Local realism ruled out? (was: Photon entanglement and )

[ThomasT]

Akhmeteli, I would prefer nonlocality. The reasons are simple. First, because the Bell theorem strongly suggests (I will not say proves) that the quantum world is nonlocal ...

Is Bell's theorem about the way the quantum world is, or is it about limitations on the formalization of entangled states?

 

[nikman]

As an aside, I went to Foundations of Physics for Zeh's most recently mentioned paper on his web-site, "Quantum discreteness is an illusion", which is not yet published but is available as an "online first" paper. The quality of the (69!) papers in the "online first" queue (that's probably 6 months ahead) shows signs of 't Hooft's tenure as editor starting to make a very big difference. The list of authors who have decided to publish at FoP is close to stellar.

One was gratified that 't Hooft published Suarez's "Nonlocal 'Realistic' Leggett Models" paper. It's hard to imagine two scientists with more starkly contrasting world-views than that pair.

http://www.springerlink.com/content/v5652005u01628h2/

or, for you members of the vast unfunded public, grab it gratis:

http://www.quantumphil.org/SuarezFOOP201R2.pdf

 

[yoda jedi]

Well, this way out works even if you replace the word "known" by the word "real". I am not saying here that reality is necessary or needed or desirable (nor I'm saying that it is not), but I AM saying that reality may be compatible with SR and nonlocality. Maybe there is no reality, but SR+nonlocality are not a valid argument against reality.

and in any case, the fact, that if there is no CFD, does not mean that there is no reality,
cos we can ask, what do you observe ? (or measure) its something, and then, something its reality.

same thing for suarez:
http://arxiv.org/PS_cache/arxiv/pdf/0705/0705.3974v1.pdf

.....Additionally, Bohm’s objective description can no longer be considered completely “realistic” since in experiments involving entangled polarized photon pairs neither of the two photons carries a definite polarization when it leaves the source....

 

[akhmeteli]

Akhmeteli, I would prefer nonlocality. The reasons are simple. First, because the Bell theorem strongly suggests (I will not say proves) that the quantum world is nonlocal, while experiments confirm the predictions of quantum mechanics. Second, because the wave function is a single mathematical object describing all particles at once, and nobody knows a reformulation of quantum mechanics in which this fact can be avoided. See also
http://xxx.lanl.gov/abs/quant-ph/0703071

Thank you for your answer. So it looks like you prefer nonlocality not because you like it more than locality, but because you think theory and experiment favor it. However, as I argued starting this thread, there are no no-go theorems or no-go experiments ruling out locality, so I don't have your reasons to favor nonlocality, and I regard it as a radical notion, and the burden of proof is very high for such radical ideas. As for the absence of a local reformulation of quantum mechanics, let me give you an example. For a quarter of a century after formulation of modern quantum mechanics, the de Broglie - Bohm interpretation, while existed (in the form offered by de Broglie), was dead, for all intents and purposes. Nevertheless, it was resuscitated by Bohm. And even now, as far as I know, there is no generally recognized relativistic form of this interpretation (actually, you told me that some time ago, and I don't think much has changed since then). But I guess you believe there will be such relativistic form in the future, and even have your own suggestions. So we don't know what can happen in the future. And I mentioned one possibility how a nonlocal theory can be a local theory in disguise.

So it started with your question: what's so special about locality. I gave you my reasons. Again, if there were some iron-clad no-go arguments, I would have to accept nonlocality. So far I see no reasons for that.

 

[Demystifier]

while the theory of relativity (including relativistic quantum field theory) requires dynamical locality ("Einstein locality").

You have a too narrow view of the concept of relativity. If by relativity one means only that the laws of physics do not depend on the choice of spacetime coordinates, then relativity does not require locality.

 

[Demystifier]

theory and experiment favor it. However, as I argued starting this thread, there are no no-go theorems or no-go experiments ruling out locality, so I don't have your reasons to favor nonlocality, and I regard it as a radical notion, and the burden of proof is very high for such radical ideas.

I still don't understand your logic. So I'll start with a question. Do you agree that theory and experiment favor nonlocality? (I'm not asking if they definitely prove it, because they don't. I'm only asking if they favor it.)

And I mentioned one possibility how a nonlocal theory can be a local theory in disguise.

If you mean your idea that a single charged particle guided by the wave function can be viewed as being guided by the electromagnetic potential (which is an interesting idea), then it has nothing to do with locality and nonlocality. To say anything about nonlocality, you must consider a system of at least two entangled particles.

 

[Maaneli]

If you mean your idea that a single charged particle guided by the wave function can be viewed as being guided by the electromagnetic potential (which is an interesting idea), then it has nothing to do with locality and nonlocality. To say anything about nonlocality, you must consider a system of at least two entangled particles.

I think Akhmeteli is referring to this claim in one of his prior posts:

... for pretty much any system A of (nonlinear) PDE in 3+1 dimensions one can construct a system of linear differential equations in the Fock space, which is equivalent to A on the set of solutions of A (see the outline of this result by Kowalski/Steeb in my post https://www.physicsforums.com/showpos...3&postcount=90 - some time ago I read about this result in nightlight's posts). That means that if quantum unitary evolution is successfully described by a linear system of equations in the Fock space (which is broader than any configuration space), you cannot be sure that system cannot be successfully replaced by a system of nonlinear equations in 3+1 dimensions. Therefore, you cannot be sure the system in the Fock space describes nonlocal reality.

 

[jambaugh]

You have a too narrow view of the concept of relativity. If by relativity one means only that the laws of physics do not depend on the choice of spacetime coordinates, then relativity does not require locality.

Not as such, of course. (Special) Relativity however sets the stage for the argument of local causality. If SR is valid and the light-cone is not a causal horizon then we have the potential of (not certainty of) constructing causal paradoxes. So absent local causality how are such paradoxes prohibited? If we actually (in our conceptual model of how nature works) allow causal feedback, future to past, it seems to me then we must invoke a "meta-time" over which such phenomena would decay out or reinforce to a caustic threshold or stable oscillation, (the local "reality" oscillating w.r.t. this meta-time). This was an attractive idea to me once, as e.g. a model for superposition and interference phenomena. But eventually I rejected it as fanciful and meaningless.

The problem as I see it is this sort of speculation is not operationally meaningful. It's no different than supposing an invisible aether, or Everette many worlds. Sure you can speculate but you can't test within the bounds of science. Such phenomena are by their nature beyond observation. Again I see the "reality" of it as meaningless within the context of science. That isn't an argument, just the results of my many internal arguments over past years.

What in the end do we mean by "reality"? Generally it is the reality of a universe of objects with always defined (though not always observed) objective properties or states of being.
Classically that is either the particles or the field quantities at each point of space.

Quantum mechanically we work in a language of phenomena, observables and observations and interactions between systems. I think it incorrect to objectify the mathematical constructs (esp. wave function=hilbert space vector). For that matter I think we should abandon the use of the Hilbert spaces all together except in the mathematics of constructing the Lie algebras and groups where the observables and dynamics are represented.

As to causal locality, that is easily enough described within QM and QFT via the structure of the dynamics. And it is easily enough tested both conceptually via though experiments, and in the lab. The only evidence I can conceive of, for true non-local causation is a classical FTL signal, e.g. a "Bell telephone". If you can't send a classical signal then you aren't talking about observable non-locality and thus speculating beyond the scope of science.

Now having said all that, I do think that if we're ever going to succeed at merging GR and QM we'll need to start with a "pre-local" theory. That is to say a theory of interacting quantum systems out of which condenses the macroscopic classical world. In which case I envision the local causality definition to be rather reversed. Nearness is ultimately defined by causal interactions and the causal structure of interacting systems ultimately defines the light-cones, and space-time metric structure. Objects are spatially close because they look close. This means they strongly interact with our eyes and our flashlights, or our radar antennas, or our fingers or sticks in our hands.

So ultimately I think causality will by definition be local because locality is ultimately based on causal interactions. At the microscopic quantum level this may break down, but not in the causal aspect, but rather the loss of meaning to geometry (and possibly even topology) at the small scale.

 

[nikman]

You have a too narrow view of the concept of relativity. If by relativity one means only that the laws of physics do not depend on the choice of spacetime coordinates, then relativity does not require locality.

You should really take that up with Herr Professor-Doktor Heinz-Dieter Zeh. I suspect he's making a deeper distinction relating to fundamental correlation and causality. Kinematics does of course rear its head in Relativity with the Lorentz contraction.

 

[RUTA]

Objects are spatially close because they look close. This means they strongly interact with our eyes and our flashlights, or our radar antennas, or our fingers or sticks in our hands.

It's possible to have a distant object be brighter than a closer object, e.g., the Sun is much brighter than this computer screen. Likewise the angle subtended by an object doesn't discriminate relative spatial distance. How do you envision relating distance and interaction? And, how do you see your approach giving a Lorentz invariant result, since it can't give a definite spatial separation and be Lorentz invariant?

 

[akhmeteli]

I still don't understand your logic. So I'll start with a question. Do you agree that theory and experiment favor nonlocality? (I'm not asking if they definitely prove it, because they don't. I'm only asking if they favor it.)

I will try to answer your question in the evening (Central time zone:-) )

If you mean your idea that a single charged particle guided by the wave function can be viewed as being guided by the electromagnetic potential (which is an interesting idea)

Thank you very much, I highly value your opinion.

, then it has nothing to do with locality and nonlocality. To say anything about nonlocality, you must consider a system of at least two entangled particles.

I agree, but Maaneli was right - I was not discussing my research, and I did have in mind my post #74 in this thread and the reference there.

 

[jambaugh]

It's possible to have a distant object be brighter than a closer object, e.g., the Sun is much brighter than this computer screen. Likewise the angle subtended by an object doesn't discriminate relative spatial distance. How do you envision relating distance and interaction? And, how do you see your approach giving a Lorentz invariant result, since it can't give a definite spatial separation and be Lorentz invariant?

It is the light which we feel and the light which is then by definition "close". Chains of propagating effect are the meter sticks (and the clocks) of our universe.

Then again the sun IS close in the frame near that of the propagating light, that is to say the events of emission and absorption are distance near zero given the single photon carrier of the propagating effect.

The sun is also intimately close on the scale of the other stars in the universe. But we can also see that on our scale it is big by how it effects so many other systems near us, the light reflecting off the moon, and the planets, their very orbits, tell us that the sun is both big and (relatively) near. Then the (also relative) distance of the sun is to an extent the ratio of its affect on us and the scale of its effect on things near and far to us. This I think is quantifiable at least to the point of ordering which gives us topological structure.

What after all is a measuring rod but a rigid solid, e.g. a condensate of strongly coupled component atoms. The lengths are essentially measured by counting blocks of those atoms and thus the number of interactional links between the ends of the rods.

As we refine our description of interacting phenomena we however (lately) replace the rigid measuring rod with light signals and clocks.

What then is a clock but a series of "tick" events each causing the next and being caused by the previous.

The nullness of space-time distance between emission-absorption events points to that as the elementary unit of measurement, the --by definition-- invariant phenomenon by which all others are given relative scale.

In formulating any operationally meaningful definitions in the context of science we start with the primaries of observations vis a vis causally interacting with one's environment. It is sensible then that all other concepts, including metric distance and time are derivative of causal connection. The mystery to be solved is rather the extent to which mutually interacting systems either accidentally or necessarily resolve themselves into the space-time-field structure we are able to perceive and map with our theories. In doing that I think causality is necessarily local in that localization is necessarily defined causally.

I cannot help but think rejecting local causality in order to preserve a notion of objective reality is backwards.

[EDIT: Ruta, I'm not sure I fully addressed your question. I haven't tried to make the idea formal and quantifiable. More heuristic as I've expressed above. Let me consider it for a bit and see if it can be given a more formal, rigorous encoding... possibly the attempt will show the idea invalid. It should be a useful exercise.]

 

[RUTA]

In formulating any operationally meaningful definitions in the context of science we start with the primaries of observations vis a vis causally interacting with one's environment. It is sensible then that all other concepts, including metric distance and time are derivative of causal connection. The mystery to be solved is rather the extent to which mutually interacting systems either accidentally or necessarily resolve themselves into the space-time-field structure we are able to perceive and map with our theories. In doing that I think causality is necessarily local in that localization is necessarily defined causally.

It seems difficult to define space and time using interacting systems because you need the concepts of space and time to make sense of what you mean by "systems" to begin the process. That is, what you mean by "a system" seems to require trans-temporal identification and to have "two systems" requires spatial separation -- what else would you use to discriminate between otherwise identical systems? That's why we chose a co-definition of space, time and sources (as understood in discrete QFT) as our fundamental operating principle. I look forward to your solution.

 

[akhmeteli]

I still don't understand your logic. So I'll start with a question. Do you agree that theory and experiment favor nonlocality? (I'm not asking if they definitely prove it, because they don't. I'm only asking if they favor it.)

I know that it is generally recognized that "theory and experiment favor nonlocality". But no, I am afraid I don't agree with that for reasons outlined in my post #1 in this thread.

 

[Demystifier]

I know that it is generally recognized that "theory and experiment favor nonlocality". But no, I am afraid I don't agree with that for reasons outlined in my post #1 in this thread.

Then my next question is: What WOULD you accept as a good argument for nonlocality? For example, if someone would make better detectors with higher efficiency such that the fair sampling loophole is avoided, and if the experiments would still violate Bell inequalities, would you accept THAT as a good evidence for nonlocality?

 

[Demystifier]

If we actually (in our conceptual model of how nature works) allow causal feedback, future to past, it seems to me then we must invoke a "meta-time" over which such phenomena would decay out or reinforce to a caustic threshold or stable oscillation, (the local "reality" oscillating w.r.t. this meta-time).

That's interesting, because my explicit Bohmian model of relativistic nonlocal reality does involve a "meta time".

The problem as I see it is this sort of speculation is not operationally meaningful. It's no different than supposing an invisible aether, or Everette many worlds. Sure you can speculate but you can't test within the bounds of science. Such phenomena are by their nature beyond observation. Again I see the "reality" of it as meaningless within the context of science. That isn't an argument, just the results of my many internal arguments over past years.

That objection can, of course, be also attributed to the nonrelativistic Bohmian interpretation that does not involve the "meta time".

 

[akhmeteli]

Then my next question is: What WOULD you accept as a good argument for nonlocality? For example, if someone would make better detectors with higher efficiency such that the fair sampling loophole is avoided, and if the experiments would still violate Bell inequalities, would you accept THAT as a good evidence for nonlocality?

Yes, that would certainly be a good evidence of nonlocality (I mean if violations of the genuine Bell inequalities, without loopholes, are demonstrated experimentally). In that case I would certainly have to reconsider my position. To be frank, I cannot promise I'll reject locality in that case and not free will, for example, but I will certainly have hard time trying to adapt to new reality. The problem is locality will not be the only thing I'll need to reconsider in that case. Such experimental demonstration would also undermine my firm belief in unitary evolution and relativity. And this is in fact the main reason I don't expect any violations of the genuine Bell inequalities.

To give a direct answer to your question "What WOULD I accept as a good argument for nonlocality?", I should also add that experimental demonstration of faster-than-light signaling would certainly be a much more direct and convincing evidence of nonlocality. But again, locality would not be the only casualty of such demonstration. Unitary evolution and relativity would also have hard time trying to survive.

 

[Demystifier]

Akhmeteli, that seems to be a reasonable answer. However, I think that nonlocality is compatible with relativity and unitary evolution. For more details see
https://www.physicsforums.com/showthread.php?t=354083
especially posts #1 and #109. I would like to see your opinion on that.

 

[DrChinese]

The problem is locality will not be the only thing I'll need to reconsider in that case. Such experimental demonstration would also undermine my firm belief in unitary evolution and relativity. And this is in fact the main reason I don't expect any violations of the genuine Bell inequalities.

First, Bell tests ARE genuine. I think you mean "loophole" free. All experiments have "loopholes", some are simply more relevant than others - and you are free to your personal opinion. But it is manifestly unfair to characterize the hundreds/thousands of different Bell tests themselves as "not genuine".

Second: that is quite a bold prediction you are making, not sure what would make you think that quantum mechanics is actually incorrect (an absolute deduction from your statement).

And last: why do you need to abandon relativity in the case of a confirmed (for you) violation of a Bell Inequality? The speed of light will still remain a constant in all local reference frames. Mass and clocks will still follow the standard rules. So what changes? The only thing that changes are physical effects not described by relativity in the first place. I do not consider relativity to include the absolute prediction that nonlocal elements cannot exist. I think it is an implied result, and one that could well fit within a larger theory. In fact, that is a result that Demystifier has been expressing for some time.

 

[jambaugh]

It seems difficult to define space and time using interacting systems because you need the concepts of space and time to make sense of what you mean by "systems" to begin the process. That is, what you mean by "a system" seems to require trans-temporal identification and to have "two systems" requires spatial separation -- what else would you use to discriminate between otherwise identical systems? That's why we chose a co-definition of space, time and sources (as understood in discrete QFT) as our fundamental operating principle. I look forward to your solution.

Well consider for example the entangled electron pair, totally anti-correlated . We typically factor the system into left-moving and right-moving particles (picking our orientation frame appropriately). And we then speak of entanglement of their spins. We could as easily speak of the up z-spin and the down z-spin particle. This is a distinct factorization of the composite system into "two particles". Another distinct factorization is into x-spin up vs down. Each is a different "reality" and the plurality of choices specifically shows our classical bias in thinking of the composite system as two objects. We should rather refer to "a factor" instead of "the component". (And I think equating different factorizations is the principle mistake in parsing the EPR experiment and other entangled systems.)

Now you may argue that spin is also a space-time concept but I could as easily used quark color instead of spin. More to the point, We may find it "difficult to define space and time using interacting systems because" We "need the concepts of space and time to make sense of what [We] mean by 'systems' to begin the process" due to our being space-time entities. That is to say it is a failing of our imagination and artifact of our nature not the universe itself.

Agreed initially we need a concept of time but it need not be metric, only topological and ordered to reflect causal sequence. I can then conceive of a large dimensional quantum system with a complicated random Hamiltonian. (reparametrizing time to make it t independent = pick a t-metric or class of metrics dictated by the dynamics.)

I can also conceive of factoring that system into N 2-dimensional components where 2^N is close to the dimension. Each 2-dim factor has its own U(2)~U(1)xSO(3) structure and I look at the global Hamiltonian and ask what form it takes in terms of internal plus interaction terms. I can then consider different choices of factorization which for the given Hamiltonian might simplify its form.

If I could find some way to formulate an iteration over cases and optimization principle (say minimum sum of component entropies, i.e. minimal entanglement, or otherwise some quantification of symmetry or near-symmetry of the Hamiltonian, or ...) then I might find a global su(2)xsu(2)~so(4) group [so(4) being the compact deformaton if iso(3) of the Euclidean group of spatial geometry. ] naturally emerges for random Hamiltonians under appropriate factorizations and as t increases sufficiently. In short a "natural" condensation into a 3-dimensional space as a spin network and with imperfections effecting e.g. gauge defects. Maybe with some arm-waving and invocation of anthropic principles I could reconstruct the universe in such a fashion.

The question is, for a random large quantum system, can we extrapolate how an entity within that system, able to develop science and formulate physics, would paint his universe. What is the range of possibilities?

I haven't yet of course and such a program may not be "the right way to go about it" (and indeed I can already see many problems) but it is an example of how one might go about constructing/determining spatial structure from scratch. It is not inconceivable to me.

 

[RUTA]

Well consider for example the entangled electron pair, totally anti-correlated. We typically factor the system into left-moving and right-moving particles (picking our orientation frame appropriately). And we then speak of entanglement of their spins. We could as easily speak of the up z-spin and the down z-spin particle. This is a distinct factorization of the composite system into "two particles". Another distinct factorization is into x-spin up vs down. Each is a different "reality" and the plurality of choices specifically shows our classical bias in thinking of the composite system as two objects. We should rather refer to "a factor" instead of "the component". (And I think equating different factorizations is the principle mistake in parsing the EPR experiment and other entangled systems.)

You've snuck spatiality in the backdoor -- you need two experimental outcomes, so you need two detectors. You don't need to talk about spatiality in the context of a "quantum system," but you do need those detectors. And, of course, you need to define what you mean by "up" and "down" outcomes in the context of those detectors. [In fact, we don't have any graphical counterpart to "quantum systems" in our approach.]

Now you may argue that spin is also a space-time concept but I could as easily used quark color instead of spin. More to the point, We may find it "difficult to define space and time using interacting systems because" We "need the concepts of space and time to make sense of what [We] mean by 'systems' to begin the process" due to our being space-time entities. That is to say it is a failing of our imagination and artifact of our nature not the universe itself.

Moving to charge doesn't help -- you need "some thing" to "possess" the charge, even if you attribute it to the detectors. So, again, how do you distinquish two such otherwise identical "things" without space?

Agreed initially we need a concept of time but it need not be metric, only topological and ordered to reflect causal sequence. I can then conceive of a large dimensional quantum system with a complicated random Hamiltonian. (reparametrizing time to make it t independent = pick a t-metric or class of metrics dictated by the dynamics.)

Exactly what we concluded, "time" is inextricably linked to what we mean by "things" (discrete QFT sources for us). This is topological not geometric as you say. Now are you going to argue that time is "special" in this sense over "space?" That is, we "need" a notion of temporality at the topological level but not space?

I can also conceive of factoring that system into N 2-dimensional components where 2^N is close to the dimension. Each 2-dim factor has its own U(2)~U(1)xSO(3) structure and I look at the global Hamiltonian and ask what form it takes in terms of internal plus interaction terms. I can then consider different choices of factorization which for the given Hamiltonian might simplify its form.

Interaction between ... ? Again, more than one "thing" will require some form of differentiation. Are you saying you will have a theoretical counterpart to every particle in the universe? That is, you can't talk about electrons, quarks, muons, ... in general?

I haven't yet of course and such a program may not be "the right way to go about it" (and indeed I can already see many problems) but it is an example of how one might go about constructing/determining spatial structure from scratch. It is not inconceivable to me.

I don't see, as I argue above, that you've succeeded even conceptually. You need the notions of identification and differentiation to have "things."

 

[akhmeteli]

Akhmeteli, that seems to be a reasonable answer. However, I think that nonlocality is compatible with relativity and unitary evolution. For more details see
https://www.physicsforums.com/showthread.php?t=354083
especially posts #1 and #109. I would like to see your opinion on that.

Dear Demystifier,

I did not say that "nonlocality is incompatible with relativity and unitary evolution". Indeed, tachyons are thinkable. However, it seems to me that relativity and unitary evolution in their current form leave little space for nonlocality. I remember studying quantum field theory many years ago. The lecturer was Professor Shirkov. Of course, we used his well-known book (N N Bogolyubov and D V Shirkov, `Introduction to the Theory of Quantized Fields'). One of the basic principles used in that book was microcausality. So I tend to believe nonlocality would lead to completely different forms of unitary evolution and relativity (for example, one of such new form may require tachyons). Explicit or implicit faster-than-light signaling does not follow from the current form of unitary evolution and relativity. To get such nonlocality in the Bell theorem you need something extra - such as the projection postulate. And this postulate generates nonlocality in a very direct way: indeed, according to this postulate, as soon as you measure a projection of spin of one particle of a singlet, the value of the projection of spin of the other particle immediately becomes determined, no matter how far from each other the particles are, and this is what the Bell theorem is about..

I looked at the references you gave. Again, I agree that unitary evolution and relativity, strictly speaking, do not eliminate nonlocality. However I wanted to ask you something. If I am not mistaken, you mentioned recently that Bohm's theory is superdeterministic.That seems reasonable. Furthermore, maybe unitary evolution is also, strictly speaking, superdeterministic. Indeed, it can include all observers and instruments, at least in principle. So my question is: What does this mean for nonlocality of Bohm's theory?

 

[yoda jedi]

Akhmeteli, that seems to be a reasonable answer. However, I think that
nonlocality is compatible with relativity and unitary evolution.
For more details see
https://www.physicsforums.com/showthread.php?t=354083

i think the same.

http://arxiv.org/PS_cache/arxiv/pdf/0912/0912.0177v1.pdf

specifically:

Tumulka:
http://arxiv.org/PS_cache/quant-ph/pdf/0406/0406094v2.pdf
and
http://arxiv.org/PS_cache/quant-ph/pdf/0602/0602208v2.pdf




Bedingham:
http://arxiv.org/PS_cache/arxiv/pdf/0907/0907.2327v1.pdf

 

[ThomasT]

... if someone would make better detectors with higher efficiency such that the fair sampling loophole is avoided, and if the experiments would still violate Bell inequalities, would you accept THAT as a good evidence for nonlocality?

No, of course not.

I asked in a previous post:

Is Bell's theorem about the way the quantum world is, or is it about limitations on the formalization of entangled states?

The formalism is in effect modelling, and must be compatible with, the experimental design(s) that it's associated with.

Quantum nonseparability, vis the SQM representation, has to do with the nonfactorability of entangled state representations, which reflects the necessary statistical dependency between A and B -- not some property of the underlying quantum world.

The predictions of Bell LHV models (characterized by their incorporation of the Bell locality condition, ie. factorability of the joint entangled state representation) don't fully agree with experimental results precisely because these models are incompatible with the salient feature of experiments designed to produce entanglement, namely statistical dependence between A and B.

And, the statistical dependence between A and B is produced solely vis the local transmissions and interactions involved in the pairing process.

So, the incompatibility of Bell LHV models with SQM and the experimental violation of Bell inequalities has nothing to do with nonlocality in Nature.

It might also be noted that calling SQM a local or nonlocal theory (whether due to Bell associated considerations or some interpretation of the formalism by itself) is more obfuscating than enlightening.

 

[jambaugh]

RUTA,
As we seem to have moved into an independent conversation I thought it would be appropriate to move to a new thread. I took the liberty of creating one:

https://www.physicsforums.com/showthread.php?p=2562136#post2562136"

I posted there a reply to your last post.

 

[jambaugh]

That's interesting, because my explicit Bohmian model of relativistic nonlocal reality does involve a "meta time".
...
That objection can, of course, be also attributed to the nonrelativistic Bohmian interpretation that does not involve the "meta time".

Yes I can see how the presence/absence of a meta-time would fit in and I don't object to its invocation per se. I see e.g. BI (and MW) not so much as an interpretation as it is a model given as I argue it is invoking non-operational components.

Thus if one were to simply drop the word "interpretation" from BI I'd be all for it.

Acknowledged as such, I think Bohmian QM could be a nice tool comparable to e.g. treating space-time as a dynamic manifold with its own meta-time and meta-dynamics to which it must relax to a stationary state yielding a solution of Einstein's equations. I don't have to assert the "reality" of extra dimensions or that meta-time in which space-time is embedded to use the model as a tool for calculation and enumeration of cases.

But I find "reality" is inherently a classical concept, and indeed the epitome of classical-ness. I see trying to hold onto the "reality" part of the negated local reality as regressive. (and should be replaced with non-objective "actuality".) That's a somewhat intuitive judgment of course but I believe based on good heuristic principles.

 

[ThomasT]

Yes, that would certainly be a good evidence of nonlocality (I mean if violations of the genuine Bell inequalities, without loopholes, are demonstrated experimentally).

Experimental loopholes have nothing to do with it. Bell's LHV ansatz is incompatible with QM, because QM, a statistical theory, correctly models the statistical dependency between A and B of the entangled state (vis nonfactorability of the joint state representation) while Bell's formulation doesn't.

To get such nonlocality in the Bell theorem you need something extra - such as the projection postulate. And this postulate generates nonlocality in a very direct way: indeed, according to this postulate, as soon as you measure a projection of spin of one particle of a singlet, the value of the projection of spin of the other particle immediately becomes determined, no matter how far from each other the particles are, and this is what the Bell theorem is about..

The assumption underlying the projection postulate is that what is being jointly analyzed at A and B during the same coincidence interval is the same thing. Where's the nonlocality?

 

[akhmeteli]

First, Bell tests ARE genuine. I think you mean "loophole" free. All experiments have "loopholes", some are simply more relevant than others - and you are free to your personal opinion. But it is manifestly unfair to characterize the hundreds/thousands of different Bell tests themselves as "not genuine".

Thank you for your comments.

I did not say the tests were not genuine. I just did not say that. However, the Bell inequalities violated in those tests were not genuine, i.e. those defined in the Bell theorem, because either they were doctored using the fair sampling assumption or the spatial separation was not sufficient. So I insist that genuine Bell inequalities were not violated in those experiments, and this is not just my opinion, this is mainstream (I admit that, strictly speaking, there is no consensus on that as you strongly disagree:-) )

Second: that is quite a bold prediction you are making, not sure what would make you think that quantum mechanics is actually incorrect (an absolute deduction from your statement).

What makes me think that is the fact that unitary evolution and the projection postulate contradict each other, so they cannot be both correct.

And last: why do you need to abandon relativity in the case of a confirmed (for you) violation of a Bell Inequality? The speed of light will still remain a constant in all local reference frames. Mass and clocks will still follow the standard rules. So what changes? The only thing that changes are physical effects not described by relativity in the first place. I do not consider relativity to include the absolute prediction that nonlocal elements cannot exist. I think it is an implied result, and one that could well fit within a larger theory. In fact, that is a result that Demystifier has been expressing for some time.

I answered this question replying to Demystifier. In brief, I admit that relativity and nonlocality, strictly speaking, are not incompatible, but I tend to believe that relativity and unitary evolution in their current form do not suggest nonlocality.

 

[akhmeteli]

i think the same.

Please see my answers to Demystifier and DrChinese

 

[akhmeteli]

Experimental loopholes have nothing to do with it. Bell's LHV ansatz is incompatible with QM, because QM, a statistical theory, correctly models the statistical dependency between A and B of the entangled state (vis nonfactorability of the joint state representation) while Bell's formulation doesn't.

The assumption underlying the projection postulate is that what is being jointly analyzed at A and B during the same coincidence interval is the same thing. Where's the nonlocality?

Dear ThomasT,

I am awfully sorry, I've read your post several times, but I just cannot understand a word.