DLA (Witten-Sander 1981): Particles diffuse randomly from far away. When they touch the cluster, they stick. Tips capture more walkers (Laplacian screening) → branching fractal.
Fractal dimension: d_f ≈ 1.71 in 2D (not a simple fraction — emerges from the growth dynamics).
Laplacian growth: DLA clusters are related to viscous fingering (Hele-Shaw), dielectric breakdown, and lightning — all governed by Laplace's equation on the boundary.
Color encodes arrival time (early=blue, late=orange).