The correct meaning of Hugh Everett’s thesis should not be “many-(different)-worlds interpretation”. Instead, it should refer to the fact that the whole universe is described by a single wavefunction, which is a superposition a lot of eigenstates. Also the wavefunction of the universe can never collapse since there is no “environment” for it to have decoherence with.
Macroscopically, a lot of, if not all, the eigenstates are corresponding to one single classical reality, e.g.
1 + 1 + 2 = 4
1 + 3 + 0 = 4
So there are no multiple (different) universes. Even if the universe is a superposition of several distinct macrostates, the wavefunction cannot collapse to a single macrostate, because there is no “environment” for it to lose information to.
2011.10.18 Tuesday (c) All rights reserved by ACHK