Was the Big Bang the beginning of the universe? Are there other universes where time runs 'backwards'? Why can't you unscramble an egg? Such questions are the focus of this book, in which one of the world's leading theoretical physicists addresses unsolved problems in our understanding of the rules of nature. Surveying different models that have been used to explain the mysterious 'arrow of time', the author proposes a new theory of how we came to exist.