Fictional
device for
instantaneous communication popular in
science fiction settings. Preferrable over
radio (which is limited by the
speed of light) when travelling vast
distances in
space.
The ansible first appeared in Ursula K. Le Guin's The Left Hand of Darkness, had its origin explained by Le Guin in The Dispossessed, and was later popularized by Orson Scott Card in Ender's Game.
The ansible uses something called the "Constant of Simultaneity" for operation. This required one end of the ansible link to be hosted on a planet, or similar object of non-trivial mass.