In one minute

Francisco Lobo and Matt Visser use warp drive spacetimes as thought experiments that probe the foundations of general relativity. They formulate the Alcubierre and Natário spacetimes carefully, make the notion of superluminal communication precise and confirm that both violate the classical energy conditions non-perturbatively. They apply linearised gravity to weak-field Alcubierre and Natário drives and test the energy conditions to first and second order in bubble velocity. They highlight a feature not remarked on before: a warp drive would be a reactionless drive. For both drives, significant energy condition violations persist even at arbitrarily low speeds. Treating the ship as a finite mass, the net negative energy in the warp field must be a significant fraction of the ship's mass.

Fundamental limitations on 'warp drive' spacetimes