The many-worlds interpretation implies that there are very many universes, perhaps infinitely many.^[11] It is one of many multiverse hypotheses in physics and philosophy. MWI views time as a many-branched tree, wherein every possible quantum outcome is realised. This is intended to resolve some paradoxes of quantum theory, such as the EPR paradox^{[5]:462[2]:118} and Schrödinger's cat,^[1] since every possible outcome of a quantum event exists in its own universe.

In 1952, Erwin Schrödinger gave a lecture in Dublin in which at one point he jocularly warned his audience that what he was about to say might "seem lunatic". He went on to assert that while the Schrödinger equation seemed to be describing several different histories, they were "not alternatives but all really happen simultaneously". Schrödinger stated that replacing "simultaneous happenings" with "alternatives" followed from the assumption that "what we really observe are particles", calling it an inevitable consequence of that assumption yet a "strange decision". According to David Deutsch, this is the earliest known reference to many-worlds

MWI's main conclusion is that the universe (or multiverse in this context) is composed of a quantum superposition of an infinite^[11] or undefinable^[17]:14–17 amount or number of increasingly divergent, non-communicating parallel universes or quantum worlds.^[2]