----- Original Message ----- From: "Richard Baker" <[EMAIL PROTECTED]> To: "Brin-L" <[EMAIL PROTECTED]> Sent: Monday, March 04, 2002 6:57 AM Subject: Quantum non-locality (was Re: The Shooting Room Paradox)
> Dan said: > > > I found it interesting that it got to be a hot topic after I was > > involved with it. > > I suppose this is because Bell had just proven his celebrated theorem in > 1971 and at about the same time the state of the art in quantum optics > had advanced far enough that it was possible to actually perform EPR > experiments, as Freedman and Clauser did in 1972. It must've been an > exciting time :) Well, it was a lot of fun, but we felt that most people were not very interested in the subject. One of the reasons that we were interested was that Bell had spent time working on his theorem at Wisconsin. It hadn't hit Physics Today at all yet. I did a philosophy of QM course in the philosophy department as part of my minor. I also took a foundations of physics course in the physics department with Conceptual Foundations of Quantum Mechanics by Bernard D' Espagnat as the text. FWIW, virtually no one assumed that the experiments would produce proof of hidden variables. > > I do try to keep up. I'm also in a bit of a different position, since > > I do have a philosophy degree and have illusions of semi-retiring and > > spending some time writing in the area of the philosophy of QM. :-) > > That would be really fun. Have you read Redhead's _Incompleteness, > Nonlocality and Realism_? > > [Fitting together QM and SR] No, I haven't. > > > I'm not quite sure what you are getting at. I think they do fit > > together well, and I do see basic principals that are underlie they > > interrelationship. > > Here's roughly what I meant. Quantum mechanics and special relativity > both have a number of conceptual innovations with respect to the > Newtonian worldview. Special relativity gives us a new view of the > causal structure of the past in which past/present/future is replaced > by "absolute past" / "causally disconnected" / "absolute future". In > special relativity, there is no absolute standard of simultaneity and > any communication that is simultaneous in a given inertial reference > frame can be used to violate causality in another (actually, this is > not quite true - it requires two such simultaneous communications). > Quantum mechanics, in contrast, preserves Newtonian causality but > introduces such ideas as objective randomness, irreducible uncertainty > in measurements and non-locality. It might therefore seem that the two > theories wouldn't fit together because non-locality could be used to > communicate simultaneously and so violate causality. However, this > isn't the case because, although QM has non-local correlations between > measurements, one of the other conceptual innovations, objective > randomness, steps in to prevent us from using non-locality for > communication. It's this that seems to me to be surprising - that we > can take these two entirely separate sets of conceptual innovations and > use them all. (Indeed, we can make quantum field theory by treating > them all as axioms, and get such wonderful new things as the > spin-statistics theorem by imposing the need for a Minkowskian causal > structure more rigorously. Not that quantum field theory is entirely > free of problems...) Well, I agree that its neat, but I'm far less surprised by it. I sorta fit it into the idea that there isn't really paradoxes between theories: that there has to be a way to come up with a consistent viewpoint. Sorta like seeing electricity and magnetism having to fit together. Part of the difference in our viewpoints on this may have to do with our metaphysical outlook when we seriously considered this stuff. By the time I took modern physics, I did have a very neat metaphysical place from which to view it: I didn't have to force it into realism. > > But, those principals are metaphysical, not physical. > > What are these principles? > To put it in a nutshell: phenomenon is the interface between mind and nomenon. (I base my understanding mostly on the metaphysics in "The Critique of Pure Reason" by Kant.) Spacetime is an aspect of our mind: it is the a priori form of our intuition (intuition is used here as our means of interfacing with reality apart from our mind). > Yes. I knew that, of course. You just used the word "interpretation" and > I was wondering if they'd come up with a full interpretation of QM. I > wouldn't call Bell's theorem an "interpretation" as such - I'd save > that word for things like the Many Worlds interpretation or the > Copenhagen interpretation. Fair enough, I should have been more careful and not merged two thoughts. Wigner did come up with an extension of Copenhagen which explicitly talked about the need for a mind to force the universe into eigenstates. > > I think that a statement like "the universe is a spin foam of > such-and-such a type" is as nice and simple as "the universe is a > Riemannian manifold" as a view of space and time. Indeed, it might even > be simpler because it doesn't rely on stuff from analysis and > differential geometry but only graph theory. If it can easily be described that way, then you are right. I'm guessing, though, that we'll need fudges like renormalization before things work out. But, that is indeed only a hunch. One thought that struck me in all of this. What if we have two theories that give different descriptions of "reality" but give the same results. For example, if there were a way to discuss gravity in terms of gravitons and in terms of the interrelationship between the curve of space and the existence/action of matter. It might be possible to come up with two descriptions that produce the same results but have far different narratives of how the universe works. Dan M.
