The Pilot-Wave Perspective on Spin

Abstract: The alternative pilot-wave theory of quantum phenomena -- associated especially with Louis de Broglie, David Bohm, and John Bell -- reproduces the statistical predictions of ordinary quantum mechanics, but without recourse to special \emph{ad hoc} axioms pertaining to measurement. That (and how) it does so is relatively straightforward to understand in the case of position measurements and, more generally, measurements whose outcome is ultimately registered by the position of a pointer. Despite a widespread belief to the contrary among physicists, the theory can also account successfully for phenomena involving spin. The main goal of the paper is to explain how the pilot-wave theory's account of spin works. Along the way, we provide illuminating comparisons between the orthodox and pilot-wave accounts of spin and address some puzzles about how the pilot-wave theory relates to the important theorems of Kochen and Specker and Bell.