The Big Bang theory of the birth of the universe teaches that billions of years ago there was a hot, violent explosion of elementary particles and radiation. What do we know about this ultimate moment of creation, and how do we know it? This is an introduction to scientific cosmology, and the third edition of this book provides a sweeping account of events. New to this edition are: photographs and measurements from the Hubble Space Telescope, Cosmic Background Explorer Satellite and Infrared Space Observatory; new ideas in string and superstring theory; and ideas about black holes, worm holes, quantum foam and multiple universes.