A Imaginary-Science device invented by James Blish for the story "Beep" (February 1954 Galaxy; exp vt The Quincunx of Time 1973), and used by him also in other stories. It is an instantaneous communicator, named after the great theoretical physicist Paul Dirac (1902-1984); the Blish story contrasts it with Faster Than Light but non-instantaneous Ultrawave communications. Others have since borrowed the device, but more recently Ursula K Le Guin's Ansible has been the communicator of preference for sf writers.
The Dirac communicator is accompanied by what many regard as undesirable philosophical baggage, since it has the peculiar property that all the Dirac messages ever sent – past, present and future – are received in highly time-compressed (but decipherable) form each time such a device is used. It thus functions as a restricted Time Radio or Time Viewer and, as Blish did not fail to note in his original story, implies a determinism-ruled universe in which free will is illusory. [PN/DRL]
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