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

[yoda jedi]

why the glue ?

LOCAL REALISM ruled out?

"which concept, locality or realism, is the problem?"

i understand, is a type of realism (are jointly false).
a realism that is local.

cos the real, observed or not, exist.









-------------------
Bell inequalities are based on poincare relativity, have to be seen what happen in a sitter relativity.

 

[Demystifier]

Generally, Bell says:
No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

It is important to understand the assumptions under which the Bell theorem is obtained. As stressed, e.g., in
http://xxx.lanl.gov/pdf/quant-ph/0702225 [Rev. Mod. Phys. Vol. 81, No. 2, pp. 865-942 (2009)]
page 3, the assumptions are:
(i) realism
(ii) locality
(iii) free will
The theorem says that QM violates at least one of these 3 assumptions.

In particular, it is possible to retain both realism and locality if you give up free will. That's the idea of superdeterminism. The problem with that option is that it is very difficult to construct an explicit local-realistic model that has the same predictions as QM. ('t Hooft has attempts in this direction, but I don't think that these attempts are very successfull.)

On the other hand, if you give up locality, then it is easy to construct a nonlocal-realistic model consistent with QM. The simplest known model of that sort is Bohmian mechanics, which also turns out to be a superdeterministic model (no free will).

 

[Demystifier]

The http://arxiv.org/abs/0908.3408" won't be ruled out anytime soon.

Indeed. In fact, probably it will never be ruled out.

 

[Demystifier]

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

 

[DrChinese]

Indeed. In fact, probably it will never be ruled out.

And indeed, it is a loophole for all physical theories, not just quantum mechanics. Relativity, evolution, big bang... all can be equally well explained by superdeterminism. With a mere wave of the hand, at that!

 

[ThomasT]

It is important to understand the assumptions under which the Bell theorem is obtained. As stressed, e.g., in
http://xxx.lanl.gov/pdf/quant-ph/0702225 [Rev. Mod. Phys. Vol. 81, No. 2, pp. 865-942 (2009)]
page 3, the assumptions are:
(i) realism
(ii) locality
(iii) free will
The theorem says that QM violates at least one of these 3 assumptions.

I don't think this is the clearest (read: correct) way to talk about what Bell's theorem means.

In particular, it is possible to retain both realism and locality if you give up free will. That's the idea of superdeterminism.

Superdeterminism and free will have nothing to do with it. It just has to do with the formal expression of locality.

The problem with that option is that it is very difficult to construct an explicit local-realistic model that has the same predictions as QM. ('t Hooft has attempts in this direction, but I don't think that these attempts are very successfull.)

Bell advanced a certain generic formulation for LHV models of quantum entangled states whose salient formal characteristic was assumed to be necessary for any LHV model of a quantum entangled state.

But that has by no means been proven to be the case.

The current state of affairs is that there's no formal expression of locality that is compatible with entanglement experimental designs and the salient feature of SQM formalization of entangled states (nonseparability or nonfactorability). Does 't Hooft's match all the precictions of SQM? Is it explicitly local?

A successful LHV model of entangled states can't be rendered in the straightforward factorable form proffered by Bell, because this alone contradicts a necessary condition of entanglement experiments which is the statistical interdependency of Alice's and Bob's results (outcome dependence) -- ie., Bell's locality condition is ambiguous.

On the other hand, if you give up locality, then it is easy to construct a nonlocal-realistic model consistent with QM. The simplest known model of that sort is Bohmian mechanics, which also turns out to be a superdeterministic model (no free will).

What's so realistic about the quantum potential and instantaneous action-at-a-distance?

Besides, there's no reason to give up locality.

So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists?

Because of Bell?

Why nonlocality seems so difficult or weird to them?

It has no empirical foundation. Just an easy explanation for entanglement corrolations.

 

[MaxwellsDemon]

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

I think locality is valued for a couple different reasons:

1. Simplicity, the assumption of locality makes calculations easier. For example, you can describe the physics of a game of billiards without having to worry about whether the planet Jupiter is moving through the constellation Gemini. You don't have to consider the effect of some ancient dinosaur's sneeze in your calculation when figuring out what force you should hit the 8 ball with.

2. Reductionism. Reductionism is the idea that you can completely describe the whole in terms of its parts and their interactions. Non-locality would be bad news for reductionism I think. (I can elaborate on why I suspect that if you would like...) Since reductionism seems to be the paradigm favored in modern science, an abandonment of locality would be distasteful to most.

 

[akhmeteli]

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

I have been trying to avoid answering this question, but I guess your post was the last straw:-)

First, why was I reluctant to answer (of course, I cannot answer for other people)? Because, as long as there are no clear-cut theoretical or experimental reasons to reject locality (and I don't believe there are such reasons), this is a matter of personal preferences, maybe philosophical views, which a) take a long time to outline and b) are not very appropriate for this forum. So I'll try to stick to physical reasoning. I believe relativity strongly favors locality, and partial differential equations, which are all-pervading in physics, also favor locality. The absense of faster-than-light signaling also tends to suggest locality.

However, this is still a matter of preferences, so let me ask you, all other things equal, would you prefer a local theory, or a nonlocal one?

 

[DrChinese]

I think locality is valued for a couple different reasons:

1. Simplicity, the assumption of locality makes calculations easier. For example, you can describe the physics of a game of billiards without having to worry about whether the planet Jupiter is moving through the constellation Gemini. You don't have to consider the effect of some ancient dinosaur's sneeze in your calculation when figuring out what force you should hit the 8 ball with.

2. Reductionism. Reductionism is the idea that you can completely describe the whole in terms of its parts and their interactions. Non-locality would be bad news for reductionism I think. (I can elaborate on why I suspect that if you would like...) Since reductionism seems to be the paradigm favored in modern science, an abandonment of locality would be distasteful to most.

You don't need to change your calculations as is, Demystifier has tried to show this on many occasions. So that doesn't seem a fair critique. And if you did need to change them, that would actually be a near-proof of non-locality.

As to reductionism, the alternative is to abandon realism (which I am personally OK with). So that is probably equally distasteful if it comes down to taste.

 

[RUTA]

However, this is still a matter of preferences, so let me ask you, all other things equal, would you prefer a local theory, or a nonlocal one?

Causally local, constitutively non-local, i.e., non-separable.

 

[MaxwellsDemon]

Special Relativity is certainly local, but I would argue that General Relativity is not. In GR, the geometry is a global description, not a local one. Locally the geometry is flat, its only on a large scale that spacetime curvature comes into play. I would think that the principle of general covariance (where all “regular” derivatives in local laws are replaced with covariant derivatives when talking about large scale phenomena) is where this difference is most apparent. The covariant derivative still applies locally, but the extra term added in is dependent on the overall geometry. The curvature is something extra that requires a knowledge of the energy-momentum distribution in a region that goes beyond simply knowing the distribution in the here and now. The fact that we have to change our calculations in GR depending on the global geometric features of a region suggests to me that it is locality that needs to be abandoned. To me, abandoning realism is far more distasteful anyway. I prefer to think that concepts like position and momentum aren’t just ideas I have about nature, or biases from my human way of thinking, but that they have some objective foundation in reality. Even if they don’t exist exactly as I conceive of them, I’d like to think that a concrete objective phenomenon can be related to my ideas in some way. Color and temperature don’t exist as I perceive them, but there are still well defined objective things like wavelengths of light and atomic vibrations that can be related to my sensory experiences.

 

[Demystifier]

and partial differential equations, which are all-pervading in physics, also favor locality.

Schrodinger equation for two particles is a partial differential equation, so it is local but in the (6+1)-dimensional CONFIGURATION space, not in the ordinary (3+1)-dimensional space. This is exactly why QM is nonlocal (or nonseparable to be more precise) in the ordinary space, even though it is described by a partial differential equation. You may say that the world is still local, but then you must also say that the world contains a huge number of dimensions (3 new space dimensions for each particle). Does such a multi-dimensional local world makes you more happy?

 

[Demystifier]

And indeed, it is a loophole for all physical theories, not just quantum mechanics. Relativity, evolution, big bang... all can be equally well explained by superdeterminism. With a mere wave of the hand, at that!

Exactly.

 

[akhmeteli]

Schrodinger equation for two particles is a partial differential equation, so it is local but in the (6+1)-dimensional CONFIGURATION space, not in the ordinary (3+1)-dimensional space. This is exactly why QM is nonlocal (or nonseparable to be more precise) in the ordinary space, even though it is described by a partial differential equation. You may say that the world is still local, but then you must also say that the world contains a huge number of dimensions (3 new space dimensions for each particle). Does such a multi-dimensional local world makes you more happy?

First, I said PDE favor locality, not dictate it.

Second, we don't know what the final theory will look like: according to your papers and our previous discussions, you don't even believe all predictions of quantum theory will be confirmed experimentally.

Third, 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/showpost.php?p=1825523&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.

And I would very much appreciate your answer to my question: everything els being equal, would you prefer a local theory, or a nonlocal one?

 

[yoda jedi]

Can you be more specific?

have not a unified dynamics for microscopic and macroscopic systems.
its physically incomplete.

 

[RUTA]

Special Relativity is certainly local, but I would argue that General Relativity is not. In GR, the geometry is a global description, not a local one. Locally the geometry is flat, its only on a large scale that spacetime curvature comes into play. I would think that the principle of general covariance (where all “regular” derivatives in local laws are replaced with covariant derivatives when talking about large scale phenomena) is where this difference is most apparent. The covariant derivative still applies locally, but the extra term added in is dependent on the overall geometry. The curvature is something extra that requires a knowledge of the energy-momentum distribution in a region that goes beyond simply knowing the distribution in the here and now. The fact that we have to change our calculations in GR depending on the global geometric features of a region suggests to me that it is locality that needs to be abandoned. To me, abandoning realism is far more distasteful anyway. I prefer to think that concepts like position and momentum aren’t just ideas I have about nature, or biases from my human way of thinking, but that they have some objective foundation in reality. Even if they don’t exist exactly as I conceive of them, I’d like to think that a concrete objective phenomenon can be related to my ideas in some way. Color and temperature don’t exist as I perceive them, but there are still well defined objective things like wavelengths of light and atomic vibrations that can be related to my sensory experiences.

First, it looks like you’ve conflated causal and constitutive locality. Your argument for the “nonlocality” of the covariant derivative is of the constitutive variety. See Howard, D., “Spacetime and Separability: Problems of Identity and Individuation in Fundamental Physics” in Potentiality, Entanglement and Passion-at-a-Distance, edited by R.S. Cohen et al., Kluwer Academic, Great Britain, 1997, pp. 113-141. Then you argue to keep “realism,” but realism in this sense is associated with constitutive locality, i.e., that entanglement violates causal locality and/or realism per EPR --> causal and/or constitutive nonlocality per Healey and Howard, for example. See also Healey, R.: Holism and Nonseparability in Physics: In: Zalta, E.N. (ed.) The Stanford Encyclopedia of Philosophy (Spring 2009 Edition), http://plato.stanford.edu/archives/spr2009/entries/physics-holism. For the term “constitutive locality” see Healey, R.: Gauging What’s Real: The Conceptual Foundations of Gauge Theories. Oxford University Press, Oxford (2007).

Essentially, EPR said there are quantum “objects” which possesses definite properties in and of themselves (realism) that are revealed by measurements independent of what’s being done to entangled partners at space-like separated events (causal locality). If you keep the causality requirement, you can explain the entangled outcomes by saying the quantum objects’ properties are not possessed in and of themselves, but they are “co-possessed” by entangled partners. That’s constitutive nonlocality/nonseparability.

Second, I don't agree that your argument establishes the constitutive nonlocality of the covariant derivative. As a differential geometry prof once emphasized, despite being definable via parallel transport, the covariant derivative is a local object independent of the choice of curve along which you parallel transport at a point on the manifold. You do need to input a vector in the tangent space of said point if by "covariant derivative" you mean the exterior derivative so restricted, but it's still local. See Misner, C.W., Thorne, K.S., Wheeler, J.A.: Gravitation. W.H. Freeman, San Francisco (1973).

So, while the measurement devices and outcomes are separated (constitutively local), the properties of the objects being measured are not per constitutive nonlocality. It’s hard to imagine (for most people, anyway) how nonseparability would be modeled, as the rest of your post indicates. If you’d like to see how we model constitutive nonlocality via discrete path integrals over graphs, see arXiv 0908.4348. It’s in the “revise and resubmit” mode at Foundations of Physics, but substantively it’s sound (at least the referees and editors had no complaints about its substance—if you find a mistake, please let us know).

 

[Demystifier]

And I would very much appreciate your answer to my question: everything els being equal, would you prefer a local theory, or a nonlocal one?

I don't understand what do you mean by "everything else".

 

[akhmeteli]

I don't understand what do you mean by "everything else".

That means just that - "everything else" :-), but since you insist:-), let me define it as follows. Let us imagine for a moment that in ten or twenty years from now, as a result of progress both in theory and experiment or just because some god told us the ultimate truth:-), we have a final quantum theory, which is fully self-consistent and perfectly agrees with all experiments. Would you prefer this theory to be local or nonlocal, provided that your own well-being and success of your own research does not depend on whether it is local or nonlocal?

You may wonder why I am persistently asking this question - because I would like to save some time:-) If you answer "yes", it'll be easier for me to answer or for you to understand why some people prefer locality, if you answer "no", maybe you'll be able to explain to me why you personally prefer nonlocality. So I am just trying to understand if your current preference for nonlocality can be explained by your personal preferences or you just believe that the current case for nonlocality is too strong to even think about a possibility of a local theory.

 

[Demystifier]

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

 

[jambaugh]

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.

(If I may hum yet another chorus of the CI song...)

It is hard to say an RAA argument "suggests" which of the prior assumptions should be considered false. It rather points that the assumptions as a whole are mutually inconsistent. However to my mind we can't have "reality" if we sacrifice local causality if one is to accept special relativity.

SR + violation of local causality implies future actions can affect past states of reality. What then is the meaning of "reality" if it is not objectively defined and immutable once in the past?

I think it no more strange to reject absolute reality in QM than to reject absolute time in SR. It just takes some getting used to. The alternative is not nihilism or illusory mind created phenomena. It is a relative actuality of observed phenomena without the underlying assumption of a clockwork objective mechanism. We don't assume, we don't deny we simply pay attention only to the scientifically meaningful observations and observables without painting our own prejudices about what must lie beneath.

Alternative "interpretations" always remind me of the epicycles invented to hold onto the Platonic perfection of circular motion in spite of the evidence to the contrary in observed planetary behavior. I think the "absolute objective reality" hypothesis is similar to the Platonism of old in this sense.

 

[Demystifier]

SR + violation of local causality implies future actions can affect past states of reality. What then is the meaning of "reality" if it is not objectively defined and immutable once in the past?

There is a way out of this problem. Due to violation of local causality, some properties of the system in the past are determined by some properties of the system in the future. However, it does not mean that the past can be changed. Since there is only one future (the one that will actually happen), there is only one past as well (the one that has actually happened). Once the past is known, the future cannot be changed in a way that would contradict the known past.

See also the attachment in
https://www.physicsforums.com/showpost.php?p=2455753&postcount=109

 

[jambaugh]

There is a way out of this problem. Due to violation of local causality, some properties of the system in the past are determined by some properties of the system in the future. However, it does not mean that the past can be changed. Since there is only one future (the one that will actually happen), there is only one past as well (the one that has actually happened). Once the past is known, the future cannot be changed in a way that would contradict the known past.

See also the attachment in
https://www.physicsforums.com/showpost.php?p=2455753&postcount=109

I understand that. But that just boils it all down to "known" past i.e. observables instead of states. As a philosophical foundation, the "reality" of the "unobserved past" is meaningless in this context so why continue to work with it? The reason for invoking the "reality hypothesis" is no less invalid given this "way out".

If you are going to work with "tentative reality" then call it what it is, classes of possible observations. My point is that one can still reject the absolute reality of what is not observed (past, present, and future) while retaining the desired local causality. The reverse just isn't possible, your comments not withstanding.

Either you have violation of local causality with its implied invalidation of (unobserved) reality or you have local causality with QM+Bell invalidation of unobserved reality.

So reality being lost, we can still retain local causality if it, by itself, is consistent with observation. We know it to be consistent with predicted observations in QM, via the "no Bell telephones" theorem.

 

[Demystifier]

I understand that. But that just boils it all down to "known" past i.e. observables instead of states. As a philosophical foundation, the "reality" of the "unobserved past" is meaningless in this context so why continue to work with it? The reason for invoking the "reality hypothesis" is no less invalid given this "way out".

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.

 

[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.

 

[Peter Morgan]

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.

All through this thread, I find no distinction made between dynamical nonlocality and nonlocality of initial conditions (not that the distinction is much made in the literature). Dynamical locality is essentially preferred by classical physics. Initial conditions of a classical dynamics, however, are essentially always nonlocal, whether the dynamics are Newtonian or Lorentz invariant, because at a given time we have to specify the position and momentum of all particles, everywhere on a space-like hyperplane. Furthermore, classically, if we observe some phenomenon that requires a weird set of initial conditions, then that just means that the initial conditions in the past were also weird. This is all that superdeterminism is --- if what we observe now is weird, the setup must have been weird too. It makes no difference whether we introduce local or nonlocal dynamics. All of which is to say, Demystifier, that I say with you that "reality may be compatible with SR and nonlocality".

The only superdeterminism that is required to model the Bell-EPR situation, however, is superdeterminism of the evolution of probability densities. That is, if the probability density now is weird, then the probability density in the past must also have been weird. Superdeterminism of the state of a classical deterministic dynamics is not necessary. Amongst other consequences, it's therefore not necessary to impinge much on free will, unless, I suppose, one wants to deny that probability can be applied to model people's microbehaviour.

Another distinction not introduced here, in my look through, is contextuality. It's well-established that noncontextuality alone is enough to derive Bell inequalities. The distinction can also be put in terms of whether we regard settings of an instrument as parameters of a model or as observables in the model. Noncontextuality is rather against the spirit of classical particle modeling, and arguably can be thought of as anti-realist relative to particle properties, but it is not against the spirit of classical field models. Indeed, for field systems at thermal equilibrium the global configuration of an experimental apparatus condition the thermal equilibrium state, just as the Copenhagen interpretation insists it should. Think heat equation in contact with various heat reservoirs. I include a sketch of an experiment that gives more detail (which is of course needed) in a recent preprint, http://arxiv.org/abs/1001.4993" (this says nothing against any of the sophisticated interpretations that are out there, each of which gives its own interesting way of thinking about QM, and each of which a person may reasonably find more-or-less in tune with their own intuitive preferences).

Happy hunting!

 

[DrChinese]

All through this thread, I find no distinction made between dynamical nonlocality and nonlocality of initial conditions (not that the distinction is much made in the literature). Dynamical locality is essentially preferred by classical physics. Initial conditions of a classical dynamics, however, are essentially always nonlocal, whether the dynamics are Newtonian or Lorentz invariant, because at a given time we have to specify the position and momentum of all particles, everywhere on a space-like hyperplane. Furthermore, classically, if we observe some phenomenon that requires a weird set of initial conditions, then that just means that the initial conditions in the past were also weird. This is all that superdeterminism is --- if what we observe now is weird, the setup must have been weird too. It makes no difference whether we introduce local or nonlocal dynamics. All of which is to say, Demystifier, that I say with you that "reality may be compatible with SR and nonlocality".

The only superdeterminism that is required to model the Bell-EPR situation, however, is superdeterminism of the evolution of probability densities. That is, if the probability density now is weird, then the probability density in the past must also have been weird. Superdeterminism of the state of a classical deterministic dynamics is not necessary. Amongst other consequences, it's therefore not necessary to impinge much on free will, unless, I suppose, one wants to deny that probability can be applied to model people's microbehaviour.

Another distinction not introduced here, in my look through, is contextuality. It's well-established that noncontextuality alone is enough to derive Bell inequalities. The distinction can also be put in terms of whether we regard settings of an instrument as parameters of a model or as observables in the model. Noncontextuality is rather against the spirit of classical particle modeling, and arguably can be thought of as anti-realist relative to particle properties, but it is not against the spirit of classical field models. Indeed, for field systems at thermal equilibrium the global configuration of an experimental apparatus condition the thermal equilibrium state, just as the Copenhagen interpretation insists it should. Think heat equation in contact with various heat reservoirs. I include a sketch of an experiment that gives more detail (which is of course needed) in a recent preprint, http://arxiv.org/abs/1001.4993" (this says nothing against any of the sophisticated interpretations that are out there, each of which gives its own interesting way of thinking about QM, and each of which a person may reasonably find more-or-less in tune with their own intuitive preferences).

Happy hunting!

I saw that a few days ago on the arxiv and just starting reading it. For those interested, it comments on a paper by Navascues and Wunderlich regarding classic-quantum correspondence. It also has some good references.

 

[nikman]

FWIW in "Quantum nonlocality vs. Einstein locality" Dieter Zeh makes a distinction between "dynamic" and "kinematic" (quote):

Quantum theory is kinematically nonlocal, while the theory of relativity (including relativistic quantum field theory) requires dynamical locality ("Einstein locality"). How can these two elements of the theory (well based on experimental results) be simultaneously meaningful and compatible? How can dynamical locality even be defined in terms of kinematically nonlocal concepts?

http://www.rzuser.uni-heidelberg.de/~as3/nonlocality.html

 

[Peter Morgan]

I saw that a few days ago on the arxiv and just starting reading it. For those interested, it comments on a paper by Navascues and Wunderlich regarding classic-quantum correspondence. It also has some good references.

Thanks, DrC, and I'd be glad of your comments as always, here or by e-mail. There's an after-thought to this Comment, which is that a friend pointed out that the arXiv version of the paper it comments on does not includes the word "field" at all. To appreciate the details of the argument therefore requires the Proc.Roy.Soc.A paper. I'm somewhat curious whether the published version only introduces the classical field concept because a referee introduced the question (which might slightly improve the chances of the Comment being accepted, because the Proc.Roy.Soc.A editorial procedure for Comments includes the original paper's referee if the editors decided to send it to referees).

Fortunately, I believe the published version is freely available at http://rspa.royalsocietypublishing.org/content/466/2115/881" because of the Proc.Roy.Soc.A anniversary celebrations.

The chance of this Comment being accepted by Proc.Roy.Soc.A is small. The editorial board will presumably understand that discontent would be expressed in some quarters if they were to accept it, so I presume they will only accept it if it touches something of their own interests in the question.

 

[yoda jedi]

"A glance beyond the quantum model"

Happy hunting!

http://arxiv.org/PS_cache/arxiv/pdf/0907/0907.0372v1.pdf

...Here we propose a fundamental axiom that we believe any reasonable post-quantum theory should satisfy, namely, that such a theory should recover classical physics in the macroscopic limit...

coincidence (a correlation, or better yet a metaphysical corelation), i am reading:


On the Classical Limit of Quantum Mechanics
http://www.springerlink.com/content/p57117239x631547/fulltext.pdf


...In spite of many results of the standard approach, it is not yet clear how to explain within standard quantum mechanics the classical motion of macroscopic bodies.....


but suffers the same problems that standard quantum theory, is a patchwork proto-theory.

 

[Peter Morgan]

FWIW in "Quantum nonlocality vs. Einstein locality" Dieter Zeh makes a distinction between "dynamic" and "kinematic" (quote):

Quantum theory is kinematically nonlocal, while the theory of relativity (including relativistic quantum field theory) requires dynamical locality ("Einstein locality"). How can these two elements of the theory (well based on experimental results) be simultaneously meaningful and compatible? How can dynamical locality even be defined in terms of kinematically nonlocal concepts?

http://www.rzuser.uni-heidelberg.de/~as3/nonlocality.html

Thanks for this. Definitely worthwhile. I'm not as familiar with Zeh's thinking on environmental decoherence as I should be.

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.