An ansible is a hypothetical machine capable of superluminal communication and used as a plot device in science fiction literature.
The word ansible
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
tells of the invention of the ansible within her Hainish Cycle
The name of the device has since been borrowed by authors such as Orson Scott Card
, Vernor Vinge
, Elizabeth Moon
, Jason Jones
, L.A. Graf
, and Dan Simmons
. Similarly functioning devices are present in the works of numerous others, such as Frank Herbert
and Philip Pullman
, who called it a lodestone resonator
. The subspace radio
, best known today from Star Trek
and named for the series' method of achieving faster-than-light travel, was the most commonly used name for such a faster-than-light (FTL) communicator in the science fiction of the 1930s to the 1950s. One ansible-like device which predates Le Guin's usage is the Dirac communicator
in James Blish
's 1954 short story "Beep". Isaac Asimov
solved the same communication problem with the hyper-wave relay
in The Foundation Series
. Stephen R. Donaldson
, in his Gap Series, introduces Symbiotic Crystalline Resonance Transmission
, clearly ansible-type technology which is very difficult to produce and limited to text messages.
Le Guin's ansible was said to communicate "instantaneously", but other authors have adopted the name for devices explicitly only capable of finite-speed communication (though still faster than light).
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." Le Guin's ansibles are not mated pairs as 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
is a widely read series which 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"). His description of ansible functions in Xenocide
involve a fictional subatomic particle, the philote
, and contradicts not only standard physical theory but the results of empirical particle accelerator
experiments. In the "Enderverse", the two quarks
inside a pi meson
can be separated by an arbitrary distance while remaining connected by "philotic rays". This is similar in concept to quantum teleportation
due to entanglement
, although even that is not capable of faster-than-light communication. Also, in the real world, quark confinement
prevents one from separating quarks by more than microscopic distances.
There is no known way to build an ansible. The theory of special relativity predicts that any such device would allow communication from the future to the past, which raises problems of causality. For this reason, most physicists believe that they will eventually be proven impossible. Quantum entanglement is often proposed as a mechanism for superluminal communication, but our current understanding of that phenomenon is that it cannot be used for any sort of communication—superluminal or otherwise—because of the no cloning theorem in quantum mechanics. See time travel and faster-than-light for more discussion of these issues.