Both a priest and a cosmologist, Georges Lemaître (1894-1966), perhaps not unexpectedly, spent much of his career studying the origin of the universe. After a stint as an artillery officer in the Belgian army during World War I, he entered a seminary and was ordained a priest in the early 1920s. Shortly after, however, his interest in astronomy brought him to Cambridge University in England and then to the Massachusetts Institute of Technology. While there, he became captivated by the new idea of an expanding universe. He reasoned that if the universe was expanding now, then the further you go in the past, the universe’s contents must have been closer together. He envisioned that at some point in the distant past, all the matter in the universe was crushed into a single object he called the “primeval atom.” This primeval atom then exploded, with all its constituent parts rushing away. His basic idea has become the most widely accepted model for how the universe originated, what we today call the Big Bang.