On the wave-mechanical derivation of the statistical atom model

T.A.H. PEACOCKE

Mladen Abramovic

Abstract This paper intends to provide instruction for a single lesson in an introductory course on quantum mechanics by tying together probabilistic methods from statistical mechanics, the use of complex numbers, and a more founded explanation for the derivation of Schrödinger’s time-independent equation. Here presented derivation strongly supports the Copenhagen interpretation of quantum mechanics. Niels Bohr suggested a hydrogen atom model (similar to Kepler’s sun-planet model), where the negatively-charged electron moves in orbit around the heavy positively charged nucleus, this electron having some kinetic and potential energy. Starting from Hamilton’s differential equation for Kepler like atomic model, Schrödinger introduced a new unknown real function ψ in his derivation of time-independent equation (initially, he did not recognize it as the wave function). We show that hypothetical statistical spread of action on many (indefinite) levels is mandatory for the derivation of Schrödinger’s time-independent equation. The result of this hypothesis, the statistical probability constraint formula, is used in this derivation as we look for a minimum of probability for the electron energy distribution E ψ in the whole space. The Euler–Lagrange equation, with normalization of ψ as a constraint limitation, then gives Schrödinger’s time-independent equation for real numbers. A closer inspection of the normalized function ψ shows that it could be complex and is related to the de Broglie–Bohr model of the hydrogen atom. It can be postulated that the classical solution of Schrödinger’s time-independent equation should be a normalized complex function ψ .

Richard Joseph Oldani

Einstein showed in his seminal paper on radiation that molecules with a quantum-theoretical distribution of states in thermal equilibrium are in dynamical equilibrium with the Planck radiation. The method he used assigns coordinates fixed with respect to molecules to derive the A and B coefficients, and fixed relative to laboratory coordinates to specify their thermal motion. The resulting dynamical equilibrium between quantum mechanical and classically defined statistics is critically dependent upon considerations of momentum exchange. When Einstein’s methods relating classical and quantum mechanical statistical laws are applied to the level of the single quantum oscillator they show that matrix mechanics describes the external appearances of an atom as determined by photon-electron interactions in laboratory coordinates, and wave mechanics describes an atom’s internal structure according to the Schrödinger wave equation. Non-commutation is due to the irreversibility of momentum exchange when transforming between atomic and laboratory coordinates. This allows the “rotation” of the wave function to be interpreted as the changing phase of an electromagnetic wave. In order to describe the momentum exchange of a quantum oscillator the Hamiltonian model of atomic structure is replaced by a Lagrangian model that is formulated with equal contributions from electron, photon, and nucleus. The fields of the particles superpose linearly, but otherwise their physical integrity is maintained throughout. The failure of past and present theoretical models to include momentum is attributed to the overwhelming requirement of human visual systems for an explicit stimulus.

T.A.H. PEACOCKE, D.F. SHAW

Malcolm S. Longair

The discovery of the spin of the electron by Uhlenbeck and Goudsmit was a major advance in the understanding of physics at the atomic level. Its discovery coincided with the development of both matrix and wave mechanics and its incorporation into the scheme of quantum mechanics and statistics led to deeper understanding of the underlying structure of quantum mechanics. Almost immediately, Heisenberg and Jordan used the new scheme of matrix mechanics to derive the expression for the g -factor which Landé had derived empirically from a very close study of the anomalous Zeeman effect. An important consequence of these developments was that the different approaches of matrix and wave mechanics were brought together. In particular, the discovery of spin as a new quantum number suggested the possibility of understanding systems containing more than one electron. Heisenberg's analysis of the helium atom was to pave the way for the full incorporation of spin into quantum mechanics and quantum statistics. Spin and the Landé g -factor The story of the discovery of the spin of the electron by Uhlenbeck and Goudsmit (1925a) was told in Sect. 8.5. As discussed in that section, their discovery was based upon empirical studies of the regularities observed in the anomalous Zeeman effect, inspired by the intricate analyses of Landé. Although based originally upon the classical concept of a rotating electron, electron spin is a purely quantum mechanical property intrinsic to the electron.

Yu. L. Klimontovich