Why all the clinging to locality?

[bhobba]

how can exist a spin without electrons ?

Errrrr. You missed the point entirely. Its the claim quantities in a theory must be attached to objects - not that quantities can be attached to objects.

Thanks
Bill

 

[bhobba]

Did you mean, how can spin exist if not mapped to a particle?

The original claim was:

'pre existing properties' are values, values of who or what ? OBJECTS. then there are 'existent things' without values, just that. you can't talk about values without objects.

Theories can, and sometimes do, contain 'values' without them being associated with objects eg the example I gave about dimensional regularization.

Statements like that IMHO show a limited exposure to what a mathematical model is, and understanding that physical theories are basically mathematical models.

However QM has the opposite problem - assigning values independent of a measurement context.

Thanks
Bill

 

[audioloop]

http://www.nature.com/nature/journal/v485/n7396/full/nature10974.html

i posted some time ago that stuff.
spinons, electrons with spin only (splited electrons).
there are too, holons and orbitons.


http://www.nature.com/news/not-quite-so-elementary-my-dear-electron-1.10471

 

[craigi]

i posted some time ago that stuff.
spinons, electrons with spin only (splited electrons).
there are too, holons and orbitons.


http://www.nature.com/news/not-quite-so-elementary-my-dear-electron-1.10471

Are there any measurements or postulates as to how the mass is distributed, why these quantities are so often found at the same location and how they decay once split?

 

[audioloop]

Are there any measurements or postulates as to how the mass is distributed, why these quantities are so often found at the same location and how they decay once split?

yes, QED quantum electrodynamics.-----
same location ? can delve the question please ?.

 

[bohm2]

So I say:
EPR Realism = objective reality =
hidden variables = pre-existing properties =
non-contextual reality = counterfactual definiteness

I don't see that any of these can be said to exist or be ruled out except along with the others.

Why can't one exist (or be ruled out) without the others? Bohmian mechanics is an example. In Bohmian mechanics all properties are contextual except position. So one can have an objective realism (with respect to position) but with contextuality of other properties. Moreover, some recent papers suggest that there are contextual classical systems, so I don't think one can conclude that objective reality=non-contextual reality:

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 non-contextuality. 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

An interesting question posed by this author:

If contextuality by itself is not a token of non-classicality, then what makes quantum theory so different? Or more generally, which conceptual features distinguish quantum mechanics from classical theories.

Isn't non-locality/entanglement (whether the realistic or non-realistic variety) the key feature that distinguishes QM from classical theories?

 

[stevendaryl]

Why can't one exist (or be ruled out) without the others? Bohmian mechanics is an example. In Bohmian mechanics all properties are contextual except position. So one can have an objective realism (with respect to position) but with contextuality of other properties. Moreover, some recent papers suggest that there are contextual classical systems, so I don't think one can conclude that objective reality=non-contextual reality:

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

An interesting question posed by this author:

Isn't non-locality/entanglement (whether the realistic or non-realistic variety) the key feature that distinguishes QM from classical theories?

I don't think that contexuality by itself is particularly weird. Since a measurement necessarily involves an interaction between the measuring device and the object being measured, it's perfectly understandable that result may not have existed prior to the measurement process.

However, in the specific case of EPR type experiments, one finds perfect correlations between distant measurements of different particles. That was Einstein's original argument: If measuring one particle tells us something with certainty about the result of a second distant measurement (one that may not have even been performed yet), then the result in some sense "already existed" before the second measurement. Or at least, that's one would expect based on pre-quantum intuitions.

So it's not that contexuality by itself is weird, it's that contextuality, together with perfect distant correlations, is weird.

 

[bohm2]

So it's not that contexuality by itself is weird, it's that contextuality, together with perfect distant correlations, is weird.

I agree but then why equate non-contextual realism (by itself) with objective realism and/or counterfactual definiteness? Note that 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.

 

[DrChinese]

1. Why can't one exist (or be ruled out) without the others? Bohmian mechanics is an example. In Bohmian mechanics all properties are contextual except position. So one can have an objective realism (with respect to position) but with contextuality of other properties. Moreover, some recent papers suggest that there are contextual classical systems, so I don't think one can conclude that objective reality=non-contextual reality:

2. Isn't non-locality/entanglement (whether the realistic or non-realistic variety) the key feature that distinguishes QM from classical theories?

1. I realize that Bohmians view their theory as both contextual and objectively real. Just as MWIers view their interpretation as both local and realistic. But I don't see it that way for either.

All I can agree to is that BM is non-local, and that MWI is subjectively real (since observers in different branches see different things). I think most stop there.

2. I do agree that quantum non-locality is a critical difference relative to the classical world. That also features (under that same name) what might be called "quantum non-temporality*". Ie a future setup can be a participant in the context, just as a distant one can. *I doubt that is even a word.

 

[bohm2]

All I can agree to is that BM is non-local, and that MWI is subjectively real (since observers in different branches see different things). I think most stop there.

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).

 

[audioloop]

.

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


.

 

[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.


.

existent objects without values, just that.


.

 

[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.