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Initial Conditions

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Cosmology

Instructions

  • Watch how small initial density perturbations grow into cosmic web structure
  • Particles start nearly uniform and cluster under gravity
  • Filaments, walls, and voids emerge from gravitational instability
  • Higher spectral index creates more small-scale power
  • Adjust cosmology to see how dark energy slows growth

Physics

This simulation uses the Zel'dovich approximation for structure formation: particles are displaced from a uniform grid by a displacement field proportional to the growing mode D(a). The displacement field is generated from initial Gaussian random density perturbations with a power spectrum P(k) ∝ k^n.

As the universe expands, gravity amplifies overdensities into the cosmic web we see today: dense clusters at nodes, filaments connecting them, walls surrounding voids, and empty voids where matter has flowed out.