How to detect an anti-spacetime

TL;DR

This paper investigates whether the sign of the Lapse function in spacetime can be physically distinguished through fermion dynamics, suggesting it might be a measurable quantity beyond the metric, with implications for quantum gravity.

Contribution

It demonstrates that fermion behavior can differentiate between spacetimes with identical metrics but opposite Lapse signs, highlighting a potential new physical observable.

Findings

Fermion dynamics can detect the sign of the Lapse.

The sign of the Lapse may be physically meaningful.

Implications for quantum gravity theories.

Abstract

Is it possible, in principle, to measure the sign of the Lapse? We show that fermion dynamics distinguishes spacetimes having the same metric but different tetrads, for instance a Lapse with opposite sign. This sign might be a physical quantity not captured by the metric. We discuss its possible role in quantum gravity.