Two weeks ago, cosmologists cheered an observation that many called a "smoking gun" for cosmic inflation—a wild theory that says that in a sliver of a second after the big bang, the universe expanded exponentially, stretching subatomic distances to cosmic lengths in a flash. Yet, as the smoke clears, the finding raises puzzles of its own. Cosmologists say that the observation from Background Imaging of Cosmic Extragalactic Polarization jibes with the simplest model of inflation and lays waste to more complicated ones. Paradoxically, however, the surviving models suffer from a conceptual problem that may render them internally inconsistent. To resolve that problem, some theorists are turning to string theory.