Many-Worlds Interpretation

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 realized.

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 Schrödinger's 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.