Dark energy and I came of age together. In 1998, two competing groups of astronomers discovered that the expansion of the universe was accelerating; the same year, I graduated from college with a degree in physics and began work on a Ph.D. Though much of my research chased down other paths, I kept returning to dark energy. Call it a 16-year on-and-off-again dysfunctional relationship with no end in sight.
Of course, I'm very much not alone in trying to understand dark energy: It stands as one of the central problems in modern cosmology. Even the name “dark energy” is a placeholder for our ignorance, representing the fact of cosmic acceleration without indicating its identity. Astronomers have measured the acceleration rate and determined that dark energy constitutes more than two-thirds of the energy content of the cosmos, but its identity has defeated theoretical physicists.