Far, far away: an endless void or a guiding hand?

Relativity, however, was simplicity itself compared with the next great leap forward: quantum theory. We already knew that things get a bit exotic at the atomic level. But as you get even smaller, there stop being things altogether. At the quantum (roughly, subatomic) level, there are no longer entities, or even well-defined events; there are only ranges of specified probabilities. Moreover, some subatomic events (I know I just said there aren't any events at that level, but we -- or at any rate, I -- can't do without the word) happen without a cause. Particles appear or disappear, or move across barriers, for no reason. It's not just that we don't yet know the cause -- there is no cause.

Lately, physicists have become convinced that the fundamental units of space-time are strings, infinitely thin filaments that form tiny (approximately 10- to 25-centimeter) vibrating loops, which are in fact the elementary particles, as well as curling up into nine extra but undetectable space-time dimensions. On paper, string theory unifies relativity and quantum theory -- a staggering achievement. In practice, it has proven hard to carry out, or even imagine, experiments that would test it.

You might think all these utterly counterintuitive results would have discouraged physicists and astronomers from venturing forth to construct an all-embracing explanation of the cosmos. Not a bit. As Alex Vilenkin, director of the Tufts Institute of Cosmology, relates in ``Many Worlds in One," the 20th century was a golden age of cosmological theorizing, and the scientific community is hoping excitedly that the 21st will yield the scientific Holy Grail: the Theory of Everything.