Strong interaction
= Strong interaction
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The strong interaction is the color interaction described by <quantum chromodynamics>. <Quarks> carry <color charge>, <gluons> mediate the interaction and also carry color themselves, and physical low-energy states organize into color-singlet <hadrons>.
At short distances, <asymptotic freedom> makes a perturbative treatment useful. At hadronic distances, <confinement> and strong collective dynamics require other methods. The binding of quarks into a <proton> and the residual interaction between nucleons in an <atomic nucleus> are related effects at different descriptive levels. The latter can be modeled using hadrons rather than pretending that a free gluon simply travels between two structureless nucleons. Scattering resolves the short-distance constituents, while hadron and nuclear spectra constrain their low-energy collective behavior.