Many-worlds interpretation
A formulation of quantum mechanics, first proposed by Hugh Everett III in 1957, which holds that the wave function never collapses — instead, every quantum event causes the universe to branch into multiple parallel histories, each representing a different outcome. Where the Copenhagen interpretation treats measurement as a special process that collapses superpositions into a single result, MWI regards all outcomes as equally real, playing out in branches that cannot interact with one another. Popularised by physicist Bryce DeWitt and later championed by David Deutsch as the only interpretation consistent with a realist view of quantum theory, it remains a minority but growing position in physics. Its philosophical consequences — for identity, free will, probability, and the sheer scale of reality — have made it a recurring subject in both science fiction and serious philosophy.