The
many-body theory (or
many-body physics) is an area of
physics which provides the framework for understanding the collective behavior of vast assemblies of interacting particles. In general terms, the many-body theory deals with effects that manifest themselves only in systems containing large numbers of constituents. While the underlying physical laws that govern the motion of each individual particle may (or may not) be simple, the study of the collection of particles can be extremely complex. In some cases
emergent phenomena may arise which bear little resemblance to the underlying elementary laws.