Gwen knew the answer to this! She was nearly bouncing out of her seat as her hand went up. Being a muggleborn was turning out to be good for something, right? "You're illustrating an event known as the Big Bang! It's the most commonly accepted theory as to how the universe began. The universe is still, expanding from that point, see? So they think it must have all been compacted, then it exploded and here we are!"

Which brought on all sorts of controversy. Like 'could an explosion in a printing press create a dictionary?' The human body of course being the dictionary in the analogy, but Gwen figured it had taken a long time for evolution to get it right, so she mostly accepted the theory.