Lighthugger

Lighthuggers were large spacecraft used by humans in the Revelation Space Universe that traveled at just below the speed of light, taking months or years to accelerate to their cruising speed, reaching 99% of the speed of light in about 1 earth year.

They used Conjoiner drives for propulsion which used quantum mechanics to propel them up to relativistic speeds. They contained a small wormhole linked to the very deep past, through which they draw their propulsion energies from the Quark-gluon plasma created by the Big Bang. As the drive power was increased, so did the risk of an uncontrolled, ship-destroying explosion. The emission of tau-neutrinos by the drives was eventually found to attract the Inhibitors, and so Stealth Conjoiner driver were invented.