Many-worlds interpretation

The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wave function is objectively real, and that there is no wave function collapse. This implies that all possible outcomes of quantum measurements are physically realized in different "worlds". The evolution of reality as a whole in MWI is rigidly deterministic and dynamically local. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett, who first proposed it in 1957. Bryce DeWitt popularized the formulation and named it many-worlds in the 1970s. In modern versions of many-worlds, the subjective appearance of wave function collapse is explained by the mechanism of quantum decoherence. Decoherence approaches to interpreting quantum theory have been widely explored and developed since the 1970s. MWI is considered a mainstream interpretation of quantum mechanics, along with the other decoherence interpretations, the Copenhagen interpretation, and hidden variable theories such as Bohmian mechanics. In the many-worlds interpretation, the universal wave function evolves unitarily without collapse. Interactions lead to decoherence, producing dynamically independent components of the wave function that correspond to different macroscopic outcomes. These components are sometimes called "worlds", though they are emergent, approximate, and not fundamental entities. This is intended to resolve the measurement problem and thus some paradoxes of quantum theory, such as Wigner's friend, the Einstein–Podolsky–Rosen (EPR) paradox and Schrödinger's cat, since the universal wave function contains components corresponding to every possible outcome of a quantum event.