Raft — Stephen Baxter

THE SURVIVAL OF HUMANKIND

Imagine a universe whose force of gravity is one billion times stronger than today's. Human beings have detectable gravity fields. Stars are only a mile across and burn out within a year of their formation.

Centuries before these events, a spaceship accidentally crossed into this universe and promptly collapsed upon itself. Somehow the crew survived. They emerged into a cloud of breathable atmosphere. centuries later their descendants are still struggling for existence....