there were several different scientific theories about the origin of the universe, as recently as 30 years ago, as I recall. There was the Steady State theory (it's always been here) and another theory I didn't quite get the hang of, something to do with the universe being saddle-shaped. Anyway, subsequent scientific discovery has ruled out the other ones. Some people, particularly fundamentalist Bible-believers, may not accept it, of course; and they may be correct.
I'm not too sure how it could be 'proved'; scientists have deduced it from what they know, and I suspect that's the best we'll ever get.