The 20th century was a remarkable time for cosmology, the study of the origins and evolution of the universe. Previously, we had a very limited view of what the universe looked like. We assumed that the Milky Way galaxy contained all existing stars and planets, and that the universe was fixed and eternal, according to Newton’s law of gravity. Within a few decades, however, our view of the universe changed dramatically. Einstein’s general theory of relativity replaced Newton’s gravity and revealed how matter and energy influence the shape of spacetime. His equations also showed that the universe could not be static, but…