The final installment in the Remembrance of Earth's Past trilogy, this novel spans the first responses to the Trisolaran contact to the heat death of the universe, and humanity's struggle to survive in the face of discovery of the wider universe.

An enormous artificial world that has a livable surface on the inside. Has a radius of about 1 AU so the inside surface has conditions like a livable planet. Centrifugal force keeps inhabitants firmly planted on the ring.