Chronology Protection in String Theory

TL;DR

The paper investigates chronology protection in string theory by analyzing BMPV-like geometries and their ten-dimensional D1-D5-P descriptions. It demonstrates that naively allowed closed timelike curves are preempted by stringy effects that trigger massless degrees of freedom at a chronology protection radius, leading to a corrected geometry with no CTCs. The authors connect this geometric mechanism to unitarity in the dual CFT via AdS3/CFT2, showing that the gravity causality bound coincides with a CFT unitarity bound and that the corrected configuration remains unitary. The results support a generalized enhancon-like resolution where giant gravitons and shell dynamics preserve chronology across dual descriptions.

Abstract

Many solutions of General Relativity appear to allow the possibility of time travel. This was initially a fascinating discovery, but geometries of this type violate causality, a basic physical law which is believed to be fundamental. Although string theory is a proposed fundamental theory of quantum gravity, geometries with closed timelike curves have resurfaced as solutions to its low energy equations of motion. In this paper, we will study the class of solutions to low energy effective supergravity theories related to the BMPV black hole and the rotating Wave--D1--D5--brane system. Time travel appears to be possible in these geometries. We will attempt to build the causality violating regions and propose that stringy effects prohibit their construction. We will show how the geometry is corrected and that, once corrected, causality is preserved. We will track our chronology protection proposal in the dual conformal field theory. The absence of closed timelike curves in the geometry coincides with the preservation of unitarity in the conformal field theory. The agent of chronology protection for the geometries studied here mirrors the enhancon mechanism, a mechanism string theory employs to resolve a class of naked singularities.