Three days after learning that he won the 2006 Nobel Prize in Physics, George Smoot was talking about the universe. Sitting across from him ... was Saul Perlmutter, a fellow cosmologist. Smoot's and Perlmutter's work is part of a revolution that has forced their colleagues to confront a universe wholly unlike any they have ever known, one that is made of only 4 percent of the kind of matter we have always assumed it to be. The rest - 96 percent of the universe - is ... Dark." This is not "dark" as in distant or invisible. This is "dark" as in unknown. It lies ... beyond the entire electromagnetic spectrum. The motions of galaxies don't make sense unless we infer the existence of dark matter. Understanding dark energy ... seems to really require understanding and using both [general relativity and quantum mechanics] theories at the same time. "It's been so hard that we're even willing to consider listening to string theorists," Perlmutter says, referring to work that posits numerous dimensions beyond the traditional (one of time and three of space). According to quantum theory, particles can pop into and out of existence. In that case, maybe the universe itself was born in one such quantum pop. And ... why not many universes? This is just one of a number of theories that have been popping into existence ... in the past few years: parallel universes, intersecting universes or, in the case of Stephen Hawking and Thomas Hertog just last summer, a superposition of universes.