Pusey–Barrett–Rudolph theorem
With respect to certain realist hidden variable theories that attempt to explain the predictions of quantum mechanics, the theorem rules that pure quantum states must be "ontic" in the sense that they correspond directly to states of reality, rather than "epistemic" in the sense that they represent probabilistic or incomplete states of knowledge about reality.[2] This theorem, which first appeared as an arXiv preprint[3] and was subsequently published in Nature Physics,[1] concerns the interpretational status of pure quantum states.Under the classification of hidden variable models of Harrigan and Spekkens,[4] the interpretation of the quantum wavefunctionis ψ-ontic, or else non-entangled quantum states violate the assumption of preparation independence, which would entail action at a distance.In conclusion, we have presented a no-go theorem, which—modulo assumptions—shows that models in which the quantum state is interpreted as mere information about an objective physical state of a system cannot reproduce the predictions of quantum theory.