The steady-state theory is the theory that the universe looks pretty much the same now as it has always done and that, to maintain a constant density of matter in the face of cosmic expansion, matter is continuously created out of empty space (at a rate of 2.8 × 10^–46 grams per cubic centimeter per second, or roughly one nucleon per cubic kilometer per year). It rose to prominence in the 1960s under its three greatest champions, Fred Hoyle, Thomas Gold, and Hermann Bondi. However, the discovery of the cosmic microwave background persuaded most astronomers to reject the steady-state model in favor of its rival, the Big Bang theory.