On the nature of the quantum states of macroscopic systems

Abstract

It is assumed that the quantum state that may describe a macroscopic system at a given instant of time is one of the eigenstates of the reduced density matrix calculated from the wave function of the system plus its environment. This implies that the above quantum state is a member of a special orthonormed set of states. Using a suitable Monte-Carlo simulation, this property is shown to be consistent with the extremely small standard deviation for the coordinates and the momenta of macroscopic systems. Consequences for statistical mechanics and possible observable effects are discussed.