Critical Phenomena

Abstract

Critical Phenomena is a part of Physics which has developed rapidly over the last 15 years, as exempled by the 1982 Hobel price for Physics which was awarded to K. Wilson for his major contribution in the field. Indeed the domain covered by this field is very large. The concept of a 2^nd order phase transition, which is detailed below, allows many different phenomena encountered near a transition to be considered as being equivalent and so they can be formulated by the same universal laws. This universality applies to both the physical phenomena — not only critical points are involved but also percolation, fractals, etc. — and the physical systems. Indeed a very large number of physical systems, such as simple fluids, binary^* or multicomponent fluid mixtures^**- including metallic liquid mixtures -, liquid crystals, microemulsions, polymers, molten salt, alloys^***, superfluid Helium, magnets, ferroelectrics, etc. exhibit the same universal behaviors. These systems can be classified into a few “universality classes”, according to very simple criteria as we will see below. In the following we will mostly deal with the “class” of fluids.