Faster - Faster-than-light From Wikipedia the free...

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Faster-than-light From Wikipedia, the free encyclopedia Jump to: navigation , search "Faster than the speed of light" redirects here. For other uses, see Faster than the speed of light (disambiguation) . This article needs additional citations for verification . Please help improve this article by adding reliable references . Unsourced material may be challenged and removed . (September 2009) Faster-than-light (also superluminal or FTL ) communications and travel refer to the propagation of information or matter faster than the speed of light . Under the special theory of relativity , a slower-than-light particle with nonzero rest mass needs infinite energy to accelerate to the speed of light, although special relativity does not forbid the existence of particles that travel faster than light at all times (see tachyons ). On the other hand, what some physicists refer to as "apparent" or "effective" FTL [1] [2] [3] [4] is the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations faster than what it would take light in the normal or undistorted spacetime. However, according to current theories, matter is still required to travel subluminally with respect to the locally distorted spacetime region. Apparent FTL is not excluded by general relativity . Examples of apparent FTL proposals are the Alcubierre drive and the traversable wormhole , although the physical plausibility of these solutions is uncertain. Contents [ hide ] 1 Travel 2 Possibility 3 Justifications o 3.1 Faster light (Casimir vacuum and quantum tunnelling) o 3.2 Give up causality o 3.3 Give up (absolute) relativity o 3.4 Non-physical realms o 3.5 Space-time distortion o 3.6 Heim theory o 3.7 Lorentz symmetry violation 4 Tachyons 5 General relativity 6 FTL phenomena o 6.1 Daily motion of the Heavens o 6.2 Light spots and shadows o 6.3 Closing speeds o 6.4 Proper speeds
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o 6.5 Phase velocities above c o 6.6 Group velocities above c o 6.7 Universal expansion o 6.8 Astronomical observations o 6.9 Quantum mechanics 6.9.1 Hartman effect 6.9.2 Casimir effect 6.9.3 EPR Paradox 6.9.4 Delayed choice quantum eraser 7 Variable speed of light 8 Notes 9 See also 10 References 11 External links o 11.1 Scientific links o 11.2 Proposed FTL Methods links [ edit ] Travel In the context of this article, FTL is transmitting information or matter faster than c , a constant equal to the speed of light in a vacuum, 299,792,458 meters per second, or about 186,282.4 miles per second. This is not quite the same as traveling faster than light, since: Some processes propagate faster than c , but cannot carry information (See below ). Light travels at speed c/n when not in a vacuum but traveling through a medium with refractive index = n (causing refraction ), and in some materials other particles can travel faster than c/n (but still slower than c ), leading to Cherenkov radiation Neither of these phenomena violates special relativity or creates problems with causality , and thus neither qualifies as FTL as described here.
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