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40 years of the Nobel prize in physics: then and now

The findings for which Aage Bohr and Ben R. Mottelson became co-winners of the 1975 Nobel prize in physics provided the basis for a comprehensive and operative answer to the central problem in the study of the nuclear structure, namely the identification of the appropriate concepts and degrees of freedom that are suitable for describing the phenomena encountered. To do so they produced a breathtaking unification of a number of well established concepts, namely liquid drop and shell models, elementary modes of excitation, superconductivity and quantum electrodynamics, resulting eventually in the paradigm of broken symmetry restoration to determine the nuclear collective variables (CV, elementary modes of excitation): violation of translation invariance by the mean field and by scattering states (single-particle motion), of rotational invariance in the variety of spaces, in particular in 3D- and in gauge-space, leading to surface vibrations and to quadrupole rotations, as well as to pairing vibrations and rotations, with associated emergent properties of generalized rigidity in these spaces, resulting from the coupling to single-particle degrees of freedom.