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Why are Bell's inequalities violated?

by JK423
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Nugatory
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Jan26-13, 07:23 PM
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Quote Quote by nanosiborg View Post
We're only concerned with realism as formalized in Bell-type hidden variable models of quantum entanglement. Bell writes A(a,λ)=1, B(b,λ)=1 , denoting that individual results are determined by unit vectors, a and b, and an underlying parameter, λ. That's Bell realism.
That is very true.

At first glance, this might appear to be a limitation of Bell's model, but in fact these models do cover just about anything that an intuitive layman (and probably Einstein, Podolosky, Rosen and kindred spirits) would accept as "non-weird".

Thus, the real importance of Bell's inequality and its observed violations is that we're stuck with quantum weirdness. Post-Bell, we don't talk about whether the world is weird, we talk about how to deal with that weirdness.
nanosiborg
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Jan26-13, 08:20 PM
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Quote Quote by Nugatory View Post
That is very true.

At first glance, this might appear to be a limitation of Bell's model, but in fact these models do cover just about anything that an intuitive layman (and probably Einstein, Podolosky, Rosen and kindred spirits) would accept as "non-weird".

Thus, the real importance of Bell's inequality and its observed violations is that we're stuck with quantum weirdness. Post-Bell, we don't talk about whether the world is weird, we talk about how to deal with that weirdness.
I don't think I'd use weird to describe Bell tests, though they are incompletely understood. I think the real importance of Bell's theorem is the experimental and interpretational innovation that's happened because of it.
bohm2
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Jan26-13, 08:35 PM
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Quote Quote by nanosiborg View Post
I don't think I'd use weird to describe Bell tests, though they are incompletely understood. I think the real importance of Bell's theorem is the experimental and interpretational innovation that's happened because of it.
It is interesting to read Bell's thoughts on this issue:
For me then this is the real problem with quantum theory: the apparently essential conflict between any sharp formulation and relativity. That is, to say we have an apparent incompatibility, at the deepest level, between the two fundamental pillars of contemporary theory...
Speakable and Unspeakable in quantum mechanics
http://www.futuretg.com/FTHumanEvolu...0Mechanics.pdf
morrobay
#76
Jan26-13, 09:08 PM
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Its been close to 50 years and why Bells inequalities are violated has not been explained.
So first , is it possible to have ' spin rotations ' and ' geometric phase' as taken from the PDF paper I referenced ? If not then Admin can delete this post.
But if so then A(aλ)=1 where λ is a phase variable related to entangled two photon spins
from a Calcium atoms' 6s level can be considered. And this table:
A________B
xyz______xyz
+++______---
++-______--+
+-+______-+-
+--______-++
-++______+--
-+-______+-+
--+______++-
---______+++

And this P[x-z+]≤ P[y+x-] + [x+z+] being violated could be explained by the above table not having fixed values but with ' rotating spins ' and it would be like an 8 level slot
machine set in motion. The challenge would be to explain why the spins at two equal angular settings are always opposite.
Im only taking the initiative here because the question is not being answered when limited
to EPR/Bell realism
nanosiborg
#77
Jan27-13, 12:22 AM
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Quote Quote by morrobay View Post
Its been close to 50 years and why Bells inequalities are violated has not been explained.

...

Im only taking the initiative here because the question is not being answered when limited
to EPR/Bell realism
As I mentioned above, we're only concerned with realism as formalized in Bell-type hidden variable models of quantum entanglement.

BIs are based on a linear correlation between θ and rate of coincidental detection, which is due to the form that Bell's locality condition requires his lhv-supplemented qm expectation value formulation to take, ie., that the probability distribution be factorizable into the functions that determine individual detection.

I mentioned in an earlier post that A(a,λ)=1, B(b,λ)=1 are Bell realism. A(a,λ) and B(b,λ) are also explicitly local. As opposed to the explicitly nonlocal A(a,b,λ) and B(a,b,λ), A(a,λ) and B(b,λ) specify that A doesn't depend on b, and B doesn't depend on a.

The intensity of light (or photon flux) transmitted by the analyzing (or second) polarizer in sequenced two polarizer (local) setups is always a nonlnear function of the angular difference of the polarizer settings. (In the two polarizer Bell test setups both polarizers are the analyzer, and rate of coincidental detection is intensity.)

BIs are (must be) violated because a necessarily linear correlation expectation is being applied to a setup that must necessarily (even if nothing nonlocal is happening, as in local sequenced setups) produce nonlinear correlations.
nanosiborg
#78
Jan27-13, 04:42 AM
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Quote Quote by bohm2 View Post
It is interesting to read Bell's thoughts on this issue:

Speakable and Unspeakable in quantum mechanics
http://www.futuretg.com/FTHumanEvolu...0Mechanics.pdf
Thank you bohm2.
ZealScience
#79
Jan27-13, 10:46 AM
P: 351
I don't quite understand your question. Because Bell's equation follows from Hidden variable and statistics which is orthogonal to QM prediction.

And it is later EXPERIMENTALLY proven to be violated. Maybe the only thing we could ask is the validity of the experiment rather than the reason...

Personal opinion
DrChinese
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Jan27-13, 07:22 PM
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Quote Quote by morrobay View Post
Its been close to 50 years and why Bells inequalities are violated has not been explained.
So first , is it possible to have ' spin rotations ' and ' geometric phase' as taken from the PDF paper I referenced ? If not then Admin can delete this post.
But if so then A(aλ)=±1 where λ is a phase variable related to entangled two photon spins
from a Calcium atoms' 6s level can be considered. And this table:
A________B
xyz______xyz
+++______---
++-______--+
+-+______-+-
+--______-++
-++______+--
-+-______+-+
--+______++-
---______+++

And this P[x-z+]≤ P[y+x-] + [x+z+] being violated could be explained by the above table not having fixed values but with ' rotating spins ' and it would be like an 8 level slot
machine set in motion. The challenge would be to explain why the spins at two equal angular settings are always opposite.
Im only taking the initiative here because the question is not being answered when limited
to EPR/Bell realism
Asked and answered, morrobay. They are violated because local realism is untenable. And no one knows the answer to that any more than anyone can answer why c is the specific value it is. Further, QM explains why spins are opposite as mentioned.
bohm2
#81
Feb3-13, 01:23 PM
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Quote Quote by bohm2 View Post
There seems to be only 3 options based on assumptions made by Bell:

1. Non-locality
2. Anti-realism
3. Superdeterminism (no freedom of choice)
I just realized that these are not the only options. Another possibility is backward causation, where future apparatus settings can affect system in past. I think the Transactional Interpretation and Aharonov presented such models. I'm guessing that neither non-locality or anti-realism is required. And of course, the MWI, which denies that the results of measurements have definite outcomes (e.g. measurement outcomes are relative to a branch).
DrChinese
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Feb3-13, 03:08 PM
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Quote Quote by bohm2 View Post
I just realized that these are not the only options. Another possibility is backward causation, where future apparatus settings can affect system in past. I think the Transactional Interpretation and Aharonov presented such models. I'm guessing that neither non-locality or anti-realism is required. And of course, the MWI, which denies that the results of measurements have definite outcomes (e.g. measurement outcomes are relative to a branch).
I think of retro-causal as being non-realistic. That is because realistic implies PRE-existing hidden variables. If the hidden variables are in the future, then it is not realistic.
bohm2
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Feb3-13, 04:50 PM
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Quote Quote by DrChinese View Post
I think of retro-causal as being non-realistic. That is because realistic implies PRE-existing hidden variables. If the hidden variables are in the future, then it is not realistic.
I've seen retro-causal interpretations also described as being non-local. In fact, that's how it's typically described but I've also read what I wrote above (e.g. backward causation does not imply non-locality) so I'm a bit confused.
DrChinese
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Feb4-13, 10:04 AM
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Quote Quote by bohm2 View Post
I've seen retro-causal interpretations also described as being non-local. In fact, that's how it's typically described but I've also read what I wrote above (e.g. backward causation does not imply non-locality) so I'm a bit confused.
I think it comes down to your (or perhaps my) definition. The time symmetric (TS) and retrocausal interpretations do not have any effects propagating directly faster than c. But obviously you do have correlations and indirect effects that exceed c. I call that non-realistic, you might call it non-local.

I call anything non-realistic if the interpretation has as adjunct that there are no values for counterfactual measurements - i.e. there is a dependency on the observer. I call anything local if there exists a light cone bounded by c which limits propagation of effects. So by that, TS is local non-realistic. MWI is the same. And to me, Bohmian class theories are non-local AND non-realistic (because there is always a measurement context to consider).

By contrast: I have seen Relational Blockworld (a TS class theory) described by one of its authors as both local and realistic. MWI is often called local realistic. And Bohmian is often described as non-local realistic. Yet by the definitions of EPR, I think my viewpoint is just fine. I don't think it matters all that much, the essential points seem to come out the same in the end.
bohm2
#85
Feb7-13, 03:20 PM
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Quote Quote by DrChinese View Post
I think it comes down to your (or perhaps my) definition. The time symmetric (TS) and retrocausal interpretations do not have any effects propagating directly faster than c. But obviously you do have correlations and indirect effects that exceed c. I call that non-realistic, you might call it non-local.
Yes, I think the paper by Wood and Spekkens summarizes a lot of the problems with these definitions. On pages 16-18:

Superluminal causation: One option for explaining Bell correlations causally is to assume that there are some superluminal causes, for instance, a causal influence from the outcome on one wing to the outcome on the other, or from the setting on one wing to the outcome on the other, or both. In the most general case one allows hidden variables that can causally influence the measurement outcomes.

Retrocausation: "Retrocausation" refers to the possibility of causal influences that act in a direction contrary to the standard arrow of time. It has been proposed as a means of resolving the mystery of Bell-inequality violations by purportedly saving the relativistic structure of the theory: rather than having causal influences propagating outside the light cone, they propagate within the light cone although possibly within the backward light cone.

The authors also discuss some of the difficulties in distinguishing retrocausality from superluminal causation:
Even if one takes spatio-temporal notions to be primary, the fact that the location of μ seems to be mere window-dressing in the context of a causal explanation of Bell-inequality violations undermines the distinction between retrocausation and superluminal causation. Fine-tuning is just as necessary within the retrocausal explanations as it was in the ones that posited superluminal influences or superdeterminism.
The lesson of causal discovery algorithms for quantum correlations: Causal explanations of Bell-inequality violations require fine-tuning
http://arxiv.org/pdf/1208.4119v1.pdf

To be honest, I've always found Gisin's description as quantum correlations lying *beyond* spacetime as the most interesting suggestion. At first it didn't make sense to me but then, when one thinks about the early "creation" of matter and space, it seems that it appeared out of something pre-spatial/temporal. So, why can't a remnant of that "pre-spatial stuff" still be with us at some level and play some role in physical laws. I understand this is mere speculation. But others have suggested this:
While the wave-function realist will deny that 3-dimensional objects and spatial structures find a place in the fundamental ontology, this is not to say that the 3-dimensional objects surrounding us, with which we constantly interact, and which we perceive, think and talk about, do not exist, that there are not truths about them. It is just to maintain that they are emergent objects, rather than fundamental ones. But an emergent object is no less real for being emergent...It is also worth keeping in mind that many workers in quantum gravity have long taken seriously the possibility that our 4-dimensional spacetime will turn out to be emergent from some underlying reality that is either higher-dimensional (as in the case of string theory) or not spatio-temporal at all (as in the case of loop quantum gravity). In neither case is it suggested that ordinary spacetime is non-existent, just that it is emergent.
Against 3-N Dimensional space
http://spot.colorado.edu/~monton/Bra.../Articles.html
morrobay
#86
Feb17-13, 11:56 PM
P: 380
Its a fact that the Bells inequalities are violated for expected spin measurements when detector settings are not parallel. And its natural to consider: loopholes . Clifford algebra, disproofs.superluminal signals. time reversal, many worlds, no conspiracy, and other theories to explain the experimental results that do not agree with local realism.A local realism that assigns spin values based on perfect correlations when detector settings are parallel. It seems there is alot of talent here and out there devoting time to the above theories to the exclusion of exactly what the mechanism is that is causing the violations. When the research focus should be on why and how spins of entangled particles change.
harrylin
#87
Feb18-13, 02:24 AM
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Quote Quote by morrobay View Post
[..] It seems there is alot of talent here and out there devoting time to the above theories to the exclusion of exactly what the mechanism is that is causing the violations. When the research focus should be on why and how spins of entangled particles change.
I agree; some research is going on to investigate explanations, but not enough (some of this came up in http://physicsforums.com/showthread.php?t=597171).
my_wan
#88
Feb18-13, 10:48 AM
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Quote Quote by DrChinese View Post
I call anything non-realistic if the interpretation has as adjunct that there are no values for counterfactual measurements - i.e. there is a dependency on the observer. I call anything local if there exists a light cone bounded by c which limits propagation of effects. So by that, TS is local non-realistic. MWI is the same. And to me, Bohmian class theories are non-local AND non-realistic (because there is always a measurement context to consider).
What is highlighted in blue actually makes a good answer to the OP question.

This very succinctly defines something I suspected about your perspective from previous debates, and indicates a lot of disagreement is mere semantics. I even considered a thread asking for how people defined non-realism in this context.

Has it occurred to you that Relativity is a non-realistic theory under this definition? In fact you can use an ad hoc characterization of the addition of velocities equation to violate Bell's inequality, even slightly more so than EPR correlations do.

To illustrate consider the composition law for velocities. If we try to call a velocity 'real' in the EPR sense it is easy to demonstrate that the counterfactual velocities do not add up. For instance consider 2 spaceships A and B leaving a point of origin at 50% c. This entails that A and B have a velocity of 80% c relative to each other. If you boost the point of origin toward A then A will lose relative velocity faster than B gains relative velocity. In effect there is no counterfactual total value for composite velocities. All thermodynamic state variables as well as velocity, momentum, energy, entropy, etc., associated with a classical object can be demonstrated to have the same lack of counterfactual properties.

From this you can create an ad hoc analogy with EPR correlations, which can be made to violate Bell's inequality even more than EPR correlations. Just assign a probability for a gun at the point of origin to destroy the spaceships in proportion to the relative velocity, or total momentum. You can also treat the ships as doppelgangers such that if a given speed destroys A that same speed destroys B, or other variations. The key feature is that velocities lack a counterfactual total value. A destroyed ship is then analogous to an EPR path A, and survival is path B. The survival correlations between spaceship A and B will then not counterfactually add up under different boost of the gun.

If this is the nature of the variables you define as non-realistic then I would go so far as to bet that all variable we have direct empirical access to are non-realistic, that the world we perceive as physical is actually a purely relational construct. Once you recognize the classical absurdity of parts with a background of absolute space and time, where space and time are pre-existing independent variables as if by magic, this notion of realism is prima facie absurd. Once you accept these variables we call space and time, as we measure them, as state variables then the loss of counterfactual variables, even for a basic variable like velocity or photon paths in EPR, is assured.

Classically we had masses or particles to underpin the relational variables lacking counterfactuals, which we replaced with 'proper' values requiring an observer frame. It is the nature of these particles we are now dealing with. The real difference in the perspective of a realist, at least a serious one, is not the loss of counterfactuals, but a lack of underpinning real variables to generate them. Yet the problem is we know that we can't use a backdrop of space and time to put them in, since these variables are required to be the generators of space and time itself.

Bottom line is that given you definition of non-realism a serious realist can't honestly object. What realist seek is a substructure model that provides what particles provided for classical physic. We can't return to Newtonian style realism but we already know how wrong this is even without resorting to QM. I don't think you have addressed the issues of interest to realist.
danR
#89
Feb18-13, 05:45 PM
P: 351
Quote Quote by bohm2 View Post
To be honest, I've always found Gisin's description as quantum correlations lying *beyond* spacetime as the most interesting suggestion. At first it didn't make sense to me but then, when one thinks about the early "creation" of matter and space, it seems that it appeared out of something pre-spatial/temporal. So, why can't a remnant of that "pre-spatial stuff" still be with us at some level and play some role in physical laws. I understand this is mere speculation. But others have suggested this:

Against 3-N Dimensional space
http://spot.colorado.edu/~monton/Bra.../Articles.html
I mentioned this notion speculatively last week and assumed it was nothing but another of my usual own layperson's metaphysical babblings.

Inasmuch as most inflationary cosmogenies seem to entail some sort of 'quantum fluctuation' originating at a nanoscopic scale, why should we assume that its quantum attributes were necessarily entrained in the expansion of 4-space, or dependent on the evolution of the forces? Since the evidence shows non-locality only too clearly and no force-mediation involvement whatever, isn't it simpler, more elegant, and more Einsteinian-ly beautiful to assert locality (I find realism 'meh, take it or leave it'—I have no preference) to be an extraordinary claim requiring extraordinary evidence?

Edit: or to use a biological analogy: all living systems, however much evolved, retain something of the original RNA-world.
bohm2
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Feb18-13, 09:35 PM
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Quote Quote by danR View Post
I mentioned this notion speculatively last week and assumed it was nothing but another of my usual own layperson's metaphysical babblings...or to use a biological analogy: all living systems, however much evolved, retain something of the original RNA-world.
As an aside and to pursue somewhat analogous speculations, I've come across arguments that the breakdown of spatio-temporality can be seen as a minimum requirement to make sense of consciousness or the so-called "hard" problem of consciousness. For example consider Mcginn's "spatial problem for mind" argument:
How do conscious events cause physical changes in the body? Not by proximate contact, apparently, on pain of over-spatialising consciousness, and presumably not by action-at-a-distance either. Recent philosophy has become accustomed to the idea of mental causation, but this is actually much more mysterious than is generally appreciated, once the non-spatial character of consciousness is acknowledged. To put it differently, we understand mental causation only if we deny the intuition of non-spatiality. The standard analogy with physical unobservables simply dodges these hard questions, lulling us into a false sense of intelligibility....

Conscious phenomena are not located and extended in the usual way; but then again they are surely not somehow 'outside' of space, adjacent perhaps to the abstract realm. Rather, they bear an opaque and anomalous relation to space, as space is currently conceived. They seem neither quite 'in' it nor quite 'out' of it. Presumably, however, this is merely an epistemological fact, not an ontological one. It is just that we lack the theory with which to make sense of the relation in question. In themselves consciousness and space must be related in some intelligible naturalistic fashion, though they may have to be conceived very differently from the way they now are for this to become apparent. My conjecture is that it is in this nexus that the solution to the space problem lies. Consciousness is the next big anomaly to call for a revision in how we conceive space-just as other revisions were called for by earlier anomalies. And the revision is likely to be large-scale, despite the confinement of consciousness to certain small pockets of the natural world. This is because space is such a fundamental feature of things that anything that produces disturbances in our conception of it must cut pretty deeply into our world-view....That is the region in which our ignorance is focused: not in the details of neurophysiological activity but, more fundamentally, in how space is structured or constituted. That which we refer to when we use the word 'space' has a nature that is quite different from how we standardly conceive it to be; so different, indeed, that it is capable of 'containing' the non-spatial (as we now conceive it) phenomenon of consciousness.
Consciousness and Space
http://www.nyu.edu/gsas/dept/philo/c...nessSpace.html


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