🕸️ Cosmic Web

Gravitational Instability & the Cosmic Web

The large-scale structure of the Universe — filaments, walls, voids and clusters — grew entirely from gravitational amplification of tiny quantum fluctuations (~10⁻⁵ amplitude) imprinted during inflation.

This simulation solves Newton's direct-summation N-body problem with softened gravity: a_i = G·Σ_j m_j·(r_j−r_i) / (|r_j−r_i|² + ε²)^(3/2), where ε prevents singularities when particles approach each other. Periodic boundary conditions wrap particles at the box edges, mimicking a representative volume of the Universe.

Initial conditions use a uniform grid plus small sine-wave density perturbations (Zel'dovich approximation) to seed the collapse. The density field (colour map) is computed by counting particles per grid cell — brighter regions host more mass. Over time, matter streams from voids into filaments and collapses into dense nodes.