December 20, 2006

String Theory Seems to Unravel: Two New Books Seriously Question Whether the Once-Lauded String Theory Has Been Good for the Field of Physics

``The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next'' by Lee Smolin; Houghton Mifflin ($26)

``Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law'' by Peter Woit; Basic Books ($26)


I recently completed writing a high school/college-level history of physics in the 20th century. It was a great opportunity to catch up on developments in the field.

The biggest surprise turned out to be historical. For the first three-quarters of the century, progress in both theoretical and experimental physics steadily transformed our fundamental understanding of the physical universe. Then a multidimensional mathematical approach called string theory caught fire. To many physicists, it appeared to be the path to their science's holy grail, the "grand unification" of all known forces and fundamental particles into a single theory.

But, instead of continuing the advance of theoretical physics, the rise of string theory began a period filled with tantalizing near-miss formulations that continues until today. That is "The Trouble With Physics,'' according to the title of a new book by Lee Smolin, a onetime physics wunderkind who in mid-career founded the Perimeter Institute for Theoretical Physics in Waterloo, Ontario.

Smolin hasn't completely given up on string theory but is clearly pessimistic. His central argument is that it is time to start asking whether too many people are putting too much effort following ideas in string theory that seem promising at first but inevitably lead down blind alleys.

Smolin's assessment is downright rosy compared with the critique offered by Columbia University mathematician Peter Woit in "Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law.'' He draws his title from a famous remark by Wolfgang Pauli, who once described a particularly poorly written paper as "not even wrong." A wrong idea can be valuable if it ultimately leads one in a productive direction. String theory is not even wrong, Woit asserts, because each refinement seems to lead physicists further astray.

How can a science that has been so successful in describing the universe suddenly find itself in such a quandary? To answer that question, both books go deeper into physical theory and mathematical detail than most readers will be able to follow, but skimming will suffice for most to catch the authors' central train of thought. It is useful to read the two books in parallel, grappling with a chapter or two of "Trouble'' to get the physical perspective, then turning to "Wrong'' for more mathematical depth. (The latter also has a much more detailed description of the science and history of particle accelerators.)

Most readers will never succeed in envisioning extra curled-up dimensions of space-time or understand the implications of symmetries in those additional dimensions. Still, the books can enable them to appreciate how more mathematically oriented minds can see unification between grainy quantum mechanics and smooth theories of the gravitational force. Both books convey the scientific excitement as two "revolutions" in string theory made it look as if grand unification were at hand.

A common theme in both is the difference between the usual kind of scientific consensus, which builds on the steady accumulation of experimental evidence, and the situation in string theory, where the prevailing view shifts almost yearly and the predilections of the leading researchers hold sway. But then, each book veers into a different explanation of what went wrong.

"Wrong devotes a chapter to the regrettable Bogdanov affair, in which a pair of French brothers apparently perpetrated a hoax, publishing "five articles, three of which were nearly identical, in peer reviewed journals." Woit pulls no punches: "Evidently, five sets of editors and referees had gone over these papers and accepted them for publication, without noticing that they were egregious nonsense." The implication is that the string theory has gotten so complex that most practitioners don't really understand it.

"Trouble takes a very different tack, describing alternatives to string theory and devoting the last fourth of the book to an elaborate discussion of the sociology of the string theory community, the way scientific careers are built, the way academic research is funded, and what society needs to do to correct the problems that have led physics off course. Smolin sees a need for both master craftspeople and seers, and puts himself (correctly if a bit egocentrically) in the latter group. Near the end of the book, he admits, "It may seem strange to be discussing academic politics in a book for the general public, but you, the public, individually and collectively, are our patrons."

I remain content to let science run its course. Physics has hit an uncommonly long dry spell, but history has a way of putting such periods into perspective. In fact, both authors mention a speech that may have some bearing on this controversy.

In the closing address at the 23rd Solvay Conference in Physics in Brussels in December 2005, physics Nobel laureate David Gross reflected on the first such conference in 1911, the year that Ernest Rutherford announced his discovery of the atomic nucleus.

He compared the present state of string theory with the puzzling discoveries of radioactivity in 1896, which was not fully understood until quantum mechanics was well developed. Physicists "were missing something absolutely fundamental" at the time of the first Solvay Conference, he noted. "We are missing perhaps something as profound as they were back then."

Smolin may be correct in his philosophizing about the problems in the practice of science today, but for me "The Trouble With Physics'' is simply this: We don't know if string theory is right, wrong, or "Not Even Wrong,'' and it looks as if we will need another decade or two to find out.