Simple explanation of the classical limit

Abstract

The classical limit is fundamental in quantum mechanics. It means that quantum predictions must converge to classical ones as the macroscopic scale is approached. Yet, how and why quantum phenomena vanish at the macroscopic scale is difficult to explain. In this paper, quantum predictions for Greenberger–Horne–Zeilinger states with an arbitrary number q of qubits are shown to become indistinguishable from the ones of a classical model as q increases, even in the absence of loopholes. Provided that two reasonable assumptions are accepted, this result leads to a simple way to explain the classical limit and the vanishing of observable quantum phenomena at the macroscopic scale.