CP-1 was constructed to demonstrate a controlled chain reaction of nuclear fission. The experiment was spectacularly successful and led to applications of nuclear physics which changed the world. The fissionability of a nucleus results from collective motion of the nucleons within this quantum many-body system. The interplay of collective and two or three body interactions is still not quantitatively understood. Modern nuclear structure experiments use nuclei with neutron skins or halos to probe this question.
Heating nuclei to very high temperature produces a phase where the quarks and gluons are no longer bound together and can move freely. This quark gluon plasma has vanishingly small shear viscosity to entropy density ratio and ﬂows essentially without internal friction. Recent data suggest that even very small colliding systems may produce a droplet of plasma. The similarities to strongly coupled or correlated systems in ultra-cold atoms and condensed matter are striking, and have inspired novel theoretical descriptions growing out of string theory. It remains a mystery how this plasma emerges from cold, dense gluonic matter deep inside nuclei, but we will find out with the help of a new electron-ion collider.