A new result from the MicroBooNE experiment at the U.S. Department of Energy's Fermi National Accelerator Laboratory probes the Standard Model—scientists' best theory of how the universe works. The model assumes there are three kinds of neutrinos. Yet for more than two decades, a proposed fourth kind of neutrino has remained a promising explanation for anomalies seen in earlier physics experiments. Finding the theorized sterile neutrino would be a major discovery and radical shift in our understanding of the universe.