The standard model of particle physics dictates that the world is made up of sixteen types of particles divided into two types: fermions and bosons. The way these particles behave with each other shows that there are four possible kinds of interactions: electromagnetic, strong, weak, and gravitational.
The different types of particles delineated by the standard model embody different interactions. Quarks, a type of fermion, are stuck together by the strong force to make protons, neutrons, and related particles. The electromagnetic force binds electrons to the atomic nuclei consisting of protons and/or neutrons.
The bosons are force-carrying particles that facilitate the rest of the interactions. The weak force is responsible for radioactive decay, and is the result of the absorption or loss of W or Z bosons. Photons are a type of boson that transmit light and facilitate the electromagnetic force. Bosons called gluons facilitate the strong force, and are what hold protons and neutrons together.
Gravitational force and general relativity, while clearly present, are not represented well in the particle model, and this is an issue scientists are struggling to remedy. The existence of the Higgs boson, a particle predicted by the standard model, would explain why certain particles have mass while others don’t, and thereby explain relativistic and gravitational interactions. The Large Hadron Collider is expected to resolve whether the Higgs boson exists, and thereby pave the way to unifying the four types of particle interactions into a unified theory.