The concept of multiverse (see Many Worlds and David Deutsch) refers to an infinite multiplicity of separate (multi-dimensional) universes (where all possible possibilities are realized). Not even our universe is unique.

Well, maybe not.

In set theory it is possible to show, by a variation on Cantor’s diagonal argument, that the universal set, or set of all sets, is a contradiction in terms. Essentially you demonstrate by construction that the universal set cannot contain at least one member of its set of subsets, and since that member of the set of subsets is itself a set, it must be a member of the set of all sets. A flat contradiction. Therefore the universal set cannot exist.

It would require a lot fancier dancing than I can do to show that this same argument could be made to apply to our ordinary concept of the universe, but I do think it is ultimately feasible.

So, based upon this argument I cannot even make but only point in the general direction of, I would assert that the very idea of a universe is a contradiction in terms, and that we must fall back– defeated– to the metaverse.