Wednesday, November 30, 2005

String theory as mathematics

Is string theory post-modern physics? No, it's more like pure mathematics. Indeed, some string theorists are paid by math departments. Though he doesn't say so, what the author of the article linked to above is really arguing is that string theory should be treated as pure math (i.e., funded less).

However, string theory and competitors like loop quantum gravity are not merely mathematics. They are are attempts to describe the entire universe by a single grand mathematical model. Right now, we essentially have two partial mathematical models of the universe which, when patched together, are empirically correct (so far) but mathematically inconsistent. To see the physical incompleteness of this patchwork, one currently must consider cosmological questions about the distant past and future, or questions about the behavior of a infeasibly high-energy particle accelerators. For the more practically minded, these questions are not worth expending resources on. So, why is anybody paid to be a string theorist? We should all know the answer: there is an innate, prerational human desire (albeit stronger in some than others) to explain all that we encounter.

Notice how the above question elides the issue of how much funding string theory should get. I don't have a firm opinion on the matter, but I lean towards a truth-in-labeling policy: let string theorists ask for funding as mathematicians working on a very, very interesting mathematical problem, unless they have a promising research proposal for getting us closer to a feasible empirical test of string theory. Such a policy probably amounts to the status quo, for I would hope that the people making the relevant funding decisions already know that string theory is nowhere near empirically falsifiable. (The most promising route I know of is to look for violation of Lorentz invariance in natural particle accelarators like supernova; such tests (all negative so far) rule out some variants of string theory and loop quantum gravity.) I can't bring myself to get agitated over whether a string theorist is officially titled a physicist or a mathematician. (Tangentially, I generally prefer private funding for things that don't have practical applications.)

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