Expanding Universe
Flat ΛCDM scale factor a(t) with a stretching comoving grid and galaxies in WebGL.
About this tool
How does the universe grow? Choose H₀ and matter density, then Calculate. Scale factor a describes distances relative to today: a = 0.5 means half the distances and redshift z = 1. Gyr means billion years; lookback time is today's age minus the age at the selected state.
The number, slider, chart marker and 3D grid describe the same state. Play advances uniformly in cosmic time until today; the full model age corresponds to about 20 playback seconds. Editing or hiding the browser tab pauses playback. Calculate applies changed parameters; Reset restores the default parameters, a = 0.5 and the chart view, stops playback and clears results without calculating again.
Model: a spatially flat Friedmann universe with matter, radiation and a cosmological constant. Ω_Λ = 1 − Ω_m − Ω_r is derived automatically; fixed Ω_r = 0.00009 is a learning approximation, including when H₀ changes. H(a) = H₀√(Ω_r/a⁴ + Ω_m/a³ + Ω_Λ); time is integrated numerically from a = 0. Inflation, structure formation and galaxy evolution are not simulated.
The finite grid is a schematic patch, not a boundary or centre of the universe. Galaxy positions follow expansion; their marker sizes stay fixed to represent bound objects. The visual range starts at a = 0.01 and does not depict a real distribution. Calculation and chart remain usable without WebGL.