The multiverse (or meta-universe, metaverse) is the hypothetical set of multiple possible universes (including our universe) that together comprise everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. The term was coined in 1895 by the American philosopher and psychologist William James. The different universes within the multiverse are sometimes called parallel universes.
The structure of the multiverse, the nature of each universe within it and the relationship between the various constituent universes, depend on the specific multiverse hypothesis considered. Multiverses have been hypothesized in cosmology, physics, astronomy, philosophy, transpersonal psychology and fiction, particularly in alternate history. In these contexts, parallel universes are also called "alternative universes", "quantum universes", "interpenetrating dimensions", "parallel dimensions", "parallel worlds", "alternative realities", and "alternative timelines", among others.
Examples of multiverses in fiction
- Author Michael Moorcock used a multiverse for many of his works. Central to these works is the concept of an Eternal Champion who has potentially multiple identities across multiple dimensions. The Multiverse contains a legion of different versions of Earth in various times, histories, and occasionally, sizes. One example is the world in which his Elric Saga takes place. The multiplicity of places in this collection of universes include Melnibone, Tanelorn, the Young Kingdoms, and the Realm of Dreams.
- James, William, The Will to Believe, 1895; and earlier in 1895, as cited in OED's new 2003 entry for "multiverse": "1895 W. JAMES in Internat. Jrnl. Ethics 6 10 Visible nature is all plasticity and indifference, a multiverse, as one might call it, and not a universe."