Are we alone? Or is the universe teeming with intelligent life? Can we expect extraterrestrial civilizations to be common? Occasional? Rare? In this wide-ranging Assessment, historian/writer W. H. Collier explores the probabilities of the existence of extraterrestrial, technological life based on the latest scientific findings. Not content with the well-worn assertion that life must be common because there are so many stars and planets, Collier undertakes...