An American physicist, David Bohm, devised a radical alternative at midcentury, visualizing “pilot waves” that guide every particle, an attempt to eliminate the wave-particle duality. For a long time, he was mainly lambasted or ignored, but variants of the Bohmian interpretation have supporters today. Other interpretations rely on “hidden variables” to account for quantities presumed to exist behind the curtain. Perhaps the most popular lately — certainly the most talked about — is the “many-worlds interpretation”: Every quantum event is a fork in the road, and one way to escape the difficulties is to imagine, mathematically speaking, that each fork creates a new universe.
So in this view, Schrödinger’s cat is alive and well in one universe while in another she goes to her doom. And we, too, should imagine countless versions of ourselves. Everything that can happen does happen, in one universe or another. “The universe is constantly splitting into a stupendous number of branches,” said the theorist Bryce DeWitt, “every quantum transition taking place on every star, in every galaxy, in every remote corner of the universe is splitting our local world on earth into myriads of copies of itself.”
This is ridiculous, of course. “A heavy load of metaphysical baggage,” John Wheeler called it. How could we ever prove or disprove such a theory? But if you think the many-worlds idea is easily dismissed, plenty of physicists will beg to differ. They will tell you that it could explain, for example, why quantum computers (which admittedly don’t yet quite exist) could be so powerful: They would delegate the work to their alter egos in other universes.
Is any of this real? At the risk of spoiling its suspense, I will tell you that this book does not propose a definite answer to its title question. You weren’t counting on one, were you? The story is far from finished.
When scientists search for meaning in quantum physics, they may be straying into a no-man’s-land between philosophy and religion. But they can’t help themselves. They’re only human. “If you were to watch me by day, you would see me sitting at my desk solving Schrödinger’s equation…exactly like my colleagues,” says Sir Anthony Leggett, a Nobel Prize winner and pioneer in superfluidity. “But occasionally at night, when the full moon is bright, I do what in the physics community is the intellectual equivalent of turning into a werewolf: I question whether quantum mechanics is the complete and ultimate truth about the physical universe.”