Monday, December 18, 2006

Post-modern physics?

A persistent if sotto voce criticism of string theory during its period of dominance (post-1984) has been that it's "theology," "unverifiable," "pure sociology," and so on. These perceptions contain a large grain of truth, and then some, but they've also made string theorists extraordinarily sensitive to the charge that they're not doing science. Occasionally, a string true believer strikes back with attempts at "tu quoque" ("you too!"). Perhaps psychologists of the future can analyze the faulty defenses of string theory in terms of projection.

One of the strangest of these charges is that the critics of string theory are dangerous post-modernists or nihilists. Certain string theorists have leveled this charge against Smolin in particular, entirely without foundation. Smolin's recent book is a fair-minded, politely polemical, if ultimately devastating, look at what's gone wrong with fundamental physics in the last 20 years. If he were a post-modernist as charged, he wouldn't care about these questions enough to have written the book. But even more, the book exhibits a concern and thoroughness with regard to foundational questions about spacetime and quantum gravity that makes it absolutely incompatible with post-modernism, which after all rejects "foundational" anything as nothing more than ideology. The charge of post-modernism should be dropped and, if anything, is better applied to string theorists.

Or perhaps string theorists are more pre-modernists, naively believing in their theory on faith, that it "must" be true, even though there's not only no way of knowing, but not even a theory, properly speaking. It's situation that brings to mind what Galileo called a state of "guilty innocence," here the not-so-innocent dishonesty and self-deception rampant in high-energy theory for the last decade. The guilty innocence is reinforced by a fad-driven culture where fashions are set by small number of powerful senior people, who are rarely the source of major breakthroughs in science in any case.

A perfect compliment to Smolin's book is the new book by Peter Woit, Not Even Wrong. Woit's argument is more compact, more detached (he's a mathematician with a strong interest in string theory and quantum field theory), but also more blunt. Some readers will find the alternation between journalistic and technical prose jarring. But Woit is concise and also devastating, and his killer instinct rarely fails him. He nails every weakness and absurdity in the culture of string theory and shows how the field has drifted into fantasy and abandonment of scientific standards - again, demonstrating that it is string theorists, not their critics, who are on the wrong track.

Let's imagine string theory had never gotten its hold on theoretical physics and go back to the situation in the mid-80s. We fall back on the achievements of gauge theory, grand unification, supersymmetry, and supergravity. Although baryon number violation has not been observed, neutrino masses and dark matter have been, and these can be counted as tentative successes. Beyond that, it's clear that no further progress is possible without a quantum theory of gravity, and string theory is not that theory.

Feynman put it perfectly in 1987: string theorists make no predictions, only excuses. That used to be an objection to string theory. String theorists have tried to turn this objection into a new sort of "science" - the way the media and Wall Street flacks tried to justify the stock bubble of the late 90s by redefining every canonical standard of value and turning economics on its head. It's trying to "win" the game by twisting the rules. Of course, economics and the theory of stock value were right; the stock bubble was just that, a bubble. So is string theory. As an example, Woit discusses the disturbing Bogdanov affair, a kind of reverse Sokal hoax, where two physicists were able to get published, in 2002, several completely nonsensical papers about quantum gravity - in serious technical journals. This is surely a giveaway sign that something has gone badly wrong. Another sign is the difficulty Woit had in getting his book published by a scientific press. (It was eventually published by Basic Books.) The book was subject to hostile anonymous criticism for not being "in" with the right crowd - but no significant technical errors were found. Not Even Wrong is also a model of clarity and brevity, unlike so much of the physics literature these days, which exhibits a disturbing similarity to the work of another "in" crowd, the humanists laboring under the degenerate and authoritarian obscurantism of post-modernism.

While too much as been sunk into string theory, string theorists like Witten and others have made very important contributions to old-fashioned quantum field theory and thereby stimulated some important new lines of mathematical research. This has been an important feature of the strange era of strings, wherein most high-energy theorists are fashion-followers, and every academic physics department feels it has to scramble for the crumbs from the string table. But it also indicates that string theorists are very smart people - they just labor under the delusions created by the false-messianic expectations surrounding string theory as the putative Theory of Everything. It's clear now that string theory is actually of Theory of Anything (anthropic principle again) or maybe a Theory of Nothing.

Not Even Wrong makes many of the same points that Smolin's book does, but being shorter, it's more demanding on the reader; Smolin is more leisurely and parses the physics more explicitly for the non-technical reader. That shouldn't deter Woit's potential readers. A generation of theorists have worked in an ultracompetitive environment, constrained by limited resources, under a cloud of intellectual failure. Theoretical physics should not be allowed another generation to stew in such a dead-end. As a mathematician, Woit has a different approach to getting theoretical physics out of this rut. Without experiment to keep them honest, theorists need to adopt an attitude much closer to mathematics, one where rigor and precision take the place of experiment as guiding lights. String theory has been neither good physics nor good mathematics. It's not physics in the usual sense - there are not only no experiments, there are not even predictions - but it's too speculative, conjectural, and full of holes to be serious mathematics. A lot of important work in pure quantum field theory in the last 25 years does fit this bill, however, and that should be a starting point for the future.

Woit also points out that physicists have barely made use of the full power of symmetry and symmetry representations. Strings add no new symmetry principle to physics. For all the hype surrounding string theory as a beautiful theory, the theory is actually quite ugly and full of apparently unresolvable difficulties. That's another sign it's the wrong road.

Woit's mathematics makes a nice complement to the more physical arguments of Smolin. Both books are superb pieces of popular science and deserve to be taken very seriously by physicists, academic and goverment leaders responsible for the direction and funding of science research, and the general reader.

POSTSCRIPT: Smolin moved in 2001 to the Perimeter Institute in Ontario. Woit has a very readable blog at his home base (Columbia), with lots of interesting links.

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