The significance of the correspondence between the classical limit of quantum theories and the laws of classical physics is explained. It is proved that this correspondence yields constraints on acceptable quantum theories. The variational principle is taken as the basis of the analysis. The discussion shows that the first order Dirac equation abides by these constraints, whereas second order quantum equations fail to do that.
References
[1]
Landau, L.D. and Lifshitz, E.M. (1960) Mechanics. Pergamon, Oxford.
[2]
Goldstein, H., Poole, C. and Safko, J. (2002) Classical Mechanics. 3rd Edition, Addison Wesley, San Francisco, CA.
[3]
Landau, L.D. and Lifshitz, E.M. (2005) The Classical Theory of Fields. Elsevier, Amsterdam.
[4]
Dirac, P.A.M. (1958) The Principles of Quantum Mechanics. Oxford University Press, Lon-don.
[5]
Schiff, L.I. (1955) Quantum Mechanics. McGraw-Hill, New York.
Pauli, W. and Weisskopf, V. (1934) The Quantization of the Scalar Relativistic Wave Equation. Helvetica Physica Acta, 7, 709-731. English Translation: Miller, A.I. (1994) Early Quantum Electrodynamics, University Press, Cambridge, 188-205.
[18]
Jackson, J. D. (1975). Classical Electrodynamics. John Wiley, New York.
[19]
Dirac, P.A.M. (1928) The Quantum Theory of the Electron. Proceedings of the Royal Society of London A, 117, 610.
[20]
Darwin, C.G. (1928) The Wave Equations of the Electron. Proceedings of the Royal Society of London A, 118, 654.