neutrino mass hierarchy

The neutrino mass hierarchy refers to the order of the three types of neutrinos based on their masses. These tiny particles come in three "flavors" (electron, muon, tau), and their masses aren’t yet precisely known. Scientists are trying to determine whether the lightest neutrino is the first or the third in mass order. There are two main possibilities: Normal hierarchy, where the lighter neutrinos are the first and second, and the third is heavier; or Inverted hierarchy, where the two heavier ones are the first and second, and the third is lighter. This helps understand fundamental physics and the universe’s evolution.