The 95% Mystery: Exploring the Invisible Universe

Okay, here’s a number for you. Less than five percent. Everything you've ever seen—every star, every planet, every grain of sand, you, me—all of it makes up less than five percent of the known universe. It’s an incredible thought, isn’t it? Last week we talked about the universe’s tendency toward chaos, like shuffling a deck of cards. But this is a whole other level of mystery. It’s not about the order of the cards; it’s about the fact that most of the deck is invisible. Exactly! So my big question is... what IS the other ninety-five percent? What are we missing? Well, scientists have split that giant question mark into two parts.

The first is called Dark Matter, and the second is called Dark Energy. Dark Matter. That sounds very dramatic. What does it do? Okay, so think of a galaxy, like our own Milky Way. It’s spinning, right? And you'd expect the stars on the far, far edges to be spinning slower than the stars near the center. Yeah, like a merry-go-round. The horses on the outside don't have to move as fast. Uh, actually the opposite. The horses on the outside have to go WAAAY faster to keep up. But in a galaxy, gravity is what holds it all together. So the stars on the edge, where the gravity from all the visible stuff is weaker, should be moving slower.

If they moved too fast, they’d just... fly off into space. Okay, that makes sense. So they’re moving slower. But they aren't! That’s the whole mystery. When astronomers measured them in the 1970s, a scientist named Vera Rubin found that the stars on the edge were moving just as fast as the ones closer in. It broke the rules. Whoa. So... what’s stopping them from flying away? Exactly! There must be a huge amount of extra mass in that galaxy that we can't see, providing the extra gravitational glue to hold those speedy stars in place. That invisible mass… that's dark matter. It has gravity, but it doesn’t reflect light, or block light, or give off light.

It’s just… dark. So it’s not just, like, dust clouds or a bunch of black holes? Scientists have checked! They’ve done the math, and all the normal stuff we know—even the dark, non-glowing normal stuff—doesn't add up to nearly enough. It has to be something completely new. Some kind of particle that zips right through us without a trace. Okay, so that’s Dark Matter. That’s about twenty-seven percent of the universe, you said. What about the rest? The biggest piece of the pie? Ah. Now we get to Dark Energy. And honestly, this might be the single strangest discovery in all of science. Stranger than invisible gravity glue?

Oh yeah. So, for most of the twentieth century, we knew the universe was expanding since the Big Bang. And the big question was, will it expand forever, or will gravity eventually pull everything back together in a "Big Crunch"? Like throwing a ball up in the air. Gravity is always trying to pull it back down. Precisely. So in the late 1990s, two teams of astronomers set out to measure the rate of that slowdown. They used distant supernovae—these incredibly bright exploding stars—as cosmic mile-markers. And they found the opposite of what they expected. The expansion of the universe isn't slowing down at all.

Wait—what? It's speeding up. Hold on. How? What could be powerful enough to push the entire universe apart against the pull of gravity? We have absolutely no idea. That’s the honest answer. There is some kind of energy, some kind of pressure woven into the fabric of space-time itself that is acting like anti-gravity. We gave that mysterious force a name: Dark Energy. And it makes up about sixty-eight percent of everything. So the universe is being held together by invisible matter while it’s simultaneously being pushed apart by an invisible energy. You got it. We are living in the five percent. We’re just the foam on top of this deep, dark, mysterious ocean.

It means the biggest, most fundamental questions are still completely unanswered. And all of our physics, everything we think we know, is based on that tiny little slice of reality we can actually see. Yep. It’s a pretty good reminder that we don't get to tell the universe how it should work. We just get the amazing job of trying to listen to what it's telling us.