Georges Lemaître, a Belgian cosmologist and Catholic priest, was one of the first scientists to use Einstein’s general theory of relativity to describe the universe as a whole. In 1927, he showed how the expansion of the universe, observed by Hubble, was a natural consequence of the equations of general relativity.
Lemaître also thought about the expansion of the universe in a radically new way. If we could imagine tracing the expansion backward in time, we would see it getting smaller and smaller. Wouldn’t there be a limit to how small it could get? In 1931, Lemaître proposed that at some point in the distant past, the universe was compressed into a tiny object which he called the “cosmic egg.” This cosmic egg would have exploded—launching the expansion of space itself that we still see today. This theory later became known as thebig bangand provided the first scientific description of how the universe began.