Physics has unfortunately reached a place where explanations are often replaced by math. When people do attempt explanations, they often seem pretty far out. Nevertheless, one current theory of physics is the so-called 'string theory' which requires many extra dimensions (a total of 12 or 14, I think) for small, fundamental structures. Just as a three-dimensional object can contain and affect a two-dimensional object (e.g., a spherical surface or layer inside of a solid sphere), our three-dimensional (or four-dimensional if you include time) universe could be a small part of a much larger, multi-dimensional universe of universes, of universes, etc.

Steve