A tour through the borderlands where today’s science turns into tomorrow’s science fiction, from the physicist and Nebula- and Hugo Award—winning novelist (Aftermath, 1998, etc.). Scientific facts, Sheffield contends, can generate ideas in the reader’s imagination and function as a wellspring for potential writers, because “new science and new applications mean an endless supply of new story ideas.” And he demonstrates how much more enjoyable science fiction is when the author’s facts are in order. Consequently, his primary—and potentially large—audience is science-fiction readers and those who write, or might consider writing, SF. Out of the 14 well-organized chapters here, physics predictably looms large. One beefy chapter examines atoms and smaller entities, quantum theory, relativity, and low and high temperatures. Another scrutinizes such large phenomena as stars and black holes. On a still larger scale come galaxies, cosmology, and the “eschaton,” the final state of all things, and the subject of a recent Sheffield novel. Chemistry, however, places firm limits on the range of possible alien metabolisms: A helium-breathing life form, for instance, simply isn’t possible. But how did life originate on the earth, and is there life on other planets? There are such possibilities, even within our own solar system. To explore fully, Sheffield points out, we need space flight, and for that we require propulsion systems, space elevators, and the like. Meanwhile, we can search for signs of extraterrestrial intelligence and develop computers, robots, nanotechnology, and artificial life forms. In recent years, chaos theory—Sheffield’s most technical section—has spawned some intriguing notions. Finally, he ponders the future of war, looks at such scientific heresies as cold fusion, free energy, and telepathy, and wonders if science itself may be coming to an end (reassuringly, no). Bang on target, in terms of appeal for both constituents and beneficiaries. As Mr. Spock would say: fascinating.