The Manifold is an infinite sheaf of alternative universes which Baxter explores in terms of Fermi's Paradox. There's no reason why humanity should be unique; logically there should be alien races, some long enough established to have made their mark on the galaxy; where are they?

Book one, Time, offered a vision of lonely humanity extending to the far end of eternity and finally rebooting a "better" universe. Space showed the consequences of teeming interstellar life, a cruel struggle for resources, punctuated by galactic-sized extinction events. Now Origin confronts the whole Manifold and its and humanity's manipulation by enigmatic "Old Ones".

Astronaut Reid Malenfant (versions of whom starred in Time and Space) again encounters advanced technology as a huge, glowing blue circle--a portal to and from the Red Moon that wanders between universes and has just replaced our own moon. It's habitable and populated by an extraordinary medley from all stages of human evolution, scooped up from different Earths. There's much conflict with primitives leading nasty, brutish and short lives... plus super-evolved humans who debate whether we are truly sentient.

At its core the Red Moon contains the failing World Engine which flips between universes. Also down there is the secret history of this multi-verse, right back to the cataclysmic branch-point from which the Manifold flowered. Who are the Old Ones? "They made the manifold"--but were maybe not so different from us and rash, quixotic Malenfant after all. Highly superior SF, guaranteed to jolt one's sense of wonder. --David Langford

Synopsis
At last Malenfant gets to kick-start his own universe in this final volume of the Manifold series. The Fermi Paradox concerning extraterrestrials runs: If they existed the would be here. Since they are not here, they don't exist. In TIME, in a universe empty of other sentient beings, Malenfant discovered the aberrant development that led to humanity's uniqueness, our sole occupation of space. Then, incredibly, he changed everything, with the aid of the Blue Children from the future. In SPACE, aliens were everywhere but they were just arriving in the Solar System. And the same Fermi Paradox unravelled to reveal that all life in the universe is temporary: the aliens and life on Earth are periodically wiped out, only to start over, and over, and over. In ORIGIN, our astronaut hero has the chance to reach out to where both universes cross, their origin, and at last make sense of life on Earth and elsewhere.