Quantum Chromodynamics

Unlike Quantum Electrodynamics or QED, which describes the motion and interaction of electromagnetic forces at the atomic and subatomic level, Quantum Chromodynamics or QCD is a branch of theoretical physics that describes the strong force, which is one of the four fundamental forces of nature, along with gravity, electromagnetism and weak nuclear force. Much like calling men and women humans, because protons and neutrons are found inside the nucleus of atoms, physicist call them nucleons collectively, each consisting of three quarks in perfect balance with each other, which is an incredible feat given the fact that quarks move near the speed of light in the tight confines of an atomic nucleus.

Strong Force

What holds these quarks together is known as strong force, which, unlike the plus or minus electric charge theorized in Quantum Electrodynamics, strong force has three varieties of color charges—red, blue and green—which, just to make things more confusing, has nothing to do with color as we know it. In strong force, instead of exchanging photons as theorized in quantum electrodynamics, the colored quark particles exchange gluons, which are the massless charged elemental particles of strong force. Within a nucleon, three quarks possessing red, green and blue color charges must combine to cancel out their opposing charges in a state of white balance—thus the name chromo in Chromodynamics.

Detachment and Rebirth

As quarks move away from one another, the energy in the gluon field increases, adding more gluons until the energy becomes so intense that they break apart, creating new imbalanced and isolated quark-antiquark pairs, leading to a phenomenon known as confinement, when isolated quark pairs join together in newly born red, green and blue-balanced nucleons. Another property of QCD is asymptotic freedom, which states that as quarks and gluons come closer together, the strong force weakens, allowing for the use of perturbation theory to accurately describe their interactions. Validated repeatedly in high-energy particle accelerators like the Large Hadron Collider in Switzerland, Quantum Chromodynamics provides yet another window in man’s growing understanding of the universe.