It’s quite a trick to picture a theory even weirder than quantum mechanics. Yet many physicists think the best way to make sense of quantum mechanics is to imagine what might have been. Within a vast radiation of conceivable theories, they look for principles that single out the quantum. In so doing, they aim to do for quantum mechanics what astronomers have done for Pluto. Once considered the planetary ugly duckling, Pluto proved to be the leading member of the Kuiper Belt that rings our solar system. Likewise, quantum mechanics begins to look less mysterious when you consider the larger class of postclassical theories of which it is one.