At least 10 years.
It's derived from the Everett, Wheeler, Graham multi-verse interpretation of Quantum mechanics (ie, every quantum event which could go either way creates multiple universes where one has one outcome and one has another).
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Hagbard ... it's been a long time.,
Sat 18 Jun 2005, 13:05,
archived)
Oh yes.
It was popular 35 years ago, and backed up by the double-slit experiment, and still most people intuitively decide that multiple universes are bullshit. But it sounds more reasonable to me than 17 dimensions or fate.
(
_Felix 's school of dance and occult sciences,
Sat 18 Jun 2005, 13:17,
archived)