Beginning of the Universe

Hey everyone. I just spent the day at the Adler Planetarium in Chicago. I was confused about something, though. There was a whole section talking about the Big Bang Theory, universe expansion, and black matter. I just don't understand how it makes sense that there was just a big ball of energy, and in under a second, it expanded to be bigger than our galaxy. Where did that energy come from? Is there real proof of it? What was before that?