Something like 13.8 billion years ago, all energy in the universe was condensed into a single point. Until suddenly it wasn't. The resulting detonation was the most massive explosion in all of the universe's history, but from it, energy formed into all matter, atoms, molecules, planets and all life on Earth.
This is the Big Bang theory, a model that explains much of what we observe when we look out at the universe. Between all the stars, galaxies and clouds of gas is cosmic background radiation — heat residue from the Big Bang, which is still faintly visible today, and is one of the most glaring pieces of evidence that the universe started from a single point. Measurements using multiple different tools, including satellites and telescopes, indicate this residue is consistent with models of an explosive birth to our universe.
