Strong interaction

The strong interaction or strong force is the fundamental interaction that binds quarks together to create composite particles known as hadrons. Since matter is made of atoms, whose nuclei are composed of protons and neutrons, which in turn are made of quarks, the strong interaction is responsible for the stability of all atomic matter in the Universe.

The modern theory of strong force is quantum chromodynamics (QCD), which explains strong force in a manner similar to quantum electrodynamics, but instead of having a singular electric charge, it has three color charges. The strong interaction is an exchange interaction mediated by the gluon, one of the four known gauge bosons.

The strong interaction has a tiny range of only approximately $10^{-15}\text{ m}$, which is about the size of an atomic nucleus. It is therefore relegated to interactions within the nucleus.

Coupling constant#

The binding energy of the bound state of a neutron–proton system (the deuterium nucleus) is about 2 MeV, so the energy required to break a nucleus is generally on the order of 10 MeV. The effective strong coupling constant at this scale is, loosely

Taking the rest energy of a proton $m_{p}\sim 1\text{ GeV}$, through more complicated QFT math one finds

Compared to the other coupling constants at this scale, it is indeed the strongest of them all. The closest is electromagnetism, at $1/137\simeq 0.07$, which is about 10 times weaker.