Alternatives to quantum nonlocality
The EPR correlations in quantum mechanics are a strong evidence that nature is nonlocal. Yet, many physicists don't like nonlocality and attempt to construct interpretations of QM that avoid nonlocality. All such attempts introduce something rather strange (perhaps much stranger than nonlocality itself), but neither of such possibilities should be rejected automatically.
In this blog I give a list of some of such alternatives to nonlocality. I don't give references (except for the most recent one introduced by myself a few days ago):
- Copenhagen - nature is local, but objective reality does not exist (Bohr, Mermin, Rovelli-relational, Zeilinger, ...)
- many worlds - objective reality exists and is "local", but not in the 3-space (Everett, Deutsch, Tegmark, ...)
- superdeterminism - objective reality exists, it is local and deterministic, but initial conditions are fine tuned ('t Hooft)
- backward causation - objective reality exists and is local, but there are signals backwards in time (transactional interpretation)
- noncommutative hidden variables - objective reality exists and is local, but is not represented by commutative numbers (Joy Christian)
- solipsistic hidden variables - objective reality exists and is local, but objective reality describes only the observers, not the observed objects (H. Nikolic, http://xxx.lanl.gov/abs/1112.2034 )
If I missed to mention some (local) approach, please add it to the list!
In this blog I give a list of some of such alternatives to nonlocality. I don't give references (except for the most recent one introduced by myself a few days ago):
- Copenhagen - nature is local, but objective reality does not exist (Bohr, Mermin, Rovelli-relational, Zeilinger, ...)
- many worlds - objective reality exists and is "local", but not in the 3-space (Everett, Deutsch, Tegmark, ...)
- superdeterminism - objective reality exists, it is local and deterministic, but initial conditions are fine tuned ('t Hooft)
- backward causation - objective reality exists and is local, but there are signals backwards in time (transactional interpretation)
- noncommutative hidden variables - objective reality exists and is local, but is not represented by commutative numbers (Joy Christian)
- solipsistic hidden variables - objective reality exists and is local, but objective reality describes only the observers, not the observed objects (H. Nikolic, http://xxx.lanl.gov/abs/1112.2034 )
If I missed to mention some (local) approach, please add it to the list!
Total Comments 11
Comments
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Not sure if this one is on the list but there's this local theory by Travis Norsen:
The Theory of (Exclusively) Local Beables
http://lanl.arxiv.org/PS_cache/arxiv...909.4553v3.pdfPosted Dec29-11 at 04:29 PM by bohm2 
Updated Dec30-11 at 02:18 AM by bohm2 -
The Norsen's theory is not a local theory, as he himself explained to me at one occasion.
Namely, the theory is "local" only in the sense that the wave function in the configuration space is eliminated. But it is still nonlocal in the sense that there is an instantaneous action at a distance between the particles.Posted Dec30-11 at 08:07 AM by Demystifier
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If I am reading this right, then MWI only have trouble explaining the Born rule? I was under the impression that it also suffered from the"nonlocality" of all other realist interpretations....
Posted Jan5-12 at 06:54 PM by NumeroUno
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I would agree that the Born rule is the only serious trouble with MWI. Some hold the opinion that the non-existence of reality in the 3-space is even a more serious trouble, but I don't agree with such an opinion.
Posted Jan16-12 at 03:14 AM by Demystifier
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- consistent histories - objective reality exists and is local, but classical propositional logic is replaced with a different logic (Griffiths, http://lanl.arxiv.org/abs/1110.0974, http://lanl.arxiv.org/abs/1105.3932 )
Posted Jan16-12 at 09:02 AM by Demystifier
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I would like to mention my local theory based on elimination of matter field from the equations of electrodynamics and interpretation of the configuration space as an artifact of Carleman linearization - Int'l Journ. Quantum Inf., v.9, Supplement (2011), p. 17 (http://www.akhmeteli.org/akh-prepr-ws-ijqi2.pdf ). See also J. Math. Phys., v.52, p. 082303 (2011) (http://akhmeteli.org/wp-content/uplo...28082303_1.pdf ) and later preprints.
Posted Jan23-12 at 08:17 AM by akhmeteli
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Akhmeteli, can you be so self-critical to point out the major "but" of your approach? As you can see, I have given such a "but" for all the approaches I've mentioned, including my own.
For example, from Sec. 5 of the first paper I suspect that the major "but" of your approach could be the following:
... but the theory, unlike QM, predicts that Bell inequalities cannot be violated, provided that both the detection and the communication loopholes are closed.
Would that be correct?
Or, from the end of Sec. 4:
"... (but) it remains to be seen whether (the theory is) compatible with experimental data ..."Posted Jan24-12 at 03:15 AM by Demystifier
Updated Jan24-12 at 03:47 AM by Demystifier -
Dear Demystifier,Quote:Quote by Demystifier
Akhmeteli, can you be so self-critical to point out the major "but" of your approach? As you can see, I have given such a "but" for all the approaches I've mentioned, including my own.
For example, from Sec. 5 of the first paper I suspect that the major "but" of your approach could be the following:[*]... but the theory, unlike QM, predicts that Bell inequalities cannot be violated, provided that both the detection and the communication loopholes are closed.[*]
Would that be correct?
Thank you very much for your comments.
Your statement that I marked with[*][*] is certainly correct. However, I am not sure this is indeed a “but” (let alone “major “but””) of the approach, if “but” means a “drawback”. On the one hand, this prediction has not been proven wrong experimentally so far, as there have been no loophole-free experiments. On the other hand, the proof of violation of the Bell inequalities in QM uses mutually contradictory assumptions: unitary evolution and projection postulate.
Yes, this is certainly a major drawback of the current status of the approach. I’d like to emphasize, however, that an awful lot of experimental data is already described correctly in this approach, as it fully incorporates such realistic models as scalar electrodynamics or spinor electrodynamics. It is not clear though that higher orders of QED are emulated correctly in this approach. Maybe some modifications will be needed to achieve this goal.Quote:Quote by DemystifierOr, from the end of Sec. 4:
"... (but) it remains to be seen whether (the theory is) compatible with experimental data ..."Posted Jan24-12 at 09:11 AM by akhmeteli
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A recent review
http://www.scholarpedia.org/article/Bell's_theorem
presents good arguments against some of the alternatives to quantum nonlocality. Here I quote some highlights from it:
If one's criteria for accepting a sentence as being meaningful lead to the conclusion that any sentences that talk about "elements of physical reality" are meaningless then, according to such criteria, the relevant notion of locality for Bell's theorem (and thus Bell's theorem itself) becomes meaningless. Those who hold that position will avoid concluding that the quantum predictions imply non-locality, but they will also avoid the conclusion that the quantum predictions are compatible with locality! So refusing to talk about elements of reality is not a strategy by which one can defend the locality of quantum theory.
While classical mechanics is a physical theory which has been shown to be not empirically viable, classical probability theory and classical logic are methods of reasoning and cannot be tested empirically: such reasoning tools are what we use in order to draw conclusions from experiments so that we can decide which physical theories are or are not compatible with the results of those experiments.
The locality condition for the Lagrangian, local commutativity and the impossibility of superluminal signalling are all, of course, conditions that are related to the concept of locality that is relevant for Bell's theorem. But they are not equivalent to it.
The fact that non-locality does not imply the possibility of superluminal signalling might appear particularly surprising; this fact will seem less surprising, however, if one keeps in mind that the concept of superluminal signalling involves anthropocentric notions such as controllability and observability that play no role in the concept of locality. In simpler words, the possibility of superluminal signalling is not just non-locality, it is a form of controllable non-locality.
Thus, in CH [Consistent Histories], a "quantum measurement" is really supposed to be a measurement, simply revealing the pre-existing value of the measured observable; it is not the interaction with the apparatus that creates the observed value. That sounds a lot like a non-contextual hidden variables theory, which, as we now know, must lead to inconsistencies with the quantum predictions. ... The proponents of CH ... have imposed a rule which says essentially that arguments involving probabilities for several histories, not all of which belong to the same decoherent family, are forbidden. ... By forbidding the reasoning used to prove inequality (1), the aforementioned rule of CH prevents us from arriving at the contradiction. But a physical theory is not simply a game for which one can impose arbitrary rules about what reasonings are permitted for the propositions of the theory; if a physical theory implies both P and Q then the logical consequences of both P and Q will hold in a world governed by that theory and there is nothing that the proponents of the theory can do to prevent that. One might try to find an actual objection against the reasoning leading to inequality (1), but one cannot simply state as a "rule" that the reasoning is forbidden. ... We suspect that the proponents of CH would object to the proof of inequality (1) (within CH) by claiming that one cannot assume that all the random variables Zαi are defined over the same probability space because on each run of the experiment the value of only one among the Zα1 and the value of only one among the Zα2 is going to be observed. But if the experiments merely reveal pre-existing values then, on each run of the experiment, all the variables Zαi have a well-defined value (which may or may not turn out to be observed). ... The objection against the possibility of modeling the Zαi as random variables on the same probability space is effective only when one takes their values to be created by the experiments ... But reinterpreted in terms of values being created by experiment, CH would be pointless — it would just be orthodox quantum theory.Posted Apr4-12 at 10:21 AM by Demystifier
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I would like to comment about "backward causation"
It does not seem to provide valid explanation but the reason as I see it is quite subtle. The problem is not that we can't analyse things as "caused backwards" but that we can't combine backward and forward causation in the same analysis.
Basically we have to transform everything into forward causation picture or everything into backward causation picture. Like in special relativity we do not mix reference frames in analysis.Posted Jun19-12 at 12:02 PM by zonde
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In a way we are now in a similar situation as around 1900. As you mentioned Joy Christian's approach, I like to add the following "local" approach by De Raedt et al which looks similar but is quite different (and I hope that I fairly describe their point of view):
Bell's theorem doesn't (and can't) fully account for all the possibilities of physical reality, even if one assumes that QM makes correct statistical predictions for realistic situations.
Their main approach is to pragmatically create "local-realistic" simulation software that increasingly matches observations (Lorentz-style "work in progress", and it's not yet 1904!).Posted Sep22-12 at 07:30 AM by harrylin
Updated Sep22-12 at 08:08 AM by harrylin (improve phrasing; shorten)
