Islands and the de Sitter entropy bound

TL;DR

This paper applies the island formula to de Sitter space, showing that the fine-grained entropy follows a Page curve and challenges the traditional dS entropy bound, implying potential modifications to the semiclassical understanding.

Contribution

It introduces a novel semiclassical calculation of entropy in dS space using island techniques, questioning the validity of the dS entropy bound.

Findings

Entropy follows a Page-like curve, not exceeding dS entropy.

The calculation suggests the entropy bound may not hold semiclassically.

Challenges the thermodynamical interpretation of dS space.

Abstract

The de Sitter (dS) entropy bound gives the maximal number of e-folds that non-eternal inflation can last before violating the thermodynamical interpretation of dS space. This semiclassical argument is the analogue, for dS space, of the Black-Hole information paradox. We use techniques developed to address the latter, namely the island formula, to calculate semiclassically the fine-grained entropy as seen by a Minkowskian observer after inflation and find that this follows a Page-like curve, never exceeding the thermodynamic dS entropy. This calculation, performed for a CFT in 2D gravity, suggests that the semiclassical expectation should be modified in such a way that the entropy bound might actually not be present.