Hawking poses the ultimate of ultimate questions: Why does the universe exist and why does it follow rules and laws? What's the point of the enormous, endless cosmos, and why is it so perfectly tuned to allow life to exist? Finding out leads to the very deepest of secrets, to the one principle that's at the heart of everything in the cosmos -- string theory. He goes from Newton's groundbreaking discovery of gravity, through hidden extra dimensions, to a muti-verse of billions of more universes where anything - and everything - is possible.