The multiverse is just a naive way of conceptualizing the idea that our universe is not the only one. Our universe is all that exists. If something else exists which can interact with our universe, then it is also our universe. If there are other universes that we cannot interact with, then they don't exist. The multiverse is not some bookshelf of universes. There simply may be several realities that exist each from their own perspective, but with no temporal, spatial, or other manner of relating them, they each are nonexistent from any outside frame of reference.
