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History 181B: Modern Physics

Class 27 (3/31/03)
Making use of quantum mechanics

 
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Outline Moving towards the many-body problem
    A new quantum number and Pauli's exclusion principle
    Spin, a (sort of) intuitive picture
    Counting indistinguishable particles: Quantum statistics
        Fermi-Dirac (half-integral spin)
        Bose-Einstein (integral spin)
    Consequences, including the many-body problem

Putting QM to work on the structure of matter
Quantum chemistry and chemical physics
    Explaining the chemical bond: The hydrogen molecule (H2)
    The sociology of a border domain
    Reducing chemistry to physics?
Names and terms
Primary Secondary
Wolfgang Pauli (1900-1958), NP 1945
exclusion principle
spin
Enrico Fermi (1901-1954), NP 1938
Paul Dirac (1902-1984), NP 1933
Albert Einstein (1879-1955), NP 1921
Satyendra Nath Bose (1894-1974)
Fermi-Dirac statistics, Bose-Einstein statistics
fermions, bosons		 Samuel Goudsmit (1902-1978)
George Uhlenbeck (1900-1988)
angular momentum
spin-statistics theorem
Walter Heitler (1904-1981)
Fritz London (1900-1954)
resonance
Assignment Wolfgang Pauli, "Exclusion Principle and Quantum Mechanics" (1946), in Nobel Lectures: Physics, 1942-1962 (Amsterdam: Elsevier, 1964), 27-42.

    This is hard and will draw on your knowledge of chemistry. Read pp. 27-36. You can read the rest if you like quantum field theory.
    When Pauli came up with his "two-valuedness not describable classically," what problems were concerning him: abstract theory or practical spectroscopy? Since you probably can't follow those problems, what would you need in order to understand what he was doing?
    What did he call the exclusion principle?
    At the start, could Pauli give a deep meaning to this "two-valuedness" or a logical reason for the exclusion principle? What did it take before they were better understood?
    On p. 33, what are examples of particles in the antisymmetrical class (Fermi-Dirac)? In symmetrical class (Bose-Einstein)? What do these classes have to do with spin?
Copyright © Cathryn Carson 2003