Can a circulating light beam produce a time machine?

TL;DR

This paper critically examines Mallett's solution suggesting a circulating light beam could create a time machine, revealing that such closed timelike curves occur only at unphysical distances and that the solution has a singularity, questioning its physical plausibility.

Contribution

The paper demonstrates that Mallett's proposed time machine solution involves unphysical conditions and contains a curvature singularity, challenging its relevance to real-world physics.

Findings

CTCs occur at distances vastly exceeding the observable universe.

Mallett's solution has a curvature singularity on the axis.

The solution is not physically realizable with realistic energy densities.

Abstract

In a recent paper, Mallett found a solution of the Einstein equations in which closed timelike curves (CTC's) are present in the empty space outside an infinitely long cylinder of light moving in circular paths around an axis. Here we show that, for physically realistic energy densities, the CTC's occur at distances from the axis greater than the radius of the visible universe by an immense factor. We then show that Mallett's solution has a curvature singularity on the axis, even in the case where the intensity of the light vanishes. Thus it is not the solution one would get by starting with Minkowski space and establishing a cylinder of light.