  Nuclear many-body theory is based on the tenet that nuclear systems can be
accurately described as collections of point-like particles. This picture,
while providing a remarkably accurate explanation of a wealth of measured
properties of atomic nuclei, is bound to break down in the high-density regime,
in which degrees of freedom other than protons and neutrons are expected to
come into play. Valuable information on the validity of the description of
dense nuclear matter in terms of nucleons, needed to firmly establish its limit
of applicability, can be obtained from electron-nucleus scattering data at
large momentum transfer and low energy transfer. The emergence of y-scaling in
this kinematic region, unambiguously showing that the beam particles couple to
high-momentum nucleons belonging to strongly correlated pairs, indicates that
at densities as large as five times nuclear density -- typical of the neutron
star interior -- nuclear matter largely behaves as a collection of nucleons.
