechanics needs non-locality because it's only deterministic, not superdeterministic.

 

[kurt101]

The point is that, at the microscopic level, not only that the the future can be determined from the past, but also the past can be determined from the future.

No, these are just words with underlying assumptions that I don't have access to. Can you give me an example of one experiment that demonstrates what you mean by the past can be determined from the future?

 

[mattt]

No, these are just words with underlying assumptions that I don't have access to. Can you give me an example of one experiment that demonstrates what you mean by the past can be determined from the future?

It just means that in Bohmiam Mechanics (and also in Classical Mechanics) the set of all the points (in Phase Space) that a system will be in (both past and future) are fully determined by any single point.

Said in another way: the possible trajectories of the system in Phase Space are disjoint.