What do violations of Bell's inequalities tell us about nature?

[bohm2]

Please vote and if possible state the reasons for holding your belief. As a review here are the two major views with quotes by leading physicists in quantum foundations:

1. Observed violations of Bell's inequalities implies that nature is non-local:

In 1964, Bell proved that any serious version of quantum theory (regardless of whether or not it is based on microscopic realism) must violate locality. He showed that if nature is governed by the predictions of quantum theory, the "locality principle," precluding any sort of instantaneous (or superluminal) action-at-a-distance, is simply wrong, and our world is nonlocal.

What is most relevant to Bell's Theorem is that the non-locality which it makes explicit in Quantum Mechanics is a small indication of pervasive ultramicroscopic nonlocality. If this conjecture is taken seriously, then the baffling tension between Quantum nonlocality and Relativistic locality is a clue to physics in the small.

2. Observed violations of Bell's inequalities implies anti-realism (e.g. quantum measurement results do not pre-exist)

...quantum measurement results do not preexist in any logically determined way before the act of measurement.

...unperformed tests have no outcomes: it is wrong to try to account for the outcomes of all the tests you might have performed but didn’t.

 

[VantagePoint72]

This is a bizarre question. Violations of Bell's inequalities just tell us that at least one of (1) and (2) must be true. It doesn't prefer one or the other, nor does it rule out both of them being true (as is the case in the Copenhagen interpretation). Various people may well have preference for either anti-realism or non-locality but that preference can't possibly come from Bell's theorem alone. It's complete nonsense to say, "Observed violations of Bell's inequalities implies that nature is non-local," or, "Observed violations of Bell's inequalities implies anti-realism." Observed violations of Bell's inequalities imply neither.

Either you're misunderstanding Bell's theorem, or you did an extremely poor job of phrasing your question.

 

[VantagePoint72]

Also, your "other" category seems very confused. Alternative interpretations of QM are not exempt from having to deny either locality or counterfactual definiteness. Many worlds, for instance, does the latter.

 

[bohm2]

Either you're misunderstanding Bell's theorem, or you did an extremely poor job of phrasing your question.

The exact same question was posed to leading experts in quantum foundations in this book here (see chapter 8). I'm interested in how people on this forum would respond. Some of those quotes come from that book chapter:

Elegance and Enigma: The Quantum Interviews
https://www.amazon.com/dp/3642208797/?tag=pfamazon01-20

 

[Maui]

There are different interpretations, but generally violations of Bell's inequalities imply what's already known - that classical mechanics(strict materialism) is just one aspect of reality and so no longer an adequate explanation of observations. As Heisenberg once put it/quoted by Nick Herbert in Quantum Reality/:

"The ontology of materialism rested upon the illusion that the kind of existence, the direct 'actuality' of the world around us, can be extrapolated into the atomic range. This extrapolation, however, is impossible... atoms are not things."

The way to keep the strict materialism intact is by accepting a small conspiracy - superdeterminsim or hidden variables(or to deny interest into the inner workings of reality).

 

[bohm2]

The way to keep the strict materialism intact is by accepting a small conspiracy - superdeterminsim or hidden variables(or to deny interest into the inner workings of reality).

I don't think anybody has ever given a good definition of "materialism". Do you have one? And why do you think that a non-local, "realistic" model would still be considered "materialistic"?

 

[DennisN]

I voted "anti-realism". My reasons/opinions are:

• "Nature is non-local"; I wouldn't accept this without an underlying mechanism which describes it.
  
• "Other: Superdeterminism, backward causation, many worlds, etc"; I can't see how any of these interpretations would be falsifiable, and this makes me doubt their scientific value.

Therefore I lean towards "anti-realism". I am however pretty agnostic, and my views could change depending on future science and experiments. I would have preferred to vote on a fourth "softer" option; (observed violation of Bell's inequality tell us) there are parts of QM we can't yet fully comprehend/explain.

 

[nanosiborg]

Please vote and if possible state the reasons for holding your belief.

I would vote that violations of Bell inequalities tell us nothing about nature if your poll had that as an option.

Bell's theorem proves that there's no function, ρ(λ), for which this correlation coefficient,
C(a,b) = ∫ ρ(λ) A(a,λ) B(b,λ) dλ , matches Malus' Law (cos²θ) .

The results of Bell tests involving photons entangled in polarization support the generalization of results from classical and quantum wave optics involving crossed polarizers in that the QM treatments of optical Bell test setups are evaluated using Malus' Law.

The results of Bell tests don't reveal anything new regarding fundamental empirically based tenets of wave optics. They certainly don't imply that nature is nonlocal ... though it's tempting to assume that nature is nonlocal by virtue of the fact that nonlocal hidden variable models of quantum entanglement are viable. They also don't imply the "other" option, which, as DennisN pointed out, are all untestable assumptions. For me they're just either meaningless (backward causation, many worlds) or superfluous (superdeterminism) as well. As for anti-realism, it isn't clear to me what is meant by "quantum measurement results do not pre-exist". The measurement results in Bell tests are either detection or nondetection within a coincidence interval. Obviously, these results don't "pre-exist". If it's simply meant that realism (ie., hidden variable accounts, or the existence of hidden variables) is ruled out, then we know that that's false. Realism isn't ruled out.

So, what are we left with? Just that there are hidden parameters operating to produce quantum entanglement stats that remain hidden (ie., unknown) -- and from that it still isn't known whether there is some sort of nonlocality in nature or if nature is evolving exclusively according to the principle of local action. But we do know that formulating models of Bell tests in terms of Bell locality is ruled out. Which means that models of quantum entanglement can't take the form that Bell's locality condition requires them to take.

 

[Nugatory]

I wish you had given us a fourth choice: "abstain, until such time as someone can propose an experiment that could distinguish (a) from (b)". That way my abstention could be recorded

 

[bohm2]

I wish you had given us a fourth choice: "abstain, until such time as someone can propose an experiment that could distinguish (a) from (b)". That way my abstention could be recorded

That's option 3: Other

 

[Nugatory]

Either you're misunderstanding Bell's theorem, or you did an extremely poor job of phrasing your question.

I don't think that's a completely fair criticism (and I say this despite having already complained about the lack of an "abstain" option).

Both locality and realism are so natural and so deeply ingrained in our thinking that once we know we can't have both, it's interesting to ask "if you had to give one up, which would it be?"... And I doubt that many people would join Bohr and answer "lose 'em both!", although that answer certainly is not excluded by Bell experiments or anything else we know.

 

[Nugatory]

That's option 3: Other

No, no, no... I will not cast a vote that might be counted with "superdeterminism, backwards causation, many worlds, etc.". I DEMAND a respectable abstention that allows me to shut up and calculate without committing myself to any position

 

[danR]

I vote for 1. I not only see no reason why quantum behaviour cannot be non-local, I could conjecture that some property/variable of the original universe did not expand with 4-space, which we might call quantum-field, and is a property that particles near the original size of the universe share.

 

[bohm2]

I vote for 1. I not only see no reason why quantum behaviour cannot be non-local, I could conjecture that some property/variable of the original universe did not expand with 4-space, which we might call quantum-field, and is a property that particles near the original size of the universe share.

That was my reason also. It just seems that some "remnant" or "property" of the non-spatial-temporal stuff that gave "birth" to the big bang should still be with us.

 

[DrChinese]

No, no, no... I will not cast a vote that might be counted with "superdeterminism, backwards causation, many worlds, etc.". I DEMAND a respectable abstention that allows me to shut up and calculate without committing myself to any position

I love it. Nugatory is not to be denied...

 

[danR]

That was my reason also. It just seems that some "remnant" or "property" of the non-spatial-temporal stuff that gave "birth" to the big bang should still be with us.

I can't share the "seems...should" part, however. I just offer it as a conjecture: untestable, unfalsifiable.

Having said that, I would metaphysically ask why every single property of the primordial dimensionless point should necessarily be bound to a macroscopic, relativistically-governed spatio-temporal address.

Indeed, isn't the extraordinary part about the universe in that any property of it should have expanded at all? Why didn't it just all stay there in one a/non -local 'place' in the first place?

I asked one of my profs once what was the objection to non-locality was (i.e. "what really upsets you guys about it?"), and with me being an arts major he may have geared his answer to my understanding, and I may have misunderstood it, but it was something along the lines that it just made too many connections between distant objects.

In other words, they don't like non-locality because it sucks.

Well, that's just to bad. In our lectures and assignments and exams (this was a different prof, the first was teaching a more classical topic, though his specialty was quantum gravity) we were required to express confusion, puzzlement and great explanatory power in dealing with, say, two emitted photons; the spin of the one measured in Paris, and the spin of the other measured in Japan.

The wording is perpetually prejudiced toward the idea that two different spins, or spin-attributes, are being measured, instead of just one shared property. Perhaps I'm missing some deeper aspect to the issue that makes non-locality a problem nevertheless.

 

[bohm2]

In other words, they don't like non-locality because it sucks.

Einstein felt the same way:

It is further characteristic of these physical objects that they are thought of as arranged in a space-time continuum. An essential aspect of this arrangement of things in physics is that they lay claim, at a certain time, to an existence independent of one another, provided these objects ‘are situated in different parts of space’. Unless one makes this kind of assumption about the independence of the existence (the ‘being-thus’) of objects which are far apart from one another in space—which stems in the first place from everyday thinking— physical thinking in the familiar sense would not be possible. It is also hard to see any way of formulating and testing the laws of physics unless one makes a clear distinction of this kind. This principle has been carried to extremes in the field theory by localizing the elementary objects on which it is based and which exist independently of each other, as well as the elementary laws which have been postulated for it, in the infinitely small (four-dimensional) elements of space.

Others like Gisin question this preference of non-realism to non-locality, however:

It might be interesting to remember that no physicist before the advent of relativity interpreted the instantaneous action at a distance of Newton’s gravity as a sign of non-realism (although Newton’s nonlocality is even more radical than quantum nonlocality, as it
allowed instantaneous signaling).

Is realism compatible with true randomness?
http://arxiv.org/pdf/1012.2536v1.pdf

 

[DennisN]

Perhaps I'm missing some deeper aspect to the issue that makes non-locality a problem nevertheless.

I don't know, but I could quote Isaac Newton;

"It is inconceivable that inanimate brute matter should, without the mediation of something else, which is not material, operate upon, and affect other matter without mutual contact...[] That gravity should be innate, inherent and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of any thing else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers." (source)

which is a sort of caveat to his law of universal gravitation (his law implies that gravitational force is transmitted instantaneously, which we now understand is not correct). This quote is of course about gravitation, not quantum entanglement. But my point is that many people find it hard (incl. me) to accept any kind of action at a distance without any mediator/medium in between and/or without any mechanism which describes it in more detail. And if the action seems to be instantaneous, it's even worse (considering the finite value of the speed of light). That pretty much sums up my own problems with action at a distance .

(I saw bohm2 already had replied to this while I was writing my reply)

 

[Nugatory]

I find myself wondering which of realism and locality is more "natural" to our thinking, more easily accepted at an intuitive level.

I'm inclined to think that it's realism:
- A cat and a bird are outside watching one either right now... I am quite confident that the biochemical computers that guide their behavior are programmed to analyze the situation in purely realistic terms. I doubt that this bias would change if either were to develop greater capacity for abstract thought.
- People are discouragingly willing to accept magical non-local explanations such as astrology. These non-local magical explanations are generally realistic; the astrologers don't question whether the moon and the planets are there when no one is looking.
- Few people are disturbed by the truly egregious non-locality of Newtonian gravitation; and I expect that most laypeople find Schrodinger's cat more disturbing/confusing/"wrong" than gravitational action at a distance.

Interesting though (at least to me) is that the poll results are running the other direction...

 

[danR]

I don't know, but I could quote Isaac Newton;


which is a sort of caveat to his law of universal gravitation (his law implies that gravitational force is transmitted instantaneously, which we now understand is not correct). This quote is of course about gravitation, not quantum entanglement. But my point is that many people find it hard (incl. me) to accept any kind of action at a distance without any mediator/medium in between and/or without any mechanism which describes it in more detail. And if the action seems to be instantaneous, it's even worse (considering the finite value of the speed of light). That pretty much sums up my own problems with action at a distance .

(I saw bohm2 already had replied to this while I was writing my reply)

I don't see how 'action at a distance' applies to entanglement in quantum world, even by analogy, where/(if) there is no 'action' or 'distance'. Of course ultramicroscopic particles are subject to other properties dependent on space and time. They are 4-space dependent, but quantum-wise non-local. Or to put it less prejudicially (since 'non-local' has the connotation of being somehow defective, deviant, odd), quantum-entanglement has only one locale.

Of course, there are spins that are not entangled, but I could speculate further that all spin-baggage, correlated or not, is permanently stuck in some cosmic LaGuardia airport.

 

[Nugatory]

I don't know, but I could quote Isaac Newton;

true enough... but also worth noting that Newton is something of an outlier here. For every person who has shared Newton's (and many other thinkers') discomfort with action at a distance, probably thousands of people have cheerfully accepted and swallowed the notion.

 

[DennisN]

true enough... but also worth noting that Newton is something of an outlier here. For every person who has shared Newton's (and many other thinkers') discomfort with action at a distance, probably thousands of people have cheerfully accepted swallowed the notion.

True. I have once been one of those thousands of people . But I changed.

 

[Maui]

I don't think anybody has ever given a good definition of "materialism". Do you have one? And why do you think that a non-local, "realistic" model would still be considered "materialistic"?

Materialism would be the old mechanistic concept of reality but this is beside the point. The point is not why there could potentially be non-locality but why there is locality. When you answer that question from the point of view of qm(since this is the quantum theory forum!), then we can know why under certain circumstances non-locality could be observed. People seem to forget(even in this forum) that reality is quantum mechanical and not classical. If you treat classical mechanics as fundamental(not emergent) you get action at a distance, nonlocality, tunneling through barriers, many worlds, backward causation, objects spinning in two directions at the same time and other wonderful phenomena. And people go on to extrapolate all the time the reality of tables and chairs to the quantum realm as if they are somehow interchangeable or compatible.

 

[bohm2]

In hindsight, I'm not sure Gisin's argument that Newton's non-locality is more "radical" is accurate. For instance, quantum non-locality would not also have to be FTL (instantaneous) but would also have to be unattenuated and discriminating as Maudlin and others note:

The quantum connection is unattenuated:

Since the gravitational force drops off as the square of the distance it eventually becomes negligible if one is concerned with observable effects...The quantum connection, in contrast, appears to be unaffected by distance. Quantum theory predicts that exactly the same correlations will continue unchanged no matter how far apart the two wings of the experiment are.

The quantum connection is discriminating:

The effects of the sparrow’s fall ripple outward, diminishing as distance increases, jiggling every massive object in its way. Equally massive objects situated the same distance from the sparrow feel identical tugs. Gravitational forces affect similarly situated objects in the same way...The quantum connection, however, is a private arrangement between our two photons. When one is measured its twin is affected, but no other particle in the universe need be...The quantum connection depends on history. Only particles which have interacted with each other in the past seem to retain this power of private communication. No classical force exhibits this kind of exclusivity.

Quantum non-locality & Relativity
https://www.amazon.com/dp/0631232214/?tag=pfamazon01-20

The point is not why there could potentially be non-locality but why there is locality.

That's a good point.

 

[danR]

Quote by Maui
"The point is not why there could potentially be non-locality but why there is locality."
​

That's a good point. --bohm2

Locality is simply entailed by the original expansion of 4-space, the condensation of matter, and the fractionation of the forces. There's no reason to require that every attribute of the original entity was dragged along with the emergence of locality.

PS: I've now mangled the quotes thoroughly, but hope y'all can sort it out.

 

[rubi]

The "Shut up and calculate" choice is definitely missing. Unless there are some observable differences between different interpretations of QM or unless they make calculations easier, it's a waste of time to think about it. I also don't want to be counted to option #3.

However, if i had to choose between non-locality and anti-realism, i would choose anti-realism, because i don't really see why realism is so desirable apart from the fact that otherwise, one has to give up his beliefs and prejudices about nature that originate from the naive assumption that we can extrapolate the laws of the macroscopic world to the microscopic world as well.

On the other hand i'd rather not give up locality, because that would mean that some events in the andromeda galaxy or even outside the observable universe could in principle influence events on earth, unless you impose some strong limitations on the non-locality in your theory (and if you do so, then you'd have to justify them somehow). That would make physics entirely pointless, because it would mean that our equations would have to depend on parameters that can't be measured here on earth. So even if the world were non-local, it's reasonable to assume that it's not, in order to even be able to write down equations that are of any use.

 

[danR]

On the other hand i'd rather not give up locality, because that would mean that some events in the andromeda galaxy or even outside the observable universe could in principle influence events on earth, unless you impose some strong limitations on the non-locality in your theory (and if you do so, then you'd have to justify them somehow).

Limitations are precisely what are involved. Spin correlation of co-generated photons, for example. Since quantum entanglement is not a mediator of any of the forces, I would want to know what the influence would be.

If Bob measures ↓ here and Alice measures ↑ at the Andromeda galaxy, they are only measuring a single down-up attribute shared (somewhere in nowhere-ville) by two co-generated particles.

 

[DrChinese]

... by two co-generated particles.

Of course that is not a requirement for entanglement, that they are co-generated. They don't even need to interact by conventional means - or even have interacted at all if entanglement swapping is considered.

 

[nanosiborg]

In hindsight, I'm not sure Gisin's argument that Newton's non-locality is more "radical" is accurate. For instance, quantum non-locality would not also have to be FTL (instantaneous) but would also have to be unattenuated and discriminating as Maudlin and others note:
The quantum connection is unattenuated:

Quantum theory predicts that exactly the same correlations will continue unchanged no matter how far apart the two wings of the experiment are.

That QM predicts (and experiment confirms) that quantum entanglement is unaffected by distance is based on the classical conservation laws and empirically based optics principles (eg., Malus' Law). The quantum entanglement correlations (and the idea that distance isn't a factor) aren't unexpected or 'weird' given what's been ported from classical physics and wave optics to the quantum theory.

The quantum connection is discriminating:

...The quantum connection ... is a private arrangement between our two photons. When one is measured its twin is affected, but no other particle in the universe need be...

This is essentially correct, except for the bolded part (and also that the 'private arrangement' need not be between just two particles). In a typical optical Bell test involving paired photons, measurement at one end need not be affecting the photon at the other end in order to produce the observed correlations. There just needs to have been a relationship produced between the motional properties of paired photons. The production of such an entanglement doesn't require that the photons have interacted or that they have a common source.

It's true that ...

The quantum connection depends on history.

... but it's not true, as DrChinese has pointed out, that ...

Only particles which have interacted with each other in the past seem to retain this power of private communication.

The motional properties of entangled particles need only to have undergone some sort of similar modification which produces a measurable relationship between their resulting motions.

In light of the contributions of the classical conservation laws and classical wave optics to the QM treatment of polarization entangled photons, it's maybe a bit misleading to say that ...

No classical force exhibits this kind of exclusivity.

The difference between the sorts of relationships that can be produced in classical preparations and those that can be produced in quantum preparations is one of degree. But the principle is essentially the same. A common origin, interaction, or imparting a common or related motional property to spatially separated particles produces statistical dependence and predictable correlations ... with the underlying fine tuning of quantum entanglement correlations remaining something of a mystery.

Regarding the question of why there is locality, this is similar to the question of why disturbances in media expand more or less omnidirectionally (depending on the properties of the medium in which the disturbance is produced), in that they both might well be unanswerable questions. That is, they both might be irreducibly fundamental properties of physical reality, and as such would form part of the axiomatic structure of a comprehensive theory. Which is sort of the place that the principle of local action, along with causal determinism, has in contemporary physical science. These are (at least tacitly held) assumptions that are required for physical science to have any unambiguously communicable meaning.

The metaphysical speculations about nonlocality, etc. remain just that. If violations of Bell inequalities actually informed regarding nature, well, that would be great. Unfortunately, they don't.
But that doesn't make Bell's theorem 'short-sighted', as another current thread asked. Bell's analysis provides a very clear answer to the question he was asking. Namely, are QM-compatible LHV models of quantum entanglement possible? The answer, mathematically proven, is no, they aren't. If you take Bell's formulation to be generalizable, and I do, then QM-compatible LHV models of quantum entanglement are definitively ruled out. Beyond that, violations of Bell inequalities tell us nothing about nature. If that doesn't do it for you, then you might be talking round and round about this stuff, and getting nowhere, for a really long time.

 

[stevendaryl]

That QM predicts (and experiment confirms) that quantum entanglement is unaffected by distance is based on the classical conservation laws and empirically based optics principles (eg., Malus' Law).

Here's a wild idea that's probably nonsensical, but I wonder if anyone has investigated it: Kaluza-Klein theory introduced the trick of having extra spatial dimensions that are unobservable because they are wrapped into tiny little circles. I'm wondering if there is some topology that can be constructed using extra dimensions, so that, essentially, every point in space is the same, very short, distance from every other point, if one travels in the hidden dimensions. For illustration, imagine a flat sheet of paper, crumpled into a ball and compressed to a tiny volume. Travel within the plane of the paper is unaffected by the crumpling, but the crumpling allows a "short-cut" between any two points, by traveling perpendicular to the plane of the paper.

So I'm wondering if there is a way to understand the "instantaneous" quantum interactions of Bohm theory as interactions that only seem instantaneous because they only travel a short distance.

 

[stevendaryl]

I don't see how 'action at a distance' applies to entanglement in quantum world, even by analogy, where/(if) there is no 'action' or 'distance'.

Well, following the Bohm interpretation of quantum mechanics, the weird statistics is explained through action at a distance via an instantaneous "quantum potential" term in the equations of motion.

 

[nanosiborg]

Here's a wild idea that's probably nonsensical, but I wonder if anyone has investigated it: Kaluza-Klein theory introduced the trick of having extra spatial dimensions that are unobservable because they are wrapped into tiny little circles. I'm wondering if there is some topology that can be constructed using extra dimensions, so that, essentially, every point in space is the same, very short, distance from every other point, if one travels in the hidden dimensions. For illustration, imagine a flat sheet of paper, crumpled into a ball and compressed to a tiny volume. Travel within the plane of the paper is unaffected by the crumpling, but the crumpling allows a "short-cut" between any two points, by traveling perpendicular to the plane of the paper.

Interesting stevendaryl, but I think that whatever you're getting at is way over my head.

So I'm wondering if there is a way to understand the "instantaneous" quantum interactions of Bohm theory as interactions that only seem instantaneous because they only travel a short distance.

In line with danR's statement, I don't think that instantaneous action at a distance is understandable. There's no mechanics, no propagation, no time for any sort of physical interaction. I view it as basically a collection of terms that function as a placeholder for our ignorance and refer to something that happens in the mathematics of a theory.

But it sounds like you might be able to fashion some sort of novel mathematical contrivance or other. Not that that would provide any understanding either, but then mathematical contrivances (and placeholders) don't have to. They just need to help facilitate the calculation of accurate quantitative predictions.

 

[nanosiborg]

Well, following the Bohm interpretation of quantum mechanics, the weird statistics is explained through action at a distance via an instantaneous "quantum potential" term in the equations of motion.

But the statistics aren't weird. They're understandable through the QM incorporation and application of classical laws.

 

[stevendaryl]

But the statistics aren't weird. They're understandable through the QM incorporation and application of classical laws.

They seem pretty weird to me. When you are measuring, for instance, the projection of the spin of an electron on the z-axis, for example, I think it's understandable that the result may be nondeterministic. The measurement process may interact with the electron in an uncontrollable way, and so a deterministic prediction might not be possible. But if that electron is part of an electron-positron twin pair, then it's weird to me that you can tell with absolute certainty that if you measure spin-up in the z-direction, then whoever checks the spin of the positron will find spin-down in the z-direction.

That's the weirdness of quantum randomness--not the randomness by itself, but the combination of randomness with a kind of certainty of the distant correlations.

 

[nanosiborg]

They seem pretty weird to me. When you are measuring, for instance, the projection of the spin of an electron on the z-axis, for example, I think it's understandable that the result may be nondeterministic. The measurement process may interact with the electron in an uncontrollable way, and so a deterministic prediction might not be possible. But if that electron is part of an electron-positron twin pair, then it's weird to me that you can tell with absolute certainty that if you measure spin-up in the z-direction, then whoever checks the spin of the positron will find spin-down in the z-direction.

That's the weirdness of quantum randomness--not the randomness by itself, but the combination of randomness with a kind of certainty of the distant correlations.

So, what can be inferred from the predictability of distant correlations? Can it be said, for example, that there has been an invariant relationship between entangled particles created through the entangling process, ie., through common source, interaction, common motion imparted to particles that don't have a common source and have never interacted, etc.? If so, does this seem weird? It doesn't to me, and the fact that the totality of results of optical Bell tests are in line with the conservation laws and optics principles further supports that view.

 

[stevendaryl]

So, what can be inferred from the predictability of distant correlations? Can it be said, for example, that there has been an invariant relationship between entangled particles created through the entangling process, ie., through common source, interaction, common motion imparted to particles that don't have a common source and have never interacted, etc.? If so, does this seem weird?

Yes.

It doesn't to me, and the fact that the totality of results of optical Bell tests are in line with the conservation laws and optics principles further supports that view.

My general feeling is that if you don't find quantum mechanics weird, you haven't thought about it enough. Conservation laws don't by themselves explain the correlations.

Think about the following situation: You prepare an electron with spin-up along some axis \vec{S}. Then later you measure its spin along a different axis \vec{A}. Then the result will be non-deterministic: with a certain probability, the electron will be found afterwards to have spin-up in the \vec{A} direction, and with a certain probability, it will be spin-down. In either case, the angular momentum of the electron was changed by the measurement: its final angular momentum is not the same as its initial angular momentum. That isn't a violation of conservation of angular momentum, because you can attribute the change to the interaction between the detector and particle. The angular momentum of the particle changes, and the angular momentum of the detector changes in a complementary way, so that the total angular momentum is unchanged by the detection process. But note that there is a small amount of angular momentum, \delta \vec{L} transferred from the electron to the detector.

Now, if that electron happened to have come from an EPR twin-pair experiment, then each of the two detectors can be expected to receive a tiny amount of angular momentum from whichever particle is detected. But in the case of perfectly aligned detectors, we know that the \delta \vec{L_1} received by one detector must exactly correlate with the \delta \vec{L_2} received by the other detector, so that the resulting spins of the twin particles are perfectly anti-correlated.

So the perfect anti-correlation is not simply a matter of conservation of angular momentum. Angular momentum would be conserved whether or not the twin particles are found to be anti-correlated--it's just that different amounts of angular momentum would be transferred to the detectors. The perfect anti-correlation of twin pairs is a matter of cooperation between nondeterministic processes involving distant macroscopic objects (the detectors).

 

[bohm2]

If you take Bell's formulation to be generalizable, and I do, then QM-compatible LHV models of quantum entanglement are definitively ruled out. Beyond that, violations of Bell inequalities tell us nothing about nature.

That's where the disagreement is with those who contend that Bell's formulation does not make those further assumptions, like hidden-variables, realism, etc. As one example of such authors making those arguments consider Norsen:

One can divide reasons for disagreement (with Bell’s own interpretation of the significance of his theorem) into two classes. First, there are those who assert that the derivation of a Bell Inequality relies not just on the premise of locality, but on some additional premises as well. The usual suspects here include Realism, Hidden Variables, Determinism, and Counter-Factual-Definiteness. (Note that the items on this list are highly overlapping, and often commentators use them interchangeably.) The idea is then that, since it is only the conjunction of locality with some other premise which is in conflict with experiment, and since locality is so strongly motivated by SR, we should reject the other premise. Hence the widespread reports that Bell’s theorem finally refutes the hidden variables program, the principle of determinism, the philosophical notion of realism, etc.

Norsen also discusses why Bell felt that his theorem does tell us something about nature:

Since all the crucial aspects of Bell’s formulation of locality are thus meaningful only relative to some candidate theory, it is perhaps puzzling how Bell thought we could say anything about the locally causal character of Nature. Wouldn’t the locality condition only allow us
to assess the local character of candidate theories? How then did Bell think we could end up saying something interesting about Nature?...That is precisely the beauty of Bell’s theorem, which shows that no theory respecting the locality condition (no matter what other properties it may or may not have – e.g., hidden variables or only the non-hidden sort, deterministic or stochastic, particles or fields or both or neither, etc.) can agree with the empirically-verified QM predictions for certain types of experiment. That is (and leaving aside the various experimental loopholes), no locally causal theory in Bell’s sense can agree with experiment, can be empirically viable, can be true. Which means the true theory (whatever it might be) necessarily violates Bell’s locality condition. Nature is not locally causal.

Local Causality and Completeness: Bell vs. Jarrett
http://arxiv.org/pdf/0808.2178v1.pdf

With respect to a discussion of Bell's concept of local causality see this paper with this interesting quote:

That is, the idea that SR is compatible with non-local causal influences (but only prohibits non-local signaling) seems afflicted by the same problem (reviewed in Section III) that necessarily afflicts theories whose formulations involve words like “observable”, “microscopic”, “environment”, etc. In particular, the notion of “signaling” seems somehow too superficial, too anthropocentric, to adequately capture the causal structure of Figure 1.

J.S. Bell’s Concept of Local Causality
http://arxiv.org/pdf/0707.0401.pdf

 

[morrobay]

That's where the disagreement is with those who contend that Bell's formulation does not make those further assumptions, like hidden-variables, realism, etc. As one example of such authors making those arguments consider Norsen:

Norsen also discusses why Bell felt that his theorem does tell us something about nature:

Local Causality and Completeness: Bell vs. Jarrett
http://arxiv.org/pdf/0808.2178v1.pdf

With respect to a discussion of Bell's concept of local causality see this paper with this interesting quote:

J.S. Bell’s Concept of Local Causality
http://arxiv.org/pdf/0707.0401.pdf

Pages 9 &10 of the Bell vs Jarrett paper are about the completeness of λ .
And from both these papers it seems that Bell presupposes that completeness holds.
While at the same time Bell limits and qualifies completeness of λ to properties of
candidate theories. So this is a conflict on completeness. And I cannot agree that because
no local casual theory agrees with experiment that nature is nonlocal, conclusion.
Rather it is that the description of λ the hidden variable that is not complete .
And when it is the violations of the inequalities can be understood.
And I voted to reject realism, in its limited definition

 

[ttn]

Hi folks. I voted for "non-locality". And so, incidentally, did Bell -- though, being dead, he is unable to vote in this particular poll. But here are his words (from the classic paper "Bertlmann's socks and the nature of reality"):

"Let us summarize once again the logic that leads to the impasse. The EPRB correlations are such that the result of the experiment on one side immediately foretells that on the other, whenever the analyzers happen to be parallel. If we do not accept the intervention on one side as a causal influence on the other, we seem obliged to admit that the results on both sides are determined in advance anyway, independently of the intervention on the other side, by signals from the source and by the local magnet setting. But this has implications for non-parallel settings which conflict with those of quantum mechanics. So we cannot dismiss intervention on one side as a causal influence on the other."

For the convenience of the people who are confused here (i.e., the people who voted that we should conclude, from Bell's theorem, that "realism" is wrong) I have bolded the relevant part of the argument above. Note that it is just the EPR argument. The point is that "realism" just means the existence of variables which determine, in advance, what the result on each side will be. What Bell points out here -- and what EPR already pointed out long ago -- is that such variables are (i.e., "realism" is) the *only* way to account *locally* for the perfect correlations that are observed "whenever the analyzers happen to be parallel". So the idea that we can still account for the QM predictions with a model that respects locality but denies "realism" is simply wrong. It will not, does not, and can not work.

Still don't agree? Still think that one can have a local explanation of even this small subset of the quantum predictions -- namely, the perfect correlations that are observed "whenever the analyzers happen to be parallel"? Let's see the model. (Note: the model should also respect the "free choice" aka "no conspiracies" assumption, if it is to be taken seriously.)

This is a serious challenge. Anybody who voted for (b) in the poll evidently thinks (or at least is unwittingly committed to thinking) that these perfect correlations can be explained by a local, non-realist model. Let's see it.

 

[nanosiborg]

@ bohm2, re your post #38

I agree with Norsen, and Bell, that it's Bell's locality condition that causes Bell's LHV formulation to be incompatible with QM and experiments, and that realism (hidden variable models) is not ruled out. Bell locality is necessarily realistic, but a realistic model need not be Bell local. We know from deBB that realism isn't ruled out. Which leaves only locality.

I disagree with Norsen, and Bell, that violations of Bell's inequalities tells us anything about nature. I think that the incompatibility with QM and experiment is determined by some feature of Bell's locality condition other than the assumption of locality.

 

[nanosiborg]

So, what can be inferred from the predictability of distant correlations? Can it be said, for example, that there has been an invariant relationship between entangled particles created through the entangling process, ie., through common source, interaction, common motion imparted to particles that don't have a common source and have never interacted, etc.? If so, does this seem weird?

Yes.

Do you find it weird that particles which have interacted or have a common source are measurably related? Or is it weird that the quantum correlations can only be approximated by classical preparations (and only approximately described by classical LHV models)? I suppose it's the latter. But is the creation of invariant relationships between and among particles, by the means described, beyond any sort of classical comprehension (ie., weird), or is it, as I suggested in an earlier post, just a matter of degree?

My general feeling is that if you don't find quantum mechanics weird, you haven't thought about it enough.

Some of the interpretations of QM are weird, but I don't think of standard QM as weird. Is it possible that those who find QM weird haven't thought about it enough?

On the other hand, some quantum phenomena (the physical, instrumental stuff, not the theory) do seem weird, but I wouldn't include entanglement correlations in there.

Conservation laws don't by themselves explain the correlations.

I agree, and I didn't say they do. But the conservation laws plus the applicable optics laws plus the repeatability of the preparations and the correlations don't seem so weird. The correlations are quite unsurprising when all those things are taken into consideration.

[... snip nice discussion ...]

So the perfect anti-correlation is not simply a matter of conservation of angular momentum. Angular momentum would be conserved whether or not the twin particles are found to be anti-correlated--it's just that different amounts of angular momentum would be transferred to the detectors.

OK.

The perfect anti-correlation of twin pairs is a matter of cooperation between nondeterministic processes involving distant macroscopic objects (the detectors).

As you said in your discussion, it's the individual results that are nondeterministic (ie., random). Because the correlations are predictable (and the unknown underlying processes therefore apparently repeatable) we can retain the assumption that the processes are deterministic.

So, I would change your last sentence to read: the perfect anti-correlation of paired (entangled) particles is a matter of a repeatable relationship between, and deterministic evolution of, certain motional properties of the entangled particles subsequent to their creation via a common source, their interaction, or their being altered by identical stimulii. Which doesn't seem weird to me.

 

[ttn]

Bell locality is necessarily realistic, but a realistic model need not be Bell local.

I don't think that's right. Here's a model that non-realistic but perfectly Bell local: each particle has no definite, pre-existing, pre-scripted value for how the measurements will come out. Think of each particle as carrying a coin, which, upon encountering an SG device, it flips -- heads it goes "up", tails it goes "down". That is certainly not "realistic" (in the sense that people are using that term here) since there is no fact of the matter, prior to the measurement, about how a given particle will respond to the measurement; the outcome is "created on the fly", so to speak. And it's also perfectly local in the sense that what particle 1 ends up doing is in no way influenced by anything going on near particle 2, or vice versa. Of course, the model doesn't make the QM/empirical predictions. But it's non-realist and local. And hence a counter-example to any claim that being Bell local requires/implies being "realist".

We know from deBB that realism isn't ruled out.

I think you must be using "realism" in a different way than most other people. deBB is a hidden variable theory, to be sure, but it is *not* a hidden variable theory about spin! That is, there is no fact of the matter, in deBB, about how a given particle will respond to a measurement of some component of its spin. This is sometimes described by saying that, for deBB, spin is a "contextual" property. It would be more accurate, though, to say that, in deBB, the particles simply do not have any such property as spin.

I disagree with Norsen, and Bell, that violations of Bell's inequalities tells us anything about nature. I think that the incompatibility with QM and experiment is determined by some feature of Bell's locality condition other than the assumption of locality.

I would be very interested to hear precisely what you have in mind. Have you carefully studied Bell's paper "la nouvelle cuisine" (where he is most explicit about how "locality" is formulated)? If you think the very formulation of "locality" smuggles in some other requirement, I want to know exactly what and how.

 

[stevendaryl]

Do you find it weird that particles which have interacted or have a common source are measurably related?

As I thought I said, but maybe I just thought it it's certainly not weird that particles with a common history could share state information. For example, two people could agree on some random number, and then separate to large distances. Then there would be a nonlocal correlation due to shared state information from a common past.

It's weird that distant particles would be connected in any way other than shared state information.

But is the creation of invariant relationships between and among particles, by the means described, beyond any sort of classical comprehension (ie., weird), or is it, as I suggested in an earlier post, just a matter of degree?

Yes, I think it's weird.

On the other hand, some quantum phenomena (the physical, instrumental stuff, not the theory) do seem weird, but I wouldn't include entanglement correlations in there.

I don't think you can separate entanglement from measurement. Or rather, entanglement is only weird to the extent that it implies nonlocal correlations between distant macroscopic measurements.

As you said in your discussion, it's the individual results that are nondeterministic (ie., random). Because the correlations are predictable (and the unknown underlying processes therefore apparently repeatable) we can retain the assumption that the processes are deterministic.

So, I would change your last sentence to read: the perfect anti-correlation of paired (entangled) particles is a matter of a repeatable relationship between, and deterministic evolution of, certain motional properties of the entangled particles subsequent to their creation via a common source, their interaction, or their being altered by identical stimulii. Which doesn't seem weird to me.

Are you saying anything different from: It's not weird, because it's predicted by quantum mechanics? Whether something is weird or not is a matter of taste, I suppose.

 

[nanosiborg]

Bell locality is necessarily realistic, but a realistic model need not be Bell local.

I don't think that's right. Here's a model that non-realistic but perfectly Bell local: each particle has no definite, pre-existing, pre-scripted value for how the measurements will come out. Think of each particle as carrying a coin, which, upon encountering an SG device, it flips -- heads it goes "up", tails it goes "down". That is certainly not "realistic" (in the sense that people are using that term here) since there is no fact of the matter, prior to the measurement, about how a given particle will respond to the measurement; the outcome is "created on the fly", so to speak. And it's also perfectly local in the sense that what particle 1 ends up doing is in no way influenced by anything going on near particle 2, or vice versa. Of course, the model doesn't make the QM/empirical predictions. But it's non-realist and local. And hence a counter-example to any claim that being Bell local requires/implies being "realist".

I've been using 'hidden variable' to refer to any denotation (in a Bell test model) which refers to an underlying parameter which contributes to the determination of individual results. It doesn't have to include a pre-existing, pre-scripted value for how any specific measurement will come out. It's just included in the model to refer to any underlying parameter which contributes to the determination of individual results.

My understanding of Bell locality is that the denotation of Bell locality in a Bell test model requires some such hidden variable, whether the definition of that hidden variable includes a denotation about precisely how the hidden variable affects individual detection or not.

In other words, I would consider your example to be realistic in the same sense that Bell's λ is realistic, and therefore not a counter-example to my statement.

I think you must be using "realism" in a different way than most other people. deBB is a hidden variable theory, to be sure, but it is *not* a hidden variable theory about spin! That is, there is no fact of the matter, in deBB, about how a given particle will respond to a measurement of some component of its spin. This is sometimes described by saying that, for deBB, spin is a "contextual" property. It would be more accurate, though, to say that, in deBB, the particles simply do not have any such property as spin.

As per my above, the particles don't have to have any property in particular. They're underlying entities (that presumably have some property or properties) that are denoted in the deBB model. As such, and as you note, deBB is a hidden variable theory, and thus, in my lexicon, a realistic theory. But, due to the nonmechanical (ie., nonlocal vis the quantum potential) aspects of the theory it's also not a Bell local theory. I think of standard QM as a nonrealistic theory that is also not a Bell local theory, although not nonlocal in exactly the same sense that deBB is deemed nonlocal.

I would be very interested to hear precisely what you have in mind. Have you carefully studied Bell's paper "la nouvelle cuisine" (where he is most explicit about how "locality" is formulated)?

I haven't studied "la nouvelle cuisine". I have read a few of Norsen's papers, including the one where he discusses Jarrett's parsing of Bell's locality condition. I'm inclined toward Jarrett's interpretation that Bell locality encodes the assumptions of statistical independence (that paired outcomes are statistically independent of each other) as well as the independence defined by the principle of local action (that the result at A is not dependent on the setting at b, and the result at B is not dependent on the setting at a).

Since Bell tests are prepared to produce outcome dependence, and since this does not necessarily inform regarding locality or nonlocality in nature, and since this might be the effective cause of the incompatibility between Bell LHVs and QM, and between Bell LHVs and experimental results, then violations of Bell inequalities don't inform regarding locality/nonlocality in nature.

There is another aspect to the form that Bell locality imposes on LHV models of quantum entanglement to consider. Any Bell LHV model of quantum entanglement must necessarily denote coincidental detection as a function of the product of the independent functions for individual detection at A and B. So the relevant underlying parameter determining coincidental detection is the same underlying parameter determining individual detection. I think the underlying parameter determining coincidental detection can be viewed as an invariant (per any specific run in any specific Bell test preparation) relationship between the motional properties of the entangled particles, and therefore a nonvariable underlying parameter. I'm not sure how to think about this. Is it significant? If so, how do we get from a randomly varying underlying parameter to a nonvarying underlying parameter?

 

[nanosiborg]

As I thought I said, but maybe I just thought it it's certainly not weird that particles with a common history could share state information. For example, two people could agree on some random number, and then separate to large distances. Then there would be a nonlocal correlation due to shared state information from a common past.

It's weird that distant particles would be connected in any way other than shared state information.

I agree. That (eg., nonlocally connected) would be weird. But I hope I've made it clear that I don't think the particles are connected in any way other than statistically through shared information imparted through local channels (common source, interaction, common 'zapping', etc.).

But is the creation of invariant relationships between and among particles, by the means described, beyond any sort of classical comprehension (ie., weird), or is it, as I suggested in an earlier post, just a matter of degree?

Yes, I think it's weird.

Ok, so I take it that you find the invariance of the relationship between entangled particles in any particular run of any particular Bell test to be weird. But why should that be weird?

Consider, for example, the polarization entangled photons created via atomic cascades. Entangled photons are assumed to be emitted from the same atom (albeit a different atom for each entangled pair). Is it surprising (weird) that their spins and therefore their polarizations would be related in a predictable way via the application of the law of conservation of angular momentum? Is it surprising that each entangled pair would be related in the same way? After all, the emission process is presumably the same for each pair, and the selection process is the same for each pair.

I don't think you can separate entanglement from measurement. Or rather, entanglement is only weird to the extent that it implies nonlocal correlations between distant macroscopic measurements.

Ok, I agree with this, and since I don't think the correlations imply nonlocal connections between distant macroscopic measurements (because I think they can be understood in terms of related properties produced via local channels, and because the correlations are in line with empirically based optics laws involving the analysis of polarizations via crossed polarizers), then I don't view the correlations as being weird.

Are you saying anything different from: It's not weird, because it's predicted by quantum mechanics?

I think so. I'm saying that we can understand why QM predicts what it does in the case of Bell tests by referring to the applicable (eg., conservation and optics) classical laws which are preserved in the QM treatment.

Whether something is weird or not is a matter of taste, I suppose.

I would say that it's a matter of interpretation, and that interpretation isn't solely a matter of taste.

 

[ttn]

I've been using 'hidden variable' to refer to any denotation (in a Bell test model) which refers to an underlying parameter which contributes to the determination of individual results. It doesn't have to include a pre-existing, pre-scripted value for how any specific measurement will come out. It's just included in the model to refer to any underlying parameter which contributes to the determination of individual results.

Yes, OK. So then the point is just that "hidden variable theories" (like, e.g., deBB) need not be "realist theories".

My understanding of Bell locality is that the denotation of Bell locality in a Bell test model requires some such hidden variable, whether the definition of that hidden variable includes a denotation about precisely how the hidden variable affects individual detection or not.

It's not correct that Bell's formulation of locality (i.e., "Bell locality") assumes the existence of hidden variables. Maybe we're still not quite on the same page about what "hidden variables" means, because we're not on the same page about what "underlying" means in your formulation above. Usually the phrase "hidden variable" is used to mean some *extra* thing, beyond just the standard wave function of ordinary quantum theory, that is in the mix. So then, e.g., deBB is a hidden variable theory because it uses not only the wave function, but also the added "definite particle positions", to account for the results. In any case, though, the point is that "Bell locality" does not presuppose "realism" and it also does not presuppose "hidden variables". You can meaningfully ask whether ordinary QM (not a hidden variable theory!) respects or violates "Bell locality". (It violates it.)

In other words, I would consider your example to be realistic in the same sense that Bell's λ is realistic, and therefore not a counter-example to my statement.

OK, but then you're using the word "realistic" in a different way than (I think) most other people here do. I think most people use that word to mean that there are definite values pre-encoded in the particles somehow, such that there are meaningful answers to questions like: "What would the outcome had been if, instead of measuring along x, I had measured along y?"

As per my above, the particles don't have to have any property in particular. They're underlying entities (that presumably have some property or properties) that are denoted in the deBB model.

I certainly agree that it makes sense to call deBB "realist" by some meanings of the word "realist". But it is important to understand that the theory is *not* "realist" in the narrow sense I explained above. Stepping back, that's what I wanted to point out here. The word "realism" is a slippery bugger. Different people use it to mean all kinds of different things, such that miscommunication and misunderstanding tends to be rampant.

I think of standard QM as a nonrealistic theory that is also not a Bell local theory, although not nonlocal in exactly the same sense that deBB is deemed nonlocal.

Me too, though I'm not sure what the two "senses" of nonlocality here might be. They both violate "Bell locality". What other well-defined sense does anybody have in mind?

I haven't studied "la nouvelle cuisine". I have read a few of Norsen's papers, including the one where he discusses Jarrett's parsing of Bell's locality condition. I'm inclined toward Jarrett's interpretation that Bell locality encodes the assumptions of statistical independence (that paired outcomes are statistically independent of each other) as well as the independence defined by the principle of local action (that the result at A is not dependent on the setting at b, and the result at B is not dependent on the setting at a).

I'm this "norsen" guy, by the way. So, you know what I think of Jarrett already.

Since Bell tests are prepared to produce outcome dependence, and since this does not necessarily inform regarding locality or nonlocality in nature, and since this might be the effective cause of the incompatibility between Bell LHVs and QM, and between Bell LHVs and experimental results, then violations of Bell inequalities don't inform regarding locality/nonlocality in nature.

I can't follow this. Are you just repeating Jarrett's idea that "Bell locality" is actually the conjunction of two things, only one of which really deserves to be called "locality"? So then, from the mere fact that "Bell locality" is violated, we can't necessarily infer the (genuine) "locality" is violated? If that's it, you know I disagree, but if the "Bell vs. Jarrett" paper didn't convince you, nothing I can say here will either. =)

 

[ttn]

Dear Travis, I'd be happy to submit a (say) 3-page PDF to support my rejection of nonlocality.

Would it directly answer the "challenge" I posted above (to explain the perfect correlations locally but without "realism")? If so, I don't see why you shouldn't be permitted to post it here. That's perfectly relevant to this thread.

 

[Nugatory]

I've been using 'hidden variable' to refer to any denotation (in a Bell test model) which refers to an underlying parameter which contributes to the determination of individual results. It doesn't have to include a pre-existing, pre-scripted value for how any specific measurement will come out. It's just included in the model to refer to any underlying parameter which contributes to the determination of individual results.

My understanding of Bell locality is that the denotation of Bell locality in a Bell test model requires some such hidden variable, whether the definition of that hidden variable includes a denotation about precisely how the hidden variable affects individual detection or not.

In other words, I would consider your example to be realistic in the same sense that Bell's λ is realistic, and therefore not a counter-example to my statement.

If the heads/tails value of Norsen's coin is considered realistic before we've flipped it, I'm not sure what you'd consider not to be realistic. Could I ask for an example?

That's a trick question, of course. If you do come up with such an example I'll use it instead of Norsen's coin in his example to produce a local but not realistic model. If you can't, then I'll argue that something is wrong with your definition of realism because it includes everything.

 

[nanosiborg]

Yes, OK. So then the point is just that "hidden variable theories" (like, e.g., deBB) need not be "realist theories".

I'm using hidden variable theory and realistic theory interchangeably. So, any hidden variable theory is a realistic theory. Any theory which does not incorporate hidden variables is a nonrealistic theory.

It's not correct that Bell's formulation of locality (i.e., "Bell locality") assumes the existence of hidden variables. Maybe we're still not quite on the same page about what "hidden variables" means, because we're not on the same page about what "underlying" means in your formulation above. Usually the phrase "hidden variable" is used to mean some *extra* thing, beyond just the standard wave function of ordinary quantum theory, that is in the mix. So then, e.g., deBB is a hidden variable theory because it uses not only the wave function, but also the added "definite particle positions", to account for the results. In any case, though, the point is that "Bell locality" does not presuppose "realism" and it also does not presuppose "hidden variables". You can meaningfully ask whether ordinary QM (not a hidden variable theory!) respects or violates "Bell locality". (It violates it.)

If Bell locality doesn't require hidden variable representation, then how would Bell locality be formulated and incorporated into a model of a Bell test without the explicit denotation of a hidden variable, such as Bell's λ, that contributes to the determination of individual results?

Ok, you could write A(a) = ±1 and B(b) = ±1, but then your formulation has already deviated from one of the primary requirements of the exercise aimed at finding an answer to the suggestion that QM might be made a more complete theory, perhaps a more accurate (or at least a more heuristic) description of the physical reality with the addition of supplementary 'hidden' variables.

To further clarify how I'm using the terms underlying and hidden variable, underlying refers to the sub-instrumental 'quantum realm' where the evolution of the 'system' being instrumentally analyzed is assumed to be occurring. Hidden variable refers to unknown variable parameter(s) or property(ies) of the quantum system being instrumentally analyzed that are assumed to exist 'out there' in the 'quantum realm' in the pre-detection evolution of the system.

OK, but then you're using the word "realistic" in a different way than (I think) most other people here do. I think most people use that word to mean that there are definite values pre-encoded in the particles somehow, such that there are meaningful answers to questions like: "What would the outcome had been if, instead of measuring along x, I had measured along y?"

A hidden variable, such as Bell's λ, need not provide a meaningful answer to a question such as, "What would the outcome at A have been if, instead of the polarizer being set at 20° it had been set at 80°?", because λ can refer to any variable underlying parameter(s) or property(ies) of the system, or any collection thereof. The denotation of λ in the model acts as a placeholder for any unknown underlying parameter(s) or property(ies) which, together with the relevant instrumental variable(s), contribute to the determination of individual results. The hidden variable is needed in this way in order to explicitly denote that something in addition to the instrumental variable, something to do with the 'system' being analyzed, is determining the individual results, because this is what the LHV program, the attempt to answer the question of whether or not QM can be viably supplemented with underlying system parameters and made explicity local, is predicated on.

I certainly agree that it makes sense to call deBB "realist" by some meanings of the word "realist". But it is important to understand that the theory is *not* "realist" in the narrow sense I explained above. Stepping back, that's what I wanted to point out here. The word "realism" is a slippery bugger. Different people use it to mean all kinds of different things, such that miscommunication and misunderstanding tends to be rampant.

I understand, I think. But I'm just using realistic synonymously with hidden parameter. If a theory includes explicit notation representing non-instrumental hidden (or underlying or unknown ... however it might be phrased) parameter(s), then it's a realistic theory, if not, then it isn't.

Me too, though I'm not sure what the two "senses" of nonlocality here might be. They both violate "Bell locality". What other well-defined sense does anybody have in mind?

Yes, I agree that the fact that they both violate Bell locality is the unambiguous criterion and statement of their non-(Bell)localness. What I had in mind was that the way in which deBB is explicitly nonlocal (and nonmechanical) through the quantum potential is a bit different than the way standard QM is (to some) explicitly nonlocal (and nonmechanical) through instantaneous collapse and establishment and projection of a principle axis subsequent to detection at one end or the other.

I'm this "norsen" guy, by the way. So, you know what I think of Jarrett already.

Oh, cool. Yes, I read that paper some time ago. I think that I don't quite understand your reason, your argument for dismissing Jarrett's idea. Maybe after reading it again I'll get it. If you have time, would a brief synopsis here, outlining the principle features of your argument, be possible?

I can't follow this. Are you just repeating Jarrett's idea that "Bell locality" is actually the conjunction of two things, only one of which really deserves to be called "locality"? So then, from the mere fact that "Bell locality" is violated, we can't necessarily infer the (genuine) "locality" is violated? If that's it, you know I disagree, but if the "Bell vs. Jarrett" paper didn't convince you, nothing I can say here will either. =)

Yes, that's basically it. I would say, following Jarrett, that Bell locality encodes two assumptions, one of which, the assumption that paired outcomes are statistically independent, is the effective cause of the incompatibility between Bell LHV and QM, and the incompatibility between Bell LHV and experiment, and that this doesn't tell us anything about locality or nonlocality in nature.

But, as I mentioned, I still have this feeling that I don't fully understand your argument against Jarrett ... but will say that if your argument is correct, then there wouldn't seem to be anything left but to conclude that nonlocality must be present in nature. (Unless the idea that this nonlocality must refer to instantaneous action at a distance is also correct, and then I have no idea what it could possibly mean.)

 

[ttn]

If the heads/tails value of Norsen's coin is considered realistic before we've flipped it, I'm not sure what you'd consider not to be realistic.

Good point! But I think the real lesson here is again just that "realistic" is used to mean all kinds of different things by all kinds of different people in all kinds of different contexts. There is surely a sense in which the coin-flipping-particles model could be considered "realistic" -- namely, it tells a perfectly clear and definite story about really-existing processes. There's nothing the least bit murky, unspeakable, metaphysically indefinite, or quantumish about it. So, if that's what "realistic" means, then it's realistic. But if "realistic" means instead specifically that there are pre-existing definite values (supporting statements about counter-factuals) then the coin-flipping-particles model is clearly not realistic.

So... anybody who talks about "realism" (and in particular, anybody who says that Bell's theorem leaves us the choice of abandoning "realism" to save locality) better say really really carefully exactly what they mean.

Incidentally, equivocation on the word "realism" is exactly how muddle-headed people manage to infer, from something like the Kochen-Specker theorem (which shows that you cannot consistently assign pre-existing definite values to a certain set of "observables"), that the moon isn't there when nobody looks.