In the early twentieth century, Albert Einstein published his equations of general relativity and a Dutch astronomer, Willem de Sitter, found a solution to them that predicted an expanding universe. This, too, was a highly significant prediction because if the universe has been expanding and if galaxies are moving farther apart, this implies that in the past they once were closer together. If the universe has been “blowing up” for the duration of its existence, that means that it must have had an actual beginning.