A new realistic stochastic interpretation of Quantum Mechanics

[PeterDonis]

what appears to be a
causally local hidden-variables formulation of quantum
theory

This claim, of course, depends on using a different definition of "locality" from the one Bell, GHZ, etc. used to prove their theorems. Basically, it means something like "Alice's and Bob's measurement actions are local--they only act on the particle they are measuring". But again, we already knew this: the standard QM math tells us that the operator that describes Alice's measurement only acts on Alice's qubit, and the operator that describes Bob's measurement only acts on Bob's qubit. The nonlocality is in the wave function: acting on either qubit changes the entire entangled wave function, which includes the other qubit. In other words, there is nothing new here, just a choice of terminology that makes it seem like there's something new when there actually isn't.

 

[DrChinese]

This makes them your claims, too.

Note that by making a very selective choice, you heavily bias the quite controversial collection of claims in the literature towards your own preference. That's why I refer to your claims.

I notice that you manage to pick apart the specific words I use, without making any comments of substance about the physics. So let's see:

a. "you heavily bias the quite controversial collection of claims in the literature" Controversial? Really? You think GHZ is controversial (that was one of 2 experiments I mentioned)? GHZ says that in tests of 3 photons entanglement of GHZ states, local realism predicts 4 of 8 possible outcomes while QM predicts the other 4 outcomes - without the need for a statistical correlations. Experiments have confirmed the predictions of QM. I would say that this disproves local realism without leaving the wiggle room sometimes associated with Bell tests. But it could also be considered as disproving realism, unless you are into strange hypothetical FTL signaling mechanisms between 3 (or more) remote particles. What would you call biased or controversial?

On the other hand, your response to my reference on GHZ was to provide a reference with no mention of GHZ? Perhaps you would care to address (counter) GHZ with a relevant citation of what you consider a good experimental team/paper?

b. I also mentioned Remote Entanglement Swapping (where the final entangled pair has never existed in a common backward light cone). Is that a "biased" or "controversial" finding?

---

Yes, my references are quite selective. That's because they leave little room for doubt as to the results or related theory. In that sense, you are correct: they are "biased". And the references are selected to highlight the state of the art in entanglement as it related to the thread. In that sense, you are correct again: they are "controversial", simply because they are not known to many readers.

Something new is often considered "controversial". Hey, the Beatles were controversial when they came out too... and now they are old hat.

 

[PeroK]

Hey, the Beatles were controversial when they came out too... and now they are old hat.

Perhaps the Rolling Stones would be a better example. They were the British bad boys of the 1960's and now it's Sir Mick Jagger!

 

[PAllen]

This claim, of course, depends on using a different definition of "locality" from the one Bell, GHZ, etc. used to prove their theorems. Basically, it means something like "Alice's and Bob's measurement actions are local--they only act on the particle they are measuring". But again, we already knew this: the standard QM math tells us that the operator that describes Alice's measurement only acts on Alice's qubit, and the operator that describes Bob's measurement only acts on Bob's qubit. The nonlocality is in the wave function: acting on either qubit changes the entire entangled wave function, which includes the other qubit. In other words, there is nothing new here, just a choice of terminology that makes it seem like there's something new when there actually isn't.

Except that this formulation doesn't use wave functions at all, except as derived convenience. As I understand it so far, the correlations in measures at A and B are due to the non-factorizability of the hidden (uni-stochastic) configuration underlying Q and R, and this latter is the result of their interaction in their past. However, the part that I agree seems just playing with definitions is that the (Q,R) configuration encompasses continued influences between Q and R following the interaction. That is, while actions of A or B (Alice and Bob) are 'factored out', Q and R still seem non-locally coupled in any every-day sense of the term: the probability of a configuration change at Q remains coupled to the configuration at R, and vice versa. At least, that is my understanding based on pp. 12-13 of the third paper.

 

[PeterDonis]

this formulation doesn't use wave functions at all, except as derived convenience

But that just means the nonlocality--the whatever-you-want-to-call-it that actually enables the Bell inequality violations--is shoved somewhere else in the model. It can't be made to go away. The somewhere else might not be called a wave function in this formulation, but it has the same effect. As you note, it's just "playing with definitions".

 

[Morbert]

I saw the last of these papers when it was dropped into Arxiv a few days ago. The first thing I look for is their treatment of remote Entanglement Swapping* and GHZ**. These are some of the strongest experiments against all forms of local realism. If you aren't addressing these, then you really can't make any useful/serious claims in today's environment.

Of course, those seminal works aren't mentioned at all. (There is a passing GHZ reference, but it is not discussed at all.) The main idea of the paper seems to be to define local causality in a very specific manner, then deny that. Well, experiment reigns supreme. I will give this a better look once modern (last 30 years) experiments are explained in terms of the new interpretation. This paper is closer to 1980's era ideas. ***

The papers submit a new definition of causal locality and argue it is superior when quantum theory is understood as a theory of stochastic processes characterized by an indivisible transition matrix. GHZ etc might be an interesting homework exercise for this interpretation, but it's not clear that it poses any substantive challenge above and beyond simpler, ordinary EPRB-like experiments.

The interpretation itself might be interesting if it ends up saying something re/ intuitions about stochastic processes and the Markov property.

*In these experiments, distant photons are entangled (and violate a Bell inequality) that have never existed in a common backward light cone. Pretty hard to get locality with that.

As i have shown in this thread (you will have to ask the mods for the deleted post). That the photons have never existed in a common backward light cone does not pose any additional challenge to the question of locality beyond standard EPRB because, in the same way the EPRB system is a noncommutative generalization of a classical system, entanglement swapping experiments are are nocommutative generalization of a "correlation swapping" classical experiments where two classical systems that have never existed in a common backward light cone become correlated.

 

[WernerQH]

The interpretation itself might be interesting if it ends up saying something re/ intuitions about stochastic processes and the Markov property.

At first sight it looks more like a refurbished presentation of quantum theory's mathematical apparatus than an interpretation. The transition matrix in the form $\Gamma_{ij}(t) = \rm{tr}(\Theta^\dagger(t) P_i \Theta(t) P_j)$ (eq.26 in the first paper) reminds me of the well-known Schwinger-Keldysh formalism. Unfortunately the configuration space of the "system" is completely abstract, and it's unclear how it relates to the objects that we experience in the real world. One would also desire a clearer picture of those "division events" which permit approximating a non-Markovian process by a Markov process. In some cases the emission of a photon can be thought of as such an event, but in others the emission process cannot be considered as instantaneous and must be treated as a pair of two correlated events (two short-lived, strongly localized currents). My hunch is based on Kubo formulas, and I commented on it in an earlier post.

Yes, I do think that stochastic elements are essential for quantum theory. How could continuous and deterministic evolution according to Schrödinger's equation provide a faithful description of what happens in the real world, for example, the sudden decay of an atomic nucleus?

 

[DrChinese]

1. GHZ etc might be an interesting homework exercize for this interpretation, but it's not clear that it poses any substantive challenge above and beyond simpler, ordinary EPRB-like experiments.

2. That the photons have never existed in a common backward light cone does not pose any additional challenge to the question of locality beyond standard EPRB because, in the same way the EPRB system is a noncommutative generalization of a classical system, entanglement swapping experiments are are noncommutative generalization of a "correlation swapping" classical experiments where two classical systems that have never existed in a common backward light cone become correlated.

1. That's a quick dismissal of GHZ. It's not a homework exercise, we are talking about a major no-go theorem here. The realistic assumption ("causal locality" in "a model that consists of a set of random variables connected by a collection of conditional probabilities") leads to opposite predictions compared to experiment.

2. Whoa! Another big statement, and yet no peer-reviewed reference supporting your statement. You are basically denying the quantum nature of entanglement. Hmmm. I'll pay you $10 (I'm a cheap bettor, but I'll give you decent odds) if you can find a classical "correlation swapping" example with the following attributes, which are demonstrated in quantum experiments such as this or this.

• a. The photons (or whatever classical objects you prefer) detected by Alice and Bob never exist/interact in a common light cone. Let's call these objects 1 and 4 to match my experimental references.
• b. 1 and 4 cannot be entangled or otherwise made identical in their initial states, because the decision to entangle them (or not) will be made in a remote (FTL distant) place by Chris. So Alice, Bob and Chris are spacelike separated at the time that 1 and 4 become entangled - or correlated, or whatever you care to call it. They are also all spacelike separated when Alice and Bob perform their chosen measurements.
• c. Alice and Bob can choose to measure either i) on any same basis (in which case we must see perfect correlation); or ii) on different bases (a la CHSH, and violating a Bell inequality). I'll be impressed if you can do this for even just case i).
• d. Chris can choose to entangle - or not - the 1 and 4 objects. The observed Alice/Bob correlations must change along with this choice. No correlation if Chris chooses not to classically correlate.

This is impossible in any classical scenario, as it should be obvious - which is why the Remote Entanglement Swapping experiments are critical to interpretation analysis. I certainly have never seen a concrete example that could even remotely (pun intended) pull this off.


Note to moderators: If this is too far off the thread subject, we could split off the discussion. The relationship to the thread subject is that new interpretations should be able to explain experiments like GHZ and Remote Swapping if they are to be taken seriously. Otherwise, we are just dialing the clock back 35 years. Bell sadly passed away before the impact of these newer experiments were evident. I'm certain he would have accepted this important science, and be justifiably proud of what his groundbreaking work has given birth to.

 

[PeterDonis]

As i have shown in this thread

You were thread banned in that thread because what you claim to have "shown" there was not "shown" and you were hijacking the discussion with off topic unjustified claims. Given that, you have now been thread banned from this thread.

 

[kurt101]

2. Whoa! Another big statement, and yet no peer-reviewed reference supporting your statement. You are basically denying the quantum nature of entanglement. Hmmm. I'll pay you $10 (I'm a cheap bettor, but I'll give you decent odds) if you can find a classical "correlation swapping" example with the following attributes, which are demonstrated in quantum experiments such as this or this.

• a. The photons (or whatever classical objects you prefer) detected by Alice and Bob never exist/interact in a common light cone. Let's call these objects 1 and 4 to match my experimental references.
• b. 1 and 4 cannot be entangled or otherwise made identical in their initial states, because the decision to entangle them (or not) will be made in a remote (FTL distant) place by Chris. So Alice, Bob and Chris are spacelike separated at the time that 1 and 4 become entangled - or correlated, or whatever you care to call it. They are also all spacelike separated when Alice and Bob perform their chosen measurements.
• c. Alice and Bob can choose to measure either i) on any same basis (in which case we must see perfect correlation); or ii) on different bases (a la CHSH, and violating a Bell inequality). I'll be impressed if you can do this for even just case i).
• d. Chris can choose to entangle - or not - the 1 and 4 objects. The observed Alice/Bob correlations must change along with this choice. No correlation if Chris chooses not to classically correlate.

This is impossible in any classical scenario, as it should be obvious - which is why the Remote Entanglement Swapping experiments are critical to interpretation analysis. I certainly have never seen a concrete example that could even remotely (pun intended) pull this off.

Would you extend this bet for anyone? And would you extend it for my variant? Can I make the example myself or does it have to be something peer reviewed and published?

I don't deny entanglement. I don't deny entanglement swapping when the swap operation performed at 2 & 3 is performed before (in an absolute time sense) measuring 1 & 4. However, when the measurement on 1 & 4 is performed first (in an absolute time sense) before the swap operation at 2 & 3, I think photons 2 & 3 have all the information about 1 & 4 at the time of the swap operation to decide whether the measurements of 1 & 4 (made in the absolute past) have the property of being entangled or not. And to me this would be the part of the experiment that calls into question the classical nature, but I suppose that depends on what you mean by classical.

 

[PeterDonis]

Can I make the example myself or does it have to be something peer reviewed and published?

Any claim about what QM interpretation says about a scenario needs to be backed up by a published peer reviewed reference.

 

[DrChinese]

1. Would you extend this bet for anyone? ... Can I make the example myself or does it have to be something peer reviewed and published?

2. I don't deny entanglement. I don't deny entanglement swapping when the swap operation performed at 2 & 3 is performed before (in an absolute time sense) measuring 1 & 4. However, when the measurement on 1 & 4 is performed first (in an absolute time sense) before the swap operation at 2 & 3, I think photons 2 & 3 have all the information about 1 & 4 at the time of the swap operation to decide whether the measurements of 1 & 4 (made in the absolute past) have the property of being entangled or not. And to me this would be the part of the experiment that calls into question the classical nature, but I suppose that depends on what you mean by classical.

1. Sure! If you can keep the example simple enough, I'll give it a go. Obviously, it must follow accepted science of some kind (and if an interpretation, it should follow Peter's admonition).

2. Whew... you scared me for a moment. Your idea about order reversal (measuring 1 & 4 before 2 & 3) has one major problem. This issue is normally overlooked by those seeking some kind of traditional causal order where cause precedes effect (a very reasonable expectation, of course).

The final entangled photons are 1 & 4. They become entangled upon successful interaction (indistinguishable overlap) of photons 2 & 3. Let's specify and agree that this interaction of 2 & 3 occurs AFTER 1 & 4 are already detected (per your idea). But here are a couple of other conditions to consider:

a) The angle choices for detection of 1 & 4 are unknown to each other because they are far distant (no signal can travel between them). There are an infinite* number of combinations possible which either show perfect correlations (in each and every case when the angle choices are the same), or violate Bell inequalities via statistical averages (in many cases when the angle choices are different).

b) Likewise, at the time 1 is detected, its entangled partner 2 is far away. Ditto between 3 & 4. No signal can propagate between them. You are going to need to have some kind of remote action at a distance to have 2 "know" how 1 was measured. (But that is what we were trying to avoid!)

c) All cases - and not just some as you might imagine - in which the 2 & 3 photons overlap lead to entanglement of 1 & 4. But there are only 4 permutations of the 2 & 3 photon overlap. Those are the 4 possible Bell states. It is not possible to map those 4 cases to an infinite* number of permutations of choices for measuring 1 & 4. It's just not a wide enough channel. There are only a few variables in a pair of indistinguishable photons (2 & 3). Which is a requirement for a swap.

d) And keep in mind that the decision by Chris to overlap 2 & 3 is in fact made AFTER 1 & 4 are detected. That means that there can be no correlation at all in those cases.

Good luck! I am setting aside your future winnings aside as we speak...


*If it is not infinite, then it's a very large number.

 

[PAllen]

1. That's a quick dismissal of GHZ. It's not a homework exercise, we are talking about a major no-go theorem here. The realistic assumption ("causal locality" in "a model that consists of a set of random variables connected by a collection of conditional probabilities") leads to opposite predictions compared to experiment.

One thing here is that the author uses a new definition of causal locality which is not the same as used in any theorems (and, as @PeterDonis has noted, has arguably no content beyond established 'no messaging' results). Also, his 'hidden reality' is not equivalent to a collection of random variables. So on this question, it seems to me that existing no-go theorems are not applicable. In fact, it seems to me that properties he derives for it make it equivalent to a wave function with different mathematical representation.

 

[PAllen]

The relationship to the thread subject is that new interpretations should be able to explain experiments like GHZ and Remote Swapping if they are to be taken seriously. Otherwise, we are just dialing the clock back 35 years. Bell sadly passed away before the impact of these newer experiments were evident. I'm certain he would have accepted this important science, and be justifiably proud of what his groundbreaking work has given birth to.

This, I strongly agree with. But due to the formal mathematical equivalences demonstrated in the OP references, I think this is likely to be possible. However, the author must do it at some point to be taken seriously.

 

[DrChinese]

One thing here is that the author uses a new definition of causal locality which is not the same as used in any theorems (and, as @PeterDonis has noted, has arguably no content beyond established 'no messaging' results). Also, his 'hidden reality' is not equivalent to a collection of random variables. So on this question, it seems to me that existing no-go theorems are not applicable. In fact, it seems to me that properties he derives for it make it equivalent to a wave function with different mathematical representation.

Well, that's kinda the issue, isn't it? He says here: "one can reformulate quantum theory in terms of old-fashioned configuration spaces together with 'unistochastic' laws. These unistochastic laws take the form of directed conditional probabilities, which turn out to provide a hospitable foundation for encoding microphysical causal relationships. This unistochastic reformulation provides quantum theory with a simpler and more transparent axiomatic foundation, plausibly resolves the measurement problem, and deflates various exotic claims about superposition, interference, and entanglement."

That abstract sounds exotic to me! Superposition and interference are merely "claims? Measurement problem: solved! And entanglement... well I think it is very clear entanglement is a great big target on the back of this formulation. No, you cannot define/redefine the phrase "causal locality" to be different than "local causality", and then expect to dodge GHZ, advanced entanglement issues and the latest no-go's.

That's a far cry from agreeing with the idea that there is signal locality - which as far as I know is disputed by essentially no one. And if in fact you are correct, he has a new mathematical representation: so is it in fact exactly identical (since he drops the standard mathematical methods entirely) ? How would a reader understand that either way? His abstract contains some big claims, and I certainly missed the elements where he convinces of the abstract's claims.

Here is the last sentence of his conclusion, you tell me if he thinks he is onto something different and important. Because it certainly reads to me that the Bell conclusion* (along with GHZ etc.) is being thrown out.

"Remarkably, one therefore arrives at what appears to be a causally local hidden-variables formulation of quantum theory, despite many decades of skepticism that such a theory could exist."


*Which is: "No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics."-DrC

 

[A. Neumaier]

Experiments have confirmed the predictions of QM. I would say that this disproves local realism

Everybody knows that local realism has been disproved with high confidence.

But it could also be considered as disproving realism

Realism need not be local in Bell's sense.

To match Nature, it is enough that it is local in the sense of quantum field theory. Indeed, neither Bell experiments nor GHZ experiments testify against quantum field theory. The latter has a nonlocal realist interpretation, namely the thermal interpretation. See also Quantum mechanics via quantum tomography.

 

[kurt101]

b) Likewise, at the time 1 is detected, its entangled partner 2 is far away. Ditto between 3 & 4. No signal can propagate between them. You are going to need to have some kind of remote action at a distance to have 2 "know" how 1 was measured. (But that is what we were trying to avoid!)

You are correct, I need to have some kind of remote action. So is ok to have remote action as long as it is impossible to use that remote action in any way to communicate a signal?

Does the following classical model seem accurate and acceptable for such a bet?

The state of photon 1 is measured and this causes the remote action that changes the state of photon 2. This is ok to do as long as the action can't be exploited to communicate a signal.
Likewise, the state of photon 4 is measured and this causes the remote action that changes the state of photon 3. And likewise this is ok as long as the action can't be exploited to communicate a signal.
Photons 2 and 3 enter the BSM. The BSM will result in 4 possible states each with a 25% probability. The BSM can only calculate the states using the local state variables of photons 2 and 3 as they enter the BSM. The 4 states will be used to group the corresponding measurements of photons 1 and 4 into 4 different buckets where each bucket must show a maximum entangled correlation between the photons 1 and 4.

Good luck! I am setting aside your future winnings aside as we speak...

I am not ready to accept the challenge yet. I need to think about this further and better understand the 4 bell states and how I would present an argument without violating rules.

From my perspective, either way I win. As paying $10 and learning I am wrong is as valuable as learning I am right.

 

[PeterDonis]

Does the following classical model seem accurate

How is your model "classical"? What theory of classical physics includes the kind of "remote action" you are postulating?

 

[kurt101]

How is your model "classical"? What theory of classical physics includes the kind of "remote action" you are postulating?

I agree that part is not classical, but I understood @DrChinese use of the term classical to mean classical thinking with cause and effect reasoning and not anything to do with entanglement. Here is the context of his comment:
" but I'll give you decent odds) if you can find a classical "correlation swapping" example with the following attributes, which are demonstrated in quantum experiments such as this or this."

 

[PeterDonis]

I understood @DrChinese use of the term classical to mean classical thinking with cause and effect reasoning and not anything to do with entanglement.

I would strongly advise you to ask @DrChinese what he meant instead of assuming--particularly as you have a bet down.

Also note that your "remote action" is entanglement. Again, there would be no such "remote action" with classical particles. You have to have entangled quantum particles for it to work.

 

[kurt101]

I would strongly advise you to ask @DrChinese what he meant instead of assuming--particularly as you have a bet down.

Yes and that is why I did ask. "Does the following classical model seem accurate and acceptable for such a bet?"

 

[PeterDonis]

Yes and that is why I did ask. "Does the following classical model seem accurate and acceptable for such a bet?"

It isn't a classical model. Read the rest of my post #55 (I edited it because I hit "post" too soon).

 

[kurt101]

Also note that your "remote action" is entanglement. Again, there would be no such "remote action" with classical particles. You have to have entangled quantum particles for it to work.

Yes, I agree and I agree that technically that would not make my the model classical. If you want me to edit my original message and remove the word "classical" I am fine with doing that. Or I could just try to go for word salad to describe my model: realist, causal, cause and effect, non-local realism, deterministic. I am never sure what the correct terminology to use on this forum is as we get into endless debates over terminology (maybe for good reason as people on this forum have so much trouble understanding each other). So in general I try to use terminology how the other person I am corresponding it used it and try to get them to explain misunderstandings.

 

[PeterDonis]

I agree that technically that would not make my the model classical.

No "technically" about it. The model isn't classical and therefore does not meet the requirement @DrChinese gave in the bet he offered.

What other terminology you want to use to describe your model is immaterial: all you're doing is restating what the QM wave function does in different language.

 

[kurt101]

No "technically" about it. The model isn't classical and therefore does not meet the requirement @DrChinese gave in the bet he offered.

This is just very confusing. Maybe you can try to clarify. @Morbert who isn't denying entanglement says
"That the photons have never existed in a common backward light cone does not pose any additional challenge to the question of locality beyond standard EPRB because, in the same way the EPRB system is a noncommutative generalization of a classical system, entanglement swapping experiments are are nocommutative generalization of a "correlation swapping" classical experiments where two classical systems that have never existed in a common backward light cone become correlated."

He seems to be talking about classicality of the correlation between two systems (whether the systems are classical or treated as quantum). I disagree with @Morbert statement in general, but I think he correct for the case that I am discussing.

Then @DrChinese replies to @Morbert and says
"if you can find a classical "correlation swapping" example with the following attributes, which are demonstrated in quantum experiments such as this or this."

And I am trying to find a classical correlation swapping example that @DrChinese is wagering the bet on, but where I differ from @Morbert is I only think it happens in the case where the 2 & 3 swap is done last.

@PeterDonis I don't think you are helping as you seem to be giving your own spin on this conversation. I think I am best off hearing it from the horses mouth @DrChinese. I am not saying your wrong about what @DrChinese means, but as far as I can tell you are saying different things.

 

[PeterDonis]

Maybe you can try to clarify.

The clarification is simple: the QM math is the same regardless of the ordering of the measurements, and so are the observed correlations, which violate the Bell inequalities and related inequalities. And that, by Bell's and other theorems, rules out any model of the type you are calling "classical", for any ordering of the measurements.

So any purported "explanation" that says a "classical" model works for some orderings of measurement but not for others, can't be right. The correlations are not "classical" for any ordering of the measurements.

I am not saying your wrong about what @DrChinese means, but as far as I can tell you are saying different things.

@DrChinese is of course welcome to correct me, but I think the concept of "classical" he is using is intended to be ruled out by both the QM math and actual experimental results for any ordering of the measurements, for the basic reason I gave above. Indeed, he has made a similar argument to the one I made above in other threads on this general topic.

In other words, @DrChinese did not offer to bet you because he thought you had any chance at all of winning the bet. He believes (and I do too) that you are doomed to lose no matter what you do, because for you to win would have to mean that proven mathematical theorems are not correct.

 

[PeterDonis]

I disagree with @Morbert statement in general, but I think he correct for the case that I am discussing.

You would be well advised to read my post #44.

 

[Mister T]

Don't we have enough interpretations already? Unless something is making testable predictions then what is the point? Mathematically I'm sure you can cook things an infinite number of ways.

I think the hope is that an interpretation will gain an overwhelming majority of support from physicists. Other branches of physics enjoy this feature, and it facilitates explaining the theory to students and the public at large.

 

[DrChinese]

And I am trying to find a classical correlation swapping example that @DrChinese is wagering the bet on, but where I differ from @Morbert is I only think it happens in the case where the 2 & 3 swap is done last.

@PeterDonis I don't think you are helping as you seem to be giving your own spin on this conversation. I think I am best off hearing it from the horses mouth @DrChinese. I am not saying your wrong about what @DrChinese means, but as far as I can tell you are saying different things.

If you have any kind of communication between entangled particles (1 & 2 or 3 & 4), that violates locality. That's what @PeterDonis is saying... so it's already not classical. Classical ideas strictly obey locality.

When you get into FTL mechanisms - which the Remote Entanglement Swapping (RES) experiments seem to require - you quickly realize that even those have issues. In the RES type, there are 3 parties (Alice, Bob, Chris) distant to each other and there would need to be some kind of communication/coordination between all 3 to make things work out.

I personally have no idea how that would work, but it is easy to see that all of the "simple" explanations quickly fall to the wayside. That's because there are too many rules that must be obeyed all at once with the 3 parties. Alice and Bob must see perfect correlations when Chris decides to execute a swap, but they must see NO correlations when Chris does not execute the swap. And like any Bell test, a Bell inequality (such as CHSH) must be violated when Alice and Bob's respective entangled photons are measured at specific angle settings. Meanwhile, the photons sent to Alice and Bob cannot have ANY correlation initially, because they are entangled with other particles.

This is why I use GHZ and RES as a measuring stick. If the author won't tackle these head on, it's nearly a certainty that there is hand-waving occurring somewhere - although it may be hidden. If the author does tackle these experiments explicitly, at least you have a chance to agree or disagree with the line of thinking. And oftentimes, the author simply says "the math is the same so the predictions are the same" - and you know you have a true interpretation - but it actually doesn't shed much new light on things. But it may still be of benefit for some people. Anything that helps me grasp what is happening a little better is... good.

 

[martinbn]

2. Whoa! Another big statement, and yet no peer-reviewed reference supporting your statement. You are basically denying the quantum nature of entanglement. Hmmm. I'll pay you $10 (I'm a cheap bettor, but I'll give you decent odds) if you can find a classical "correlation swapping" example with the following attributes, which are demonstrated in quantum experiments such as this or this.

• a. The photons (or whatever classical objects you prefer) detected by Alice and Bob never exist/interact in a common light cone. Let's call these objects 1 and 4 to match my experimental references.
• b. 1 and 4 cannot be entangled or otherwise made identical in their initial states, because the decision to entangle them (or not) will be made in a remote (FTL distant) place by Chris. So Alice, Bob and Chris are spacelike separated at the time that 1 and 4 become entangled - or correlated, or whatever you care to call it. They are also all spacelike separated when Alice and Bob perform their chosen measurements.
• c. Alice and Bob can choose to measure either i) on any same basis (in which case we must see perfect correlation); or ii) on different bases (a la CHSH, and violating a Bell inequality). I'll be impressed if you can do this for even just case i).
• d. Chris can choose to entangle - or not - the 1 and 4 objects. The observed Alice/Bob correlations must change along with this choice. No correlation if Chris chooses not to classically correlate.

This is impossible in any classical scenario, as it should be obvious - which is why the Remote Entanglement Swapping experiments are critical to interpretation analysis. I certainly have never seen a concrete example that could even remotely (pun intended) pull this off.

I'll give this one a go. On each trial prepare 1 and 4 in any way you want. They can be spacelike and at different times and in arbitrary states. Entirely up to you. All measurements are made along the same axis. Alice measures 1 and records the result. Bob measures 4 and records the result. This is done on all trials. Then the spread sheets are sent to Chris. Now he can do one of two things. He can do nothing then the data shows no correlation whatsoever between the results of measurements on 1 and 4. Or he can go through the results trial by trial and keep only those that are opposite i.e. if Alice's is "up" and Bob's is "down" he keeps the result, same if they were the other way round, and discards all others. Then the data shows perfect anti-correlation. If the measurements are done along different axis, then Chris discards all trials that are not along the same axis and then proceeds as above. This way the data for 1 and 4 shows exactly the same as if 1 and 4 were in the usual Bell state. Conclusion the act of Chris, choosing to do one or the other thing, entangles photons 1 and 4. Which of course can be chosen so that they have never coexisted in whatever sense you want.

 

[PeterDonis]

Conclusion the act of Chris, choosing to do one or the other thing, entangles photons 1 and 4.

This is interpretation dependent. On an ensemble interpretation this viewpoint would be reasonable (although I'm not sure that even all versions of the ensemble interpretation would agree). But on an interpretation where the quantum state is taken to represent the state of individual systems, the viewpoint you describe does not work. @DrChinese, in threads on this topic, has always adopted the latter type of interpretation.

 

[martinbn]

This is interpretation dependent. On an ensemble interpretation this viewpoint would be reasonable (although I'm not sure that even all versions of the ensemble interpretation would agree). But on an interpretation where the quantum state is taken to represent the state of individual systems, the viewpoint you describe does not work. @DrChinese, in threads on this topic, has always adopted the latter type of interpretation.

I am playing the devil's advocate. I don't agree with what I wrote. But I also don't agree with some of the things @DrChinese writes about entanglement swaping. I have tried to write it the same way as he does to see if he thinks it is different and if yes why?

 

[PeterDonis]

I am playing the devil's advocate. I don't agree with what I wrote. But I also don't agree with some of the things @DrChinese writes about entanglement swaping.

We should expect disagreement on any issue that involves QM interpretations, since different interpretations say different and mutually contradictory things. There is no way to resolve such disagreements since all QM interpretations make the same experimental predictions. The guidelines for this subforum spell that out.

 

[martinbn]

We should expect disagreement on any issue that involves QM interpretations, since different interpretations say different and mutually contradictory things. There is no way to resolve such disagreements since all QM interpretations make the same experimental predictions. The guidelines for this subforum spell that out.

I disagree with the statement that Chris causes the entanglement no matter what the interpretation is. In any case i want to hear if i get the 10$ or at least a pint of lone star.

 

[DrChinese]

I'll give this one a go. On each trial prepare 1 and 4 in any way you want. They can be spacelike and at different times and in arbitrary states. Entirely up to you. All measurements are made along the same axis. Alice measures 1 and records the result. Bob measures 4 and records the result. This is done on all trials. Then the spread sheets are sent to Chris. Now he can do one of two things. He can do nothing then the data shows no correlation whatsoever between the results of measurements on 1 and 4. Or he can go through the results trial by trial and keep only those that are opposite i.e. if Alice's is "up" and Bob's is "down" he keeps the result, same if they were the other way round, and discards all others. Then the data shows perfect anti-correlation. If the measurements are done along different axis, then Chris discards all trials that are not along the same axis and then proceeds as above. This way the data for 1 and 4 shows exactly the same as if 1 and 4 were in the usual Bell state. Conclusion the act of Chris, choosing to do one or the other thing, entangles photons 1 and 4. Which of course can be chosen so that they have never coexisted in whatever sense you want.

None of this fits the requirements I presented. So you don't get the $10, but as consolation prize: I'll buy you that Lone Star anytime you are in Dallas.

And I agree that Chris keeping a spreadsheet can be considered classical.

But that is not what Chris' role is. He is independently choosing to entangle photons 1 & 4 by doing something to photons 2 & 3. And when Chris chooses to entangle, the final stats should show the perfect correlations (or anti-correlations); and when Chris chooses not to entangle, there can be no correlation. Alice, Bob and Chris are sufficiently distant that their results will be independent. They all send their independent results to some other party for summarizing. We can call that person Dave. Dave buys the beer, by the way.

For those that don't see this kind of experiment as a diehard proof of (quantum) nonlocality, seriously, how do you propose to explain it? There is clearly a dependency on the results obtained a 3 distant locations regarding photons from independent sources that have never overlapped in a common light cone.

And just to strike home a point that seems to get lost at times: in ALL cases in which there is indistinguishable overlap of photons 2 & 3 at Chris' beamsplitter, there is a swap. There are 4 possible Bell states, current technology only allows 2 (max) of these to be distinguished. But it is possible to look at the 1 & 4 photons' arrival times, and therefore determine which trials there *could* have been overlapping (of 2 & 3) at Chris' beamsplitter. But you need info from Chris to learn if that overlap was allowed - or blocked - by Chris's decision. The frequency of the 2 identifiable Bell states (all of which occur randomly) will constitute very nearly 2/4 of all possible overlaps (since half of the cases cannot be identified as to Bell state). That you only identify 2 of the 4 Bell states in no way affects the conclusion. So in those 2 identifiable Bell states, there is a four-fold coincidence (based on relative arrival times, adjusted for travel distance). One click at Alice's station (photon 1), one click at Bob's station (photon 4), and two clicks at Chris' station (2 & 3).

So @martinbn: You said you don't agree with what I say about this type of remote entanglement swapping. What specifically do you not agree with? I am describing actual experiments, there's not much to imagine. As @PeterDonis says, different interpretations tend to take different views as to whether Chris' decision is the "cause" of the swap. So I get that. Also, some disagree that anything nonlocal was transmitted, even a quantum state. Nonetheless, Chris's decision is undeniably a part of the overall experimental context in which the final quantum state of 1 & 4 is different than the initial quantum states of 1 & 4. Which were always nonlocal to each other.