them from ever becoming "timeholes", allowing superluminal communication without the additional complication of allowing communication with the past. Fictional devices Tachyon-like The Dirac communicator features in several of the works of James Blish, notably his 1954 short story "Beep" (later expanded into The Quincunx of Time). As alluded to in the title, any active device received the sum of all transmitted messages in universal space-time, in a single pulse, so that demultiplexing yielded information about the past, present, and future. Superluminal transmitters and ansibles The terms "ultrawave" and "hyperwave" have been used by several authors, often interchangeably, to denote faster-than-light communications. Examples include: E. E. Smith used the term "ultrawave" in his Lensman series, for waves which propagated through a sub-ether and could be used for weapons, communications, and other applications. In Isaac Asimov's Foundation series, "ultrawave" and "hyperwave" are used interchangeably to represent a superluminal communications medium. The hyperwave relay also features. In the Star Trek universe, subspace carries faster-than-light communication (subspace radio) and travel (warp drive). The Cities in Flight series by James Blish featured ultrawave communications which used the known phenomenon of phase velocity to carry information, a property which in fact is impossible. The limitations of phase velocity beyond the speed of light later led him to develop his Dirac communicator. Larry Niven used hyperwave in his Known Space series as the term for a faster-than-light method of communication. Unlike the hyperdrive that moved ships at a finite superluminal speed, hyperwave was essentially instantaneous. In Richard K. Morgan's Takeshi Kovacs novels human colonies on distant planets maintain contact with earth and each other via hyperspatial needlecast, a technology which moves information "...so close to instantaneously that scientists are still arguing about the terminology". A later device was the ansible coined by Ursula K. Le Guin and used extensively in her Hainish Cycle. Like Blish's device it provided instantaneous communication, but without the inconvenient beep. The ansible is also a major plot element, nearly a MacGuffin, in Elizabeth Moon's Vatta's War series. Much of the story line revolves around various parties attacking or repairing ansibles, and around the internal politics of ISC (InterStellar Communications), a corporation which holds a monopoly on the ansible technology. The ansible is also used as the main form of communication in Orson Scott Card's Ender's Game series. It is controlled by an energy based, non-artificial sentient creature called an Aiúa that was