Theorists Snap Over String Pieces

NATURE|Vol 443|5 October 2006 NEWS

JAVA MUD VOLCANO SEEMS UNSTOPPABLE Could Indonesia’s mud flow be put to good use? www.nature.com/news CRISP Theorists snap over string pieces

Two recently published books are riling the Brian Greene’s 1999 bestseller The Elegant small but influential community of string Universe, which said that the approach might theorists, by arguing that the field is wandering unify the incompatible theories of gravity and D. F. GRASER F. D. dangerously far from the mainstream. quantum mechanics. The books’ titles say it all: Not Even Wrong, a phrase that physicist Wolfgang Pauli used Strung up to describe incomplete ideas, and The Trou- But the theory has its share of problems, and ble with Physics: The Rise of String Theory, the these are the focus of the new works. For one Fall of a Science, and What Comes Next. Both thing, recent calculations suggest that it gen- articulate a fear that the field is becoming too erates 10500 possible models of the Universe abstract and is focusing on aesthetics rather (see Nature 439, 10–12; 2006). This renders than reality. Some physicists even warn that the theory essentially meaningless, according the theory’s dominance could pose a threat to to critics. When these countless possibilities the scientific method itself (see page 507). were first announced, Lee Smolin was already Those accusations are vehemently denied working on the book that eventually became “None of the major string theory by string theorists, and the books — written by The Trouble With Physics. A physicist at the outsiders — have stirred deep resentment in the Perimeter Institute for Theoretical Physics groups has hired someone tight-knit community. Not Even Wrong was pub- in Waterloo, Canada, Smolin had previously working in any of the other lished in June and The Trouble with Physics came worked on string theory. “I and many other approaches to quantum gravity.” out in September; shortly after they appeared on people began to get worried,” he says. the Amazon books website, string theorist Luboš Another difficulty is that if strings exist, Motl of Harvard University posted reviews furi- they would be detectable only at energies far theorist at Swansea University in Wales, agrees. ously entitled “Bitter emotions and obsolete above anything that today’s experiments can In recent years, he says, string theory has been understanding of high-energy physics” and measure. “As you’re not constrained by hav- proven equivalent to a conventional ‘field “Another postmodern diatribe against modern ing to reproduce experiments, you can go off theory’, of the type being used to predict how physics and scientific method”. As Nature went and play with whatever you want,” says Peter particles will behave at the soon-to-open Large to press, the reviews had been removed. Woit, a mathematician at Columbia Univer- Hadron Collider, sited near Geneva. “There Few in the community are, at least publicly, sity in New York City, and author of Not Even has been a lot of cross-talk between field theory as vitriolic as Motl. But many are angry and Wrong. “The danger is that you’ll end up with and string theory,” says Perkins. In some cases, struggling to deal with the criticism. “Most the theoretical community becoming com- string theory has provided far simpler approxi- of my friends are quietly upset,” says Leonard pletely isolated from the rest of physics.” mations than its field-theory counterpart. Susskind, a string theorist at Stanford Univer- Smolin, whose book promotes an alternative But strings have yet to provide the elusive sity in California. theory known as loop quantum gravity, adds link between gravity and quantum mechanics, String theory postulates that the Universe that string theorists have intentionally cut hoped for by so many theorists. “The claims, consists of tiny strings vibrating in ten or so themselves off. “None of the major string theory when it comes to theoretical physics, tend to dimensions. Its fortunes have been buoyed groups has hired a postdoc or faculty member be exaggerated,” says Abhay Ashtekar, who by popular books in the past — most notably working in any of the other approaches to quan- works on quantum gravity at Pennsylvania State tum gravity,” he says. “But other research groups University in University Park. He believes the in quantum gravity have often hired young inability of the community to live up to those

P. CRUZ people working in string theory out of a sense expectations has made it defensive. that it should be encouraged.” The books leave string theorists such as Suss- kind wondering how to approach such strong Boundary issues public criticism. “I don’t know if the right thing String theorists dispute the claim that they is to worry about the public image or keep are isolating themselves. In recent years the quiet,” he says. He fears the argument may “fuel theory has contributed significantly to heavy- the discrediting of scientific expertise”. ion physics, according to Joe Polchinski, a string That’s something that Smolin and Woit theorist at the Kavli Institute for Theoretical insist they don’t want. Woit says his problem Physics in Santa Barbara, California. When the isn’t with the theory itself, just some of its more Relativistic Heavy Ion Collider at Brookhaven grandiose claims. “There are some real things National Laboratory in Upton, New York, first you can do with string theory,” he says. “The danger is that you’ll end up produced a hot quark gas, it was string theory Smolin agrees, and says he hopes theorists that correctly predicted, retrospectively, some will read his book to get a better understanding with the theoretical community of the gas’s properties. “In many ways, I feel of his specific issues. “If they don’t want to buy becoming completely isolated the boundaries with other areas of physics are it, tell them to get in touch with me and I’ll send from the rest of physics.” coming down,” Polchinski says. them a copy.” ■ Warren Perkins, a cosmologist and particle Geoff Brumfiel