Explaining Colour Charge
It’s particle physics time! In the Standard Model, quarks are the the building blocks of hadrons (i.e. protons and neutrons), which in turn are the building blocks of the atom. There are two types of hadrons: baryons, made up of three quarks, and mesons, made up of one quark and one antiquark. Protons are baryons, and so they’re made up of two up quarks and one down quark—and at first glance, this appears to violate the Pauli Exclusion Principle, which states that no two identical objects can occupy the same place. So, how can two up quarks be bound together in the same proton? It’s proposed that aside from properties like mass and spin, quarks have another more unique property: the colour charge, which binds them together. There are six manifestations, described as red, green, blue, antired, antigreen, and antiblue, but colour charge actually has nothing to do with visible colours—it’s just a convenient label, because it can be related to the three primary colours. The property allows quarks to obey the Exclusion Principle, as a hadron can contain three different ‘colour’ quarks, and a meson can contain a quark and anti quark of the corresponding colour and anticolour. The colour charge does more than that, though: it’s a description of how a quark responds to the strong nuclear force. In the Standard Model, four fundamental forces hold elementary particles together—strong force, weak force, electromagnetic force, and gravity—and since quarks interact via the strong force, colour charge is basically what holds quarks together—and by extension, what holds together all matter.