A Critic Looks at QBism

Abstract

This chapter comments on that by Chris Fuchs on qBism. It presents some mild criticisms of this view, some based on the EPR and Wigner's friend scenarios, and some based on the quantum theory of measurement. A few alternative suggestions for implementing a sub-jectivist interpretation of probability in quantum mechanics conclude the chapter. "M. Braque est un jeune homme fort audacieux. [...] Il méprise la forme, réduit tout, sites et figures et maisons, ` a des schémas géométriques, ` a des cubes. Ne le raillons point, puisqu'il est de bonne foi. Et attendons." 1 Thus commented the French art critic Louis Vauxcelles on Braque's first one-man show in November 1908, thereby giving cubism its name. Substituting spheres and tetrahedra for cubes might be more appropriate if one wishes to apply the characterisation to qBism-the view of quantum mechanics and the quantum state developed by Chris Fuchs and co-workers (for a general reference see either the paper in this volume, or Fuchs (2010)). In this note, I shall not comment on other possible analogies, nor shall I present an exhaustive critical review of qBism (for an excellent one, see Timpson