"How can we understand the world in which we find ourselves? Over twenty years ago I wrote "A Brief History of Time", to try to explain where the universe came from, and where it is going. But that book left some important questions unanswered. Why is there a universe--why is there something rather than nothing? Why do we exist? Why are the laws of nature what they are? Did the universe need a designer and creator? It was Einstein"s dream to discover the grand design of the universe, a single theory that explains everything. However, physicists in Einstein"s day hadn"t made enough progress in understanding the forces of nature for that to be a realistic goal. And by the time I had begun writing A Brief History of Time, there were still several key advances that had not yet been made that would prevent us from fulfilling Einstein"s dream. But in recent years the development of M-theory, the top-down approach to cosmology, and new observations such as those made by satellites...