Saturday, November 17, 2007

"Why am I surrounded by idiots?"

That's the worry, at the moment, of Luboš Motl. It is prompted, at the moment, by the fact that this preprint, that Motl calls "a huge joke", is attracting significant media attention.

When such "manifestly crackpot" work can cause such excitement, one is inclined to sympathise with Motl when he frets: 'Would cranks with their "theories of everything" who know less than 1% what I do and whose IQ is 45 below mine - literally an inferior species - would be placed upon us or even dictate what we can think about physics? Well, this epoch just here...'

Motl observes that the author, Garrett Lisi, is so ignorant of basic physics as to add fermions to bosons, or Grassman numbers to ordinary numbers. As he says, high school students know not to add quantities of different dimensions. So this Lisi guy must be quite a crank.

But the media quotes some well-known physicists -- Lee Smolin, for one -- as being quite excited by Lisi's work. And Abhay Ashtekar is quoted here as being receptive to the work, and unconcerned about its defects: "You have to solve problems one at a time." We're surrounded by crackpots.

Or maybe Motl missed something? Lisi thinks so.

What is this work that is causing so much fuss? It is a preprint with the bombastic title "An Exceptionally Simple Theory of Everything", placed online by Garrett Lisi earlier this month. (Its categorisation on the arXiv seems itself to have been a matter of some controversy.) The title is partly a parody of the grandiose claims that have been made by string theorists in recent times, and partly a pun on its subject matter: it deals with the E8 group, a Lie group that is simple and exceptional.

Unfortunately (or fortunately) I studied quite different areas of physics, and have only a hazy idea of what this preprint is about (much less whether it is correct). However, it is clearly not a theory of everything; Lisi himself says it is at best a starting point that may prove to be wrong.

The background is that the "holy grail" of physics, since the middle of the twentieth century, has been to unify the four "fundamental interactions" known in nature. Three -- the strong, weak, and electromagnetic interactions -- are unified in the "standard model" that has been accepted since the 1970s. Efforts to include the fourth -- gravitation -- have proven futile.

Since the late 1970s, a particular idea has taken hold among a section of the physics community: the idea that the fundamental entities of nature are not particles, but one-dimensional strings. There has never been any empirical evidence for this, but many physicists have found the mathematics very attractive, with the result that an enormous body of work on "string theory" has been done in the past three decades. Yet there is not a single testable prediction. Worse, recent results in string theory suggest that our universe may be only one of 10500 possible universes. Such a result destroys any predictive power of the theory, without resorting to the "anthropic principle" ("our universe is the way it is because if it weren't so, we wouldn't be here") -- a principle understandably scorned by many physicists. Dissatisfaction with string theory resulted in the publication of two books, Lee Smolin's "The trouble with physics" and Peter Woit's "Not even wrong", last year. These authors argued that physics was in crisis because of the over-focus on string theory for three decades that had not only failed to produce any useful predictions, but had usurped some of the best younger minds (and funding) in the process. The books upset many string theorists; Motl is one of those who took up cudgels on behalf of his field, writing savage reviews on of Smolin's book (that was later removed by Amazon) as well as Woit's book, and also attacking them on his own blog and elsewhere.

Other approaches to "quantum gravity" have been tried, with no better success; "loop quantum gravity" is one of the more popular. Smolin and Ashtekar belong in the LQG camp, that attracts Motl's hostility.

As far as I can tell, Garrett Lisi doesn't claim to have solved the problem, but he claims to have found a significant piece of the puzzle. He believes that the "particle zoo" that we know today is related by the E8 symmetry (much as the strong interaction is associated with a SU(3) symmetry and the electroweak interaction with SU(2)xU(1)), associating particles with the 248 basis elements of E8, and that this framework predicts 20 new particles that could conceivably be found by the Large Hadron Collider (thus making his theory testable). His theory makes a number of other concrete predictions, many of which agree with what is observed so far. Notably, it requires only the three spatial and one temporal dimension that we actually know; string theory requires many additional dimensions to work.

That's about all I understand of the work. I'm hoping some of my colleagues will tell me what they think.

Garrett Lisi himself is an unorthodox character: he has a Ph.D. from UCSD, but no current association with any university; he spends his non-physics time surfing, snowboarding, or doing odd jobs to make ends meet (he says, "Being poor sucks. It's hard to figure out the secrets of the universe when you're trying to figure out where you and your girlfriend are going to sleep next month."). However, he is a recent recipient of a sizeable grant from the Foundational Questions Institute, enabling him to do independent research.

If this theory turns out to make correct predictions, he can certainly expect much bigger prizes to come his way. And string theorists may need to think of changing their field.

A fun take on the story is from Uncyclopedia (which, for the uninitiated, is a sort of bizarro-Wikipedia).
(Dr Lisi purportedly says:) "String theory is something that doesn't work, for guys without charm or a personality. No romantic prospect worth talking to will take a string theorist seriously."
Dr Lisi is not fazed [by Motl's attacks]. "String theory is a dying field," he said. "I mean, it's not like they're going to reproduce."

1 comment:

km said...

If "Wired" covered it, is it still science?

Why do people read Wired?