Reality Dust
Reality Dust is the sixth work in the Xeelee Sequence. The plot begins not very long after the Third Expansion began (the First Expansion ended when humanity was conquered by the Squeem; the Second Expansion ended with the conquest of humanity by the Qax, and the Third Expansion, ~5400 CE, began after the events of Timelike Infinity, pursuant to Jim Bolder's destruction of the Qax home-system). The protagonist, one "Hama", an investigator for Earth's Truth Commission, is investigating the surviving Qax-collaborators (as the Qax restricted access to AS- anti-senescence technology – to collaborators, they are rather old, and are known as "Pharaohs"); he follows one renegade Pharaoh to Callisto.
Mayflower II
Mayflower II is the eighth work in the Xeelee Sequence. The plot centers on five generation ships leaving a doomed planet. As thousands of years pass, the humans forget that they are on a spaceship and begin running its mechanisms only through religious ritual. After 25,000 years, the humans on the ship have split in their evolution with half becoming short-lived childlike tribal people and half becoming cannibalistic animals. The ending speaks to the fact that although this situation seems gruesome and terrible that life and evolution find a way and that humans found a way to continue on living even if it meant giving up what is traditionally thought of as human.
The story begins on Pluto in the distant future. Its inhabitants, former collaborators of the Qax, humanity's erstwhile conquerors, are under attack from the new-formed Coalition, seeking revenge for humanity's enslavement. As such, the inhabitants send five generation ships out of the solar system in the hopes that they will be able to form colonies of their own that can survive the Coalition. Rusel, the protagonist, is admitted onto Mayflower II, one of the ships, at the last minute. Shortly after takeoff, it is revealed that the ship's intended destination is outside the galaxy, requiring a flight time of 50,000 subjective years, even with the effects of time dilation.
The ship's captain selects a few individuals to receive medical treatment granting them immortality, allowing them to guide the ship through its millennia-long voyage. Over time, however, these individuals die through malfunctions or boredom, leaving Rusel as the only immortal on board, but he becomes increasingly dependent on life-support and gradually merges with the ship.
Over time, the other inhabitants of the ship form several different societies, gradually becoming detached from their original humanity. Eventually, they form an almost unrecognisable tribal civilisation. Having forgotten that they are on a spaceship at all, they only maintain it through religious tradition.
After 25,000 years have passed, the Mayflower II is contacted by Pirius and Torec (protagonists of Exultant), former soldiers of the Coalition, which is revealed to have fallen. They offer to remove the inhabitants from the ship and care for them elsewhere. Rusel, now completely merged with the ship's systems, allows them to do so. Pirius and Torec then leave Rusel to continue into space without the burden of the crew, which he gladly accepts.