Tachyons are a type of particle that always travel faster than light.In Omni 01, it is possible to produce and detect certain types of tachyon, allowing them to be used in superluminal communications.
Tachyons travel faster than light. They only possess an imaginary rest mass, but can possess energy and the more energy a tachyon has, the closer to the speed of light it will travel. The less energy a tachyon has, the faster it will go.
These particles naturally lose energy via gravitational radiation, causing them to speed up over time. After a certain speed, it is impossible for this radiation to be detected and so the range of tachyonic communication is theoretically limited to a few million light years.
It is possible to produce tachyons by bombarding atomic nuclei larger than that of hydrogen-1 with electrons. Deuterium is favoured, as the larger the nucleus, the more energy the tachyon will possess on production and so the slower it will travel. This can be concentrated into a beam that is aimed at the destination point. Naturally, the true location of the target detector must be known to a degree of precision within a few kilometres, which is difficult due to light delay, where the target will be observed through a telescope as it was a long time ago.
The detection of tachyon beams is achieved through the use of (usually large) laser interferometers. The beam is shifted slightly by the passing tachyons as they radiate gravitational waves. It is impossible to use this form of communication near powerful sources of gravitational waves due to interference, though a very advanced race might be able to compensate for this.
Only limited information content can be encoded into a tachyonic beam.