Part 2/9:
At the heart of atomic structures, protons and neutrons, composed of trios of quarks bound by gluons, depict a system that goes far beyond elementary interactions. Describing this interaction is the challenge of quantum chromodynamics (QCD). Unlike quantum electrodynamics (QED), which deals with electromagnetic interactions, QCD operates on three different charge types known as color charges, and the complexities multiply as quarks are inherently unable to exist in isolation, forming composite particles called hadrons instead.