The conclusion of "The Elegant Universe," physicist Brian Greene's exploration of string theory, the "theory of everything" that ties quantum mechanics to general relativity, looks at where it could lead---to 11 dimensions and parallel universes. "Things that used to seem like science fiction aren't so far-fetched," says Greene. The theoretical underpinnings for this were solidified in 1995 by Princeton's Robert Witten, who united five divergent string theories into one "m" theory (no one knows what the "m" stands for). If it's proved (and an atom-smasher under construction in the Alps might do it), "not only would our universe be nothing special," says Greene, "but we'd have lots of company." And some of the universes might have their own laws of physics.