What Are Dark Matter and Dark Energy?

Look up at the night sky, and you can see stars, planets, and the glowing band of our own galaxy, the Milky Way. All of these things—every star, every planet, every cloud of gas and dust—are made of “normal matter,” the stuff that makes up everything we can touch and see. But what if I told you that all of this amazing stuff is only a tiny part of the universe?

In fact, all the things we can see and study, all the stars and galaxies, only make up about 5% of the entire universe. The other 95% is made of two mysterious things that we cannot see: dark matter and dark energy. These two things are the biggest secrets of the cosmos, and they are essential to understanding how the universe works and where it is going.

In this article, we will explain in simple terms what these two mysterious forces are, what they do, and why they are so important to the story of our universe.

The Universe We Can See

Before we talk about the dark parts of the universe, let’s talk about the part we know. The normal matter in the universe includes everything we can see with our telescopes. It’s the atoms that make up you, me, the Earth, the Sun, and all the billions of stars in the night sky. This is called baryonic matter. While it seems like a lot, all of it together makes up only a small fraction of the universe’s total contents.

For decades, scientists thought that all the gravity in the universe came from this normal matter. But as they looked deeper into space, they found that something wasn’t right.

The Invisible Glue: What Is Dark Matter?

The first clue that something was missing came in the 1930s. A scientist named Fritz Zwicky was studying a group of galaxies called the Coma Cluster. He noticed that these galaxies were moving incredibly fast—so fast that they should have flown apart, much like water flying off a spinning merry-go-round. He realized that there had to be more gravity to hold the cluster together, and that gravity must be coming from something he couldn’t see. He called this missing stuff “dark matter.”

Decades later, in the 1970s, another scientist named Vera Rubin studied how stars were moving inside galaxies. She expected the stars on the outside of a galaxy to move slower than the ones on the inside, just like planets farther from the Sun move slower. But what she found was shocking: the stars on the outside were moving at about the same speed as the stars on the inside. This again showed that there had to be a huge amount of unseen mass holding the galaxy together, a giant invisible “halo” of something.

So, what is dark matter? In simple words, it is a type of matter that has gravity, just like normal matter, but it does not give off, reflect, or absorb any light. It is completely invisible. Scientists believe that dark matter acts like the “cosmic scaffolding” that pulled normal matter together to form the first stars and galaxies. Without the gravity of this dark matter, our own galaxy probably would not have formed the way it did.

The evidence for dark matter is very strong. Scientists can see its effects even if they can’t see the matter itself. For example, the gravity of huge clumps of dark matter can bend the light from galaxies behind them. This effect, called gravitational lensing, works like a giant magnifying glass in space. By measuring how much the light is bent, we can figure out how much dark matter is there, and where it is.

What Is Dark Matter Made Of?

This is one of the biggest questions in science right now. We know what dark matter does, but we don’t know what it is. It cannot be made of normal protons and neutrons, because if it was, we would be able to see it.

Scientists have many ideas about what dark matter could be. One of the leading ideas is that it is made of a type of particle called a WIMP (which stands for Weakly Interacting Massive Particle). The name itself tells you a lot about the particle:

• Weakly Interacting: It doesn’t interact with light, and it doesn’t really interact with normal matter. This is why we can’t see it.
• Massive Particle: It is a particle with a lot of mass, which gives it gravity.

We have built huge science labs deep underground to try and catch a WIMP as it passes through the Earth, but so far, we haven’t found anything. The search for what dark matter is continues to be a top priority for physicists all over the world.

The Pushing Force: What Is Dark Energy?

The story of dark energy began in the late 1990s and it was a huge surprise. For a long time, scientists thought that the expansion of the universe, which started with the Big Bang, would be slowing down. This made sense because of gravity. Gravity from all the galaxies should be pulling everything back together, acting like a brake on the universe’s expansion.

But when scientists used a special kind of star explosion called a supernova to measure how fast the universe was expanding, they found something completely unexpected. They discovered that the universe’s expansion wasn’t slowing down; it was speeding up!

This was a shocking discovery. It’s like throwing a ball in the air and expecting it to slow down because of gravity, but instead, it starts going faster and faster into the sky. Something had to be pushing the universe apart, acting like a kind of “anti-gravity.” Scientists called this mysterious pushing force dark energy.

The Main Evidence for Dark Energy

The biggest piece of evidence for dark energy comes from studying Type Ia supernovae. These are a special kind of supernova that always explode with the same brightness. Because of this, scientists can use them as “standard candles” to measure distances in space. By comparing how bright these supernovae look from Earth to how bright they should be, scientists can figure out how far away they are.

When they looked at very distant supernovae, they found that they were dimmer than they should have been. This meant they were farther away than expected. The only way this could be true is if the universe had been expanding faster over time, pushing the distant galaxies farther away from us. This finding led to the conclusion that dark energy is real and it is causing the universe’s expansion to accelerate.

What Is Dark Energy Made Of?

This is an even bigger mystery than dark matter. We have no real clue what dark energy is.

• One idea is that dark energy is a property of space itself. Einstein’s theory of relativity said that empty space could have its own energy. If this is true, then as the universe gets bigger and more empty space is created, more dark energy is also created. This would cause the universe to expand faster and faster, which is what we see. This idea is called the “cosmological constant.”
• Another idea is that dark energy is a new kind of force or field that we don’t know about yet. This force would be very weak and would only work over huge distances.

Whatever dark energy is, we know that it makes up about 70% of all the energy and matter in the universe. It is a huge force, but we can’t see it, touch it, or even be sure of what it is.

The Cosmic Pie: Putting It All Together

So, what is the universe made of? When we put all the evidence together, we get a pie chart that looks like this:

• Normal Matter (5%): This is all the stuff we can see: stars, galaxies, planets, and us.
• Dark Matter (25%): This is the invisible matter that holds galaxies together with its gravity.
• Dark Energy (70%): This is the mysterious force that is pushing the universe apart faster and faster.

The universe is mostly dark, and the things we see and touch are just a small part of a much bigger cosmic story.

Conclusion

Dark matter and dark energy are two of the greatest mysteries in modern science. We can’t see them, but we can see their effects all over the universe. Dark matter is the invisible glue that holds galaxies together, while dark energy is the powerful force that is speeding up the expansion of the cosmos.

Scientists continue to work hard to solve these mysteries. Huge experiments are being built to try and find the particles of dark matter, and powerful telescopes are being used to get better measurements of dark energy. Uncovering the nature of these two things is not just a quest for new knowledge; it is a quest to understand 95% of our universe. The answers will change our understanding of the universe’s past, its present, and its ultimate future.