The Multiverse theory is a theory that there be many spherical universes in an extremely large Multiverse. The spherical universes may appear to be like bubbles. Some may have color depending on the universe's contents. They also greatly vary in size, with some only being a billion lightyears across to being as large as many quadrillions of lightyears.
- Page 23, First Space Encyclopedia by Caroline Bingham, DK Publishing Inc. (2008)