Timelike Infinity by Stephen Baxter

Set in an expansive future where humanity lives under the domination of an alien power, the novel follows scientists, engineers and dissidents who pursue radical physics, relativistic engineering and time-manipulation gambits to undermine their overlords and reclaim agency. As plans to exploit timelike paradoxes and cosmic-scale technologies unfold, characters confront political betrayal, moral cost and the staggering implications of artifacts left by a vastly older, almost godlike civilization; the story blends hard science, large-scale space opera and intimate human drama as it probes freedom, survival and the nature of the universe.