  The utility of a cooperative length scale for describing the dynamics of
small molecule glass-formers is shown. Molecular Dynamics and Monte Carlo
simulations reveal a distribution of cooperatively moving fractal events below
the temperature Ta at which dynamics become caged. Guided by these results,
four straightforward methods emerge to recognize Ta in experimental data and
quantify the length scale that grows on cooling below Ta. This length scale is
consistent with 4-D NMR experiments which are sensitive to the slow moving
population.
