Null geodesics in the Alcubierre warp drive spacetime: the view from the bridge

TL;DR

This paper investigates null geodesics in the Alcubierre warp drive spacetime, revealing optical effects and causal horizons that imply quantum energy divergences prevent superluminal travel.

Contribution

It provides a numerical analysis of photon trajectories and horizons in warp drive spacetime, linking optical phenomena to quantum energy divergence issues.

Findings

Stars appear closer in the forward direction at high warp speeds

Horizon-like regions form behind and in front of the starship

Quantum vacuum energy divergence likely prevents superluminal speeds

Abstract

The null geodesic equations in the Alcubierre warp drive spacetime are numerically integrated to determine the angular deflection and redshift of photons which propagate through the distortion of the ``warp drive'' bubble to reach an observer at the origin of the warp effect. We find that for a starship with an effective warp speed exceeding the speed of light, stars in the forward hemisphere will appear closer to the direction of motion than they would to an observer at rest. This aberration is qualitatively similar to that caused by special relativity. Behind the starship, a conical region forms from within which no signal can reach the starship, an effective ``horizon''. Conversely, there is also an horizon-like structure in a conical region in front of the starship, into which the starship cannot send a signal. These causal structures are somewhat analogous to the Mach cones associated with supersonic fluid flow. The existence of these structures suggests that the divergence of quantum vacuum energy when the starship effectively exceeds the speed of light, first discovered in two dimensions, will likely be present in four dimensions also, and prevent any warp-drive starship from ever exceeding the effective speed of light.