Raft by Stephen Baxter

Survivors find themselves stranded in an alternate cosmos where gravity and density are dramatically different, so space behaves like a crowded, fluid medium filled with filamentary structures and strange, immense lifeforms. Isolated on a tenuous sheet of matter, the human community must adapt, scavenge and engineer solutions to survive hostile predators, scarce resources and rival groups, while probing the alien physics and vast timescales that shape their environment.