Cosmology For Kids

Updated: Aug 27

Hello everybody! Today we will be writing about cosmology! Cosmology is the study of how the universe came about, works, and how it is changing. It basically took history to a much, much wider scale going all the way back to the Big Bang. I hope you enjoy it!

Big Bang

The Big Bang was the beginning of when space and time combined to create spacetime 13.8 billion years ago.

Although “Big History” starts at the beginning of everything, there wasn’t really a then before the Big Bang because there was no space, or time. A concept us minor beings struggle to understand. So, don’t feel bad if this isn’t making crystal clear sense, we’re all confused.

The story of Big History starts at the Big Bang, but also ends many trillions of years from now when the universe dies. Yes, we do believe that the universe will die in around 2.8 billion years. Luckily not anywhere near our lifetime.

Human history is pretty fascinating, but it is time for us to realize that humans' are only a tiny piece. We’ve evolved to make amazing technologies. We really haven’t been here for that long.

The Big Bang was when the universe started expanding from nothing extremely quickly. When the Big Bang happened, all matter except one billionth of it was alienated making the one billionth, all matter that exists. Imagine all of it. All the stars, planets, galaxies. All of it, only one billionth of what was first created when the Big Bang first happened.

At first, the only elements were hydrogen and helium. But, then one day they started to combine making pressure and heat forming stars.

We can see what was happening 13.8 billion years ago by viewing matter 13.8 billion light years away. Scientists using powerful telescopes can't see anything happening before that.

Cosmic Background Radiation (CBR) was the leftover radiation of the Big Bang allowing us to use radiation for many electrical devices we have today. CBR is also probably the best evidence we have for the Big Bang theory too. We can study the series of events in the universe by listening to CBR and studying the disruptions. This makes it very helpful when rediscovering what happened before humans even existed!

Exploring the Universe

Everything used to be stars. And everything is pretty much all composed in the bellies of stars. So, how do we know this?

When the universe inflated there were quantum fluctuations that happened. A quantum fluctuation is when a force changes the amount of energy there is in a certain amount of space. So, since these fluctuations can be in different amounts of space some of them are less powerful, and some of them are more powerful. And sometimes, they can change how powerful they are. This is what happened!

As the universe expanded more and more, the fluctuations grew too. These fluctuations got powerful enough to merge hydrogen and helium together. The universe started getting really cold and really boring before hydrogen and helium connected. So, if hydrogen and helium hadn't clumped together, nothing would've ever happened in the universe at all. It would’ve just stayed cold and boring and there wouldn’t even be humans!

The combination of hydrogen and helium started increasing pressure. And when there is a mass amount of pressure, there is also a mass amount of heat. Eventually this created stars with the heat, and ability to forge new elements.

As things between the helium and hydrogen get warmer and warmer the atoms start getting really jumpy and fly everywhere. Eventually they all compact into stars. The only way for a star to form is when the right amount of helium and hydrogen is compacted and the cloud of the gasses is big enough. Then that cloud has to build up the right amount of pressure and heat to compact into a star.

As stars run out of hydrogen and helium, the outer part of the star swells starting up the fusion that creates other elements. This fusion of elements can only make elements up to as heavy as iron.

So where did the rest of the elements come from? The rest of the elements are formed when giant stars collapse and then make a giant explosion, flinging newly created elements across the universe.

The Evolutionary Epic

Populations tend to overpopulate and strain their resources. This has been seen over history, and can also be seen now with humans. “Natural Selection” means that all the different traits of different living beings all have been chosen naturally. An example is giraffes long necks that are used to get leaves off of tall trees. Its long neck was chosen to be that way, you guessed it, naturally. Humans have unusually large brains to make up for our puny bodies, and weak muscles.

The selection of everything's traits is done so with the motivation to stay alive, and to reproduce. Knowing that death may be around the corner motivates nature to give us some good traits, like legs! If we just flopped around like fish, it would be very hard to run away from a lion who is trying to eat us.

Evolution is just a theory, just as gravity is just a theory. Except it’s not like you find a random guy on the side of the road who says “I have a theory we’re all cucumbers!!!” In science, in order for something to be a theory, it has to be backed up with a bunch of evidence. If things don't have evidence, the theory might fit in the league of the random guy shouting about cucumbers. The theories such as gravity and evolution are backed up with mountain loads of evidence.

Long ago, Earth used to be a giant ball of ice. And as you can probably guess, earth was probably not the best place for life. There may have been some organisms that lived off photosynthesis in places with some heat and liquid water… but that was pretty much it.

But over time, these individual cells would start working together to create complex multicellular life. If you are wondering why they did this, it’s because it is probably pretty hard to live in a tiny hot spot that just so happened to be here on earth. Things would probably be much easier if us humans worked together just like the tiny organisms that made us!

This multicellular life has gone through five mass extinctions. We are not going to tell you about all the names of all the extinctions and periods, nor are we going to make you memorize all the multicellular organisms that participated in these mass extinctions. But what we are going to do is tell you how it all worked.

The competition for life is grouped in something called niches. Which are groups of different animals that get food the same way and reproduce the same way. When there are more multicellular beings in a niche, there is more competition. SPOILER ALERT: Usually all this competition ends in a mass extinction.

When there is a mass extinction within a niche, there is barely any competition between species allowing rapid adaptation and then the niche can be quickly filled again. This process keeps repeating in between small niches and large niches.

The only reason why there are so many mammals is because the niche with the dinosaurs got wiped out allowing it to be filled rapidly with mammals somewhat like the ones alive today.


Thank you for reading about cosmology! I hope you enjoyed and that you have learned a lot about the history of the universe. Remember, we will be adding more and more content! So tune in for more about cosmology, and many other subjects! I hope you enjoyed!