Faster-than-light: Encyclopedia II - Faster-than-light - General relativity

Faster-than-light - General relativity

General relativity was developed after special relativity, to include concepts like gravity. It maintains the principle that no object can accelerate to the speed of light in its own reference frame. However, it permits distortions in spacetime that allow an object to move faster than light from the point of view of a distant observer, even though it always moved slower than light in its own reference frame. One such distortion is the Alcubierre drive, which can be thought of as producing a ripple in spacetime that carries an object along with it. Another possible system is the wormhole, which connects two distant locations as though by a shortcut. To date there is no feasible way to construct any such special distortion; they all require unknown exotic matter, enormous (though finite) amounts of energy, or both.

General relativity also agrees that any technique for faster than light travel could also be used for time travel. This raises problems with causality. Many physicists believe that the above phenomena are in fact impossible, and that future theories of gravity will prohibit them. One theory states that stable wormholes are possible, but that any attempt to use a network of wormholes to violate causality would result in their decay.

Adapted from the Wikipedia article "General relativity", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki