The big bang was the beginning of what we call the observable universe. One theory is the infinite parallel universes. Basically think of a room full of balloons. Each balloon is a universe like our own. Each balloon can expand, collapse or contract. Also, they do not effect each other as the gaps between them is large. Maybe these universes can interact, but that's just theory anything could be possible.
The balloons expanding and contracting would be the http://en.wikipedia.org/wiki/Big_Bounce theory. Think of a universe as a period of time between the balloon first being blown up and then deflating over time.
The real answers are beyond our knowledge though for the moment. So I guess a lot of people could surmise 'who is the one blowing up the balloons'?







