After the Big Bang, the universe expanded rapidly. And, once upon a time, conventional wisdom held that that expansion would eventually slow, dragged back inwards by the gravitational pull of all the matter in the universe. But in 1998, two groups studying supernovae discovered that not only was the universe continuing to expand, but that the expansion was accelerating.That accelerating expansion has been attributed to a force cosmologists have called dark energy. The energy itself has been represented by a number—thought to be a universal constant—called the cosmological constant. But recent data presented by a group called DESI, the Dark Energy Spectroscopic Instrument, says that possibly, the constant may not be a constant. Instead, dark energy may be evolving over time.The finding, if it holds true, would be a big deal, requiring cosmologists to redo their equations for the way the universe works and, possibly, develop new physics to explain the phenomenon. Dr. Dillon Brout, an assistant professor of astronomy at Boston University and part of the DESI collaboration, joins Ira to talk about the data from the first year of the DESI instrument, and what may lie ahead in years to come.Transcript for this segment will be available the week after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.