You might be surprised to know that our universe is expanding at a speed of 70 kilometers per second per megaparsec. Space itself is stretching every second. Not due to an explosion, but because the very fabric of the universe is growing.
But why is the universe expanding? And what does that mean for us?
Let’s break it down.
Space Itself Is Growing
When scientists say the universe is expanding, they’re not talking about galaxies flying through space like rockets. What’s actually happening is called metric expansion — space itself is stretching, which increases the distance between galaxies.
Imagine a sheet of graph paper where the squares keep getting bigger. The objects on the paper stay in place, but the distance between them increases. That’s how our universe works. It's not expanding into anything, there’s no outer edge or central point. Space is everything, and it's expanding everywhere, all at once.
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| Expanding universe visual shows fixed galaxies as space stretches and distances grow. |
How Do We Know Space is expanding?
The First Big Discovery in 1929
The first solid clue came in 1929 when a scientist named Edwin Hubble made an amazing discovery. He was looking at light from galaxies far away in space. Hubble noticed something strange about this light. The light looked more red than it should. Scientists call this redshift.
When galaxies move away from us, their light gets "stretched out." This makes the light look more red. The faster they move away, the more red the light looks. Hubble found that all distant galaxies were moving away from us. The farther away a galaxy was, the faster it was moving. This became known as Hubble’s Law and was the first strong evidence that the universe is constantly expanding.
The Second Big Discovery in 1964
Thirty-five years later, scientists made another incredible discovery. They found something called the Cosmic Microwave Background, or CMB for short.
The CMB is like finding an old baby photo of the universe. Scientists discovered that the universe was once extremely hot and packed together. As the universe expanded and grew bigger, it cooled down. This left behind a faint glow of radiation we can still detect today. This radiation is everywhere in space.
The CMB proved that the universe had a beginning, started very hot and dense, has been expanding and cooling ever since, and we can actually see evidence from when the universe was very young.
These two major discoveries work together to paint a picture of our universe. The universe is expanding as galaxies move away from us. The universe had a hot beginning that we can see evidence of. The universe is very old, and these discoveries help us understand cosmic history.
Dark Energy
In 1998, scientists made a discovery that surprised everyone. They were studying how fast the universe was growing. Most scientists thought the universe should be slowing down over time due to gravity. But they found something completely different. The universe wasn't slowing down at all. Instead, it was speeding up. The space between galaxies was growing faster and faster every day.
What is Dark Energy?
This strange discovery led scientists to think about a new kind of force they had never seen before. They called it dark energy. The word “dark” doesn’t mean it’s literally black or invisible. It just means scientists don’t fully understand it yet.
Dark energy is everywhere in space. In fact, scientists believe it makes up almost 75% of everything in the universe. That means most of our universe is made of something we barely understand!
How Dark Energy Works?
You know how gravity pulls things together like how Earth pulls you down when you jump? Well, dark energy does the opposite. It pushes things apart.
Dark energy acts like an invisible force that pushes galaxies away from each other. The more space there is between galaxies, the stronger this pushing force becomes. This is why the universe keeps expanding faster and faster.
What Could Dark Energy Actually Be?
Scientists have ideas about what dark energy might be, but nobody knows for sure. Interestingly, Albert Einstein once proposed a concept called the cosmological constant — a form of energy built into space itself. Today, some scientists believe dark energy may be related to that very idea.
The discovery of dark energy changed how we think about our universe. Before 1998, scientists thought they understood most of what was out there in space. Now they realize that most of the universe is made of mysterious dark energy that they're still trying to figure out.
Stay Curious
The universe is expanding, but so is our curiosity. Want to keep exploring the cosmos and its mysteries? Leave your questions in the comments or share this article with a fellow stargazer.
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