What Happened Before the Big Bang?

Where did everything come from? How did it all begin, the universe and everything? Easy. There was a big bang, 13.7bn years ago, since when the universe has been expanding, right? Well, that used to be correct. But now a bunch of pointy heads are beginning to question this, and Horizon: What Happened Before the Big Bang? attempts to put their thinking across in a way that might make some sense to those of us whose heads are less pointy.