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What is the universe?
Quick answer
The universe is everything that exists — all of space, time, matter, and energy, from the tiniest particle to the largest galaxy. It began about 13. 8 billion years ago in the Big Bang and has been expanding ever since.
Key things to understand
- The universe is all of space and time and everything in it — galaxies, stars, planets, matter, and energy.
- It began roughly 13.8 billion years ago in the Big Bang and has been expanding outward ever since.
- It contains hundreds of billions of galaxies, each with billions of stars.
- Most of it appears to be invisible 'dark matter' and 'dark energy' that we detect only through their effects.
- The observable universe is about 93 billion light-years across, but the whole may be far larger.
People also ask
How big is the universe?
The observable universe is about 93 billion light-years across. The full universe may be much larger — possibly infinite — but we can only see the part whose light has reached us.
How old is the universe?
About 13.8 billion years, measured from the Big Bang — the event from which space, time, and matter as we know them began.
Is the universe still expanding?
Yes, and the expansion is speeding up. Galaxies are moving apart, driven by a mysterious effect attributed to 'dark energy'.
Part of the guide: Space & Astronomy →