Timelike Infinity

Timelike Infinity is a 1992 science fiction book by Stephen Baxter. The second book in the Xeelee Sequence, Timelike Infinity introduces a universe of powerful alien species and technologies which manages to maintain a realistic edge due to Baxter's physics background; it largely sets the stage for the magnum opus of the Xeelee Sequence, Ring (as opposed to Vacuum Diagrams, Flux, or Raft, which concern themselves with side-stories).