In the Star Trek universe, subspace carries faster-than-light communication (subspace radio) and travel ( warp drive).

In Isaac Asimov's Foundation series, 'ultrawave' and 'hyperwave' are used interchangeably to represent a superluminal communications medium.

Smith used the term 'ultrawave' in his Lensman series, for waves which propagated through a sub-ether and could be used for weapons, communications, and other applications.

The terms 'ultrawave' and 'hyperwave' have been used by several authors, often interchangeably, to denote faster-than-light communications. As alluded to in the title, any active 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. The Dirac communicator features in several of the works of James Blish, notably his 1954 short story 'Beep' (later expanded into The Quincunx of Time). Some hypotheses of wormhole formation would prevent them from ever becoming 'timeholes', allowing superluminal communication without the additional complication of allowing communication with the past. Considering the immense energy or exotic matter with negative mass/ negative energy that current theories suggest would be required to open a wormhole large enough to pass spacecraft through, it may be that only atomic-scale wormholes would be practical to build, limiting their use solely to information transmission. If wormholes are possible, then ordinary subluminal methods of communication could be sent through them to achieve effectively superluminal transmission speeds across non-local regions of spacetime. Some authors have argued that using the no-communication theorem to deduce the impossibility of superluminal communication is circular, since the no-communication theorem assumes that the system is composite. A special case of this is the no-communication theorem, which prevents communication using the quantum entanglement of a composite system shared between two spacelike-separated observers. Technically, the microscopic causality postulate of axiomatic quantum field theory implies the impossibility of superluminal communication using any phenomena whose behavior can be described by orthodox quantum field theory. However, it is now well understood that quantum entanglement does not allow any influence or information to propagate superluminally. The impossibility of superluminal communication led Einstein, Podolsky, and Rosen to propose that quantum mechanics must be incomplete (see EPR paradox). Entangled states lead to correlations in the results of otherwise random measurements, even when the measurements are made nearly simultaneously and at far distant points. Quantum mechanics is non-local in the sense that distant systems can be entangled. However, such fields have luminal signal velocity and do not allow superluminal communication.

By contrast, tachyonic fields – quantum fields with imaginary mass – certainly do exist and exhibit superluminal group velocity under some circumstances. These would allow superluminal communication, and for this reason are widely believed not to exist. Tachyonic particles are hypothetical particles that travel faster than light. Ī number of theories and phenomena related to superluminal communication have been proposed or studied, including tachyons, neutrinos, quantum nonlocality, wormholes, and quantum tunneling.

This complicates causality, but no theoretical arguments conclusively preclude this possibility. Superluminal communication other than possibly through wormholes is likely impossible because, in a Lorentz-invariant theory, it could be used to transmit information into the past. The current scientific consensus is that faster-than-light communication is not possible, and to date it has not been achieved in any experiment.

Superluminal communication is a hypothetical process in which information is conveyed at faster-than-light speeds.

Superliminal voice actor