  The future electron-ion collider (EIC) will produce the first-ever high
energy collisions between electrons and a wide range of nuclei, opening a new
era in the study of cold nuclear matter. Quarks and gluons produced in these
collisions will propagate through the dense nuclear matter of nuclei,
imprinting its structure into subtle correlations in the energy flux of final
state hadrons. In this Letter, we apply recent developments from the field of
jet substructure, namely the energy correlator observables, to decode these
correlations and provide a new window into nuclear structure. The energy
correlators provide a calibrated probe of the scale dependence of vacuum QCD
dynamics, enabling medium modifications to be cleanly imaged and interpreted as
a function of scale. Using the eHIJING parton shower to simulate
electron-nucleus collisions, we demonstrate that the size of the nucleus is
cleanly imprinted as an angular scale in the correlators, with a magnitude that
is visible for realistic EIC kinematics. Remarkably, we can even observe the
size difference between the proposed EIC nuclear targets ${}^3$He, ${}^4$He,
${}^{12}$C, ${}^{40}$Ca, ${}^{64}$Cu, ${}^{197}$Au, and ${}^{238}$U, showing
that the energy correlators can image femtometer length scales using asymptotic
energy flux. Our approach offers a unified view of jet substructure across
collider experiments, and provides numerous new theoretical tools to unravel
the complex dynamics of QCD in extreme environments, both hot and cold.
