Conventional wisdom says that quantum mechanics is a theory of discreteness, describing a world of irreducible building blocks. It stands to reason that computers—which process information in discrete chunks—should be able to simulate nature fully, at least in principle. But it turns out that certain asymmetries in particle physics cannot be discretized; they are irreducibly continuous. In that case, says David Tong, author of "Is Quantum Reality Analog after All?" in the December 2012 issue of Scientific American, the world can never be fully simulated on a computer.