Nonlocality: correlation vs causation

[Ken G]

But Bohr already found the refutation of that position when he said "there is no quantum world." The "cut" is more a Heisenberg creation, I believe-- Bohr never thought there was anything like we imagine on the other side of the cut. So Bohr would not hold that we are "composed of" quantum stuff, instead he would probably have said that whatever we are actually made of, we have no choice but to study it by conceptualizing it with the elements of the theory of quantum mechanics, and no choice but to test the success of that conceptualization but interacting with it via classical instruments. I don't think anything in that stance can be refuted, it is all simply true. The philosophical stance appears when one goes beyond what cannot be refuted, and says, "but it has to be more than that, it has to actually be 'quantum stuff' or quantum mechanics couldn't work so well." To that argument, I simply ask "how do you know?" After all, Newtonian gravity sure seemed like what gravity had to "actually be" to many who studied it throughout the eighteenth and nineteenth centuries, so weren't they asking "but if gravity wasn't really a force created by masses, then how could Newton's theory work so well?" In my opinion, physics really doesn't do ontology-- it just creates what it needs to imagine is ontology, and it suffices for awhile.

 

[Len M]

But that is the logical morass I was referring to. Of course you may assume whatever you like, but physics is not about making assumptions, it is about verifying them. How are you going to verify that the particle positions are determined by "the laws of physics" (whatever that is) without first using an observer to establish that? And how is that observer going to establish that the particle positions, thus established by the observer, are what determines the observer? If we stick to what we can demonstrate, we cannot hold that particle positions determine observers.

And isn’t this the crux – a crux that is more often and not ignored or brushed under the carpet by so many. The people doing the ignoring are often highly intelligent and knowledgeable about physics and on reading these accounts from the perspective of a non physicist, the confidence of the author just oozes out. Yet important questions (for me at any rate) about what actually the physics refers to in an ontological sense take on an almost default position by the author (i.e. the physics refers to nature as it exists without our involvement). To argue against that stance is taken by many (not all) as an argument against the physics and if you can’t take a proper part in that discussion because of the very technical nature of it, then objections of a philosophical nature are treated with some contempt.

I have noticed on a few threads now that extremely knowledgeable physicists just do not take into consideration the philosophical perspective that surrounds their very high order of physics. That perhaps is of no issue within a close minded group of similar people, but when that very high order of physics smothers any questions about the relationship of that physics to nature as it exists outside of the means in which the physics is practiced, then the losers are not the physicists but the rest of us reading these public forums (as well as “popular” accounts written by physicists) who are recipients of the physics that implies a “default” position (nature outside of our involvement is described by our physics). Some (including myself on a personal level) attempt to delve a little into the philosophy within physics, but it’s difficult. So I value the physicists who are prepared to do this and I value the extent that Ken G explores these issues on this forum.

 

[Ken G]

To argue against that stance is taken by many (not all) as an argument against the physics and if you can’t take a proper part in that discussion because of the very technical nature of it, then objections of a philosophical nature are treated with some contempt.

That's true even if you can take part in the technical discussion! The problem is, any "technical" discussion already starts with certain implicit assumptions about what physics should be regarded as trying to do, so if you deign to look under the hood of those assumptions, the technical discussion is not yet even relevant. But those with technical mastery hate to take such a "backward step" to look at their own implicit assumptions, so end up "proving" things without recognizing that their proofs are unjustified by different philosophical priorities. It's a big problem that creates a lot of misunderstanding and disagreements even among experts who are technically proficient but who are unwilling or unable to think philosophically. As one example, I offer the issue of interpretation of QM, where we find people who must be considered experts in quantum mechanics like Penrose saying that Deutsch is "not serious" about QM, while Deutsch says Penrose is "doing aesthetics not physics." Is one of them right, and the other a fool? I doubt it, I suggest they simply translate their own philosophical priorities into different conclusions.

 

[Demystifier]

Penrose saying that Deutsch is "not serious" about QM

Why is Penrose saying that Deutsch is "not serious" about QM?

 

[Ken G]

Penrose doesn't think any set of postulates that could create a theory like we should be trying to create for QM could entail a structure in which our perceptions of wavefunction collapse could stem from unitary evolution, and indeed this can be proven under certain assumptions (which is what I mean by the philosophical priorities that I assume Deutsch would reject). Penrose believes that "collapse" is a real dynamical effect, and as such must emerge dynamically from whatever postulates are used for QM. The direction he looks for this to be included in the postulates is in quantum gravity, because he thinks that wavefunction collapse is a kind of true dynamical instability that appears on scales above the Planck mass, owing to a kind of dynamical collapse of spacetime itself. In that way, he thinks QM needs to be made more consistent with dynamical theories of spacetime like GR, rather than the other way around.

As near as I can tell (best would be to have him comment on this, but it seems pretty clear this is what he is saying), he views as "not serious" anyone who is not looking for a dynamical explanation of wavefunction collapse (though I believe he does not require that people be looking at quantum gravity to be considered serious about QM, but he thinks serious efforts must point toward postulates in which everything that we perceive follows directly from the theory without any ad hoc steps). Of course this means he regards as non-serious any work from the perspective of CI (where the collapse is itself a postulate) and MWI (where collapse never happens in reality, but is perceived as a kind of error of interpretation by the perceiver), and maybe even Bohmian mechanics (where there is no collapse, the system always starts out collapsed but we don't know it). I'm not sure about Bohmian mechanics, because perhaps Penrose's picture can be made consistent with that, but there would seem to be some disagreement about whether or not the collapse has already occurred for quantum systems that have never interacted with anything on the scale of a Planck mass.

 

[Demystifier]

That's a very strange view of what it means to be not serious about QM.

By the way, Penrose is not fully satisfied with Bohmian mechanics, in my opinion for wrong reasons. Anyway, this is what he says about Bohmian mechanics:
"My difficulty is that there is no parameter defining which systems are, in an
appropriate sense, ‘big’, so that they accord with a more classical ‘particle-like’
or ‘configuration-like’ pictures, and which systems are ‘small’, so that
the ‘wavefunction-like’ behaviour becomes important"
[quote from "The Road to Reality", Sec. 29.9]

 

[Ken G]

That sounds like a general complaint that Penrose has about QM writ large, not just Bohmian approaches, and indeed the way he seems to criticize lots of QM interpretations is not that they are wrong, but rather that they "don't solve the problem." That appears to be why Penrose targets the Planck mass as an appropriate place for the "cut" (the other Planck scales are mind-bogglingly small, but the Planck mass is curiously large, only about the mass of a dust particle). Note also that Penrose doesn't think it is "serious" to leave the cut as a postulate, he wants a theory that describes the Born rule in a completely dynamical way, like how classical mechanics describes the cut between individual particle trajectories and fluid models. I applaud Penrose that he is willing to attempt that daunting task, though I agree that characterizing essentially everything else as "non-serious" is an unfortunate choice of words! I think he is trying to separate what he views as his own more mathematically rigorous mission from other kinds of inquiry, without being too insulting, but most people would take "non serious" as an insult.