In 1930, German physicist Wolfgang Pauli postulated a new particle to explain the apparent nonconservation of energy in radioactive decays. But the theoretical particle he described had properties that made it so elusive that even Pauli wondered whether anyone would ever see it. In 1933, Italian physicist Enrico Fermi gave the particle a name, "neutrino," and in 1956 two American physicists, Frederick Reines and Clyde Cowan, discovered it.