The universe is everything. It’s all of space, all the matter and energy that space contains, and even time itself. Every galaxy, every star, every planet, every atom, the empty space in between, and yes, you reading this, are all part of the universe. As far as we know, it’s about 13.8 billion years old, it began with the Big Bang, and it has been expanding ever since.
That’s a definition so vast it’s almost impossible to hold in your head. So let’s break the universe down into pieces we can actually grasp: how old it is, how big it is, what it’s made of, and the humbling place we occupy within it.
The Universe Is, Quite Simply, Everything
It’s worth pausing on just how total that word “everything” is. The universe isn’t just the stars and galaxies. It’s the space they sit in and the time they move through. NASA puts it beautifully: the universe includes all of space, all the matter and energy space contains, time itself, and, of course, it includes you.
Earth and the Moon are part of the universe. So are the other planets, the Sun, and the hundreds of billions of other stars in our Milky Way galaxy. And the Milky Way is just one of trillions of galaxies out there. Everything that exists, everything that has ever existed, and even the parts we can’t see, are all bundled together into this single thing we call the universe.
How Old Is the Universe, and How Did It Begin?
The universe is roughly 13.8 billion years old, and it began with the Big Bang. But the Big Bang wasn’t an explosion that went off in some pre-existing empty space. There was no space. There was no time. Both of them began with the Big Bang itself.
At the very start, everything, all matter, all energy, and all of space, was packed into a single unimaginably hot, dense point. Then it began expanding, and space itself stretched outward, cooling as it grew, allowing atoms, stars, and galaxies to form over billions of years. Our guide to the Big Bang tells that origin story in full. One strange consequence: you can’t point to a spot where the Big Bang happened, because it happened everywhere at once. The whole universe was that spot.
The Universe Is Expanding, and Speeding Up
Here’s one of the most important discoveries in all of science: the universe isn’t static. It’s growing. Astronomers can see that almost every distant galaxy is racing away from us, and the farther away a galaxy is, the faster it’s receding. Space itself is stretching, carrying the galaxies apart like dots on an inflating balloon.
Stranger still, that expansion is accelerating. You might expect gravity to gradually slow everything down, but instead the universe is flying apart faster and faster, pushed by a mysterious something scientists have named dark energy. Nobody knows what it is. Our explainer on dark energy digs into the biggest unsolved puzzle in cosmology.
What Is the Universe Made Of?
Now for the most humbling fact of all. Everything we can see, every star, planet, galaxy, and living thing, makes up less than 5% of the universe. The other 95% is stuff we can’t see and barely understand.
| Component | Share of the universe |
|---|---|
| Ordinary matter (everything we can see) | About 5% |
| Dark matter (invisible, felt through gravity) | About 27% |
| Dark energy (driving the expansion) | About 68% |
That’s right: about 27% of the universe is dark matter, an invisible substance we detect only by its gravity, and roughly 68% is dark energy. Our guide to dark matter explains the invisible scaffolding that holds galaxies together. In short, the universe we can actually observe is just the thin visible froth on a vast, dark ocean we’ve barely begun to understand.
How Big Is the Universe?
Honestly? We don’t fully know. The part we can see, called the observable universe, stretches about 93 billion light-years across. But that’s only the region whose light has had time to reach us since the Big Bang. The universe almost certainly continues far beyond that boundary, and it may even be infinite.
It also has no known center and no edge. When it expands, it isn’t expanding “into” anything, because there is no outside. Space itself is simply getting bigger everywhere at once. Our piece on how vast the universe really is tries to do justice to a scale that genuinely breaks the imagination.
Our Tiny Place in It All
Step back and take in the full picture. The universe is nearly 14 billion years old. Our entire solar system is only 4.6 billion years old, life on Earth about 3.8 billion, and humans have existed for just a few hundred thousand years. Our species is a brand-new arrival in a cosmos almost unimaginably older than us.
And we sit on one small rocky planet, orbiting one ordinary star, in one of trillions of galaxies. It could feel diminishing, but it’s the opposite. We’re the part of the universe that has somehow woken up and started to understand itself. NASA’s own overview of what the universe is is a wonderful place to keep wondering.
So the next time someone asks what the universe is, you can give them the honest, staggering answer: it’s everything there is, everywhere there is, for all the time there has ever been. And we’ve only just begun to explore it.
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