Because I was there when it happened. Jehovah, my little brother, came into the room excited because he got one of those Build your own universe kits in the mail(what a dork). He spent all Saturday trying to get the stars to burn hot enough, so I just helped him by giving him some better bulbs.
Seriously, I believe in both creationism and evolution. I figure God is all powerful so he can create us in his own image and apparently God looks like an amoeba. Then he made us grow like he made plants grow. But yeah, something had to start the big bang. Though is could be that the universe is a big cycle, but then everything starts but then how could the universe start when there was no reality before. But then if that were true how could anything do anything ever?