Wolfgang Pauli 's exclusion, or "Pauli," principle asserted the later-proven existence of the neutrino , a chargeless, massless particle. This discovery led to the Nobel Prize-winning theory of a fourth quantum number with only two possible values (a quantum number expresses the distinct state of a quantum system). The exclusion principle limits the number of electrons possible in the first level of energy to two, a restriction not previously seen in quantum physics.

Wolfgang Ernst Pauli was born on April 25, 1900, in Vienna, in what was then Austria-Hungary. His father was Wolfgang Joseph Pauli, a medical doctor and biochemist who later became a professor at the University of Vienna. His mother was the former Bertha Schültz, an author. R. E. Peierls reports in Biographical Memoirs of Fellows of the Royal Society that Pauli's parents' "background and their acquaintance with the leading authorities in many fields had a profound...