That depends on who you ask. If the M-Theorists are right, which seems likely, eleven. Unless you mean to ask how many parallel universes there are, in which case one would assume, at this point, the answer is an infinite number.
What a poorly designed website! I could design a better interface in my sleep! Sure, there's something to be said for inventiveness, but you can't completely throw out heuristics! Who do they expect to actually read something like that?