The Universe Timeline

t = 0

The observable Universe begins expanding from a hot, dense state about 13.8 billion years ago.

~10⁻³⁶ s

A hypothesised burst of exponential expansion smooths and flattens the Universe (leading paradigm, not yet confirmed).

~3 minutes

The first light nuclei — hydrogen, helium, and traces of lithium — form.

~380,000 years

Atoms form and the Universe becomes transparent, releasing the cosmic microwave background.

~0.38–150 million years

Neutral gas fills a starless Universe, slowly drawn together by gravity and dark matter.

~100–400 million years

The first stars and galaxies ignite; JWST is now observing this era directly.

~150 million–1 billion years

Radiation from the first galaxies re-ionizes the intergalactic hydrogen.

~1–10 billion years

Galaxies grow and assemble into clusters and the filamentary cosmic web.

~9.2 billion years

Formation of the Solar System

About 4.6 billion years ago, the Sun and planets form from a collapsing cloud in the Milky Way.

~13.8 billion years

Today the Universe is flat, expanding ever faster, and dominated by dark energy and dark matter.

Far future

Future Scenarios

If dark energy remains constant, expansion continues forever toward a cold, dilute 'heat death'. The outcome depends on the nature of dark energy — an open question, not a certainty.