- [Dianna] Thank you to Brilliant for supporting PBS.
This is a detector.
It stands 50 feet, tall weighs 14,000 tons.
And yet, it's meant to detect the tiniest particles
in the universe.
Detectors like CMS.
Like this one, can only be found in one place,
the largest scientific facility on earth.
Why do you build this?
Along with an underground tunnel,
27 kilometers around and powerful superconducting magnets.
Why do you accelerate particles so small
we could never see them with a microscope?
Close to the speed of light and smash them together.
What even is a particle?
What exactly are these detectors for,
and what is it like to work at
and visit the most expensive
scientific experiment in history, Cern?
Hey, I'm Dianna and you're watching Physics Girl.
If you've seen my two previous videos
on anti-matter and dark matter,
then you know that over the summer
I visited CERN in Geneva, Switzerland.
This is my face seeing CMS for the first time.
(laughs)
When you visit CERN,
you need to drive pretty far
along winding country roads
to get to one of the four main detectors.
Situated along that, 27 kilometer ring.
To go underground, you need special access,
and usually you only get to go see one detector
because it's a whole process.
You get your helmet on.
- Oh, we got to put on some helmets.
Oh, thank you.
(laughs)
- [Dianna] You go through security doors one by one,
you descend a hundred meters in an elevator.
You get briefed on not using the stairs
if anything goes wrong.
And you stop to admire the strange signs and equipment.
- And if you devote two entire days of your life,
you might just get to see a couple of the detectors
like we did.
We were there for awhile.
I think they wanted us to leave.
- We're about to go down and sem us.
- So the elevator is like the safest place to be.
- Yeah. - So in any emergency,
that's the, soft of, meeting point.
- This is the video where I get into the essence of CERN.
It's the most advanced and expensive
scientific lab on earth.
And it's used to study particles.
I know, not the most fashionable area of physics
upon first inspection,
but it's the most fundamental question.
It's the one we all asked when we were kids.
What are we all made up of?
What are the fundamental particles
that make up everything in the universe?
Oh.
(laughs)
Sorry.
And how did these detectors
go about answering that question?
This is what I was most interested in,
and it was a bit of a rough start
because after three minutes of thinking,
I realized I didn't even know what a particle is.
Turns out that I don't know what a particle is
because I never got to quantum field theory
in my physics classes.
So if you don't know either, join the club.
So let's start there.
What are these particles that CMS is studying?
Like say, the Higgs boson.
- So the Higgs was discovered in 2012,
- 2012. - July 4th.
So we call this, Higgs dependence day.
(laughs)
- The discovery of the Higgs
was the crowning achievement
of the large Hadron Collider at CERN.
By the way, the large Hadron Collider, the LHC
and CERN are two different things,
which I didn't really know going into my tour at CERN.
The large Hadron Collider is the giant ring.
The particle Collider, that is part of the facility,
the entire place called CERN.
They're actually smaller colliders that were built
starting in the fifties.
I didn't know any of this.
But the large Hadron Collider is the large ring
that collides hadrons.
Duh.
Anyways, the discovery of the Higgs.
The Higgs is the tip of the iceberg
when it comes to particles.
It's just one of 30 fundamental particles
that make up everything in the universe.
Take any material, any wood,
any frogs, any cats, any aliens,
any snatoms, shout out to Derek, any Dereks,
any non materials like anti matter,
or even beams of light,
break them down into their fundamental bits
and you'll get 30 fundamental particles.
Maybe 31 if you count the graviton,
but let's not because it's not observed.
So 30 fundamental particles
and the standard model of particle physics.
I'm not going to read off all the particles
'cause there are too many,
but there are some fun ones to say,
like the charm quark and the gluon,
and some familiar ones like the electron,
the photon and the up and down quarks.
Okay, maybe those are not as familiar,
but those are the ones that make up neutrons and protons.
So elegant.
But the real story is more complicated.
The universe is actually made of quantum fields
not particles, if you want to be really accurate.
And if you want to know what particles are,
cause particles are a phenomenon
that emerges from quantum fields.
- The universe is a collection of these quantum fields.
For each particle, there's an associated quantum field.
Of course, for the photon,
the associated quantum field is the electromagnetic field.
- What's a field?
- What I mean by a field is just
having a value, a number perhaps
at each point in space that can evolve with time.
- A field is like a grid,
like a 3d map onto all of space.
It's like a topographical map with numbers,
except instead of showing Hills and ditches,
with a quantum field,
you measure something like
the energy density of the gluon field.
Even if this point in space right here
doesn't have an electron,
it still has a value for the electron field.
Just like if there's no hill on the topographical map,
there's still a number value
to represent the elevation there.
Particles are like little Hills in the quantum fields.
They're actually vibrations in the field,
which kind of start to make it clear
on how a particle can act like a wave.
The quantum field exists
even if there's no particle in it,
just like an ocean can exist
even if there's no wave in it.
This seems like a good moment to pause for dramatic effect
because all the stuff that we're familiar with
that we typically describe as being made of particles,
is actually made of a bunch of fields.
I'm not even going to say, "So cool"
because I can't even wrap my head around this.
Physics is so bizarre.
More bizarre is that particles are not absolute.
Particles can appear to exist
for one person looking at the field
and not for another,
depending on how fast they're both moving,
which has to do with changing reference frames.
- A particle that can travel at the speed of light
will travel at the speed of light.
The fact that you were traveling slower
than the speed of light means that
an observer, a different observer,
you can change reference range.
- If you're moving super fast,
like close to the speed of light,
then the value of the field changes,
which is kind of like time dilation,
the phenomenon where if you're moving fast,
then your clock appears to tick slower
than a person who's stationary,
which is a real thing
that if you've never heard of,
then I envy how blown your mind is right now.
So this all indicates that the fields are fundamental
and not the particles.
And once you start to think in terms of the fields,
then the experiments at the LHC
start to make a lot more sense
because the LHC smashes protons,
which are made of two up quarks and one down quark
held together with gluons.
So you might've thought
that you get a mess of quarks and gluons
out of the collision like I initially thought,
but they managed to get a Higgs boson.
It's like you blend it up a bunch of fruit in a smoothie
and popped out a chicken nugget.
But the thing is, the quantum fields can interact.
- One way you can see it
is there's this sort of instrument
or musical instrument analogy
where you might have, maybe a piano strikes a chord,
and if there's other instruments around,
there might be residents, right?
So one of the strings on a guitar might start vibrating
because the piano is hitting the right note.
- So it makes more sense
if you think that collisions are creating great disturbances
in the quantum fields
rather than thinking about particles colliding.
You can imagine the energy of one field
transferring to another and another,
like a vibration in the up quark field
causing a vibration in the electron neutrino field
or the Higgs field.
Speaking of the Higgs boson,
which was the most elusive particle for physicists
to detect in the standard model of particle physics.
I'm not really going to go
into the significance of it or what it is
'cause there's so much material out there
on the internet about it.
But now that we understand what particles are,
I want to talk about how we detect the Higgs boson.
The insane sensitivity of detecting it
and the crazy methods,
because we don't actually ever directly detect
the Higgs boson with detectors like CMS.
So how do we do it?
- The decay products from the Higgs decay
are fundamentally indistinguishable
from the decay of other particles.
- Decay products refers to the fact
that particles like the Higgs, which are unstable,
can spontaneously turn into other particles.
- So, a scientist that's trying to find
a new species that's invisible.
Well, what do you do?
You have to look at the decay products.
So let's look for poop, right?
- Yeah.
- And then how do you distinguish this animal's,
this new species' poop from other species.
- Yeah.
- The answer is that you don't, you can't.
If you produce a Higgs particle,
again you don't see the Higgs,
you have a bunch of poop in the forest.
That's the challenge is you have to be super
confident in your prediction.
And then you have your measurement,
you have to go to the forest and actually find this poop.
What if you think this is poop, but it's, I don't know, mud.
I don't, have no idea.
Can you, is there anything in the poop
that you can use to identify the species?
You can see why we need a lot of data.
You only produce the Higgs very rarely in these collisions.
Another way to say this is that
most of the poop that you think comes from the Higgs,
comes from other species.
You have to very confident about your prediction
and be very confident about your measurement.
If your prediction and your measurement match exactly.
Let's say you somehow calculate,
okay, we're going to find 100,000 poops
and you find 100,200.
There's an excess of 200.
- Yeah. - Is that significant?
So that's why when we discovered the Higgs,
we had to had a lot of data
and that's why it took so long
because we needed to compare the prediction
to the observation.
And when we finally said, "We did discover the Higgs"
it was actually after we had many, many collisions.
Sorry, if this analogy is kind of gross by the way, but--
(laughs)
- I was pretty happy with the fact that you used poop.
That was my first thought.
I was like, "Oh, you could use poop."
And I was like, "I shouldn't say that."
you could also use footprints
and then you said poop and I was like, "Yes!"
- Well yeah, I usually use footprints
- Okay. - for this analogy,
but Sarah encouraged me to go for poop.
- Go for the poop. (laughs)
- Go for the poop.
- So we're looking for an excess of poop.
It all makes sense now, except why do we need all of that?
The giant colliders, the massive detectors.
Why do we have to smash protons at such high energies?
Well, the Higgs boson
is the second heaviest fundamental particle
after the top quark.
And the heavier the particle,
the more energy you need to produce it.
E equals MC squared.
Thanks Einstein.
So if you transfer enough energy into the Higgs field,
you get a Higgs boson.
So you need a lot of energy
to make particles out of seemingly nothing,
but then you need massive detectors
to see all of the debris that comes out
and all of the particles that those particles decay into
'cause there's a ton of it.
And they're all going really close to the speed of light.
So they're going to make it pretty far, pretty fast.
So you need massive detectors
with massive magnets and massive numbers of wires.
But let's rewind a bit
because the whole purpose of making this video
is that I went there.
I went to see these detectors.
So I really wanted to know what it was like
to work with them.
What's it like to work at CERN?
- [Scientist] A little bit like a college campus,
but it's really dedicated,
it's sort of like everybody is on that mission.
Let's try to understand the universe.
People here are super passionate.
I feel like people here
would be willing to work almost for free
that their motivation is to understand the universe.
- I very much support scientists
getting paid for the amazing work that they do.
But I definitely understand the excited sentiment
because it was almost as exciting being there,
just visiting.
So were they colliding particles while we were there?
No.
See those guys?
They were in the beam path.
No one is in the beam path when it's on.
Cern has been in shutdown since December, 2018
and it's going to reopen in 2021,
then they'll close those giant magnetic doors
we were looking at
and then it'll take an entire day to do so
because they weigh hundreds of tons
and you don't want to bump a multi-million dollar magnet,
but it was super lucky that it was shut down when we went,
because we got to go underground and see everything.
There were wires everywhere.
Cables and wires are like the wallpaper of Cern.
And the internationalness was so noticeable.
Every person that we met was from a different country.
- [Man] CMS is a very large collaboration, over 3000 people.
- So what's next for particle physics at CERN?
Well just in 2018, they made some crazy discoveries
like finding evidence of another exotic particle,
made a four quarks, a Terra quark.
Precisely measuring the spectrum of anti hydrogen
and making the first 3d color x-ray of a human body,
which is based on technology developed at CERN.
And in the future, hopefully dark matter.
- Maybe not dark matter,
but maybe we find some other type of particle
that then decays into dark matter.
And this other type of particle,
maybe it lives pretty long.
Like maybe it lives for awhile.
So that means they can have a collision
and then a particle pops out.
Maybe it moves outside your detector
and then it decays into dark matter.
So you're missing that.
We have our detector a hundred meters underground.
We're considering to install
the texture modules in the surface
in case one of the particles struggles
a hundred meters through the surface
and then it decays.
- I'm super pumped to see what happens
when CERN turns back on in 2021
cause that collaboration
of thousands of scientists and engineers
from around the world
are digging into the fundamental physics of our universe.
And that
is cool.
- It's hard for me to understand
how you would not be fascinated at what we do here.
It's really remarkable.
And the fact that this all works as well,
like I mentioned all these careful predictions,
this careful measurements,
the fact that we've made the Higgs discovery
simultaneously with the Atlas detector,
the Atlas collaboration.
To me, it's super cool.
- Thanks for watching and happy physicsing.
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