FOR MOST PEOPLE, THE GREAT MYSTERY OF TIME IS THAT THERE NEVER seems to be enough of it. If it is any consolation, physicists are having much the same problem. The laws of physics contain a time variable, but it fails to capture key aspects of time as we live it—notably, the distinction between past and future. And as researchers try to formulate more fundamental laws, the little t evaporates altogether. Stymied, many physicists have sought help from an unfamiliar source: philosophers.
From philosophers? To most physicists, that sounds rather quaint. The closest some get to philosophy is a late-night conversation over dark beer. Even those who have read serious philosophy generally doubt its usefulness; after a dozen pages of Immanuel Kant, philosophy begins to seem like the unintelligible in pursuit of the undeterminable. “To tell you the truth, I think most of my colleagues are terrified of talking to philosophers—like being caught coming out of a pornographic cinema,” says physicist Max Tegmark, now at the Massachusetts Institute of Technology.
It was not always so. Philosophers played a crucial role in past scientific revolutions, including the development of quantum mechanics and relativity in the early 20th century. Today a new revolution is under way, as physicists struggle to merge those two theories into a theory of quantum gravity—a theory that will have to reconcile two vastly different conceptions of space and time. Carlo Rovelli of the University of the Mediterranean in Marseille, France, a leader in this effort, observes that “the contributions of philosophers to the new understanding of space and time in quantum gravity will be very important.”
Two examples illustrate how physicists and philosophers have been pooling their resources. The first concerns the “problem of frozen time,” also known simply as the “problem of time.” It arises when theorists try to turn Einstein's general theory of relativity into a quantum theory using a procedure called canonical quantization. The procedure worked brilliantly when applied to the theory of electromagnetism, but in the case of relativity, it produces an equation—the Wheeler-DeWitt equation—without a time variable. Taken literally, the equation predicts that the universe should be frozen in time, in direct contradiction with what we see.