Type I

A Type I multiverse, the least like a multiverse as written above, is a natural consequence of an infinite, isotropic, homogenous universe: if the probability of a cosmological region – be it a cubic centimeter or a Hubble volume – having certain contents in a certain arrangement after the Big Bang is nonzero, then an infinite universe would contain infinitely many such regions. Popularly, this argument is taken to mean that an exact copy of our own observable universe exists somewhere else in the universe. It can be crudely estimated that identical regions the size of our Hubble volume are spaced apart by approximately 10^10^115 meters, identical regions 100 light-years in radius are spaced apart by approximately 10^10^91 meters, and identical copies of a person are spaced apart by approximately 10^10^29 meters.

Type II

A Type II multiverse would instead be a consequence of the chaotic inflationary theory of cosmology, which purports that quantum fluctuations shortly after the Big Bang created mutually inaccessible pockets of space that, having evolved differently from the unified high-energy physics before them, may have ended up with different physical constants or even geometries. In the nested interpretation, each pocket could itself be a Type I multiverse. Such an argument is sometimes invoked to explain apparent cosmological fine-tuning, in which an infinite number of different, perhaps inhospitable, universes exist alongside our own so that our physical constants thus come across as less extraordinary.

Type III

A Type III multiverse would be a consequence of the many-worlds interpretation of quantum mechanics, in which quantum events with probabilistic outcomes resolve in all ways at once, passing into a vast number of Everett branches each considered to be its own universe. Such a multiverse would function identically to a Type I, only in alternate quantum branches rather than alternate locations in 3-space; one could model a divergence as either a single branch that splits into two, or as a pair of Hubble volumes in the Type I multiverse which begin to differ only upon the resolution of one particular quantum function, If a Type III multiverse is working with infinite Higher Dimensions, where each Higher Dimensions Transcend infinitely uncountable one another, one should not compare any Higher Dimensions, as each of them is infinitely countless above one another, so it will never end, as it will infinitely countlessly piling upwards for all eternity, forming the infinite Higher Dimensions that exist in the Type III multiverse.

Type IV

A Type IV multiverse abstracts even further from the above, positing that alternate spaces with different general principles of physics and mathematics exist independently of ours. Tegmark asks "why these equations and not others?" and resolves the question with the assumption that any other set of equations also exists as a distinct mathematical – and thus physical – structure. This may be analogous to a megaverse or gigaverse, in which one needs even fewer starting assumptions than a set of laws of physics. It contains all mathematics.

Multiverse and Omniverse

It is common, especially in fiction, to see the terms "multiverse" and "omniverse" used interchangably to describe a set of universes, often specifically written as the set of all possible universes or all fictional universes. On this wiki, the omniverse is taken to be some number of levels above the multiverse, perhaps infinitely many, but neither one is seen as an insurpassable boundary. Because fiction can be written involving structures beyond a multiverse or omniverse, interpreting either as a container of all fiction, human thought, or otherwise is incorrect by this view.

An Interdimensional Void is the area in between every single verse, dimension, realm, etc. in a multiverse.

Extra universal space is the term for the empty void of pure vacuum (or, in some interpretations, nothing at all) filling multiverses in between the universes inside. It is essentially a smaller-scale version of The Outside or perhaps even the "place" known as Beyond. Some methods of travelling between universes involve going through this space. It has an arbitrary number of dimensions in both space and time.

This "space" does not always have to exist. Multiverses can be constructed so that all of their universes are in the same spatial location but overlapped on top of each other, and there are undoubtedly many other ways to arrange a huge or infinite number of universes without needing a space beyond it.

A Megaverse is a collection of multiple different Multiverses, either a finite or infinite amount of them, usually each having different properties and interuniversal laws, such as different cosmic events being possible, such as Big Booms, etc.

A megaverse can be contained by a Gigaverse or a Teraverse, or other -verses in the metric hierarchy, but this eventually leads back up to the Archverse chain.

To inhabitants of a multiverse, other multiverses in the same megaverse can be referred to as parallel multiverses, alternate multiverses, or simply other multiverses, depending on the degree of similarity between multiverses in the megaverse. The former two are multiversal analogues of altverses. Some civilisations call the Megaverse an Omniverse, since they haven't discovered the Gigaverse yet.