Locality and the classical limit of quantum mechanics

TL;DR

This paper argues that the classical behavior of macroscopic bodies is primarily due to local interactions, with deviations from classicality being exponentially small in system volume, except for black holes which lack a local quantum field theory description.

Contribution

It challenges conventional estimates of classicality criteria by emphasizing the role of locality in quantum field theory, highlighting black holes as unique non-local objects.

Findings

Deviations from classical behavior are exponentially suppressed in system volume.

Local quantum field theory accurately describes most macroscopic systems.

Black holes are exceptions due to their non-local nature.

Abstract

I argue that conventional estimates of the criterion for classical behavior of a macroscopic body are incorrect, because they do not take into account the locality of interactions, which characterizes the behavior of all systems described approximately by local quantum field theory. Black holes are the only localized objects which do not have such a description. The deviations from classical behavior of a macroscopic body, except for those which can be described as classical uncertainties in the initial values of macroscopic variables,are {\it exponentially} small as a function of the volume of the macro-system in microscopic units.