The Big Bang
Space, time, and everything in it begin to expand
Quick facts
- Age of the universe
- About 13.8 billion years
- First instant
- Cosmic inflation, space expanding faster than light
- Still happening
- The universe is still expanding today
- Status
- The earliest instants remain an open scientific question
What happened
About 13.8 billion years ago, the universe began in an extraordinarily hot, dense state and started to expand, and it has been expanding ever since. In the first tiny fraction of a second it went through a burst of runaway growth that cosmologists call cosmic inflation, during which space itself stretched faster than the speed of light. As it expanded it cooled, and over the following minutes the first atomic nuclei formed out of the cooling soup of particles. Every atom in your body, every star you can see, and every event further along this timeline traces back to this single beginning. NASA notes that the origin, evolution, and nature of the universe are still being worked out, so parts of the earliest instants remain open questions.
Why it matters
This is the zero point of everything. Each later event here, and on every other timeline the site holds, from the rise of the dinosaurs to yesterday's news, sits somewhere in the 13.8 billion years that unfold from this moment. It is the widest possible frame for history.
How we know
The 13.8-billion-year age is not a guess but a measurement, pinned down by studying the oldest light in the sky with missions like NASA's WMAP and the European Space Agency's Planck, which independently arrive at roughly the same number. NASA's own summary of the universe's history describes the inflation and expansion, while being candid that the very first instants are still under study.
Sources
- NASA. The Universe: overview and history (NASA Science) (2024) · Reputable sourcescience.nasa.gov · The domain "science.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- NASA. The Big Bang (NASA Science) (2024) · Reputable sourcescience.nasa.gov · The domain "science.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- European Space Agency (Planck). Planck reveals an almost perfect Universe: age 13.8 billion years (European Space Agency) (2013) · Reputable sourceesa.int · The domain "esa.int" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Part of a timelineBig Bang to Now19 events · 13.8 billion years on one timeline you can zoom, from the first light to the present. Every turning point cited.View all →