Multiple universes have been hypothesized in cosmology, physics, astronomy, religion.
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.
Search for evidence
Around 2010, scientists such as Stephen M. Feeney analyzed Wilkinson Microwave Anisotropy Probe (WMAP) data and claimed to find evidence suggesting that this universe collided with other (parallel) universes in the distant past.
Different theories of multiverse
There are models of two related universes that e.g. attempt to explain the baryon asymmetry – why there was more matter than antimatter at the beginning – with a mirror anti-universe.
Black-hole cosmology is a cosmological model in which the observable universe is the interior of a black hole existing as one of possibly many universes inside a larger universe.
This includes the theory of white holes, which are on the opposite side of space-time.
A multiverse of a somewhat different kind has been envisaged within string theory and its higher-dimensional extension
The quantum multiverse creates a new universe when a diversion in events occurs, as in the real-worlds variant of the many-worlds interpretation of quantum mechanics.
The simulated multiverse exists on complex computer systems that simulate entire universes.