A new interpretation of Quantum Mechanics

[DrChinese]

1. Is that true? As I understand it, even if there is no artificially imposed delay, it is still possible that the photons do not arrive within the required time window to cause a swap; that is not under the experimenter's control. So there is no way to affirmatively say that a swap must occur if there is no artificially imposed delay.

1. If they would have arrived within the BSM's time window without the delay, there would affirmatively be a swap. Suppose as an example, we had the following timings (not realistic) with exactly equal path lengths (also not particularly realistic). Assume no delay added to the photon 3 path unless specified. Check out especially a. versus d.

a. 1 arrives at .200 ms; 2 & 3 (indistinguishably) arrive at .200 ms (i.e. 2 clicks); 4 arrives at .200 ms. A swap occurs. The 1 & 4 times are the same.

b. 1 arrives at .200 ms; 2 arrives at .200 ms; 3 arrives at .400ms; 4 arrives at .400 ms. No swap occurs since 2 & 3 are distinguishable. This is the most common case that Chris sees for 2 & 3, because the creation times for 2 & 3 aren't nearly close enough together. This b. variation might occur 1000 times more often than a.

c. 1 arrives at .200 ms; 2 arrives at .200 ms; 3 arrives at .201ms; 4 arrives at .201 ms. No swap occurs since 2 & 3 are distinguishable even though the difference in arrival times is small. The creation times for 2 & 3 aren't quite close enough together.

Now Chris adds a .001 ms delay to the photon 3 path, sufficient to insure no swap occurs in case d.

d. 1 arrives at .200 ms; 2 arrives at .200 ms; 3 arrives at .201ms (.200 + .001 delay); 4 arrives at .200 ms. No swap occurs since 2 & 3 are distinguishable even though they are close. But note that the 1 & 4 times are the same! That means without the .001 delay of photon 3, there affirmatively would have been a swap. Because there would have been overlap, and proper overlap always leads to a swap.

e. 1 arrives at .201 ms; 2 & 3 (indistinguishably) arrive at .201 ms; 4 arrives at .200 ms. A swap occurs. Notice that the 1 & 4 photons traveled the same length as always, but their arrival times were different. No problem, because them arriving simultaneously is not a requirement. This counts as a 4 fold coincidence.

2. Wouldn't this only be true for some very precisely chosen values of the delay timing?

2. Not at all! The precision timing is the overlap at Chris' beamsplitter (photons 2 & 3). It doesn't matter at all when photon 2 was created relative to photon 3. And the overlap is simply randomly occurring, with the majority of Chris' clicks being a lone 2 or a lone 3 - easily distinguished because there are only 2 of 4 total possible clicks within the time window. When Chris does get 2 clicks within the small time window, the next step will be to associate the click that Alice gets with Chris' double click. Ditto for Bob. Then you have the 4 fold results. From the reference below: "In the BSM, it is critical that the signal photons sent by Alice and Bob arrive at the 50:50 beam splitter (BS) simultaneously."

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Below is from Field test of entanglement swapping over 100-km optical fiber with independent 1-GHz-clock sequential time-bin entangled photon-pair sources
It's just another permutation of these remote setups whereby Alice, Bob and Chris (here named Charlie) are all distant from each other when their respective measurements are performed. Here Alice is located next to source I and Bob is near source II but are delayed by the addition of fiber, so technically the photons each observe are in each others' light cones. Nonetheless, you can see that the positioning (and distances) are arbitrary; Alice, Bob and Charlie (my Chris) can be located further away from each other simply by placing them physically further away from each other with less coiled fiber.

 

[PeterDonis]

If they would have arrived within the BSM's time window without the delay, there would affirmatively be a swap.

But whether they arrive in the time window is not completely controllable by the experimenter, correct? The experimenter can force them not to by imposing a delay, but if the experimenter doesn't do that, it's still not guaranteed that they will arrive within the time window, as I understand it.

The reason I keep harping on this is that, if it is possible for the experimenter (Chris) to guarantee that a swap does happen, then we have the problem @PAllen brought up earlier: in a setup where the 1 & 4 measurement results are in the past light cone of Chris making the decision of what, if anything, to do to photons 2 & 3 before they arrive at the BSM, Chris could wait until he sees a pair of 1 & 4 results that are inconsistent with entanglement (for example, a combination of results that is impossible in the entangled state), and then force a swap to happen at the BSM--which would contradict the predictions of QM, since QM predicts that if the 1 & 4 results show no entanglement, a swap cannot happen. The only way to avoid this contradiction is to not have Chris be able to force a swap to happen--i.e., to have at least some factors involved in determining whether a swap happens be out of Chris's control.

 

[PAllen]

But whether they arrive in the time window is not completely controllable by the experimenter, correct? The experimenter can force them not to by imposing a delay, but if the experimenter doesn't do that, it's still not guaranteed that they will arrive within the time window, as I understand it.

The reason I keep harping on this is that, if it is possible for the experimenter (Chris) to guarantee that a swap does happen, then we have the problem @PeroK brought up earlier: in a setup where the 1 & 4 measurement results are in the past light cone of Chris making the decision of what, if anything, to do to photons 2 & 3 before they arrive at the BSM, Chris could wait until he sees a pair of 1 & 4 results that are inconsistent with entanglement (for example, a combination of results that is impossible in the entangled state), and then force a swap to happen at the BSM--which would contradict the predictions of QM, since QM predicts that if the 1 & 4 results show no entanglement, a swap cannot happen. The only way to avoid this contradiction is to not have Chris be able to force a swap to happen--i.e., to have at least some factors involved in determining whether a swap happens be out of Chris's control.

That is exactly the point I was raising as well. Maybe you meant me, not @PeroK ?

 

[PeroK]

That is exactly the point I was raising as well. Maybe you meant me, not @PeroK ?

It must be. I shot my bolt as far as this thread is concerned many posts ago.

 

[PeterDonis]

That is exactly the point I was raising as well. Maybe you meant me, not @PeroK ?

Oops, yes, fixed now.

 

[DrChinese]

But whether they arrive in the time window is not completely controllable by the experimenter, correct? The experimenter can force them not to by imposing a delay, but if the experimenter doesn't do that, it's still not guaranteed that they will arrive within the time window, as I understand it.

The reason I keep harping on this is that, if it is possible for the experimenter (Chris) to guarantee that a swap does happen, then we have the problem @PeroK brought up earlier: in a setup where the 1 & 4 measurement results are in the past light cone of Chris making the decision of what, if anything, to do to photons 2 & 3 before they arrive at the BSM, Chris could wait until he sees a pair of 1 & 4 results that are inconsistent with entanglement (for example, a combination of results that is impossible in the entangled state), and then force a swap to happen at the BSM--which would contradict the predictions of QM, since QM predicts that if the 1 & 4 results show no entanglement, a swap cannot happen. The only way to avoid this contradiction is to not have Chris be able to force a swap to happen--i.e., to have at least some factors involved in determining whether a swap happens be out of Chris's control.

1. You are correct in that the experimenter has no control over which 2 & 3 pairs will arrive at the BSM such that they overlap indistinguishably - that's strictly random. When the 1 & 4 photons arrive is of course related to the 2 & 3 arrival time(s) at the BSM. But... there aren't any 1 & 4 results that are inconsistent with an entangled state - at least not without considering the 2 & 3 results.

Remember that when it comes to timing and time windows, everything must be adjusted/normalized relative to everything else. And likewise, the 2 independent sources and all observers can be located as close or as far apart relative to each other as desired. No combination of locations/distance (ideal case) changes the observed outcomes.

If you didn't follow the permutations I presented in post #106 (lol), then consider this one instead. All of the sources, detectors and observers are in the same room. The distance to the 1 & 4 detectors from their respective sources is exactly the same. The distance to the 2 & 3 BSM (beamsplitter portion) is the same, plus there is an extra 20 km of fiber rolled up on the floor that the 2 & 3 photons must travel through. The distance from the beamsplitter to the BSM detectors is exactly equal. So Alice and Bob will see their mutual results together, a little before Chris decides to add a bit of delay (or not) to the photon 3 line.

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2. We only consider cases where Alice (photon 1) and Bob (photon 4) both see simultaneous clicks (defined as being within the specified time window, of course). As mentioned, this is simply something that occurs randomly. The basic scenario is as follows with Chris adding no delay, and ideal lossless conditions (and very fast observers LOL):

a) Every outcome has photons 1 & 4 entangled. Every, single one. If 1 & 4 arrive at their detectors simultaneously, so will 2 & 3. That's because 1 & 4 traveled the same distance relative to each other, and so did 2 & 3 relative to each other. So they will all appear in the same adjusted time window.


b) If Alice and Bob are checking photons 1 & 4 at the same angle settings: They can tell Chris the information needed (match or no match) to predict - with certainty - which of 2 Bell states will occur at the BSM. The BSM being in the future of what Alice and Bob just witnessed. If Alice and Bob matched (at same angles), then the BSM can only yield 2 possible outcomes: ψ+ or φ+ entanglement. If Chris got 2 clicks, it's ψ+; if only one click, it's φ+. Which of those occurs is simply random. The total number of clicks is 4 if ψ+/-; or 3 if φ+/-.

Nothing Alice or Bob do can any way affect whether the outcome is ψ+ or φ+, so there is no way to send a signal from Alice and Bob to Chris using the entanglement channel. Even though Alice and Bob can pass information on their results to Chris before Chris knows how many clicks show up at the BSM from the 2 & 3 photons. Keeping in mind that φ+/- outcomes only yield a single click at the BSM - but if Chris knows that Alice and Bob simultaneously matched at the same angles, then the φ- case can be ruled out.

Importantly: When Chris does see see 2 clicks, it will ALWAYS be a BSM combination that indicates ψ+ (if Alice and Bob matched) or ψ- (if Alice and Bob did not match). There are multiple permutations of clicks at the BSM that indicate this. On the other hand: if Chris sees only a single click at the BSM, that is neither proof nor disproof that the appropriate φ+ or φ- case occurred. Because a single click at the BSM cannot distinguish these.


c) If Alice and Bob are checking photons 1 & 4 at the different angle settings (such as for CHSH): They cannot tell Chris the information needed to predict which of 4 Bell states will occur at the BSM. That's because any combination of outcomes that Alice and Bob see is consistent with any of the 4 Bell states. Alice and Bob could provide information to Chris as to what is likely to occur though. Because there are outcomes that are more likely by far. (Typically a bit less than 75% accurate and a bit more than 25% inaccurate in the CHSH angle settings.)

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3. Hopefully everything presented so far makes sense. Now, everything the same as above, but instead: Chris chooses to implement the delay feature before knowing what Alice and Bob saw (match or no match).

d) Every outcome has 1 & 4 NOT entangled. There is no correlation at all with anything that happens at the BSM. Of course, Alice and Bob don't know this. In each and every case, the 2 & 3 photons arrived at the BSM far enough apart in time that Chris can pick out the 2 photon as the one arriving earlier, and the 3 photon as the one arriving later. Since they are distinguishable, there cannot be a swap.

Regardless of the clicks that Chris sees, there will be absolutely 0 correlation between those clicks (i.e. what they would otherwise indicates as to which Bell state occurred - and whether Alice and Bob matched or not.

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4. I would say that Chris' decision to add the delay time (or not) to photon 3's travel time - which occurs AFTER photons 1 & 4 outcomes are registered - was the "causal factor" in whether or not entanglement was swapped. There is absolutely no other factor involved, as you can clearly see, and the outcome is certain. Chris makes that decision while ignorant of the outcomes that Alice and Bob see, and in fact it wouldn't matter anyway.

Now, most anyone is going to say that Chris' decision to entangle or not - which is 100% demonstrably* a result of that decision - cannot change something that occurred in the past. And certainly, regardless, how to properly explain what happens is interpretation dependent. But what is not interpretation dependent is that Alice, Bob and Chris can literally be anywhere relative to each other - distant in terms of spacetime - and the outcomes will be exactly as I describe. And of course in no known situation can anyone send a signal that would violate signal locality, and no one can cause anything to occur in the past (or future) that would be inconsistent with the present.

-DrC

*If you are unsure about this, compare again cases a) and d) above. Note that the absolute proof can ONLY be seen in cases in which Chris sees 2 clicks at the BSM. 2 BSM clicks, no delay -> 100% correlation. 2 BSM clicks, with delay -> 0% correlation.

 

[PeterDonis]

You are correct in that the experimenter has no control over which 2 & 3 pairs will arrive at the BSM such that they overlap indistinguishably - that's strictly random.

Ok, good. That's what I thought.

When the 1 & 4 photons arrive is of course related to the 2 & 3 arrival time(s) at the BSM.

"Related" only in a very weak sense. Obviously if the 1 & 4 measurements are going to be in the past light cone of the BSM operation, there has to be a significant delay involved with the 2 & 3 photons. But the precise length of that delay is not exactly controllable by the experimenter. So the experimenter also has no exact control over the relationship between the 1 & 4 photon measurement times and the time window required for the BSM to do a swap.

there aren't any 1 & 4 results that are inconsistent with an entangled state - at least not without considering the 2 & 3 results.

Hm. I guess this is because all 4 of the entangled Bell states are possible outcomes of the BSM swap operation--it's just that we don't (at least currently) have any experimental setups that can distinguish all 4 of them. In experiments I remember being discussed in previous threads, the only entangled state that could be distinguished was the singlet state, and of course any pair of 1 & 4 results that give the same outcome for measurements in the same direction is inconsistent with that state. But from what you're saying, that would not mean 1 & 4 could not be entangled at all; it would just mean that if they are entangled, they're not in the singlet state. So as long as whatever 2 & 3 outcomes were measured were consistent with them not being in the singlet state, that would be ok. And the experimenter can't control the outcome of the 2 & 3 operation: even if it is a swap, the experimenter can't dictate that it is a swap into a particular entangled state.

the 2 independent sources and all observers can be located as close or as far apart relative to each other as desired. No combination of locations/distance (ideal case) changes the observed outcomes.

Yes, agreed.

 

[DrChinese]

1. Ok, good. That's what I thought.


2. "Related" only in a very weak sense. Obviously if the 1 & 4 measurements are going to be in the past light cone of the BSM operation, there has to be a significant delay involved with the 2 & 3 photons. But the precise length of that delay is not exactly controllable by the experimenter. So the experimenter also has no exact control over the relationship between the 1 & 4 photon measurement times and the time window required for the BSM to do a swap.


3. Hm. I guess this is because all 4 of the entangled Bell states are possible outcomes of the BSM swap operation--it's just that we don't (at least currently) have any experimental setups that can distinguish all 4 of them. In experiments I remember being discussed in previous threads, the only entangled state that could be distinguished was the singlet state, and of course any pair of 1 & 4 results that give the same outcome for measurements in the same direction is inconsistent with that state. But from what you're saying, that would not mean 1 & 4 could not be entangled at all; it would just mean that if they are entangled, they're not in the singlet state. So as long as whatever 2 & 3 outcomes were measured were consistent with them not being in the singlet state, that would be ok. And the experimenter can't control the outcome of the 2 & 3 operation: even if it is a swap, the experimenter can't dictate that it is a swap into a particular entangled state.


Yes, agreed.

1. Yay!


2. Peter, this is not correct. The relationship of the relative timings is extremely precise. And is completely under control of the experimenter - from millimeters apart to kilometers apart. This is in fact demonstrated in almost all swapping experiments, as well as many Bell type experiments. You already know this, but it may have gotten lost with all the back and forth.

Below is the HOM dip, which is measured in picoseconds; while the window is usually measured in nanoseconds. These are 4 fold coincidences. Obviously, the experiments I am citing are typically 10-15 years old. Recent advances are moving timings into much greater resolution, such as this from 2018: Attosecond-Resolution Hong-Ou-Mandel Interferometry.

In delayed choice variations, where the BSM is performed in the future of photons 1 & 4: usually that delay to the future is relatively short - exactly as you imagine - on the order of 100 meters (about 500 ns) as in here. After all, there is no specific theoretical difference between 100 meters and 100 times that. Of course, swapping itself has been demonstrated over distances of as much as 100 km (here and here*) without the delayed choice version. Since there is no particular open question related to the many delayed choice quantum experimental variations - all confirming the predictions of QM - I am not sure there is much experimental interest in setting new records for one particular version.

*From the reference: "As shown in Fig. 2, the typical peak-to-peak delays between arrival times of photons from Alice and Bob changes are 200 ps, 500 ps, and 1000 ps in rainy days, cloudy days, and sunny days, respectively, which are much larger than the coherent time of signal photons (∼ 110 ps). We use the difference between the arrival times of signal photons from Alice and Bob as error signals and feed them into a delay line to suppress the relative delay to 6 ps under all weather conditions, which is <<∼ 110 ps to ensure high interference visibility."


3. Yes and no. Assuming 1 & 4 are measured at the same angles when entangled, the results (match or mismatch) reduces the possible Bell states to 2 (which occur randomly). But only 1 of those can be discerned explicitly by the BSM. When doing the CHSH inequality, you are correct: any of the 4 Bell states would be compatible with any individual 1 & 4 result. And only 2 of those 4 can be discerned.

In some experiments, it is easier for the experimenter to look for a single specific Bell state with the BSM (what you can the singlet). So it depends what the experimenter is looking to do (in the particular paper) that determines whether to consider 1 or 2 of the 4 Bell states. If they are looking for 2 Bell states: it is possible to discern ψ+ or ψ- (most common), or φ+ or φ- (less common). But in no scenario does it make any difference to the scientific conclusion. Keep in mind that the experimenters know perfectly well that each Bell state occurs randomly and very nearly equally. If there were any hint otherwise, that would be a major issue.


4. Yay again

 

[PeterDonis]

he typical peak-to-peak delays between arrival times of photons from Alice and Bob changes are 200 ps, 500 ps, and 1000 ps in rainy days, cloudy days, and sunny days, respectively, which are much larger than the coherent time of signal photons (∼ 110 ps)

This was the sort of thing I was thinking of in what you labeled as item 2.

We use the difference between the arrival times of signal photons from Alice and Bob as error signals and feed them into a delay line to suppress the relative delay to 6 ps under all weather conditions

So this looks like the experimenters are correcting for the issue above. That looks like a key factor that I was missing.

 

[AndreasC]

Don't we have enough interpretations already?

Well it's not like we pay tax on them.

 

[Fra]

The point is Conceptual clarity.

At first I would agree but this is apparently one of the most relative notions ever invented. What is clear to you may well be hazy to someone else. So I think the discriminator is still whatever makes progress on open questions easier, clear or not.

/Fredrik

 

[Fra]

I skimmed some of

https://arxiv.org/abs/2302.10778
https://arxiv.org/abs/2309.03085
https://arxiv.org/abs/2402.16935

I skimmed these but I lack any for me preferred new conceptual grip, it seems mainly descriptive as I find no references to the observer or the context.

In the last paper he writes...

"At the level of dynamics, the microphysical laws consist of conditional or transition probabilities of the form Γij(t) ≡ p(i, t|j, 0) [for i, j = 1, . . .N], (18) each of which supplies the probability for the system to be in its ith configuration at a continuously variable time t..."

Sounds reasonable and these obviously encode the corresponding hamiltonian details, but the question is, what is the process whereby these laws (transition probabilities) are inferred by a real observer. Without this, this seems to be out of taste for me. In principle I can imagine some elaborations where these transition amplities are constructed, but I see no traces of that in this thikning from skimming the papers. without this, this remains pursely descriptive, treating the "observer" as an implicit non-interacting context, just like most other interpretations.

/Fredrik

 

[RUTA]

TL;DR Summary: I attended a lecture that discussed the approach in the 3 papers listed below. It seems to be a genuinely new interpretation with some interesting features and claims.

These papers claim to present a realistic stochastic interpretation of quantum mechanics that obeys a stochastic form of local causality. (A lecture I recently attended mentioned these papers). It also claims the Born rule as a natural consequence rather than an assumption. This appears to me to be a genuinely new interpretation. I have not delved into the papers in detail, but figured some people here may be interested.

https://arxiv.org/abs/2302.10778
https://arxiv.org/abs/2309.03085
https://arxiv.org/abs/2402.16935

Here is a talk he gave this month

 

[RUTA]

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

His last statement is correct, given his redefinition of local causality. But, as many of you have pointed out, changing the semantics will not solve the mystery of quantum entanglement for most people.

 

[Fra]

While I see other problems, not at all addressed by this "new interpretation" (such as constructing the transition matrixes rather than just assume their existence), I appreciate the attempt to clarify the meaning and definition of causality as I think the "nature of causation" is indeed at the heart of the matter, so it might be a more compatible with bayesian interpretations.

As the various traditional bell defintions of terms based on what violates bell inequalities are conceptually entangled with assumptions going into Bells ansatz. But those assumptions I see as a outdate legacy.

His last statement is correct, given his redefinition of local causality. But, as many of you have pointed out, changing the semantics will not solve the mystery of quantum entanglement for most people.

quantum nonlocality are probabilistic, and therefore do not constitute evidence of what might be labeled as "causal" anyway.

I think as long as one refuse to include the observers actions into the physics, we will likely not make progress.

The merit I find in defining causality in terms of conditional probabilities instead of single events is that they are what would be expected to causally influence an agents actions towards it's environment, rather than single events.

The only for me at least conceptually meaningful notion of local causality principle, is that local decisions are influence only by local information. Thus "causality" would then not be a statement of future correlations, but a statement about present actions. It is in this sense I also envision (but maybe differently Barandes) that "hidden variables" CAN explain the correlations in entanglement as per Reichenbach's Principle, while violating bell inequality, because the causal mechanism is not on "outcomes" but on "actions"; so the Reichenbach's keys is still hidden, so the ignorance anzats of Bell cant' be valid. This is the confusion that I always felt is built into the legacty anzats of Bell, as it implies a "ignorance interpretation".

But this conceptual understanding still needs to be realized in reconstructing the interactions (transition matrixes) that would essentiall encode the actions of matter (linking to unification). So a massive task! But I think some simply would see this conceptual possibility until the full theory is explicit. While others(me included) find it a guiding principle - I find no clues of this in his papers though. Which is why I appreciate attacking the nature of causality, but don't yet understand what else it adds.

/Fredrik

 

[iste]

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. ***


*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.

**In these experiments, each and every individual run violates realism (since he assumes locality). The quantum prediction is exactly opposite the realistic prediction, and experiment matches QM.

***Note that everyone already agrees that there is signal locality; and that the many demonstrations of quantum nonlocality are probabilistic, and therefore do not constitute evidence of what might be labeled as "causal" anyway.

Barandes' formulation will violate local realism and uphold contextuality insofar that you can just describe ordinary quantum mechanics through his formulation. He gets non-local correlations in entanglement like it occurs ordinarily in quantum mechanics. The new paper I think is just denying that correlation is causation which, to my understanding, is not so conceptually different from what people have already said about things like no-signaling. I think the novelty is trying to demonstrate it through causal modeling of the explicit stochastic systems that underlie the quantum formalism in his formulation... or something like that.

The big thing about the formulation is that it does always realize definite, localized outcomes even when there are no measurements going on like during coherent superposition. This doesn't contradict non-locality or contextuality for the simple reason that these definite outcomes don't explicitly exist in orthodox quantum mechanics. All of the kinds of no-go theorems and contextual phenomena are not at the level of the realized outcomes in this formulation. In Barandes' formulation, the wavefunction is clearly not physically real (neither is wave collapse) and just predicts the actual localized outcomes. Obviously someone like yourself might want to explicitly see the following, but in principle, the fact he hasn't given an explicit treatment of GHZ or entanglement swapping doesn't matter because 1) the formulation isn't explicitly proposing any predictions or mathematical machinery explicitly different from ordinary quantum mechanics and 2) the whole point of what he has demonstrated in the first two papers is that any scenario with a unitarily evolving quantum system can be shown to be equivalent to a generalized stochastic system that realizes definite outcomes - doesn't matter the specifics of GHZ or entanglement swapping or anything else. The objects of quantum mechanics are "translated" directly from statistical information in stochastic matrices or vice versa. It's all just statistics except for the actual realized outcomes which are not explicit in the orthodox formalism (in the sense that they even occur when unmeasured), except perhaps in one place - the path integral formulation. People are encouraged to look at the Feynman paths that are summed over as computational tools but actually, they are clearly explicit expressions of stochastic trajectories in the same way you get out of Barandes' formulation or perhaps other stochastic formulations. From the pov of Barandes' formulation, these paths are in the theory because this is exactly what the theory is trying to say happens - it is not an inexplicable tool.

Because contextuality is just context-dependent statistics in lieu of a unique joint probability distribution, there is absolutely no conflict with the notion of definite outcomes as long as their relative frequencies are constituting the statistics being described. Seems to me that only if you interpret the wave-function as a physical object, do you get any conflict.

We then only have to look at Fine's theorem to see where the non-causal correlations come from. Barandes has not mentioned this but it's just a general, notable result in quantum mechanics.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.48.291

"It is shown that the following statements about a quantum correlation experiment are mutually equivalent… (3) There is one joint distribution for all observables of the experiment, returning the experimental probabilities. (4) There are well-defined, compatible joint distributions for all pairs and triples of commuting and non-commuting observables. (5) The Bell inequalities hold."

Bell violations are just an indicator of absent joint probability distributions which follow come from the presence of local incompatibility. It doesn't seem to me that there is any indication from this kind of result that it depends on the nature of actual physical events. Similar to how, if I rotate a physical object along different directions, and find that the order I make the rotations in matters for the final result… well this result has nothing directly to do with the physical scenario. It is a formal property that follows from the mathematics of 3D rotations. The physical scenario just has to satisfy the formal conditions, but it is not the physical scenario itself that is the cause of the rotation phenomena when I rotate a book or something. Similarly, Bell violations are just an unintuitive formal consequence of absent joint probability distributions, a connection first discovered by George Boole in the 1800s:

https://arxiv.org/abs/2010.13326

"(Pitowsky quote within paper - For certain families of events the theory stipulates that they are commeasurable. This means that, in every state, the relative frequencies of all these events can be measured on one single sample. For such families of events, the rules of classical probability — Boole’s conditions in particular — are valid. Other families of events are not commeasurable, so their frequencies must be measured in more than one sample. The events in such families nevertheless exhibit logical relations (given, usually, in terms of algebraic relations among observables). But for some states, the probabilities assigned to the events violate one or more of Boole’s conditions associated with those logical relations. - End)

The point we would like to emphasize is that tables such as the Bell table in section 2.1 can — and do — arise from experimental data, without presupposing any particular physical theory."

These absent joint probability distributions are implicit in Barandes' paper. He doesn't talk about it explicitly but his violated Markov property in the first two papers can just be seen as violations of the law of total probability for Markov trajectories. You also see in the papers that quantum interference terms can be constructed from them in the exact same way that follows from violations of total probability in orthodox quantum formulations. So it's safe to say the violated markov property plays the same role as total probability violations in causing quantum behavior from absent joint probability distributions. Classical stochastic trajectories are explicitly characterized in terms of joint probabilities along time points, as you can see through things like Kolmogorov extension theorem / consistency conditions, so these are the kinds of joint probability distributions being implied by the Markov property. Incidentally, the failure of total probability for classical stochastic trajectories have been explicitly characterized in terms of failures of "pre-existing" dynamics or non-invasive measurement, analogously to quantum mechanics:

https://arxiv.org/abs/2012.01894

Stochastic processes also have a unique explanatory value for non-local correlations in that if an individual particle's state trajectory has random dynamics then there is no issue about how particles "knew" what the measurement settings were in a Bell-type experiment, because outcomes are not fixed at source. States are always fluctuating along particle trajectories so that if you think about it, the eventually measured outcomes must have randomly occurred at the point of measurement, and this will be according to a joint probability distribution that depends on the measurement setting. However, none of these context-dependent distributions can be found from marginalization of a unique, context-invariant distribution that underlies them.

Effectively when you combine this latter stochastic advantage with what is implied by Fine's theorem, the mystery of Bell violations can be entirely deflated as a consequence of purely statistical behavior in particles that have definite locations, states, trajectories. Again, this is allowed because these realizations are not explicit in the orthodox quantum formalism; all the usual non-local correlations and contextuality co-exist happily with them. Barandes' papers are just concretely showing this by demonstrating that quantum mechanics corresponds to generalized stochastic systems, which actually do not need to be dressed in the quantum formalism in order to exhibit non-local behavior either.

 

[iste]

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. ***


*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.

**In these experiments, each and every individual run violates realism (since he assumes locality). The quantum prediction is exactly opposite the realistic prediction, and experiment matches QM.

***Note that everyone already agrees that there is signal locality; and that the many demonstrations of quantum nonlocality are probabilistic, and therefore do not constitute evidence of what might be labeled as "causal" anyway.

I put this next part in a separate post because clearly I was getting carried away but I still want to emphasize the generality of these ideas though maybe it drifts away a bit from my original post.

In recent years, Bell violations have come up in social science too. Not just experiments but even in online data you can find violations of CHSH inequalities:

https://arxiv.org/abs/2012.01894

What is the commonality between quantum mechanics and this kind of online data? I think most parsimoniously, the common factor is that we just have violations of total probability here. Phenomenologically statistical, non-deterministic theories will be able to violate Bell inequalities purely as a formal stipulation, not as a direct consequence of local physical interactions. The great Daniel Kahneman died this week, having won a Nobel prize in economics for a body of work showing that humans are "irrational". Incidentally, this stuff is the exact kind of thing that is now being modeled with quantum probability theory and in which we find phenomena like Bell violations and quantum interference. Why? Because human behavior is context-dependent. There are scenarios where the statistics of human behavior vary with context in ways that were not expected from traditional rational choice theory in economics and so naive applications of classical probability theory failed to model this behavior appropriately. How does this manifest formally? Violations of total probability. Where does this also happen? Quantum contextuality.

Abramsky has shown this absence of joint probability distribution is the fundamental underlying feature that brings us quantum contextuality and non-locality:

https://iopscience.iop.org/article/10.1088/1367-2630/13/11/113036/meta

Which essentially just generalized the result Arthur Fine and various people like him found back in the mid-late 20th century.

Barandes' work reiterates the notion that such statistical phenomena are fundamentally ambivalent to how those statistics are physically instantiated, consequently there is no reason why theories which always have definite, localized outcomes cannot reproduce the same quantum phenomena if they conform to the required statistics. Barandes shows such theories are indeed equivalent to quantum mechanics in his first two papers. Does this mean we have quantum mechanical theories in psychology now? Well, arguably yes, insofar as people are now actually explicitly using quantum theory to model psychology. Not because psychology is weird, mysterious and full of woo - it is just because psychology is sometimes contextual in ways which cannot be modeled by Markov decision processes - non-Markovian just as Barandes explicitly characterizes the generalized stochastic systems in his papers.

 

[DrChinese]

1. Barandes' formulation will violate local realism and uphold contextuality insofar that you can just describe ordinary quantum mechanics through his formulation. He gets non-local correlations in entanglement like it occurs ordinarily in quantum mechanics. The new paper I think is just denying that correlation is causation which, to my understanding, is not so conceptually different from what people have already said about things like no-signaling....

The big thing about the formulation is that it does always realize definite, localized outcomes even when there are no measurements going on like during coherent superposition. This doesn't contradict non-locality or contextuality for the simple reason that these definite outcomes don't explicitly exist in orthodox quantum mechanics.

...Barandes' papers are just concretely showing this by demonstrating that quantum mechanics corresponds to generalized stochastic systems, which actually do not need to be dressed in the quantum formalism in order to exhibit non-local behavior either.

2. All of the kinds of no-go theorems and contextual phenomena are not at the level of the realized outcomes in this formulation. In Barandes' formulation, the wavefunction is clearly not physically real (neither is wave collapse) and just predicts the actual localized outcomes. Obviously someone like yourself might want to explicitly see the following, but in principle, the fact he hasn't given an explicit treatment of GHZ or entanglement swapping doesn't matter because 1) the formulation isn't explicitly proposing any predictions or mathematical machinery explicitly different from ordinary quantum mechanics and 2) the whole point of what he has demonstrated in the first two papers is that any scenario with a unitarily evolving quantum system can be shown to be equivalent to a generalized stochastic system that realizes definite outcomes - doesn't matter the specifics of GHZ or entanglement swapping or anything else.

I'm impressed, quite a defense.

1. Hmmm... so which is it?

a. It will "violate local realism", OK, that's a requirement of Bell. No sound person is really going to accept otherwise. And this paper certainly isn't the one to accomplish that.

b. It will "uphold contextuality" which in essence means it is non-realistic. Statistical outcomes are dependent on a future context, even when the measurement setting are changed midflight and are far distant. That's good, dozens of experiments show this exact point. It also means that particle observables don't have definite values outside of when they have an eigenvalue.

c. There are "non-local correlations in entanglement like it occurs ordinarily in quantum mechanics". Fine, that is generally accepted and is called "quantum nonlocality". There are about 5000 papers with this in the title on arxiv.

d. "The big thing about the formulation is that it does always realize definite, localized outcomes even when there are no measurements going on like during coherent superposition." What?? That is exactly the opposite of b. How can a superposition yield definite values on all bases simultaneously? And even if they could, how do those values appear when measured on a specific basis such that it follows quantum statistics if they are to be called "localized". (Whatever that is supposed to mean in this context, since c. above implies exactly the opposite.)

e. "This doesn't contradict non-locality or contextuality for the simple reason that these definite outcomes don't explicitly exist in orthodox quantum mechanics." Admittedly they don't exist in orthodox QM. After Bell, this is explicitly ruled out! You cannot have such outcomes - well they are even outcomes as they aren't measured - and also say it will agree with the predictions of QM. They call that...hand-waving.

f. "...quantum mechanics corresponds to generalized stochastic systems [or really?], which actually do not need to be dressed in the quantum formalism in order to exhibit non-local behavior either." So stochastic systems exhibit nonlocal behavior but feature no nonlocality? Or what?

Yes, if there is some nonlocal mechanism here that keeps entangled systems synchronized or otherwise in some kind of contact when their spatial extent grows, then all is good and I am satisfied. But that is not what I am reading.


2. How can anyone say with a straight face that they are presenting something novel, it's just like QM only better, and then blatantly ignore the obvious hurdles of things like swapping and GHZ.

a. Swapping: Systems become entangled without ever existing in a common local region. You think that is a "stochastic" result? I don't think that does very far as an argument.

b. GHZ: The assumption that particles have pre-existing values for observables yields predictions that are diametrically opposed to experiment in each and every case?

In stochastic theories, there are supposed to be many unknowns leading to various apparently random outcomes (Wiki: "Stochastic processes are widely used as mathematical models of systems and phenomena that appear to vary in a random manner."). Neither of these apply to a. or b. above.

So yes, I would insist any interpretation explain these. They are a lot more critical than something to be dismissed ("GHZ or entanglement swapping doesn't matter") by saying the basic elements are the same as orthodox QM. Either it's the same, in which it adds nothing, or it posits different elements. We know it posits different elements, because of the items discussed in 1. above.

To be fair: Please note that most "new" interpretations of QM are in the same boat. They have worked so hard to try and get around Bell (1964) by some new twist or variation, but ignore all the incredible theoretical work since: GHZ, PBR*, Kochen-Specker-Bell, Leggett, Hardy, just to name a few. All of these are serious and significant hurdles, and every one should be addressed explicitly in any new work.


*Psi-epistemic is a common term for "the wavefunction is clearly not physically real". Directly disproven by PBR.

 

[DrChinese]

1. In recent years, Bell violations have come up in social science too. Not just experiments but even in online data you can find violations of CHSH inequalities:

https://arxiv.org/abs/2012.01894

What is the commonality between quantum mechanics and this kind of online data? I think most parsimoniously, the common factor is that we just have violations of total probability here. Phenomenologically statistical, non-deterministic theories will be able to violate Bell inequalities purely as a formal stipulation, not as a direct consequence of local physical interactions.

2. The great Daniel Kahneman died this week, having won a Nobel prize in economics for a body of work showing that humans are "irrational".

1. Don't make me laugh at these ridiculous contrived examples. I've seen plenty of attempts to try and parallel classical situations with quantum entanglement, and they all fall woefully short. Because they all fail in one GIANT* manner: They cannot reproduce perfect correlations on bases chosen after the fact. That is of course ignoring the obvious fact that the examples themselves are self-chosen by the author as being "like quantum mechanics". I'll pick the human/classical scenario, let the author find the parallel.

So: How about two independently shuffled decks of cards (not initially correlated in any way) that have been shuffled by Alice and Bob, who have not communicated in any manner? Say: the 30th card in each stack should be the same color. Or the 42nd card in each? Etc. That actually happens in Bell tests featuring swapping**. That is what needs to be handled by any example purporting to show classical violations a la Bell. Think you can find a way to present them as entangled and showing perfect correlations? That's just the beginning of the challenge, good luck. (If you can solve that, we can proceed to the second half.)


2. Wow, I missed that! I am a long-time fan of his and Tversky (also Nisbett and Ross if you are familiar with them, work along similar lines of thinking). After reading your post, I picked up the paper (WSJ) and there was a nice front page article about him.


*And glaring manner. The person inventing the example forgot to consider the lesson of EPR (1935) which features perfect correlations. Bell didn't forget it, that's why his 1964 paper was titled: "On the Einstein Podolsky Rosen paradox".

**See experiments such as: High-fidelity entanglement swapping with fully independent sources

 

[Fra]

1. Don't make me laugh at these ridiculous contrived examples. I've seen plenty of attempts to try and parallel classical situations with quantum entanglement, and they all fall woefully short. Because they all fail in one GIANT* manner: They cannot reproduce perfect correlations on bases chosen after the fact. That is of course ignoring the obvious fact that the examples themselves are self-chosen by the author as being "like quantum mechanics". I'll pick the human/classical scenario, let the author find the parallel.

In recent years, Bell violations have come up in social science too. Not just experiments but even in online data you can find violations of CHSH inequalities:

https://arxiv.org/abs/2012.01894

What is the commonality between quantum mechanics and this kind of online data? I think most parsimoniously, the common factor is that we just have violations of total probability here. Phenomenologically statistical, non-deterministic theories will be able to violate Bell inequalities purely as a formal stipulation, not as a direct consequence of local physical interactions. The great Daniel Kahneman died this week, having won a Nobel prize in economics for a body of work showing that humans are "irrational". Incidentally, this stuff is the exact kind of thing that is now being modeled with quantum probability theory and in which we find phenomena like Bell violations and quantum interference. Why? Because human behavior is context-dependent. There are scenarios where the statistics of human behavior vary with context in ways that were not expected from traditional rational choice theory in economics and so naive applications of classical probability theory failed to model this behavior appropriately.

A conceptual commonality is also that social interactions is explicitly about interacting information processing agents (humans). This is why this analogy makes conceptual sense at least for me, due to my interpretation. This means we can understand "quantum interactions" as something that emerges naturally in systems containing information processing agents or beeing isomorphic to that.

The problem with many models that find that humans are not rational is that the MEASURE of rationality is not as simply to define. Clearly a human beeing is not a money machine, processing emotions is just as information and in principle that is also "information". Even within this way of thinking there are alot of variation.

I quoted tses papers in an old thread

Nashian game theory is incompatible with quantum physics​

"We suggest to look at quantum measurement outcomes not through the lens of probability theory, but instead through decision theory. We introduce an original game-theoretical framework, model and algorithmic procedure where measurement scenarios are multiplayer games with a structure all observers agree on. Measurement axes and, newly, measurement outcomes are modeled as decisions with nature being an action-minimizing economic agent
...
Most significantly, we observe that game theory based on Nash equilibria stands in contradiction with a violation of Bell inequalities. Hence, we propose that quantum physics should be analyzed with non-Nashian game theory, the inner workings of which we demonstrate using our proposed model."
-- https://arxiv.org/abs/1507.07341

​

Quantifying and Interpreting Connection Strength in Macro- and Microscopic Systems: Lessons from Bell’s Approach​

"As a macroscopic example from the financial world, we show how the unfair use of insider knowledge could be picked up using Bell statistics. Finally, in the discussion of realist interpretations of quantum mechanical Bell experiments, cheating strategies are often expressed through the ideas of free choice and locality. In this regard, violations of free choice and locality can be interpreted as two sides of the same coin, which underscores the view that the meaning these terms are given in Bell’s approach should not be confused with their everyday use. In general, we conclude that Bell’s approach also carries lessons for understanding macroscopic systems of which the connectedness conforms to different causal structures."
-- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8947266/

The conceptual association here I mave between "breaking isolation" of entangled particles, and "unfair use of inside information". Just like in a quantum experiment, we can "detect" if the isolation is broken, one might detect the use of inside information as it changes the results of the total game over time.

For me these are just conceptual parallellts, I didn't bother study or nitpick the papers in details as the conceptual analogue is clear to me anyway.

/Fredrik

 

[PeterDonis]

*Psi-epistemic is a common term for "the wavefunction is clearly not physically real". Directly disproven by PBR.

More precisely, PBR disproves "epistemic" models in which the wave function is treated as a distribution over underlying "ontic" states. But that is not the only kind of model in which the wave function is "not physically real" in the sense that it doesn't describe the real physical state of individual quantum systems. For example, PBR says nothing, as far as I can see, that rules out ensemble or statistical interpretations such as Ballentine's, or the thermal interpretation of @A. Neumaier, since those interpretations do not treat the wave function as a distribution over underlying ontic states--but they also don't treat it as describing the physically real state of individual quantum systems.

 

[martinbn]

More precisely, PBR disproves "epistemic" models in which the wave function is treated as a distribution over underlying "ontic" states. But that is not the only kind of model in which the wave function is "not physically real" in the sense that it doesn't describe the real physical state of individual quantum systems. For example, PBR says nothing, as far as I can see, that rules out ensemble or statistical interpretations such as Ballentine's, or the thermal interpretation of @A. Neumaier, since those interpretations do not treat the wave function as a distribution over underlying ontic states--but they also don't treat it as describing the physically real state of individual quantum systems.

Which imterpretations are disproven? I asking for examples.

 

[Fra]

It may be useful to summarize the assumptions that are necessary for the result. Three can be identied
...
The third assumption is that measuring devices respond solely to the physical properties of the systems
they measure. We do not assume underlying determinism. Even given a full specication of , it may only be possible to make probabilistic predictions about the outcome of a measurement.


-- https://arxiv.org/abs/1111.3328v1

Their third assumption is exactly the one that was objectionable to me, even in bells ansatz, it is no different. It assumes that the interaction betwee measurement device and the "quantum system" in a single interaction, depends ONLY on the physical property of the quantum system, namely the hidden variable.

The only for me at least conceptually meaningful notion of local causality principle, is that local decisions are influence only by local information. Thus "causality" would then not be a statement of future correlations, but a statement about present actions. It is in this sense I also envision (but maybe differently Barandes) that "hidden variables" CAN explain the correlations in entanglement as per Reichenbach's Principle, while violating bell inequality, because the causal mechanism is not on "outcomes" but on "actions"; so the Reichenbach's keys is still hidden, so the ignorance anzats of Bell cant' be valid. This is the confusion that I always felt is built into the legacty anzats of Bell, as it implies a "ignorance interpretation".

This is directly contrast to this. By "local information" means expectations on the system, by the measurement device, the opposite of unknown actual states of hidden variables.

The third assumption alone makes no sense for any scenario where the interaction is changed by the mutual EXPECTATION of the physical states. This is exactly what is going on in social interactions too to connect to the analogy, and IMO the reason why "games of expectations" does not fulfill the assumptions that is used in bells theorem, pbr etc. The missing component, is the understnading of causation or interaction in the first place. IF one looks at social interactions, I would argue that it is in fact intuitive that interactions are not depending only on the hidden STATE of the interacting object, but our OWN EXPECTATIONS of does change our response, and thus the whole interaction.

/Fredrik

 

[DrChinese]

More precisely, PBR disproves "epistemic" models in which the wave function is treated as a distribution over underlying "ontic" states. But that is not the only kind of model in which the wave function is "not physically real" in the sense that it doesn't describe the real physical state of individual quantum systems. For example, PBR says nothing, as far as I can see, that rules out ensemble or statistical interpretations such as Ballentine's, or the thermal interpretation of @A. Neumaier, since those interpretations do not treat the wave function as a distribution over underlying ontic states--but they also don't treat it as describing the physically real state of individual quantum systems.

Amazingly, all psi-epistemic interpretations deny the applicability of PBR. Go figure.

Which interpretations are disproven? I asking for examples.

Ditto, all psi-epistemic interpretations deny the applicability of PBR. Of course, there are many others that think they are generally disproven. But being a gentleman, and considering we are talking about interpretations, I try to leave the conclusion to each person.

Their third assumption is exactly the one that was objectionable to me, even in bells ansatz, it is no different. It assumes that the interaction between measurement device and the "quantum system" in a single interaction, depends ONLY on the physical property of the quantum system, namely the hidden variable.

Consider this: What device/detector are we talking about? In a typical Bell test, there are 4 detectors and 2 polarizing beam splitters (PBS). So... is it the beam splitter where your objection arises? Because that implies Alice's beam splitter contains hidden variables that influence the outcome as H> or V>. That result has never been observed - just consider what happens when any pure H> beam goes into a PBS. It comes out one port with nearly perfect consistency/accuracy. So: No relevant hidden variables there. And what about the detectors? The only thing left up to the detector is to click - or not. No chance of a detection by the H> detector causing the V> detector to click, right? Nothing about the measurement apparatus is going to distort any statistical results, and certainly not with the extremely high quality gear today.

But none of that matters. We already know there is nothing material added by any of the measurement devices, and therefore the "third assumption" is valid. The measurement device could not possibly affect the statistical outcomes, unless remote apparati (of Alice and Bob) are themselves entangled with each other - a possibility that is far-fetched in the extreme.

How do we know this? There are perfect correlations at identical angles! If the measurement devices were part of the equation, you would see that clearly - sometimes the measurement would yield a different answer than expected. But no, we get as close to 100% matching as is experimentally feasible. So there can't be some hidden variables residing in one detector - and influencing the result - unless the same hidden variables are present in the other. Let's face it, your objection does not fit with experiment fact.

 

[martinbn]

Amazingly, all psi-epistemic interpretations deny the applicability of PBR. Go figure.

Ditto, all psi-epistemic interpretations deny the applicability of PBR. Of course, there are many others that think they are generally disproven. But being a gentleman, and considering we are talking about interpretations, I try to leave the conclusion to each person.

Can you name some that are disproven, at leaseast according to you or the original PBR paper.

 

[PeterDonis]

all psi-epistemic interpretations deny the applicability of PBR.

The interpretations I described are not "psi-epistemic" by the PBR definition. That's why PBR is not applicable to them.

 

[Fra]

Consider this: What device/detector are we talking about? In a typical Bell test, there are 4 detectors and 2 polarizing beam splitters (PBS). So... is it the beam splitter where your objection arises? Because that implies Alice's beam splitter contains hidden variables that influence the outcome as H> or V>. That result has never been observed - just consider what happens when any pure H> beam goes into a PBS.

Has this really been tested, separating the source and detector, by distance that would required FTL transfer?

It comes out one port with nearly perfect consistency/accuracy. So: No relevant hidden variables there. And what about the detectors? The only thing left up to the detector is to click - or not. No chance of a detection by the H> detector causing the V> detector to click, right? Nothing about the measurement apparatus is going to distort any statistical results, and certainly not with the extremely high quality gear today.

In how I interpret this: each beam splitter is tuned to("informed") the give preparation procedure. The interference pattern IMO is caused by the interaction between the preparation and the splitter. This means I think that splitter actually interacts differently with the beam of particles due to the preparation procedure.

One way to falsify this idea would be if the preparation procedure was prepared in one way, and the beam was equilibrated, then the preparation procedure would suddenly change, faster than the time it will take for light to propagate from preparate device to splitter and without breaking the entanglement. Not sure if it has been done. But if it would be done, and it still gives the interference, it would probably make me sleepless for some time.

Note, the decision of Alice or Bob to change the polarizer angle does not change the preparation and is a different experiment, we know this has been done. But a "decision" to change the preparation procedure at the source, without giving the information to propagate to Alice and Bob in time before the detection, would be very interesting.

If anyone knows if this experiment has been done, I would be very thankful.

/Fredrik

 

[DrChinese]

The interpretations I described are not "psi-epistemic" by the PBR definition. That's why PBR is not applicable to them.

PBR On the reality of the quantum state: "One [assumption] is that a system has a “real physical state” – not necessarily completely described by quantum theory, but objective and independent of the observer. ... Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum state is merely a calculational tool for making predictions concerning macroscopic measurement outcomes."

So exactly as you say.

Except that's throwing something of a baby out with the bathwater. Denying there is a state that is "objective and independent of the observer" doesn't sound so reasonable if you are saying there is just an update of knowledge via a "calculational tool". But an out is an out.

 

[martinbn]

PBR On the reality of the quantum state: "One [assumption] is that a system has a “real physical state” – not necessarily completely described by quantum theory, but objective and independent of the observer. ... Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum state is merely a calculational tool for making predictions concerning macroscopic measurement outcomes."

So exactly as you say.

Except that's throwing something of a baby out with the bathwater. Denying there is a state that is "objective and independent of the observer" doesn't sound so reasonable if you are saying there is just an update of knowledge via a "calculational tool". But an out is an out.

So, what are the names of some interpretations that the PBS theorem applies to?

 

[DrChinese]

Has this really been tested, separating the source and detector, by distance that would required FTL transfer?

In how I interpret this: each beam splitter is tuned to("informed") the give preparation procedure. The interference pattern IMO is caused by the interaction between the preparation and the splitter. This means I think that splitter actually interacts differently with the beam of particles due to the preparation procedure.

One way to falsify this idea would be if the preparation procedure was prepared in one way, and the beam was equilibrated, then the preparation procedure would suddenly change, faster than the time it will take for light to propagate from preparate device to splitter and without breaking the entanglement. Not sure if it has been done. But if it would be done, and it still gives the interference, it would probably make me sleepless for some time.

Note, the decision of Alice or Bob to change the polarizer angle does not change the preparation and is a different experiment, we know this has been done. But a "decision" to change the preparation procedure at the source, without giving the information to propagate to Alice and Bob in time before the detection, would be very interesting.

If anyone knows if this experiment has been done, I would be very thankful.

/Fredrik

Not sure what you are asking about, Fredrik. The distance from the Alice's source to Alice's detector cannot be FTL by definition, and ditto for Bob's setup.

What is FTL (I call usually call it "distant" or "remote") and outside of backward light cones is between:

a. Alice's source as compared to Bob's source and Bob's detector.
b. Alice's detector as compared to Bob's source and Bob's detector.

There are a number of experimental realizations of this in a variety of permutations:

These have everything remote:
High-fidelity entanglement swapping with fully independent sources
Experimental delayed-choice entanglement swapping

In this one, the measurement settings are also changed mid-flight:
Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km

 

[PeterDonis]

Denying there is a state that is "objective and independent of the observer" doesn't sound so reasonable if you are saying there is just an update of knowledge via a "calculational tool".

That's not the only kind of interpretation that the PBR theorem doesn't address. Neither of the interpretations I named--the statistical interpretation as described by, for example, Ballentine, and the thermal interpretation published by @A. Neumaier--say that "there is just an update of knowledge". They do talk about "update of knowledge", but that is not the only meaning ascribed to states. The key point is that they do not treat the quantum wave function as an epistemic distribution over underlying ontic states of individual quantum systems.

Note that we had a thread some time ago discussing whether the PBR theorem rules out the Ballentine ensemble interpretation:

https://www.physicsforums.com/threa...ion-inconsistent-with-the-pbr-theorem.998624/

I don't think that thread reached a conclusive answer either way--which just underscores the fact that there are unresolved disagreements in this area, and indeed with regard to QM interpretations in general.

 

[PeterDonis]

Other relevant older threads on the PBR theorem:

https://www.physicsforums.com/threads/is-there-an-additional-assumption-in-the-pbr-theorem.960246/

https://www.physicsforums.com/threads/understanding-pbrs-additional-assumption.961010/

 

[Fra]

Not sure what you are asking about, Fredrik. The distance from the Alice's source to Alice's detector cannot be FTL by definition, and ditto for Bob's setup.

You are right, I did mean what isn't possible but I was too fast.

I was trying to make a quick reply about what could maybe falsify my understanding, but obviously that idea didn't work

/Fredrik

 

[Fra]

Denying there is a state that is "objective and independent of the observer" doesn't sound so reasonable if you are saying there is just an update of knowledge via a "calculational tool".

I see no conflict here.

The conclusion you make seems to make sense if you tink that the "information" is not contextual to the observer, but just a matematical tool that human physicists use, and where the observer is just like an objective bayesian perspective. But it's not the option I think makes most sense anway.

In an interpretation where "information update" is performed by the "observer beeing an agent and part of the universe" and thus constrained by it's physical resources, it clearly is not fundamentally observer independent nor objective.

But is possbility is the there exists an equivalence class of observers and subjective information updates that are consistent. And this symmetry can be either fixed (given from laws of physics in a timeless manner), or "emergent".

/Fredrik

 

[PeterDonis]

that is probably as far as I can go without violating rules

No, you've gone further than that. You have been cautioned before about not having any model to back up your claims. Now you're being cautioned again, and warned and banned from further posting in this thread to boot.