Nuclear Physics and the Standard Model

In 1925, the Austrian physicist Wolfgang Pauli formulated the exclusion principle, stating that no two electrons in an atom can occupy exactly the same quantum state. This single rule explained why electrons fill successive shells around the nucleus rather than collapsing into the lowest energy level together, accounting for the entire structure of the periodic table of elements. Pauli later predicted, in 1930, the existence of an almost undetectable particle, the neutrino, to preserve energy conservation in radioactive beta decay; he received the Nobel Prize in 1945.