The multiverse is a hypothetical group of multiple universes. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them. The different universes within the multiverse are called “parallel universes”, “other universes”, “alternate universes”, or “many worlds”.
History of Concept
Early recorded examples of the idea of infinite worlds existed in the philosophy of Ancient Greek Atomism, which proposed that infinite parallel worlds arose from the collision of atoms. In the third century BCE, the philosopher Chrysippus suggested that the world eternally expired and regenerated, effectively suggesting the existence of multiple universes across time. The concept of multiple universes became more defined in the Middle Ages.
In Dublin in 1952, Erwin Schrödinger gave a lecture in which he jocularly warned his audience that what he was about to say might “seem lunatic”. He said that when his equations seemed to describe several different histories, these were “not alternatives, but all really happen simultaneously”. This sort of duality is called “superposition”.
The American philosopher and psychologist William James used the term “multiverse” in 1895, but in a different context. The term was first used in fiction and in its current physics context by Michael Moorcock in his 1963 SF Adventures novella The Sundered Worlds (part of his Eternal Champion series).
Multiple universes have been hypothesized in cosmology, physics, astronomy, religion, philosophy, transpersonal psychology, music, and all kinds of literature, particularly in science fiction, comic books and fantasy. In these contexts, parallel universes are also called “alternate universes”, “quantum universes”, “interpenetrating dimensions”, “parallel universes”, “parallel dimensions”, “parallel worlds”, “parallel realities”, “quantum realities”, “alternate realities”, “alternate timelines”, “alternate dimensions” and “dimensional planes”.
The physics community has debated the various multiverse theories over time. Prominent physicists are divided about whether any other universes exist outside of our own.
Some physicists say the multiverse is not a legitimate topic of scientific inquiry. Concerns have been raised about whether attempts to exempt the multiverse from experimental verification could erode public confidence in science and ultimately damage the study of fundamental physics. Some have argued that the multiverse is a philosophical notion rather than a scientific hypothesis because it cannot be empirically falsified. The ability to disprove a theory by means of scientific experiment has always been part of the accepted scientific method. Paul Steinhardt has famously argued that no experiment can rule out a theory if the theory provides for all possible outcomes
In 2007, Nobel laureate Steven Weinberg suggested that if the multiverse existed, “the hope of finding a rational explanation for the precise values of quark masses and other constants of the standard model that we observe in our Big Bang is doomed, for their values would be an accident of the particular part of the multiverse in which we live.”