Speed Limits in General Relativity

TL;DR

This paper reviews initial value problem results in general relativity, demonstrating that gravitational perturbations do not exceed light speed and that warp drives require exotic matter, highlighting fundamental physical constraints.

Contribution

It applies standard results to establish speed limits for gravitational perturbations and rules out warp drives without exotic matter in general relativity.

Findings

Finite gravitational perturbations travel no faster than light.

Warp drives cannot be constructed without exotic matter.

Provides foundational insights into causality and exotic matter requirements.

Abstract

Some standard results on the initial value problem of general relativity in matter are reviewed. These results are applied first to show that in a well defined sense, finite perturbations in the gravitational field travel no faster than light, and second to show that it is impossible to construct a warp drive as considered by Alcubierre (1994) in the absence of exotic matter.