External Observer Reflections on QBism, Its Possible Modifications, and Novel Applications

Abstract

In this critical essay, I present my personal reflections on QBism. I have no intrinsic sympathy neither to QBism nor to subjective interpretation of probability in general. However, I have been following the development of QBism from its very beginning, observing its evolution and success, sometimes with big surprise. Therefore my reflections on QBism can be treated as “external observer” reflections. I hope that my view on this interpretation of quantum mechanics (QM) has some degree of objectivity. It may be useful for researchers who are interested in quantum foundations, but do not belong to the QBism community, because I tried to analyze essentials of QBism critically (i.e., not just emphasizing its advantages, as in a typical QBist publication). QBists, too, may be interested in comments of an external observer who monitored development of this approach to QM during the last 16 years. (However, this paper cannot serve as an introduction to QBism. It neither concerns the philosophic issues around QBism.) Two sections are devoted to comparison of QBism with two interpretations of QM, the Växjö and information interpretations, which are close to QBism in two very different aspects, probabilistic and informational. The second part of the paper is devoted to interpretations of probability, objective versus subjective, and views of Kolmogorov, von Mises, and de Finetti. De Finetti’s approach to methodology of science is presented and compared with QBism. One of the outputs of this comparison is understanding of restrictiveness of QBism, where the subjective probability viewpoint is applied only to QM. One of the main messages of this paper is that QBism has to be completed by CBism (classical physics Bayesianism). Finally, the possibility to use QBism as the general interpretational basis for applications of the quantum probabilistic formalism for decision-making outside of physics (in cognitive, social, and political sciences, psychology, economics, finances) is considered.