Hawking and Mlodinow return with a unifying 'Grand Design'

"No one seems to know what the 'M' stands for," the authors write, "but it may be 'master,' ''miracle,' or 'mystery.' It seems to be all three." A Feynman-like interpretation of M-theory predicts the simultaneous existence of multiple universes, each with different sets of fundamental constants and particles.

Because M-theory allows for so many possible universes - 10 to the 500th power, give or take a factor of a googol (10 to the 100th) - critics dismiss it not as the theory of everything but the theory of anything. Hawking and Mlodinow take a different view: "It could be that the physicists' traditional expectation of a single theory of nature is untenable."

In their view, a small fraction of those possible universes (but still a very large number) are suitable for the evolution of stars, planets, and life such as we experience on our particular world in our particular galaxy. In other words, according to M-theory, a universe like ours is not a miracle but an inevitability.

M-theory, they conclude, is the Grand Design that scientists have been seeking. Furthermore, it provides a better answer to the key question of existence - why our universe behaves as it does - than either religion or philosophy can.

A lot of scientists, theologians, and philosophers will beg to differ.