Bell's theorem and local realism

[TrickyDicky]

Well actually it can:
http://en.wikipedia.org/wiki/Quantum_geometry

Yes, there are multiple attempts at quantum gravity theories that use more or less geometrical methods.
I didn't mean that, I was just giving an example of an obvious(at least to me, but I have never seen it mentioned) type of hidden variables theories (nonlocal but at this point I'm not really sure if they would be considered nonlocal by all experts) just relying on a spacetime geometry which spacelike separated events are obviously correlated by the metric relations and would therefore give correlated outcomes that are not causally related for the measurements of geometrical properties(i.e. say quantum spin was such a geometrical feature).

 

[nikman]

"When drawing conclusions from this most important and profound theorem, I wonder if somebody has interpreted its proof of the falseness of local realism as implicitly referring to elementary particles as realistic objects."

You can't go wrong going with Zeilinger, a Bellmeister who goes this far and no farther: "A photon is a click in a photon detector." Now, we can probably agree that a photon detector is a real object and a click is a real sound (if we all indicate synchronously, intersubjectively, that we hear it). Could a real-not entity affect a real one in that manner, probably not imo. Although that may be way too naively classical.

 

[bhobba]

Could a real-not entity affect a real one in that manner, probably not imo. Although that may be way too naively classical.

We know what QFT says it is.

Why not simply say that's the reality - sounds simple to me instead of getting caught up in this semantic quagmire of what a real object is yada yada yada. Its what I do.

Such is generally a philosophers game and they really haven't gotten anywhere - physicists will likely not either.

The real import of Bell's theorem is we have a precise definition of naive reality - and we know what the theorem says. You won't get anywhere with questions like what a photon is without similar definitions and then you have the problem of getting people to agree.

Thanks
Bill

 

[nikman]

I didn't want to diss the post that began the thread. And you're right, that's exactly what BT is: the concise expression of classical realism. Although it's not really naive in the macroworld we live in (unless, like say the dreadful Joy Christian, one is a hopeless crackpot) because you can't violate it with ordinary macroscopic objects. It's the world life and our brains evolved in. That truth needs to be accepted if it's to be in any sense transcended.

You can't have too much philosophical reflection about this stuff if it's sophisticated and knowledgeable philosophy. You want to get humanists into the game or just shunt them aside and snark at them? Screw, with respect, your yada yada. That attitude's a serious part of the problem. Ever read, for example, Jeffrey Bub's SEP article on quantum entanglement and information? It's called Philosophy of Science.

 

[bhobba]

You can't have too much philosophical reflection about this stuff if it's sophisticated and knowledgeable philosophy. You want to get humanists into the game or just shunt them aside and snark at them? Screw, with respect, your yada yada. That attitude's a serious part of the problem. Ever read, for example, Jeffrey Bub's SEP article on quantum entanglement and information? It's called Philosophy of Science.

Well I think if that's what interests you a forum whose rules specifically preclude philosophy may not be the appropriate place to discuss your issues.

My view is very similar to Wienberg:
http://www.phys.washington.edu/users/vladi/phys216/Weinberg_Against_philosophy.doc
'Physicists do of course carry around with them a working philosophy. For most of us, it is a rough-and-ready realism, a belief in the objective reality of the ingredients of our scientific theories. But this has been learned through the experience of scientific research and rarely from the teachings of philosophers'.

If you want to chat about it at that level start a thread over at philosophy forums and drop me a line linking to it. Happy to comment over there. But I have to say from my forays over on that forum I find I speak a different language, the language of applied math, and we talk past one another. That's why I prefer here because the rough and ready view of Weinberg suits me better.

And of course humanists under no circumstances should be excluded, I can go down that path with you and any anyone else that wants to participate if you want - just not here. My only concern, like I said, is I speak the language of applied math - not philosophy. Applied mathematicians have a very rough and ready view of such things.

Thanks
Bill

 

[nikman]

Sorry. I suspect I shouldn't have said "screw your ..." However, the first post on this thread asked a certifiably, purely, quintessentially metaphysical question (go ahead, deny that):

"When drawing conclusions from this most important and profound theorem, I wonder if somebody has interpreted its proof of the falseness of local realism as implicitly referring to elementary particles as realistic objects."

Bit of a double standard you're employing here but hey. Anyway I've spent a fair amount of time over the years explaining or trying to explain Bell, Wigner-d'Espagnat, CHSH, Dirk Aerts' macroworld Bell isomorphisms, Joy Christian's pathology, the Quantum Randi Challenge, why "Shut Up and Calculate" isn't entirely indefensible etc. to liberal arts types in informal discussions and a few times I've encountered variations of the above question. JSB himself took it up at least obliquely in "Bertlmann's Socks". The point of that last being he was a competent applied mathematician with an adequate understanding of QFT who didn't dodge issues Weinberg cocks a snoot at. However I'm outtahere.

 

[morrobay]

Bell's theorem refers to correlations between "classical" or "macroscopic" experimental outcomes. So as long as one believes that the experimental outcomes in a Bell test are "classical", then the violation of the inequality does rule out local realism.

There are some assumptions that go into this conclusion. For example, it assumes that each measurement produces only one outcome. In many-worlds each measurement has more than one outcome, so the Bell test don't rule out that many-worlds is a local realistic theory.

With the assumption that one measurement produces one outcome can a Bell inequality violation be numerically shown
(non statistically) with the two forms of the inequality below ?
Given that ø between detectors is 0⁰,120⁰and 240⁰
So that the inequality violation is function of + or - signs in the inequality alone.
P ++ = P-- = 1/2 sin²ø/2
P+- = P-+ = 1/2cos²ø/2

(1) M = AB + AB' - A'B + A'B' = (A-A')B + (A+A')B' .... -2 ≤ M ≤ 2
(2) C(a,b) - C(a,c)|+|C(a',b) + C(a',a) ≤ 2 ...... A₁ and A₂ (+ or -) 1

 

[jk22]

Since the function for the result in A is a one point function, it depends only on the angle in a, this formula should in fact modelize the following experiment : we have a single polarized photon beam and we generate 4 time series for the four direction of measurement ? So Bell's experiment does not need a bbo crystal nor an entangled pair ?

To see this we take simply the initial state a single qbit along z and the tensor product becomes the matrix product (which represent in som sense the time ordering i think) and we get the same result.

 

[stevendaryl]

With the assumption that one measurement produces one outcome can a Bell inequality violation be numerically shown
(non statistically) with the two forms of the inequality below ?
Given that ø between detectors is 0⁰,120⁰and 240⁰
So that the inequality violation is function of + or - signs in the inequality alone.
P ++ = P-- = 1/2 sin²ø/2
P+- = P-+ = 1/2cos²ø/2

(1) M = AB + AB' - A'B + A'B' = (A-A')B + (A+A')B' .... -2 ≤ M ≤ 2
(2) C(a,b) - C(a,c)|+|C(a',b) + C(a',a) ≤ 2 ...... A₁ and A₂ (+ or -) 1

I don't know if the three angles $0, 120, 240$ provide an example of a violation of Bell's inequality. It actually looks like you're using the CHSH inequality above. If so, I think you have a sign error. According to Wikipedia, it should be:

$C(a,b) + C(a,b') + C(a', b) - C(a',b') \leq 2$

For spin-1/2, the correlation is given by:

$C(a,b) = - cos(\theta)$

where $\theta$ is the relative angle between the two detector orientations. So we have:

• $\theta = 0 \Rightarrow C = -1$
• $\theta = 60 \Rightarrow C = -0.5$
• $\theta = 120 \Rightarrow C = +0.5$
• $\theta = 180 \Rightarrow C = +1$
• $\theta = 240 \Rightarrow C = +0.5$

So here's a choice for $a, b, a', b'$ that violates the inequality:

• $a = 0$
• $b = 180$
• $a' = 60$
• $b' = 120$

Then:

• $C(a,b) = +1$
• $C(a, b') = +0.5$
• $C(a',b) = +0.5$
• $C(a',b') = -0.5$

Then $C(a,b) + C(a,b') + C(a',b) - C(a',b') = 1 + 0.5 + 0.5 - (-0.5) = 2.5$

I don't think you can get a violation with just $0, 120, 240$.

 

[morrobay]

Thanks for the clarification on CHSH with P(a,b)_QM = -cos ø.
While P++ = P-- = 1/2 sin²ø/2 and P-+ = P+- = 1/2 cos²ø/2 do not seem to apply to CHSH inequality.
They can show violations when spin 1/2 particles are measured with Stern - Gerlach apparatuses oriented along a and b when ø is angle difference with detectors at three settings :
A.....B
a=0....a'=0
b=120.....b'=120
c=240.....c'=240

With this form of inequality: P(a+b'+) ∠ P(a-c'+) + P(c+b'-) with expected outcomes taken from measurements when detector settings at A and B are aligned at 0⁰,120⁰,240⁰ ( ++-...--+) one of eight

Then the inequality violation is 1/2sin²120/2 ∠ 1/2cos²240/2 + 1/2cos²120/2 = .375 ∠ .125 + .125

 

[gill1109]

No particles in Bell's theorem

I think it is worth pointing out that Bell (1981) himself argued forcibly that his "theorem" (by which he meant his inequality - an elementary probability and calculus exercise) is not about particles or even about quantum theory. It is about what you would expect to see according to a completely conventional picture of the macroscopic physical world about a completely macroscopic experimental set-up. The following is quoted from his (IMHO) masterpiece, "Bertlmann's socks and the nature of reality". Ch. 16 of "Speakable and unspeakable". But you can also find it on internet.

You might suspect that there is something specially peculiar about spin-1/2 particles. In fact there are many other ways of creating the troublesome correlations. So the following argument makes no reference to spin-1/2 particles, or any other particular particles.
Finally you might suspect that the very notion of particle, and particle orbit, freely used above in introducing the problem, has somehow led us astray. Indeed did not Einstein think that fields rather than particles are at the bottom of everything? So the following argument will not mention particles, nor indeed fields, nor any other particular picture of what goes on at the microscopic level. Nor will it involve any use of the words ‘quantum mechanical system’, which can have an unfortunate effect on the discussion. The difficulty is not created by any such picture or any such terminology. It is created by the predictions about the correlations in the visible outputs of certain conceivable experimental set-ups.
Consider the general experimental set-up of Fig. 7

To avoid inessential details it is represented just as a long box of unspecified equipment, with three inputs and three outputs. The outputs, above in the figure, can be three pieces of paper, each with either ‘yes’ or ‘no’ printed on it. The central input is just a ‘go’ signal which sets the experiment off at time t1. Shortly after that the central output says ‘yes’ or ‘no’. We are only interested in the ‘yes’s, which confirm that everything has got off to a good start (e.g., there are no ‘particles’ going in the wrong directions, and so on). At time t1 + T the other outputs appear, each with ‘yes’ or ‘no’ (depending for example on whether or not a signal has appeared on the ‘up’ side of a detecting screen behind a local Stern–Gerlach magnet). The apparatus then rests and recovers internally in preparation for a subsequent repetition of the experiment. But just before time t1 + T, say at time t1 + T – δ, signals a and b are injected at the two ends. (They might for example dictate that Stern–Gerlach magnets be rotated by angles a and b away from some standard position). We can arrange that cδ << L, where c is the velocity of light and L the length of the box; we would not then expect the signal at one end to have any influence on the output at the other, for lack of time, whatever hidden connections there might be between the two ends.
Sufficiently many repetitions of the experiment will allow tests of hypotheses about the joint conditional probability distribution P(A,B|a, b) for results A and B at the two ends for given signals a and b.​

 

[TrickyDicky]

I think it is worth pointing out that Bell (1981) himself argued forcibly that his "theorem" (by which he meant his inequality - an elementary probability and calculus exercise) is not about particles or even about quantum theory. It is about what you would expect to see according to a completely conventional picture of the macroscopic physical world about a completely macroscopic experimental set-up. The following is quoted from his (IMHO) masterpiece, "Bertlmann's socks and the nature of reality". Ch. 16 of "Speakable and unspeakable". But you can also find it on internet.

I was actually aware of that particular chapter, but even if Bell himself clearly made an effort to distance his theorem from interpretations related specifically to particles, be it classical , or quantum (whatever the latter are, which sometimes seems like it is not clear even for experts, but let's agree on whatever experts mean when they use the word particle in the context of quantum theory), I think it is reasonable that some kind of more general object or what I referred above from a reference on the theorem as local "individual entity" is implicit in Bell's own interpretation of his theorem, calling these objects "particles" and whether this leads to further confusion is just a semantic issue.

Consider this comment by Bell in the quote above:
"We are only interested in the ‘yes’s, which confirm that everything has got off to a good start (e.g., there are no ‘particles’ going in the wrong directions, and so on)."

It seems obvious we are still implicitly concerned by certain objects(in scare quotes).

 

[gill1109]

Consider this comment by Bell in the quote above:
"We are only interested in the ‘yes’s, which confirm that everything has got off to a good start (e.g., there are no ‘particles’ going in the wrong directions, and so on)."

It seems obvious we are still implicitly concerned by certain objects (in scare quotes).

Bell puts the word "particles" in quotes for a very good reason. They are not *scare* quotes. They are quotes indicating that we are briefly talking another language, assuming some particular physical theory, which we want to test in this experiment.

Suppose a quantum physicist tries to engineer this experiment. He wants to win the Nobel prize by doing the first ever succesfull loophole-free Bell type experiment (it seems that this might happen without a year from now - so it will have only taken a bit more than 50 years to achieve). The quantum physicist does have the word "particle" in his vocabulary. Bell was thinking of an experiment in which three particles are emitted simultaneously and registering one of them is used to "announce" that there are another two on their way. He did this because he was thinking of experiment where you try to "excite" some "molecule" but you may or many not have success in causing the desired emission of "particles".

Nowadays we think more often of pulsed experiments where we make sure that per short time window there is only one emission of "particles". Then we don't need to have a third particle emitted in order to tell us that the other two are successfully launched.

You can read about the experiment he had in mind in chapter 13 of "Speakable and unspeakable". This was before people started having success with the photon polarisation type experiments (Aspect et al ...). Different physical systems.

People still talk about experiments with "event ready detectors". Possibly we could get two atoms very far apart entangled, by doing entanglement swapping with photons. But photons are slippery creatures and this often doesn't succeed. So you have to make sure you know you have succeeded e.g. by successful detection of another "particle"

 

[gill1109]

Interesting remark that there may be no philosophy in this forum. Nowadays Bell's theorem is called part of "experimental metaphysics". The experiment allows one to distinguish between whole classes of physical theories. It's not about testing one particular theory.

Even if philosophy is not allowed, I hope that metaphysics is allowed. If not, then Bell's theorem is .a not-allowed topic

 

[TrickyDicky]

You seem to be missing my point, you are describing experiments that involve particles aren't you?

 

[gill1109]

You seem to be missing my point, you are describing experiments that involve particles aren't you?

The experiments don't have to involve particles. The experiments might be experiments in which theories are tested/implemented in which the word particle occurs. But they could also be experiments in which theories are tested/implemented in which there are only waves. It depends what the physicist puts inside (or rather: thinks he or she is putting inside) that big long box drawn in the figure from "Bertlmann". There is no particle drawn in the picture. There was no need whatever to use the word "particle" in the description of the experiment. There are three inputs and three outputs on a long box, and there is some time schedule which needs to be adhered to.

For instance, *inside* that long box one could place a network of three computers. The one in the middle sends some messages to the ones at each end, and also delivers an output saying "I did it". The ones at each end do some local computation based on their respective inputs and the message that came from the central computer.

What we very well understand, is that if we put three classical computers in the box, and do the experiment, the resulting statistics will satisfy the Bell-CHSH inequality. We imagine that if instead we put some quantum source and some quantum detectors inside the box and are really smart with our quantum engineering (creating some "particles" in a desired "state" and implementing certain "quantum measurements" on those "particles") then we would violate the Bell-CHSH inequality. (It hasn't been done yet, but maybe it will be done soon).

 

[TrickyDicky]

I was using the word particle in a broadest sense, as quantum objects that are local(interact at points) and have defined properties as individual or countable entities, in other words local realistic objects, you may call them particles, waves, messages from computers...

 

[gill1109]

I was using the word particle in a broadest sense, as quantum objects that are local(interact at points) and have defined properties as individual or countable entities, in other words local realistic objects, you may call them particles, waves, messages from computers...

The words "quantum" and "particle" are not needed to describe the experiment. We can put in that box whatever we like, and we can use whatever theory we like to describe our understanding of what we goes on inside. If you want to say that two "particles" go from the source to the measurement stations while another has just let the experimenter know that the two particles are on their ways, that's fine.

 

[TrickyDicky]

The words "quantum" and "particle" are not needed to describe the experiment. We can put in that box whatever we like, and we can use whatever theory we like to describe our understanding of what we goes on inside. If you want to say that two "particles" go from the source to the measurement stations while another has just let the experimenter know that the two particles are on their ways, that's fine.

The words used are irrelevant, it is quite clear the kind of objects you are putting in the box, they are the local agents I described in my previous post and what Bell's theorem claims that any physical theory based on them cannot reproduce Quantum experiments correlations.

 

[gill1109]

The words used are irrelevant, it is quite clear the kind of objects you are putting in the box, they are the local agents I described in my previous post and what Bell's theorem claims that any physical theory based on them cannot reproduce Quantum experiments correlations.

Bell's theorem shows indeed that what Bell considered as local realist agents cannot reproduce quantum correlations. One could also say "local realist agents" = "what can be simulated by classical computers communicating one-way".

Of course there is another question whether or not Nature can exhibit quantum correlations in the rather restricted context of the long box experiment. So far it has not been observed in Nature (ie in the Lab).

 

[TrickyDicky]

I could use an analogy to clarify what I meant above by a spacetime geometry as an obvious way to get a "nonlocal" hidden variables theory compatible with quantum correlations. (I'll explain later why I put nonlocal in quotes.)

Consider the amplituhedron, here we have a geometric object with certain properties that give rise to probability distributions of the outcomes of QFT experiments that are usually understood in terms of 'particles' interactions.

I would say this would be an example of nonlocality, since it is claimed that locality is removed and it would only appear as emergent property.

Similarly in an actual spacetime geometry that putatively were able to give the right probabilistic distributions of outcomes observed in quantum experiments, we'd either consider the physical theory based on it as nonlocal, or consider that such geometry exploits a "conceptual loophole" in Bell's theorem if it was viewed as local.

Of course here the difficult part is to find such a geometry, which many physicists probably will think doesn't exist. However the amplituhedron seems to hint that it might.


See also this reference that uses the geometric Malus law in the context of Bell's theorem:
J. of Nonlinear Math. Phys. Volume 11, Supplement (2004), 104–109
"EPR-B correlations: non-locality or geometry?" Kracklauer A F

 

[gill1109]

See also this reference that uses the geometric Malus law in the context of Bell's theorem:
J. of Nonlinear Math. Phys. Volume 11, Supplement (2004), 104–109
"EPR-B correlations: non-locality or geometry?" Kracklauer A F

That 2004 paper has so far only been cited once ... and that was in another paper by the same author (according to Google scholar).

Now this paper by de Raedt and others attempts to show that the quantum correlations of the singlet state can de deduced from some geometric and informational principles: http://arxiv.org/abs/1303.4574

Quantum mechanics is not in conflict with locality. There is no action at a distance, no "Bell telephone", no way to use the quantum correlations to communicate instantaneously over some distance. It is only when one hypothesizes an otherwise invisible hidden layer which "explains" those correlations in a classical (mechanistic, deterministic) way that one runs into locality issues.

 

[harrylin]

[..]
See also this reference that uses the geometric Malus law in the context of Bell's theorem:
J. of Nonlinear Math. Phys. Volume 11, Supplement (2004), 104–109
"EPR-B correlations: non-locality or geometry?" Kracklauer A F

Found it: http://iopscience.iop.org/1464-4266/6/6/012
As far as I am aware, Kracklauer did not really "crack" the problem: as a matter of fact I have tested his simulation program and also studied the "laboratory confirmation", but found both of those wanting (of course, I could have made a mistake).

However, perhaps he was thinking in the right direction.
It reminds me of an old thread on this forum, which IMHO left some intriguing questions wide open: https://www.physicsforums.com/showthread.php?t=490571.

Neumaier argued that from the perspective of QFT the problem is caused by the "particle" concept (that is: countable, unalterable objects), and that in contrast, classical (Maxwellian) EM can break Bell's inequality.

A recently published paper on classical optics seems to make similar suggestions, if I understand correctly what the authors are saying:

" [..] we have presented the first study of nonlocal correlations in classical optical beams with topological singularities. These nonlocal correlations between two different light modes are manifested through the violation of a Bell inequality using the Wigner function for this system of classical vortex beams. [..]
Clearly, the violation of the Bell inequality for classical light fields and the existence of nonlocal correlations bring out totally new statistical features of the optical beams. [..] "
Phys. Rev. A 88, 013830 (2013) - http://arxiv.org/abs/1307.2981

PS. Note that according to Bell his theorem does not depend on "local hidden variables":
"It is notable that in this argument nothing is said about the locality, or even localizability, of the variables λ."
- Bertlmann's socks and the nature of reality

 

[TrickyDicky]

Found it: http://iopscience.iop.org/1464-4266/6/6/012
As far as I am aware, Kracklauer did not really "crack" the problem: as a matter of fact I have tested his simulation program and also studied the "laboratory confirmation", but found both of those wanting (of course, I could have made a mistake).

I found the paper googling a couple of keywords, and some paragraph in page 106 seemed an example of what I was talking about wrt to geometry and nonlocality, on rereading it is probably not the most relevant reference I could find.

However, perhaps he was thinking in the right direction.
It reminds me of an old thread on this forum, which IMHO left some intriguing questions wide open: https://www.physicsforums.com/showthread.php?t=490571.

Neumaier argued that from the perspective of QFT the problem is caused by the "particle" concept (that is: countable, unalterable objects), and that in contrast, classical (Maxwellian) EM can break Bell's inequality.

Thanks for pointing me to that thread, it answers what I asked in the OP about others interpreting Bell's theorem in that way.

 

[gill1109]

Found it: http://iopscience.iop.org/1464-4266/6/6/012
As far as I am aware, Kracklauer did not really "crack" the problem: as a matter of fact I have tested his simulation program and also studied the "laboratory confirmation", but found both of those wanting (of course, I could have made a mistake).

However, perhaps he was thinking in the right direction.
It reminds me of an old thread on this forum, which IMHO left some intriguing questions wide open: https://www.physicsforums.com/showthread.php?t=490571.

Neumaier argued that from the perspective of QFT the problem is caused by the "particle" concept (that is: countable, unalterable objects), and that in contrast, classical (Maxwellian) EM can break Bell's inequality.

A recently published paper on classical optics seems to make similar suggestions, if I understand correctly what the authors are saying:

" [..] we have presented the first study of nonlocal correlations in classical optical beams with topological singularities. These nonlocal correlations between two different light modes are manifested through the violation of a Bell inequality using the Wigner function for this system of classical vortex beams. [..]
Clearly, the violation of the Bell inequality for classical light fields and the existence of nonlocal correlations bring out totally new statistical features of the optical beams. [..] "
Phys. Rev. A 88, 013830 (2013) - http://arxiv.org/abs/1307.2981

PS. Note that according to Bell his theorem does not depend on "local hidden variables":
"It is notable that in this argument nothing is said about the locality, or even localizability, of the variables λ."
- Bertlmann's socks and the nature of reality

It is easy to create *half* the cosine curve by LHV. It is easy to create the cosine curve by the detection loophole or by the coincidence loophole. I forget which one Kraklauer was using in his simulation, but it was one or the ither.

The problem is not the " particle" concept in the hidden layer, in the physics behind the scenes, it is the discreteness of the manifest outcomes. Click or no-click. +1 or -1. Within a time interval of fixed duration.

The recent paper needs more looking at http://arxiv.org/abs/1307.2981. They don't talk about regular CHSH but some generalization for continuous outcomes. And as far as I can see there is no spatial dimension. They are measuring at the same time different observables "in the same place". Bell is about "same time different places". The paper is hard and one thing is clear to me: the authors don't actually know much about / understand the conventional Bell story.

Note that *if* they had found a classical physical system violating Bell-CHSH within a rigorous time-space no-loopholes Bell type experimental framework, they would have disproved Bell's theorem. And someone could win the quantum Randi challenge by programming the math. And get famous and win the Nobel prize: loophole-free experimental violation of Bell-CHSH by a classical physical system (network of classical computers). Hell, it hasn't even yet been done in the quantum lab...

 

[harrylin]

[...]
The problem is not the " particle" concept in the hidden layer, in the physics behind the scenes, it is the discreteness of the manifest outcomes. Click or no-click. +1 or -1. Within a time interval of fixed duration.

Me thinks that you are in disagreement with Neumaier:

"the traditional hidden variable assumption only amounts to a hidden classical particle assumption.
And the experiments demonstrating their violation only disprove classical models with particle structure. [..]
We conclude that classical field theory models for a quantum phenomenon are not excluded by traditional no-go theorems for hidden variables."
- http://arnold-neumaier.at/ms/lightslides.pdf

As you are an expert in statistics and he is an expert in QFT (and I'm an expert in neither), I don't know...

The recent paper needs more looking at http://arxiv.org/abs/1307.2981. [..] as far as I can see there is no spatial dimension. They are measuring at the same time different observables "in the same place". [..]

With "nonlocal" they ( http://arxiv.org/abs/1307.2981) clearly mean a spatial separation, just like everyone else:

"Let us now consider the situation where the quadrature phase components of two correlated and spatially separated light fields are measured. [..] The strength of the correlations increases with n(m), asymptotically reaching the limit of perfect correlations as n becomes very large [..] This feature thus further corroborates our earlier results of increase in Bell violations for larger orbital angular momentum of LG beams."

 

[gill1109]

Me thinks that you are in disagreement with Neumaier:

"the traditional hidden variable assumption only amounts to a hidden classical particle assumption.
And the experiments demonstrating their violation only disprove classical models with particle structure. [..]
We conclude that classical field theory models for a quantum phenomenon are not excluded by traditional no-go theorems for hidden variables."
- http://arnold-neumaier.at/ms/lightslides.pdf

As you are an expert in statistics and he is an expert in QFT (and I'm an expert in neither), I don't know...


With "nonlocal" they ( http://arxiv.org/abs/1307.2981) clearly mean a spatial separation, just like everyone else:

"Let us now consider the situation where the quadrature phase components of two correlated and spatially separated light fields are measured. [..] The strength of the correlations increases with n(m), asymptotically reaching the limit of perfect correlations as n becomes very large [..] This feature thus further corroborates our earlier results of increase in Bell violations for larger orbital angular momentum of LG beams."

Yes I disagree strongly with Neumaier. He needs to read "Bertlmann" so that he understands the issues. This is not a matter of QFT vs statistics. This is a matter of ignorance of basic logic, basic facts.

OK good that the Indian gentlemen do have space in their picture. Next then is to check out the (non-standard) Bell inequality for continuous variables they are using: is there also a Bell theorem based on that inequality? Is the experiment they have in mind loophole-free? A lot of work to do. I am sceptical: there hasn't yet been done a successful loophole-free Bell-type experiment in the quantum physics lab yet, after 50 yrs trying. I doubt that classical optics can give a successful experiment. I conclude that the Indian gentlemen know a lot about optics, little about Bell's theorem (ie that's my working assumption. Sceptical = scientific. Extraordinarily radical scientific claims require extraordinarily strong scientific evidence).

 

[harrylin]

Yes I disagree strongly with Neumaier. He needs to read "Bertlmann" so that he understands the issues. This is not a matter of QFT vs statistics. This is a matter of ignorance of basic logic, basic facts.

It's of course not a matter of QFT vs statistics; I suppose that one cannot teach QFT without a reasonably good understanding of statistics! Indeed, it appears that he understands the issues, see also his publication list here: http://arnold-neumaier.at/papers/physpapers.html. In that list I now found an older, rather unpolished paper of him in which he explains his conclusions in more detail:

http://lanl.arxiv.org/abs/0706.0155

It looks like implicit advice to De Raedt to change his modelling approach...

OK good that the Indian gentlemen do have space in their picture. Next then is to check out the (non-standard) Bell inequality for continuous variables they are using: is there also a Bell theorem based on that inequality? Is the experiment they have in mind loophole-free? A lot of work to do. I am sceptical: there hasn't yet been done a successful loophole-free Bell-type experiment in the quantum physics lab yet, after 50 yrs trying. I doubt that classical optics can give a successful experiment.

I have similar questions as you, but "only" a successful semi-classical model is desired...

I conclude that the Indian gentlemen know a lot about optics, little about Bell's theorem (ie that's my working assumption. Sceptical = scientific. Extraordinarily radical scientific claims require extraordinarily strong scientific evidence).

I agree; note that I regard "Bell's theorem" (the math plus its usual metaphysical interpretation) to be such an "extraordinarily radical scientific claim".

 

[TrickyDicky]

The problem is not the " particle" concept in the hidden layer, in the physics behind the scenes, it is the discreteness of the manifest outcomes. Click or no-click. +1 or -1. Within a time interval of fixed duration.

Let's give some context. It is not that the theorem introduces any "particle" concept as its premise. It is about the conclusions from the theorem given certain assumption that is virtually shared by the whole physics community, namely atomism, the atomic theory as explanation of matter(the fundamental building blocks narrative) . Now the thing is atomism implies realism. So if one assumes the atomic theory(and I have yet to meet any physicist in academia that doesn't, then logically with Bell's theorem one is discarding any theory that includes objects with particle properties(locality) as able to explain quantum correlations experiments.

Now it is true that there are physicists that when it comes to QM claim not to be realists in order to keep locality, but if they follow the atomic theory they are realists even if they don't know it so they are simply not being logical, and then it begs the question why they would consider Bell's theorem which is based on logic.

Now I have to say that I disagree with Neumaier that Classical field theory like electrodynamics as understood at least since Lorentz, violates Bell's inequalities as a theory. The reason is that electrodyamics includes classical particles. So it is both local and realistic.

 

[billschnieder]

http://lanl.arxiv.org/abs/0706.0155

It looks like implicit advice to De Raedt to change his modelling approach...

The conditional probability of detecting a photon which is in state λ and passes through filter k when Ak = A and A3−k = 0 is pk(A, λ).

Did no one else see the contradiction in talking about "probability of detecting" a photon, and yet saying LHV theories can not reproduce the QM predictions. There are of examples of LHV models doing just that with individial particles (rather than "classical fields", See De Raedt's own model for example). But I guess it could all be dismissed as "detection loophole" as though it makes sense to talk of "probability of detection" (different from unity), when everything is detected.

 

[stevendaryl]

Let's give some context. It is not that the theorem introduces any "particle" concept as its premise. It is about the conclusions from the theorem given certain assumption that is virtually shared by the whole physics community, namely atomism, the atomic theory as explanation of matter(the fundamental building blocks narrative) . Now the thing is atomism implies realism. So if one assumes the atomic theory(and I have yet to meet any physicist in academia that doesn't, then logically with Bell's theorem one is discarding any theory that includes objects with particle properties(locality) as able to explain quantum correlations experiments

I'm not sure what all you are lumping into the concept of atomism. I also don't understand where you think that atomism comes into play in discussions of Bell's theorem. What Bell's local realism amounts to--as described already by Richard Gill--is basically the idea that any fact about the universe can be factored into facts about tiny little regions of the universe, together with facts about how neighboring regions fit together. Facts about each tiny region can either be continuous (the values of fields) or discrete (the locations, momenta, angular momenta, charges, etc. of particles within the region). There is a second component to local realism that is added by relativity, which is that the evolution of one little region cannot depend on facts about distant regions.

The violation of Bell's inequality implies (in one way of looking at, at least) that there are facts about the universe that don't factor into facts about the little regions making up the universe. I don't see the connection with atomism, though.

Now, there are nonlocal facts about the universe. In particular, it's topology can't be determined just by looking at little regions--it's a fact about how all the little regions are glued together to make a whole. On the other hand, since topology doesn't suddenly change in normal physics, topology is not a likely candidate for explaining nonlocal correlations. Contrary to what Joy Christian seems to believe, I don't think that you can use topology to violate Bell's inequality (unless you suppose a really weird topology, such as every point is connected to every other point).

 

[gill1109]

Did no one else see the contradiction in talking about "probability of detecting" a photon, and yet saying LHV theories can not reproduce the QM predictions. There are of examples of LHV models doing just that with individial particles (rather than "classical fields", See De Raedt's own model for example). But I guess it could all be dismissed as "detection loophole" as though it makes sense to talk of "probability of detection" (different from unity), when everything is detected.

De Raedt has LHV models for every experiment done to date, which is possible since so far no experiment was loophole-free. In fact everyone knew (or should have known) that all those experiments had local-realistic explanations. Certainly Aspect, Weihs etc etc know that. Just last year there have been two photon polarisation experiments which overcome the detection loophole (Giustina et al; Christensen et al.). They don't have the required space-time constraints - fast rapid generation of new random settings, Alice's measurement result fixed before Bob's setting could arrive at Alice's place ... On the other hand, that constraint was achieved in the Aspect and Weihs experiments. So it really does look as though the experimenters are nearly there. And they think they'll be they in about a year. And then De Raedt will no longer be able to play his game. He and I discussed this a month ago. He agrees. He is already doing some rather different work, deriving the quantum correlations from informational and geometric axioms ...

 

[gill1109]

Now, there are nonlocal facts about the universe. In particular, it's topology can't be determined just by looking at little regions--it's a fact about how all the little regions are glued together to make a whole. On the other hand, since topology doesn't suddenly change in normal physics, topology is not a likely candidate for explaining nonlocal correlations. Contrary to what Joy Christian seems to believe, I don't think that you can use topology to violate Bell's inequality (unless you suppose a really weird topology, such as every point is connected to every other point).

If every point is connected to every other point ... this could be thought of as a violation of locality. A wormhole connecting Alice and Bob's measurement apparatus (or connecting the source with both their measurement devices) so that everything everywhere knows what is happening everywhere else... yes, that is a way you can explain the quantum correlations. Christian needs a random sign flip when transporting Alice's or Bob's outcome +/- 1 to a central location in order to calculate the correlation. Like a Möbius band. Nobody saw it happen before ...

 

[stevendaryl]

If every point is connected to every other point ... this could be thought of as a violation of locality. A wormhole connecting Alice and Bob's measurement apparatus (or connecting the source with both their measurement devices) so that everything everywhere knows what is happening everywhere else... yes, that is a way you can explain the quantum correlations. Christian needs a random sign flip when transporting Alice's or Bob's outcome +/- 1 to a central location in order to calculate the correlation. Like a Möbius band. Nobody saw it happen before ...

Well, a Mobius band seems to be an example of where topology can cause correlations to weaken with distance. On a Mobius strip, two objects initially with the same "handedness" will continue to have the same handedness if they stay close together, but if they get too far apart, their relative handedness can change.

That was actually one of my many objections to Christian's model. It seems to me that the difference between two different topologies--$R^3$ versus $S^3$, for example--would only come into play for experiments that take place over a large enough area. Localized experiments are not going to see a difference between the two. So it seems to me--without actually doing the calculations--that Christian's model couldn't possibly predict the same results as standard QM, that instead his model would predict a distance-dependency in the correlations where standard QM doesn't.

 

[bhobba]

Quantum mechanics is not in conflict with locality.

Hmmmm.

Certainly the cluster decomposition property is obeyed - but that only applies to non correlated systems. Correlated systems - well that's where the argument lies.

You can't use it to send information FTL - but that isn't quite the same as locality.

I personally believe QM violates both parts of naive reality - but that is just my view - you can have either - but not both.

Thanks
Bill