By Ryan Holmes
One of the greatest theoretical physicists of the 20th Century, Wolfgang Pauli is best known for his exclusion principle, for which he won the Nobel Prize in 1945. However, Pauli made numerous contributions to quantum mechanics and had strong beliefs about the role of symmetry in nature.
The Pauli Exclusion Principle, which was first explained in a 1924 paper, states that two identical fermions may not occupy the same quantum mechanical state (fermions are particles that obey Fermi-Dirac statistics, such as electrons, protons, and neutrons). This means that, for example, it is impossible to find two electrons with identical energies in the same region of space.
Pauli was a firm believer in the role of symmetry in some areas of physics. For example, he was staunch in his support of the law of conservation of energy (the total energy in a system before a reaction is the same as the total energy in the system after the reaction). In the early 1930's certain phenomena called into question the validity of energy conservation in the subatomic realm. Rather than abandoning conservation of energy, like many physicists (including Niels Bohr) considered doing, Pauli took the drastic step of proposing a new fundamental particle, the neutrino. Although it took over two decades, he was proven correct when the neutrino was discovered in late 1953.
Another instance of symmetry in Pauli's work was his analysis of systems of spin 0 particles. This examination resulted in the prediction of antiparticles, which have the same mass as regular particles, but opposite charge.
Wolfgang Pauli will always be famous for the exclusion principle, but his affirmation of the role of symmetry was perhaps his most important contribution to physics.