The term ansible is used in science fiction literature to describe a hypothetical faster-than-light (in fact instantaneous) communication device. The term was coined by Ursula K. Le Guin in her 1966 novel, Roccannon's World. Her award-winning 1974 novel The Dispossessed tells of the invention of the ansible within her Ekumen milieu.
Some have claimed that the word was an intentional anagram of "lesbian". Le Guin herself states that she derived it 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.
The name and basic function of the device have since been borrowed by authors such as Orson Scott Card, Elizabeth Moon and Vernor Vinge.
Faster-than-light communication is problematic because the theory of special relativity implies that such a device may allow communication from the future to the past, and would thus for instance allow the user to learn about tomorrow's lottery numbers today. See time travel for a discussion of the physics involved in building such systems. It is not clear that this is possible, or that the problems of causality could be resolved, but these questions are undergoing serious review by many reputable physicists. (The character in Le Guin's novel who invents the ansible is a theoretical physicist, working in a framework very different from ours.)
Ansible is a science fiction fanzine published by Dave Langford, named after the faster-than-light communicator.
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