the three forces in the model

Of the four forces we know in nature, the Standard Model describes three. Leave out gravity for a moment and you are left with the trio that runs the subatomic world: electromagnetism, the weak force, and the strong force. The model does not just list them — it explains each as the same kind of thing: a force carried by exchanged particles and demanded by an underlying symmetry.

Electromagnetism is the familiar one — it holds electrons to nuclei, makes magnets work, and is light itself; it is carried by the photon and reaches across any distance. The strong force is the most powerful; it glues quarks into protons and neutrons and binds those into nuclei, carried by gluons but with a strange twist — it gets stronger, not weaker, as you try to pull quarks apart, so they can never be separated. The weak force is the odd one out: it is feeble and very short-ranged, carried by the heavy W and Z bosons, and it is the only force that can change a particle's flavor, which is why it drives radioactive beta decay and powers the Sun's first fusion step. Crucially, at high energies electromagnetism and the weak force reveal themselves as two faces of a single 'electroweak' force.

Treating all three within one mathematical framework — gauge theory — is the central achievement of the Standard Model. It is why a theory of light, a theory of radioactivity, and a theory of nuclear binding can be written in one consistent language. The conspicuous absence is gravity, which has stubbornly refused to fit into this scheme.