Editing Faster-than-light (section)

{{Short description|Propagation of information or matter faster than the speed of light}}
{{Other uses}}
[[File:Tachyon04s.gif|thumb|330x330px|Because the sphere travels faster than light, the observer sees nothing until it has already passed. Then, two images appear: one of the sphere arriving (on the right) and one of it departing (on the left).]]
'''Faster-than-light''' ('''superluminal''' or '''supercausal''') [[Superluminal motion|travel]] and [[Superluminal communication|communication]] are the conjectural propagation of [[matter]] or [[information]] faster than the [[speed of light]] in vacuum ({{mvar|'''c'''}}). The [[special theory of relativity]] implies that only particles with zero [[mass in special relativity|rest mass]] (i.e., [[photons]]) may travel ''at'' the speed of light, and that nothing may travel faster.

Particles whose speed exceeds that of light ([[tachyon]]s) have been hypothesized, but their existence would violate [[causality (physics)|causality]] and would imply [[time travel]]. The [[scientific consensus]] is that they do not exist. 

According to all observations and current scientific theories, matter travels at '''slower-than-light''' ('''subluminal''') speed with respect to the locally distorted spacetime region. Speculative faster-than-light concepts include the [[Alcubierre drive]], [[Krasnikov tube]]s, [[wormhole#Traversable wormholes|traversable wormholes]], and [[quantum tunnelling|quantum tunneling]].<ref>{{cite web |url=https://physicsworld.com/a/quantum-tunnelling-time-is-measured-using-ultracold-atoms/ |title=Quantum-tunnelling time is measured using ultracold atoms |website=Physics World |date=22 July 2020 |format= |accessdate=}}</ref><ref name="urlQuanta Magazine">{{cite web |url=https://www.quantamagazine.org/quantum-tunnel-shows-particles-can-break-the-speed-of-light-20201020/ |title=Quanta Magazine |date=20 October 2020 |format= |accessdate=}}</ref> Some of these proposals find loopholes around general relativity, such as by expanding or contracting space to make the object appear to be travelling greater than ''c''. Such proposals are still widely believed to be impossible as they still violate current understandings of causality, and they all require fanciful mechanisms to work (such as requiring [[exotic matter]]).

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