Undergrad Entanglement: is there 'action at a distance' due to measurement?

[PeterDonis]

Ah, yes, thanks. I have confused eigenstate and eigenvalue. So, until B is measured it has an eigenstate of spin. Correct?

It depends on what you mean. Please read my post again, carefully.

 

[martinbn]

Einsteinian Locality (denying remote effects of any kind) seem untenable.

Why is that untenable? And what exactly is a remote effect?

 

[DrChinese]

Why is that untenable? And what exactly is a remote effect?

Entanglement Swapping/Quantum Teleportation are remote effects. Obviously, there are interpretations that attempt to retain locality in the face of this. But most of those interpretations are needing progressively more convoluted descriptions to accommodate Swapping experiments while maintaining something they call "locality".

An example of that is MWI, which now appears to require something resembling "global" splitting of worlds in order to make sense of swapping. How else to explain that there is syncing of observation results of particles that have never been in a common area of spacetime?

Similarly, for interpretations that do not posit the Swap (Bell State Measurement) as being physical: How to explain the "revealing" of correlations of independently produced systems? (As noted in these experiments themselves, those systems were previously uncorrelated before the swap.)

Each person is free to view the various arguments as they like. (And I am constantly surprised at how many people essentially even advocate Local Realistic explanations in the face of Bell.) For me: Swapping experiments are the nail in the coffin for locality.

 

[Fra]

I think we share an underlying desired to understand or find a mechanism, but we currently have very different ideas and thinking... this is why i liket it where we can at least agree on something as it makes discussions more constructive than more "confrontative". Just concluding that we disagree or think differently is not leading to progress.

(And I am constantly surprised at how many people essentially even advocate Local Realistic explanations in the face of Bell.) For me: Swapping experiments are the nail in the coffin for locality.

Are you by any chance lumping Barandes ideas into these "people"?

/Fredrik

 

[martinbn]

Entanglement Swapping/Quantum Teleportation are remote effects. Obviously, there are interpretations that attempt to retain locality in the face of this. But most of those interpretations are needing progressively more convoluted descriptions to accommodate Swapping experiments while maintaining something they call "locality".

An example of that is MWI, which now appears to require something resembling "global" splitting of worlds in order to make sense of swapping. How else to explain that there is syncing of observation results of particles that have never been in a common area of spacetime?

Similarly, for interpretations that do not posit the Swap (Bell State Measurement) as being physical: How to explain the "revealing" of correlations of independently produced systems? (As noted in these experiments themselves, those systems were previously uncorrelated before the swap.)

Each person is free to view the various arguments as they like. (And I am constantly surprised at how many people essentially even advocate Local Realistic explanations in the face of Bell.) For me: Swapping experiments are the nail in the coffin for locality.

No, my question was why is Einstein locality untenable? Everyone agrees about Bell non-locality.

 

[sahashmi]

I agree with this too. I was formerly of the view that Local Realism is untenable (due to Bell's Theorem). But with more and more experiments: Both Realism (basically contradicted by the HUP anyway) and Einsteinian Locality (denying remote effects of any kind) seem untenable.

(And every hypothetical mechanism for nonlocality seems equally untenable LOL.)

The HUP does not contradict realism. It simply says that we can’t simultaneously measure two different properties of something physical. And even if certain properties at measurement are merely contextual, it just means that what we measure depends on what we measure. This is a trivial point and has nothing to say about objective reality. It merely means that we don’t know how to describe objective reality before measurement.

 

[Sambuco]

The HUP does not contradict realism

I believe @DrChinese is referring to realism as something like "the system has well-defined properties independent of measurements" (correct me @DrChinese if I misunderstood you).

It simply says that we can’t simultaneously measure two different properties of something physical

I think this is wrong in the sense that the HUP only states that, for two non-commuting observables, there is no quantum state that determines, i.e. predicts with probability one, the outcome of each of the two measurements.

Lucas.

 

[Sambuco]

I agree with this too. I was formerly of the view that Local Realism is untenable (due to Bell's Theorem). But with more and more experiments: Both Realism (basically contradicted by the HUP anyway) and Einsteinian Locality (denying remote effects of any kind) seem untenable.

(And every hypothetical mechanism for nonlocality seems equally untenable LOL.)

That also reflects how my understanding of this topic has changed over time. Your last statement explains why, today, I believe that the experimental verification of the violation of Bell's inequality and the evidence of remote entanglement swapping strongly point against the notion of causation at a fundamental level.

Lucas.

 

[Morbert]

There are a good few well-established projects in foundations of quantum mechanics that preserve Einstein locality and statistical independence for all known experiments: E.g. Instrumentalism, minimal Statistical, Oxford Everettianism, Decoherent/Consistent Histories, topos-theoretic interpretations, and QBism.

There is also no consensus about the correctness of any project in foundations of quantum mechanics.

 

[DrChinese]

Are you by any chance lumping Barandes ideas into these "people"?

It depends on the day of week for my lumping him in with those writers, as well as even a few posters here.

We already know Barandes' view on locality: "...Causally Local Formulation of Quantum Theory". What he says on realism is not clear to me: "Moreover, superposition is no longer a literal smearing of configurations, interference is just a breakdown in divisible dynamics, and decoherence is merely the leakage of statistical correlations out into the larger environment." (That's word salad to me.) Whenever I hear someone using the term "stochastic", I immediately think they are a realist at their core.

We had a long discussion about Mjelva's paper. He seems to be a local realist without saying so. Many others as well, I have a lot of bookmarks to papers of that type (Christian, Laudisa, Sica, Santos, De Raedt, etc.). Most identify an element of Bell that they can claim is "wrong" in some manner, so as to avoid the Bell conclusion.

 

[DrChinese]

I believe @DrChinese is referring to realism as something like "the system has well-defined properties independent of measurements" (correct me @DrChinese if I misunderstood you).


I think this is wrong in the sense that the HUP only states that, for two non-commuting observables, there is no quantum state that determines, i.e. predicts with probability one, the outcome of each of the two measurements.

Lucas.

Correct, you can also call it objective reality or non-contextual reality.

The obvious point about the HUP: It is a prima facie case for rejecting realism. Of course, realists will inevitably point to its application to experimental results - but HUP does not represent the underlying reality. But that's pretty close to saying a horse is actually a unicorn in disguise. You can say that about almost anything.

Ditto for attempts to ignore the obvious signs of "action at a distance" in Entanglement Swapping experiments. "It might look like nonlocality, but it isn't." Or maybe things are exactly as they appear at first blush.

 

[physika]

realism as something like the system has well defined properties independent of measurements

Realism is more than that, is not simply about properties.
Which things/entities have that
properties ?

.....

 

[martinbn]

Ditto for attempts to ignore the obvious signs of "action at a distance" in Entanglement Swapping experiments. "It might look like nonlocality, but it isn't." Or maybe things are exactly as they appear at first blush.

To me it doesn't look like "action at distance". In fact it doesn't look like any kind of action at all. I know that to some it looks like it, and for some (you for example) it is unconditionally proven, but I think you are wrong.

 

[PeterDonis]

the obvious signs of "action at a distance" in Entanglement Swapping experiments. "It might look like nonlocality, but it isn't."

"Nonlocality" and "action at a distance" are not the same thing.

Nonlocality, if by that we mean violations of the Bell inequalities, is an experimental fact---and since you're relying on experimental facts for your argument, that's the definition of "nonlocality" you are implicitly using.

"Action at a distance" is a feature of some QM interpretations (including the QM interpretation you are implicitly using), but not all. It is of course possible that at some point, we will have a more comprehensive theory, with experimental support, to which our current QM is an approximation, that will have "action at a distance" as an explicit part of its dynamics, and will tell us how to confirm experimentally that this "action at a distance" actually happens. But we don't have any such theory now, and in the absence of one, claims about "action at a distance" are interpretation dependent, and therefore are not resolvable by experiment; they're a matter of personal opinion.

 

[Fra]

I think it's the fact that we do not have (one way or the other) any explanatory mechanisms, that some of just accept, and some of use refuse to settle with that is one difference.

It seems to me that Dr Chinese can't accept this, and neither can I. So I symphatise with that.

But "explanation" can come in different forms, Bells theorem provides a no-go theorem for certain types of explanation in terms of "objective beables", which would explain "quantum phenomena" by marginalise them out.

But the quest for an explanation does not end with that. It only means that a viable explanation has to evade some of the premises.

Dr Chinese's thinking seems to currently lean strongly towards some explanation in terms of action at distance, probably not because it make so much sense, but because he seems to see no other solution in the face of entanglement swapping + bells theorem? Have I understood you here?

And then to those that say, that this makes no sense, it's fair to ask: What is the better idea?

/Fredrik

 

[Fra]

Whenever I hear someone using the term "stochastic", I immediately think they are a realist at their core.

Do you see the difference in the Bell type stochastics which is marginalising over objective hidden variables that influence the total system dynamics (via dynamical law)? and the stochastics over subjective hidden variables which is identified with the irreducible stochastic law? There is no objective margninalization going on in Barandes stochastics; it's irreducible.

Why that is satsifactory to me is that (expcet that the timeevolution of the matrices needs to be explained from new first princuipoes) a stochastic law, is as simple as it gets, and the only law thay need no further explanation.

After all, it's not the randomness of outcomes in QM that we seek to explain - this is indeed I think irreducible - it's all about the correlaction of remote experiments. Barandes view does not restore determinsim, via margnialized HV.

/Fredrik

 

[DrChinese]

"Nonlocality" and "action at a distance" are not the same thing.

Nonlocality, if by that we mean violations of the Bell inequalities, is an experimental fact---and since you're relying on experimental facts for your argument, that's the definition of "nonlocality" you are implicitly using.

"Action at a distance" is a feature of some QM interpretations (including the QM interpretation you are implicitly using), but not all. …

I think your differentiation of “nonlocal” and “action at a distance” is fair.

I usually employ AAAD as a term to reference something that is interpretation dependent. But I also use the word “distance” in the phrase to refer to distance in spacetime, and in ways that could be considered to defy Einsteinian causality. There is a somewhat analogous usage in the word “nonlocality”, going back to various delayed choice type experiments. For example: entanglement of particles that never coexist.

So when we are trying to put together a storyline about what is going on beneath the hood, regarding the (factual) nonlocality of experiments, we are necessarily speculating when adopting an interpretation.

I believe the factual conclusions of many cited experiments can be assembled into a more comprehensive narrative that rules out many popular interpretations. I know this won’t convince most advocates of those interpretations. But it is fair to challenge those viewpoints if I lead with accepted science.

claims about "action at a distance" are interpretation dependent, and therefore are not resolvable by experiment; they're a matter of personal opinion.

I’ve been pretty clear that each person is free (within everything I reference in the way of experiments) to hold their own views. Here in the interpretations forum it is common to profess a perspective and explain its pros and hopefully, its cons.

 

[PeterDonis]

I believe the factual conclusions of many cited experiments can be assembled into a more comprehensive narrative that rules out many popular interpretations.

Such a "narrative", if it actually did what you claim, would be the sort of more comprehensive theory that I described, to which our current QM would be an approximation. In other words, it would make experimental predictions that current QM does not make, which would be true if the "narrative" was true, but false if it was not--so that the claim could actually be checked.

But as far as I know, no such thing actually exists. Nobody has a more comprehensive model that makes actual predictions that go beyond the standard predictions of QM, enabling an experimental test of the model, where those tests have actually come out as predicted. (There are examples of alternate theories to standard QM, such as the GRW stochastic collapse model, but all of them so far have been falsified by experiments; their predictions haven't worked.)

it is fair to challenge those viewpoints if I lead with accepted science.

But you're not doing that; you're leading with a claim about possible future science that doesn't currently exist. See above.

Our current "accepted science" simply cannot distinguish between the various interpretations that are out there. That's why, while it's fine to state your preferred interpretation and its pros and cons in this forum, it's not fine to claim that other interpretations are ruled out by experiment. That's simply not the case. All QM interpretations make the same experimental predictions. You might not like how some of them get there, but that's a matter of personal opinion.

 

[DrChinese]

1. DrChinese's thinking seems to currently lean strongly towards some explanation in terms of action at distance, probably not because it make so much sense, but because he seems to see no other solution in the face of entanglement swapping + bells theorem? Have I understood you here?

2. And then to those that say, that this makes no sense, it's fair to ask: What is the better idea?

1. You hit the nail on the head.

2. Correct here too. Keeping in mind that AAAD is for me a bucket that includes all those ideas other than the usual interpretations, but that are pretty well expressed in orthodox QM:

There is a saying attributed to Sherlock Holmes: “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.”

For example: retrocausal (they go under a lot of names) interpretations might have utility. (I’m not pushing that in particular.)

I’m just saying: We’ve been examining Bohmian ideas since the 40’s and Everettian ideas since the 50’s and have so far got zilch from either. And I believe there’s now sufficient accepted evidence to rule out both of those. But that’s simply my opinion and assessment.

 

[DrChinese]

All QM interpretations make the same experimental predictions. You might not like how some of them get there, but that's a matter of personal opinion.

No, they all claim to make the same predictions. Each has assumptions that are fair to challenge. This forum is the place to discuss within the context of a specific idea.

This thread is about AAAD, but believe me I don’t want to derail others expressing their ideas. I am just one voice. I’ve probably said enough for today…

 

[PeterDonis]

There is a saying attributed to Sherlock Holmes: “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.”

This assumes that we know all the possibilities to check. We don't.

For example, I've mentioned statistical interpretations in some of these discussions. Statistical interpretations are non-realist in the sense that the quantum state only describes statistical ensembles (or, equivalently, preparation procedures); it does not describe individual quantum systems. Which means such interpretations don't even try to provide the kind of "narrative" you are looking for. To you, that's a bug. To me, it's a feature, because I think we are simply too ignorant at this stage of our development of understanding quantum mechanics to even know what kinds of models we should be looking at. All we've found out so far is what kinds of underlying models don't work. I'm not saying such research shouldn't continue; of course it should. But we should be very, very cautious about making claims about how an underlying model "has to work". We might simply not even be aware yet of the kinds of models that will ultimately end up working. Bear in mind that before the early 1900s, nobody was even aware that the kinds of models that now make up standard QM were even possible.

 

[PeterDonis]

they all claim to make the same predictions.

I don't think you've given a single example of an interpretation which made such a claim wrongly. Your basis for criticizing interpretations you don't like, as far as I can tell, has nothing to do with any actual demonstration that they make wrong predictions. You just don't like the underlying models that they use to explain how they arrive at those predictions. Which is fine as a matter of opinion, but not if you're going to make a factual claim about what predictions an interpretation does or does not make.

 

[PeterDonis]

And I believe there’s now sufficient accepted evidence to rule out both of those. But that’s simply my opinion and assessment.

Evidence ruling out a model should not be a matter of opinion. Either you can cite the specific evidence and the specific prediction it falsifies, or you can't. Either way this should be a factual matter, not a matter of opinion.

 

[physika]

(There are examples of alternate theories to standard QM, such as the GRW stochastic collapse model, but all of them so far have been falsified by experiments; their predictions haven't worked.)

Not all.

 

[PeterDonis]

Not all.

Which ones have not? Can you give references?

 

[PeroK]

No, they all claim to make the same predictions. Each has assumptions that are fair to challenge. This forum is the place to discuss within the context of a specific idea.

This thread is about AAAD, but believe me I don’t want to derail others expressing their ideas. I am just one voice. I’ve probably said enough for today…

The pure QM approach is to take the abstract state mechanics as the mechanism. It's not always possible to find physical characteristics that map to all aspects of what the states imply.

A good example might be where an electron rotated by 360 degrees is not in the same state as it was originally, despite having all the same measurable quantities. It's clear from the state formalism why this is and you can exploit this by a suitable experiment involving interference. If you want to be a realist you need, dare I say, an element of physical reality that corresponds to the change of sign of the state.

Similarly, there is no measurable difference between a particle that is effectively in an eigenstate of spin and one that has been measured. The mechanics according to pure QM is not action at a distance- or any other realist mechanism- but the abstract state mechanics.

What QM, Bell and entanglement swapping show is that abstract state mechanics is richer than any realistic mechanics. And, somehow, nature manages to operate under this abstract regime.

 

[physika]

Which ones have not? Can you give references?

https://www.mdpi.com/1099-4300/25/4/645#B30-entropy-25-00645

"The largest particles interfered so far are of mass 10⁴ amu in the Vienna interferometers [24,25]. This experiment is still about two orders of magnitude too small to test the CSL model with the strongest bound according to Adler"

"Future plans for matter-wave interferometers which achieve even larger macroscopicity involve the OTIMA and LUMI interferometers at Vienna [25,29]. OTIMA and LUMI are Talbot–Lau interferometers and should be able to interfere with particles of masses up to 10⁷ amu and beyond."

"Experiments with a particle of 10 nm diameter [l = 100 nm, t = 2 ms] would directly test the CSL model with Adler’s parameter choice [34]"

----------

Testing the foundation of quantum physics in space via Interferometric and non-interferometric experiments with mesoscopic nanoparticles

https://www.nature.com/articles/s42005-021-00656-7


.....

 

[Fra]

What QM, Bell and entanglement swapping show is that abstract state mechanics is richer than any realistic mechanics.

I agree...

And, somehow, nature manages to operate under this abstract regime.

...but we still seek an understanding of the descriptions in this abstract regime.

And the correlation of separated measurements, still begs for some kind of explanation with some form of causal order, even if abstract. And herein lies also I think a problem of timeless physics, because the causal order is not fundamental, it's more like an arbitrary parameterisation. And something just doesn't seem right with that.

And it seems an explanation in any direction is going to be "controversial" one way or the other. I think action at distance is really weird, but subjective reality is not weird for me. But others refuse to give up objective reality, and pay the price of other pathologies. So which pathological implication are easier to live with?

/Fredrik

 

[DrChinese]

I don't think you've given a single example of an interpretation which made such a claim wrongly. Your basis for criticizing interpretations you don't like, as far as I can tell, has nothing to do with any actual demonstration that they make wrong predictions.

Evidence ruling out a model should not be a matter of opinion. Either you can cite the specific evidence and the specific prediction it falsifies, or you can't. Either way this should be a factual matter, not a matter of opinion.

I don't really think I have been criticizing interpretations; so much as bringing out and citing specific experiments that all interpretations claiming to make the same predictions as QM must be able to explain. For example, it is generally agreed that any interpretation or theory that posits Local Realism must be rejected. I did mention a batch of those (by writer name), true, but surely there is no "opinion" on this point in this subforum. That is generally accepted science per your definition.

For many interpretations, the details of their mechanism to follow Bell (either by rejecting Locality, Realism, or both) are muddy*. I am hoping that one of their adherents - not particularly in this thread or anytime soon - can fill in detail and compare to some of the experiments I cite. Perhaps an Entanglement Swapping experiment, or a Delayed Choice experiment. That would be enlightening for me. Try as I have, searching the literature for rock solid discussion in this area, I have yet to find it. So I hope to read that here. I think that is what many readers/posters in this subforum seek, I don't think I am alone on this.

This thread is based on a fair question: is there 'action at a distance' due to measurement? In my preferred interpretation (I might even call it Orthodox QM), there is. You and anyone else might say "Orthodox QM does not feature AAAD"; but by right, I believe I am entitled to believe it does. However, when posting here, there are fair limits imposed: I would (and should and usually do) label that belief as "not generally accepted" and/or subject to the reader's own opinion or viewpoint.

---

So you seem to be asking me to name and document an interpretation that wrongly claims (in my view) to follow all existing experiments. That wasn't my objective, so I am only providing the below to fulfill what I think you are asking.

There are forms of MWI that claim Locality and deny AAAD. They also claim a form of Realism that evades Bell. Bell himself had this to say about MWI (per MWI proponent Vaidman*): "The ‘many world interpretation seems to me an extravagant, and above all an extravagantly vague, hypothesis. I could almost dismiss it as silly. And yet... It may have something distinctive to say in connection to ‘Einstein Podolsky Rosen puzzle’ and it would be worthwhile, I think, to formulate some precise version of it to see if it really so." He said it is vague, and needs to be more precise. I would agree with this, in light of modern experiments which are demanding.

Of course, Bell never got to see the likes of experiments from the groundbreaking teams of Zeilinger and others. Many of these seem to be flat out demonstrations of cause and effect that span distances that will not fit into traditional light speed limits. To quote Zeilinger et al from one such experiment (144 km of separation) here: "Here we report a quantum eraser experiment, in which by enforcing Einstein locality no such [signal] communication is possible. ... No naive realistic picture is compatible with our results ... It is therefore suggestive to abandon such pictures altogether."

Certainly this is not a "disproof" of MWI. But it is relevant to this thread regarding AAAD, see also comments * below. I would state my opinion as saying MWI is incompatible with experiment in this regard, but again, it's just one person's view.

---

Any person who states or advocates a preferred Interpretation, or criticizes any element of any other Interpretation, is implicitly expressing their opinion. It is normal for posters to express this in this Subforum. And it would be no more or no less factual than anyone's else's similar comments. In fact, anyone who denies there is AAAD is expressing their opinion too.

I don't want to derail further discussion on this thread topic, nor do I want to see the thread closed. I promise that I won't turn this thread into a repeat of some of our previous extended threads. I will limit my comments to addressing specific limited ideas. I have already expressed more than my share of ideas sufficiently.

But I believe that I have stayed within the (more lenient) Foundations/Interpretations subforum rules. In this subforum, I am well-known for experimental (and other) citations; I can't believe my supporting citations fall short of any standard. If they do, just let me know and I will try to fill in the gaps.

Cheers,

-DrC


* Vaidman on Locality in MWI (per Stanford Plato here): "We have to add some ingredients to our theory and adding locality, the property of all known physical interactions, seems to be very natural (in fact, it plays a crucial role in all interpretations). ... Since interactions between particles are local in space, this is what is needed for finding causal connections ending at our experience." Also Vaidman (here): "Although there is no action at a distance [AAAD] in the MWI, it still has nonlocality." And also: "Bell inequalities lead us to a hard choice: either we believe that there is some kind of action at a distance, or that there are multiple realities". Clearly it's not so easy to nail down MWI on the particulars. And even Vaidman sees that rejection of MWI entails embracing AAAD.

 

[PeterDonis]

it is generally agreed that any interpretation or theory that posits Local Realism must be rejected.

Yes, because that's been ruled out by Bell's Theorem and experimental evidence of Bell inequality violations. But while individual writers might be trying to advocate for some form of this, none of the well known QM interpretations are local realistic.

For many interpretations, the details of their mechanism to follow Bell (either by rejecting Locality, Realism, or both) are muddy*.

For some interpretations, there is no mechanism at all. I gave the statistical interpretation, as described in, for example, Ballentine, as an example. The statistical interpretation accounts for Bell inequality violations by pointing at the standard math of QM, and the experiments that confirm its predictions, and saying "that's all we can say".

As for "rejecting locality, realism, or both", if you insist on categorizing things that way, the statistical interpretation "rejects" both (in the sense of not even talking about them at all). My personal quick rundown of some other well known interpretations in this regard would be:

Copenhagen -- rejects both.
MWI -- rejects both. (Though, as you comment, whether MWI actually rejects locality is a subject of some debate.)
Bohmian -- rejects locality.

However, I'm not sure how much value there is in this kind of categorization. But that's probably an aspect of the fact that I'm not sure how much value there is in discussions of QM interpretations, period. What we need are some alternative theories that make different predictions from standard QM, so we can get some idea of what experiments we might run to test them. That's how physics is supposed to be done: building models that make correct predictions. Not telling stories about "what's really going on" that can't be tied to any experiment, because other people are telling other, mutually incompatible stories about the same experiment.