APS News

May 2009 (Volume 18, Number 5)

This Month in Physics History

May 31, 1957: DeWitt’s Letter on Everett’s “Many Worlds” Theory

In the 1950s, a young physicist named Hugh Everett III first postulated the existence of other worlds, in which every possible forking of every possible path is ultimately realized in its own separate universe. Dubbed the “Many Worlds” interpretation of quantum mechanics, the notion remains controversial among theoretical physicists, although it launched an entire subgenre of science fiction.

Born and raised in the Washington, DC, area, Everett evinced an early interest in math and science. When he was 12, the young Hugh wrote to Albert Einstein asking if it was “something random or unifying that held the universe together.” Einstein’s response: “There is no such thing like an irresistible force and immovable body. But there seems to be a very stubborn boy who has forced his way victoriously through strange difficulties created by himself for this purpose.”

Everett earned a degree in chemical engineering from the Catholic University of America and then won an NSF fellowship for graduate study at Princeton. Initially he focused on math, specifically game theory, but soon drifted into physics, where he became fascinated by quantum mechanics.

Like many physicists of his day, Everett was dissatisfied with the troubling implications of quantum mechanics, specifically the “measurement problem,” i.e., the question of what happens to every other possible outcome in a subatomic superposition of states once the wave function collapses. The “Copenhagen Interpretation” embraced by Niels Bohr and other early quantum pioneers assumed that other potential outcomes vanish by necessity once a measurement is made.

Everett took a different tack. In 1954, while indulging in a spot of sherry with Princeton classmate Charles Misner and a visiting physicist named Aage Petersen, the colleagues began brainstorming “ridiculous things about the implications of quantum mechanics.” That conversation gave Everett the germ of an idea, which he subsequently developed into a dissertation. He called it the “relative state” formulation; it eventually became known as “Many Worlds.”

Everett reasoned that a wave function merely appears to collapse from the vantage point of the observer. In “reality,” it continues to evolve, forever splitting into other wave functions, each branch becoming its own separate universe, with a “copy” of the observer in each one. Once formed, the branches cannot interact with each other, continuing to evolve independently. An observer can only experience one “reality” at a time, Everett argued, but all other possible “realities” were nonetheless realized in parallel universes.

This was a radical departure from the views of Bohr and Heisenberg, introducing the notion of a universal wave function linking observers and objects as components of a single quantum system. It thus dispensed entirely with the need for the discontinuity in the evolution of the wave function engendered by its collapse.

Everett’s theory was met with considerable skepticism. His Princeton advisor, John Wheeler, initially championed his brilliant protégé’s work, taking the draft dissertation to Copenhagen in hopes that it would be published by the Royal Danish Academy of Sciences and Letters. But the Copenhagen contingent was uncomfortable with the implications of Everett’s work, with one prominent scientist dismissing the thesis as “theology.”

In April 1957, a thesis committee accepted a drastically abridged version of Everett’s dissertation, published three months later in Reviews of Modern Physics. On May 31, 1957, Everett received a letter from Bryce DeWitt consisting of a detailed eight-page review of Everett’s paper. While DeWitt was not convinced by Many Worlds, Everett nonetheless liked his astute analysis, even sending excerpts to other scientists with whom he was corresponding.

Unfortunately, Everett’s published paper soon slipped into obscurity. When Everett first met his future business colleague, Donald Reisler, in 1973, he asked whether Reisler had read his 1957 paper. “Oh my god, you’re that Everett, the crazy one who wrote that insane paper,” Reisler exclaimed. (The two men nonetheless became good friends.)

Even Wheeler eventually abandoned his early support of the “Many Worlds” hypothesis. Wheeler recalled shortly before his death that Everett “was disappointed, perhaps bitter, at the nonreaction to his theory,” and expressed regret that he lost touch with Everett in later years. “The questions he brought up were important.” Everett left theoretical physics entirely to work for the Pentagon, and later founded his own companies in defense analysis and worked as a commercial consultant.

Ironically, it was Bryce DeWitt who changed his mind and became a vocal champion of Everett’s ideas. He published an article in Physics Today in 1970, and included the unabridged version of Everett’s thesis in a book of physics papers, The Many Worlds Interpretation of Quantum Mechanics. This brought Everett’s ideas to the attention of the broader physics community. The concept also became popularized in science fiction circles after the term “many worlds” appeared in the sci-fi magazine Analog in 1976.

For all his later business success, Everett was “not a sympathetic person,” Reisler recalled. He was a chain-smoker and heavy drinker, often indulging in three-martini lunches he then slept off in his office in the afternoons. Emotionally distant, he barely knew his troubled children, Elizabeth and Mark. Elizabeth suffered from schizophrenia and committed suicide in 1996, after numerous prior unsuccessful attempts. She left a note saying she was going to join her father in a parallel universe.

Mark Everett became a successful musician with the rock band Eels. It was Mark who discovered his father’s body in bed one morning on July 19, 1982. The cause: a heart attack, at the relatively young age of 51. He had asked that his ashes be thrown out with the trash, and his wife eventually complied with that request. It was a suitably bleak end to man with a fundamentally bleak outlook. As Everett wrote in his original 1957 dissertation: “Once we have granted that any physical theory is essentially only a model for the world of experience, we must renounce all hope of finding anything like the correct theory … simply because the totality of experience is never accessible to us.”

Physics History

This Month in Physics History
APS News Archives

Historic Sites Initiative
Locations and details of historic physics events

APS encourages the redistribution of the materials included in this newspaper provided that attribution to the source is noted and the materials are not truncated or changed.

Editor: Alan Chodos

May 2009 (Volume 18, Number 5)

Table of Contents

APS News Archives

Contact APS News Editor

Articles in this Issue
March Meeting Highlights Energy Storage, Generation
Supercomputers Simulate Stars, Cars, Hurricanes, and Blood
A Nanoscale Peek Inside the Cell
<em>60 Minutes</em> Got It Wrong
Evolution Stirs Tempest in Turkish Teapot
Harvard, APS Reconcile Copyright Policy
Doing Research with Mass Appeal Can Be a Double-edged Sword
Nanotech Advances Include Data Storage and Sharper Metal Tips
Letters to the Editor
The Back Page
Members in the Media
This Month in Physics History
Zero Gravity: The Lighter Side of Science
The Education Corner
Inside the Beltway