 Hugh Everett III

Hugh Everett III proposed treating an observer and a measured quantum system within one unitary quantum dynamics. For an ideal quantum measurement, $\alpha |0⟩|R⟩+\beta |1⟩|R⟩$ evolves into $\alpha |0⟩|A_0⟩+\beta |1⟩|A_1⟩$: the apparatus records become correlated with the alternatives. A relative state describes the measured quantum system conditional on a particular record, while the joint quantum state remains entangled. His 1957 formulation sought to account for records within this common dynamics, without adding a separate dynamical wave function collapse postulate.^[ref]

A physicist who proposed a unitary relative-state account of quantum measurement, developed in the many-worlds interpretation.

Hugh Everett III was an American physicist and mathematician best known for his work in quantum mechanics, particularly for formulating the "many-worlds interpretation" of quantum mechanics in 1957. This interpretation suggests that all possible outcomes of quantum measurements are realized in separate, branching universes, effectively positing the existence of an infinite number of parallel realities.