Original subtitles

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.