A final chapter forecasts that string theory will become the standard physical model in the next century. Greene deftly summarizes these findings, in areas from subatomic-particle theory to cosmology, with occasional forays into deeper waters such as the ten-dimensional structure of the universe, with several dimensions folded undetectably back into themselves.

Still, it has the right look about it, and two waves of enthusiasm (one in the mid-1980s, the other ten years later) have convinced many physicists of the theory’s probable validity. And despite its formidable explanatory power, its mathematical expressions were often even more formidable-Greene describes some of the equations as nearly impossible to understand, let alone solve. It took a while for physicists to embrace string theory for one thing, it seemed to predict things nobody had ever seen. The relationships would make sense if elementary particles were not pointlike, but elongated and vibrating, like tiny musical strings-in one sense, a modern version of the ancient metaphor of the music of the spheres. Its foundations were laid down some 30 years ago by Gabriele Venizano, who found that a two-century-old formula by Leonard Euler described subatomic particles more elegantly than existing theory. Out of the search for a more complete explanation came string theory. Yet increasingly, physics deals with phenomena such as black holes, where the conflicts are impossible to avoid. Normally, the two realms can be kept separate. Relativity works for large, massive objects quantum theory for tiny ones.

Quantum mechanics and general relativity both work perfectly, and they cannot both be right. Greene (a professor of physics and mathematics at Columbia and Cornell) begins by pointing out the central problem of modern physics. Here is a look at the current state of the quest. Superstring theory may provide the long-sought unification of physics for which Einstein sought in vain.

The Elegant Universe by Brian Greene