Why all the clinging to locality?

[audioloop]

.

and not hinging on pre-existing electrons v a l u e s
to say that is realistic or not.


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[DrChinese]

I would think most view BM as non-local and realistic. As noted above (I just edited it), even experiments demonstrating violation of Leggett's inequalities (e.g. Groblacher et al.) do not rule out objective reality but only certain types of non-local realism. For example, Bohmian mechanics is consistent with such experiments because position takes priority over all other properties (and those experiments, at the most, rule out realism about polarization).

I agree about the non-local and realistic just fine. It is the comment about "non-realism" about polarization that I object to. I realize that BMers are to a certain degree "polarization deniers". But there is no difference in the evidence that polarization observables are any different than the usual other observables.

Just saying that polarization is "non-realistic" in BM is not really adequate. It is as realistic as anything else is, even if it is a derived property and not fundamental. (Of course, I think it is fundamental.)

 

[bohm2]

I agree about the non-local and realistic just fine. It is the comment about "non-realism" about polarization that I object to. I realize that BMers are to a certain degree "polarization deniers". But there is no difference in the evidence that polarization observables are any different than the usual other observables.

They aren't. Everything is contextual, except the actual particle positions. So all the contextual stuff is contained in the wave function and not primitive/fundamental, unlike position, which is. Maybe you're questioning why position is "real"/primitive unlike all the other contextual stuff/observables?

 

[DrChinese]

Maybe you're questioning why position is "real"/primitive unlike all the other contextual stuff/observables?

It's part and parcel of the theory, as I understand it. So I respect that.

 

[audioloop]

.

and not hinging on pre-existing electrons v a l u e s
to say that is realistic or not.


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existent objects without values, just that.


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[bohm2]

I do agree that quantum non-locality is a critical difference relative to the classical world.

Just wondering what your opinion is on arguments by this author presenting certain classical systems that are local yet violate Bell's inequality. The author suggests that such "supercorrelated" systems can be both local and realistic (at least contextual realistic):

Bell's Theorem: Two Neglected Solutions
http://arxiv.org/ftp/arxiv/papers/1203/1203.6587.pdf

Violation of the Bell-Inequality in Supercorrelated Systems
http://arxiv.org/vc/arxiv/papers/1211/1211.1411v1.pdf

My impression is that some of the difficulties here is again with the definition of "realism". I'm guessing you interpret contextualism with non-realism since contextuality would imply non-realism? But then, the problem is that such classical systems are contextual yet we don't consider them non-real?

 

[Demystifier]

I'm guessing you interpret contextualism with non-realism since contextuality would imply non-realism? But then, the problem is that such classical systems are contextual yet we don't consider them non-real?

I also think that DrChinese identifies contextuality and non-reality, and I am very curious to see how will he answer your question.

 

[craigi]

My impression is that some of the difficulties here is again with the definition of "realism". I'm guessing you interpret contextualism with non-realism since contextuality would imply non-realism? But then, the problem is that such classical systems are contextual yet we don't consider them non-real?

I think we must consider non-realism to apply to equally to classical systems. Classical systems can exist in an unkown and unkowbable state. The difference with quantum systems is that they exist in a superposition of possible states. Any record of the result and context of a measurement isn't real in the sense that it is unkown, unkowable and all possibilites exist, until conveyed to the subjective observer, but we don't require that they exist in a superposition for them to lack objective reality.

 

[Demystifier]

I think we must consider non-realism to apply to equally to classical systems. Classical systems can exist in an unkown and unkowbable state. The difference with quantum systems is that they exist in a superposition of possible states. Any record of the result and context of a measurement isn't real in the sense that it is unkown, unkowable and all possibilites exist, until conveyed to the subjective observer, but we don't require that they exist in a superposition for them to lack objective reality.

You might like
http://arxiv.org/abs/quant-ph/0505143 [Found.Phys.Lett. 19 (2006) 553-566]
http://arxiv.org/abs/0707.2319 [AIPConf.Proc.962:162-167,2007]
where some similar ideas are elaborated.

 

[stevendaryl]

I think we must consider non-realism to apply to equally to classical systems. Classical systems can exist in an unkown and unkowbable state. The difference with quantum systems is that they exist in a superposition of possible states. Any record of the result and context of a measurement isn't real in the sense that it is unkown, unkowable and all possibilites exist, until conveyed to the subjective observer, but we don't require that they exist in a superposition for them to lack objective reality.

This is getting down to very subtle matters of definition, but I think when people talk about realism, they are not making any assumptions about whether a state is knowable or not. That is, in a realistic model, the system has a state at every moment, whether or not that state is knowable; it may not be, because there may be no way to probe the state without disturbing it.

That's sort of the point of Bell's theorem. He was investigating whether there were any testable consequences to the assumption that there was a pre-existing state prior to measurement, even if that state is not knowable.

 

[DrChinese]

Just wondering what your opinion is on arguments by this author presenting certain classical systems that are local yet violate Bell's inequality. The author suggests that such "supercorrelated" systems can be both local and realistic (at least contextual realistic):

Bell's Theorem: Two Neglected Solutions
http://arxiv.org/ftp/arxiv/papers/1203/1203.6587.pdf

Violation of the Bell-Inequality in Supercorrelated Systems
http://arxiv.org/vc/arxiv/papers/1211/1211.1411v1.pdf

My impression is that some of the difficulties here is again with the definition of "realism". I'm guessing you interpret contextualism with non-realism since contextuality would imply non-realism? But then, the problem is that such classical systems are contextual yet we don't consider them non-real?

I equate contextuality with non-realism, recognizing fully that they can be defined differently. In EPR terms: contextuality means that the result of a measurement here is dependent on the nature of a measurement elsewhere. So that is a "subjective" reality. On the other hand, they view (elements of) reality as meaning a prediction with certainty can be made even if all such possible predictions cannot be demonstrated simultaneously. I see those as being mutually exclusive. Ie you cannot have contextuality *and* realism.

As to Vervoort's superdeterminism and variants: I do not consider these lines of reasoning to be a part of physical science in their current form. You may as well say evolution is due to superdeterminism rather than being due to natural selection from random mutation.

 

[DrChinese]

To clarify: Ie you cannot have contextuality *and* counterfactual realism within the same system. Again: if you tweat the definitions enough you probably can find a way to make these work, but then you won't match up to the EPR definitions. The EPR definitions have stood the test of time.

 

[craigi]

This is getting down to very subtle matters of definition, but I think when people talk about realism, they are not making any assumptions about whether a state is knowable or not. That is, in a realistic model, the system has a state at every moment, whether or not that state is knowable; it may not be, because there may be no way to probe the state without disturbing it.

That's sort of the point of Bell's theorem. He was investigating whether there were any testable consequences to the assumption that there was a pre-existing state prior to measurement, even if that state is not knowable.

Are you sure that you mean that? Are you not aruging that realist interpretations actually forbid the superposition of states?

 

[bohm2]

I equate contextuality with non-realism, recognizing fully that they can be defined differently... I see those as being mutually exclusive. Ie you cannot have contextuality *and* realism.

As to Vervoort's superdeterminism and variants: I do not consider these lines of reasoning to be a part of physical science in their current form. You may as well say evolution is due to superdeterminism rather than being due to natural selection from random mutation.

I posted a paper previously showing contextuality in classical systems:

Contextuality lays at the heart of quantum mechanics. In the prevailing opinion it is considered as a signature of "quantumness" that classical theories lack. However, this assertion is hardly justified. Although contextuality is certainly true of quantum mechanics, it can not be taken by itself as discriminating against classical theories. Here we consider a representative example of contextual behavior, the so-called Mermin-Peres square, and present a simple discrete model which faithfully reproduces quantum predictions that lead to contradiction with the assumption of noncontextuality. This shows that quantum-like contextual effects have their analogues in the classical realm too.

Classical systems can be contextual too: Analogue of the Mermin-Peres square
http://arxiv.org/pdf/1310.4990.pdf

So if one cannot have both contextuality and realism (as you argue), then such classical systems would then also be non-real? But one doesn't normally think of such systems as being non-real. With respect to Vervoort's papers, I think his focus is on supercorrelated classical systems not superdeterminism.

As a big aside, there are a number of prominent evolutionary biologists that question natural selection as being tautological. See my post here:

Spandrels/Exaptations vs Adaptations
https://www.physicsforums.com/showthread.php?t=701690

 

[craigi]

To clarify: Ie you cannot have contextuality *and* counterfactual realism within the same system. Again: if you tweat the definitions enough you probably can find a way to make these work, but then you won't match up to the EPR definitions. The EPR definitions have stood the test of time.

Now I'm confused. Contextuality is an observerable phenomenon. Counterfactual definiteness is interpretational issue, which is a feature of the de Broglie-Bohm interpretation. So how does the de Broglie-Bohm interpretation explain contextuality?

So if one cannot have both contextuality and realism (as you argue), then such classical systems would then also be non-real? But one doesn't normally think of such systems as being non-real. With respect to Vervoort's papers, I think his focus is on supercorrelated classical systems not superdeterminism.

I wouldn't equate counterfactual definiteness with realism. I think there is an important distinction in that realism, pertains to observer independence, whereas counterfactual definiteness pertains to definite state in the absence of observation. We can have neither, either or both.

I don't consider lack of counterfactual definiteness to be restricted to quantum systems. In fact, I don't see how we can make the Many Worlds interpretation work, for instance, with counterfactual definiteness in the classical realm.

 

[bhobba]

So how does the de Broglie-Bohm interpretation explain contextuality?

I am not an expert on DBB but my understanding is in that interpretation contextuality is hidden in the pilot wave it assumes is very real and actually exists.

That's my understanding anyway - there are some genuine DBB experts that post around here - maybe they can chime in.

Added later:

I did manage to dig up the following:
http://philsci-archive.pitt.edu/3026/1/bohm.pdf

Thanks
Bill

 

[stevendaryl]

Are you sure that you mean that? Are you not aruging that realist interpretations actually forbid the superposition of states?

A superposition of states is another state. The sense in which quantum mechanics is not realistic is that individual particles don't have states. There is a state of the entire universe, but there is no state of a single particle, if it's entangled with another particle.

 

[DrChinese]

So how does the de Broglie-Bohm interpretation explain contextuality?

From the link provided above, Oliver Passon says the following:

"In common jargon these properties are called contextual, i.e. the measurement does not reveal a pre-existing value of a system-property but depends crucially on the experimental arrangement (the context)."

Sounds contextual to me.

Also sounds non-realistic, since the value measured here is dependent on an observer's choice of measurement there. EPR says no reasonable definition of reality would permit this.

Of course EPR also has an explicit out for non-local theories as well, such as superluminal signaling. dBB doesn't exactly feature that so much as everything participates in the context. In the end, I see dBB as both non-local AND non-realistic (or contextual). But that is just me.

 

[Demystifier]

DrChinese, concerning the contextuality/non-reality dilemma, I think it is about english language, not about physics. To test this hypothesis, let me use a simple example not related to quantum mechanics.

Consider the well-known picture attached below. Is it a rabbit or a duck? Is it contextual, in the sense that it is a rabbit when you look at it one way, and a duck one you look at it another way? Is it real, in the sense that it is a duck and a rabbit even if you don't look at it? Or non-real, in the sense that it is neither a duck nor a rabbit when you don't look at it? Or is it real or non-real in some other sense?

I think answering these questions for such a simple example can significantly help to explain what one means by (non)-real and contextual.

 

[DrChinese]

DrChinese, concerning the contextuality/non-reality dilemma, I think it is about english language, not about physics. ...

I quite agree. Although I think it is a difficulty in ANY language other than the language of physics.

 

[craigi]

DrChinese, concerning the contextuality/non-reality dilemma, I think it is about english language, not about physics. To test this hypothesis, let me use a simple example not related to quantum mechanics.

Consider the well-known picture attached below. Is it a rabbit or a duck? Is it contextual, in the sense that it is a rabbit when you look at it one way, and a duck one you look at it another way? Is it real, in the sense that it is a duck and a rabbit even if you don't look at it? Or non-real, in the sense that it is neither a duck nor a rabbit when you don't look at it? Or is it real or non-real in some other sense?

I think answering these questions for such a simple example can significantly help to explain what one means by (non)-real and contextual.

Putting aside my objections that it's not completely objective what "it" is that I'm describing and that "it" doesn't look that much like either; entering into to spirit of the question:

It's contextual in that an observer can get a different result depending upon how they "observe" it.

It's real in the sense that all observers, presuming that they they have sufficient image recognition capability and prior records of ducks and rabbits for comparison, would have the same experience of it.

It's not counterfactual definite in that it doesn't specifically depict either, without the interaction of the observer.

Obviously, we should be careful in extrapolating this to quantum mechanics, but as it happens these match my preferred interpretations. It would be interesting if someone who prefers the de Broglie-Bohm interpretation, would describe it a different way. I suspect if someone were to do so, I would cringe at the abuse of poetic license in the definition of the terms or what "it" is that they choose to describe. Interestingly, I would probably be more forgiving of someone who prefers the same interpretations, yet operates on different definitions.

 

[bohm2]

It would be interesting if someone who prefers the de Broglie-Bohm interpretation, would describe it a different way. I suspect if someone were to do so, I would cringe at the abuse of poetic license in the definition of the terms or what "it" is that they choose to describe. Interestingly, I would probably be more forgiving of someone who prefers the same interpretations, yet operates on different definitions.

1. Rabbit or duck (analogous to contextual properties such as spin, etc. in deBroglie-Bohm) plus
2. An underlying ontological stuff (e.g. the actual picture-analogous to non-contextual Bohmian position) that determines both the rabbit and duck view

As I see it, a non-realist would deny 2. and argue that we can only talk about 1.

 

[Demystifier]

It would be interesting if someone who prefers the de Broglie-Bohm interpretation, would describe it a different way.

I prefer dBB interpretation, and my view is quite similar to that of bohm2 above.

 

[stevendaryl]

1. Rabbit or duck (analogous to contextual properties such as spin, etc. in deBroglie-Bohm) plus
2. An underlying ontological stuff (e.g. the actual picture-analogous to non-contextual Bohmian position) that determines both the rabbit and duck view

As I see it, a non-realist would deny 2. and argue that we can only talk about 1.

It seems to me that the term "realist" or "non-realist" should be augmented by "about ..." Just about any theory can be considered realist about something and non-realist about something else.

MWI and Bohm are realist about the wave function, but not about spin (in the sense that there is no fact about an electron that would make it spin-up; in the Bohm theory, it only becomes a spin-up electron when you try to measure its spin--I think I have that right).

 

[bohm2]

It seems to me that the term "realist" or "non-realist" should be augmented by "about ..." Just about any theory can be considered realist about something and non-realist about something else.

The argument is that some interpretations (e.g. Copenhagen) aren't clear about what is "real"; in particular, there's a clear difference between many of the different versions of Copenhagen on the one hand and realistic interpretations (e.g. BM, GRW). The latter are fully precise about what belongs to the primitive ontology (e.g. particle trajectories, flashes, etc.) whereas the Copenhagen interpretation is vague. The basic philosophy of the necessity for so-called primitive ontology in physical theory for those who favour "realism" in physics can be found here:

Primitive Ontology and the Structure of Fundamental Physical Theories
http://www.niu.edu/~vallori/AlloriWFOlast-dopo%20editing%20finale.pdf

On the Metaphysics of Quantum Mechanics
http://www.niu.edu/~vallori/Allori%20-%20LeBihan-On%20the%20Metaphysics%20of%20Quantum%20Mechanics-finale.pdf

With respect to Copenhagen, the criticism from this perspective is the following:

Thus in contemporary quantum theory it seems that the world must be divided into a wavy quantum system, and a remainder that is in same sense classical... It introduces a fundamental ambiguity into fundamental physical theory (Bell 1987).

Allori repeats this criticism:

Even the Copenhagen interpretation (orthodox quantum theory, OQT) involves a dual structure: what might be regarded as its primitive ontology (PO) is the classical description of macroscopic objects which Bohr insisted was indispensable-including in particular pointer orientations conveying the outcomes of experiments-with the wave function serving to determine the probability relations between the successive states of these objects. In this way, ψ governs a PO, even for OQT. An important difference, however, between OQT on the one hand and BM, GRWm, and GRWf on the other is that the latter are fully precise about what belongs to the PO (particle trajectories, respectively continuous matter density or flashes) whereas the Copenhagen interpretation is rather vague, even noncommittal, on this point, since the notion of ‘macroscopic’ is an intrinsically vague one: of how many atoms need an object consist in order to be macroscopic? And, what exactly constitutes a ‘classical description’ of a macroscopic object?

On the Common Structure of Bohmian Mechanics and the Ghirardi–Rimini–Weber Theory
http://www.niu.edu/~vallori/bmgrw.pdf

 

[infamous80518]

Awesome thread! I've never thought the DBB interpretation was more valid than hearing someone reference descarte as his philosophical source. To conclude that a human nervous system causes wave-function collapse just never sat well with me... Especially considering that the human nervous system, more often than not, doesn't even interact directly with the system; It merely interprets the data...
The best definition for "observation" I've heard is a "change of entropy".

 

[ZapperZ]

Closed, pending moderation.

Zz.