The levels of self-organization of a system. In physical systems, complexity is associated with broken symmetry and the ability of a system to have different states between which it can make phase transitions. It is also associated with having coherence in space over a long range. Examples of complexity include superconductivity, superfluidity, lasers, and ordered phases that arise when a system is driven far from thermal equilibrium (see Bénard cell). It is not necessary for a system to have a large number of degrees of freedom in order for complexity to occur. The study of complexity is greatly aided by computers in systems that cannot be described analytically. Complexity is also very important in a number of other fields, including theoretical biology.