In Yalda's universe, light has no universal speed and its creation generates energy. On Yalda's world, plants make food by emitting their own light into the dark night sky. As a child Yalda witnesses one of a series of strange meteors, the Hurtlers, that are entering the planetary system at an immense, unprecedented speed. It becomes apparent that her world is in imminent danger—and that the task of dealing with the Hurtlers will require knowledge and technology far beyond anything her civilisation has yet achieved. Only one solution seems tenable: if a spacecraft can be sent on a journey at sufficiently high speed, its trip will last many generations for those on board, but it will return after just a few years have passed at home. The travellers will have a chance to discover the science their planet urgently needs, and bring it back in time to avert disaster.

Greg Egan’s The Clockwork Rocket introduced readers to an exotic universe where the laws of physics are very different from our own, where the speed of light varies in ways Einstein would never allow, and where intelligent life has evolved in unique and fascinating ways. Now Egan continues his epic tale of alien beings embarked on a desperate voyage to save their world ... The generation ship Peerless is in search of advanced technology capable of sparing their home planet from imminent destruction. In theory, the ship is traveling fast enough that it can traverse the cosmos for generations–and still return home only a few years after they departed. But a critical fuel shortage threatens to cut their urgent voyage short, even as a population explosion stretches the ship’s life-support capacity to its limits. When the astronomer Tamara discovers the Object, a meteor whose trajectory will bring it within range of the Peerless, she sees a risky solution to the fuel crisis. Meanwhile, the biologist Carlo searches for a better way to control fertility, despite the traditions and prejudices of their society. As the scientists clash with the ship’s leaders, they find themselves caught up in two equally dangerous revolutions: one in the sexual roles of their species, the other in their very understanding of the nature of matter and energy. The Eternal Flame lights up the mind with dazzling new frontiers of physics and biology, as only Greg Egan could imagine them.

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.