Instabilities and Pattern Formation

The notion of irreversibility is frequently associated with a tendency of the systems towards spatial homogeneity and rest, i.e. towards equilibrium. Although this observation is true in isolated systems, it is no longer verified in closed and open systems, which may exhibit organized structures in space and time. This organization arises as a consequence of occurrence of instabilities in systems driven far from equilibrium by external forces. Instabilities may be considered as phase transition phenomena, because they manifest under the form of a discontinuous change of the physical behaviour at a critical value of an external control parameter.