Summary

Even though this paper was published fairly recently, it has become somewhat of a classic already. It was one of the first to describe how 'faster than light' space travel could be possible within the framework of the physical rules established by Einstein's General Relativity Theory. Unlike special relativity which is based on the postulate than no information or object can travel faster than the speed of light, general relativity qualifies this statement by changing it to: nothing can travel faster than the speed of light locally. Alcubierre uses this to develop a space-time geometry much like a 'warp-shell' that surrounds the hypothetical space craft, and while the vessel itself never exceeds the speed of light inside this shell, the shell itself does just that by contracting spacetime itself in front of it and expanding it again in its 'wake'. However, to generate the necessary conditions to create such a warp-shell, exotic matter (mass with a negative energy content) is required. In addition, others have pointed out that it might be impossible for the vessel inside the warp-shell to control where the shell is moving. None the less, this paper has become an often cited reference and a base line for comparison between various concepts and ideas.

Abstract

It is shown how, within the framework of general relativity and without the introduction of wormholes, it is possible to modify a space-time in a way that allows a spaceship to travel with an arbitrarily large speed. By a purely local expansion of space-time behind the spaceship and an opposite contraction in front of it, motion faster than the speed of light as seen by observers outside the disturbed region is possible. The resulting distortion is reminiscent of the "warp drive" of science fiction. However, just as happens with wormholes, exotic matter will be needed in order to generate a distortion of space-time like the one discussed here.

Paper