RGB color charge, gluon exchange, confinement, and asymptotic freedom
The strong force has three kinds of charge, and its carriers carry charge too. That is why quarks never appear alone.
Switch between baryon and meson mode and drag the quarks to explore how colors combine. Notice that every real particle ends up white.
Quantum Chromodynamics (QCD) is the theory of the strong nuclear force. Unlike electromagnetism, QCD has three types of charge — red, green, and blue — and its force carriers (gluons) themselves carry color charge. This leads to two remarkable properties: confinement and asymptotic freedom.
Just as electromagnetism has one charge (positive/negative), QCD has three: red, green, and blue. All observable particles must be "white" (color neutral) — either a color-anticolor pair (mesons) or all three colors (baryons).
Step through the exchanges with Prev and Next and watch each quark change color when a gluon passes between them.
Gluons carry one color and one anti-color charge. When a gluon is exchanged between quarks, the quarks change color. There are 8 types of gluons (not 9, because the color singlet combination is excluded).
Drag the two quarks apart and watch the flux tube store energy. Keep pulling until it snaps into a new quark-antiquark pair.
Try to pull two quarks apart and the color field forms a "flux tube" — a string of gluon field energy. The energy stored grows linearly with distance. Eventually, there's enough energy to create a new quark-antiquark pair, and the string breaks into two hadrons. You can never isolate a single quark!
Drag along the energy axis and watch αs fall. Notice the quarks in the picture below go from confined to nearly free.
At high energies (short distances), the strong coupling constant α_s decreases — quarks behave almost as free particles. This is asymptotic freedom, discovered by Gross, Politzer, and Wilczek (2004 Nobel Prize). At low energies, α_s → 1 and perturbation theory breaks down: this is the confinement regime.
Drag quarks and antiquarks into the build zone. Three colors make a baryon; a color and its anti-color make a meson.
Only color-neutral combinations of quarks can exist as free particles. Build mesons (quark + antiquark) and baryons (three quarks) from the color palette.
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