Particles and Symmetries

Abstract

Symmetry simplifies the description of physical phenomena, in such a way that humans can understand them: the Latin word for “understanding,” capere, also means “to contain”; and as we are a part of it we cannot contain the full Universe, unless we find a way to reduce its complexity–this is the meaning of symmetry. Symmetry plays a particularly important role in particle physics, as it does in astrophysics and in cosmology. The key mathematical framework for symmetry is group theory: symmetry transformations form groups. Although the symmetries of a physical system are not sufficient to fully describe its behavior—for this purpose, one needs a complete dynamical theory—it is possible to use symmetry to discover fundamental properties of a system. Examples of symmetries include space–time symmetries, internal symmetries of particles, and the so-called gauge symmetries of field theories.