  We introduce a coarse-grained model for atomic glass formers. Its elements
are physically motivated local microscopic dynamical rules parameterized by
observables. Results of the model are established and used to interpret the
measured behaviors of supercooled fluids approaching glass transitions. The
model predicts the presence of a crossover from hierarchical super-Arrhenius
dynamics at short length scales to diffusive Arrhenius dynamics at large length
scales. This prediction distinguishes our model from other theories of glass
formers and can be tested by experiment.
