Particles released from a distant circle perform random walks until touching the growing cluster. The result: a fractal with d_f ≈ 1.71 in 2D. Screened tips grow faster, creating dendritic branching.
Witten & Sander (1981): DLA fractal dimension d_f ≈ 1.71 in 2D. Measured by N(R) ~ R^d_f where N(R) is number of particles within radius R. Multifractal: the growth measure (harmonic measure) has spectrum f(α). Screening: inner branches stop growing — only tips accessible to random walkers. Connection to Laplacian growth, dielectric breakdown, viscous fingering.