Universality and scaling in critical behavior

The behavior of systems near critical points is a long‐standing puzzle in statistical mechanics and solid‐state physics. Experimentally this behavior is characterized by divergences in a variety of thermodynamic quantities as powers of the deviation from criticality. These divergences are described by critical indices, which are the exponents in power laws; for example, the susceptibility of a ferromagnet diverges like $(T−Tc)γ$ as T approaches $Tc.$