  To gain insight into the kinetics of colloidal gel evolution at low particle
volume fractions $\phi$, we utilize differential dynamic microscopy to
investigate particle aggregation, geometric percolation, and the subsequent
transition to nonergodic dynamics. We report the emergence of unexpectedly rich
multiscale dynamics upon the onset of nonergodicity, which separates the wave
vectors $q$ into three different regimes. In the high-$q$ domain, the gel
exhibits $\phi$-independent internal vibrations of fractal clusters. The
intermediate-$q$ domain is dominated by density fluctuations at the length
scale of the clusters, as evidenced by the $q$-independence of the relaxation
time $\tau$. In the low-$q$ domain, the scaling of $\tau$ as $q^{-3}$ suggests
that the network appears homogeneous. The transitions between these three
regimes introduce two characteristic length scales, distinct from the cluster
size.
