Cosmology and the S-matrix

TL;DR

This paper investigates the conditions under which asymptotic observables, like an S-matrix, could exist in different cosmological models, highlighting differences between accelerating and decelerating universes and their observational limitations.

Contribution

It provides a comparative analysis of the existence of asymptotic observables in various cosmologies, challenging assumptions about the universality of the S-matrix in such settings.

Findings

Accelerating universes allow arbitrarily long observations and large entropy states.

Decelerating universes share similarities with accelerating ones regarding thermalization.

No realistic cosmology supports global S-matrix observations due to observational limitations.

Abstract

We study conditions for the existence of asymptotic observables in cosmology. With the exception of de Sitter space, the thermal properties of accelerating universes permit arbitrarily long observations, and guarantee the production of accessible states of arbitrarily large entropy. This suggests that some asymptotic observables may exist, despite the presence of an event horizon. Comparison with decelerating universes shows surprising similarities: Neither type suffers from the limitations encountered in de Sitter space, such as thermalization and boundedness of entropy. However, we argue that no realistic cosmology permits the global observations associated with an S-matrix.