Editing Faster-than-light (section)

==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 the reference frame of any coincident observer.{{citation needed|date=October 2009}} However, it permits distortions in [[spacetime]] that allow an object to move faster than light from the point of view of a distant observer.{{citation needed|date=March 2012}} 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. Both distortions would need to create a very strong curvature in a highly localized region of space-time and their gravity fields would be immense. To counteract the unstable nature, and prevent the distortions from collapsing under their own 'weight', one would need to introduce hypothetical [[exotic matter]] or negative energy.

General relativity also recognizes that any means of faster-than-light [[travel]] could also be used for [[time travel]]. This raises problems with [[causality]]. Many physicists believe that the above phenomena are 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.{{Citation needed|date=March 2013}} In [[string theory]], Eric G. Gimon and [[Petr Hořava (theorist)|Petr Hořava]] have argued<ref>{{Cite arXiv |eprint=hep-th/0405019 |first1=Eric G. |last1=Gimon |first2=Petr |last2=Hořava |title=Over-rotating black holes, Gödel holography and the hypertube |year=2004}}</ref> that in a [[supersymmetric]] five-dimensional [[Gödel metric|Gödel universe]], quantum corrections to general relativity effectively cut off regions of spacetime with causality-violating closed timelike curves. In particular, in the quantum theory a smeared supertube is present that cuts the spacetime in such a way that, although in the full spacetime a closed timelike curve passed through every point, no complete curves exist on the interior region bounded by the tube.