http://www.closertotruth.com/series/many-worlds-quantum-theory#video-2139
Universes in a multiverse
6:23. Each one of these things that represent reality represent different histories of atoms and they are affecting each other.
How many universes/histories are there?
6:54. For example, if we are talking of a number of different histories that happens in let say a cubic meter of air then we are talking in terms of ten to the power of ten to twenty three different histories (10^10^23).