Hagedorn transition and chronology protection in string theory

TL;DR

This paper proposes that string theory prevents time travel paradoxes through a phase transition caused by winding string condensation near closed null curves, ensuring the resulting spacetime remains causal.

Contribution

It introduces a new mechanism where light winding string condensation enforces chronology protection via an infrared effect in string theory.

Findings

Winding string states become unstable and condense in non-causal regions.

Infrared divergences in the partition function indicate this condensation.

The end-point geometry after the phase transition remains chronological.

Abstract

We conjecture chronology is protected in string theory due to the condensation of light winding strings near closed null curves. This condensation triggers a Hagedorn phase transition, whose end-point target space geometry should be chronological. Contrary to conventional arguments, chronology is protected by an infrared effect. We support this conjecture by studying strings in the O-plane orbifold, where we show that some winding string states are unstable and condense in the non-causal region of spacetime. The one-loop string partition function has infrared divergences associated to the condensation of these states.