The Quantum Measurement Problem

This preprint Can the Quantum Measurement Problem be resolved within the framework of Schroedinger Dynamics and Quantum Probability? addresses a fundamental problem in the foundations of physics. Traditionally a quantum measurement consists of two physical subsystems: a quantum subsystem (like an atom) and a classical subsystem (like a measuring instrument). The quantum subsystem is modelled using the often counterintuitive framework of quantum theory and the classical subsystem is modelled using the less startling laws of classical physics. Each subsystem in isolation evolves in a reasonably straightforward deterministic fashion, but when the two subsystems are coupled together something rather mysterious happens: a quantum measurement, which is fundamentally probabilistic in nature.

Ultimately, it's expected that the "classical" subsystem should be modelled by quantum theory as well and so too the composite of the two subsystems. After all, the classic subsystem is in term made up of constituents (like atoms) which obey the laws of quantum theory. However, it's been difficult to work out a completely quantum description of the measurement process. So much so that there has even been speculation that consciousness might be irreducibly involved.