Splitting Image

July 23, 2008

Back in 1957, a young Princeton graduate student named Hugh Everett III dared to challenge the prevailing "Copenhagen interpretation" of quantum physics with a controversial theory called Many Worlds: the notion that there could be an infinite number of parallel universes lying just beyond our ken. The notion has spawned a plethora of science fiction stories, but was largely ignored by Everett's peers when he proposed it. Crushed by the rejection, Everett left physics entirely, struggling with depression and drink until he died of a heart attack many decades later. He didn't live to see his theory begin to gain some measure of acceptance by the community of physicists who once scorned him.

Everett's tragic story is the focus of Parallel Worlds, Parallel Lives, a documentary that follows the journey of Everett's son, Mark Oliver Everett, as he discovers the brilliant father he barely knew. Mark Everett is better known as E, lead singer of a cult band called the Eels (their tune "Souljacker" is on permanent rotation on my iPod workout playlist). He knows nothing about physics, which makes him the perfect guide for those who have never heard of Hugh Everett III, or of Many Worlds. The film debuted last fall in England, and made its American premiere in May at the World Science Festival in new York. And NOVA will air the film on PBS this October.

The young Hugh Everett wasn't happy about some of the troubling implications of quantum mechanics: specifically, the notion that observation determines reality -- or at least the outcome of an experiment. In any quantum system (such as a subatomic particle like a photon or electron), every possible outcome is present simultaneously in a sort of superimposed limbo state. The technical term is a superposition of states.

The sum of all those outcomes is described by an equation known as the wave function. It's only when we check to see what happened -- when we observe the quantum system by making a measurement -- that the wave function collapses and all those possibilities reduce to a single "real" event: the outcome we have observed.

But what happens to the other possibilities once the wave function collapses? The strictest interpretation of quantum theory -- espoused by physics giant Neils Bohr, among others -- simply ignored the question, assuming that all other potential outcomes vanish once a measurement is made.

Everett wasn't satisfied with that. He proposed that perhaps the wave function only appears to collapse from our limited vantage point as human observers. Perhaps it continues to evolve, forever splitting into other wave functions in a never-ending tree, with every branch becoming a parallel universe with a different outcome. Every potential outcome gets its own separate universe. There is no such thing as the road not taken.

Many Worlds has its own intriguing implications -- like doppelgangers. Think about it: if there is a separate universe for all possible outcomes of an experiment, for example, then each universe must contain "copies" of those who perform the experiment. So, you might opt to order the kung pao chicken for dinner one night at your local Chinese takeout in this universe, but somewhere else, in a parallel universe, another version of you orders the mapo tofu, and in still another, you order the sweet and sour pork -- a separate universe and a carbon copy of you for every item on the menu.

That's a lot of parallel universes, just for that one decision about what to have for dinner on a given night. There are branchings upon branchings of possible choices, an infinite number of paths our lives can take, and per Many Worlds, each must give rise to its own parallel universe. So there must be an infinite number of other worlds, linked through a vast network of forks in the proverbial road.

Back in 1957, physicists were none too happy with Everett's theory because of this. Taken down to the subatomic level, it would mean the universe must split into 10<100> copies every second, each equally "real" -- although we can only perceive one at a time. (Here's an amusing explanation as to why that even a dog can understand.) This also makes it pretty much impossible to test the Many Worlds hypothesis: how can we prove there are an infinite number of parallel worlds if our perception is limited just to this one?

The finite human brain tends to balk at the notion of infinity; mine certainly does. My husband, a cosmologist, is far more comfortable contemplating such a possibility, as is MIT physicist Max Tegmark, a featured personage in the film. In fact, Tegmark tells Mark Everett in the film that his father's theory is "one of the most important discoveries of all time in science," comparing it to Einstein's theory of relativity and Newton's theory of gravity. There's plenty of physicists who might take issue with that assessment, but only time will tell. In the meantime, Mark Everett has made his peace with his father, and his past. And he's also made a very thought-provoking, heartfelt film that deserves a wider audience.

Photo: Mark Oliver Everett and his doppelganger, in a still from Parallel Worlds, Parallel Lives.

Comments

[Lori Cuthbert]

Loved the amusing explanation - even my very, very silly dogs could get that!