Greg Bear 
Eternity 

The New York Times–bestselling author of Eon continues the interstellar saga of the Way.   A devastating war has left Earth a nuclear wasteland. Orbiting the planet is the asteroid-starship containing the civilization of Thistledown, humanity’s future descendants. For decades, they have worked to heal their world and its survivors, but their resources are finite. They need to reopen the Way.   An interdimensional gateway to a multiverse of realities, the Way was severed from Thistledown to stop an alien invasion and now exists as its own universe. Reopening the gate would not only benefit Earth but would also help the asteroid’s residents return home.   But on the alternate world of Gaia, Rhita Vaskayza, daughter of mathematician Patricia Vasquez, has taken up her mother’s cause to find her own Earth, one that was never touched by nuclear war. There is a gateway on Gaia that could lead Rhita there—or unleash an even greater apocalypse across the multiverse . . .   “Whether he’s tinkering with human genetic material or prying apart planets, Bear goes about the task with intelligence and a powerful imagination. Eternity offers many delights” (Locus).