Episode 163: The Standard Model of Particle Physics

In the Standard Model of particle physics, the strong nuclear force is about 60 times stronger than the electromagnetic force at the scale of quarks, yet it operates over such a short range that it only binds particles together inside atomic nuclei. The weak nuclear force is weaker still—about one ten-thousandth the strength of electromagnetism—and does not form any bound states at all, instead mediating radioactive decay processes that can turn a neutron into a proton. These are the two forces, alongside electromagnetism, that the Standard Model describes, leaving gravity—10⁻⁴¹ times weaker than electromagnetism—to general relativity.

The Three Forces and Their Mediators

The Standard Model organizes the universe's fundamental interactions into three quantum field theories built on the template of quantum electrodynamics (QED). In QED, the electromagnetic force is carried by photons, which are electrically neutral and do not interact with each other. The strong nuclear force is mediated by gluons, but unlike photons, gluons themselves carry a "color charge"—the strong-force analogue of electric charge—so they interact with each other, making the theory far more complex. Color charge comes in three varieties (red, green, blue) plus their anticolors, and particles with color charge (quarks) are never found in isolation because the strong force actually grows stronger as quar