A microscopic derivation of the quantum measurement postulates

TL;DR

This paper derives the quantum measurement postulates from the unitary evolution of large systems, showing that measurement outcomes can be explained without additional postulates, similar to how thermodynamics is derived from mechanics.

Contribution

It provides a microscopic derivation of quantum measurement postulates from unitary evolution and simple assumptions, unifying measurement with quantum dynamics.

Findings

Measurement features are derivable from unitary evolution.

Large system assumptions reproduce probabilistic measurement outcomes.

The model clarifies the measurement process for physicists.

Abstract

In the mid-19th century, both the laws of mechanics and thermodynamics were known, and both appeared fundamental. This was changed by Boltzmann and Gibbs, who showed that thermodynamics can be *derived*, by applying mechanics to very large systems, and making simple statistical assumptions about their behavior. Similarly, when Quantum Mechanics (QM) was first discovered, it appeared to require two sets of postulates: one about the deterministic evolution of wavefunctions, and another about the probabilistic measurement process. Here again, the latter is derivable from the former: by applying unitary evolution to large systems (apparatuses, observers and environment), and making simple assumptions about their behavior, one can derive all the features of quantum measurement. We set out to demonstrate this claim, using a simple and explicit model of a quantum experiment, which we hope will be clear and compelling to the average physicist.