Our universe began about 13.8 billion years ago in an extremely hot, dense early state. The Big Bang was not an explosion in space — it was an expansion of space itself. Very early on, temperatures may have exceeded 10^32 Kelvin, but physics at that stage is uncertain because our current theories are incomplete. The simulation starts with a stylised compressed state and then shows spacetime rapidly expanding outward.

Fractions of a second after the Big Bang, the universe underwent exponential expansion called inflation — growing by a factor of at least 10^26 in an unimaginably brief moment. This solved the horizon problem (why the universe looks uniform in all directions) and the flatness problem. Quantum fluctuations during inflation seeded the density variations that would later grow into galaxies. In the simulation, the rapid outward burst of particles with high velocity represents this inflationary epoch.

After the early plasma cooled enough for electrons to combine with nuclei (recombination), the universe became transparent — but also dark. No stars existed yet. This cosmic dark age lasted for a few hundred million years, during which gravity slowly pulled matter into the first overdensities. The simulation models this as a period of slow, damped motion where gravity wells begin forming and particles drift toward them — the seeds of the first galaxies.

As gravity amplified density fluctuations over hundreds of millions of years, the first stars ignited (Population III stars — massive, short-lived, metal-free). These clustered into the first galaxies. Dark matter halos provided the gravitational scaffolding around which visible matter collapsed. The large-scale structure that emerged — the 'cosmic web' of filaments, voids, and galaxy clusters — is visible today in surveys like SDSS. The gravity wells in the simulation represent these dark matter halos drawing particles into galactic structures.

Today's universe contains roughly 2 trillion galaxies, each hosting hundreds of billions of stars. The Milky Way sits in the Local Group, part of the Virgo Supercluster. The universe is still expanding — and accelerating, driven by dark energy (Λ, the cosmological constant). In the simulation's final phase, particles have settled into stable orbits around gravity wells, twinkling like stars, while the cosmic age counter reaches 13.8 billion years — the present moment in the 13.8-billion-year story.