Hugh Everett III

A Princeton PhD student under John Wheeler who asked a simple question: what if the Schrödinger equation is all there is, including for the observer?

His 1957 thesis, published as 'Relative State Formulation of Quantum Mechanics', dropped the collapse. When an observer measures a superposed system, the observer becomes entangled with it, and each outcome is seen by a version of the observer that sees that outcome. The theory is deterministic. The branches do not interact once they have decohered. Bryce DeWitt later popularised it as 'many worlds'.

Bohr's circle did not welcome it; a 1959 visit to Copenhagen went badly. Everett left academic physics for military operations research at the Pentagon, working on nuclear war planning, and died of a heart attack at fifty-one.

Many-worlds was almost ignored in his lifetime and is now one of the main interpretations, favoured by many cosmologists and by David Deutsch, who used it to motivate quantum computing. Its great merit is that it takes the equation at its word; its cost is a vast multiplication of outcomes that some find unbearable and others find simply the way things are.