Existential Crisis! Many Worlds Theory Confirmed!

27 September 2007

“There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.” So declares Shakespeare’s Hamlet after discovering, among other things, the reality of ghosts. Now quantum physicists have taken a step closer to embracing a theory that says there are not only more things in heaven and earth; there are more heavens and earths — in fact an infinitude of them, making up a “multiverse” of all possible things.

The news here, which I’ll try to clarify in layman’s terms below, comes from a small conference of quantum physicists in Waterloo, Ontario, last weekend, where two Oxford researchers, David Wallace and Simon Saunders, reported a solid mathematical confirmation of the controversial “many worlds interpretation” of quantum physics.

New Scientist magazine quoted Andy Albrecht, a physicist at UC-Davis, saying, “This work will go down as one of the most important developments in the history of science.” That could be an understatement. Acceptance of the many-worlds interpretation, in its present form, could cause an existential earthquake more severe even than those brought about by Darwin and Galileo.

The many-worlds interpretation (MWI) is sometimes popularly referred to as the “theory of parallel universes.” As such, it is apt to seem like a bit of hand-waving, sci-fi speculation ginned up by some cosmologist in his spare time. In fact it is anything but that.

Remember how Einstein used to fret about some of the implications of quantum theory? That the theory did not allow firm predictions about the behavior of particles at the quantum level, but threw up only a haze of probabilities, really bothered him. In a letter to fellow scientist Max Born in 1926, he famously wrote, “Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the Old One. I, at any rate, am convinced that He does not throw dice.”

A Maryland-born physicist, Hugh Everett III, felt much the same way. At Princeton in 1957, where he studied under the famous physicist and cosmologist John Archibald Wheeler (coiner of the term black hole), he published the concept of MWI as his Ph.D. thesis. Essentially, Everett argued that God does not play dice – that all the possible characteristics of a particle at any given moment, as defined in the equations of quantum mechanics, are not an abstract set of “probabilities” but are all the real characteristics of the particle in all possible alternate “worlds.”

Everett’s work was a challenge to the prevailing “Copenhagen interpretation” of quantum probability, according to which the act of consciously measuring a characteristic of a particle causes the particle’s cloudy mathematical wavefunction to “collapse” to a specific set of values. To Everett there is no mysterious “collapse” caused by an interaction with human consciousness. In his MWI concept any event that can have more than one outcome has all those outcomes, each representing a new branch of the multiverse. A coin toss, for example, would result in two sets of worlds, one in which versions of you observe the result “heads” and the other in which versions of you observe “tails.”

Where do these constantly branching worlds go? Everett’s interpretation assumes that they more or less coexist. At large scales the quantum states of all their elements are so dissimilar that they do not interact. But at small scales, with very simple systems, the alternate outcomes of an event may be similar enough to interfere with each other. In the classic demonstration of quantum spookiness, known as the two-slit experiment, a single electron is fired at a metal plate with two slits, and somehow forms a rippled interference pattern on the other side. According to the MWI concept, the pattern represents the interference of all the possible trajectories of that electron.

By the 1960s Everett had abandoned theoretical physics, in part because MWI (which he called, less colorfully, “the relative state formulation”) had been virtually ignored. He worked in the defense industry, eventually became a consultant and entrepreneur, and died of a heart attack in 1982, at the age of only 51.

But by then other physicists had discovered and begun to work with Everett’s concept, including Nobel Prize winner Richard Feynman at Caltech, and Stephen Hawking at Cambridge. In the past decade or so, quantum computing pioneer David Deutsch, currently at Oxford, has become MWI’s best known proponent. Deutsch has tried to show mathematically that the “probability” distributions observed in quantum physics experiments are essentially illusions generated by the ever-branching structure of the multiverse. The work reported in Ontario by Wallace and Saunders is being described as a rigorous confirmation of Deutsch’s ideas.

MWI appears to be a more elegant and comprehensible explanation for the weirdness of “quantum probability” than any other that has been discussed so far (in my worlds anyway). And many top physicists have already adopted it – or some variant of it – in their work. But many others still dislike it, if only for the obvious existential reasons. Even those who have embraced it find it disconcerting. “The multiverse will drive you crazy if you really think about how it affects your life, and I can’t live like that,” Saunders told New Scientist. “I’ll just accept Everett and then think about something else, to save my sanity.”

Worries about sanity are understandable here. For example, although MWI is normally thought of as prohibiting communication between two worlds at a usefully large scale, Deutsch happens to think that there are circumstances where the transference of information would be possible. This would permit something like time travel. The idea that separate worlds could interfere with each other also hints at explanations for such weird phenomena as ghosts and ESP (which would be ironic, given that Everett’s mentor, John Wheeler, has long been a vocal opponent of the “pseudoscience” of parapsychology).

But the most profound impact of MWI, now harder to ignore thanks to Saunders and Wallace, could be its conflict with human religious and moral ideas – which seem silly in a “multiverse” of all possible choices and behaviors.

From the perspective of the multiverse, any idea, any life, presumably would be as good as any other, and as infinitesimally insignificant. Morality would be as illusory as the notion of personal “choice.”

MWI also would seem to make the experience of consciousness less exalted. A living person records in conscious memory the experiences of a particular life path. He may be tempted to ask such questions as, “Why am I here, in this world, rather than in a different one?” The chilling answer implied by MWI is that he has to be here – because the path that stretches back into the past could have brought him nowhere else. All alternative paths, all alternative worlds, are populated with other, conscious versions of himself — and perhaps most of those versions are asking the same fruitless question, “Why am I here, in this world?”

Everett himself, though he attended Catholic University as an undergraduate, was an atheist by the time he developed his theory. Strangely (or perhaps not so strangely, given human nature) he took a rather heavenly view of MWI, believing that his consciousness at each branching is bound to follow the path that keeps it alive. If that is true, then there are even now some Everetts still living and working, and accepting Nobel Prizes, in other, friendlier universes.  In any case, Everett certainly wasn’t the only one attracted to such beliefs. Frank Tipler and Paul Davies have proposed, for example, that future worlds can have causative influences on past worlds to ensure the survival of intelligent life in the multiverse.

It is all speculative and wishful thinking, of course — a sort of space-age version of the philosopher Leibniz’s notion that “we live in the best of all possible worlds.” MWI in its less optimistic, unadorned form seems much more plausible, and much more depressing. On the other hand, if we really do live in the best of all possible worlds, then perhaps a convincingly happy version of the many-worlds concept is just what we should expect to emerge.