From Ice to Fire: The Incredible Science of Temperature (2018): Season 1, Episode 3 - Playing with Fire - full transcript

Physicist Dr Helen Czerski explores the science of heat. She reveals how heat is the hidden energy contained within matter with the power to transform it from state to state.

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Dr. Helen Czerski: Everything
around us exists somewhere

on a vast scale from
cold...to hot.

Whether living or dead,
solid or liquid, visible or

invisible, everything
has a temperature.

It's the hidden energy
contained within matter.

And the way that energy
endlessly shifts and flows

is the architect that
has shaped our planet

and the universe.

Across three programs,
we're going to explore

the extremes of the
temperature scale,

from some of the coldest
temperatures...



to the very hottest

and everything in-between.

In this program,
the incredible

science of heat.

What temperatures does
it reach on the inside there?

100 million degrees.

That's just
a ludicrous number!

We'll reveal how our ability
to harness heat lies behind

some of humanity's greatest
achievements...from the

molten metals
that gave us tools...

[Hammering]

[Crackling]

to the searing energy
of plasmas...

[Loud crack]



that offer
the promise of almost

unlimited power.

Temperature is in every single
story that nature has to tell,

and in this series
we'll show you why.

[Engine huffing]

[Whistle blows]

I love steam engines 'cause
they're so raw. You can see

where the energy's coming
from and where it's going to.

This one's called "Braveheart,"
built in 1951, but still

going strong.

The steam out
there is amazing!

[Whistle blows]

Steam locomotives like
"Braveheart" are a symbol of

an age when it seemed that our
ability to harness heat knew

no bounds...

allowing us to
drive our trains, run our

factories, and
propel our ships.

But to get the engineering
right, people had to ask

previously unanswered
questions about what heat

really was.

And with the answers came an
understanding of just how much

heat could do for us.

We're going past the
modern world and the houses

and computers and technology
that we take for granted,

all of which required
control of heat.

But all of that is built
on the foundation

of the Industrial Revolution,
things like this engine.

And right at the heart of
the engine is the rawest bit

and the first form of
heat that humans learned

to control--

and that is fire.

In all of human history,
there can be few moments more

significant than the
discovery of fire.

A spark is so brief, such
a tiny flash of light,

and yet the start of
such a huge story.

A long time ago, perhaps
around a million years,

our ancestors could sit around
a fire for the first time when

they chose.

And I'm sure that fire was
just as mesmerizing for them as

it is for us, this flood of
heat and light conjured

up at will.

You don't need any
understanding of physics to

appreciate this or to
be fascinated by it.

It must have seemed amazing
that something as apparently

dead and inert as wood could
suddenly change into flame,

releasing so much heat.

Our ancestors couldn't have
known it, but mastering that

spark opened the door to a
whole new way of being human.

The ability to create fire
provided our ancestors

with warmth, protection,
as well as a means

of cooking food.

But for all the usefulness
of fire, unlocking its full

potential was still
a long way off.

For almost all of human
history, we had no idea what

heat could do for us, because
we just didn't know what it

really was.

It wasn't that long ago
that people thought heat was

a substance in its own right--
a weightless fluid called

Caloric that could flow in and
out of solids and liquids,

altering their temperature.

Not until the early 20th
century did we, in fact,

discover that heat isn't
a substance but something

else entirely.

[Kernels clattering in pan]

What I've got here are popcorn
kernels, and each one is the

seed of a plant, but inside
them they've got a little

bit of water.

And what's happening is that
energy is flowing into

the kernels, and the water
molecules as they heat up are

moving faster and faster.

That water, the liquid water,
is being pulled apart,

and so the liquid is becoming
a gas and the popcorn kernels

are filling up with steam.

Every single one of these
kernels is now a very small

pressure cooker.

And eventually....

Oop! Ha ha ha!

And the pressure bursts the
kernel outer shell.

The whole kernel turns inside
out, and then you get popcorn

that is flying everywhere!

And the important point here

is that the heat energy
is all about movement.

As atoms and molecules take
energy on board, they start

to speed up.

The faster they're moving,
the hotter the substance is.

And the crucial point about
all this movement or energy is

its extraordinary ability
to transform things...

even matter itself.

In the year 793, Anglo-Saxon
Britain came under attack...

[Shouting]

when Viking raiders
first landed

on the Northumbrian coast.

While the Vikings' reputation
as fearsome warriors is well

documented, what's less
well known is their skillful

craftwork,
especially with metals.

[Chainmail rattling]

A skill calling for not only
a sense of design, but also

a sophisticated understanding
of temperature.

[Hammering metal]

And historical blacksmith
Jason Green is going to

show us why.

And how hot will
it get in there?

Around 1300 degrees.

Czerski: Under Jason's watchful
eye, we're going to attempt to

make a Viking dagger, a process
that starts with heating up

a small piece of steel before
hammering it into shape.

- That's it.
- OK.

Ooh! Not setting
the grass on fire.

The only way you're
gonna learn is to do it.

Czerski: Is by doing it.

Right. Well, there's gonna be a
lot of doing, isn't there?

[Tapping]

It's funny.
You can feel as it cools.

It suddenly stops going
anywhere.

Green: Yeah, it starts getting
harder, so...

Czerski: Blow, by blow,

the dagger starts to take
Shape, both externally and,

more importantly,
deep inside the metal.

We don't tend to think of
metals as being crystals,

but in fact they are.

That means their atoms
are arranged into a highly

regular, repeating pattern.

What's happening as we heat is
that the crystals are changing

because the heat makes
them slightly more mobile.

It allows you to
push atoms around.

As the metal is hammered,
each impact rearranges

the atoms inside creating
tiny knots within

the crystalline structure.

As these knots accumulate,
it becomes harder

for the atoms to move
over each other.

And this helps make
the metal stronger.

And so all of this
raw action, this hammering,

thumping, and the heating,
is changing things at a very

tiny scale inside the metal
itself, and that's what gives

iron and steel it's strength
and that's why it's so useful.

But a blade's strength doesn't
come from hammering alone.

It also requires
clever manipulation

of its temperature.

The knife's now back in
the forge glowing cherry-red,

and that means it's about 800
degrees C, and that matters

because the crystal structure
at this temperature, this is

the one we want.

It's very strong,
it's really useful.

If I let it cool down slowly,
it will change back to the

room temperature structure.

And so in order to keep this
crystal structure so it's

a useful knife,
this is what we do,

which is very satisfying.
Ha ha!

As the hot metal is
plunged into the water, its

temperature plummets in
just a few seconds.

By cooling it so quickly,
the atoms haven't got time to

shift into the shape that they
want to have and so they're

stuck, locked in, with
a very strong structure.

Finally, one last round
of heating to remove any

remaining brittleness.

There we go.

One finished fighting blade.

Czerski: I'm so impressed that
with such simple tools you can

make something so useful.

That's brilliant.
Thank you very much.

By turning wood into flames,

rock into metal,

and soft metal into hard,

our ancestors' growing

understanding that heat could
transform matter altered the

course of human civilization.

But for thousands of years,
this knowledge was only

applied to solids.

The next leap forward would
see people using heat to

exploit another form
of matter, one

with astonishing potential.

[Steam hissing]
Gas.

But to understand how gases
respond to heat, we first need

to take a step back and look
at what gases are and how

they work.

Humans love a bit of
spectacle, anything

with color and music and fun.

But the stereotype of a
scientific experiment is

almost exactly the opposite,
a dusty basement with someone

who hasn't seen daylight for a
week writing down measurements

that no one will ever read.

But there have
been exceptions.

There have been experiments
set up with a theatrical drama

to match their
scientific significance.

And one of my favorites
happened in 1654, and it was

all organized by a man
called Otto von Guericke.

The aim of the experiment was
to demonstrate a very specific

and extraordinary
property of air.

And heading up the guest list
was none other than the

Holy Roman Emperor,
Ferdinand III.

Once the Emperor was seated,
Von Guericke took a pair

of metal hemispheres, placed
them together, and then began

to pump the air
out from inside.

This created a vacuum,
which held the two halves

of the sphere together.

He then attached each end to
a team of horses and gave

the command to pull.

To show you what happened
next, we're going to attach

our sphere to the modern
equivalent of Von Guericke's

horses--a pair of 4x4s.

Man: OK, stand by!

I'm actually
quite nervous.

Man: 3, 2, 1, go!

Czerski: So the tension's
out of the rope.

So now a little bit on the
accelerator just up to 1,000.

Feel it taking the strain.

OK, keep going
up to 1,300.

[Revving engine]

Feel it in the car.

OK, up to 1,600.

[Revving engine]
The engine's not happy. Ha ha!

I think we might have
established the sphere

really works.

OK, let's pause
there, so stop.

It's impressive!
It really is impressive.

Just as our sphere stood up
to a pair of 4x4s,

so Von Guericke's was also able
to resist the pull of two sets

of horses.

To Von Guericke, it was the
proof of something he had long

suspected, that gases like
air, exert an incredibly

strong force.

While the air around us may
appear calm, it is in fact

a mass of moving molecules.

As these molecules collide,
it produces an invisible push

that we know as air pressure.

That we don't notice this
pressure is because there's

an equal pressure inside
each one of us pushing

in the opposite direction.

And so the two
cancel each other out.

And that was why Von Guericke
needed to generate a vacuum.

You can only see how strong
the air pressure really is when

you take away the push
from the other side.

At the end of the
demonstration, all they needed

to do was let a little bit of
air back in, and it was almost

as though the pressure
hadn't been there.

[Air hissing]

The ability of molecules
to exert pressure is one

of the most fundamental
properties of not just air,

but all gases.

But Von Guericke's
discovery also raised

an important question.

If cold air molecules could
have such a powerful effect,

what might be achieved if
those same molecules were

heated up?

I've travelled to the north
of England to meet a bunch

of enthusiasts with
a head for heights.

Harry Stringer is from
the Pennine Region

Balloon Association.

He's been flying hot air
balloons for over 25 years.

Right, so where
are we going today?

Well, we'll clear
the treetops here.

That sounds like
a good start.

Yeah, and then
we'll go up to

about 1,000 feet.
- OK.

Hands on!

Czerski: The very first hot air
balloon, launched in 1783,

was the brainchild of two
brothers called Joseph

and Etienne Montgolfier.

Oh! We're free!

Stringer: OK,
we're away, John!

One story goes that Joseph
had been staring into his

fireplace one evening, when
he had the idea of filling

a paper bag with hot air.

On letting the bag go,
he observed that it

began to rise.

And this encouraged the
brothers to repeat

the experiment, but this time
with a much larger,

purpose-built balloon.

And the really ingenious thing
about balloons is how they

exploit a crucial
property of hot gasses.

The mechanism of these
is beautifully simple.

There's a bag above me
filled with hot air.

What the burner does is
allows the balloonist to play

around with the density of
the air by controlling

its temperature.

And as the air inside there is
heated up--and it could get up

to 100 degrees
Celsius--it expands.

As the air expands,
its individual molecules push

outwards, making the air
inside the balloon less dense.

Gravity is pulling everything,
everything I can see down to

the ground.

But because the air inside the
balloon is less dense than

the air around it, everything
around us is being pulled down

more, so it's squeezing the
less dense balloon upwards.

And so balloonists are
floating on top of the denser

air around them.

But temperature doesn't just
enable a balloon to rise.

It also controls how it falls.

So how do you
make us come down?

Stringer: We'll have a
parachute vent.

It's massive.
You can see it.

I could pull this red line,
and it will open the valve,

and then I just close it and
the gulp of hot air lost will

cause the balloon to descend.

We are safe.

- Can we stand up now?
- We can. We can.

Czerski: The discovery that
heating up air could make it

expand enough to lift people
into the skies was a milestone

in human innovation.

And it wasn't long before we
began to put that very same

heat energy to a much
more practical purpose.

It was something that
emerged from a very

18th-century problem.

300 years ago, mine owners
in Britain were facing

a serious crisis.

Since many ore deposits sat
well below the water table,

they were finding that their
mines could only go as deep as

the drainage technology at
the time allowed, resulting

in many mines going
out of business.

What was needed was a way to
haul all that water up to

the surface so the miners
could get to the ore below.

And in 1712, an ironmonger
called Thomas Newcomen hit

upon the answer, with the
world's first commercial

steam engine.

And it worked by harnessing
the immense energy

contained within
hot steam.

The principle behind
Newcomen's engine is exactly

the same one that Otto Von
Guericke had demonstrated.

And that's just how hard air
pressure can push, especially

when there's a vacuum
on the other side.

I've got a plastic bottle here
with some water in the bottom,

and I'm gonna put it in
the microwave to heat

the water up.

What's happening inside the
microwave is that the water

molecules are being given
energy, and they're not just

heating up but some of them are
turning into a gas, into steam.

And that steam is starting
to fill up the bottle.

And it's what happens
next that's important.

[Microwave dings]

Tip it into this water here.

Ooh! Ha ha ha!

And you can see that what
happened is that the bottle

has been crushed, and
it's now full of water.

And the reason for that
is that as it filled up

with steam, the
air was pushed out.

And then when I cooled the
steam down, it condensed from

a gas back into a liquid,
which takes up much less space.

And so there's a partial
vacuum left in the bottle

and so there was all the air
pressure pushing in, nothing

pushing back, and the
bottle was crushed.

And this is the principle that
Newcomen used to drive

his engine.

At the heart of Newcomen's
engine lay a large metal

cylinder housing a piston
and filled with hot steam.

Cooling this steam with
water simultaneously created

a vacuum and caused the weight
of the atmosphere to push down

on the piston,
driving the engine.

The cylinder was then refilled
with hot steam

and the cycle repeated.

Soon, Newcomen's steam engines
were popping up all over

Britain, each one a symbol
of heat's ability to perform

useful work.

But Newcomen's design had
one major weakness.

It was hugely inefficient.

Of all the energy in the coal
that it consumed, only 1%-2%

was converted into
useful mechanical work.

The mystery was why?

Where was all that
heat energy going

and what could be
done to retrieve it?

To discover the answer, we've
come to Coldharbour Mill

in Devon.

Originally built in 1797,
it's one of the oldest

steam-powered woolen mills
left in Britain.

Man: OK, try not to kill
anybody with the other end.

Czerski: John Jasper runs the
mill's giant steam engine.

- That's good.
- Like that?

- You are a natural.
- OK.

- Right side.
- Yes.

[Clang]
Oop! Ha ha ha!

So tell me
about these boilers.

This is a
Lancashire boiler.

It holds 20,000
gallons of water.

Above that water level,
you have steam.

[Steam hissing]

- Get a bit of steam up.
- Right.

So it's basically a
sort of steam kettle.

So these bits are
the heating elements.

Effectively, you're shoveling
fire into the heating element,

and then all of this is the
kettle which is full of water.

That's right.

But instead of coming out
of the spout, it goes to

a steam engine.

It takes a little longer
to get to the boil.

Ha ha! Better do some
more shoveling then.

Jasper: Yeah.

The engine here is a
descendent of a type that was

built to address the problem
of Newcomen's lost energy.

It was designed by a Scottish
instrument maker called

James Watt.

Watt had recently become
familiar with a new

theory of heat.

Creating steam is all about
putting heat energy into water.

But there's this strange
observation, which is that as

you start to heat water up,
you see the thermometer rise.

And it goes up and up and up,
and then it gets to

100 degrees and it won't
go any further.

So you can be pumping in
huge amounts of heat energy,

and yet the thermometer
isn't moving.

And that's because once water
reaches its boiling point,

all that heat energy is being
used up, turning the water

into steam.

And this led to the idea that
there are two forms of heat--

first the sort that causes
a thermometer to rise,

and second the heat required
to change matter from one

state to another,
called latent heat.

And the amount of latent heat
needed to turn water

into a gas is enormous.

And the reason that all this
matters for steam engines is

that steam is expensive
in terms of energy.

And when you've got it,
you certainly don't want

to waste it.

It was this revelation that
creating steam requires huge

amounts of latent heat that
was one of the main reasons

why Newcomen's engine
was so wasteful.

At the heart of every steam
engine, there's a piston.

That's where the hot gas
molecules are pushing to

create mechanical work.

And the problem with
Newcomen's engine was that

in order to reset, the water
needed to be condensed, cooled

down, and that happened
inside the pistons.

So the metal itself had to
be cooled down as well.

And then you needed to use
more steam energy to heat it

up again to create
the next stroke.

In order to conserve all that
valuable steam, Watt came up

with an ingenious invention.

Watt's solution was a
condenser, and this is it.

So instead of having the
condensation happening inside

the piston, the steam was
vented out to a separate

chamber, and that was where
the condensation occurred.

And the reason it was a
brilliant solution was that

the hot parts of the engine
stayed hot, and the cool parts

of the engine stayed cool and
much less heat was wasted.

Watt's great insight that the
more an engine can conserve

heat, the more efficient it
will be was a watershed moment

in the history of steam power.

Other improvements followed,
such as the introduction

of steam at high pressure to
generate even greater force.

These innovations ushered in a
mechanical revolution, founded

upon the energy of
hot gas molecules.

But as our population grew and
our coal supplies dwindled,

so we began to turn
elsewhere for our energy.

And in some places, that
has involved tapping into

a different source of heat...

one that's responsible

for some of the most
violent natural phenomena

on the planet.

Just a short distance
from Reykjavik lies one

of Iceland's top tourist
attractions...

an outdoor health
spa known as the Blue Lagoon.

This is the real attraction
round here, lovely warm water

at 38 degrees Celsius and
full of minerals, which are

apparently very good for you.

So, on a day like today and
in a country with a reputation

for being chilly, this
is clearly the perfect

place to relax.

But despite appearances,
this is no natural

beauty spot.

In fact, the Blue Lagoon is
entirely manmade...

fed by hot water from the nearby
Svartsengi Geothermal

Power Station.

Every day, Svartsengi
produces enough electricity

for around 130,000 homes.

And the source of all that
power is the same heat energy

that created Iceland
in the first place.

Directly below Iceland lies a
giant column of super-heated

rock, known as a mantel plume,
fed by heat rising up from

the Earth's core.

To tap into this immense
source of energy, Svartsengi

sits above 13 bore holes,
stretching 2 kilometers into

the rock below.

The basic premise here is
that a mixture of hot water

and steam is pumped up from
deep down, and the steam is

separated out and sent through
a turbine that generates

75 megawatts of electricity.

That goes into the grid.

And then the same steam comes
back around and reheats

the water, and that supplies
domestic hot water

for about 20,000 homes
on this peninsula.

For the engineers around here,
the hot water beneath their

feet is just one
massive treasure trove.

Channeling the heat of the
planet itself has allowed us

to take steam power to
a new level.

But today, scientists are
attempting to harness another,

even hotter, form of energy...
derived from a strange type

of matter that here on Earth
makes the occasional,

spectacular appearance.

[Footsteps climbing stairs]

Inside the University of
Manchester's High Voltage Lab,

a team of researchers is getting
ready to re-create one

of the most awesome natural
phenomena on the planet...

[Loud crack]
Lightning.

This beast of a device is an
impulse generator, and this

one is capable of generating
2 million volts between

the bottom and the top,
and here's how it works.

Normally when you get a
voltage, electric charge will

flow, but here, each of these
red things is a capacitor,

and so the electric charge
can't go anywhere.

It's stored on the plates,
and that means that energy is

building up.

And it's this point here
that's the important bit,

because when the switch over
there is pressed, all of that

charge is gonna get dumped
through that point

in around a millionth
of a second.

In charge of the controls
is Dr. Viddy Peesapati.

So what we're going to do
right now is make sure that

no one else can walk in.

So if you want to press the
black button on the interlock.

- That?
- Yes, that's the one.

[Buzzer]
Now it's ready.

Czerski: Under Viddy's
supervision,

we're going to
trigger a lightning strike...

You wanna press
F4 on the keyboard.

which we'll also capture
using a high-speed camera.

Peesapati: Now it's charging.

Czerski: So we can see the
voltage going up here.

Peesapati: Absolutely, so it
takes around 60 seconds

for the entire kit
to be charged up.

When this gets to the
end, we'll be ready to go.

Peesapati: We'll let the siren
go telling us that there's going

to be a flash-over, and it
automatically triggers

the first stage.

Czerski: 60 seconds later, and
the generator is ready to fire.

So when I hear the siren--

[Siren blares]

[Loud crack]

That is an echo
and a half, isn't it? Wow!

It is very loud, and that is
basically a sonic boom.

It's like a giant
electric whip-crack.

It is, absolutely.

Czerski: But it's only
when you play back

the slow-motion video

that you begin to see exactly
what lightning really is...

[Loud crack]

a super-heated channel of air,
with so much energy that it's

become an entirely
different form of matter.

[Loud crack]

We're used to the idea of
3 states of matter--

solid, liquid, and gas.

But what we've got here,
is a 4th, because the source

of all of that
light is a plasma.

[Crackling]

From the Sun's fiery surface...

to the clouds of interstellar

gas known as nebulae, plasmas
are found across our solar

system and beyond.

And it's this super-heated
form of matter that scientists

are hoping will enable them
to unlock a brand-new type

of energy...

by manipulating one of its
strangest properties.

This is a Crookes Tube,
named after the British

physicist William Crookes
who was one of the people to

design and use
it in the 1870s.

This was the piece of
equipment that opened the door

to plasma physics.

It's a sealed glass vessel,
and it's got two electrodes--

the negative one here and
a positive one here.

And on the inside, there's
just a little bit of gas

at very low pressure.

And when Crookes turned up the
voltage, this is what he saw.

[Loud crackling]

You can see that this is quite
noisy, but there's a green

glow down this
end of the tube.

Crookes called this eerie
light "radiant matter."

But Crookes didn't understand
what was going on, but we do,

and it's this.

When high voltage is applied
across the two electrodes,

it frees up negatively charged
electrons from the gas inside

that are then accelerated
towards the flat end

of the tube.

As they strike the glass,
they excite the molecules

on the surface, causing
them to give off light.

And it's the free movement of
electrons like this that is

the defining characteristic
of a plasma and which gives it

one of its most
distinctive properties.

I've got a magnet here,
just a small one.

So when I bring the magnet in
here, you can see that that

beam of electrons is being
pushed to one side or the other.

It's being deflected
by the magnet.

So I can actually control
what's going on inside

a plasma using electric and
magnetic fields, and that is

what makes a plasma
really interesting.

It's this in-built
electromagnetism that's opened

up the possibility of one
day channeling the enormous

energy inside super-hot plasma
and putting it to use...

by exploiting here on Earth a
different source of energy,

the same type of
energy that powers our Sun.

Inside a vast hanger at the
Culham Science Centre near

Oxford sits a machine so
complex, it contains well over

100,000 separate parts.

This is a fusion reactor.

Its job is to channel streams
of extremely hot plasma

and use them to manipulate
matter at the atomic scale.

The aim is to unleash the
power of the atom itself

and reach the holy
grail of physics--

nuclear fusion.

There's no way anyone would be
this close to a fusion reactor

if it was running, because it
throws off enormous numbers

of neutrons which can
do a lot of damage.

And that's why everything
around me here is surrounded

in concrete 3 meters thick.

Just at the moment, they're in
a maintenance phase so we can

get a little bit closer.

Showing us around the
reactor is Dr. Joanne Flanagan.

Czerski: What exactly is it
that all of this kit is

trying to do?

We are essentially trying to
create an artificial star.

Actually we do.
We create artificial stars.

We take hydrogen gas
and heat it up to very high

temperatures, where
it becomes ionized.

It becomes a plasma.

Czerski: What sort of
temperatures does it reach

on the inside there?

We routinely reach
temperatures of about

100 million degrees, which is
about 10 times hotter than

the center of the Sun.

That's just
a ludicrous number!

It's a number you can't
even get your head around.

It's a crazy
hot temperature.

We need such high temperatures
because hydrogen nuclei

repel each other.

To get them to stick, we need
them to collide at high speed,

and that's fundamentally
what temperature is--

high-speed particles.
- Right.

How do you make
anything that hot?

A first step is to run
a current through the plasma.

It's like an old-style
electrical light bulb.

And that gets us to a few
tens of millions of degrees.

But then we need
to pull additional heating

systems online to boost us
the rest of the way.

So you're just throwing
everything at it to get

energy into it.

Since there is no material
on earth that can withstand

temperatures of 100 million
degrees, the scientists

instead contain the plasma by
using its electromagnetism.

At the heart of the reactor
lies a giant metal doughnut

called a Tokamak that uses
a powerful magnetic field to

keep the plasma confined long
enough for the collisions that

cause fusion to happen.

The plasma would be in the
space that we're in here

and the magnetic fields,
where do they go?

The magnetic fields
curve around in the shape

of the vessel.

They have a sort of
an onion-like structure.

And they hold the plasma to
the shape of this vessel,

about 5 centimeters
away from the edges.

And the plasma is then
here in the middle, is it?

Right where you are.

Czerski: As all this plasma
is heated up,

so the hydrogen nuclei

inside accelerate, getting
faster and faster, until they

reach a speed where they can
get close enough to fuse.

So once you've had
a successful collision,

what happens next?

Then you have a very
fast neutron that comes out

of that reaction.

So it's the neutrons that are
carrying the energy out.

It's the speed, yes.

Czerski: Yeah, that would go
flying off, and it would heat

something up.
- Yeah.

Flanagan: The idea is that you
would have a lithium blanket

surrounding the entire device,
which would capture those

neutrons and heat up,
and you'd have heat exchanger

pipes that run through that
blanket that would then heat

water to drive steam turbines.

Czerski: But if we're ever to
master the searing temperatures

of fusion, then there's one
major obstacle that still has

to be overcome...

because for now, at least,
we've yet to find a way

of getting more energy out
from a fusion reactor than

we put in.

Until then, commercial-scale
nuclear fusion lies

tantalizingly
just out of reach.

I think it's very likely that
fusion energy, this technology

made possible by fantastically
high temperatures, will form

a significant power
source in the future

of our civilization.

Even though there's not yet
one clear solution, when it

comes to fusion,
the game is afoot.

From the searing heat of the
early Earth to the cooling

that transformed it and
allowed life to flourish,

temperature has been
fundamental to the story

of our planet,

but it's
also driven our story.

As our understanding of
temperature has grown,

so we've learnt
how to use it

to create new materials...

drive our machines...

and advance technology.

Temperature is such a big
idea encapsulated in just

one number.

As a physicist, it's the
first thing I measure.

And as a human, it's
the first thing I feel.

And yet our direct experience
of temperature is limited to

a really narrow range.

But once you learn about
what's beyond that--

the extreme heat, the extreme
cold, and all the subtleties

in-between--it's clear
that the possibilities that

temperature
offers are endless.