Quantum chromodynamics

The strong interactions -- of quarks and gluons emerging into hadrons -- affect the world we see in many ways. For example, the mass of everyday objects stems from these interactions, which we now understand from first principles, namely quantum chromodynamics (QCD). More esoteric phenomena, such as the different reaction rates of matter and antimatter, are influenced by QCD effects too. These features arise at long distances, where QCD is nonperturbative and, thus, very challenging. This colloquium discusses this range of phenomena and the tools used to establish their nature from QCD, and shares some perspective on some pending problems in particle physics, nuclear physics, and astrophysics.