An ansible [an-si-bull] is a hypothetical machine capable of instantaneous or superluminal (faster-than-light) communication. They are used as science fiction plot devices and in thought experiments of theoretical physics. The word was coined by American author Ursula K. Le Guin in her 1966 novel, ‘Rocannon’s World.’

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. The name of the device has since been borrowed by authors such as Orson Scott Card and Vernor Vinge; similar devices are present in the works of numerous others, such as Frank Herbert. One ansible-like device which predates Le Guin’s is the ‘Dirac communicator’ in James Blish’s 1954 short story ‘Beep.’ The 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.

There is no currently 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. Quantum entanglement is often proposed as a mechanism, however. Entangled particles act in unison and become a system. They behave like one object, but remain two separate objects. It is as if they now sit on the same teeter-totter seesaw. No matter how long the seesaw is, even if it is one million miles long, if one end is down the other end must be up, and this happens instantly. Even though each particle can tell what the other is doing, they do not send messages back and forth.


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