Probing time orientability of spacetime

TL;DR

This paper investigates whether spacetime can be non-orientable in time by analyzing quantum electromagnetic fluctuations and their effects on charged particles, proposing a method to detect time non-orientability through a statistical indicator.

Contribution

It introduces a novel approach to detect time non-orientability in spacetime using quantum vacuum effects and develops an analytic statistical indicator for this purpose.

Findings

Time non-orientability can influence quantum vacuum fluctuations.

A statistical indicator can distinguish time non-orientable topology.

Inversion patterns in the indicator signal non-orientability.

Abstract

In general relativity, cosmology and quantum field theory, spacetime is assumed to be an orientable manifold endowed with a Lorentz metric that makes it spatially and temporally orientable. The question as to whether the laws of physics require these orientability assumptions is ultimately of observational or experimental nature, or the answer might come from a fundamental theory of physics. The possibility that spacetime is time non-orientable lacks investigation, and so should not be dismissed straightaway. In this paper, we argue that it is possible to locally access a putative time non-orientability of Minkowski empty spacetime by physical effects involving quantum vacuum electromagnetic fluctuations. We set ourselves to study the influence of time non-orientability on the stochastic motions of a charged particle subject to these electromagnetic fluctuations in Minkowski spacetime equipped with a time non-orientable topology and with its time orientable counterpart. To this end, we introduce and derive analytic expressions for a statistical time orientability indicator. Then we show that it is possible to pinpoint the time non-orientable topology through an inversion pattern displayed by the corresponding orientability indicator, which is absent when the underlying manifold is time orientable.