The Many-worlds Interpretation (MWI) is an
interpretation of quantum mechanics. It asserts the objective reality of the universal wavefunction, but
denies the actuality of wavefunction collapse. MWI implies that all possible alternative histories and
futures are real—each representing an actual "world" (or "universe").
Many-worlds claims to reconcile how we can
perceive non-deterministic events, such as the random decay of a radioactive atom, with the deterministic equations
of quantum physics. Prior to MWI, reality had been viewed as a single unfolding history. Many-worlds
interpretates reality as a many-branched tree, wherein every possible quantum outcome is
The appearance of wavefunction collapse is
explained by the mechanism of quantum decoherence. Decoherence is MWI’s attempt to resolve all of the
correlation paradoxes of quantum theory, such as the EPR paradox and
Cat, since every possible outcome of every event defines or exists
in its own "history" or "world". In layman's terms, there is a very large—perhaps infinite—number of
universes, and everything that could possibly have happened in our past, but didn't, has occurred in the past of
some other universe or universes.
MWI is one of many multiverse hypotheses in
physics and philosophy. It is currently considered a mainstream interpretation along with the other
decoherence interpretations and the Copenhagen interpretation.