[Tycho]

My personal favourite explanation is that since in the beginning there was nothing, there wasn't just no matter there were no rules. So there was no rule to say 'you can't get something from nothing' so out of true nothingness things would happen. And from there it was a matter of generating the right set of rules (which could have taken an unimaginably large number of iterations) where nothing was contradictory and then viola, the universe was ready.