Topological censorship and chronology protection

TL;DR

This paper reviews how physical laws and principles, including topological censorship and chronology protection, prevent exotic spacetime structures and causal violations, ensuring the observed universe's consistency.

Contribution

It provides a comprehensive overview of recent advances in understanding topological censorship, event horizon topology, and chronology protection in classical, semiclassical, and quantum gravity.

Findings

Topological censorship restricts observable spacetime topologies.

Chronology protection prevents time travel paradoxes.

Quantum energy inequalities support classical causality principles.

Abstract

Over the past two decades, substantial efforts have been made to understand the way in which physics enforces the ordinary topology and causal structure that we observe, from subnuclear to cosmological scales. We review the status of topological censorship and the topology of event horizons; chronology protection in classical and semiclassical gravity; and related progress in establishing quantum energy inequalities.