Is there any hope at all for Locality?

[bhobba]

I Guess if QM and Space-Time is emergent as several independent thinkers suggest: Nima Arkani-Hamed et al., Gerard 't Hooft and most recently Lee Smolin et al. then you could get a deterministic interpretation that isn't non-local *or* local because Space itself isn't fundamental.

These theorems only apply to QM. They may or may not apply to a theory from which QM emerges as classical mechanics emerges from QM. However it does seem highly unlikely a theory from which QM emerges would have local realism and QM not.

Thanks
Bill

 

[Quantumental]

But naturally as there is no Space in these proposals then I don't see the problem.

Realistic causality is still alive.

Think about it in terms of computer code. The code is deterministic and real, but talk of local/nonlocal makes no sense in that context. The Space of a simulation ran by this computer code isn't the most fundamental and non-local Things can occur in such a thing.I am beginning to agree with these intellectual giants more and more. QM just won't yield it's own interpretation. Ever. The attempts by Wallace et al. is as "hardcore" as it gets and they still don't got the born rule nor preferred basis solved

 

[meBigGuy]

QM just won't yield it's own interpretation. Ever. The attempts by Wallace et al. is as "hardcore" as it gets and they still don't got the born rule nor preferred basis solved

You are saying that QM as a science is just fine within any interpretation that is consistent with QM. All of the interpretations are a simply a search for a higher truth. That sounds trivial as I write it, but it's an important point, isn't it?

 

[harrylin]

Anyway, apart from bell inequalities there are other arguments confirming non-locality:

"Finally, our results demonstrate that one doesn’t need the “big guns” of Bell’s theorem to rule out locality for any theories in which ψ is given ontic status; more straightforward arguments suffice. Bell’s argument is only necessary to rule out locality for ψ-epistemic hidden variable theories."
http://arxiv.org/pdf/0706.2661v1.pdf
http://link.springer.com/article/10.1007/s10701-009-9347-0

.

Ehm no, it just means that "local realism" models cannot work if they model quantum states as reality itself instead of our knowledge of reality - that's basically the same issue.

"we show that for models wherein the quantum state has the status of something real, the failure of locality can be established through an argument considerably more straightforward than Bell’s theorem. [..] the same reasoning is present in Einstein’s preferred argument for incompleteness"

 

[harrylin]

I am with Dr Chinese on this.

All loopholes seem to be closed - local realistic theories are ruled out. Unless one comes up with a specific counter example like De Brogle-Bohm was with Von Neumann's proof then I think the evidence is far too overwhelming. And in Von Neumann's proof the error (it wasn't an error in the theorem per see - you do not expect a mathematician of Von Neumann's caliber to make errors in proofs - and he didn't - but a key assumption he made - namely for hidden variable theories the observable of a sum must be the sum of observables - it holds in the mean but not necessarily otherwise) was glaring if anyone had given it just a bit of thought - and it is a slight mystery why only a few people like Grette Hermann pointed it out. That does not apply here however- the current theorems have been given a HUGE amount of attention, so much so that I think one can assume they are as watertight as you can reasonably get.

Thanks
Bill

A theorem of physics necessarily includes the physical assumptions about the validity of the application of the mathematics. There is a number of professors in that field who published where exactly the error(s) are according to them. Those publications are far less in number than publications that accept the theorem, which is in part due to publication bias - for example, yesterday I learned that one such paper which I found in Arxiv and of which I would have liked a reviewed version to discuss here, wasn't accepted by Physical Review Letters because it lacks novelty! In other words, if already a few papers have been published that appear to disprove Bell's theorem then according to those editors, that should be enough for their readers (you).

 

[stevendaryl]

There is a number of professors in that field who published where exactly the error(s) are according to them. Those publications are far less in number than publications that accept the theorem, which is in part due to publication bias...

Yeah, there's a bias in scientific journals against bad papers. By far, the majority of the anti-Bell papers are mistaken. I think they all are, but I haven't read all of them.

 

[harrylin]

Yeah, there's a bias in scientific journals against bad papers. By far, the majority of the anti-Bell papers are mistaken. I think they all are, but I haven't read all of them.

That may certainly be part of the issue. However, as your comment on my words doesn't match what I wrote (exactly following the part that you cited): are you suggesting that those editors are dishonest, or did you misunderstand my explanation to Bill?

 

[f95toli]

A theorem of physics necessarily includes the physical assumptions about the validity of the application of the mathematics. There is a number of professors in that field who published where exactly the error(s) are according to them. Those publications are far less in number than publications that accept the theorem, which is in part due to publication bias - for example, yesterday I learned that one such paper which I found in Arxiv and of which I would have liked a reviewed version to discuss here, wasn't accepted by Physical Review Letters because it lacks novelty! In other words, if already a few papers have been published that appear to disprove Bell's theorem then according to those editors, that should be enough for their readers (you).

"Lack of novelty" usually means that there is not enough new ideas in the paper. If, for example, the paper is largelly based on ideas that have been published elsewhere then it won't get published in PRL. Nor will it get published if it is too similar to work that has been already been published by others.
The "novelty" criteria is much stricter in PRL than in most other journals (e.g. the other Physical Review journals will accept manuscripts that are "only" extentions or improvements of previously published results).

Hence, in order for a paper of this type to be accepted by PRL it would -even if it is correct- have to be based on a complettely new approach, which is somewhat unlikely considering how long Bell's theorem has been around.

 

[bhobba]

In other words, if already a few papers have been published that appear to disprove Bell's theorem then according to those editors, that should be enough for their readers (you).

Yea I get it. But what we really need, if Bells theorem is to be attacked, is a counter example like De Broglie-Bohm was to Von Neumann. Do you know of any? Without that I have a hard time believing there is an issue. And we also have Gleason's Theorem - it needs to evade that as well and be explicitly contextual. A tough ask.

Thanks
Bill

 

[harrylin]

"Lack of novelty" usually means that there is not enough new ideas in the paper. If, for example, the paper is largelly based on ideas that have been published elsewhere then it won't get published in PRL. Nor will it get published if it is too similar to work that has been already been published by others.
The "novelty" criteria is much stricter in PRL than in most other journals (e.g. the other Physical Review journals will accept manuscripts that are "only" extentions or improvements of previously published results).

Hence, in order for a paper of this type to be accepted by PRL it would -even if it is correct- have to be based on a complettely new approach, which is somewhat unlikely considering how long Bell's theorem has been around.

That's certainly correct, although I have the impression that quite some similar papers in support of Bell's interpretation have been published. And that same originality argument is used by many other journals.
As it appears that I was not clear enough, here once more: because of selection criteria that have nothing to do with the validity of the contents, the number of papers isn't a reliable measure of the validity of the arguments contained in them.

 

[harrylin]

Yea I get it. But what we really need, if Bells theorem is to be attacked, is a counter example like De Broglie-Bohm was to Von Neumann. Do you know of any? Without that I have a hard time believing there is an issue. And we also have Gleason's Theorem - it needs to evade that as well and be explicitly contextual. A tough ask.

Thanks
Bill

I'm looking into two approaches - the one is the Accardi approach already mentioned in this thread: try to disqualify the derivation by a counter derivation (now, did he or did he not??).

The other approach is a to come up with a simulation that does what is impossible according to Bell or Herbert; and I'm now examining a simulation that pretends to do just that. I'll present it here if it looks serious to me. As Nick Herbert's variant of Bell's theorem is the clearest of all, I'll try to modify it to exactly reflect Nick Herbert's presentation.

 

[DrChinese]

The other approach is a to come up with a simulation that does what is impossible according to Bell or Herbert; ...

The impact of Bell is that it tells us: "No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics."

You must have tried examples and seen for yourself WHY a simulation can't really do that. There are now hundreds if not thousands of Bell Inequalities to be considered as well! So coming up with a single simulation would not even come close to pointing the way to a theory. Don't confuse a simulation with a theory!

And no one can even hand pick a single example set that recreates the QM predictions without breaking the observer independence requirement of EPR - for even the most basic Bell Inequality.

Disproving Bell does not mean you find some error in his assumptions, definitions, logic, etc. It means showing us a physical theory of local hidden variables. If you want to know why papers are routinely rejected "disproving" Bell, it is because they completely ignore this element. It is a tough standard, but such is the scientific method.

The experimentalists developing new and more sophisticated entanglement experiments must be scratching their heads each time a new paper "proves" entanglement is an illusion (ie a spurious correlation).

 

[bohm2]

I Guess if QM and Space-Time is emergent as several independent thinkers suggest: Nima Arkani-Hamed et al., Gerard 't Hooft and most recently Lee Smolin et al. then you could get a deterministic interpretation that isn't non-local *or* local because Space itself isn't fundamental.

I find the idea that spacetime as emerging from a non-spatiotemporal structure (e.g. causal sets, etc.) interesting but there are authors that argue the idea of an emergent spacetime is incoherent:

While dynamical approaches to spacetime give priority to the dynamics over the geometry, it is not always clear in what sense they do so...Another, stronger sense of this idea that seems to be associated with dynamical approaches, is that not only the symmetries of the geometry but also the very concept of spacetime as a geometric structure can be fully derived from the dynamics without assuming geometric notions such as length or volume. We will argue that this stronger sense of deriving the geometry from the dynamics is untenable. At best one can show that the dynamics can be given a geometric interpretation. This, however, in our view does not amount to a strict derivation but rather to a sort of a consistency proof. Consistency proofs, however, are a far cry from ”derivations”, and so in this stronger sense it seems to us misleading to think about the geometry as ”emerging” from the dynamics alone.

The primacy of Geometry
http://mypage.iu.edu/~hagara/Geom.pdf

But I'm not sure I buy this argument. In some sense, I tend to agree with Gisin that non-locality itself may be suggesting to us that the universe at bottom, might not be "in" space and time. Other authors suggest the same thing:

that in some way spacetime as we find it in our existing theories is not a fundamental ingredient of the world, but instead, like rainbows, plants or people, `emerges' from some deeper, non-spatiotemporal physics.

The emergence of spacetime in quantum theories of gravity
http://philsci-archive.pitt.edu/9928/1/HuggettWuthrichIntro_06.pdf

I'm still confused, however, about the relationship between non-locality and spatio-temporality. Does non-locality itself imply non-spatio-temporality (as some like Gisin seem to imply) or does non-spatiotemporality preclude non-locality (that is, locality/non-locality make sense only if one assumes spatio-temporality)?

 

[audioloop]

I Guess if QM and Space-Time is emergent as several independent thinkers suggest: Nima Arkani-Hamed et al., Gerard 't Hooft and most recently Lee Smolin et al. then you could get a deterministic interpretation that isn't non-local *or* local because Space itself isn't fundamental.

It seems this is becoming the unavoidable conclusion for realists. We all know GR and QM is in trouble and the measurement problem has no satisfactory solution. Both may be solved by a deeper underlying theory.

Sure it seems radical, but no more radical than *any* other interpretation when you really think about it

as said gisin, order come from outside space-time.

 

[audioloop]

Ehm no, it just means that "local realism" models cannot work if they model quantum states as reality itself instead of our knowledge of reality - that's basically the same issue.

"we show that for models wherein the quantum state has the status of something real, the failure of locality can be established through an argument considerably more straightforward than Bell’s theorem. [..] the same reasoning is present in Einstein’s preferred argument for incompleteness"

thanks to repeat the post, consequently pray for an epistemic view...



.

 

[harrylin]

The impact of Bell is that it tells us: "No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics." [..] such is the scientific method [..]

It would be an awful lot of work to test all proposed models for all predictions. That would be needed to test full correspondence with QM, but it is not needed to test Bell's theorem or Herbert's proof. Instead, to test their proofs it suffices to test for the one or two predictions that according to Bell and Herbert cannot be reproduced. Such is the scientific method! Compare Popper

 

[stevendaryl]

It would be an awful lot of work to test all proposed models for all predictions.

I think that the twin-pair EPR experiment is good enough. Pretty much all the strangeness of quantum mechanics is captured by that one experiment. If there were a local realistic explanation for that, I think most people would find it believable that the rest of quantum mechanics could be explained along the same lines.

 

[DrChinese]

It would be an awful lot of work to test all proposed models for all predictions. That would be needed to test full correspondence with QM, but it is not needed to test Bell's theorem or Herbert's proof. Instead, to test their proofs it suffices to test for the one or two predictions that according to Bell and Herbert cannot be reproduced. Such is the scientific method! Compare Popper

Please note that the question is whether a local realistic theory can reproduce all of the predictions of QM. What good, may I ask, is one that is 50% correct (useful)? Sorry, that is the scientific method! You can't compare QM to such a theory and expect it to be taken seriously. And the reason this criteria is important is that most local realistic models start with unphysical assumptions that will obviously never fly. So they are DOA.

But as stevendaryl says, one successful prediction would be a good start. But there are none currently on the table. Again, for a simulation to be considered, it must postulate a hypothesis (mechanism) that will itself be subject to test. (Which again will almost certainly render it useless.)

-----------------------

Sometimes it is easy to forget where things started. EPR thought QM was an approximation to a better theory which would be both local and realistic. Bell essentially says that a local theory will not agree to QM in critical respects, specifically it cannot be context independent per EPR. In fact, even a non-local theory will not be context independent. Any way you look at it, for the entangled particle pair scenario to work, the nature of the measurement on Alice changes the statistics for Bob instantaneously and without regard to distance. No local model can account for that, obviously.

 

[RUTA]

Sometimes it is easy to forget where things started. EPR thought QM was an approximation to a better theory which would be both local and realistic. Bell essentially says that a local theory will not agree to QM in critical respects, specifically it cannot be context independent per EPR. In fact, even a non-local theory will not be context independent. Any way you look at it, for the entangled particle pair scenario to work, the nature of the measurement on Alice changes the statistics for Bob instantaneously and without regard to distance. No local model can account for that, obviously.

Time-symmetric views of QM are local and realistic because they exploit a loophole in Bell's theorem, i.e., they use information about detector settings to explain the correlations.

 

[bhobba]

Time-symmetric views of QM are local and realistic because they exploit a loophole in Bell's theorem, i.e., they use information about detector settings to explain the correlations.

I can't quite understand that. If you have 'influences' traveling back in time how can that be local? That means influences can effectively travel at any speed - even infinite.

Thanks
Bill

 

[bhobba]

EPR thought QM was an approximation to a better theory which would be both local and realistic. Bell essentially says that a local theory will not agree to QM in critical respects, specifically it cannot be context independent per EPR

That's an interesting view - and of course was Einsteins. It is often forgotten that Einstein after his debates with Bohr accepted QM as correct - but incomplete in the sense it was an approximation to a theory that conformed to his intuition. But being an approximation means it is not QM - but a theory from which QM emerges - a sub quantum theory. Such theories have been proposed eg Primary State Diffusion:
http://arxiv.org/pdf/quant-ph/9508021.pdf

Bells theorem applies to QM - it may or may not apply to a sub quantum theory. But I find it very hard to accept QM, being not local and realistic, can emerge from one that is.

Thanks
Bill

 

[RUTA]

I can't quite understand that. If you have 'influences' traveling back in time how can that be local? That means influences can effectively travel at any speed - even infinite.

Thanks
Bill

Non-local interactions are represented by space-like worldlines (superluminal speed). The causal paths in TSQM are time-like (subluminal speed).

 

[RUTA]

Bells theorem applies to QM - it may or may not apply to a sub quantum theory. But I find it very hard to accept QM, being not local and realistic, can emerge from one that is.

Thanks
Bill

QM is not necessarily non-local or non-realistic. In order for that to obtain, one must subscribe to all of the assumptions of Bell's theorem. One assumption of Bell's theorem is that future detector settings are not to be used in explaining the correlations. If you get rid of that assumption, then QM can be understood as local and realistic.

 

[bhobba]

Non-local interactions are represented by space-like worldlines (superluminal speed). The causal paths in TSQM are time-like (subluminal speed).

Hold on here. If future settings can influence the past, those influences are tachyon like traveling faster than light and hence non local.

I personally am not enamored with the transactional interpretation but local I think it aren't.

Thanks
Bill

 

[bhobba]

QM is not necessarily non-local or non-realistic. In order for that to obtain, one must subscribe to all of the assumptions of Bell's theorem. One assumption of Bell's theorem is that future detector settings are not to be used in explaining the correlations. If you get rid of that assumption, then QM can be understood as local and realistic.

If future settings influence the past that is explicitly FTL and non local.

Added Later:
From my recollection articles I read on the transactional interpretation always stated it must be non local, as from its assumptions it must be, unless my understanding of SR is somehow drastically mistaken (not out of the question though). So I hunted down an article on it:
http://www-users.york.ac.uk/~mijp1/transaction/TI_30.html
'With these goals in mind, we now present the transactional interpretation of quantum mechanics (TI). We will find that the TI, which is objective and explicitly nonlocal, satisfies each of these goals. It provides a description of the state vector as an actual wave physically present in real space. It provides a mechanism for the occurrence of nonlocal correlation effects through the use of advanced waves. The collapse of the state vector in the TI is the formation of a transaction which occurs by an exchange of retarded and advanced waves. The transaction model provides a way of clearly visualizing and developing intuition about the quantum phenomena which have remained mysterious and counter-intuitive for half a century.'

It must be - its based on the Wheller-Feynman model and that is well known and obviously nonlocal.

Thanks
Bill

 

[bohm2]

I can't quite understand that. If you have 'influences' traveling back in time how can that be local? That means influences can effectively travel at any speed - even infinite.

This link on fqxi may help:

Retrocausality gives a means to decompose that spooky non-local action into two local actions, the first one backwards in time," said Price. In other words, according to Price, the properties of the entangled particles are correlated backwards in time, from the point in spacetime where the measurement is made, to the point in spacetime where they become entangled, allowing the correct hidden variables to be encoded into the pair of particles. "In a case with retrocausality, the measurement that one observer makes affects her particle ‘backwards’ to the point where they are together," says Price. "There’s a zigzag path connecting the two particles through time and space and no need for instantaneous action at a distance.

Time to Go Retro
http://fqxi.org/community/articles/display/170

 

[RUTA]

If future settings influence the past that is explicitly FTL and non local.

Thanks
Bill

That's not correct. See the beable in Figure 5 of this paper for example http://arxiv.org/pdf/1001.5057v3.pdf

 

[bhobba]

This link on fqxi may help:

Even the article on the TI states it plainly - the TI is nonlocal - as it must be right from the very foundations of SR. If influences can travel back in time locality is broken. If its an issue for SR is another matter - if it can't be used to send information to sync clocks then SR remains intact. What the TI proposes is like that so its not an issue for SR - but locality goes down the tube.

Thanks
Bill

 

[bhobba]

That's not correct. See the beable in Figure 5 of this paper for example http://arxiv.org/pdf/1001.5057v3.pdf

Sorry - don't agree with you, and it is clearly and obviously nonlocal. Even the link I gave states it plainly - it is a nonlocal theory.

Added Later:
Something occurred to me. I am basing this on the Transactional Interpretation of QM - I believe RUTA is advocating the RBW interpretation which is different. But if it has the feature of detector settings affecting the past can't see how it is local. Perhaps he can explain the key difference - why is the Transactional nonlocal and the RBW isn't? That is if that's what's going on - if RUTA is talking about the Transactional Interpretation then I am bemuseed - the guy that put forth the interpretation clearly states its nonlocal.

Thanks
Bill

 

[harrylin]

Please note that the question is whether a local realistic theory can reproduce all of the predictions of QM. [..] .

That's not what I was talking about: I talked about testing Bell's and Herbert's proofs. That would be an essential step in the direction of answering the bigger question.

 

[bohm2]

Even the article on the TI states it plainly - the TI is nonlocal - as it must be right from the very foundations of SR. If influences can travel back in time locality is broken.

There are local and non-local retrocausal models, as I understand it. Yes, TI is stated as being non-local but Price's model is local and the differences are kind of glossed over in the article I posted previously, I think:

As we shall explain, the new argument shows that quantization makes a crucial difference. Time-symmetry alone doesn't guarantee that causation ever works backwards, but quantization gives us a new kind of influence, which -assuming time-symmetry- must work in both temporal directions. This new kind of influence is so subtle that it can evade spooky nonlocality, without giving us an even more spooky ability to send signals into the past. One of the striking things about the apparent action at a distance in quantum mechanics (QM) is that it, too, is subtle in just this way: there's no way to use it to build a "Bell Telephone", allowing superluminal communications. The argument hints how this subtlety might arise, as a consequence of quantization, from an underlying reality that smoothly links everything together, via pathways permitted by relativity...

As we noted earlier (see Box 1), there are several retrocausal proposals on the table. But some, like the Aharonov-Vaidman Two State proposal, or the earlier Transactional Interpretation, try to build their retrocausal models with the same kind of elements that Einstein objected to-wave functions not properly located in space and time. If we want to stay close to the spirit of Einstein's program, then, we'll need to start somewhere else.

Dispelling the Quantum Spooks-a Clue that Einstein Missed?
http://arxiv.org/pdf/1307.7744.pdf

So retrocausality does not imply non-locality nor superdeterminism, for that matter. See links.

 

[bhobba]

So retrocausality does not imply non-locality nor superdeterminism, for that matter. See links.

Even though I am heavily into math I am kind of a simple guy.

Would someone explain to me clearly, not linking to an article, but in clear language the subtlety here. Why is the TI nonlocal and what Ruta advocates isn't? Right from the foundations of SR if you have influences traveling back in time you break causality. The TI interpretation states it explicitly and logically, from the foundations of SR it must be so.

So exactly what is the difference - what is this very subtle point that makes this massive change in perspective and allows Bell to be violated. For if it's true, like De Brogle-Bohm was to Von Neumann we have a specific counter example to Bell - and I sense an immediate Nobel Prize in the wind.

Thanks
Bill

 

[wle]

I think that the twin-pair EPR experiment is good enough. Pretty much all the strangeness of quantum mechanics is captured by that one experiment. If there were a local realistic explanation for that, I think most people would find it believable that the rest of quantum mechanics could be explained along the same lines.

If you're talking specifically about EPR or EPR-Bohm correlations (as opposed to, say, CHSH-type correlations), then they don't violate any Bell inequality and it's a fairly simple exercise to come up with a toy local model that reproduces them.

 

[RUTA]

Sorry - don't agree with you, and it is clearly and obviously nonlocal. Even the link I gave states it plainly - it is a nonlocal theory.

Thanks
Bill

Did you look at Figure 5? Where are the space-like causal paths in that figure? Maybe you mean something else by nonlocal?

 

[RUTA]

Would someone explain to me clearly, not linking to an article, but in clear language the subtlety here. Why is the TI nonlocal and what Ruta advocates isn't? Right from the foundations of SR if you have influences traveling back in time you break causality. The TI interpretation states it explicitly and logically, from the foundations of SR it must be so.

Thanks
Bill

I don't think causality need be defined as you specify, but that's semantics. We're talking about locality here and by that I simply mean space-like causal influences.

Maybe you're thinking about the ambiguity of temporal ordering for space-like worldlines and conflating causality with locality in that sense? In other words, that A causes B when B precedes A in some frame means there must be a frame in which A precedes B, therefore A and B are space-like related and the causal connection is nonlocal.