The expansion did not expand into anything, because space itself was expanding. Even though this is weird to imagine with our limited cognitive abilities, this seems to be the consensus on the issue. The question might not even make sense. Remember also that according to Einsteins general relativity space and time is not the central stage in which the cosmic drama plays out, but that they themselves are central characters in the play.

Perhaps the thread should get back to what it was initially though, and we could continue these questions and this discussion in the science forum? Like a new thread? =)