Macroscopic limit of quantum systems

Abstract

The classical physics is approached from quantum mechanics in the macroscopic limit. The technical device to achieve this goal is the quantum version of the central limit theorem, derived for an observable at a given time and for the time-dependent expectation value of the coordinate. The emergence of the classical trajectory can be followed and the deterministic classical laws can be recovered in all practical purposes owing to the largeness of Avogadro's number. The emergence of a classical trajectory is followed qualitatively in Wilson's cloud chamber.