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Significant and influential work

Shortly after Wolfgang Pauli proposed his Pauli exclusion principle that two electrons cannot occupy the same quantum energy level, Enrico Fermi and Dirac both realized the principle would dramatically alter the statistical mechanics of electron systems. This work became the basis for Fermi–Dirac statistics.

Dirac wrote an influential paper in 1933 regarding the Lagrangian in quantum mechanics. The paper served as the basis for Julian Schwinger and his quantum action principle, and laid the foundations for Richard Feynman 's development of a completely new approach to quantum mechanics, the path integral formulation.

In a 1963 paper, Dirac initiated the study of field theory on anti-de Sitter space (AdS). The paper contains the mathematics of combining special relativity with the quantum mechanics of quarks inside hadrons, and lays the foundations of two-mode squeezed states that are essential to modern quantum optics, though Dirac did not realize it at the time. Dirac previously worked on AdS during the 1930s, publishing a paper in 1935.

In 1930, Victor Weisskopf and Eugene Wigner published their famous and now standard calculation of spontaneous radiation emission in atomic and molecular physics. Remarkably, in a letter to Niels Bohr in February 1927, Dirac had come to the same calculation, but he did not publish it.

In 1938, Dirac renormalized the mass in the theory of Abraham-Lorentz electron, leading to the Abraham–Lorentz–Dirac force, which is the relativistic-classical electron model; however, this model has solutions that suggest force increase exponentially with time.

Fermi's golden rule, the formula for computing quantum transitions in time dependent systems, declared a "golden rule" by Enrico Fermi, was derived by Dirac. Dirac was the one to initiate the development of time-dependent perturbation theory in his early work on semi-classical atoms interacting with an electromagnetic field. Dirac, with Werner Heisenberg, John Archibald Wheeler, Richard Feynman, and Freeman Dyson ultimately developed this concept into an invaluable tool for modern physics, used in the calculation of the properties of any physical system and a wide array of phenomena.