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Hey, smart people, Joe here.

(Big Bang explosion) Around a millionth of a second after the Big Bang, the universe was pretty weird.

Instead of atoms and stuff, it was full of this weird form of matter, a liquid soup of subatomic particles and pure energy at temperatures in the trillions of degrees.

That's hotter than anything in the universe today, or since.

And what's even weirder is this form of matter hasn't existed anywhere in the universe for 13.8 billion years.

At least, that was true until recently.

Scientists realized to learn what happened in the universe's first moments, they needed to recreate the unthinkably extreme temperatures and densities from when the universe was just a millionth of a second old.

By smashing heavy atoms together at the highest energies ever seen since the beginning of the universe.

There's only one place on Earth that we can do that.

Welcome to CERN.

(bright music) CERN is the world's largest particle physics lab.

A place where physicists test their theories under the most extreme conditions on Earth.

I took a trip to CERN to learn how scientists are trying to figure out what the universe was like in its earliest moments.

- [Off-Screen Voice] What is that?

- A snake, obviously.

The universe as we see it today is full of atoms and molecules that gravity has condensed into planets, stars and galaxies.

And tacos!

And all this matter is constantly expanding outward in a sea of unseen, dark matter and dark energy.

But if you rewind the clock and look back in time, you'll see a universe that was much smaller and denser.

The oldest light we can see today from just 380,000 years after the Big Bang has been stretched out and cooled by our expanding universe.

But what was the universe like when it was even more dense, when it was just a baby?

(baby babbling) And how did that universe give rise to all this stuff that makes up everything today?

That's what scientists at CERN wanna find out.

It's home to several huge particle accelerators, including the world's largest and most powerful, the Large Hadron Collider.

Most of the time these accelerators smash really tiny particles together at really high speeds to make new particles that don't exist under everyday conditions.

But for one month each year, they do something special.

The LHC smashes heavy particles together.

Their goal?

To recreate that weird trillion degree soup that last existed less than a second after the beginning of time.

Creating a baby universe in a lab sounds like a crazy idea.

Frankly, a little mad scientist.

I wanted to find out why anyone decided to even try it.

So I talked to one of the guys who's been involved with that project since it was just a crazy idea almost 20 years ago.

- My name is Kai Schweda, and I'm Deputy Spokesperson of the ALICE Collaboration.

- ALICE stands for A Large Ion Collider Experiment.

They called it that because it's a large ion collider experiment.

ALICE is dedicated to recreating those conditions of the early universe.

The first thing I wanted to understand is, well, we usually explore the history of the universe by looking deep into space.

So why is it so hard to study the universe when it was a baby?

I've been thinking a lot about telescopes and how we can look at stars, galaxies, from the very early universe.

But why can't we look all the way back to those very first moments that ALICE studies?

- This is due to the fact that the early universe was optically dense.

So anything you can see is 380,000 years after the Big Bang.

- [Joe] In other words, the baby universe was no more transparent than a brick wall, totally opaque to light.

Because at the time, the universe was full of loose electrons.

They were packed so tightly that any light just bounced off those electrons, zigzagging around instead of escaping.

It's like when you're in a dense crowd at a concert.

You can't leave until the crowd thins out, 'cause you just keep bumping into people.

That's what was happening with light and electrons.

In the case of the universe, things didn't thin out enough for light to escape until much later.

- 380,000 years after the Big Bang, you cannot look with a telescope which detects optic light.

You cannot look further back in time.

- [Joe] That means that no matter how good our telescopes get, we just can't see the universe before it was 380,000 years old, let alone when it was just fractions of a second old.

But even without being able to see the universe in those first instants, cosmologists are pretty sure about a few things.

Mainly it must have been mindbogglingly hot and dense.

- [Kai] Imagine you cram in our planet Earth and you cram in all other planets, our sun, and then all other 100 billion suns in our galaxy in the Milky Way, and you cram in all 100 billion galaxies we have in the universe in a sphere of 50 kilometers diameter.

That's how dense and how hot the universe was at that time, and the temperature was two trillion degrees Celsius, or Kelvin, it doesn't matter.

- [Joe] At that, yeah, when they get that high, scale doesn't matter.

- Exactly.

- You can't cram that much universe into a tiny little sphere without things getting extreme.

Trillions of degrees!

That's hot enough that neutrons and protons, I mean, the building blocks of matter itself can't exist.

In these conditions, physicists believe matter was deconstructed into an even more basic form, a cosmic soup of fundamental particles.

But scientists didn't actually know what this soup would've been like.

I mean, it's one thing to write your equations and theorize about trillion degree baby universe soup on those big physics chalkboards or whatever they do.

It's another thing to actually make it.

- Because we are experimental physicists, we want to know.

You can make up many, many theories.

Math allows practically everything you can imagine.

You can always formulate a mathematically correct theory, but whether nature cares about it or not, it's up to nature, and only experiment can decide.

- But we're not talking about just any physics experiment.

The temperatures and pressures required for this trillion degree soup haven't existed anywhere since the beginning of the universe.

Not in the center of the sun, not in the explosion of a supernova, let alone in a lab on Earth.

So the idea of recreating that substance in our cold, 13.8 billion-year-old universe, was truly bonkers.

Unless you happen to have the world's largest particle collider at your disposal.

The LHC is a ring over 16 miles long, and particles can travel around it over 11,000 times every second.

They reach 99.9999991% the speed of light.

And when they slam together, they create absolutely enormous amounts of energy.

When the LHC is running ALICE experiments, it shoots beams of lead ions into gold or more lead.

It can make a billion particle collisions a second.

The amount of energy in those collisions depends on the size of the particle.

Just like how a bus barreling down the highway is gonna have a lot more energy than a motorcycle, even if they're both going the same speed.

So by slamming together heavy stuff like lead ions, scientists using the LHC can create the most extreme energies ever produced in a lab.

Enough to cook up that cosmic soup.

- And the universe expanded since then.

After 14 billion years, it cooled down.

And today there's nothing even remotely as hot as the matter we create in ALICE.

If you go to our sun, you have 15 million degrees of temperatures.

The hottest stars have 100 million.

So what we create is 100,000 times hotter than anything else in today's universe.

- Temperatures 100,000 times the temperature at the center of the sun?

I can't even wrap my mind around that.

Anyway, it's probably a good idea that they do all of this 50 meters underground from where I'm standing.

What's through this door?

It looks really cool.

- So this door is the only access to the experiment.

And essentially, while it is used of course to operate, I mean, the various detectors whenever we have, I don't know, issues, we have to install the detector, et cetera.

Also to bring down the visitors when it is possible.

Of course, now, unfortunately, it is not, because it's period of data taking.

- [Joe] It's a little dangerous.

- [Fabrizio] And yeah.

- Yeah, sorry.

- [Fabrizio] So, - No access.

The detector for the ALICE experiment is an absolutely ginormous contraption that looks like a stargate, or space portal, honestly.

But what it actually is, is a series of sensors that can measure the path and velocity and energy of all the stuff that sprays off those collisions.

But unlike your iPhone, if they wanna install upgrades on this here big science machine, they have to pull the entire thing out.

- So that hook - This is used the.. - Will go all the way over and then lower it all the way down?

- Yes.

It's 50 meters below the surface.

- The entire detector comes through a giant garage door up to here.

It gets lowered all the way down.

That's a big crane.

Fortunately, all of this incredible engineering paid off.

In 2010, scientists at CERN smashed heavy ions and created a tiny fireball inside the LHC that was so hot, protons and neutrons melted into their fundamental components called quarks and gluons.

For a split second, they sloshed around in the same kind of cosmic soup that would've existed at the beginning of the universe.

An exotic state of matter known as a quark-gluon plasma.

Obviously making a quark-gluon plasma is hard.

But actually detecting it is a huge challenge too.

The ALICE detector sits in the LHC at the spot where the two beams of ions collide.

As thousands of particles spray out from the collisions, they deposit a small amount of their energy on the ALICE detector that creates a record of their paths, sort of like tire tracks creating a record of a car crash.

Based on these trajectories, physicists can figure out some key properties of these particles, like their velocity and mass, and work backwards to recreate a picture of what happened during the collision.

- So there's not a smoking gun where you see one signal, one peak, and that's the story.

You need to use the stuff that is created in the collision to learn something about its properties.

- So it's like you're seeing its shadow, sort of the shape around it, but you never actually see the thing?

- That's correct.

So we only see the aftermath.

- [Joe] This isn't an experiment where one collision is enough to prove it.

We're talking more like billions of collisions in each experiment.

What scales of data are we talking about?

- Ah, very good question.

So we take one terabyte of data.

One terabyte is, most people are familiar with.

It's 1,000 gigabytes, each second, 24 hours a day, seven days a week.

- [Joe] One terabyte every second.

- [Kai] Yes.

- And all that data ends up on drives that can hold over an exabyte of information.

That's over one million terabytes.

And that data has been full of surprising revelations.

- It was a complete surprise.

We thought the energy is so high that it's gonna be transparent, it's like a gas.

And the opposite is true, it's like a liquid.

So it's still strong interactions when you build this.

It was a big surprise.

No one predicted.

No one, absolutely no one.

- The quark-gluon plasma, the early universe, is a nearly perfect frictionless liquid.

I mean, that's the kind of thing we never even see in everyday life.

Even liquids like water.

I know they seem to flow freely and not have friction.

They're not actually frictionless.

The quark-gluon plasma is.

In addition to revealing what this early state of matter was like, the LHC'S experiments are also painting a picture of the transition between that strange liquid and everything we see in the universe today.

This is a huge breakthrough for scientists because it helps fill in the gaps of a crucial story.

How the sea of quarks cooled down in the moments after the Big Bang.

And how the strong force pulled those quarks into different packages of three, creating the protons and neutrons at the core of everything in the world today.

From there, we know how the rest of the story played out.

Those protons and neutrons then captured electrons, turning into atoms, and many of them joined together to form molecules.

And finally, through millions and billions of years of cosmic evolution, they turned into our universe today.

So studying quark-gluon plasma takes us a big step closer to understanding where we come from, where everything comes from.

It's hard to believe that some of humanity's biggest philosophical questions could be answered by smashing stuff together in a tube.

But by doing that, physicists were able to open this window to the past and recreate a state of matter that hasn't existed in 13.8 billion years.

And in doing that, show that everything in the universe today is linked to that moment near the beginning of time.

Stay curious.

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I mean, wow, CERN!

Awesome!

You might not know this, but CERN is in Switzerland.

And I'm not, usually.

So thank you to everyone who supports this show for help making episodes like this one possible and letting us bring you amazing stories about the universe like this.

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We'll see you in the next video.

ALICE is a great acronym.

I like that it's just A Large Ion Collider Experiment.