Philosophers
Mortimer Adler Rogers Albritton Alexander of Aphrodisias Samuel Alexander William Alston Anaximander G.E.M.Anscombe Anselm Louise Antony Thomas Aquinas Aristotle David Armstrong Harald Atmanspacher Robert Audi Augustine J.L.Austin A.J.Ayer Alexander Bain Mark Balaguer Jeffrey Barrett William Belsham Henri Bergson George Berkeley Isaiah Berlin Richard J. Bernstein Bernard Berofsky Robert Bishop Max Black Susanne Bobzien Emil du BoisReymond Hilary Bok Laurence BonJour George Boole Émile Boutroux F.H.Bradley C.D.Broad Michael Burke C.A.Campbell Joseph Keim Campbell Rudolf Carnap Carneades Ernst Cassirer David Chalmers Roderick Chisholm Chrysippus Cicero Randolph Clarke Samuel Clarke Anthony Collins Antonella Corradini Diodorus Cronus Jonathan Dancy Donald Davidson Mario De Caro Democritus Daniel Dennett Jacques Derrida René Descartes Richard Double Fred Dretske John Dupré John Earman Laura Waddell Ekstrom Epictetus Epicurus Herbert Feigl John Martin Fischer Owen Flanagan Luciano Floridi Philippa Foot Alfred Fouilleé Harry Frankfurt Richard L. Franklin Michael Frede Gottlob Frege Peter Geach Edmund Gettier Carl Ginet Alvin Goldman Gorgias Nicholas St. John Green H.Paul Grice Ian Hacking Ishtiyaque Haji Stuart Hampshire W.F.R.Hardie Sam Harris William Hasker R.M.Hare Georg W.F. Hegel Martin Heidegger Heraclitus R.E.Hobart Thomas Hobbes David Hodgson Shadsworth Hodgson Baron d'Holbach Ted Honderich Pamela Huby David Hume Ferenc Huoranszki William James Lord Kames Robert Kane Immanuel Kant Tomis Kapitan Jaegwon Kim William King Hilary Kornblith Christine Korsgaard Saul Kripke Andrea Lavazza Keith Lehrer Gottfried Leibniz Leucippus Michael Levin George Henry Lewes C.I.Lewis David Lewis Peter Lipton C. Lloyd Morgan John Locke Michael Lockwood E. Jonathan Lowe John R. Lucas Lucretius Alasdair MacIntyre Ruth Barcan Marcus James Martineau Storrs McCall Hugh McCann Colin McGinn Michael McKenna Brian McLaughlin John McTaggart Paul E. Meehl Uwe Meixner Alfred Mele Trenton Merricks John Stuart Mill Dickinson Miller G.E.Moore Thomas Nagel Friedrich Nietzsche John Norton P.H.NowellSmith Robert Nozick William of Ockham Timothy O'Connor Parmenides David F. Pears Charles Sanders Peirce Derk Pereboom Steven Pinker Plato Karl Popper Porphyry Huw Price H.A.Prichard Protagoras Hilary Putnam Willard van Orman Quine Frank Ramsey Ayn Rand Michael Rea Thomas Reid Charles Renouvier Nicholas Rescher C.W.Rietdijk Richard Rorty Josiah Royce Bertrand Russell Paul Russell Gilbert Ryle JeanPaul Sartre Kenneth Sayre T.M.Scanlon Moritz Schlick Arthur Schopenhauer John Searle Wilfrid Sellars Alan Sidelle Ted Sider Henry Sidgwick Walter SinnottArmstrong J.J.C.Smart Saul Smilansky Michael Smith Baruch Spinoza L. Susan Stebbing Isabelle Stengers George F. Stout Galen Strawson Peter Strawson Eleonore Stump Francisco Suárez Richard Taylor Kevin Timpe Mark Twain Peter Unger Peter van Inwagen Manuel Vargas John Venn Kadri Vihvelin Voltaire G.H. von Wright David Foster Wallace R. Jay Wallace W.G.Ward Ted Warfield Roy Weatherford William Whewell Alfred North Whitehead David Widerker David Wiggins Bernard Williams Timothy Williamson Ludwig Wittgenstein Susan Wolf Scientists Michael Arbib Bernard Baars Gregory Bateson John S. Bell Charles Bennett Ludwig von Bertalanffy Susan Blackmore Margaret Boden David Bohm Niels Bohr Ludwig Boltzmann Emile Borel Max Born Satyendra Nath Bose Walther Bothe Hans Briegel Leon Brillouin Stephen Brush Henry Thomas Buckle S. H. Burbury Donald Campbell Anthony Cashmore Eric Chaisson JeanPierre Changeux Arthur Holly Compton John Conway John Cramer E. P. Culverwell Charles Darwin Terrence Deacon Louis de Broglie Max Delbrück Abraham de Moivre Paul Dirac Hans Driesch John Eccles Arthur Stanley Eddington Paul Ehrenfest Albert Einstein Hugh Everett, III Franz Exner Richard Feynman R. A. Fisher Joseph Fourier Lila Gatlin Michael Gazzaniga GianCarlo Ghirardi J. Willard Gibbs Nicolas Gisin Paul Glimcher Thomas Gold A.O.Gomes Brian Goodwin Joshua Greene Jacques Hadamard Patrick Haggard Stuart Hameroff Augustin Hamon Sam Harris Hyman Hartman JohnDylan Haynes Martin Heisenberg Werner Heisenberg John Herschel Jesper Hoffmeyer E. T. Jaynes William Stanley Jevons Roman Jakobson Pascual Jordan Ruth E. Kastner Stuart Kauffman Martin J. Klein Simon Kochen Stephen Kosslyn Ladislav Kovàč Rolf Landauer Alfred Landé PierreSimon Laplace David Layzer Benjamin Libet Seth Lloyd Hendrik Lorentz Josef Loschmidt Ernst Mach Donald MacKay Henry Margenau James Clerk Maxwell Ernst Mayr Ulrich Mohrhoff Jacques Monod Emmy Noether Abraham Pais Howard Pattee Wolfgang Pauli Massimo Pauri Roger Penrose Steven Pinker Colin Pittendrigh Max Planck Susan Pockett Henri Poincaré Daniel Pollen Ilya Prigogine Hans Primas Adolphe Quételet Juan Roederer Jerome Rothstein David Ruelle Erwin Schrödinger Aaron Schurger Claude Shannon David Shiang Herbert Simon Dean Keith Simonton B. F. Skinner Roger Sperry John Stachel Henry Stapp Tom Stonier Antoine Suarez Leo Szilard William Thomson (Kelvin) Peter Tse Vlatko Vedral Heinz von Foerster John von Neumann John B. Watson Daniel Wegner Steven Weinberg Paul A. Weiss John Wheeler Wilhelm Wien Norbert Wiener Eugene Wigner E. O. Wilson H. Dieter Zeh Ernst Zermelo Wojciech Zurek Presentations Biosemiotics Free Will Mental Causation James Symposium 
Wolfgang Pauli
Wolfgang Pauli was one of the handful of theoretical physicists who formulated the quantum theory. Like Werner Heisenberg, Paul Dirac, and Pascual Jordan, Pauli was still in his twenties in the 1920's. The other great founders, Neils Bohr, Max Born, Erwin Schrödinger, and Albert Einstein, averaged twenty years older. Max Planck, who invented the quantum of action in 1900, the year Pauli was born, was forty years older.
Pauli's name is on the exclusion principle which limits to two the number of fermions that can be in the same volume of phase space. With the principal quantum number n, the angular momentum quantum number l, and the magnetic quantum number m, the electron spin s (limited to values of +1/2 and 1/2) completes the four quantum numbers needed to explain the electronic structure of all the atoms. These four numbers account for the periodic table of the elements. Pauli discovered the fourth quantum number before Goudschmidt and Uhlenbeck discovered the spin itself (just as Bohr found the principal quantum number n without a physical derivation).
While still a student, Pauli was encouraged by Arnold Sommerfeld to write an article on the theory of relativity for the Mathematical Encyclopedia that remains today one of the most important accounts of both special and general relativity. In his preface to a second edition shortly after Einstein's death in 1955, Pauli wrote of Einstein clinging to the dream of a unified field theory: I do not conceal to the reader my scepticism concerning all attempts of this kind which have been made until now, and also about the future chances of success of theories with such aims. These questions are closely connected with the problem of the range of validity of the classical field concept in its application to the atomic features of Nature. The critical view, which I uttered in the last section of the original text with respect to any solution on these classical lines, has since been very much deepened by the epistemological analysis of quantum mechanics, or wave mechanics, which was formulated in 1927. On the other hand Einstein maintained the hope for a total solution on the lines of a classical field theory until the end of his life. These differences of opinion are merging into the great open problem of the relation of relativity theory to quantum theory, which will presumably occupy physicists for a long while to come. In particular, a clear connection between the general theory of relativity and quantum mechanics is not yet in sight. In 1930, Pauli predicted the existence of another particle, electrically neutral, but carrying the needed to conserve the total spin in the beta decay of a radioactive nucleus or a neutron (n) decaying to become a proton (p). It was called the neutrino ("little neutron") by Enrico Fermi.
n^{0} → p^{+} + e^{−} + ν_{e}
The neutrino was not discovered until a quartercentury after Pauli's prediction.
Pauli on Measurements
Pauli distinguished two kinds of measurements. The first is when we measure a system in a known state ψ. (It has been prepared in that state by a prior measurement.) If we again use a measurement apparatus with eigenvalues whose states include the known state, the result is that we again find the system in the known state ψ. No new information is created, since we knew what the state of the system was before the measurement. This Pauli called a measurement of the first kind.
In the second case, the eigenstates of the system plus apparatus do not include the state of the prepared system. Dirac's transformation theory tells us to use a basis set of eigenstates appropriate to the new measurement, say the set φ_{n}. In this case, the original wave function ψ can be expanded as a linear superposition of states φ_{n} with coefficients c_{n},
ψ = ∑_{n} c_{n}φ_{n},
where c_{n}^{2} =  < ψ  φ_{n} > ^{2} is the probability that the measurement will find the system in state φ_{n}. Pauli calls this a measurement of the second kind. It corresponds to von Neumann's Process 1, interpreted as a "collapse" or "reduction" of the wave function. In this measurement, all the unrealized possibilities are eliminated, and the one possibility that is actualized produces new information (following von shannon's mathematical theory of the communication of information. We do not know which of the possible states becomes actual. That is a matter of ontological chance. If we did know, there would be no new information. There is a fundamental and deeply philosophical connection between multiple possibilities and information. When one possibility is actualized, where do all the other possibilities go? For Hugh Everett, III, they go into other universes.
Pauli and the Compton Effect
When, in 1923, the discovery of the Compton effect provided evidence for Albert Einstein's "lightquantum hypothesis, Pauli objected to the explanation that a free electron had scattered the photon (a high energy xray). An isolated "free" electron cannot scatter a photon, he maintained.
Pauli was one of the few scientists to take Einstein's lightquantum hypothesis of 1905 seriously. Einstein's 1917 paper on the emission and absorption of radiation by matter had not convinced many physicists of the reality of light quanta before Compton's experimental evidence. No one was prepared to renounce the wave theory of light, with its wellestablished interference properties. Moreover, there was almost universal unhappiness with the irreducible and ontological chance that Einstein found in the direction and timing of emitted radiation.
Pauli's biographer, Charles Enz, described the work Shortly after Pauli's paper [1], Einstein and Ehrenfest published a different interpretation of Eq. (4.22) [2]. By writing F = bρ_{ν} (a_{1} + b_{1}ρ_{ν1}) scattering may be understood as a composite process consisting of the absorption of a quantum ν followed by the emission of a quantum ν_{1}. Pauli has given a beautiful account of this entire subject in Section. 5 of his 'Quantentheorie' [3].
Pauli and Kepler
THE INFLUENCE OF ARCHETYPAL IDEAS
Works
Über das thermische Gleichgewicht zwischen Strahlung und freien Electronen," Zeitschrift für Physik, 18, 227, 1923 (PDF) "Zur Quantentheorie des Strahlungsgleichgewichts (Einstein and Ehrenfest on Pauli), "Das Wärmegleichgewicht bei Streuprozessen," Section 5, "Quantentheorie," in H. Geiger and K. Scheel (eds.), Handbuch der Physik, vol.23, 226, pp.2229, 1926 (PDF) For Teachers
For Scholars
Jagdish Mehra's 1958 quotation from Pauli (Mehra and Rechenberg v. 11, p.xxiv)
'Als ich jung war, glaubte ich der beste "Formalist" meiner Zeit zu sein. Ich glaubte, ich wäre ein Revolutionär. Wenn die grossen Probleme kämen, würde ich sie lösen und darüber schreiben. Die grossen Probleme kamen und gingen vorüber, andere lösten sie und schrieben darüber. Ich war doch ein Klassiker und kein Revolutionär..' ('When I was young I thought I was the best formalist of the day. I thought I was a revolutionary. When the great problems would come I shall be the one to solve them and to write about them. The great problems came and went. Others solved them and wrote upon them. I was of course a classicist rather than a revolutionary.') And then, as an afterthought, he added: 'Ich war so dumm als ich jung war.' ('I was so stupid when I was young.') Well, he was not to be taken literally.
