The PBR theorem is a theorem about the physical reality of quantum states due to Matthew Pusey, Jonathan Barrett, and Terry Rudolph, named after the initial letters of their surnames.
Theorem
The theorem was first published as an arXiv preprint with Pusey as the principal author, a subsequent version published in Nature Physics, that states the theorem that either the quantum state corresponds to a physically real object and is not merely a statistical tool, or else all quantum states, including non-entangled ones, can communicate by action at a distance. This preliminary result has been referred to as Pusey's theorem or the PBR theorem, and has been cited by theoretical physicist Antony Valentini as "the most important general theorem relating to the foundations of quantum mechanics since Bell's theorem". A revised version was released on 7 May 2012.