Simulate large-scale structure formation via gravitational N-body collapse. Particles flow from voids into sheets, filaments, and halos — the cosmic web skeleton.
The cosmic web (Zel'dovich 1970, Bond et al. 1996) emerges from gravitational instability of small primordial perturbations. Structure forms hierarchically: sheets (2-collapse) → filaments (1D) → halos (0D). The Zel'dovich approximation: x(q,t)=q−D(t)∇ψ(q) gives the first shell-crossing. Dark matter halos trace a scale-free mass function (Press-Schechter 1974).