I for one am not convinced by the big bang theory, it requires too much coincidence of physics. It also requires complete removal of gravity in the early universe.
That said it does give the option of a very nice repeating of expansion collapse expansion. It also provides a method of reversing the entropy issue. Problem with this being there doesn't seem to be enough slowing down for a collapse to happen, indeed further away stuff appears to be actually speeding up, although this may be an illusion of distance.
No matter what originally happened you can always ask, but what was before that? This simple question is, in the end, unanswerable - we just don't know.
It's the same as energy cannot be created or destroyed, what it should say is 'we know of no way energy can be created or destroyed' or 'we have never observed energy created or destroyed'. Similarly we can never see the beginning of the universe, although we may be able to infer some details.
This might be interesting too
http://planetpreterist.com/news-2896.html