With Freeman Dyson's astonishing forecasts for the future, it's hard to tell where science ends and science fiction begins. But far from being a wild-eyed visionary, Dyson is a clear and sober thinker -- and one not afraid of controversy or heresy.

From inventing Dyson Spheres, a sci-fi conceit postulating habitable shells around Sol-like stars, to "space chickens" and trees that grow in comets, Freeman Dyson is not afraid to go out on a cosmic limb. It would be wrong, however, to categorize him as a publicity-hungry peddler of headline-grabbing ideas. In his 60-year career as one of planet Earth's most distinguished scientists, several things characterize Dyson more than anything else: compassion, caution and overwhelming humanism.

In addition to his work as a scientist, Dyson is a renowned and best-selling author. His most recent book, A Many-Colored Glass, tackles nothing less than biotechnology, religion and the role of life in the universe. He does not shy away from controversy: His recent critiques of the politics of the global warming debate have raised the hackles of some environmentalists. But far from wielding his conclusions like a bludgeon, Dyson wants younger generations of scientists to take away one thing from his work -- the necessity to create heresies of their own.