It hasn't happened—no fully defined M theory has yet come to rule. But that isn't all. Theorists realized that string theories had more solutions than anticipated. A lot more—maybe 10500 of them, maybe an infinite number. And each solution gives a different picture of the allowable particles and laws. What to do? Some string theorists despaired. Other string theorists tried to rethink the situation to achieve the desired unique solution to a unique theory. Anti-stringers sharpened their scissors. Give up, they said, and say the laws just happen to be what they are.
Others, now including Hawking, embraced what has come to be known as the multiverse: The idea is that there are actually many universes, each with its own set of laws and particles. Advocates see it as a natural continuation of Feynman's vision. All possible histories have indeed been followed, but this time not merely to describe the many ways a photon can go from Electron A to Electron B—this time to account for the history of the universe itself and all its laws.
As Hawking puts in it The Grand Design: "the universe appeared spontaneously, starting off in every possible way. Most of these [alternative beginnings] correspond to other universes. … [S]ome … are similar to ours, most are very different." So how to understand the fact that we find ourselves in a universe with atomic laws that operate in such a way as to make matter and life possible? If the charges on a proton and an electron were not very, very close to equal and opposite, we wouldn't be here… a miracle tuning, or a divine intervention? It is no miracle, Hawking joins multiverse supporters in saying—any more than it is a miracle that we find ourselves on a planet in that narrow region of temperature where water is liquid.
Multiverse advocates contend that the origin (or, more precisely, origins) resides in quantum fluctuations—new universes pop into existence with no more fuss than a photon transforming into an electron-positron pair and then returning to its good old photonic self. The initial spark just happens because quantum mechanics tells us that, with some probability, new universes will come into existence. Physics can account not only for how the universe works but for why it is there at all. No divine help required. It is quantum physics all the way down—accompanied by just the right lot of elementary particle physics and string theory.
The archbishop of Canterbury, with the concurrence of eminent colleagues across the religious spectrum, begs to differ with Hawking. "Belief in God is not about plugging a gap in explaining how one thing relates to another within the universe," he announced. But tell that to Pope Pius XII, who half a century ago proclaimed support for the "fiat lux" in the early glimmers of a big-bang cosmology. Or tell it to the group of Cambridge physicists around the same time who were pushing for a no-first-moment account: a steady-state cosmology that would wipe out the big bang, undermining an overly religious moment of creation. Once you start reading God's presence—or his absence—into the ever-evolving equations of physics, it is hard to keep him from coming and going, creating a stir in the process. Hawking, who briefly left the door open for the mind of God two decades ago, surely knew he would stir an outcry by slamming it shut. In fact, it was no doubt part of his grand design.