The Ori-Soen time machine

TL;DR

This paper analyzes a spacetime model with closed causal curves on its boundary, exploring its causal structure and the challenges of constructing such a spacetime with normal matter.

Contribution

It provides a detailed analysis of the causal structure of Ori and Soen's proposed spacetime with boundary causality violations under the weak energy condition.

Findings

Cauchy horizon is compactly generated

Causality violation regions are on the boundary of normal causality

Constructing such spacetimes with normal matter may lead to singularities

Abstract

Ori and Soen have proposed a spacetime which has closed causal curves on the boundary of a region of normal causality, all within a region where the weak energy condition (positive energy density) is satisfied. I analyze the causal structure of this spacetime in some simplified models, show that the Cauchy horizon is compactly generated, and argue that any attempt to build such a spacetime with normal matter might lead to singular behavior where the causality violation would otherwise take place.