Once upon a time, physicists raised eyebrows when they said we existed in multiple universes. But this "many worlds" theory has become widely accepted since it was first proposed in 1957 by eccentric physicist Hugh Everett.

Everett, who died in 1982 at the age of 51, is the subject of a new documentary, Parallel Worlds, Parallel Lives, which airs today at 8 P.M. Eastern time on PBS. Journalist Peter Byrne, whose 2007 profile of Everett in Scientific American explains the theory and describes Everett's troubled private and professional life, appears in the film.

"If everything physically possible happens in the universe, why do we only see one possibility at a time? That's the question philosophers are beating their heads bloody trying to answer," Byrne tells us.  "Everett's answer is there's more than one you, and you are splitting into trillions of copies of yourself every time there's a quantum interaction of a certain size."

Sound weird? Many physicists consider it less wacky than what had been the orthodoxy: the Copenhagan Interpretation, which holds that the alternative realities simply cease to exist, or "collapse," whenever we make a measurement. The trouble with the Copenhagan Interpretation is that it offers no explanation for how the collapse would occur. Everett's take, strange as it may sound, is in many ways the most straightforward reading of the equations of quantum theory, according to Max Tegmark, who in a 2003 article for Scientific American described it as "unadulterated quantum theory." 

Now, though it was almost uniformly dismissed half a century ago, the many worlds theory has been gaining credence; it was the subject of a conference held at Oxford University last year, where philosophers pondered what happens to the concept of time when probability must be defined in terms of parallel universes.

Visitors to the film's Web site can read two previously unpublished documents that Everett's son, EELS singer-guitarist Mark, 45, found among the 25 boxes of his father's belongings. One of the documents is from an early draft of Everett's doctoral dissertation, in which he uses the metaphor of an amoeba splitting to explain his many worlds theory. In the other, he responds to cosmologist Bryce DeWitt, who told Everett that his theory was a "beautiful mathematical formula, but I do not feel myself split," according to Byrne.

In addition to Everett's many worlds concept, viewers of the documentary will learn about his time working on game theory in operations research at the Pentagon, where he created algorithms for "the best ways to fight and the best ways not to fight," Byrne says.

"He's the quintessential technocrat who went to work preparing for nuclear Armageddon and he drank himself to death—go figure," Byrne says.

(Image of Mark Everett/BBC/Adam Scourfield)