The big bang theory (remember that word) seems to keep changing, I have seen many a point from scientists over the years about it and every time it is something new.
First it was when there was nothing, no universe or anything, but there were two particles there (because magic) and they collided and made the universe.
Second it was that the universe was once a compressed form of infinite mass (where it was, how it got there, why or how infinite mass even exists i know not) but yeah then it made a universe too.
Thirdly (I saw this in some documentary bullstuff) instead of god creating it it was a god particle, yeah get that, apparently the universe was made by a "god particle" that was all particles at once and could do and be anything.
I don't listen to that stuff anymore.