Well if scientists make mistakes couldn't the "expansion of the universe" and this void be one of them?
Of course there are a lot of mistakes in astronomy (Hubble himself miscalculated the age of the universe, and it was accepted for years before anyone questioned it), but more than one astronomer works on these things. Most theories, especially the really big ones, are tested and retested by many different people. It would take some truly serious flaws in ALL of this kind of research for these things to be wrong.
HOWEVER, what most of these astronomers make clear is that the 'known' concepts of the universe are merely what we can determine with what we currently have. There is a lot of evidence for the Big Bang, and that the universe (ours at least) is not infinite.
Personally, I believe the universe as we know it did start with the Big Bang, but has been in a cycle forever. I believe this because I've read many books and articles, and taken classes on the subject (as well as on opposing beliefs) and this just makes the most sense.
If there's ever a theory that makes more sense, and is as thoroughly researched as the Big Bang, I will be more than happy to jump on that bandwagon.