Seveneves is a lumpy novel with a fascinating premise interrupted by long info dumps and weakened by scanty characterization. Earth is destroyed, civilization is reduced to seven women in a shattered spaceship, and we see the shape of the society created by their descendants 5000 years later. Fairly, this should be three books, or even more, but it's one brick of a tome.

At some point around the present day, the Moon is destroyed by a sudden and unknown cataclysm. All of humanity has only 700 days to build and crew a lifeboat, a distributed planetary ark of cheap mass-produced capsules centered around an expanded ISS. This first part of the story is the weakest, full of "as you know Bob" exposition about characters we have yet to care about. Psychological realism has never been Stephenson's strongpoint, but I can't imagine that a species knowing that it was about to die, except for 1500 people selected by esoteric criteria, would behave so rationally. They do their best to engineer and launch space solutions, and all the technology the survivors will need.

The second part is the lifeboat drama, which is one of the better parts of the books. The ramshackle life-support system is falling apart, the former President of the United States has hitched a ride to orbit on a X-37 against the rules of the Last Treaty and is causing political trouble, and the only chance to get enough precious water is to carry out a deep space grab of a comet using an unshielded nuclear rocket. Precious samples are destroyed by asteroid bombardment, people die from radiation poisoning and failure of algae farms, there's desperate boarding actions, and at the end seven childbearing women are left alive, finally safe in the bottom of a fault in the largest fragment of the moon. They decide to repopulate the human species, with each Eve getting to rewrite her genes in the image of who she thinks humanity should be.

And then, with a scratch like a bad DJ, the story skips 5000 years (5000 years separates us and Minoan Crete), where humanity has made a ring of sophisticated habitats around Earth, and is well through recreating a livable ecosystem on the surface. Humanity has splintered into a number of sub-races based around the Seven Eves, each with stereotyped behaviors and reactions, and two major political factions based around one of the Eves being on the very wrong side of lifeboat survival. The action here centers around first contact with two new subspecies of humans, who survived the apocalypse in mine-shafts and submarines, but is mostly taken up with an explanation of the massive orbital habs and military technology based around smart 'ambots' rather than dumb lead bullets.

There are some very cool ideas in here, and one or two moments of actual emotional tension, but mostly this book is just long and surprisingly sedate, given the scope of the disaster.