  We present experimental confirmation of dynamic facilitation in monodisperse
and bidisperse colloidal suspensions near the glass transition volume fraction.
Correlations in particle dynamics are seen to exist not only in space (clusters
and strings) but also as bubbles in space-time. Quantitatively, highly mobile
particles are more likely (than immobile particles) to have nearest neighbors
that were highly mobile in immediately preceding times. The interpretation is
that a particle's mobility enables or facilitates the subsequent motion of its
neighbors. Facilitation is most pronounced at the relaxation time that
corresponds with cage-breaking, when dynamic heterogeneity is also maximized.
