  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.

History and Philosophy of Physics;Nuclear Theory