Everett didn’t add particles—he didn’t think he needed them. Instead, he insisted that a single universal wave function was all there was: a massive mathematical object describing the quantum states of all objects in the entire universe. This universal wave function, according to Everett, obeyed the Schrödinger equation at all times, never collapsing, but splitting instead. Each experiment, each quantum event, spun off new branches of the universal wave function, creating a multitude of universes in which that one event had every possible outcome. Everett’s shocking idea came to be known as
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