Proxima Centauri, the nearest star outside the Solar System, is about four light-years away. In the following examples, certain influences may appear to travel faster than light, but they do not convey energy or information faster than light, so they do not violate special relativity.įor an earth-bound observer, objects in the sky complete one revolution around the Earth in one day. Neither of these phenomena violates special relativity or creates problems with causality, and thus neither qualifies as FTL as described here. In some materials where light travels at speed c/n (where n is the refractive index) other particles can travel faster than c/n (but still slower than c), leading to Cherenkov radiation (see phase velocity below).Some processes propagate faster than c, but cannot carry information (see examples in the sections immediately following).This is not quite the same as traveling faster than light, since: In the context of this article, FTL is the transmission of information or matter faster than c, a constant equal to the speed of light in vacuum, which is 299,792,458 m/s (by definition of the metre ) or about 186,282.397 miles per second. Examples of apparent FTL proposals are the Alcubierre drive, Krasnikov tubes, the traversable wormholes, and quantum tunneling. Apparent FTL is not excluded by general relativity however, any apparent FTL physical plausibility is currently speculative.
On the other hand, what some physicists refer to as "apparent" or "effective" FTL depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal or undistorted spacetime.Īccording to the current scientific theories, matter is required to travel at slower-than-light (also subluminal or STL) speed with respect to the locally distorted spacetime region. Tachyons, particles whose speed exceeds that of light, have been hypothesized, but their existence would violate causality, and the consensus of physicists is that they do not exist. The special theory of relativity implies that only particles with zero rest mass may travel at the speed of light. Spacetime diagram showing that moving faster than light implies time travel in the context of special relativity.įaster-than-light (also superluminal, FTL or supercausal) communications and travel are the conjectural propagation of information or matter faster than the speed of light.
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