It is the best of times in physics. Physicists are on the verge of obtaining the long-sought Theory of Everything. In a few elegant equations, perhaps concise enough to be emblazoned on a T-shirt, this theory will reveal how the universe began and how it will end. The key insight is that the smallest constituents of the world are not particles, as had been supposed since ancient times, but “strings”—tiny strands of energy. By vibrating in different ways, these strings produce the essential phenomena of nature, the way violin strings produce musical notes. String theory isn’t just powerful; it’s also mathematically beautiful. All that remains to be done is to write down the actual equations. This is taking a little longer than expected. But, with almost the entire theoretical-physics community working on the problem—presided over by a sage in Princeton, New Jersey—the millennia-old dream of a final theory is sure to be realized before long.

It is the worst of times in physics. For more than a generation, physicists have been chasing a will-o’-the-wisp called string theory. The beginning of this chase marked the end of what had been three-quarters of a century of progress. Dozens of string-theory conferences have been held, hundreds of new Ph.D.s have been minted, and thousands of papers have been written. Yet, for all this activity, not a single new testable prediction has been made, not a single theoretical puzzle has been solved. In fact, there is no theory so far—just a set of hunches and calculations suggesting that a theory might exist. And, even if it does, this theory will come in such a bewildering number of versions that it will be of no practical use: a Theory of Nothing. Yet the physics establishment promotes string theory with irrational fervor, ruthlessly weeding dissenting physicists from the profession. Meanwhile, physics is stuck in a paradigm doomed to barrenness.

So which is it: the best of times or the worst of times? This is, after all, theoretical physics, not a Victorian novel. If you are a casual reader of science articles in the newspaper, you are probably more familiar with the optimistic view. But string theory has always had a few vocal skeptics. Almost two decades ago, Richard Feynman dismissed it as “crazy,” “nonsense,” and “the wrong direction” for physics. Sheldon Glashow, who won a Nobel Prize for making one of the last great advances in physics before the beginning of the string-theory era, has likened string theory to a “new version of medieval theology,” and campaigned to keep string theorists out of his own department at Harvard. (He failed.)

Now two members of the string-theory generation have come forward with exposés of what they deem to be the current mess. “The story I will tell could be read by some as a tragedy,” Lee Smolin writes in “The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next” (Houghton Mifflin; $26). Peter Woit, in “Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law” (Basic; $26.95), prefers the term “disaster.” Both Smolin and Woit were journeyman physicists when string theory became fashionable, in the early nineteen-eighties. Both are now outsiders: Smolin, a reformed string theorist (he wrote eighteen papers on the subject), has helped found a sort of Menshevik cell of physicists in Canada called the Perimeter Institute; Woit abandoned professional physics for mathematics (he is a lecturer in the mathematics department at Columbia), which gives him a cross-disciplinary perspective. Each author delivers a bill of indictment that is a mixture of science, philosophy, aesthetics, and, surprisingly, sociology. Physics, in their view, has been overtaken by a cutthroat culture that rewards technicians who work on officially sanctioned problems and discourages visionaries in the mold of Albert Einstein. Woit argues that string theory’s lack of rigor has left its practitioners unable to distinguish between a scientific hoax and a genuine contribution. Smolin adds a moral dimension to his plaint, linking string theory to the physics profession’s “blatant prejudice” against women and blacks. Pondering the cult of empty mathematical virtuosity, he asks, “How many leading theoretical physicists were once insecure, small, pimply boys who got their revenge besting the jocks (who got the girls) in the one place they could—math class?”

It is strange to think that such sordid motives might affect something as pure and objective as physics. But these are strange days in the discipline. For the first time in its history, theory has caught up with experiment. In the absence of new data, physicists must steer by something other than hard empirical evidence in their quest for a final theory. And that something they call “beauty.” But in physics, as in the rest of life, beauty can be a slippery thing.

The gold standard for beauty in physics is Albert Einstein’s theory of general relativity. What makes it beautiful? First, there is its simplicity. In a single equation, it explains the force of gravity as a curving in the geometry of space-time caused by the presence of mass: mass tells space-time how to curve, space-time tells mass how to move. Then, there is its surprise: who would have imagined that this whole theory would flow from the natural assumption that all frames of reference are equal, that the laws of physics should not change when you hop on a merry-go-round? Finally, there is its aura of inevitability. Nothing about it can be modified without destroying its logical structure. The physicist Steven Weinberg has compared it to Raphael’s “Holy Family,” in which every figure on the canvas is perfectly placed and there is nothing you would have wanted the artist to do differently.

Einstein’s general relativity was one of two revolutionary innovations in the early part of the twentieth century which inaugurated the modern era in physics. The other was quantum mechanics. Of the two, quantum mechanics was the more radical departure from the old Newtonian physics. Unlike general relativity, which dealt with well-defined objects existing in a smooth (albeit curved) space-time geometry, quantum mechanics described a random, choppy microworld where change happens in leaps, where particles act like waves (and vice versa), and where uncertainty reigns.

In the decades after this dual revolution, most of the action was on the quantum side. In addition to gravity, there are three basic forces that govern nature: electromagnetism, the “strong” force (which holds the nucleus of an atom together), and the “weak” force (which causes radioactive decay). Eventually, physicists managed to incorporate all three into the framework of quantum mechanics, creating the “standard model” of particle physics. The standard model is something of a stick-and-bubble-gum contraption: it clumsily joins very dissimilar kinds of interactions, and its equations contain about twenty arbitrary-seeming numbers—corresponding to the masses of the various particles, the ratios of the force strengths, and so on—that had to be experimentally measured and put in “by hand.” Still, the standard model has proved to be splendidly useful, predicting the result of every subsequent experiment in particle physics with exquisite accuracy, often down to the eleventh decimal place. As Feynman once observed, that’s like calculating the distance from Los Angeles to New York to within a hairbreadth.