standard model of elementary particle physics
The current state of the art for describing the basic properties of matter and forces. The standard model theories are based on special relativity and quantum theory and they describe the behaviour of elementary matter particles such as electrons, neutrinos and quarks as well as their anti-particles. It also describes three quantum forces acting between them: electromagnetism, the weak nuclear force and the strong nuclear force. These forces act by the exchange of force particles. There is one elementary force for which no such quantum description exists, and which is not part of the standard model: gravity.