View Poll Results: What do observed violation of Bell's inequality tell us about nature?
Nature is non-local 11 32.35%
Anti-realism (quantum measurement results do not pre-exist) 15 44.12%
Other: Superdeterminism, backward causation, many worlds, etc. 8 23.53%
Voters: 34. You may not vote on this poll

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

by bohm2
Tags: bell, inequalities, nature, violations
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bohm2
#1
Feb10-13, 02:20 PM
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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.
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LastOneStanding
#2
Feb10-13, 02:50 PM
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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.
LastOneStanding
#3
Feb10-13, 02:52 PM
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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
#4
Feb10-13, 03:31 PM
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What do violations of Bell's inequalities tell us about nature?

Quote Quote by LastOneStanding View Post
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
http://www.amazon.com/Elegance-Enigm.../dp/3642208797
Maui
#5
Feb10-13, 04:01 PM
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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
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Feb10-13, 04:29 PM
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Quote Quote by Maui View Post
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
#7
Feb10-13, 07:14 PM
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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
#8
Feb10-13, 08:35 PM
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Quote Quote by bohm2 View Post
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
#9
Feb10-13, 09:49 PM
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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
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Feb10-13, 10:09 PM
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Quote Quote by Nugatory View Post
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
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Feb10-13, 10:14 PM
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Quote Quote by LastOneStanding View Post
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
#12
Feb10-13, 10:23 PM
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Quote Quote by bohm2 View Post
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
#13
Feb10-13, 11:40 PM
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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
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Feb11-13, 08:28 AM
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Quote Quote by danR View Post
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
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Feb11-13, 08:31 AM
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Quote Quote by Nugatory View Post
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
#16
Feb11-13, 09:29 AM
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Quote Quote by bohm2 View Post
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
#17
Feb11-13, 10:05 AM
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Quote Quote by danR View Post
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
#18
Feb11-13, 10:18 AM
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Quote Quote by danR View Post
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;
Quote Quote by 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)


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