Causal Topology in Future and Past Distinguishing Spacetimes

TL;DR

This paper demonstrates that the causal structure of future and past distinguishable spacetimes uniquely determines their manifold dimension, extending previous results and introducing a finer causal topology that encodes manifold dimension.

Contribution

It generalizes the Malament-Hawking-King-McCarthy theorem to a broader class of spacetimes and constructs a causal topology that captures manifold dimension.

Findings

Causal structure determines manifold dimension in FPD spacetimes.

A new causal topology encoding manifold dimension is constructed.

When strong causality violation regions are locally achronal, the topology matches the manifold topology.

Abstract

The causal structure of a strongly causal spacetime is particularly well endowed. Not only does it determine the conformal spacetime geometry when the spacetime dimension n >2, as shown by Malament and Hawking-King-McCarthy (MHKM), but also the manifold dimension. The MHKM result, however, applies more generally to spacetimes satisfying the weaker causality condition of future and past distinguishability (FPD), and it is an important question whether the causal structure of such spacetimes can determine the manifold dimension. In this work we show that the answer to this question is in the affirmative. We investigate the properties of future or past distinguishing spacetimes and show that their causal structures determine the manifold dimension. This gives a non-trivial generalisation of the MHKM theorem and suggests that there is a causal topology for FPD spacetimes which encodes manifold dimension and which is strictly finer than the Alexandrov topology. We show that such a causal topology does exist. We construct it using a convergence criterion based on sequences of "chain-intervals" which are the causal analogs of null geodesic segments. We show that when the region of strong causality violation satisfies a local achronality condition, this topology is equivalent to the manifold topology in an FPD spacetime.