What is the Universe?

The universe is everything. It includes all of space, and all the matter and energy that space contains. It even includes time itself and, of course, it includes you.

The Earth and Moon are part of the universe, as are other planets and their dozens of moons. The planets, along with asteroids and comets, orbit the Sun. The Sun is one of hundreds of billions of stars in the Milky Way galaxy, and most of these stars have their own planets, called exoplanets.

The Milky Way is just one of billions of galaxies in the observable universe. Every galaxy, including ours, is thought to have a supermassive black hole at its center. Every star in every galaxy, and everything else astronomers can’t even observe, are all part of the universe. That’s all.

Space may seem like a strange place, but it’s not far away. Wherever you are, it’s just 100 kilometers away. Day or night, indoors or outdoors, while you sleep, eat lunch or fall asleep in class, the universe is just a few dozen miles above your head. And he’s inside you.

On the other side of the Earth, some 8,000 miles beneath your feet, lies the unforgiving vacuum and radiation of space. In fact, you are technically in space right now. People say “out there in space,” as if he’s there and we’re here, as if Earth is cut off from the rest of the universe. But Earth is a planet, and it’s in space just like any other planet, and it’s part of the universe.

As we know, the environment near the surface of this particular planet is suitable for life, and it just so happens that there is life here. Earth is a tiny, fragile exception in the universe. For humans and all other living things on Earth, virtually the entire universe is a hostile and unforgiving environment.

How old is Earth?

Our planet Earth is an oasis not only in space but also in time. It may seem like it lasts forever, but in the life cycle of the universe, the entire planet is fleeting. For almost two-thirds of the time since the universe formed, Earth didn’t even exist. And it won’t be like this forever. In a few billion years, the Sun will expand and swallow Mercury and Venus, filling Earth’s sky. It may even expand enough to engulf the Earth itself. It’s hard to say for sure. After all, humanity is only just beginning to decipher the universe.

While the distant future is difficult to predict accurately, the distant past is less so. By studying the radioactive decay of isotopes on Earth and in asteroids, scientists have discovered that our planet and solar system formed about 4.6 billion years ago.

How old is the universe?

Meanwhile, the age of the universe is thought to be about 13.8 billion years. Scientists arrived at this figure by measuring the age of the oldest stars and the rate at which the universe expands. They also measured the expansion by observing the Doppler shift in the light of galaxies. Almost all of the galaxies are moving away from us and from each other.

The farther away a galaxy is, the faster it is moving away from us. One might expect gravity to slow down the movement of galaxies away from each other, but instead, they are accelerating, and scientists don’t know why. In the distant future, galaxies will be so far away that their light will no longer be visible from Earth.

Put another way, the matter, energy and everything in the universe (including space itself) was more compact last Saturday than it is today.

In other words, matter, energy, and everything in the universe (including space itself) was more compact last Saturday than it is today. The same is true for any point in the past: last year, a million years ago, a billion years ago, etc. But the past doesn’t last forever.

By measuring the speeds of galaxies and their distances from us, scientists have discovered that if we could go back far enough, before galaxies formed, or before stars started fusing hydrogen into helium, things were so close together that atoms couldn’t form and it was so hot. Photons had nowhere to go. Go back a little further, and everything was in the same place. Or actually, the entire universe (not just the matter in it) was one place.

However, humans cannot visit the place where the Big Bang happened, so don’t think too much about going on a mission to the birth of the universe. It’s not like the universe was a dark, empty space in which an explosion occurred and all the matter came from. The universe did not exist. Space did not exist. Time is part of the universe and therefore did not exist. Time also began with the Big Bang. As the universe expanded over time, space itself expanded from a single point into the vastness of space.

What is the universe made of?

The universe contains all the energy and matter that exists. Most of the matter we can observe in the universe is made up of individual hydrogen atoms, the simplest atomic element consisting of only protons and electrons (if the atom also contains neutrons, it’s called deuterium instead). Two or more atoms that share electrons form molecules. Trillions of atoms come together to make dust particles. Squeeze together a few tons of carbon, silicon dioxide, oxygen, ice, and some metals and you get an asteroid. Or, if you combine 333,000 Earth masses of hydrogen and helium, you get a star similar to the Sun.

For practical purposes, people classify clumps of matter based on their properties. Galaxies, star clusters, planets, dwarf planets, rogue planets, moons, rings, marigolds, comets, meteorites, raccoons – they are all collections of matter with different properties but obeying the same laws of nature.

Scientists have started counting these clumps of matter, and the numbers they have come up with are pretty staggering. Our home galaxy, the Milky Way, contains at least 100 billion stars, and the observable universe contains at least 100 billion galaxies. If all the galaxies were the same size, there would be 10 billion (or 10 sextillion) stars in the observable universe. But the universe also appears to contain a lot of matter and energy that we can’t see or directly observe.

All the stars, planets, comets, sea otters, black holes, and dung beetles combined make up less than 5 percent of the matter in the universe. The remaining roughly 27 percent is dark matter and 68 percent is dark energy, both of which are poorly understood. The universe as we understand it wouldn’t function without the existence of dark matter and dark energy. They’re called “dark” because scientists can’t observe them directly – at least not yet.

How has our view of the universe changed over time?

Human understanding of what the universe is, how it works, and how big it is has changed over time. For countless lifetimes, humans had little to no ability to understand the universe. Our ancestors instead relied on myths to explain the origins of it all. Because our ancestors themselves invented myths, they reflect human concerns, hopes, aspirations, or fears, not the nature of reality.

But a few centuries ago, people began to use mathematics, writing, and new principles of inquiry in their quest for knowledge. These principles, like scientific tools, were refined over time, eventually providing clues about the nature of the universe. Just a few hundred years ago, when humans began to systematically study the nature of things, the word “scientist” didn’t exist (for a time, researchers were called “natural philosophers” instead).

Our knowledge of the universe has continued to advance greatly since then. It was only about a century ago that astronomers first observed galaxies other than our own, and it’s only been half a century since humans began sending spacecraft to other worlds. Within one human lifetime, space probes have reached the outer solar system and sent back to Earth the first close-up images of the four outermost giant planets and their countless moons.

A rover rolled across the surface of Mars for the first time. Humans built a permanently manned space station orbiting Earth. And the first large space telescopes provided breathtaking views of more remote parts of the universe than ever before. In the early 21st century alone, astronomers have discovered thousands of planets around other stars, detected gravitational waves for the first time, and created the first images of black holes.

With ever-advancing technology and knowledge, and an endless supply of imagination, humanity continues to unlock the mysteries of the universe. New insights and inspired ideas support and emerge from this pursuit. We haven’t even managed to send a space probe to the closest star out of the billions of others in our galaxy.

Humanity hasn’t even explored every world in our solar system, which means most of the known universe remains unknown. The universe is about 14 billion years old, the solar system is 4.6 billion years old, life on Earth has existed for perhaps 3.8 billion years, and humans have existed for only a few hundred thousand years. In other words, the universe has existed about 56,000 times longer than our species.

By this standard, almost everything that happened before us exists. Of course, we have a lot of questions. In a cosmic sense, we’re still just getting here. Our first few decades of exploring the solar system are just the beginning. From this point on, in just one human lifetime, our understanding of the universe and our place in it will undoubtedly grow and evolve in ways we can only imagine today.