 In this universe, extraterrestrial sentience exists but is elusive, and interstellar travel is primarily undertaken by a class of vessel called a lighthugger which only approaches the speed of light (faster than light travel is possible, but it is so dangerous that no race uses it).Fermi's paradox is explained as resulting from the activities of an inorganic alien race referred to by its victims as the Inhibitors, which exterminates sentient races if they proceed above a certain level of technology.The trilogy consisting of "Revelation Space", "Redemption Ark" and "Absolution Gap" (the Inhibitor trilogy) deals with humanity coming to the attention of the Inhibitors and the resultant war between them.