  When a liquid is cooled below its melting temperature, if crystallization is
avoided, it forms a glass. This phenomenon, called glass transition, is
characterized by a marked increase of viscosity, about 14 orders of magnitude,
in a narrow temperature interval. The microscopic mechanism behind the glass
transition is still poorly understood. However, recently, great advances have
been made in the identification of cooperative rearranging regions, or
dynamical heterogeneities, i.e. domains of the liquid whose relaxation is
highly correlated. The growth of the size of these domains is now believed to
be the driving mechanism for the increase of the viscosity. Recently a tool to
quantify the size of these domains has been proposed. We apply this tool to a
wide class of materials to investigate the correlation between the size of the
heterogeneities and their configurational entropy, i.e. the number of states
accessible to a correlated domain. We find that the relaxation time of a given
system, apart from a material dependent pre-factor, is a universal function of
the configurational entropy of a correlated domain. As a consequence, we find
that at the glass transition temperature, the size of the domains and the
configurational entropy per unit volume are anti-correlated, as originally
predicted by the Adam-Gibbs theory. Finally, we use our data to extract some
exponents defined in the framework of the Random First Order Theory, a recent
quantitative theory of the glass transition.
