In 1925, Pauli, building on the earlier postulate of George Uhlenbeck and Samuel Goudsmit, in early 1925, that each electron has a “spinning motion”, introduced the so-called "exclusion principle", which states that when electrons are distributed into the ground and excited states of an atom, such as helium He, as shown below, that certain spin distributions, such as scenario α, where two electrons are both up spin, are excluded, i.e. not allowed, or "forbidden" (Heitler, 1956):
The exclusion principle, in other words, explains that there can never be two or more electrons in the same state.
In 1959, Pauli read Fred Hoyle’s The Black Cloud, wherein the so-called "living cloud theory" is introduced, and later discussed the philosophical implications of it, with Carl Jung, later telling Hoyle that he though it was better than Hoyle’s astronomical work.
Quotes | On
The following are quotes on Pauli:
- “Frankly, I was less interested in gathering plaudits over The Black Cloud than I was in finding out if a story from the 1920s told about Pauli was true. Those were the days in which the young German was supposed to know his place among elderly bearded senior German professors, when even lecturers knew their places precisely. At important colloquia, the professors would sit on the front row and the younger people behind, first lecturers, then the assistants, and finally the students. Except for Pauli. Pauli sat on the front row, in the middle, dressed, quite likely, in Tyrolean leather shorts. So much is known and well documented. The occasion in question was a seminar given by Einstein, at the end of which there was a hushed silence among the bearded professors, unsure of which of them should begin the discussion, each anxious to get the order of precedence right. It was then that Pauli half turned to those behind him and began: ‘What Professor Einstein has just said is not really as stupid as it may have sounded.’ This was what, in 1958, I wanted to ask Pauli about. He began to recall the occasion, and then he collapsed into helpless laughter, rolling in his chair like the ball in Galileo's famous bowl experiment. So, I never quite had it from Pauli personally that the story was true, but those who knew him well assure me that it was.”
- — Fred Hoyle (1994), “Summary of 1958 Solvay conference lunch conversation with Wolfgang Pauli”; in: Home is Where the Wind Blows (pgs. 310-11)
Quotes | By
The following are quotes:
- “Your dream about Ehrenfest's sermon on the love that I was interested and I find it much on this one, that in a context of intellectual history. In our time, we won't see the love for something as personal ‘subjectives’, as opposed to ‘objective’ scientific knowledge of nature. But in reality the feeling is just as generic as the thinking of the former and the roots go as deep. Love as a force of nature is an old idea. The alchemical elements of hate and love, e.g., or the ‘affinity’ or ‘elective affinity’ of the substances, as argued by Goethe (Elective Affinities, 1809). The dream seems to suggest that the love has not found its rightful place in the attitude of the people of our time in the cosmos and thus in natural philosophy. Because, in your dream so speaks a scholar and physicist publicly and privately not a woman.”
- — Wolfgang Pauli (1949), “Letter to Ralph Kronig”, Dec 22 
- Heitler, Walter. (1936). Elementary Wave Mechanics: with Application to Quantum Chemistry (Pauli, pg. 78). Oxford.
- Paul Davies – Hmolpedia 2020.
- Hoyle, Fred. (1994). Home is Where the Wind Blows: Chapters from a Cosmological Life (The Black Cloud, pg. 310; Pauli anecdote, pgs. 310-311). Publisher.
- Pauli, Wolfgang. (1949). “Letter to Ralph Kronig”, Dec. 22 ; in: Wissenschaftlicher Briefwechsel mit Bohr, Einstein, Heisenberg u.a. / Scientific Correspondence with Bohr, Einstein, Heisenberg a.o. : Band/Volume 3: 1940-1949 (pgs. 725-26). Springer DE, 1993.
- Wolfgang Paul – Hmolpedia 2020.