History 181B - Class 25

History 181B: Modern Physics

Class 25 (3/19/03)
Making quantum mechanics (2)

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Outline

A second route to a quantum mechanics
    The dualism of waves and particles
    Schrödinger's wave mechanics (1926)
        Distaste for the school of atomic theory
        An alternative framework: Continuous, visualizable waves
        The meaning of the wavefunction (Round 1)

Towards a resolution: Consolidating matrix mechanics and wave mechanics
    Formal identity — but what does this mean physically?
    Born's statistical interpretation of the wavefunction
        Collisions of particles
        The nature of statistics in quantum mechanics

Interpreting the theory
    Heisenberg and uncertainty
        How far can we continue to use classical concepts?
        A thought experiment: The gamma-ray microscope
        Intrinsic limitations on information, and how we speak about them
        Breakdown of the law of causality
    The Copenhagen Interpretation
    And those who, like Einstein, held out for more

Names and terms

Primary	Secondary
Louis de Broglie (1892-1987), NP 1929 electron diffraction Erwin Schrödinger (1887-1961), NP 1933 matter waves wavefunction (or wave function), written psi wave equation superposition indeterminacy [Unbestimmtheit] "On the Physical [or Perceptual] Content of Quantum Kinematics and Mechanics" (1927) delta p x delta q >= h-bar / 2 thought experiment [Gedankenexperiment] complementarity	standing wave eigenvalue problem Max Born (1882-1970), NP 1954 Werner Heisenberg (1901-1976), NP 1932

Assignment

Werner Heisenberg, "The Physical Content of Quantum Kinematics and Mechanics" (1927), in Quantum Theory and Measurement, ed. John Archibald Wheeler and Wojciech Hubert Zurek (Princeton: Princeton University Press, 1983), 62-84.

    This is Heisenberg's uncertainty paper (better, perhaps, his indeterminacy paper). Read what you can, minimally pp. 62-68 (all the way to the bottom) and pp. 82-84.
    Why did Heisenberg argue that the concepts of position and velocity needed to be redefined?
    Outline the argument with the gamma-ray microscope (pp. 64-65)? What was it supposed to show?
    What large conclusions did Heisenberg draw in the paper's final paragraphs?
    Extra: What was going on in the "Addition in proof"?