Adam Riess was 27 years old when he began the work that earned him the Nobel Prize in Physics, and just 41 when he received it. Earlier this year, Riess, who is now in his early 50s, pulled a graph-paper notebook off a bookshelf in his office at Johns Hopkins University so that I could see the yellowing page on which he’d made his famous calculations. He told me how these pen scratches led to a new theory of the universe. And then he told me why he now thinks that theory might be wrong.For nearl...