Why all the clinging to locality?

[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.