What the Universe Is Really Made Of: Dark Matter and Dark Energy Explained

Okay, get this. Everything you can see—every star, every planet, every single grain of sand on Earth—makes up less than FIVE percent of the entire universe. Hold on. Five percent? What's the other ninety-five percent? Is it just… empty space? That's what's so incredible! It is NOT empty. Last week we talked about crushing our Sun into a black hole, right? Even something that wild and powerful is part of that tiny five percent. The rest is a giant cosmic mystery we call Dark Matter and Dark Energy. Okay, "dark" makes it sound spooky. What are they? So let's start with Dark Matter. It's about twenty-seven percent of the universe.

And the best way to think about it is like… invisible glue. We can't see it, it doesn't give off light or heat, but it has gravity. A LOT of gravity. So if we can't see it, how in the world do we know it's there? Because we can see what it does! Think of a giant merry-go-round, like a whole galaxy. The stars on the outer edge are spinning so fast they should, by all rights, just fly off into space. Oh, right. Like kids flying off a playground spinner if it goes too fast. Exactly! But they don't. They stay in orbit. Something is holding them in. There’s some extra, invisible mass providing the gravity needed to keep the galaxy from flying apart.

That's dark matter. It’s the cosmic scaffolding holding everything together. Okay, so dark matter is the glue. That makes a weird kind of sense. You said that's twenty-seven percent. What's the rest? This is where it gets even stranger. The rest, about sixty-eight percent of the universe, is Dark Energy. And it does the exact OPPOSITE of dark matter. So… it's not glue? It's, uh… anti-glue? Yes! It's cosmic anti-glue! For decades, astronomers thought the expansion of the universe, you know, from the Big Bang, must be slowing down. Gravity from all the stars and galaxies should be pulling everything back together.

That makes sense. What goes up must come down. Right. But when they looked, they found the opposite. The expansion isn't slowing down. It's ACCELERATING. What? How is that possible? Imagine you throw a baseball straight up in the air. You expect it to slow down, stop, and fall back to you. Now imagine that instead, it just starts going faster and faster, shooting away into the sky. I mean… that would break my brain a little. It broke everyone's brain! That's what the universe is doing. Galaxies are flying away from each other at ever-increasing speeds. Dark Energy is just the name we give to whatever mysterious force is pushing the pedal to the metal.

So here's the part that just blows my mind every time I think about it. You take the twenty-seven percent that is dark matter, and the sixty-eight percent that is dark energy… and you're left with just five percent for everything else. Wow. So us, the Earth, the Sun, all the stars we can see… all of that is just the five percent? We are the foam on the cosmic ocean. We're the sprinkles on a giant, invisible cake. We're living in a tiny sliver of reality, and the other ninety-five percent is this stuff we can't see or touch, but that dictates the entire fate of the cosmos. That is… humbling. To put it mildly.

We're basically just bystanders. We are! And this is, without a doubt, one of the biggest puzzles in all of science. We have names for these things—dark matter, dark energy—but that’s mostly just us admitting we don't know what they are. So we know that they are, but not what they are. Precisely. It’s like we’ve stumbled into a massive, dark library. We can feel the weight of the books on the shelves, and we can feel the walls of the library itself expanding around us, pushing us outward. But we can't actually read any of the books. We can't even see them! We're just beginning to figure out that the shelves aren't empty.

It's this incredible reminder that no matter how much we learn, the universe is always going to have another, deeper secret. And the biggest ones are still out there, waiting for us in the dark.