I'm just watching a program called "The Universe - Parallell Universes". They keep insisting that every possibility is realized in some universe. For example, there would be universes where George W. Bush never became president. However, it seems to me that that assumes that the number of possible universes has the same (or lower) cardinality, in the sense of Gödel, as the number of parallel universes. That's not obvious to me. Are there any publications that discuss this ?