As a mechanism for generating the huge number of universes, multiverse physicists make use of the eternal inflation scenario. 

Moreover, the multiverse is closely associated with anthropic (the existence of human life) reasoning: 

We find ourselves in our universe the argument goes, with its particular physical laws and content of particles, not because other universes are impossible or improbable, but because our kind of life cannot exist in other universes.

So don't be beguiled by the anthropic hope  that if ET ever does appear, he will be like, 'yeah he looks like that Jimmy Smith from down the road.'