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

  • Thread starter bohm2
  • Start date

What do observed violation of Bell's inequality tell us about nature?

  • Nature is non-local

    Votes: 10 31.3%
  • Anti-realism (quantum measurement results do not pre-exist)

    Votes: 15 46.9%
  • Other: Superdeterminism, backward causation, many worlds, etc.

    Votes: 7 21.9%

  • Total voters
    32
  • #1
825
54
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.
 
Last edited:

Answers and Replies

  • #2
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.
 
  • #3
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.
 
  • #4
825
54
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&tag=pfamazon01-20
 
Last edited by a moderator:
  • #5
706
2
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).
 
  • #6
825
54
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"?
 
  • #7
1,569
3,388
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.
 
  • #8
26
0
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.
 
  • #9
Nugatory
Mentor
12,966
5,664
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 :smile:
 
  • #10
825
54
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 :smile:
That's option 3: Other
 
  • #11
Nugatory
Mentor
12,966
5,664
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.
 
  • #12
Nugatory
Mentor
12,966
5,664
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 :smile:
 
  • #13
351
4
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.
 
  • #14
825
54
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.
 
Last edited:
  • #15
DrChinese
Science Advisor
Gold Member
7,358
1,150
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 :smile:
I love it. Nugatory is not to be denied...

:smile:
 
  • #16
351
4
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.
 
Last edited:
  • #17
825
54
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
 
  • #18
1,569
3,388
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;
Isaac Newton said:
"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 :smile:.

(I saw bohm2 already had replied to this while I was writing my reply)
 
Last edited:
  • #19
Nugatory
Mentor
12,966
5,664
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...
 
Last edited:
  • #20
351
4
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 :smile:.

(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.
 
  • #21
Nugatory
Mentor
12,966
5,664
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.
 
Last edited:
  • #22
1,569
3,388
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 :smile:. But I changed.
 
Last edited:
  • #23
706
2
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.
 
Last edited:
  • #24
825
54
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&tag=pfamazon01-20

The point is not why there could potentially be non-locality but why there is locality.
That's a good point.
 
Last edited by a moderator:
  • #25
351
4
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.
 

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

Replies
58
Views
5K
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
1
Views
2K
Replies
7
Views
280
  • Last Post
Replies
5
Views
2K
  • Last Post
4
Replies
97
Views
14K
Replies
21
Views
2K
Replies
12
Views
1K
Top