Scientists used to believe in a steady universe, which had always existed in its present form, without a beginning. However, it is now known to be expanding in size. Working backwards astronomers have now calculated that the universe did have a starting point, when it was smaller than an atom. The energy expanded from this singularlity to create the universe approximately 13.7 billion years ago. This makes sense, because we take it for granted that everything which exists had a beginning, so it is logical that the universe did too.