Big Bang Expansion Simulator

The Big Bang theory describes the evolution of an incredibly hot, dense early universe as it expands and cools over billions of years — not an explosion inside space, but the stretching of space itself. This simulator solves the Friedmann equation that governs that stretching directly: a cloud of protogalaxies sits at fixed comoving coordinates while the scale factor a(t) grows underneath them, carrying them apart exactly as real cosmic expansion carries real galaxies apart. Radiation dominates the dynamics immediately after recombination, matter takes over and decelerates the expansion for billions of years, and the cosmological constant eventually wins out and accelerates it again — precisely the sequence encoded in the standard ΛCDM model. Adjust the Hubble constant and matter density to see how they reshape the universe's expansion history, and watch the scale factor, age and background temperature update in real time as the integration runs.