Big Bang & Cosmic Expansion Simulator

Λ-CDM Expansion

Matter density Ω_m 0.30

Dark energy Ω_Λ = 1 − Ω_m = 0.70

Hubble constant H₀ 70 km/s/Mpc

Time speed 2.0×

Scale factor a(t)

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Cosmic age

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Hubble parameter H(t)

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Expansion phase

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How it works

Every galaxy sits at a fixed comoving coordinate — its position in a grid that itself stretches with the universe. The Friedmann equation ties the expansion rate to what fills space: matter dilutes as volume grows (∝ a⁻³), while dark energy's density stays constant, so it eventually dominates and expansion accelerates. Each frame integrates the scale factor a(t) forward from a hot, dense a≈0 state; every galaxy's rendered position is just its comoving coordinate times a(t), so the whole field balloons outward together — no galaxy is "moving" through space, space itself is stretching.

H(a)² = H₀² [ Ωm/a³ + ΩΛ ]
da/dt = a·H(a)
z = 1/a − 1   (redshift, color-coded per galaxy)

Matter density Ωm — higher values mean gravity fights expansion harder early on; lower Ωm hands dark energy control sooner.
Hubble constant H₀ — today's expansion rate; scales how fast the scale factor grows and how quickly cosmic age accumulates.
Time speed — a playback multiplier on cosmic time, not a physical parameter.
Restart Big Bang — resets the scale factor to its hot, dense starting value and redraws a fresh galaxy field.

Real-world relevance: this is the same Λ-CDM model astronomers fit to supernova brightness, the cosmic microwave background and large-scale galaxy surveys to measure the universe's actual composition — roughly 68% dark energy, 27% dark matter, 5% ordinary matter.

Nearby galaxy Redshifted (receding) CMB afterglow

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