A co-developer of the steady-state theory of the universe—an alternative to the Big Bang theory—explores his conception of the expanding universe. Hermann Bondi's historic book was among the first to present cosmology as a branch of physics in its own right, distinct from general relativity, philosophy, and logic. The author of many popular science books, Bondi excelled at explaining difficult scientific concepts in an interesting, accessible manner, and Cosmology attests to his skills. Scientific American acclaimed this volume as "an authoritative manual, ably written and well thought out," praising its "coherent view of a lively, important and healthily controversy-ridden branch of science." The three-part treatment covers principles of cosmology, observational evidence, and cosmological theories. This edition features a new Introduction by Ian W. Roxburgh, a leading figure in cosmology.