Science
What is The Big Bang?
The Big Bang is the leading explanation for how the universe began — expanding from an extremely hot, dense state about 13.8 billion years ago and cooling into the galaxies, stars, and planets we see today.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains the big bang.
Key things to understand
- 1It describes the universe's expansion from a tiny, hot, dense beginning.
- 2It wasn't an explosion in space — space itself expanded everywhere at once.
- 3Evidence includes the cosmic microwave background and galaxies moving apart.
- 4The universe is still expanding today.
Frequently asked questions
- What caused the Big Bang?
- Science describes what happened just after the earliest moment; what 'caused' it remains an open question at the frontier of physics.
- How do we know the Big Bang happened?
- Key evidence includes the faint cosmic microwave background radiation and the observed expansion of the universe.
- Was the Big Bang an explosion?
- Not in the usual sense — it was a rapid expansion of space itself, not matter flying through pre-existing space.