Friday, September 29, 2006

Strings in the New Yorker

I think the article, which discusses the new books by Woit and Smolin, is very fair, and it ends with a surprisingly mature recapitulation of the decoupling theorem and the irrelevance of quantum gravity to applied science. Every man, woman and child should read it and then ask their local particle theorist for more clarification.

I've read chunks of Smolin's book and it's quite good, although not without flaws. I have to go back and reread it -- I picked it up in a bookstore and couldn't put it down for at least an hour. I found his discussion of finiteness of string perturbation theory confusing -- he represents Mandelstam as saying one thing in the main text, but the email quoted in the footnotes doesn't seem to back it up. If the analytic continuation is the only problem then it's not on worse footing than many other results in theoretical physics. But, then, what have D'Hoker and Phong (and my grad school colleague Nathan Berkovits) been up to all this time? If I believed in string theory I'd have to spend some time sorting this all out.

...Today, more than a decade after the second revolution, the theory formerly known as strings remains a seductive conjecture rather than an actual set of equations, and the non-uniqueness problem has grown to ridiculous proportions. At the latest count, the number of string theories is estimated to be something like one followed by five hundred zeros. “Why not just take this situation as a reductio ad absurdum?” Smolin asks. But some string theorists are unabashed: each member of this vast ensemble of alternative theories, they observe, describes a different possible universe, one with its own “local weather” and history. What if all these possible universes actually exist? Perhaps every one of them bubbled into being just as our universe did. (Physicists who believe in such a “multiverse” sometimes picture it as a cosmic champagne glass frothing with universe-bubbles.) Most of these universes will not be biofriendly, but a few will have precisely the right conditions for the emergence of intelligent life-forms like us. The fact that our universe appears to be fine-tuned to engender life is not a matter of luck. Rather, it is a consequence of the “anthropic principle”: if our universe weren’t the way it is, we wouldn’t be here to observe it. Partisans of the anthropic principle say that it can be used to weed out all the versions of string theory that are incompatible with our existence, and so rescue string theory from the problem of non-uniqueness.

...Neither Smolin nor Woit calls for the forcible suppression of string theory. They simply ask for a little more diversity. “We are talking about perhaps two dozen theorists,” Smolin says. This is an exceedingly modest request, for theoretical physics is the cheapest of endeavors. Its practitioners require no expensive equipment. All they need is legal pads and pencils and blackboards and chalk to ply their trade, plus room and board and health insurance and a place to park their bikes. Intellectually daunting as the crisis in physics may be, its practical solution would seem to demand little more than the annual interest on the rounding error of a Google founder’s fortune.

“How strange it would be if the final theory were to be discovered in our own lifetimes!” Steven Weinberg wrote some years ago, adding that such a discovery would mark the sharpest discontinuity in intellectual history since the beginning of modern science, in the seventeenth century. Of course, it is possible that a final theory will never be found, that neither string theory nor any of the alternatives mentioned by Smolin and Woit will come to anything. Perhaps the most fundamental truth about nature is simply beyond the human intellect, the way that quantum mechanics is beyond the intellect of a dog. Or perhaps, as Karl Popper believed, there will prove to be no end to the succession of deeper and deeper theories. And, even if a final theory is found, it will leave the questions about nature that most concern us—how the brain gives rise to consciousness, how we are constituted by our genes—untouched. Theoretical physics will be finished, but the rest of science will hardly notice.


Anonymous said...


What's your take on Woit's book? Smolin has also been all over public radio, see here and here, in a "debate" with Brian Greene.

Smolin and Woit seem to have a valid point: the String theorists seem to get more resources than is justified. Smolin recommends something akin to "Portfolio Diversification": why don't String Theorists take a hard look at other competing, and possibly more experimentally verifiable approaches.

Years of beatiful MATHEMATICS has not led to anything fundamentally new, or experimentally verifiable. If your Theory is really comprised of 4*10^100 sub theories, how useful is that.

Steve Hsu said...

I haven't had the chance to look at Woit's book, although I agree with many (not all) the things he writes on his blog. Our library has both books on order, so I'll eventually have a look at both of them.

My thoughts on string theory can be found by searching on the rhs of my blog for the word "string". To be concise: it might be right, it could easily be wrong, we won't know in my lifetime (probably hundreds of years at minimum). Most string theorists are very smart, but just as in the case of the Internet bubble (which I lived through), smart people can easily be wrong, esp. when social dynamics (Smolin's "groupthink", market bubbles, sociology, etc.) are involved.

Having been unsuccessful over 30 years in producing anything of use to experimentalists (real physicists), string theorists do not deserve academic compensation in excess of mathematicians. They should have roughly 1.5-2 times the teaching load of other physicists, and smaller grants. Anything else is just trading on hype.

Carson C. Chow said...

That was definitely one of the best popular pieces on physics I have ever read. The last paragraph somes up my position exactly. I once joked that I wanted to write a book in response to Greene's entitled "What the rest (and most) of us do".

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