Transcript: Neutrinos were predicted as a consequence of the conservation of energy. This fundamental principle applies to most interactions in the universe. In the 1930s particle reactions were observed where when all the energies and momenta were added up some energy and momentum was missing. The experimenters predicted the existence of a weakly interacting neutral particle to account for the missing energy and momentum. Wolfgang Pauli named it the neutrino, little neutral one. Twenty years later it was detected. Neutrinos interact very weakly with matter and could pass through thousands of miles of iron with a small probability of interacting or being stopped. There are three flavors or types of neutrino associated with the three families in the standard model of particle physics: the electron neutrino, the muon neutrino, and the tau neutrino in increasing energy or mass. For a long time physicists thought the neutrino had no mass, but now it appears the neutrino must have a small amount of mass because the three types of neutrinos can oscillate or change from one to the other. The fact that the neutrino has mass has important consequences for astronomy and cosmology because neutrinos are routine byproducts of solar fusion.