Multiverses and Blackberries - questioning the theory of multiple universes

There be nothing so absurd but that some philosopher [or cosmologist?--M.G.] has said it.

Cicero

The American philosopher Charles Sanders Peirce somewhere remarked that unfortunately universes are not as plentiful as blackberries. One of the most astonishing of recent trends in science is that many top physicists and cosmologists now defend the wild notion that not only are universes as common as blackberries, but even more common. Indeed, there may be an infinity of them!

It all began seriously with an approach to quantum mechanics (QM) called "The Many Worlds Interpretation" (MWI). In this view, widely defended by such eminent physicists as Murray Gell-Mann, Stephen Hawking, and Steven Weinberg, at every instant when a quantum measurement is made that has more than one possible outcome, the number specified by what is called the Schrodinger equation, the universe splits into two or more universes, each corresponding to a possible future. Everything that can happen at each juncture happens. Time is no longer linear. It is a rapidly branching tree. Obviously the number of separate universes increases at a prodigious rate.

If all these countless billions of parallel universes are taken as no more than abstract mathematical entities--worlds that could have formed but didn't-- then the only "real" world is the one we are in. In this interpretation of the MWI the theory becomes little more than a new and whimsical language for talking about QM. It has the same mathematical formalism, makes the same predictions. This is how Hawking and many others who favor the MWI interpret it. They prefer it because they believe it is a language that simplifies QM talk, and also sidesteps many of its paradoxes.

There is, however, a more bizarre way to interpret the MWI. Those holding what I call the realist view actually believe that the endlessly sprouting new universes are "out there," in some sort of vast super-space-time, just as "real" as the universe we know! Of course at every instant a split occurs each of us becomes one or more close duplicates, each traveling a new universe. We have no awareness of this happening because the many universes are not causally connected. We simply travel along the endless branches of time's monstrous tree in a series of universes, never aware that billions upon billions of our replicas are springing into existence somewhere out there. "When you come to a fork in the road," Yogi Berra once said, "take it."

It is true that the MWI, in this realist form, avoids some of the paradoxes of QM. The so-called "measurement problem," for example, is no longer a problem because whenever a measurement occurs, there is no "collapse of the wave function" (or rotation of the state vector in a different terminology). All possible outcomes take place. Schrodinger's notorious cat is never in a mixed state of alive and dead. It lives in one universe, dies in another. But what a fantastic price is paid for these seeming simplicities! It is hard to imagine a mote radical violation of Occam's razor, the law of parsimony which urges scientists to keep entities to a minimum.

The MWI was first put forth by Hugh Everett III in a Princeton doctoral thesis written for John Wheeler in 1956. It was soon taken up and elaborated by Bryce DeWitt. For several years John Wheeler defended his student's theory, but finally decided it was "on the wrong track," no more than a bizarre language for QM and one that carried "too much metaphysical baggage." However, recent polls show that about half of all QM experts now favor the theory, though it is seldom clear whether they think the other worlds are physically real or just abstractions such as numbers and triangles. Apparently both Everett and DeWitt took the realist approach. Roger Penrose is among many famous physicists who find the MWI appalling. The late Irish physicist John S. Bell called the MWI "grotesque" and just plain "silly." Most working physicists simply ignore the theory as nonsense.

In an article on "Quantum Mechanics and Reality" (in Physics Today, September 1970), DeWitt wrote with vast understatement about his first reaction to Everett's thesis: "I still recall vividly the shock I experienced on first encountering the multiworid concept. The idea of [10.sup.100+] slightly imperfect copies of oneself all constantly splitting into further copies, which ultimately become unrecognizable, is not easy to reconcile with common sense. This is schizophrenia with a vengeance!"

In the MWI, most of its defenders agree, there is no room for free will. The multiverse, the universe of all universes, develops strictly along determinist lines, always obeying the deterministically evolving Schrodinger equation. This equation is a monstrous wave function which never collapses unless it is observed and collapsed by an intelligence outside the multiverse, namely God.

In recent years David Deutsch, a quantum physicist at Oxford University, has become the top booster of the MWI in its realist form. He believes that quantum computers, using atoms or photons and operating in parallel with computers in nearby parallel worlds, can be trillions of times faster than today's computers. He is convinced that many famous QM paradoxes, such as the double slit experiment and a similar one involving two half-silvered mirrors, are best explained by assuming an interaction with twin particles in a parallel world almost identical with our own. For example, in the double slit experiment, when both slits are open, our particle goes through one slit while its twin from the other world goes through the other slit to produce the interference pattern on the screen.