EIC Science: Overview and Recent Developments

A century since the discovery of the proton, it is shocking how little is understood about its internal structure or how net properties like the proton mass and spin arise from its fundamental constituents. Despite a detailed knowledge of the fundamental physics of the strong nuclear force, a first-principles understanding of how proton structure emerges from these strongly-coupled, nonlinear interactions remains elusive. But with the dawning of the EIC era, all this is about to change. The Electron-Ion Collider (EIC), a next-generation facility to be hosted at Brookhaven National Laboratory, will constitute the most precise ``electron microscope'' ever created. The unprecedented kinematic reach and precision of the EIC will permit, for the first time, a detailed tomographic study of proton structure in position space, momentum space, and spin. The EIC will provide a clean, precise probe of the emergent physics of the strong force in protons and nuclei, elucidating the spin-spin and spin-orbit correlations which give rise to proton structure and peering into the high-density regime predicted to exhibit a saturation of the gluon density. The answers to these questions have implications not only for high-energy nuclear physics, but also for astrophysics, cosmic rays, and physics beyond the Standard Model.