"Theoretical physicists are Platonists. Until the last few years, they believed that the entire universe, the one universe, was generated from a few principles of symmetry and mathematical truths, perhaps throwing in a handful of parameters like the mass of the electron. It seemed that we were closing in on a vision of our universe in which everything could be calculated, predicted, and understood. However, two theories in physics, called "eternal inflation" and "string theory," now"