Adam Riess was only 41 when he was named a Nobel Prize winner. The Johns Hopkins distinguished professor of astronomy shared in the award for his work on something called “dark energy” -- a discovery that over the past 20 years has profoundly shifted our understanding of the universe. Riess made news again recently when he and colleagues working with the Hubble Space Telescope announced new findings about the rate at which the universe is expanding -- findings which simply cannot be explained by physics as we know it. It’s weird and profound stuff. Our story begins a century ago, with a riddle posed by a curious part of Einstein’s Theory of General Relativity — something called the “Cosmological Constant.” The fate of the universe just may hang in the balance.