Back to the Future: Causality on a Moving Braneworld

TL;DR

This paper demonstrates that in certain braneworld models, signals can appear superluminal or backward in time without violating causality, due to the geometry and motion of the brane within the bulk spacetime.

Contribution

It provides a classical and quantum analysis showing how causality is preserved despite superluminal signals in moving braneworld scenarios.

Findings

Superluminal signals do not violate causality in braneworlds.

Brane motion enables instantaneous or backward signals without causality breach.

Quantum microcausality supports classical causality preservation.

Abstract

Brane observers executing appropriate motion through a partially compactified Lorentz invariant bulk spacetime, such as $M_4 \times S^1$, can send signals along the brane that are instantaneous or even travel backward in time. Nevertheless, causality in the braneworld remains intact. We establish these results, which follow from superluminal signal propagation reported in arXiv:2206.13590, through classical analysis and then extend our reasoning by examining quantum mechanical microcausality. One implication is the capacity for real time communication across arbitrarily large distances.