The quantum measurement problem

Despite the spectacular success of quantum mechanics (QM) over the last 80 years in explaining phenomena observed at the atomic and subatomic level, the conceptual status of the theory is still a topic of lively controversy. Most of the discussion centers around two famous paradoxes (or, as some would have it, pseudoparadoxes) associated, respectively, with the names of Einstein, Podolsky, and Rosen (EPR) and with Schrödinger's cat. In this Viewpoint, I will concentrate on the paradox of Schrödinger's cat or, as it is often known (to my mind somewhat misleadingly), the quantum measurement paradox.