The Dirac Receiver is James Blish's transluminal communications device.
It makes its first appearance in his writings in the novella 'Beep' extended out to the novel Quincunx of Time. Unlike the Ansible, and other FTL communications devices, any Dirac Receiver is capable of receiving the transmissions of any other Dirac Receiver where, or when, ever it broadcasts. This does give massive advantage to the organisation that first gets the Dirac but not quite omniscient powers as in order to take advantage of a message you have to understand what it says.
The Dirac is also used in the Cities in Flight series but there is no evidence of it's temporal abilities in those books.
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