The Big Bang

What happened

About 13.8 billion years ago the universe began as an unimaginably hot, dense state and started to expand. In the tiniest fraction of a second it ballooned faster than the speed of light in an episode called cosmic inflation. A second later it was a searing 'soup' of light and particles at some 10 billion degrees Celsius; over the next few minutes the first atomic nuclei formed.

Why it matters

The Big Bang is the beginning of space, time, matter, and energy — the origin of everything that would eventually become stars, galaxies, planets, and life.

Sources

• NASA Science. The Universe — Overview · Reputable source