The Arrows of Time — Greg Egan

Hard science fiction's grand master delivers the stunning conclusion to his Orthogonal trilogy.

In a universe where the laws of physics and the speed of light are completely alien to our own, the travelers on the ship Peerless have completed a generations-long struggle to develop advanced technology in a desperate attempt to save their home world. But as tensions mount over the risks of turning the ship around and starting the long voyage home, a new complication arises: the prospect of constructing a messaging system that will give the Peerless news of its own future.

While some see this as a guarantee of safety and a chance to learn of their mission's ultimate success, others are convinced that the knowledge will be oppressive or worse -- that the system could be abused. The conflict over this proposed communication system tears the travelers' society apart, culminating in terrible violence. To save the Peerless and its mission, two rivals must travel to a world where time runs in reverse.

Continuing the epic multiple generation-spanning scope of The Clockwork Rocket and The Eternal Flame, Greg Egan's Orthogonal series has continuously pushed the boundaries of scientific fiction without ever losing track of the lives of the individuals carrying out this grand mission. The Arrows of Time brings this fascinating space opera to a close.