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Fit to Be Tied

Impatience with string theory boils over

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11:49am, October 17, 2006
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Jazz musician Ken Hatfield entitled his compact disc released in June String Theory. A quilt-maker, Denyse Schmidt, offers quilts with the same title in two color schemes. Elizabeth Dewberry's novel His Lovely Wife (2006, Harcourt), about a woman married to a Nobel laureate physicist, "uses string theory to weave together two women's lives," the publisher's note says. The abstruse theory asserting that infinitesimal strings of energy make up the most fundamental constituents of the universe is flourishing as an icon of scientific brilliance.

Much of the theory's mainstream popularity stems from glowing presentations of it that have been aimed at general audiences: For instance, Columbia University string theorist Brian R. Greene's The Elegant Universe (1999, W.W. Norton) and his 2003 television special based on the book. Last month, however, two new general-audience books came out—one by a mathematician with a Ph.D. degree in theoretical particle physics and the other by a physicist who sometimes works in string theory—that cast string theory in a dramatically unflattering light.

The books—Not Even Wrong (2006, Basic Books) by mathematician Peter Woit of Columbia University and The Trouble with Physics (2006, Houghton Mifflin) by theoretical physicist Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario—assail string theory as sketchy, ambiguous, and untestable.

"Any further progress toward understanding the most fundamental constituents of the universe will require physicists to abandon the now ossified ideology" of string theory, writes Woit.

The two authors also charge that string theory practitioners stifle rival theoretical approaches to fundamental physics while ignoring increasingly obvious weaknesses of their own theorizing. "The ethics of science have been to some degree corrupted" by both string theorists and their academic institutions, Smolin claims.

Defending their enterprise and themselves, string theorists excuse their model's shortcomings as typical for a work in progress. Not only has the field made important strides, they say, but also its ranks have swelled because of those successes.

Worlds apart

In string theory, the universe is at once wildly different than scientists have so far thought it to be and potentially more thoroughly explained than it is by conventional theory.

In string theory's universe, space-time includes six or seven dimensions beyond the familiar three of space and one of time. In many versions of string theory, strings of energy coexist with extended objects called branes—short for membranes—that can also exist in many-dimensional forms. In numerous iterations of the theory, extra dimensions curl up tightly upon themselves and therefore aren't observed (SN: 2/19/00, p. 122: Hunting for Higher Dimensions).

Although the string universe includes the pointlike, elementary particles of conventional physics, such as quarks and electrons, those are just vibrations of the more-fundamental strings. In string theory, there are also many yet-to-be-discovered particles that are partners to those already known. The hypothesis of partner particles arises from a concept called supersymmetry, so researchers also refer to string theory as superstring theory.

By going out on a limb with extra dimensions and extra particles, string theorists get glimpses of possible answers to major questions that conventional theory has left unanswered. For example: Are the four basic forces of nature—the electromagnetic force, the weak force that controls nuclear decays, the strong force that holds atomic nuclei together, and gravity—variations of a single, more fundamental force? Many physicists suspect that they are, but today's prevailing theory of particle physics has revealed intimate connections only between the electromagnetic and weak forces.

Yet in string theory, simple behaviors of strings—for instance, how they vibrate and whether they break or form loops—generate not only all four forces but also all the elementary particles.

For that reason and others, many researchers see string theory as a potential theory of everything—a unified, mathematical framework that accounts for all forces and particles and resolves other dilemmas about the nature of space and time.

The enthusiasts have conjectured that there is a deeper version of the theory, dubbed M theory, that they simply haven't found yet.

Hypothetical

Despite the nearly 40-year-old theory's apparent promise, string theory remains just an outline, say the new books.

Over the years, string researchers have devised explicit equations for only a few parts of the theory, and they have solved them under extraordinarily limited circumstances, Woit and Smolin both argue. And even when string theorists have done so, the answers they've gotten are often found to disagree with facts or accepted physical laws. For instance, to be compatible with Einstein's general theory of relativity, early string theory equations required a 26-dimensional universe and a highly unlikely particle, called a tachyon, that travels faster than the speed of light.

The theory is so underdeveloped that it's "not even wrong," says Woit, borrowing the phrase from the acerbic Austrian theorist Wolfgang Pauli, a pioneer of quantum mechanics.

Because the theory is so sketchy, it's unable to generate specific predictions, the critics say. The only predictions that string theory has come up with simply duplicate those made by better-established theories.

Smolin identifies string theory's dearth of predictions as "the crux" of what's amiss with the field. For a theory to be tested and accepted, he writes, "it must make a new prediction—different from those made by previous theories—for an experiment not yet done."

For both Smolin and Woit, the most glaring evidence that string theory is incapable of making testable predictions emerged in 2003 in an analysis that has convinced most researchers that 10500, or even more, versions of string theory are possible.

Some string researchers regard this plethora of theories as a hint that multiple universes exist and that a unique version of string theory plays out in each of them. Theorists refer to this array of possible universes, called vacuum states, as the landscape.

"The possible existence of, say, 10500 consistent different vacuum states for superstring theory probably destroys the hope of using the theory to predict anything," writes Woit.

Proponents of string theory readily admit in books, articles, and interviews with Science News that the theory remains rudimentary and devoid of predictions. However, the potentially extraordinary payoff—a theory of everything—makes the task of fleshing out the theory unusually deserving of patience and perseverance, supporters say. Moreover, they argue that they have been making progress.

String researcher Barton Zwiebach of the Massachusetts Institute of Technology points out, for instance, that string theorists have devised a theoretical model of black holes that seems to resolve a fundamental puzzle about those objects. Physicists hadn't figured out how a black hole—as a uniform, ultradense ball of matter—could have any substructure. Yet thermodynamics suggests that black holes aren't homogeneous.

"In string theory, the black hole can be seen as built from strings and branes," says Zwiebach. "It's a spectacular insight."

Even the landscape of possible universes, although it has alarmed some leaders of string physics, might be good thing, argues Leonard Susskind of Stanford University, one of string theory's founders. Although he declined to be interviewed for this article, he has written extensively about the landscape in scientific papers, on Web sites, and in a general-audience book published last December, entitled The Cosmic Landscape: String Theory and the Illusion of Intelligent Design (2005, Little, Brown and Co.).

Thanks to the landscape's many versions of string theory, he says, at least some of them are compatible with recent astronomical observations indicating that the universe's expansion is accelerating because of an unknown called dark energy (SN: 1/21/06, p. 35: Available to subscribers at Cosmic Push: Finding pieces of a dark puzzle).

Defenders of string theory also say that experiments will soon probe some elements of their proposals—most notably, extra dimensions—even though decisive tests aren't yet possible. String theorist Joseph G. Polchinski of the University of California, Santa Barbara notes that in the next couple of years, the Large Hadron Collider, near Geneva, Switzerland, will start operating. With this most powerful particle collider ever built, physicists will look for evidence of energy escaping into hidden dimensions or other clues of such extra realms, says Polchinski.

"Then we could say, 'Look, there they are,'" he says.

Stringled

Scientists typically abandon theories that remain inaccessible to experiment for as long as string theory has, Woit and Smolin argue. So, they ask, what keeps string theory afloat?

"What we are dealing with is a sociological phenomenon," answers Smolin. Both he and Woit attribute string theory's popularity and longevity to social and financial pressures—an excess of theoretical-physics graduates and stagnant research funding, for example—and a culture of arrogance, closed mindedness, and self-promotion among entrenched string theorists. Many researchers in the string field hotly contest that analysis.

Back in the mid-1980s, Woit and Smolin each watched from the margins as string theory's popularity surged. Woit, age 48, tells Science News that as a theoretical-physics postdoc, he felt his field turn inhospitable because he preferred to delve deeper into standard theory rather than to pursue string theory.

Now an untenured mathematician, Woit teaches courses and administers the computer system for Columbia University's math department.

Smolin, 51, has worked on string theory at times, but he has played a prominent role in developing rival theories.

Even though string theory hasn't panned out, Woit and Smolin claim, its senior practitioners cling to increasingly far-fetched dreams and use their influence to gather the lion's share of resources. Smolin devotes most of a chapter of his book to enumerating "seven unusual aspects of the string theory community" that have enabled its members to create their self-perpetuating enterprise. Among those aspects are overweening self-confidence, intellectual conformity, clannishness, and disregard for the ideas of outsiders. Smolin has even invoked a sociological theory that originated in the 1970s, called groupthink, to explain what has happened.

String proponents bristle at that characterization, suggesting that maybe the critics themselves are being arrogant. "It's a little funny for Woit and Smolin to be making a judgment about how we should be carrying on our research," says string theorist Andrew Strominger of Harvard University.

Strominger also disputes that jobs and perks, rather than string theory's scientific merits, attract young researchers. Strong string-theorist groups have arisen not because they've been buoyed by the physics establishment, he says, but because young physicists have found string theory to be the best way to answer some of the most puzzling questions that they encounter. "It was really a kind of grassroots thing," Strominger told Science News.

Woit's and Smolin's books have generated plenty of buzz in the media, earning reviews and mentions in such publications as the Wall Street Journal, the New York Times, USA Today, and Time. The books are also part of a broader debate taking place on the Web, where Woit has maintained a blog since 2004 (www.math.columbia.edu/~woit/wordpress/).

The backlash against string theory might hurt its public image. Fewer musicians, artists, novelists, and other nonscientists may want to associate their creations and products with the theory. Woit hopes the criticisms are heard. "If the public gets interested in this and causes the physics community to have a debate about the whole subject, so much the better," he says.

Even some leading string theorists say they'd welcome an image shift, but for a different reason. "I've felt for a long time that the general public's impression of what string theory had accomplished and how much of it was correct was too positive," Strominger says. Maybe if the public comes to expect less of string theory, he adds, they'll ultimately appreciate it more.


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