Juvenile exercise in gee-whiz folderol from the physicist and author of Dragon's Egg and The Flight of the Dragonfly. Young, diminutive industrialist Randy Hunter has four ambitions: to be the best horseman in the world, to become the richest and most important man in the solar system, to explore the stars, and to live forever. The one cloud on his horizon is politician Oscar, Randy's drug-addicted boyhood rival, now a spiteful opponent of Randy's grandiose dreams. Sure enough, thanks to Randy's development of orbiting linear accelerators to hurl goods and people to and from the planets, he soon becomes the richest and most important, etc. Then, after one of his planetary exploration teams discovers a Silverhair, a sort of talking space plant that's composed of negative matter, Randy's scientists and technologists are able to develop interstellar travel, both by ship and by space-warp. Then, since (how did you guess?) he's going to achieve all his ambitions, he wins the International Horseman of the Decade award--in between trips to nearby stars (oh, yes, he's married to a beautiful and understanding wife, whom he wooed away from Oscar, and has two wonderful children, too). All this--and Randy has yet to invent time travel, defeat Oscar, who tries to catch him in a time-trap, and, of course, bring back the secret of immortality from the future. Stuffed with speculations and scientific projections, most of them pretty far-fetched, held together by a footling narrative that would probably dissatisfy the average ninth grader. As for the ideas content, then: heady and furiously energetic if none too probable. Otherwise: hogwash.