The Metaverse is a Platonic, metaphysical entity comprising the panoply of all mathematically-definable entities, including all possible universes, eternal souls and gods that could be (at least in principle) identified by a sufficiently complex and detailed mathematical description. Even infinite definitions may be allowed, although the Church of Metaversalism has not yet taken a definitive position on this question.
The most fundamental premise of Metaversalism is its position that the Metaverse exists (in a mathematical sense) because it must exist, by pure logical necessity, that the Metaverse contains everything that could exist, and that no more explanation than this is required to explain why our universe exists, or to answer the question, "Why does anything exist at all?"
To see why the Metaverse must exist, suppose nothing existed at all. But it would still be true that if one were to postulate Peano's axioms of arithmetic, then all the properties of the natural numbers 1, 2, 3... would follow. Thus the entire structure of the natural numbers already exists in the logical implications of this conditional - even if the "if" part were not satisfied, because there was nobody there to postulate it. The structure of the conclusions is still there; it exists independently. The same goes for all other mathematically definable objects and structures. The concept of everything arising from nothingness in this way is embodied by the Latin phrase "Ex nihil panton" (or, new version, "Ex nihilo omnia fiunt") in Metaversalism's logo.
To see why mathematical existence ought to be enough for everyone... According to the philosophy embodied by modern physics, the detailed structure of our universe is identical to that of some complex mathematical structure (whose underlying definition is not fully known yet). This structure contains all the rich details of how galaxies, stars, and planets form, how life arises and intelligence evolves, how the mind functions. Its rich tapestry includes all of the thoughts, feelings, and emotions that we experience. Even if mathematical existence is the only kind of existence there is (Metaversalism's position), the rich, evolving structure that as a human consciousness still cannot not tell the difference between this and any other kind of existence - because all the details of that mind's activity and experiences are already contained there in the mathematical structure. Having another kind of existence would not change any of the details of that conscious structure, so would not be perceptible.
Note: The concept of the Metaverse described above is distinct from the "multiverse" concept that is encountered in discussions of the many-worlds interpretation of quantum theory. In the traditional multiverse, all the universes still obey quantum theory. But the Metaverse also includes universes that are not based on quantum theory at all, as well as mathematical structures that would not usually even be considered to represent universes at all. Our use of the term "Metaverse" is entirely distinct from its use in science fiction and elsewhere to denote certain 3-dimensional virtual reality systems. Our Metaverse is a much broader concept (and one that, we believe, is more deserving of the prefix "meta").
