For years, physicists have known there were three types of particles called neutrinos. What’s interesting about neutrinos is they switch from one type to another, and then maybe to another or back to their original state. Recently researchers discovered what could be a fourth type of neutrino. David Schmitz is a neutrino researcher at Fermi Lab. First Light host Brian O'Keefe asked him to explain the significance of this discovery, in a very basic way.