I Local mechanism for nonlocal anticorrelations inside spin theory

[DrChinese]

Before we tackle modern experiments, I want to know if you take issue with such accounts of simpler EPR experiments. E.g. Alice and Bob are spatially distant and perform joint measurements on entangled 2-particle systems. The outcomes exhibit Bell-inequality violating correlations. Without worrying about more sophisticated experiments yet, do you believe these simpler experiments cannot be accounted for with local interactions?

I follow the standard explanation that was the norm after Bell’s paper came out: local realism is ruled out. That means locality is a logical possibility when realism is ruled out.

I don’t know if I would use the term “local interactions“ in such a context. But I don’t argue with the general concept of locality as being feasible.

Of course, all of this before the discovery of remote entanglement via swapping. Just as Bell demonstrated something that had existed all along in quantum mechanics, remote swapping. demonstrates something that has also existed all along. Now that we know about entanglement swapping, it is no longer possible to entertain locality as being feasible.

 

[PeterDonis]

you can derive the Schrodinger equation and reproduce all of quantum mechanics

"All of quantum mechanics" is more than the Schrodinger equation.

That said, as far as I can tell, the stochastic interpretation is a recognized interpretation of QM. So you can adopt it as your preferred interpretation.

What you can't do, though, is assert that whatever meaning you want to give to terms like "locality" and "mechanism" based on the stochastic interpretation must also be adopted by everyone else in the discussion. If you read the guidelines for this subforum, you will see that discussions of QM interpretations are not resolvable because different interpretations make inconsistent claims, and you can't just assert that your preferred interpretation is right and all the others are wrong. There is no "right" and "wrong" in the sense of being able to test interpretations vs. each other by experiment; they all make the same predictions for all experimental results. So interpretation discussions are a matter of opinion. Even if your opinion is that the stochastic interpretation provides a "local mechanistic" account of quantum phenomena, others might not share that opinion, and there is no way for you to show that they must share it.

 

[Morbert]

I follow the standard explanation that was the norm after Bell’s paper came out: local realism is ruled out. That means locality is a logical possibility when realism is ruled out.

I don’t know if I would use the term “local interactions“ in such a context. But I don’t argue with the general concept of locality as being feasible.

The first stepping stone at least.

In a traditional EPR experiment, when Alice carries out a measurement on the 2-particle system, she immediately updates relevant probability distributions for outcomes of possible measurements Bob can (or did) perform on the same system. According to Peres, she can do this without invoking nonlocal interactions as she does not interpret these distributions as concerning objective properties of the 2-particle system.

Similarly, in an entanglement swapping experiment, when Alice carries out a BSM involving both 2-particle systems (The 1,2 system and the 3,4 system), she can immediately update distributions for outcomes of possible joint measurements on the 1,4 system without invoking nonlocal interactions as she does not interpret these distributions as concerning objective properties of the 1,4 system.

 

[PeterDonis]

when Alice carries out a BSM

Alice isn't the one who carries out the BSM. Alice and Bob each have photons they will measure, photons 1 and 4, but someone else, Charlie or Victor or whoever, carries out the BSM on photons 2 and 3. And whether or not that BSM gets carried out determines whether Alice and Bob see correlations between their measurements. And this is true even if Alice, Bob, and the location of the BSM are far apart and all of the relevant events are spacelike separated so no light signals can travel between them.

 

[Morbert]

Alice isn't the one who carries out the BSM. Alice and Bob each have photons they will measure, photons 1 and 4, but someone else, Charlie or Victor or whoever, carries out the BSM on photons 2 and 3. And whether or not that BSM gets carried out determines whether Alice and Bob see correlations between their measurements. And this is true even if Alice, Bob, and the location of the BSM are far apart and all of the relevant events are spacelike separated so no light signals can travel between them.

You can adopt any naming convention, so long as the important comparison is made: In the traditional EPR, an observer carries out a measurement and updates distributions re/ possible measurements of the other observer. In the entanglement swapping experiment, an observer carries out a BSM and updates distributions re/ possible joint measurements on the 1,4 system by the other observers.

 

[PeterDonis]

You can adopt any naming convention

The naming convention isn't the issue. The issue is that your description implied that the person who carries out the BSM is the same as one of the people who makes the measurements whose correlations will be assessed. That is not the case.

 

[Morbert]

The naming convention isn't the issue. The issue is that your description implied that the person who carries out the BSM is the same as one of the people who makes the measurements whose correlations will be assessed. That is not the case.

My description did not imply this.

 

[PeterDonis]

My description did not imply this.

It did for anyone who is familiar with the usual naming convention used for these experiments. From your post #55 I now see that you did not intend that implication, but while you say the naming convention isn't the issue, if you pick a naming convention that's different from what's usually used in the literature, you are inviting confusion.

 

[DrChinese]

1. In a traditional EPR experiment, when Alice carries out a measurement on the 2-particle system, she immediately updates relevant probability distributions for outcomes of possible measurements Bob can (or did) perform on the same system. According to Peres, she can do this without invoking nonlocal interactions as she does not interpret these distributions as concerning objective properties of the 2-particle system.

2. Similarly, in an entanglement swapping experiment, when Alice carries out a BSM involving both 2-particle systems (The 1,2 system and the 3,4 system), she can immediately update distributions for outcomes of possible joint measurements on the 1,4 system without invoking nonlocal interactions as she does not interpret these distributions as concerning objective properties of the 1,4 system.

1. What you are saying makes no sense, and to the extent you say it represents Peres’ views I reject it completely. It is the joint expectation value that is important, and that is strictly a function of a joint context. A nonlocal context…

2. Similarly, this literally makes no scientific sense. What Alice knows after her kind of measurement (on 1) is precisely nothing about 4. And has absolutely no connection of any kind to 4 unless an experimenter elsewhere makes a decision to entangle it with 4. You know, an experimenter who is far away and is… not local.

 

[iste]

"All of quantum mechanics" is more than the Schrodinger equation.

That said, as far as I can tell, the stochastic interpretation is a recognized interpretation of QM. So you can adopt it as your preferred interpretation.

What you can't do, though, is assert that whatever meaning you want to give to terms like "locality" and "mechanism" based on the stochastic interpretation must also be adopted by everyone else in the discussion. If you read the guidelines for this subforum, you will see that discussions of QM interpretations are not resolvable because different interpretations make inconsistent claims, and you can't just assert that your preferred interpretation is right and all the others are wrong. There is no "right" and "wrong" in the sense of being able to test interpretations vs. each other by experiment; they all make the same predictions for all experimental results. So interpretation discussions are a matter of opinion. Even if your opinion is that the stochastic interpretation provides a "local mechanistic" account of quantum phenomena, others might not share that opinion, and there is no way for you to show that they must share it.

I didn't say stochastic mechanics is right, I just stated my disagreement that in principle mechanistic explanations are not sustainable. I just gave an example which is no different from the examples in the post I was replying to - if you can derive quantum mechanics from a "mechanistic" perspective then surely that is a counterexample.

Also, none of the conversations I have had in this thread involving 'mechanisms' and 'locality' have been from a stochastic perspective at all. Nothing in the original post of the thread is a stochastic perspective.

 

[iste]

Sorry, virtually everything you are saying involves claiming there are local hidden variables. Bell tells us otherwise, which is generally accepted by the physics community.

Well fair enough since the description is not complete.

To be clear: there is no connection whatsoever between 1 and 4 regardless of the polarization measurements of 2 & 3.

Yes, I say this is the case and explain why that is the case in the text you quoted.

The only way you get entanglement between 1 & 4 is for 2 & 3 to interact indistinguishably.

Yes, which is just a means of performing the measurement on the photons so you can attain coincidences to condition on.

See figure 1, noting that distances in this setup are arbitrary. And please, how about addressing my point: there can be no “information update” unless a remote physical interaction occurs between 2 & 3. So obviously something physical does happen remotely, and it’s not simply an information update. Which is why it cannot be statistically conditioned on the outcome at 2 & 3, which can be performed later. Whether there are perfect correlations or not is strictly dependent on whether that physical interaction occurs.

Again: the 2 & 3 outcomes are the same - HH, HV, etc. - regardless of whether that physical interaction occurs. But if it does not occur, there are no perfect correlations. So that is the difference, and why your explanation cannot work.

From my perspective, a measurement projecting onto the Bell state is just more or less equivalent to statistical conditioning and since that is all that is really involved, there is nothing more to it than statistical conditioning.

Again: the 2 & 3 outcomes are the same - HH, HV, etc. - regardless of whether that physical interaction occurs. But if it does not occur, there are no perfect correlations. So that is the difference, and why your explanation cannot work.

Yes, because you cannot establish coincidences or do statistical conditioning until measurement given that Bell state measurement is just statistical conditioning and requires the establishment of coincidences via coherence in order to do so. I mean, this is obviously why independent sources need to be time-synchronized.

 

[Morbert]

1. What you are saying makes no sense, and to the extent you say it represents Peres’ views I reject it completely. It is the joint expectation value that is important, and that is strictly a function of a joint context. A nonlocal context…

Then my initial suspicion was correct. You do not accept such accounts of even traditional EPR experiments, never mind entanglement swapping experiments.

In the traditional EPR experiment, if we interpret all relevant distributions as about objective properties of the measured system, imperfectly known, then the Bell-inequality-violating correlations reproduced by joint measurements on the 2-particle system imply* one measurement immediately affects the site of the other, distant measurement .

If, on the other hand, we interpret all relevant distributions as about outcomes of possible measurements, and hence relax counterfactual definiteness, then the Bell-inequality-violating correlations reproduced by joint measurements on the system no longer imply one measurement immediately affects the site of the other, distant measurement.

What is your precise objection to this? Entanglement swapping scenarios are hard to address productively until this more foundational issue is resolved.

* Leaving aside topics like superdeterminism

 

[Fra]

Sorry, virtually everything you are saying involves claiming there are local hidden variables. Bell tells us otherwise, which is generally accepted by the physics community.

The implict assumptions in bells theorem has been discussed before in many threads and they aren't all obvious.

Bell type hidden variables aren't the only logical possibility to "hidden mechanism" with some sort of "hidden variables" to explain correlation. They were ineded a possibility of early investigation - and this possibility was nicely disproven via Bells theorem.

But the original inquiry is still there!

The term hidden variable or mechanism has been poisoned, as those terms are lumped with the resistnace against QM.

Can we call it "hidden parameter in a non-classical model" and keep focusing on the original inquiry, to IMPROVE our undertanding of QM? Even in a weird game of expectations, there are "mechanisms", but maybe of different kinds that are not best understood in the newtonian paradigm.

About "old descriptions that do not work for modern experiments" I will just note that Quantum mechanics as well as QFT are STILL in the newtonian paradigm.

My opinion is that it is even worse: I think the old paradigm do not work for understanding the nature of interactions in the quantum domain.

/Fredrik

 

[Nugatory]

But the original inquiry is still there!

From that perspective, Bell's Theorem isn't saying that we cannot find a "mechanism", but rather that if we ever do it will necessarily be as offensive to our classical intuition as QM already is. That seems to me a defensible proposition, although it may imply a broader definition of "mechanism" than many people are assuming.

However

I will just note that Quantum mechanics as well as QFT are STILL in the newtonian paradigm.

Here you have lost me, probably because my definition of that paradigm is more restrictive than yours. I understand it to include that effects have causes (constrained by relativity) and counterfactual definiteness, and I do not see how to reconcile these with Bell-violating QM.

 

[PeterDonis]

Alice knows after her kind of measurement (on 1)

In Morbert's terminology, Alice is the one who does the BSM, not the one who measures photon #1. I agree this is not well chosen terminology on his part. See my post #58.

 

[PeterDonis]

none of the conversations I have had in this thread involving 'mechanisms' and 'locality' have been from a stochastic perspective at all. Nothing in the original post of the thread is a stochastic perspective.

Then you are not adopting the stochastic interpretation as your preferred interpretation--which means that, according to the guidelines of this subforum, you should not be mentioning it at all. You need to pick an interpretation and stick to it. If you are not picking the stochastic interpretation, which interpretation are you picking?

From my perspective, a measurement projecting onto the Bell state is just more or less equivalent to statistical conditioning and since that is all that is really involved, there is nothing more to it than statistical conditioning.

This is a straightforward statistical interpretation, which is fine, but it's not the stochastic interpretation. So if this is the interpretation you are picking, you need to stick to it and stop mentioning the stochastic interpretation.

That said, everything in my earlier post still applies if you are picking the statistical interpretation, because @DrChinese is not using that interpretation. His preferred interpretation is one in which QM has to explain the results of individual runs of an experiment, not just the statistics over many runs. So what you are saying simply does not apply to the interpretation he is using. And, as I pointed out earlier, there is no way to resolve that, because which intepretation you pick is a matter of personal preference and opinion; there is no way to test it by experiment. So you and he are basically talking past each other.

 

[PeterDonis]

Bell type hidden variables aren't the only logical possibility to "hidden mechanism" with some sort of "hidden variables" to explain correlation. They were ineded a possibility of early investigation - and this possibility was nicely disproven via Bells theorem.

If you claim there is another possibility, you need to give a reference that describes what it is. You can't just wave your hands and gesture in the direction of a possibility that you can't even show is actually realized.

 

[PeterDonis]

You do not accept such accounts of even traditional EPR experiments

Yes, as I pointed out to the OP in post #66, the interpretation @DrChinese is using does not accept such accounts even of traditional EPR experiments. You appear to be using a statistical interpretation, which does; but @DrChinese is not.

 

[Morbert]

Yes, as I pointed out to the OP in post #66, the interpretation @DrChinese is using does not accept such accounts even of traditional EPR experiments. You appear to be using a statistical interpretation, which does; but @DrChinese is not.

I am inferring a stronger claim from @DrChinese. A claim that is not interpretation dependent: Any interpretation that can account for entanglement swapping experiments must involve actions having immediate effects in spatially distant regions.

@DrChinese If you are simply making an interpretation-dependent claim about local action, then there isn't disagreement between us. I agree that some interpretations suppose nonlocal action, while others do not.

 

[DrChinese]

From my perspective, a measurement projecting onto the Bell state is just more or less equivalent to statistical conditioning and since that is all that is really involved, there is nothing more to it than statistical conditioning.

Yes, because you cannot establish coincidences or do statistical conditioning until measurement given that Bell state measurement is just statistical conditioning and requires the establishment of coincidences via coherence in order to do so. I mean, this is obviously why independent sources need to be time-synchronized.

The idea that the Bell State Measurement (BSM) on 2 & 3 is “statistical conditioning” has been experimentally rejected. The BSM requires physical interaction between 2 & 3. That physical interaction is manifested by indistinguishability of the 2 and 3 photons. Those two must arrive near simultaneously at the beam splitter to enable them to interact. If one of the photons is delayed, then it will be distinguishable from the other. If the photons are not indistinguishable, then the entanglement swap fails. Please reference the following experiment, also from a Zeilinger team.

https://arxiv.org/pdf/1203.4834

Check out figure 3, the A chart shows Entangled state statistics when there is indistinguishability. The B chart shows Separable state statistics when there is not such indistinguishability because a delay was inserted, preventing the two photons from interacting as part of the BSM.

This experiment was performed in 2012. It has been replicated by other papers and teams. This is an application of standard quantum mechanics. Note that while there is synchronization between the independent sources, this does not cause any special entanglement or related Entangled state statistics.

 

[DrChinese]

Then my initial suspicion was correct. You do not accept such accounts of even traditional EPR experiments, never mind entanglement swapping experiments.

In the traditional EPR experiment, if we interpret all relevant distributions as about objective properties of the measured system, imperfectly known, then the Bell-inequality-violating correlations reproduced by joint measurements on the 2-particle system imply* one measurement immediately affects the site of the other, distant measurement .

…

No, I accept traditional Bell tests and explanations up to the point that I have learned something new. But your description is hardly a traditional explanation by any means. The usual explanation for Bell correlations is that parametric down conversion creates a system of two photons, a Fock state. It is called a biphoton. The biphoton has spatial extent. It is not agreed upon whether there is physical collapse or not. That tends to very from interpretation to interpretation

What we hopefully agree on is that such a biphoton, when measured by Alice and Bob, at the same angle setting, will produce perfect correlations. And hopefully, we agree that those outcomes are not pre-determined in a classical manner. After all, that would violate Bell.

 

[DrChinese]

I am inferring a stronger claim from @DrChinese. A claim that is not interpretation dependent: Any interpretation that can account for entanglement swapping experiments must involve actions having immediate effects in spatially distant regions.

@DrChinese If you are simply making an interpretation-dependent claim about local action, then there isn't disagreement between us. I agree that some interpretations suppose nonlocal action, while others do not.

I am citing experimental papers that demonstrate extremely specific behavior. That behavior must be explainable by any interpretation to remain compatible with the predictions of quantum mechanics.

It should be obvious that many of the existing interpretations fail in describing these experimental results. I can’t force anybody to discard their interpretation. But I can ask how various interpretations can explain those results. The idea that there is some magical concept buried in the idea of a “information update” should be rejected. With a BSM, the information is the same, regardless of whether there is indistinguishability or not. But the results are not the same, and so experiment rules that out. The experimenter who runs the BSM chooses freely whether to create entangled state statistics, or separable state statistics. And that experimenter is situated far away from Alice and Bob and the perfect correlations they record. Note that no specific mechanism is presented as to how that occurs. It just does.

I would call that non-local action at a distance, completely consistent with orthodox quantum mechanics as we understand it today. So by the same general reasoning that we exclude local realistic theories due to Bell: I would say we should exclude all local theories and interpretations based on experiments such as those I’ve cited.

 

[PeterDonis]

It should be obvious that many of the existing interpretations fail in describing these experimental results.

No, it's not obvious. We have had discussions along these lines before. All interpretations make the same predictions for all experimental results, because they all use the same (or equivalent) math--the math of standard QM. Unqualified claims that an interpretation cannot account for certain experimental results are simply not valid, and are out of bounds in this subforum.

You evidently do not accept the claims of many existing interpretations to account for the experimental results you cite, but that is just your opinion. You cannot state it as a fact, certainly not an "obvious" fact.

 

[PeterDonis]

I can ask how various interpretations can explain those results.

Such questions would need to be answered by giving references that use those interpretations and give explanations based on them. That includes your claims about how your preferred interpretation accounts for the results, btw. At this point, without any further references, this thread can't really go any further, because everyone has stated their positions and, since all such positions regarding interpretations are a matter of opinion (per the guidelines for this subforum), disagreements about such things are not resolvable.

 

[PeterDonis]

Given the situation described in my post #74 just now, I am closing this thread. If anyone has a reference they would like to post that describes how their preferred interpretation deals with the experimental results under discussion, you can PM me and I'll take a look, and reopen the thread if warranted.