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, traversable wormholes, and quantum tunneling. Apparent FTL is not excluded by general relativity however, any apparent FTL physical plausibility is currently speculative. "Apparent" or "effective" FTL, on the other hand, 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 ("undistorted") spacetime.Īs of the 21st century, according to current scientific theories, matter is required to travel at slower-than-light (also STL or subluminal) speed with respect to the locally distorted spacetime region. Particles whose speed exceeds that of light ( tachyons) have been hypothesized, but their existence would violate causality, and the consensus of physicists is that they do not exist, and their existence would imply time travel. The special theory of relativity implies that only particles with zero rest mass (i.e., photons) may travel at the speed of light, and that nothing may travel faster. Spacetime diagram showing that moving faster than light implies time travel in the context of special relativityįaster-than-light (also FTL, superluminal or supercausal) communications and travel are the conjectural propagation of information or matter faster than the speed of light ( c).