Around fourteen billion years ago, our entire universe was very very small. How small? Well, it was roughly a million billion billion times smaller than a single atom. Sounds like not much room for all the planets, stars, and galaxies that form our universe today. In fact, way before stars formed, the universe was a kind of soup containing an insane amount of energy crammed into that super tiny space. Sounds like a recipe for disaster. Not so much a disaster, but a cataclysmic event did happen indeed, causing a phenomenal expansion of the universe, cooling down its soup of energy, enough to form stars, then planets, including Earth, then all the creatures that live on it. That cataclysmic event is commonly known as the Big Bang.