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An ansible is a fictional machine capable of instantaneous or superluminal communication. It can send and receive messages to and from a corresponding device over any distance whatsoever with no delay. Ansibles occur as plot devices in science fiction literature.
The word ansible was coined by Ursula K. Le Guin in her 1966 novel Rocannon's World. Le Guin states that she derived the name from "answerable," as the device would allow its users to receive answers to their messages in a reasonable amount of time, even over interstellar distances. Her award-winning 1974 novel The Dispossessed, a book in the Hainish Cycle, tells of the invention of the ansible.
There is no way to build an ansible based on current technology. The theory of special relativity (and equally well the theory of general relativity) predicts that some proposed methods of creating such device would cause communication from the future to the past – a form of time travel which in general raises problems of causality (but not that couldn't be overcome based on other methods).
A Wormhole would be a method of faster-than-light communication that would not violate the rules of relativity in any way. And Wormholes are a known solution of Einstein’s equations that may be possible to engineer sometime in the future. A signal sent through a wormhole (or "micro-wormhole," one possible method of creating a working ansible) would take a "short-cut" through space, allowing instantaneous communication any place in the universe to another if they could be engineered. Wormholes wouldn't necessarily have the problem of time travel (as long as they were purposefully created not to).
Quantum nonlocality (and in particular the phenomenon of quantum entanglement) is often proposed as another mechanism for superluminal communication. Indeed, both experiments and theory show that entangled particles at some distance exhibit statistical correlations that cannot be explained in classical terms except by some kind of instantaneous effect; that is what is meant by quantum nonlocality. However, it is generally (but not universally) thought (at this time) that this effect cannot be used to communicate at speeds faster than light (but can only be used at distances slower than light, since scientists can “compare notes” at those distances about what they’ve seen). The problem with claiming, that in quantum field theory, causality is respected, and quantum correlations cannot be used to transfer information faster-than-light is that there is currently no "theory-of-everything" that unites Relativity and Quantum Mechanics, we also know relatively little about the phenomenon at this time. So we cannot say for sure that quantum entanglement will never be used for superluminal communication, nor can we say it will for sure. Therefore, it remains unknown.
While an ansible is impossible for now, it may be someday for our descendents, by one of the above methods, or another method that is currently unknown to physics.
The name of the device has since been borrowed by authors such as Orson Scott Card, Vernor Vinge, Elizabeth Moon, Jason Jones, Kim Stanley Robinson, L.A. Graf, and Dan Simmons.
Anne McCaffrey's Crystal Singer series posited an instantaneous communication device powered by rare "Black Crystal" from the planet Ballybran. Black Crystals cut from the same mineral deposit could be "tuned" to sympathetically vibrate with each other instantly, even when separated by interstellar distances, allowing instantaneous telephone-like voice and data communication. Similarly, in Gregory Keyes' series The Age of Unreason, "aetherschreibers" use two halves of a single "chime" to communicate, aided by scientific alchemy. While the speed of communication is important, so is the fact that the messages cannot be overheard except by listeners with a piece of the same original crystal.
Stephen R. Donaldson, in his Gap cycle, proposed a similar system, Symbiotic Crystalline Resonance Transmission, clearly ansible-type technology but very difficult to produce and limited to text messages.
Some hard science fiction stories use small (possibly nano-sized) paired wormholes dedicated to communication by means of a laser which traverses the wormhole. In Robert L. Forward's novel Timemaster, the wormhole is a living organism resembling a fourth-dimensional sea anemone, "stretched" to cover the distance between a spaceship and a satellite on the home planet.
Charles Stross's books Singularity Sky and Iron Sunrise make use of "causal channels" which use entangled particles for instantaneous two-way communication. The technique has drawbacks in that the entangled particles are expendable and the use of faster-than-light travel destroys the entanglement, so that one end of the channel must be transported below light speed. This makes them expensive and limits their usefulness somewhat.
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".
One ansible-like device which predates Le Guin's is the Dirac communicator that features in several of the works of James Blish, notably his 1954 short story "Beep". 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.
Isaac Asimov solved the same communication problem with the hyper-wave relay in the Foundation series. Larry Niven later used the same term for the plot device used within his Known Space series of novels and short stories, notably in the Ringworld and associated Fleet of Worlds series.
In Ivan Yefremov's 1957 novel Andromeda, a device for instant transfer of information and matter is made real by using "bipolar mathematics" to explore use of anti-gravitational shadow vectors through a zero field and the antispace, which enables them to make contact with the planet of Epsilon Tucanae.
Le Guin's ansible was said to communicate "instantaneously", but other authors have adopted the name for devices capable only of finite-speed communication, although still faster than light.
The subspace radio, best known today from Star Trek and named for the method used in the series for achieving faster-than-light travel, was the most commonly used name for such a faster-than-light communicator in the science fiction of the 1930s to the 1950s.
In the Stargate television series, characters are able to communicate instantaneously over long distances by transferring their consciousness into another person or being anywhere in the universe using "Ancient communication stones". It is not known how these stones operate, but the technology explained in the show usually revolves around wormholes for instant teleportation, faster-than-light, space-warping travel, and sometimes around quantum multiverses.
In the Avatar continuity, superluminal communication via a subtle control over the state of entangled particles is possible, but for practical purposes extremely slow and expensive: at a transmission rate of three bits of information per hour and a cost of $7,500 per bit, it is used for only the highest priority messages.
In Cordwainer Smith's Instrumentality novels and stories, interplanetary and interstellar communication is normally relayed from planet to planet, presumably at superluminal speed for each stage (at least between solar systems) but with a cumulative delay. For urgent communication there is the "instant message", which is effectively instantaneous but very expensive.
In Ernest Cline's novel Armada, alien invaders possess technology for instant "quantum communication" with unlimited range. Humans reverse engineer the device from captured alien technology.
In Le Guin's work
In The Word for World Is Forest, Le Guin explains that in order for communication to work with any pair of ansibles, at least one "must be on a large-mass body, the other can be anywhere in the cosmos."
In The Left Hand of Darkness, the ansible
doesn't involve radio waves, or any form of energy. The principle it works on, the constant of simultaneity, is analogous in some ways to gravity ... One point has to be fixed, on a planet of certain mass, but the other end is portable.
Unlike McCaffrey's black crystal transceivers, Le Guin's ansibles are not mated pairs: it is possible for an ansible's coordinates to be set to any known location of a receiving ansible. Moreover, the ansibles Le Guin uses in her stories apparently have a very limited bandwidth which only allows for at most a few hundred characters of text to be communicated in any transaction of a dialog session. Instead of a microphone and speaker, Le Guin's ansibles are attached to a keyboard and small display to perform text messaging.
In Card's work
Orson Scott Card's Ender's Game series uses the ansible as a plot device. "The official name is Philotic Parallax Instantaneous Communicator," explains Colonel Graff in Ender's Game, "but somebody dredged the name ansible out of an old book somewhere."
Card's description of the ansible's functions in Xenocide involve a fictional subatomic particle, the philote. In the "Enderverse", the two quarks inside a pi meson can be separated by an arbitrary distance while remaining connected by "philotic rays". This concept is similar to quantum teleportation due to entanglement. However, in reality, quark confinement prevents quarks from being separated by any observable distance.
The ansible is also featured in the video game Advent Rising, for which Card helped write the story.
In Elizabeth Moon's work
There is a brief reference to the ansible in Elizabeth Moon's novel Winning Colors. The ansible itself is a major plot element, nearly a MacGuffin in her 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), which holds a monopoly on the ansible technology. There is a brief reference to ansibles in "Once A Hero" (novel), "She didn't trust even Fleet ansibles to keep such messages secure ...".
- Bernardo, Susan M. & Murphy, Graham J. Ursula K. Le Guin: A Critical Companion (Westport, CT: Greenwood Press, 2006), page 18.
- Quinion, Michael. "Ansible". World Wide Words.
- Le Guin, Ursula K. (August 2001) [June 1974]. The Dispossessed (mass ppb. ed.). New York: Eos/HarperCollins. p. 276. ISBN 0-06-105488-7.
'They print Reumere's plans for the ansible.' 'What is the ansible?' 'It's what he's calling an instantaneous communication device.'
- Brilliantly Simple Explanation of Quantum Entanglement. Science and Nonduality. Retrieved on 2015-06-24.
- Pullman, Philip (2001-10-02) . The Amber Spyglass (His Dark Materials, 3. mass pbk. ed.). New York: Del Rey. p. 156. ISBN 0-345-41337-7.
'Well, in our world there is a way of taking a common lodestone and entangling all its particles, and then splitting it in two so that both parts resonate together.'
- Card, Orson Scott (July 1994) [August 1977]. Ender's Game (mass ppb. ed.). New York: Tor Books. p. 249. ISBN 0-8125-5070-6.
What matters is we built the ansible. The official name is Philotic Parallax Instantaneous Communicator, but somebody dredged the name ansible out of an old book somewhere and it caught on.
- Vinge, Vernor (1988-11-01). "The Blabber". Threats & Other Promises. Riverdale, NY: Baen. p. 254. ISBN 0-671-69790-0.
'It's an ansible.' 'Surely they don't call it that!' 'No. But that's what it is.'
- Moon, Elizabeth (1995-08-01). Winning Colors (mass ppb. ed.). Riverdale, NY: Baen. p. 89. ISBN 0-671-87677-5.
...when I was commissioned, we didn't have FTL communications except from planetary platforms. I was on Boarhound when they mounted the first shipboard ansible, and at first it was only one-way, from the planet to us.
- Jones, Jason (with Greg Kirkpatrick) (1995-11-24) Marathon 2: Durandal, computer game, Chicago, IL: Bungie Software. "A connection [?ansible] was left; awaiting the next quiet [?peace]; and though destroyed by the threes, it will scream over the void one time."
- "Any device that uses this phenomenon is called an ansible, and these devices have been constructed." (2312)
- Graf, L.A. [Julia Ecklar] (August 1996). Time's Enemy (Star Trek Deep Space 9TM : Invasion, 3. mass pbk. ed.). New York: Pocket Books. p. 203. ISBN 0-671-54150-1.
'...The two Dax symbionts can communicate with each other across space, instantaneously, because they're composed of identical quantum particles. I've become a living ansible, Benjamin.'
- Simmons, Dan (2003-07-01). Ilium (hbk. ed.). New York: Eos/HarperCollins. p. 98. ISBN 0-380-97893-8.
I can see Nightenhelser madly taking notes on his recorder ansible.
- Herbert, Frank (April 1970) . The Whipping Star. Worlds of If magazine.
- Keyes, J. Gregory (March 4, 2009). The Shadows of God. Random House LLC. ISBN 9780307559609. Retrieved 15 March 2014.
My aetherschreiber was lost when the Coweta captured us.
- Rosenberg, Jonathan (June 25, 2012). "Scenes from a Multiverse: The Ansible".
- James Cameron's Avatar: An Activist Survival Guide – pg 156-157
- Smith, Cordwainer. "On the Storm Planet" (February 1965), Chap. XII, pp. 148–149 in: Dozois, Gardner, ed. (Oct 28, 2014). Modern Classic Short Novels Of Science Fiction. New York: St. Martin's Press. pp. 94–163. Retrieved 14 August 2015.
The communicator was the kind they mount in planoforming ships right beside the pilot. The rental on one of them was enough to make any planetary government reconsider its annual budget. ... She pressed a button. "Instant message." ... Casher, knowing the prices of this kind of communication, almost felt that he could see the arterial spurt of money go out of Henriada's budget as the machines reached across the galaxy, found Mizzer and came back with the answer.
- Moon, Elizabeth (September 2004). Trading in Danger (mass ppb. ed.). Del Rey. p. 111. ISBN 0-345-44761-1.
Attack on instersystem ansibles is just...just unthinkable
- Bernardo, Susan M.; Murphy, Graham J. (2006). Ursula K. Le Guin: A Critical Companion (1st ed.). Westport, CT: Greenwood Press. ISBN 0-313-33225-8.
- Bloom, Harold, ed. (1986). Ursula K. Le Guin (1st ed.). New York, NY: Chelsea House. ISBN 0-87754-659-2.
- Sheidlower, Jesse, ed. (6 July 2008). "ansible n.". Science Fiction Citations for the OED. Retrieved 15 March 2014.