Random numbers certified by Bell’s theorem

True randomness demonstrated True randomness does not exist in classical physics, where randomness is necessarily a result of forces that may be unknown but exist. The quantum world, however, is intrinsically truly random. This is difficult to prove, as it is not readily distinguishable from noise and other uncontrollable factors. Now Pironio et al. present proof of a quantitative relationship between two fundamental concepts of quantum mechanics — randomness and the non-locality of entangled particles. They first show theoretically that the violation of a Bell inequality certifies the generation of new randomness, independently of any implementation details. To illustrate the approach, they then perform an experiment in which — as confirmed using the theoretical tools that they developed — 42 new random bits have been generated. As well as having conceptual implications, this work has practical implications for cryptography and for numerical simulation of physical and biological systems.