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Parallel Lives in Many Worlds?

July 9, 2007

Recently Nature (5 July 2007) features a special topic to celebrate the 50th anniversary of an astonishing scientific hypothesis – a many-world multiverse. This idea was introduced intro physics July of 1957 by Hugh Everett [a shortened version: Review of Modern Physics 29, 454-462 (1957)], which, as the editor of Nature put it, “neatly highlights the intersection between science and science fiction”.

Quantum theory lets us express the status of any quantum particle by the superposition of some states, in which, along with other possibilities, the particle can be in two places at once. However, an ordinary object, e.g. a baseball, is also made of quantum particles, so why don’t we see a ball in, say, the grove of a catcher and the outfield at once? Since the birth of quantum theory, such a question has been asked and argued over physicists, philosophers and mathematicians.

One answer to this conundrum — as expressed in the late 1920s by Niels Bohr and Werner Heisenberg in their famous Copenhagen interpretation — was that we don’t see these weird states because they collapse whenever we try to measure them. Everett, in bold contrast, suggested another solution — that the superpositions do affect our world, we simply don’t notice them. As he pointed out, the maths of quantum theory suggests that when we encounter an object of superposition of say, here and there, that superposition draws us in too; splitting us into one being who sees the object here, and another who sees it there. In essence, as a later physicist put it, Everett claimed that quantum physics reveals a Universe that perpetually splits into “many worlds” co-existing side by side.Nature 448, 15 (2007)

This idea got little notice in physics community until 1970, when Bryce DeWitt wrote an article for Physics Today on Everette’s relative-state theory [“Quantum Mechanics and Reality”, Physics Today 39 (9), 30-40 (1970), where the phrase, “many worlds”, was introduced by DeWitt]. Since then, the theory has attracted people, scientists or not, who either embrace or reject it.

This idea is just too weird to be believable. One thing is how one can prove the existence of many worlds. The experiments simply cannot distinguish between the many-world idea and some alternatives, nor can find evidence for the “collapse” in that Copenhagen interpretation.

However, the idea of “many worlds” isn’t new to science fiction. As Gray Wolfe quoted in the beginning of “Surfing the multiverse

The futures we fail to encounter, upon the roads we do not take, are just as real as the landmarks upon those roads. We never see them, but we freely admit their existence…

which in fact originates from “Sidewise in Time” by Myrrat Keubster published in 1934 in Astounding Stories, a science-fiction magazine, well before Everett introduced his idea.

Prof. Wolfe then listed five science-fiction books based on the theme of parallel worlds and alternative histories (each book is summarized by Prof. Wolfe):

  • Jack Williamson, The Legion of Time (1938). A pulp classic. The hero meets women from two possible futures that he may help determine.
  • Philip K. Dick, The Man in the High Castle (1962). Among the best and most influential alternative-world scenarios, in which the Allies lost the Second World War.
  • Michael Moorcock, The Eternal Champion (series, 1962–present). Several series of interconnected novels set in a multiverse of alternative realities.
  • Gregory Benford, Timescape (1981). One of science fiction’s most compelling accounts of working scientists, dealing with cross-time communication to alter the past and thus create a variant future.
  • Stephen Baxter, The Time Ships (1995). This ambitious sequel to H. G. Wells’s The Time Machine updates the classic tale with its notion of multiplicity of histories, and at one point directly alludes to Everett.

If this is true, what would I be doing in another world? 😐

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