Jonathan Cape, £18.99
"String theory is still promising," I once heard the physicist and Nobel laureate Frank Wilczek quip, "and promising, and promising." String theory is a so-called unified theory, which attempts to wrap quantum mechanics and relativity into one tidy mathematical explanation of all nature's forces, and it has been promising for more than 20 years now without delivering.
Depending on which variant you prefer, string theory holds that reality is woven out of infinitesimal strings, or loops, or membranes vibrating in a hyperspace of ten, or 11, or whatever dimensions. Advocates—I will call them "pluckers"—claim that string theory represents a "theory of everything" that will answer the most profound of all questions: how did the universe come to be? And why did it take this particular form rather than some other form that would not have permitted our existence?
In his 1988 blockbuster A Brief History of Time, Stephen Hawking nominated string theory as the best candidate for a solution to the riddle of the cosmos. Since then, proponents have continued to sing strings' praises in popular books such as Parallel Worlds by Michio Kaku, Warped Passages by Lisa Randall and the monster bestsellers The Elegant Universe and The Fabric of the Cosmos by Brian Greene (who also hosted a television series about string theory). Moreover, string theorists dominate particle physics in terms of publications, grants and tenured faculty positions—even though they have not produced an iota of evidence for the theory. The MacArthur Foundation has awarded nine fellowships for particle physics since 1981, and eight have gone to pluckers. Of the 22 physicists who have received their doctorates since 1981 and gone on to receive tenure at the leading physics universities—Berkeley, Caltech, Harvard, MIT, Princeton and Stanford—20 specialise in strings. The director of the prestigious Institute for Advanced Study and half of its physics faculty are string theorists.
String theory has always had detractors. Richard Feynman liked to say that string theorists don't make predictions, they make excuses, and his fellow Nobel laureate Sheldon Glashow has compared pluckers to medieval theologians debating how many angels can dance on the head of a pin. I have also criticised string theory in my 1996 book The End of Science and elsewhere. But Not Even Wrong by the mathematician and physicist Peter Woit of Columbia University is the first book-length critique of the theory. Woit first sent the book to Cambridge University Press three years ago, but the publisher rejected the manuscript after pro-string referees panned it. Ironically, Woit then found trade publishers—Cape in the UK and Basic Books in the US—who should help him reach a larger audience.
Woit's book expands upon arguments that he first aired on a physics website in 2001 and has elaborated on a blog also titled "Not Even Wrong," echoing the legendary put-down by physicist Wolfgang Pauli. Woit's charge is that string theory is so speculative—so utterly disconnected from the physical reality that physicists can actually probe with accelerators and other instruments—that it is "not even wrong."
Unlike string theorists, Woit—who obtained a doctorate in physics from Princeton but later turned to mathematics—does not want readers to take his arguments on faith, and so he lays them out carefully. As a result, his book can be difficult to follow, particularly in the middle chapters where he walks readers through the recent history not only of string theory but of particle physics in general. But his basic points are relatively simple and clearly stated.
First of all, strings, or membranes, or whatever, are very, very small—as small in comparison to a proton as a proton is in comparison to the entire solar system—and probing these scales requires smashing particles together with enormous force. The large hadron collider, which will be the most powerful accelerator in the world when it comes online next year at Cern, the big particle physics laboratory, is 27km in circumference. Scaling up from this technology, physicists would have to build a particle accelerator 1,000 light years in circumference to probe the micro-realm where strings supposedly shimmy and shake. But even if physicists had such an accelerator, Woit asserts, they still could not confirm string theory because it does not make any precise predictions. Or rather, it makes so many predictions that it cannot be falsified.
Some critics call this surfeit of predictions "the Alice's Restaurant problem," a reference to the refrain of the Arlo Guthrie folk song: "You can get everything you want at Alice's restaurant." "Being able to get anything one wants may be desirable in a restaurant, but isn't at all in a physical theory," Woit comments. In other words, far from answering Einstein's question about whether God had any choice in creating the universe, string theory deepens the mystery of why we find ourselves in this particular cosmos.
Woit gives much of the credit, or blame, for the popularity of string theory to Edward Witten of the Institute for Advanced Study, who has been called the most brilliant physicist since Einstein, if not Newton. Although he did not invent string theory, Witten fell in love with the theory in the early 1980s and has proselytised for it ever since, most effectively through a series of papers that have solved key theoretical problems. Woit met Witten while they were at Harvard and Princeton and clearly likes and respects him. But noting that Einstein spent his late career vainly pursuing his version of a unified theory, Woit remarks that "genius is no protection against making the mistake of devoting decades of one's life to an idea that has no chance of success."
Witten and other pluckers have often argued that string theory is too "beautiful" to be wrong. But as Woit points out, the term "beauty," when applied to scientific theories, usually refers to elegance, simplicity and clarity, and even proponents of string theory concede that it is hideously complex. Witten himself once told me that he initially found string theory to be "opaque." When pressed, some pluckers suggest that the beauty of string theory stems from the sense it evokes of mysterious, hidden depths. String theory is sometimes called M-theory, and Witten has said that the "M" stands not only for "membrane" but also for "magic" and "mystery." In other words, the aesthetic allure of string theory has less to do with simplicity and clarity than with incomprehensibility.
Woit considers, but ultimately rejects, the claim made by some critics that string theory is a cult whose guru is Witten. But Woit adds that "as years go by and it becomes clear that superstring theory has failed as a viable idea about unification, the refusal to acknowledge this begins to take on ever more disturbing implications." String theory may not be a cult, Woit concludes, but it is not really science either if advocates stubbornly refuse to acknowledge the theory's flaws and failure to yield testable predictions.
Woit tries to end his book on an optimistic note. Even if string theory represents a dead end, he contends, theoretical physics still has a future, because progress in mathematics may trigger revolutions as profound as those that took place a century ago in physics. I have my doubts. String theory already represents an attempt to understand nature through mathematical argumentation rather than empirical tests. To break out of its current impasse, physics desperately needs not new mathematics but new experimental findings, especially those that contradict the so-called standard model of particle physics, which for decades has been crushingly effective at explaining new data. But society seems increasingly reluctant to spend the enormous sums necessary to build accelerators that can probe smaller distances and higher energies.
Is the tide turning against string theory? Not Even Wrong will soon be joined in bookstores by another anti-string polemic, The Trouble with Physics, by the prominent theorist Lee Smolin of Canada's Perimeter Institute. These developments, I hope, will embolden other string critics to speak up and encourage talented young physicists to pursue other lines of research.
References to strings and membranes and higher dimensions are now a staple of New Age "science" books. Woit notes with amusement that Maharishi Mahesh Yogi, founder of the transcendental meditation movement, has declared that "40 aspects of the Veda and Vedic Literature have been derived from the mathematical formula of the united field as given by superstring theory." So even if mainstream physicists cease to take string theory seriously, I suspect that stringy memes will continue to infect the culture at large for many years to come.
