String Theory is the darling of theoretical physics but there's no way to test it. Does this qualify as a dead end?

woitbook.jpg smolinbook.jpg Credit: Mark Weiss

Not Even Wrong
By Peter Woit
(Basic Books)

The Trouble With Physics
By Lee Smolin
(Houghton Mifflin)

Is string theory like masturbation? In the past, hostile physicists have likened the stringy “theory of everything” to onanism—a self-gratifying dead-end in the search for the Ultimate Answer. It’s now been half a century since Albert Einstein’s death and scientists still don’t have a single overarching theory that reconciles quantum theory and relativity, explaining the behavior of all the particles and forces in the universe. Physicists are stuck with two mutually contradictory sets of rules, while they believe that nature herself has only one law.

Of all the attempts to create a “theory of everything,” superstring theory is by far the most famous. Despite the theory’s complexity—it posits that the tiniest motes of matter and energy are infinitesimal strings that inhabit 10 or 11 dimensions—it has become a staple of pop-science culture. Popular books, newspaper and magazine articles, websites and TV specials have brought multidimensional mathematics to the masses. As a result, string theory is perceived as the pinnacle of modern physics theory—at least to the cocktail-party cognoscenti. Within the ranks of physics, it gets more complicated.

Now two books, Peter Woit’s Not Even Wrong and Lee Smolin’s The Trouble With Physics, attempt to knock string theory off its perch. Together they make some pretty damning claims: both argue that string theory might be fashionable, but that it’s a false idol—and that, for all its tantalizing promise, string theory isn’t really even science.

The basic complaints aren’t new; for more than a decade, physicists, journalists and other critics have argued that string theory has strayed too far from its experimental moorings. A particle accelerator powerful enough to probe the theory directly, for example, would have to be much bigger than the solar system (barring almost unfathomable technological advances). This leaves open the nagging fear that string theory is untestable, and therefore unfalsifiable—which would mean it’s natural philosophy rather than science.

Credit: Rodney White

String theory has evolved since the first critics emerged, and, to some extent, so have the arguments against it. For example, within the past few years, some scientists have started attacking the “landscape problem”: the idea that there are an immense number of models, based on string theory, that can explain our universe—more models by far, than there are atoms in the universe. But the most powerful anti-string-theory arguments are fundamentally the same as they were a decade ago: that the theory fails to meet the definition of science. Woit and Smolin are the latest to take this tack, but their books go further to express a grim warning that theoretical physics has taken a very wrong turn.

Woit’s book is the more strident of the two. Even the title drips with scorn; “not even wrong” was the worst insult that quantum physicist Wolfgang Pauli could throw at a theory, deeming an idea so poor that it doesn’t even rise to the level of being wrong. Woit, a mathematical physicist at Columbia University, has devoted much of his recent career to attacking string theory (largely via his well-trafficked blog which, not so coincidentally, has the same name as his book), and many of his barbs hit home. For example, Woit spends a thought-provoking chapter attacking the large “landscape” of superstring theories. Because the landscape is so vast, no matter what you observe in nature, you’ll be able to find a theory that will fit the observations—which means that it’s impossible to prove the overall idea wrong. See something that contradicts your favorite string theory? Just move around on the landscape a little bit until you find one that suits you better. Woit argues that this prevents string theory from ever being truly testable; every time you find something that seems to disprove it, the theory can reshape itself to fit the available facts. Conversely, this means that string theory as a whole doesn’t give you any concrete predictions—and a scientific theory without predictions isn’t a scientific theory.

See something that contradicts your favorite string theory? Just move around on the landscape a little bit until you find one that suits you better.

Smolin, a theoretician at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, also takes issue with the landscape. But as a proponent of a rival theory known as loop quantum gravity, Smolin has a slightly different perspective. While string theory modifies the structure of subatomic particles—proposing that they’re stringy rather than pointlike—loop quantum gravity modifies the structure of space and time, positing that they are gnarled and tangled rather than smooth like relativity implies. Smolin, who’s worked on string theory in the past, struggles to keep his book from seeming like a partisan attack from a rival. “I can only insist that I am writing this book not to attack string theory or those who believe in it, but out of admiration for them and, above all, as an expression of faith in the physics scientific community,” he writes. However, when he accuses string theorists of “groupthink,” it’s hard to imagine it’s done out of admiration.

When the two books are placed side by side, Smolin’s comes out ahead. Woit’s Not Even Wrong is uneven; the focus is a bit fuzzy, the prose is occasionally stilted and passive and the level of detail is inconsistent—some technical terms like “synchrotron radiation” and “eigenstate” are left unexplained, making it likely that the lay reader will give up before the payoff in the later chapters. (However, the persistent will be rewarded by, among other things, a first-person account of Woit’s investigations of a scientific quasi-hoax: the curious case of the two French brothers whose publications left physicists wondering whether they were the victims of a joke.) Smolin’s The Trouble With Physics is much more polished. His prose is much smoother and the text is more coherent than Woit’s. He also possesses a talent for presenting physics from a novel and interesting perspective—such as an insightful chapter in which he presents all of the great discoveries in physics as “unifications” of one sort or another.

Nevertheless, both of these books suffer from the same flaw: a nagging double standard. Yes, string theory has a vast landscape of possible solutions and it doesn’t make any predictions that can be tested in the near future. The same could have been said of inflationary theory two decades ago, which virtually all physicists now accept without qualms. (Only very recently have cosmologists gained the ability to test which of the many versions of inflation is correct.) Yes, string theory is too malleable; it allows its proponents too much leeway to tweak their work to fit evidence, cleaving to positive results and ignoring negative ones. However, many scientists—Smolin included—will put on rose-colored glasses when their theories are constrained by contrary data. Though he only brings it up as a point of comparison, in one chapter Smolin describes an alternative gravity theory (MOND) without indicating that it has been badly undermined by telescope data. He then uses cosmic ray observations from an observatory (AGASA) that seem to have a systematic flaw in them; alludes to a measurement of light spectra from the Keck telescope without mentioning that there are several solid observations to the contrary; and hints at a breakdown of gravity on small scales, even though the group that did the experiment didn’t publish the results because it was unable to replicate them.

Scientific progress is always subject to human failings, and the line between science and philosophy, between universal truth and cloying falsehood, isn’t always clean. String theory might be completely wrong—it may be a passing fad that will be as embarrassing as the idea that a beam of light is really a disturbance of a substance called ether. But when someone comes up with a more compelling idea, physicists will shift allegiances very quickly. Until then, the debate will go on, and physicists will continue arguing about their subatomic motes and beams of light.

—Charles Seife is an associate professor of journalism at New York University and the author of Decoding the Universe: How the New Science of Information Is Explaining Everything in the Cosmos, from Our Brains to Black Holes.

Originally published September 19, 2006


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