Is action at a distance possible as envisaged by the EPR Paradox.

[DevilsAvocado]

So if we hypothetically detect all photons even those with miserable detection probability we loose any idea about interference pattern.
That's what I call unfair sampling but you can call it whatever way you want.
...
Are we still on the same line here?

I’m afraid we don’t even agree on "what’s a line"... as I said, it’s extremely simple. If we block one of the slits, we will not get the interference pattern, with or without "unfair sampling". This is an undeniable fact that should make sense even to a 10-yearold.

The physical proofs are right in front of you nose, where you step by step can see with your own eyes what happens when the "sampling increases":

https://www.youtube.com/watch?v=
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</object>

 

[zonde]

Most people would say that no photons arrive at detector 2.

What most people will say about this Feynman quote?
"It is to be emphasized that no matter how many amplitudes we draw, add, or multiply, our objective is to calculate a single final amplitude for the event. Mistakes are often made by physics students at first because they do not keep this important point in mind. They work for so long analyzing events involving a single photon that they begin to think that the wavefunction or amplitude is somehow associated with the photon. But these amplitudes are probability amplitudes, that give, when squared, the probability of a complete event. Keeping this principle in mind should help the student avoid being confused by things such as the "collapse of the wavefunction" and similar magic."

Most people will make smart face but will think by themselves: "What the heck he is talking about? Why I should avoid magic? I love magic! It gives colors to world. It makes me feel special after all. If it's not magic I don't want to understand it at all."

Well first of all to solve the problem it should be recognized as a problem. If there is no problem there is nothing to solve.

 

[DevilsAvocado]

Yes, at the fundamental level there are no "forces." The notion of "force" has to do the deviation of a worldline (matter) from geodesy in a background spacetime. In our approach, spacetime and matter are fused into spacetimematter, and the WHOLE thing is co-constructed.

This is interesting. Do you need to "redefine" any existent physical laws to make it all work...?

Quantization of "everything" is probably the best metaphor.
... We start with a quantum physics (local and nonseparable) and obtain classical physics in the statistical limit.

This is very cool. You start with quantized blocks of everything, and then plug it into the "classical player", and out comes wonderful "analog" classical "music"!

If this works, I know one guy http://en.wikipedia.org/wiki/Nick_Bostrom" perfectly – it’s all small "digital" blocks of information!

 

[unusualname]

gee, is this thread never going to end?

The answer is that spacetime is patchwork of manifolds mapping the underlying quantum Hilbert space via a holographic mechanism.

http://arxiv.org/abs/0907.2939

Lubos Motl explains it all here

Admittedly the details of the mechanism which gives rise to these emergent spacetime "patches" hasn't been fully worked out but it's only a matter of time...

So you can all stop arguing now.

 

[DevilsAvocado]

However, this thread is (ok, it sort of was at one time) about answering the question, "Is action at a distance possible as envisaged by EPR?". And here's my not quite definitive answer to that:

If there's no underlying reality, then it's possible.
Experiments suggest that there's an underlying reality.
Therefore, it's not possible.

Or, in the words of Captain Beefheart:

The stars are matter,
We are matter,
But it doesn't matter.

Not that it matter that much , but we could make it simple and say...

If QM is correct, then we are left with these options:

• locality + non-realism
  
  
• non-locality + realism
  
  
• non-locality + non-realism

"When it is obvious that the goals cannot be reached, don't adjust the goals, adjust the action steps." -- Confucius

 

[DevilsAvocado]

gee, is this thread never going to end?

NO! WHY??

( )

 

[DevilsAvocado]

Postoji problem. Mislim da je problem

Nastrovje!

What more is needed, a frying pan inset with "No LHV!" to beat some about the head?

This is probably the most accurate solution this far!

I'm ready to believe this is all going to end with Abbot & Costello asking "Who's on first?"

HAHA! LOL! Let’s try it and see what happens!

https://www.youtube.com/watch?v=
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<param name="allowFullScreen" value="true"></param>
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</object>

 

[RUTA]

This is interesting. Do you need to "redefine" any existent physical laws to make it all work...?

The only change to existing physics would be to understand GR as a separable approximation to spacetimematter.

This is very cool. You start with quantized blocks of everything, and then plug it into the "classical player", and out comes wonderful "analog" classical "music"!

If this works, I know one guy http://en.wikipedia.org/wiki/Nick_Bostrom" perfectly – it’s all small "digital" blocks of information!

I don't know if our idea is in concert with his. Ok, that was bad

 

[DevilsAvocado]

I don't know if our idea is in concert with his. Ok, that was bad

Not bad, not bad at all, if you do not know what you are talking about (= me ), the best you can do is try "Acting" in concert ... but most of the time the damned violin is broken (= terrible noise + bleeding fingers ) ...

 

[charlylebeaugosse]

Incredible!
You have got it!

So if we hypothetically detect all photons even those with miserable detection probability we loose any idea about interference pattern.
That's what I call unfair sampling but you can call it whatever way you want.

Forget about ensemble interpretation. I can explain it to you using orthodox QM in much simpler way.

Just to check that we are on the same line. Consider http://en.wikipedia.org/wiki/Mach-Zehnder_interferometer" .

After we count all the phase shifts inside different mirrors Wikipedia says that: "there is no phase difference in the two beams in detector 1, yielding constructive interference." So detector 1 fires when photon arrives there (constructive interference) but detector 2 does not fire when photon arrives there (destructive interference).
So photons arrive at both detectors but because of interference one detector fires but the other don't.

Are we still on the same line here?

NO: where the interference is destructive, no photon arrives in the sense of detection, the only valuable meaning here. On the other side, the photon can be detected (and will be if the detection is perfect). The problem is that such counting (in more general context) may hide something else than what one wants to illustrate. I propose to modify the MZ to adapted diffusers on both branches. Then the overlap of the 2 sets of classical path has positive measure, as in a two slit experiment and one can use a scree or an array of detectors. Many misinterpretations of experiments with delay (delayed measurement and/or delayed erasure) originate in the failure of defining PRECISELY what one means by interference and by using counters and technique from fourth order interferences in a context where second order is what is the issue, creating misinterpretations that lead to confusion and otherwise respectable people speaking of actions backward in time.

Black magic has invaded physics, and in recent posts I have seen again people imagining that Aspect and other similar experiments establish non-locality.
Again, the hypothesis to have Bell inequalities meaning anything of interest in physics is that one has Realism+Locality. For the experiments to have something to have anything to do with Bell theory, one must assume Realism+Locality+Fair Sampling (say R+L+FS).
Now the incompatibility of the experimentally verified quantum correlation (a twisted form of Malus' law) with the mathematically trivial Bell inequalities "prove" in the sense of physics that (R+L+FS) is false. Hence R+L+FS is false, meaning that one at least of
R, L, and FS is false.

Since QM tries to tell us in many way that realism in the form needed by Bell Theory (or in this discussion in particular) is false (something share starting 19930 by Copenhagen and by Einstein and Shrödinger -for whom both, at least Einstein for sure, realism could only be with new, yet unknown variables that contrary to what Bell used , would not permit to give simultaneous values to mutually incompatibles observables as used so far) there is no reason to consider an hypothesis as black-magical as non-locality, an hypothesis that is furthermore such that is cannot get to be verified and that violates the spirit of special relativity that has cured the well known stupidity of instant action (more violent than action at a distance and something that trouble Newton and many others, but fortunately not enough the appropriate corrections would have been well known and testing General relativity would have been harder).

Otherwise stated, if realism is false (as von Neumann thought he had proven in a weak form, but with a false proof while he had a better proof -the one he liked- who appeared much later in Wigner's paper on Bell'inequality, but physicists do not need proof and should not as physics is not the realm of proofs (which is ,ath including logic), and the truth or not of von Neumann's argument was not to trouble people like Bohr, Dirac, Einstein, etc... and even Shrödinger who did read von Neumann's book, as did Dirac I presume (? someone knows for sure: reference please)), there is no place for non-locality by Occam's razor, at least.

Another thread, recently launched by DrC to my request as I do not know how to do and he is well known in these columns, treats the issue of whether Bell's Theorem can be establish without locality. I have posted some pre/re-prints that I have there. But I am saddened to see so many physicists trapped in the maze of misinformation reading them to believe that QM is non local and the nature as well. Bell has really succeeded in mixing people up[ here. He did support both realism and non-locality. While for Wigner, Bel''s theorem is the best proof known till his time that HVs do NOT exist (and again, without HV, or whatever form of microscopic realism, why on Earth would one invoke something as baroque as non-locality? There is enough difficulty in the laws of nature to not have to invoke crazy hypotheses to give the sauce a better taste. I like my food extra hot, and find physics even hotter even without assuming that the setting of an instrument changes the output of another instrument at the other end (so to speak) of the Universe. The real physics of that is already difficult enough to understand.

 

[charlylebeaugosse]

Most people would say that no photons arrive at detector 2.

You are right: I could have dispensed of a long post. Hope that it has interest t some anyhow.

 

[ThomasT]

If there's no underlying reality, then it's possible.
Experiments suggest that there's an underlying reality.
Therefore, it's not possible.

... we could make it simple and say...

If QM is correct, then we are left with these options:

* locality + non-realism

* non-locality + realism

* non-locality + non-realism

How is this simpler? You present three alternatives. I presented only two, and offered a logical conclusion. How to decide among them? Note, we'll stipulate that qm is correct.

Note also that the OP isn't asking whether certain formulations are viable. He's asking whether EPR-type action at a distance is possible (which entails that the observation of something or other is, instantaneously, dependent on the observation of something else, which might be a million light years away).

Bell proved that a certain type of LHV formulation of individual results is compatible with the statistical predictions of qm. Subsequent experiments have verified that Bell-type LHV formulations agree with individual results.
So, Bell showed, and experiments have verified, that individual experimental results are due to properties of underlying disturbances, incident on filters and detectors, that exist prior to and independent of filtration and detection.

On the other hand, Bell also showed, and experiments have verified, that the same Bell LHV formulations which are compatible with individual results are incompatible with joint results.

So, we're faced with what might be called Bell's Paradox: individual results are produced by an observer-independent underlying reality, but joint results (vis the same representation) show that an underlying reality cannot exist.

So, what's the bottom line, the best conclusion regarding what Bell tests (or any quantum experiments for that matter) show? Well, for my money, I think that they show the undeniable existence of an underlying reality. And, of course, if there's an underlying reality, then it exists (necessarily, by definition) whether we happen to be probing it or not, ie., it exists independent of observation -- in which case EPR-type action at a distance is ruled out, ie., impossible.

Of course, there are number of other sorts of nonlocalities. But they're not properly the subject of this thread.

 

[RUTA]

If there's no underlying reality, then it's possible.
Experiments suggest that there's an underlying reality.
Therefore, it's not possible.

This is not a deductively valid argument. You (tacitly) assume if and only if in premise one. For example:

P1. If you're shot in the head, you die.
P2. You weren't shot in the head.
C. You're not dead.

But, you could've been stabbed, poisoned, run over by a truck, etc., and be dead even if you weren't shot in the head, so the conclusion is invalid.

Bell proved that a certain type of LHV formulation of individual results is compatible with the statistical predictions of qm. Subsequent experiments have verified that Bell-type LHV formulations agree with individual results.
So, Bell showed, and experiments have verified, that individual experimental results are due to properties of underlying disturbances, incident on filters and detectors, that exist prior to and independent of filtration and detection.

If experiments indicated the existence of "disturbance-causing entities," I doubt Bohr, Ulfbeck, Mottelson, and Zeilinger would have claimed otherwise. Certainly, our interpretation would not have been accepted as a possibility by the foundations community if this was held to be true.

 

[DevilsAvocado]

This is not a deductively valid argument. You (tacitly) assume if and only if in premise one. For example:

P1. If you're shot in the head, you die.
P2. You weren't shot in the head.
C. You're not dead.

But, you could've been stabbed, poisoned, run over by a truck, etc., and be dead even if you weren't shot in the head, so the conclusion is invalid.

I think ThomasT has mixed up Counterfactual Definiteness (CFD) with http://en.wikipedia.org/wiki/Counterfactual_conditional" ...

The difference between indicative and counterfactual conditionals can be illustrated with a pair of examples:

1. If Oswald did not shoot Kennedy, then someone else did.
2. If Oswald had not shot Kennedy, then someone else would have.

The first sentence is an indicative conditional that is intuitively true. The second is a counterfactual conditional that is not necessarily true.

Maybe we do need that https://www.physicsforums.com/showpost.php?p=2845966&postcount=1395" ...?

 

[charlylebeaugosse]

How is this simpler? You present three alternatives. I presented only two, and offered a logical conclusion. How to decide among them? Note, we'll stipulate that qm is correct.

Note also that the OP isn't asking whether certain formulations are viable. He's asking whether EPR-type action at a distance is possible (which entails that the observation of something or other is, instantaneously, dependent on the observation of something else, which might be a million light years away).

Bell proved that a certain type of LHV formulation of individual results is compatible with the statistical predictions of qm. Subsequent experiments have verified that Bell-type LHV formulations agree with individual results.
So, Bell showed, and experiments have verified, that individual experimental results are due to properties of underlying disturbances, incident on filters and detectors, that exist prior to and independent of filtration and detection.

On the other hand, Bell also showed, and experiments have verified, that the same Bell LHV formulations which are compatible with individual results are incompatible with joint results.

So, we're faced with what might be called Bell's Paradox: individual results are produced by an observer-independent underlying reality, but joint results (vis the same representation) show that an underlying reality cannot exist.

So, what's the bottom line, the best conclusion regarding what Bell tests (or any quantum experiments for that matter) show? Well, for my money, I think that they show the undeniable existence of an underlying reality. And, of course, if there's an underlying reality, then it exists (necessarily, by definition) whether we happen to be probing it or not, ie., it exists independent of observation -- in which case EPR-type action at a distance is ruled out, ie., impossible.

Of course, there are number of other sorts of nonlocalities. But they're not properly the subject of this thread.

What are the references of the results of Bell that are quoted: this does not resemble what I know. If this has to do with Bell1964(Physics) , then please explain the relation between this work of Bell and the proposed interpretation.
Thanks,
CleBG

 

[DevilsAvocado]

How is this simpler? You present three alternatives. I presented only two, and offered a logical conclusion. How to decide among them? Note, we'll stipulate that qm is correct.

I don’t know how many times we have to mangle this back and forth before the message goes thru. If we have two mutually dependent variables and we don’t know which is true or false, the only possible options are these:

• true/false
• false/true
• false/false
• true/true

Now, Bell's Theorem has proven that if QM is correct we can’t have locality=true/realism=true, i.e. Local Realism (LR) or Local Hidden Variables (LHV), therefore we are left with these three options:

• locality=true/realism=false
  
  
• locality=false/realism=true
  
  
• locality=false/realism=false

Note also that the OP isn't asking whether certain formulations are viable. He's asking whether EPR-type action at a distance is possible (which entails that the observation of something or other is, instantaneously, dependent on the observation of something else, which might be a million light years away).

I can’t see how the three remaining options don’t make this absolutely clear to OP...??

Bell proved that a certain type of LHV formulation of individual results is compatible with the statistical predictions of qm.

This is mumbo-jumbo and dead wrong. This is what Bell's Theorem says:

No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics.​

So, Bell showed, and experiments have verified, that individual experimental results are due to properties of underlying disturbances, incident on filters and detectors, that exist prior to and independent of filtration and detection.

Sophisticated mumbo-jumbo and dead wrong.

On the other hand, Bell also showed, and experiments have verified, that the same Bell LHV formulations which are compatible with individual results are incompatible with joint results.

Well, this is the whole point, isn’t it?? How on Earth can you say anything about locality by running your nose into ONE polarizer? I thought you took a break to study this thoroughly...??

So, we're faced with what might be called Bell's Paradox: individual results are produced by an observer-independent underlying reality, but joint results (vis the same representation) show that an underlying reality cannot exist.

There is nothing called "Bell's Paradox". If you mean http://en.wikipedia.org/wiki/Bell%27s_spaceship_paradox" it’s not about EPR or entanglement, it’s about the physical reality of length contraction.

Bell's Theorem do not say anything definite about "an underlying reality", it just says that Local Realism (or Local Hidden Variables) is not compatible with current understanding of QM. You could have Non-Local Hidden Variables (NLHV) for example, and that would be compatible with QM.

So, what's the bottom line, the best conclusion regarding what Bell tests (or any quantum experiments for that matter) show? Well, for my money, I think that they show the undeniable existence of an underlying reality. And, of course, if there's an underlying reality, then it exists (necessarily, by definition) whether we happen to be probing it or not, ie., it exists independent of observation -- in which case EPR-type action at a distance is ruled out, ie., impossible.

Dead wrong again, If QM is correct you can’t have Locality + Realism, it’s incompatible with QM.

I think we all can agree that RUTA is the only working scientist in this thread, and as a member of the scientific community, and as PhD Professor of Physics, I think we can trust in that what he has to say:

When I first entered the foundations community (1994), there were still a few conference presentations arguing that the statistical and/or experimental analyses of EPR-Bell experiments were flawed. Such talks have gone the way of the dinosaurs. Virtually everyone agrees that the EPR-Bell experiments and QM are legit, so we need a significant change in our worldview.

That the information is available AFTER the fact doesn't bear on a possible CAUSE for the correlations. The point is that the detector setting at site A is NOT available to site B BEFORE the detection event occurs at site B. If this information is available prior to detection, the correlations in the outcomes can be orchestrated to violate Bell's inequality. No one disputes this fact -- you have to keep the outcome at each site dependent ONLY upon information AT THAT SITE to have the conundrum about their correlations.

Thus, there are generally two ways to account for EPR-Bell correlations. 1) The detection events are separable and you have superluminal exchange of information. 2) The detection events are not separable, e.g., the spin of the entangled electrons is not a property of each electron. The first property is often called "locality" and the second property "realism."

Violations of Bell inequalities imply nonlocality and/or nonseparability.

So, nonseparability alone would do the trick, thereby saving locality (no FTL causal connections).

Science has not proven nonlocality. I'm a physicist who believes the Bell experiments are legit, but these experiments don't prove nonlocality; they prove nonlocality and/or nonseparability. So, it's possible that we have nonseparability and locality.

And everything that RUTA says lead unquestionably to these three (3) options, again:

• locality=true/realism=false
  
  
• locality=false/realism=true
  
  
• locality=false/realism=false

For those who do not understand this, I recommend https://www.physicsforums.com/showpost.php?p=2846608&postcount=1407".

 

[RUTA]

I think we all can agree that RUTA is the only working scientist in this thread, and as a member of the scientific community, and as PhD Professor of Physics, I think we can trust in that what he has to say

Well, my research resides in the foundations of physics and I try to convey here what I've learned from interacting with that community. However, I'm not a leader in this field by any means, so if any of my statements conflict with those of Zeilinger, Price, Vaidman, Hardy, etc., you know who to believe

 

[unusualname]

don't forget

locality=true/realism=true

and we also have superdeterminism (ie the correlations are predetermined)

Though that is too depressing to contemplate.

Once we resolve the true nature of reality, I feel these debates will seem very naive, especially if we're living in some kind of holographic construction of spacetime, with the hilbert space of QM mapping onto our perceived 3D reality in an incredibly devious manner...

 

[DevilsAvocado]

Well, my research resides in the foundations of physics and I try to convey here what I've learned from interacting with that community. However, I'm not a leader in this field by any means, so if any of my statements conflict with those of Zeilinger, Price, Vaidman, Hardy, etc., you know who to believe

It’s great to have you around RUTA. It doesn’t matter that you’re not the leader in this field – you are the "warranty" in this thread for one of the central points in PF Global Guidelines:

Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound.

Thanks!

 

[DevilsAvocado]

don't forget

locality=true/realism=true

and we also have superdeterminism (ie the correlations are predetermined)

Though that is too depressing to contemplate.

Yes, you are right. And it’s not only the correlations that are predetermined – everything is predetermined, including this conversation.

If I "decide" to type this: %&”¤%&”(=)(“()=!=?
And then "change" my mind to type this: oiwuiowurioweuwerp

You could ask – what the heck is the "predetermined meaning" of this? And I can’t find a good answer... other than it’s completely crazy, and I can’t see how science could survive this doom...

And why are we discussing something that’s already predetermined??

Also MWI will give us locality=true/realism=true, but I don’t know how to "weigh" unproven interpretations and "wild" hypothesis... maybe RUTA can tell...

Once we resolve the true nature of reality, I feel these debates will seem very naive,

Of course you are absolutely right. It will seem exactly as naive as when Newton made a strong reservation to his own law of gravity and the notion of "action at a distance".

That’s why these "personal feelings" on what is "right & wrong" almost makes me laugh. What do nature care about us and our "personal feelings" on how "things" should work?? It’s just silly.

especially if we're living in some kind of holographic construction of spacetime, with the hilbert space of QM mapping onto our perceived 3D reality in an incredibly devious manner...

Does it really have to be "incredibly devious"? Couldn’t it also be "incredibly obvious" as well? If you bake spacetime into 2D, Alice & Bob would be positioned along a straight line. If the "QM world" is 1D, then Alice & Bob would be in the same place (looking at the line from the "edge"), right?

Just some "personal thoughts"...

 

[unusualname]

Does it really have to be "incredibly devious"? Couldn’t it also be "incredibly obvious" as well? If you bake spacetime into 2D, Alice & Bob would be positioned along a straight line. If the "QM world" is 1D, then Alice & Bob would be in the same place (looking at the line from the "edge"), right?

Just some "personal thoughts"...

I sometimes wish it does turn out to be as nice and simple as that, but you've got to believe that the obvious models have been dismissed for good reasons (rather like all the simple "proofs" of fermat's last theorem never worked)

Unfortunately it's looking like it will be a bit more involved, eg:
Holography and non-locality in a closed vacuum-dominated universe

It's frustrating to live in a time with so much still unknown.

 

[nismaratwork]

I sometimes wish it does turn out to be as nice and simple as that, but you've got to believe that the obvious models have been dismissed for good reasons (rather like all the simple "proofs" of fermat's last theorem never worked)

Unfortunately it's looking like it will be a bit more involved, eg:
Holography and non-locality in a closed vacuum-dominated universe

It's frustrating to live in a time with so much still unknown.

I'm a big fan of the Holographic Principle; it resolves so many of those unknowns, but one thing... isn't it better to be deviled by questions than have every answer? I love the fodder for curiosity, and since omniscience isn't an option, I'll take a period of record progress and learning.

 

[RUTA]

It's frustrating to live in a time with so much still unknown.

“In the past, fundamental new discoveries have led to changes – including theoretical, technological, and conceptual changes – that could not even be imagined when the discoveries were first made. The discovery that we live in a universe that, deep down, allows for Bell-like influences strikes me as just such a fundamental, important new discovery. … If I am right about this, then we are living in a period that is in many ways like that of the early 1600s. At that time, new discoveries, such as those involving Galileo and the telescope, eventually led to an entirely new way of thinking about the sort of universe we live in. Today, at the very least, the discovery of Bell-like influences forces us to give up the Newtonian view that the universe is entirely a mechanistic universe. And I suspect this is only the tip of the iceberg, and that this discovery, like those in the 1600s, will lead to a quite different view of the sort of universe in which we live.” Worldviews: An Introduction to the History and Philosophy of Science, Richard DeWitt, Blackwell Publishing, 2004, p 304.

I think it's an exciting time to be a physicist!

 

[ThomasT]

I can’t see how the three remaining options don’t make this absolutely clear to OP...??

The OP is asking about what's possible in reality, not what sorts of theories are possible. Your three options are about models, not reality. They don't address the OP's question.

In order to answer the OP's question we just need to answer one question: do (any) quantum experimental phenomena indicate the existence of an underlying reality? Do, say, optical Bell tests indicate that the detectors are detecting disturbances transmitted by the filters, and that the filters are analyzing disturbances emitted by the emitters and which propagate from emitter to filter? I think they do.

Does anybody know the qualitative nature of these disturbances? Not afaik. Does it make any sense to say that they don't exist? I don't think so -- and if the emitters are producing disturbances which propagate to the filters to be transmitted or not to the detectors, then the answer to the OP's question has to be NO.

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

There is nothing called "Bell's Paradox".

Bell's Paradox is that individual results, vis Bell, are compatible with the idea of an underlying reality, but entangled results, vis Bell, seem not to be. Afaik, I coined this usage, so don't bother looking it up.

Bell's Theorem does not say anything definite about "an underlying reality" ...

I agree. It's really irrelevant wrt the OP's question.

 

[charlylebeaugosse]

don't forget

locality=true/realism=true

and we also have superdeterminism (ie the correlations are predetermined)

Though that is too depressing to contemplate.

Once we resolve the true nature of reality, I feel these debates will seem very naive, especially if we're living in some kind of holographic construction of spacetime, with the hilbert space of QM mapping onto our perceived 3D reality in an incredibly devious manner...

Wrong: realism (+locality) is enough (and compatibility with the stats of QM): no need of determinism as in Bell 1964. To my knowledge (and apparently to Leggett's and Bernhardt as well, among others) this was first observed by Stapp who introduced an hypothesis called contrafactual definiteness, then a weaker form of realism was used by Leggett who proved it weaker than Stapp's hypothesis and by Tresser who present that as the weakest form of realism needed a Bell type theorem: value of observables are pre-existent to measurement if measurement could be made and some observable is measured. There is also something that Leggett calls microscopic realism, so three concepts at least can be used, none of which require predetermination other than what is required by realism anyway.

 

[RUTA]

The OP is asking about what's possible in reality, not what sorts of theories are possible. Your three options are about models, not reality. They don't address the OP's question.

In order to answer the OP's question we just need to answer one question: do (any) quantum experimental phenomena indicate the existence of an underlying reality? Do, say, optical Bell tests indicate that the detectors are detecting disturbances transmitted by the filters, and that the filters are analyzing disturbances emitted by the emitters and which propagate from emitter to filter? I think they do.

Does anybody know the qualitative nature of these disturbances? Not afaik. Does it make any sense to say that they don't exist? I don't think so -- and if the emitters are producing disturbances which propagate to the filters to be transmitted or not to the detectors, then the answer to the OP's question has to be NO.

The original post was simply, "Is action at a distance possible as envisaged by the EPR Paradox?" The short answer is "yes." Nonetheless, PF has generated 89 web pages of responses so far

 

[JesseM]

In order to answer the OP's question we just need to answer one question: do (any) quantum experimental phenomena indicate the existence of an underlying reality? Do, say, optical Bell tests indicate that the detectors are detecting disturbances transmitted by the filters, and that the filters are analyzing disturbances emitted by the emitters and which propagate from emitter to filter? I think they do.

Does anybody know the qualitative nature of these disturbances? Not afaik. Does it make any sense to say that they don't exist? I don't think so -- and if the emitters are producing disturbances which propagate to the filters to be transmitted or not to the detectors, then the answer to the OP's question has to be NO.

Bell's theorem logically deals with all possible "disturbances" that match the assumptions of local realism. If you assume that A) the "disturbances" are in local variables that travel along with the particle (or wave, or whatever it is that travels from source to detector), and B) these local variables are only causally influenced by events in their past light cones (so the value of variables associated with particle/wave A after passing through a filter can be influenced by properties of that filter, but not by the orientation of another filter whose orientation was chosen at a space-like separation from event of A passing through its own filter), and C) the result at one detector only depends on local variables associated with the particle/wave at the moment it reaches the detector along with local variables associated with the detector itself, then any theory involving a "disturbance" matching these conditions would satisfy Bell inequalities. The theoretical proof of this doesn't depend on the specific details of what the local variables are or how they are "disturbed", it holds for any theory which is "local realist" in the sense above.

 

[unusualname]

New Scientist have a feature article on QM this week:

Is quantum theory weird enough for the real world?

Lubos Motl has posted a slightly hysterical commentary (he mostly hates NS since it promotes climate change arguments so passionately), check out the comments section for some epr/bell related links.

A couple of journal papers linked to in the NS article are available on arXiv:

A limit on nonlocality in any world in which communication complexity is not trivial
All reversible dynamics in maximally non-local theories are trivial

 

[ThomasT]

You (tacitly) assume if and only if in premise one.

Yes, I should have stated it something like this:
EPR-type action at a distance is possible iff there's no deep reality.
Experiments suggest the existence of a deep reality, ie., that this is the most reasonable assumption.
Therefore, EPR-type action at a distance is, most reasonably, not possible.

Of course, the existence or nonexistence of a deep reality can't be proven. It can only be inferred (or not, as one might choose) from instrumental behavior.

We can ask: are the various possible answers to the OP's question equally tenable? I don't think they are. The assumption of the existence of a deep reality seems to me to be an essential part of fundamental physics.

If experiments indicated the existence of "disturbance-causing entities," I doubt Bohr, Ulfbeck, Mottelson, and Zeilinger would have claimed otherwise.

We can assume that emitters don't emit anything, filters don't filter anything, and detectors don't detect anything -- ie., that there's no deep reality that's ultimately affecting and determining instrumental results. In which case, EPR-type action at a distance would be necessary, and the answer to the OP's question would be yes.

Certainly, our interpretation would not have been accepted as a possibility by the foundations community if this was held to be true.

Are you saying that the acceptance of your interpretation by the foundations communitiy is based on a generally held assumption that instrumental behavior is not determined by the existence and behavior of a reality deeper than the instrumental level?

The original post was simply, "Is action at a distance possible as envisaged by the EPR Paradox?" The short answer is "yes."

The short answer is also "no", depending on what's inferred/assumed. Of course, the most sensible answer is "we don't know", which we might express as a "definite maybe" regarding the possible answers to the OP's question.

Nonetheless, PF has generated 89 web pages of responses so far .

Yes, isn't it awesome that there are so many interesting (more or less) considerations associated with the OP's question?

 

[ThomasT]

In order to answer the OP's question we just need to answer one question: do (any) quantum experimental phenomena indicate the existence of an underlying reality? Do, say, optical Bell tests indicate that the detectors are detecting disturbances transmitted by the filters, and that the filters are analyzing disturbances emitted by the emitters and which propagate from emitter to filter? I think they do.

Does anybody know the qualitative nature of these disturbances? Not afaik. Does it make any sense to say that they don't exist? I don't think so -- and if the emitters are producing disturbances which propagate to the filters to be transmitted or not to the detectors, then the answer to the OP's question has to be NO.

Bell's theorem logically deals with all possible "disturbances" that match the assumptions of local realism. If you assume that A) the "disturbances" are in local variables that travel along with the particle (or wave, or whatever it is that travels from source to detector), and B) these local variables are only causally influenced by events in their past light cones (so the value of variables associated with particle/wave A after passing through a filter can be influenced by properties of that filter, but not by the orientation of another filter whose orientation was chosen at a space-like separation from event of A passing through its own filter), and C) the result at one detector only depends on local variables associated with the particle/wave at the moment it reaches the detector along with local variables associated with the detector itself, then any theory involving a "disturbance" matching these conditions would satisfy Bell inequalities. The theoretical proof of this doesn't depend on the specific details of what the local variables are or how they are "disturbed", it holds for any theory which is "local realist" in the sense above.

What does this have to do with my statements that you seem to be replying to, or the OP's question?

 

[JesseM]

What does this have to do with my statements that you seem to be replying to, or the OP's question?

I would think my point was pretty obvious. Bell's theorem proves that any "realist" picture of what is going on--which presumably includes your rather concrete-sounding notion of the results being dependent on some sort of physical "disturbances"--cannot be a local one. You seemed to be saying that since we don't know the exact details of the supposed "disturbances" we can't give an affirmative answer to the OP:

Does anybody know the qualitative nature of these disturbances? Not afaik. Does it make any sense to say that they don't exist? I don't think so -- and if the emitters are producing disturbances which propagate to the filters to be transmitted or not to the detectors, then the answer to the OP's question has to be NO.

But the point is, Bell's reasoning doesn't require us to know anything specific about the "qualitative nature" of what's going on with the local hidden variables (including how they might be disturbed upon passing through a filter), it shows that all local realist theories are incompatible with QM's predictions. So, if the "disturbances" are meant to be disturbances in local realistic variables, then hell yes it "makes sense to say that they don't exist", that's exactly what Bell's theorem proves!

 

[zonde]

NO: where the interference is destructive, no photon arrives in the sense of detection, the only valuable meaning here.

The problem here is that QM does not say this.
Only thing that QM says is that no photons are detected. You have to associate detection with photon in order to say that no photons arrived at detector. But that step brings you out of orthodox QM domain.

Btw, what do you mean by realism and violation of realism? Do you mean that measurements are contextual or something else?

 

[zonde]

I would think my point was pretty obvious. Bell's theorem proves that any "realist" picture of what is going on--which presumably includes your rather concrete-sounding notion of the results being dependent on some sort of physical "disturbances"--cannot be a local one. You seemed to be saying that since we don't know the exact details of the supposed "disturbances" we can't give an affirmative answer to the OP:

But the point is, Bell's reasoning doesn't require us to know anything specific about the "qualitative nature" of what's going on with the local hidden variables (including how they might be disturbed upon passing through a filter), it shows that all local realist theories are incompatible with QM's predictions. So, if the "disturbances" are meant to be disturbances in local realistic variables, then hell yes it "makes sense to say that they don't exist", that's exactly what Bell's theorem proves!

Bell's theorem proves that any "realist" picture of what is going on cannot be a local one under hypothetical experimental conditions described in his theory.
But because this hypothetical experimental conditions are too far from reality you have to establish some correspondence between this theory and feasible real experiments. That is done by CHSH inequalities. But in order to apply CHSH inequalities to real experiments you need fair sampling assumption and before this fair sampling assumption is experimentally investigated the link between Bell's theorem and physical reality is broken and Bell's theorem has quite limited bearing on possible interpretations of physical reality.

One thing that it proves (with the help of CHSH inequalities and experiments) is that non-contextual LHVs are ruled out. But that can be inferred from HUP anyways. It's just more obvious with help of Bell.

 

[DevilsAvocado]

I sometimes wish it does turn out to be as nice and simple as that, but you've got to believe that the obvious models have been dismissed for good reasons (rather like all the simple "proofs" of fermat's last theorem never worked)

Yes, you are probably right – if it were simple, it would already been solved.

But let’s at least hope it’s fairly logical and "beautiful" when completed, like when Kepler’s Mysterium Cosmographicum was explained (almost) by Newton's genius law:

F = G \frac{m_1 m_2}{r^2},\

 

[DevilsAvocado]

“In the past, fundamental new discoveries have led to changes – including theoretical, technological, and conceptual changes – that could not even be imagined when the discoveries were first made. The discovery that we live in a universe that, deep down, allows for Bell-like influences strikes me as just such a fundamental, important new discovery. … If I am right about this, then we are living in a period that is in many ways like that of the early 1600s. At that time, new discoveries, such as those involving Galileo and the telescope, eventually led to an entirely new way of thinking about the sort of universe we live in. ...”

YES! This is exactly what I believe too!

I think it's an exciting time to be a physicist!

(Even as layman I) AGREE! The Future's So Bright, I Gotta Wear Shades!

[PLAIN]http://30.media.tumblr.com/tumblr_kz11bcLl0r1qza4ndo1_400.jpg

 

[DevilsAvocado]

The OP is asking about what's possible in reality, not what sorts of theories are possible. Your three options are about models, not reality. They don't address the OP's question.

They don’t...??

"Is action at a distance possible as envisaged by the EPR Paradox."​

YES, action at a distance is possible as predicted by the EPR Paradox, because these are the 3 options:

• locality=true/realism=false
  
  
• locality=false/realism=true
  
  
• locality=false/realism=false

(locality=false --> action at a distance)

I could be wrong, but I thought that OP wanted us to describe the state of current professional mainstream science – not personal guessing...

 

[DevilsAvocado]

The original post was simply, "Is action at a distance possible as envisaged by the EPR Paradox?" The short answer is "yes." Nonetheless, PF has generated 89 web pages of responses so far

YES!

 

[DevilsAvocado]

New Scientist have a feature article on QM this week:

Is quantum theory weird enough for the real world?

Great article!

http://www.newscientist.com/article...ird-enough-for-the-real-world.html?full=true"

...
"Quantum mechanics is, in our range of experience, a correct theory. It is sort of fine and we don't know what is better." But there are niggles that make him and others itch for something new. One is the great unfinished business of unifying quantum theory with general relativity, Einstein's resolutely classical theory of gravity. "Quantum mechanics and general relativity don't like each other," says Plenio.
...
So how do we set about finding what makes quantum theory tick? Most of the recent work has homed in on one central yet unexplained feature of quantum physics- the degree of "correlation" between the states of unconnected bodies that the theory does, or does not,
...
In 1964, John Bell of the CERN particle physics laboratory near Geneva, Switzerland, described the degree of correlation that classical theories allow. Bell's result relied on two concepts: realism and locality.
...
Realism amounts to saying that the properties of an object exist prior to, and independent of, measurement. In the classical world, that second sock in my drawer is red regardless of whether or not I "measure" its state by looking at it. Locality is the assumption that these properties are independent of any remote influence.

Great description of Bell's Inequality! And in the light of this – If we look back on the hundred of posts billschnieder produced on the theme that it’s impossible to formulate a Bell Inequality – YOU GOT TO LAUGH!

Lubos Motl has posted a slightly hysterical commentary (he mostly hates NS since it promotes climate change arguments so passionately), check out the comments section for some epr/bell related links.

Hehe, "slightly" is very diplomatic... Luboš Motl seems to have several problems with the climate, girls, strange Slavic names, name of magazines... As far as I know the Czech Republic is Slavic, and Luboš Motl can be strange to some...

I wish an extremely intelligent girl, with an extremely strange name, from Bulgaria, come along and give us the new paradigm in physics – that would make both Luboš Motl & Lawrence Summers drop their jaws and fall off their chairs!

 

[DevilsAvocado]

... Of course, the most sensible answer is "we don't know", ...

Great TT! I’m with you all the way on this! :!)

 

[charlylebeaugosse]

The original post was simply, "Is action at a distance possible as envisaged by the EPR Paradox?" The short answer is "yes." Nonetheless, PF has generated 89 web pages of responses so far

The answer is in fact NO. No one as acted in any way on an event spatially remote. There is no good reasons to believe that what Einstein called spooky action is possible, and ALL conclusions to the contrary are based on erroneous reading of Bell, Aspect, etc... or misquotes by these people themselves. Many time people have recalled that QM is non-local and only realist interpreters need non-locality, a phenomenon with no measurable effect that cannot be interpreted more simply otherwise.

 

[charlylebeaugosse]

YES!

Give ONE example where influence on a spatially remote object can be proven without invoking realism of micro-physics, please, and then you can honestly say yes. I can unfortunately give countless examples of mis-quotation, wrong attributions, circular reasoning etc... from all of the tenors of remote action, even typical examples of dishonesty.
I challenge the reciprocity for the people who like Leggett, think that the wrong hypothesis in the realism-locality pair is realism. If realism (at the microscopic level) goes, all "arguments" in favor of remote action fall. Another thread is devoted to Bell theorem without locality assumption, less known of course than the work of Leggett but aiming also at booting realsim out of microphysics.

 

[JesseM]

Bell's theorem proves that any "realist" picture of what is going on cannot be a local one under hypothetical experimental conditions described in his theory.
But because this hypothetical experimental conditions are too far from reality you have to establish some correspondence between this theory and feasible real experiments. That is done by CHSH inequalities. But in order to apply CHSH inequalities to real experiments you need fair sampling assumption and before this fair sampling assumption is experimentally investigated the link between Bell's theorem and physical reality is broken and Bell's theorem has quite limited bearing on possible interpretations of physical reality.

One thing that it proves (with the help of CHSH inequalities and experiments) is that non-contextual LHVs are ruled out. But that can be inferred from HUP anyways. It's just more obvious with help of Bell.

There is a version of the CHSH inequality that incorporates the fact that not all particle pairs are detected, although it requires that at least 82% of particle pairs are detected for the inequality to be violated (67% in the case of the Clauser-Horne test), which is higher than most experiments can do. But in fact a few experiments have closed the "detector efficiency loophole" (the loophole which depends on the idea that the measured particles may not be a 'fair sample' of all particles emitted), see here and here. Neither of these experiments managed to simultaneously close the locality loophole, but I think it would require a very contrived local realist theory to exploit both loopholes at once (i.e. exploit the locality loophole in experiments that closed the detector efficiency loophole, and exploit the detector efficiency loophole in experiments that closed the locality loophole), as I argued here:

In contrast, I think lots of very smart physicists would agree with the intuition that a local realist theory consistent with all past experiments but which predicted no Bell inequality violation in ideal loophole-free experiments would have to be rather "contrived". Perhaps one reason for this is that we know what is required to exploit each loophole individually--exploiting the detector efficiency loophole requires that in some pairs of particles, one of the pair has a hidden variable that makes it impossible to detect (see billschnieder's example in posts #113 and #115 on this thread), whereas exploiting the locality loophole requires that whichever member of the pair is detected first will send out some sort of signal containing information about what detector setting was used, a signal which causes the other particle to change its own hidden variables in just the right way as to give statistics that agree with QM predictions.

Also, there are a number of papers that claim it will be possible to close both loopholes simultaneously in experiments that may be doable in the near future, see here and here.

 

[RUTA]

Yes, I should have stated it something like this:
EPR-type action at a distance is possible iff there's no deep reality.
Experiments suggest the existence of a deep reality, ie., that this is the most reasonable assumption.
Therefore, EPR-type action at a distance is, most reasonably, not possible.

Of course, the existence or nonexistence of a deep reality can't be proven. It can only be inferred (or not, as one might choose) from instrumental behavior.

We can ask: are the various possible answers to the OP's question equally tenable? I don't think they are. The assumption of the existence of a deep reality seems to me to be an essential part of fundamental physics.

I'm probably misunderstanding you, but you can correct me if that's the case. When you say "the existence of a deep reality" I picture "microscopic" or "hidden" entities at work among, and distinct from, the elements of the experimental equipment.

We can assume that emitters don't emit anything, filters don't filter anything, and detectors don't detect anything -- ie., that there's no deep reality that's ultimately affecting and determining instrumental results. In which case, EPR-type action at a distance would be necessary, and the answer to the OP's question would be yes.

In RBW, there are no "microscopic" or "hidden" entities at work among, and distinct from, the elements of the experimental equipment, but there is no action at a distance either. That's because it's not a dynamical ontology, i.e., explanation isn't based on cause and effect, but on a nonseparable "4Dism."

Are you saying that the acceptance of your interpretation by the foundations communitiy is based on a generally held assumption that instrumental behavior is not determined by the existence and behavior of a reality deeper than the instrumental level?

The acceptance is based simply on its logical possibility (as shown by relevant calculations). Do they subscribe to it? No, by and large they hate it

The short answer is also "no", depending on what's inferred/assumed. Of course, the most sensible answer is "we don't know", which we might express as a "definite maybe" regarding the possible answers to the OP's question.

Perhaps we have different interpretations of the OP question. I read it, "Is non-locality possible given EPR phenomena?" Since it is generally agreed that EPR-Bell phenomena imply non-locality and/or nonseparability, the short answer is "yes, non-locality is a possibility."

Yes, isn't it awesome that there are so many interesting (more or less) considerations associated with the OP's question?

I've sure had a lot of fun with this thread!

 

[RUTA]

The answer is in fact NO. No one as acted in any way on an event spatially remote. There is no good reasons to believe that what Einstein called spooky action is possible, and ALL conclusions to the contrary are based on erroneous reading of Bell, Aspect, etc... or misquotes by these people themselves. Many time people have recalled that QM is non-local and only realist interpreters need non-locality, a phenomenon with no measurable effect that cannot be interpreted more simply otherwise.

As far as I know the DeBroglie-Bohm interpretation has not been ruled out by the foundations community. Therefore, non-locality as a possible consequence of EPR-Bell phenomena has not been ruled out by the foundations community. I haven't heard anyone argue for the dismissal of non-locality in general. Is someone championing this view in the foundations community? As someone with a local, nonseparble interpretation of QM, I'd like to read their work.

 

[Lampshade132]

I just read something interesting about entanglement that I have not seen discussed before. What is everyones thoughts on thinking of two entangled objects as single higher dimensional object passing through our 3D universe at two different locations. Much like how a 3D object could appear at separate locations, thus appearing like two objects in a 2D plane.

 

[DevilsAvocado]

I just read something interesting about entanglement that I have not seen discussed before. What is everyones thoughts on thinking of two entangled objects as single higher dimensional object passing through our 3D universe at two different locations. Much like how a 3D object could appear at separate locations, thus appearing like two objects in a 2D plane.

Welcome to PF Lampshade132!

Maybe this link from unusualname can be helpful:

Unfortunately it's looking like it will be a bit more involved, eg:
Holography and non-locality in a closed vacuum-dominated universe

 

[DevilsAvocado]

Give ONE example where influence on a spatially remote object can be proven without invoking realism of micro-physics, please,
...
I challenge the reciprocity for the people who like Leggett, think that the wrong hypothesis in the realism-locality pair is realism. If realism (at the microscopic level) goes, all "arguments" in favor of remote action fall.

I think that we both agree that nothing is proven definitely, right? So to say; "I’m sure of this or that", is no more than personal speculations, right?

And just because "realism goes" does not prove beyond all doubts that locality is true, right?

So, one of these three options must be correct:

• locality=true/realism=false
  
  
• locality=false/realism=true
  
  
• locality=false/realism=false

Right?

Then I don’t think it’s unfair to say: YES - action at a distance is a possibility, until we know better.

(To avoid any "translation errors" – We are not talking about faster than light communication! The outcome of EPR-Bell experiments is always 100% random.)

 

[charlylebeaugosse]

As far as I know the DeBroglie-Bohm interpretation has not been ruled out by the foundations community. Therefore, non-locality as a possible consequence of EPR-Bell phenomena has not been ruled out by the foundations community. I haven't heard anyone argue for the dismissal of non-locality in general. Is someone championing this view in the foundations community? As someone with a local, nonseparble interpretation of QM, I'd like to read their work.

See the comments of of Pauli and Einstein on deB-B theory. Anyway, why spend time on a theory so violently incompatible with Lorentz invariance, beside the attacks of Wolfgang P.
Many false theories are around, such as many version of Kaluza-Klein, Weyl, variations on super-strings: at least with those progress in math have been made. In fact, Wigner would have said (and he did, but in more general form covering all HV theories satisfying the hypothesis of Bell1964) that "Bell's Theorem is the nicest proof that HVs are false". Non-locality is not physics and cannot lead to any observation that is not a consequence of an a-priori stand on pre-existence of observable values to measurement. The fact that there is a club making themselves happy with dBB makes not dBB part of physics. There are such clubs in most disciplines. The problem is that more and more crazy viewpoints of QM (many words, many minds, many schmucks, etc...) are winning more and more support. Science is in danger when the most central piece of the most central discipline is under serious attack and the evil forces of magic and fantasy become the ruling (compare the extent of Bell theory vs elementary particles or thermodynamics on the www: see how many tenors of physics claim that actions can be taken upon the past). It is true that the Copenhagen team opened the doors to the flood by allowing religious stands where perpetual re-examination and progress should be the way to go. The interpretation by Wheeler of delayed measurement was the door open to violation of the time arrow at macroscopic scale. But the errors of the past should not excuse new errors but should rather make us more cautious. What would have happened to math if seeing mistakes in rigor by the old masted would have been an excuse for more lack of rigor instead of devising methods and language to allow modern analysis and its various applications? Math would be dead by now and physics is certainly in grave danger: it may soon come under control of engineering if we accept non-sense such as dBB as something else than anecdotes on what physics could have looked like.

 

[charlylebeaugosse]

I think that we both agree that nothing is proven definitely, right? So to say; "I’m sure of this or that", is no more than personal speculations, right?

And just because "realism goes" does not prove beyond all doubts that locality is true, right?

So, one of these three options must be correct:

• locality=true/realism=false
  
  
• locality=false/realism=true
  
  
• locality=false/realism=false

Right?

Then I don’t think it’s unfair to say: YES - action at a distance is a possibility, until we know better.

(To avoid any "translation errors" – We are not talking about faster than light communication! The outcome of EPR-Bell experiments is always 100% random.)

We have to be extra cautious: in similar circumstance, when a viewpoint is odd cannot be falsified, one gets rid of it by using Occam's razor, AND here we also have the work of Leggett and a (couple of) paper(s) discussed elsewhere on PF about Bell without locality assumption which is not far from proving that realism is the only issue since an hypothesis whose negation yields super-luminal info transmission when restricted to observed quantities replaces locality to get one Bell Theorem.

Saying YES is wrong here: we could say; the YES has not yet been ruled out but standard practice of physics lead to consider that the correct answer is "NO until otherwise proven", of something of that kind.

 

[zonde]

There is a version of the CHSH inequality that incorporates the fact that not all particle pairs are detected, although it requires that at least 82% of particle pairs are detected for the inequality to be violated (67% in the case of the Clauser-Horne test), which is higher than most experiments can do.

You don't have to reach theoretical limit of elimination of fair sampling assumption to investigate it's validity.
That can be done by performing experiments with different detection efficiencies and different coincidence rates that show trends (or no trends if fair sampling is valid) in observed results. Moreover such experiment is quite trivial comparing it to all the different photon entanglement experiments performed nowadays.

But still there are no such experiments so all the talk about extrapolating results of low efficiency Bell photon experiments to high efficiency case is unjustifiable.

In contrast, I think lots of very smart physicists would agree with the intuition that a local realist theory consistent with all past experiments but which predicted no Bell inequality violation in ideal loophole-free experiments would have to be rather "contrived". Perhaps one reason for this is that we know what is required to exploit each loophole individually--exploiting the detector efficiency loophole requires that in some pairs of particles, one of the pair has a hidden variable that makes it impossible to detect (see billschnieder's example in posts #113 and #115 on this thread), whereas exploiting the locality loophole requires that whichever member of the pair is detected first will send out some sort of signal containing information about what detector setting was used, a signal which causes the other particle to change its own hidden variables in just the right way as to give statistics that agree with QM predictions.

You are not proponent of local realism so you viewpoint about what is required to exploit each loophole does not really count, right?

Lets see it in more details.
You say: "exploiting the detector efficiency loophole requires that in some pairs of particles, one of the pair has a hidden variable that makes it impossible to detect"
This model does not lead to unfair sampling if "detection-HV" is attached to particle at source. Fair sampling still applies.

However we can have a different view. First PBS can't measure polarization of particle when we perform measurement (+45/-45 base) that is non-commuting with polarization measurement (H/V base) because in that case two measurements will be commuting.
So we have to have second measurement that performs phase measurement between H and V modes (where PBS only alters phase of photons depending from their polarization). That second measurement device can be detector or alternatively interference filter.
This fits orthodox QM quite well.

You say: "exploiting the locality loophole requires that whichever member of the pair is detected first will send out some sort of signal containing information about what detector setting was used"
This of course is not quite creditable as particles would have to produce other particles to carry information to second member.

However we again can have a different view. First experiments with efficient detection utilize fermions or at least particles that are confined to equipment. So these particles don't share the same context and all correlations between them are classical i.e. they are not entangled at all.
In that case only option left is crosstalk between measurement processes. For example if we look at Rowe's et al experiment we can see that scattered photons are allowed to interfere at detector but it is just assumed that it hasn't any effect on different measurement combinations (again fair sampling assumption). In experiment performed by Matsukevich et al manipulations of ions are done using microwave pulses but microwaves are definitely subject to crosstalk. But here we can test how reasonable is assumption of independence of two measurements by varying distance between two measurement places and observing presence or absence of any trends in results.

So you see that your argument about "contrived" LHV model is very subjective.