9 - Dimension Theory
The name of this theory basically explains itself: that the universe actually has several other dimensions in addition to the three we know today. What does dimensions have to do with multiverses? Well, if we have additional dimensions to our known 3-D, they provide the space for the existence of other universes. Imagine our universe as a piece of paper, or anything similar to that. If there was another dimension in the addition to the ones we know, other universes will be like other pieces of paper, stacked upon below and above ours like a stack of paper.