Original: The multiverse ( or meta-universe , metaverse ) is the hypothetical set of multiple possible universes ( including the one unique universe we are pretty sure we consistently inhabit ) that together comprise everything that physically exists : the entirety of space and time , all forms of matter , energy and momentum , and the physical laws and constants that govern them .
Simplified: A multiverse ( or meta-universe ) is the theory of a set of multiple possible universes , including our universe , which make up reality .