the six quarks
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Quarks are the tiny grains that protons and neutrons are made of — and through them, the nuclei of every atom. You never find a quark wandering on its own; they are always locked together in groups, like beads that refuse to leave the necklace. But understanding what those beads are tells you what nearly all the weight of ordinary matter is built from.
There are six kinds, called 'flavors': up, down, charm, strange, top, and bottom. They come in the three generations — (up, down), then (charm, strange), then (top, bottom) — each pair heavier than the last. Up-type quarks (up, charm, top) carry an electric charge of +2/3; down-type quarks (down, strange, bottom) carry -1/3, which is why quarks are famous for fractional charge. A proton is two ups and a down (2/3 + 2/3 - 1/3 = +1), and a neutron is two downs and an up (charge 0). Only the up and down are light and stable enough to make everyday matter; the other four are heavy and decay quickly, appearing mainly in collisions and cosmic rays. The top quark is the heaviest of all known fundamental particles, weighing about as much as an entire gold atom.
Quarks carry a second kind of charge called color, which binds them through the strong force, and that confinement is why they never appear alone. Pinning down all six was a decades-long quest: the top quark, predicted by the model's symmetry, was not actually seen until 1995. The masses spanning from the feather-light up to the gold-atom-heavy top are some of the free numbers the Standard Model takes as given rather than explains.
A proton is made of two up quarks and one down quark held together by the strong force; their charges (+2/3, +2/3, -1/3) add up to exactly the proton's +1.
Fractional quark charges sum to the whole-number charges we see.
A quark's 'color' is just a name for a kind of charge in the strong force — it has nothing to do with the colors you see, and quarks are far too small to have any color in the everyday sense.