Many-worlds interpretation:
Many-worlds is a postulate of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the reality of wavefunction collapse, which implies that all possible alternative histories and futures are real —each representing an actual "world" (or "universe"). It is also referred to as MWI, the relative state formulation, the Everett interpretation, the theory of the universal wavefunction, many-universes interpretation, or just many worlds.
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 many-worlds, reality had been viewed as a single unfolding history. Many-worlds, rather, views reality as a many-branched tree, wherein every possible quantum outcome is realised.