Closed timelike curves and chronology protection in quantum and classical simulators

TL;DR

This paper explores the simulation of closed timelike curves (CTCs) in quantum and classical systems to investigate potential mechanisms that prevent their existence, providing insights into Hawking's chronology protection conjecture.

Contribution

It introduces the first simulations of CTCs in both quantum and classical systems, highlighting restrictions in quantum simulations as potential analogues of chronology protection.

Findings

Quantum simulations show restrictions not present in classical ones.

Classical simulations allow CTCs without restrictions.

Quantum effects may impose limits akin to chronology protection.

Abstract

In principe, General Relativity seems to allow the existence of closed timelike curves (CTC). However, when quantum effects are considered, it is likely that their existence is prevented by some kind of chronological protection mechanism, as Hawking conjectured. Confirming or refuting the conjecture would require a full quantum theory of gravity. Meanwhile, the use of simulations could shed some light on this issue. We propose simulations of CTCs in a quantum system as well as in a classical one. In the quantum simulation, some restrictions appear that are not present in the classical setup, which could be interpreted as an analogue of a chronology protection mechanism.