Schr\"odinger's cat meets Occam's razor

TL;DR

This paper explores Belavkin's approach to the Schrödinger's cat paradox, emphasizing a stochastic, non-local collapse theory where the classical world emerges dynamically from quantum evolution, clarifying interpretations through simple models.

Contribution

It simplifies and explains Belavkin's collapse approach and superselection ideas within a discrete, accessible framework, connecting quantum and classical worlds.

Findings

Classical world evolves stochastically from quantum states

The quantum/classical boundary is determined by the arrow of time

The approach clarifies the role of measurement and the Heisenberg cut

Abstract

We discuss V.P. Belavkin's (2007) approach to the Schr\"odinger cat problem and show its close relation to ideas based on superselection and interaction with the environment developed by N.P. Landsman (1995). The purpose of the paper is to explain these ideas in the most simple possible context, namely: discrete time and separable Hilbert spaces, in order to make them accessible to those coming from the philosophy of science and not too happy with idiosyncratic notation and terminology and sophisticated mathematical tools. Conventional elementary mathematical descriptions of quantum mechanics take "measurement" to be a primitive concept. Paradoxes arise when we choose to consider smaller or larger systems as measurement devices in their own right, by making different and apparently arbitrary choices of location of the "Heisenberg cut". Various quantum interpretations have different resolutions of the paradox. In Belavkin's approach, the classical world around us does really exist, and it evolves stochastically and dynamically in time according to probability laws following from successive applications of the Born law. It is a collapse theory, and necessarily it is non-local. The quantum/classical distinction is determined by the arrow of time. The underlying unitary evolution of the wave-function of the universe enables the designation of a collection of beables which grows as time evolves, and which therefore can be assigned random, classical trajectories. In a slogan: the past is particles, the future is a wave. We, living in the now, are located on the cutting edge between past and future.