The standard model of particle physics is the quantum theory that describes all of the known particles and three of the four forces they feel. Although it is called a "model," it is a full-fledged scientific theory that has been extremely well-verified over the past thirty years. Currently, all laboratory and particle collider experiments have agreed with the predictions of the standard model, making it a great success. On the other hand, the only clues pointing to more fundamental physical theories come from disagreements with the standard model, which have been frustratingly hard to find.

The standard model is composed of three parts. The first part is the matter particles, which are called quarks and leptons. The second part is the forces, or interactions, which include the electromagnetic, weak, and strong forces. (Currently, there is no verified quantum theory of...