Causality violation in plane wave spacetimes

TL;DR

This paper demonstrates that plane wave spacetimes, previously thought to be causally well-behaved, can contain closed null geodesics, revealing potential causal pathologies.

Contribution

It provides an analytical solution showing the existence of closed null geodesics in plane wave spacetimes, challenging prior assumptions about their causal structure.

Findings

Existence of closed null geodesics in plane wave metrics

Analytical solutions to geodesic equations in these spacetimes

Implication of causal pathologies in plane wave spacetimes

Abstract

It is widely held that plane wave spacetimes are causally well behaved which means that they are free from causal pathologies such as closed timelike curves or closed null geodesics. In this paper, we show that one can get closed null geodesics in a plane wave metric by analytically solving the geodesic equations.