Stringing Along
Hot on the heels of my recent post about string theory, I find that Sean Carroll has teamed up with some other physics types to start a new group blog, Cosmic Variance, and Sean has posted an article asking why people are mean to string theorists:
I am often surprised at the level of disdain and resentment with which string theory is viewed by non-string-theorists. I’m thinking not so much of people on the street, but of physicists, other scientists, and even other academics. As a physicist who is not personally identified as a string theorist, I get to hear all sorts of disparaging remarks about the field from experimental particle physicists, condensed matter physicists, astrophysicists, chemists, philosophers, and so on. I sometimes wonder whether most string theorists understand all the suspicion directed against them.
It shouldn’t be like this. String theory, with all of its difficulties, is by far the most promising route to one of the most long-lasting and ambitious goals of natural science: a complete understanding of the microscopic laws of nature. In particular, it is by far the most promising way to reconcile gravity and quantum mechanics, the most important unsolved problem in fundamental physics. At the moment, it’s a notably incomplete and frustrating theory, but not without genuinely astonishing successes to its credit.
The reasons have as much to do with sociology as physics. It's probably worth taking a little time (while the vacuum system pumps down) to lay out some of the reasons, as I see them.
I think one of the biggest problems string theorists face, on the more science-y end of things, is that the problems string theory addresses are awfully arcane and sort of abstract. Sean talks mostly about string theory as a path to a working theory of quantum gravity, which is a big deal for him, because he does cosmology, and has to worry about the intimate details of gravity as part of his everyday research. For those of us who only worry about gravity when balanced precariously atop a ladder, it's not such an immediate concern.
The other common argument for the importance of string theory is to cite the supposed ugliness of the Standard Model, and point out that you need to specify some large number of parameters in order for the theory to work. This may seem like a major crisis to people who are used to setting h-bar and c equal to one, but for those of us who work in SI units, it's not obvious why this is a big deal. The theory underlying my work requires dozens of input parameters, and I get along just fine. Yeah, it would be more satisfying if there were only one or two fundamental numbers that explained everything else. It would also be more satisfying if pi were exactly 3, but despite the best efforts of the Indiana state legislature, we're stuck with an irrational number.
(As an aside, it's a little hard to reconcile this argument against the Standard Model with Sean's counter-argument to Peter Woit's complaints about inifinite numbers of states:
Nobody complains that there are a huge number of possible quantum field theories, and we actually have to go out and measure the properties of actual particles rather than calculating them using pure thought. If string theory turns out to be the same way, that’s life.
(To be fair, though, Sean isn't using the "The Standard Model is ugly!" path to string theory, so it's not a direct conflict with anything he has said.)
The "astonishing successes" that Sean cites are also pretty abstract. Yes, you can get gravity to pop out of string theory in a very natural way, but it's still pretty abstract-- it's not like it predicts the exact correct value of the strength of gravity, or any other force for that matter. You can fiddle around with things, and make the theory reproduce the observations, more or less, but there are lots of theories you can construct that will reproduce the observed particle masses and interactions, with enough tinkering. String theory is just one among many theories with that property, only it brings with it an amazingly baroque apparatus of extra dimensions, parallel universes, and other weird and unobservable effects.
The baroque nature of string theory, in and of itself, is not a show-stopper. After all, quantum mechanics, relativity, and quantum field theory all make some pretty astounding predictions of their own-- matter waves, curved space, virtual particles. The difference is, all those theories very quickly made predictions that could be tested, and shown to be correct.
String theory, on the other hand, has been noodling around for twenty-odd years without producing a clear signature of any of this stuff. There are people out there working very hard to try to see some effect of extra dimensions, or whatever, but to the best of my knowledge, string theory has yet to make a unique prediction that has been verified. The theory can easily adapt to new observations-- neutrino masses, or whatever-- but it can just as easily be made to work with the old information.
Depending on what you take as the starting point, quantum mechanics probably took at least thirty years to gain general acceptance, and that was with clear experimental confirmation of the theory's predictions. Given the utter lack of experimental tests for string theory, it should come as no surprise that it's still looked at as something of a curiosity.
The biggest reasons for the poor opinion many scientists have of string theory are, as I said, rooted more in sociology. I know that my personal opinion of string theory is colored very strongly by a number of factors that have nothing to do with the quality of the science.
The short description of the problem is that string theorists very often present themselves and their work in a way that suggests a certain disdain for the rest of physics. There's a little of this in every discipline, but string theorists give a very strong impression of dividing the world of science into "String Theory" and "Stamp Collecting."
This manifests itself in a lot of little ways, starting with the asinine public statements made by many people who are associated with the field (see my previous post on the subject, linked above). When people pooh-pooh the need for experimental tests, as an experimental scientist I find that slightly offensive.
And string theorist in general seem to conduct their business in ways that flout the conventions of the rest of physics. It's not just the "proof by mathematical elegance" thing, but also things like the disdain for normal peer review and publishing inf avor of doing everything via the preprint server. Whether or not that's the wave of the future for physics in general, it's bound to rub some people (myself included) the wrong way.
(Of course, this is hardly confined exclusively to string theorists, though it seems to be more common among high-energy physics in general. When I was a post-doc, there were a couple of large groups that we never saw except at departmental seminars in their subfield, or at the departmental Christmas part. It was as if they regarded all other areas of physics as beneath their notice.
(And then there was the plenary talk by Steven Weinberg at the APS Centennial meeting. Weinberg was the first of three (I think) speakers, but as soon as he finished, about a third of the audience just got up and left. If you're not willing to show the minimal amount of courtesy required to listen to a talk in another field, well, that doesn't really do much for my impression of your field of research.)
Posted at 12:26 PM | link | follow-ups |