How Einstein and/or Schrödinger should have discovered Bell's theorem in 1936

Abstract

Copyright © 2015 the authors. We show how one can be led from considerations of quantum steering to Bell’s theorem. We begin with Einstein’s demonstration that, assuming local realism, quantum states must be in a many-to-one (“incomplete”) relationship with the real physical states of the system. We then consider some simple constraints that local realism imposes on any such incomplete model of physical reality, and show they are not satisfiable. In particular, we present a very simple demonstration for the absence of a local hidden variable incomplete description of nature by steering to two ensembles, one of which contains a pair of nonorthogonal states. Historically this is not how Bell’s theorem arose—there are slight and subtle differences in the arguments—but it could have been.