Faster-than-light (also superluminal or ftl) communication and travel refer to the propagation of information or matter faster than the speed of light. under the special theory of relativity, a particle (that has rest mass) with subluminal velocity 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 (tachyons). 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. although 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 ftl proposals are the alcubierre drive and the traversable wormhole, although their physical plausibility is uncertain.