The Big Bang Theory states that about 15 billion years ago a giant explosion (known as the Big Bang) started the expansion of the universe. Before the explosion, all of the matter and energy in the universe was contained at one point, and nobody really knows what existed or how it existed prior. It was not a typical explosion but was a mass distribution and expansion of matter, space, and time, and it laid the foundations for the universe. Cite one piece of scientific evidence supporting this theory