Thursday, June 05, 2008

CPA Report 5

My last session of the day yesterday was called "Around Quantum Mechanics," which is about right, since quantum mechanics was more or less secondary to each of the presenters topics. First up was Eran Tal, illustrious former guest of the former Beck-Brown-Skywalker household, doing a talk on "Simulated Evidence: Signatures of a Quantum Phase Transition." I think his case study is really interesting, and its going to blow a bunch of stuff wide open. He's looking at cases in which theorists (at Oxford?), using computer simulations based in part on the theory, and in part on the description of an experimental device used by a set of experimentalists in Zurich studying phase transitions between superfluids and Mott-insulators. By simulating both together, and varying certain assumptions about initial conditions and the background device, these theorists claim to have shown that the Zurich experiment (whose results are somewhat messy) was a successful detection of the phase transition, since the signature produced in their simulation has a qualitative match to the results produced in Zurich. In other words, they claim to have shown (a) that the Zurich experiment was reliable, and (b) that the Zurich experiment successfully measured what the theory predicted, when neither was certain before.

This is super-interesting! What they did cannot be said to be an elaborate prediction from theory, nor clarification of the data, but rather some combination of the two, plus something else besides. Most interesting to me, as I pointed out to Eran later at the reception, is how this clearly raises a problem for the Suppes/Giere theory about different levels of models which nonetheless come in two flavors: models of data and theoretical/representational models. I'm not sure what Giere should say, nor am I sure what a Deweyan should say (this process doesn't clearly fit on either side of the existential/conceptual gap distinction, either).

Next, Melanie Frappier gave a talk entitled "If 'Copenhagen' is Leibzig's Code Name, What does 'Interpretation' Mean?: A Re-examination of the Origin of the Copenhagen Interpretation." Melanie was responding to Don Howard's paper, which suggests Heisenberg invented the notion of a unified "Copenhagen" interpretation in the 1950's, but that whatever Heisenberg identified wasn't Bohr's "complementarity" view, and it wasn't really a consensus at all. She agreed with the former point, but denied the later, based on a nuance about what the physicists meant by "interpretation." She showed clearly that from much earlier on, various physicists talked about "interpretation," but that this sense of interpretation is very different from what we mean today. In particular, she gave reasons to believe that the theory has a univocal interpretation, in Heisenberg's sense of "interpretation."

If you think about it, it makes sense. A theory is not just a formal-mathematical system; it is also a set of concepts related together in a certain way, where each concept has a certain meaning, or empirical criterion of application, or something. What an alternative interpretation would have to provide, which most "interpretations" of quantum mechanics today don't, is an alternative criterion of empirical application for the terms of the theory. All the insistence by Bohmians and others that their interpretation has identical empirical results sounds to Heisenberg like they have the same interpretation. All the other stuff is not part of what physicists do. (This makes sense of something I've puzzled with for a long time, which is David Finkelstein's insistence that quantum theory already comes with an interpretation, so there is little sense to the project of "interpreting" quantum theory.)

Isaac Record gave an interesting talk on "Instruments of Explanation" which I'm not going to summarize. He was arguing, basically, that new instruments provide new realms of "technological possibility," which unlike logical and physical possibility, is sensitive to contingent facts and to practical issues like time it takes to complete a procedure. On his view, computers really open up a new realm of possible explanations, because we can realistically consider options that we couldn't before we had super-fast computers. Something to think about, with real echoes in Dewey's own concept of relations and potentials.

Off to the Aeroport!

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