In 1929, Edwin Hubble provided a comprehensive observational foundation for Lemaitre's theory. Hubble's experimental observations discovered that, relative to the Earth and all other observed bodies, galaxies are receding in every direction at velocities (calculated from their observed red-shifts) directly proportional to their distance from the Earth and each other. In 1929, Hubble and Milton Humason formulated the empirical Redshift Distance Law of galaxies, nowadays known as Hubble's law, which, once the Redshift is interpreted as a measure of recession speed, is consistent with the solutions of Einstein's General Relativity Equations for a homogeneous, isotropic expanding universe. The law states that the greater the distance between any two galaxies, the greater their relative speed of separation. In 1929, Edwin Hubble discovered that most of the universe was expanding and moving away from everything else. If everything is moving away from everything else, then it should be thought that everything was once closer together. The logical conclusion is that at some point, all matter started from a single point a few millimetres across before exploding outward. It was so hot that it consisted of only raw energy for hundreds of thousands of years before the matter could form. Whatever happened had to unleash an unfathomable force, since the universe is still expanding billions of years later. The theory he devised to explain what he found is called the Big Bang theory.