Take one.
Shall we?
Take a minute.
Look around you.
You probably never think about it, but we are living in a time
of incredible ingenuity.
Our lives are filled with fiendishly clever bits of tech that basically
make the modern world tick.
The problem is we're now so used to these devices...
..that we have forgotten to remember how clever they are.
SPEAKER: I don't have an answer for that.
I'm Professor Hannah Fry,
your hammer-wielding,
tech-curious tour guide...
Whoo!
..to the secret genius of everyday objects.
There is one law of physics that you need to know.
In each episode...
Whoa!
..I will take one seemingly ordinary item...
Immediately smoking.
..and I'll look at it in frankly...
Yeah!
..obscene detail...
Two googly eyes.
It has 180-degree view.
..meet the people who helped make it...
This is the very first air fryer.
..and follow the twisty turny journey through the history
of its invention.
If you overshoot the turning point, don't try to do this.
It's wobbly, Johnny.
Yeah, it's just the wind.
This time, it's the fridge.
Pretty much every other appliance that you get in your kitchen
is all about creating heat,
but we've had the whole cooking with fire thing down
for a very long time.
Sucking heat out of your food,
however - that is a lot trickier.
So how did this quietly cool customer come to be?
Whoa. Whoa.
It is the story of one man's explosive invention in the 1800s...
He almost blows himself up a couple of times, but it was worth it.
I feel like we're sort of matching.
..a 17th-century chicken incubator...
Look at that.
..and a revelation...
There's no doubt that CFCs are endangering the planet.
..that set fridges against the world.
It's always the quiet ones, isn't it?
The fridge has been keeping it cool in the kitchen
for just over 100 years.
From Hotpoints to Bekos, Samsungs to Smegs,
fridges are found in over a billion homes worldwide.
I'm in Germany to go behind the scenes at appliance giant BSH,
maker of all things Bosch.
They're the biggest fridge manufacturer in Europe.
They have their own railway line to get fridges to market.
And I'm going to check out the first one they ever made.
This is very cute.
I would have this in my home.
Oh, really? Yeah. It's from the '30s.
And so it was one of our first electric fridges we produced.
Meet Daniel Schweigert.
He's in charge of the production line here and is also
a rather charming host.
Do you want to have something to drink?
Obviously. Yeah. Come on.
Water? Yeah.
Great. Here you go. It's cold.
Yeah, of course it is.
Keep it chill.
This is just a 100-year-old fridge that still works.
I imagine in the 1930s, this was like a genuine revelation.
Yes. Was it expensive?
I think it was three months of salary back then.
Three months' wages. Yeah. So a lot of money for them.
Also very aesthetically pleasing.
Maybe not that practical as a design.
Yeah, but it still looks cool.
It looks really cool.
So how does this old fridge...
..and all the others that have followed...
..keep its cool?
Well, stick on those mitts and hold on to your hats, folks.
We're going to take apart the fridge and look at everything
from its smart thermostat...
..to its snuggly insulation.
But we're starting with all of these twisty, turny, tubey bits
that create the cold.
It's the cooling system.
On Bosch's production line, around 5,000 fridges
are produced every day.
So that is 1.5 million cooling systems assembled each year.
And it starts...with this bit.
This goes inside the cooling appliances and extracts the heat.
Sitting at the back of the fridge?
No, it's inside the fridge.
Inside? Yes, inside. OK.
The cooling system is essentially a component of two halves.
There's this cold bit hidden inside your fridge...
And then what else do you need?
We need this part.
It's a condenser.
You might be more familiar with it as the weirdly warm grill
that gets all dusty.
So this bit is the hot bit at the back?
Yeah, it's the hot bit.
The two parts are connected by a pump that drives the whole thing.
It's heavy. Try it.
Yeah.
The finished cooling system is what makes your fridge cold,
but not how you might think.
I think people imagine that when it comes to fridges, you're, like,
blasting cold air in, but you're not, right?
You're taking heat out.
Yeah. That's correct.
Extract the heat from the inside and gives it to the environment.
It is a nifty trick, all thanks to a hot bit, a cold bit, and a pump.
So, all right, then.
That's it really, isn't it? Bish, bash, Bosch!
More or less, yes. Bish, bash, Bosch.
They can thank me for that bit of marketing genius later.
As for exactly how the cooling system works,
let's get back to basics...
..at Fry's Fridge School.
We are in a place where people normally learn how to fix
the fridges, but I plan to do the exact opposite.
Thank you for your service, fridge.
I'm going to take you apart, but I'm not going to take you apart in a way
which means you're going to be able to be put back together, so...
This old thing was headed for recycling,
which should be the endgame for any unfixable fridge.
Faulty fridges aren't common, but their flammable innards
do pose a fire risk.
So it goes without saying, dear viewer, you must absolutely not
do this at home.
I'm extracting the cooling system, starting with the hot bit,
where heat from inside the fridge radiates away into the room...
This is the bit that gets warm, and then the compressor underneath.
..and the cold bit helpfully buried inside layers of insulation.
Oh, this is going to be fun.
I feel like an ancient Greek sculptor.
CRASHING
Think that was the shelves.
Yeah!
This is much more fun than playing with tiny screws, isn't it?
Oh, yes, there it is.
Whew! Cold bit.
Looks a bit different to Bosch's fancy pants cold bit,
but it does the same thing.
And now easy access to your eggs and milk.
These rather indecorously presented innards are where the magic happens.
Or what happened before I tore it apart.
So here we have the slightly mangled cooling system.
That's actually a really terrible name.
It should be called the heat-moving system because,
according to the laws of physics, cold isn't a thing.
Cold is just the absence of heat.
You can't cool something down.
You can only take heat away.
And that is what this one system is designed to do.
At its heart, the cooling system is just a giant snaking tube.
It is filled with a substance that is liquid in some parts
and a gas in others.
The substance is unsurprisingly called refrigerant.
More on that later.
But it's the switch between liquid and gas that's crucial.
One switch happens here in the evaporator.
You pop something in the fridge,
the heat of that thing gets absorbed by this part.
The refrigerant comes into the evaporator as liquid
and sprays out as gas.
And that process needs energy.
The gas absorbs all of the heat from anything
that you have inside the fridge cabinet.
All that heat energy then comes back round here, all the way up here,
and then into this part...
..a pump called the compressor.
This, as the name might suggest, is compressing that gas,
pumping, and pumping, and pumping to increase the pressure.
The compressor drives the refrigerant through the cooling system,
taking all that absorbed heat energy with it.
As it comes out here, then,
you've got this hot high-pressure gas that comes along
this tube, snakes its way all the way around, up and down, and up and down,
radiating heat out into the room as it goes.
And all the while it's condensing back into a liquid...
..ready to start another loop back in the same system again.
It's called the vapour compression cooling cycle, and it moves heat
energy in the opposite direction to the way it wants to go,
creating a cold space here and pushing heat energy out into
an already warm room here.
It's basically designed to cheat physics.
This is a one-way street for heat.
It's being absorbed from anything that you put inside your fridge
and then radiated out into the room
via this whole contraption.
So how did we figure out such a trick to shift heat to keep cool
in the kitchen?
Well, it all started with our enduring obsession
with cold, hard cash.
Just imagine -
the Industrial Revolution is in full swing,
but when it comes to keeping cool, things are still very much stuck
in the ice age.
I mean, they quite literally used ice.
The rivers yield a frozen harvest -
natural ice.
The ice kings of New England harvested ice from frozen lakes
and shipped it around the world, making them stupendously rich.
The demand was so great that a race began to invent a machine
that could make ice, powered by steam.
But the first attempt, built in 1834, didn't deliver anything
like enough ice to crack the US market.
Instead, the breakthrough came, perhaps unsurprisingly, somewhere
with almost no natural ice to harvest at all.
Australia.
In Geelong in southern Australia in the 1840s, there was a Scot called
James Harrison who was running the local newspaper, and that meant
he was very well aware of the issues that were facing the new colonies,
including the fact that they really struggled to keep anything cold.
Now, every now and then, there would be a shipment of ice,
but it was rare and extremely expensive.
In fact, the story goes that when the gold rush happened,
the prospectors who had a good day would go to the local hotel
and buy everyone whisky...
Give me a shot of a nugget nectar.
..but the prospectors who'd had a really, really good day
would buy whisky with ice.
Harrison had studied chemistry and mechanics and so spotted
that this was an opportunity.
Sheepskins were the country's main export, but the mutton mountain
left behind just went to waste.
Keeping food fresh was all but impossible.
And so, probably aware of earlier failed attempts, he decided
to have a go at creating cold himself.
So Harrison goes off to a cave in a nearby riverbank,
and he starts experimenting.
I mean, he almost blows himself up a couple of times,
but it was worth it...
..because, by 1855, he has built and patented
a prototype of an ice-making machine that actually works.
Harrison's invention was massive, with a steam-powered piston
driving the cooling system.
It was snapped up by businesses to chill that Aussie beer, of course,
and deep-freeze food for transport and storage.
And thanks to Harrison, we're doing the same today,
just in giant cold store facilities like this one in North London.
I mean, this is like, what, 1800s, right?
How much does this have to do with the kind of big fridges
that you get here? Quite a lot.
There are a lot of the components are essentially the same.
We're still using that vapour compression cycle today.
That is Lisa-Jayne Cook...
..president of the UK's Institute of Refrigeration
and the woman to call if you want to talk industrial-scale cooling.
I mean, this feels like a giant leap forwards.
Yeah, it was.
What is actually going on in all of this bit?
So, in the middle is the compressor elements.
The gas gets condensed over here, and then it goes
through into the evaporator, which then produces the cold side.
What's interesting about Harrison's invention - cos there were a lot
of other people already understanding the principles of it,
but they hadn't got that loop quite yet.
And that's the bit that makes this really genius.
Yes.
The telltale signs of Harrison's cooling cycle are everywhere here...
..like this hot bit on the outside.
Guess by the sound that these are the compressors.
They are the compressors. They're loud.
They are very loud.
While inside...
Because I am a newbie, I'm bringing a hat.
..it is absolutely Baltic.
Oh, my gosh, that is cold.
It is really cold.
But it like hits you as you come in.
This giant cold store can freeze up to 2,500 pallets of food.
It's crazy.
You can suck out that much energy out of a space that's this big?
It is incredible.
Thanks to Harrison,
the vapour compression cooling system had arrived.
I mean, you wouldn't last long in here, would you?
Like this place, it provided cooling for commercial customers.
But its steam-powered compressor was never going to fit
in your kitchen.
For domestic cooling, we must thank another unlikely hero -
French priest Marcel Audiffren.
It's 1894, and at his Cistercian monastery, he has a big problem -
keeping the wine cold for the monks.
Luckily, Marcel also teaches physics, and so is pretty
well-qualified to find a solution.
And so he constructs an ingenious hand-cranked compressor that sends
coolant through pipes in an insulated cabinet
and which, crucially, fits in the wine cellar.
He calls his device the dumbbell and patents it in France.
But it catches the attention of bigwigs at American
company General Electric.
In 1911, they release the electric Audiffren refrigerating machine.
At $1,000,
it costs more than the average American makes in a year.
But the fridge as we know it had arrived.
And with it came societal change that went
far beyond an ice-cold drink.
That cooling system that was built for these giant ice machines
was then shrunk down and put into domestic appliances,
and that meant that this wasn't just a technological triumph
because, OK, it might have been the ideas of a long line
of men, but it was women for whom this had a profound effect.
Because now that they had fridges, all of a sudden that daily grind
of shopping and cooking fresh had a release.
Leftovers, all of a sudden, were a thing,
and you could even go wild -
reheat food that had been cooked by somebody else.
Science presents the modern housewife with the refrigerator.
The arrival of appliances like the fridge in the early-20th century
were a game-changer for the lives of women at a time
of transformational change.
Women have joined the men in the production line,
and the percentage of women in industry is expected to be much
higher very soon.
Through the 1940s and '50s, women were joining the workforce
in significant numbers.
Finally, we were living the dream, working and still
doing the housework.
Of course, I don't let George know how easy homemaking has become
with modern equipment.
And by the 1980s, the fridge had become the kitchen staple
we know today.
The cooling system might be the heart of your fridge,
but it wouldn't work at all without our next component.
Time to find out what's in those twisty, turny tubes.
It's the refrigerant.
And back at Bosch, we are at the next step of the production line.
Here, in this area, we have the cooling system complete,
and now we need to breathe life into the refrigerator.
Breathe life. Yeah.
I like it.
That is Zoi Zachari...
..the woman who puts the actual lifeblood into your fridge.
What does the refrigerant do?
A refrigerant absorbs the heat from the food you have inside
and bring it outside through the condenser.
How much do you put in?
Between 35-55g.
Sorry, grams?
Grams, yes. 35 grams? You see it here.
That's like what? Ten teaspoons? Yeah.
And this is circulating the whole time you have your fridge.
Just ten teaspoons going round and round and round and round
and round forever. Yeah. Exactly.
Wow.
If you put more, I think it can blow up.
Which no-one wants.
Obviously, Zoi is joking, but this stuff is flammable.
The tiny amount of refrigerant gets injected
into the fridge's cooling system.
And so, naturally...
Can I do one?
Ah!
Um, I don't know.
Do you want to try it? Yes, I do.
OK.
Let me ask.
OK.
Long story short - I can.
If I get it wrong, what happens?
There will be a voice.
An alarm? An alarm, yeah.
You will hear it if you make a mistake. If I mess up.
No pressure.
Yeah.
OK.
Slightly regretting it now.
OK, so like this? Yes.
There we go.
The pipes are connected,
the system is ready,
and the refrigerant can, theoretically, flow.
So that's it, then? It's like the liquid is in there.
It's staying in there. Yeah.
So I've got a few minutes to wait until I know
whether I've mucked it up.
Number five. That's it.
At the end of the production line, the cooling system is sealed shut,
with its shot of refrigerant locked in there for the fridge's lifetime.
Oh, this is my one.
This is number five. Yes.
Ah.
It's fine. Great.
Was that an alarm? No.
Oh. It wasn't.
Everything OK.
You guys!
So, how does that tiny amount of refrigerant give
the fridge its cooling powers?
Let's discuss it over a drink.
It's got to be cold, doesn't it?
And with a few bits and bobs from behind the bar,
I'm going to show you.
OK, I have here some isobutane.
Now, this is the refrigerant that you get in most modern fridges.
Now, this stuff is flammable and dangerous to inhale
in large amounts, so don't go decanting this at home.
I'll just pour... Oh, you know what?
Safety first.
OK, right.
Thing about isobutane is that it can exist as a gas at room temperature,
but if I just pour some of this in here,
you can get it as liquid.
Now, already...
..this stuff...
..oh, it feels really cold.
And the reason is that the surface of the isobutane is evaporating.
It's kind of turning into gas.
But to do that, it needs energy.
And so it is taking in heat energy from the dish that it's in,
but also my fingers.
This is exactly how your fridge takes heat energy from your food,
as the refrigerant in the evaporator turns from liquid to gas.
Isobutane is so good at extracting heat energy from its surroundings.
If I put a little cup in here with some water,
just a tiny little bit...
..and I pop it...
Ooh.
SOFT SIZZLING
..can you hear it?
What's happening here is that the isobutane that is next to the cup
is turning into gas just by touching it.
As a result, the temperature of the water and the cup
are going to drop until eventually...
Oh, my gosh, I think it's happened.
You see the frost there? Look.
Look, look, look, look, look.
All that isobutane has evaporated.
You can see there's none left, right? It's dry on the bottom now.
And all we're left with is a little frosty cup.
Come on, little guy.
It's a teeny tiny ice cube.
Oh, it's got to be whisky on ice, doesn't it?
BAGPIPES PLAY
And there you go, look.
The world's teeniest tiny whisky on ice.
Cheers.
Don't expect me to be sober for the rest of the filming today.
Isobutane keeps things effortlessly chilled in many fridges today.
But how did we get here?
Well, it all started in the late 1740s when Scottish doctor
William Cullen realised that ether used to anaesthetise patients
had special cooling powers.
The more heat it absorbs, the quicker it evaporates.
When the spirit vanishes, the hand is left quite cold.
His work showed how liquids that evaporate easily remove heat.
But it took another 100 years for fridge inventors to catch on
and use them in those early cooling systems.
And when they did, it wasn't smooth sailing.
The refrigerants could be flammable and toxic,
and early domestic fridges were very leaky.
Albert Einstein even took time out from quantum mechanics to design
a safer cooling system after reading about a family who'd
been poisoned in their sleep.
Fridges were killer business, and in 1928,
it prompted the American company Frigidaire to act.
They called in their top chemist, Thomas Midgley, to find a solution.
Midgley started off with the periodic table, which apparently
he loved so much that he was rumoured to carry it round with him
at all times.
Now, he knew that all refrigerants at the time were compounds
that were made up from a series of elements that were largely
in this section of the periodic table.
He also knew that flammability of these compounds decreased
as you went from left to right, and toxicity decreased as you go
from bottom to top.
And all of that together pointed towards fluorine
as being a particularly promising candidate.
Midgley set about combining fluorine and related elements
like chlorine with carbon.
After just three days, finding a frontrunner -
dichlorodifluoromethane.
Try saying that after a teeny tiny whisky.
And as refrigerants go, this brand-new compound seemed perfect.
At the 1930 annual meeting of the American Chemical Society,
Midgley decides he wants to show off his new refrigerant
to all of his colleagues.
Now, this guy, he's quite the showman, and he is deeply invested
in the success of his invention.
And so he gets to the stage with a vial of the stuff and also
a candle, which he then lights.
Now, to really prove a point,
Midgley then pours the vial into a bowl...
..waits for the refrigerant to evaporate,
inhales a great lungful of the stuff...
..and then turns and exhales to the candle.
In one fell swoop, he has demonstrated that this stuff
is neither toxic nor flammable.
It's marketing genius.
This little can with a button on top is used in hundreds of ways
to make your life easier and more pleasant.
They called it Freon, and it was a roaring commercial success.
Used as cooling agents in the coils of your refrigerators,
Freon does its work by changing from a liquid to a gas.
Its low boiling point, stability, and safety meant it became
the world's most commonly used refrigerant in
air conditioners and fridges.
Freon refrigerants are ideal.
They've helped the entire refrigeration industry grow
into a $2 billion business.
It was the first of a new class of chemical called
chlorofluorocarbons,
otherwise known as CFCs.
Better things for better living...
..through chemistry.
It was in the 1980s, once CFCs had made their way into almost
all of the fridges on Earth,
that a young scientist discovered there was a problem.
If we took all the ozone from above us down to this lab,
I'd have a layer of pure ozone just three millimetres thick.
Meet Jon Shanklin
of the British Antarctic Survey.
For almost 50 years, he has been monitoring the health
of the ozone layer.
Between 10 and 25 miles above the Earth in what's called
the stratosphere is a belt of ozone.
If it wasn't for this protective layer, our planet would be a place
of uninhabitable extremes of hot and cold.
Until the 1970s, people assumed that there was nothing we could do
to destroy ozone, which is kind of like the Earth's sunscreen.
But then some theoretical chemists realised that, with time,
CFCs might interact with ozone to reduce the amount
in the ozone layer.
Recent theoretical tests appear to show when the fluorocarbon hits
the ozone layer - first, it breaks down, and when it breaks down,
it releases chlorine atoms.
The chlorine atoms attack and destroy the ozone.
At that point, it was only sort of hints that the chemistry
might support that.
It was by no means proven theory.
The only way to prove it would be to show the ozone layer
was getting thinner.
When I joined the survey, quite a big backlog of observations
had built up.
This was the data that Jon needed.
And in analysing it, he realised the most recent ozone levels
were much lower than expected.
Once you can demonstrate a consistent trend,
then either it's the instrument failing, or it's something that's
going on in the atmosphere.
The ozone data had been captured in Antarctica, and so Jon went
there to investigate.
I was convinced that the observations had been made
correctly in Antarctica, that my calculations were right,
and that something was going on.
To find out if the ozone layer was in the danger he feared,
Jon decided to go further back,
to analyse all ozone data they'd ever collected.
I'm quite bloody-minded, and once I've got my teeth into something,
I don't really want to let it go.
Plotting each individual year up on the graph seemed the obvious
thing to do.
This must be my original draft paper.
It's written in November 1984.
Between 1957 and up to 1972, you could quite easily draw
a straight line, but thereafter, it's really clear to anybody
that ozone values are dropping,
and you couldn't really disagree with that.
Jon's deep dive into the data revealed that in the space
of just ten years, over Antarctica,
half of the ozone had disappeared.
This was the smoking gun he'd been looking for.
It was really quite exciting, I think,
drawing that final line.
Once I had everything plotted out,
absolutely clear-cut.
That was, "Yeah, I've got it."
Jon's paper, published with his bosses Joe Farman and Brian Gardiner,
alerted the world to the dramatic loss of ozone,
boldly stating that the threat from CFC refrigerants was real.
And then possibly a journalist, possibly a scientist,
"Looks like a hole.
"Oh, Ozone Hole."
And that describes it instantly.
This satellite image shows the hole, coloured blue, as it moves
and changes shape.
There's no doubt that CFCs are destroying the stratospheric ozone
and may be endangering the planet.
Jon's discovery had an immediate impact.
The problem is serious.
Changes are taking place.
And therefore, in the immediate future, we should strive
for international regulations.
Within two years, it was agreed that CFC refrigerants
should be banned worldwide.
One big firm already takes back old fridges and freezers and drains
out the CFC, which is returned for recycling.
They process some 500 fridges and freezers a day.
In the late 1980s, CFCs were replaced with more
ozone-friendly hydrofluorocarbons, or HFCs.
It was great news for the ozone layer,
which has since almost recovered, but bad news, too,
because HFCs are a major cause of climate change.
And so they are being replaced, too, with a new wave of refrigerants
like isobutane that have less of an environmental impact.
Our next component isn't quite so controversial.
Always in control, and with a licence to chill,
it's the thermostat.
And back at fridge school, it seems to be hiding in here.
Smells a bit like stale milk.
May the yanking...
Let me see if I can pull this out.
That's a technical term there.
..commence.
Oh, that is satisfying.
Oh, hello.
Oh, yeah.
Oh!
This is it, then. Thermostat.
This one's a lot bigger than you would find
in a more modern fridge,
but this old gal still has a pretty smart way to control the cold.
It uses this quite clever little trick that is hidden inside here.
If I smash it open?
Yeah, let's do that.
Look, I'm about to get excited.
Oh, my gosh, look at it.
I'm so determined.
But I really want to show you... SHE CACKLES
Look at this!
Look! OK.
..just how cool this is.
All right, that's legit exciting.
Kind of want to get in there, don't we?
SHE LAUGHS
I know it's really pathetic, but I'm really excited.
Oh, yes.
Hello.
And we're in.
This wire here, then.
So this is tucked in to the coldest bit of your fridge.
This is monitoring the temperature inside.
It actually contains a tiny amount of refrigerant.
And this will expand or contract depending on the temperature.
Kind of comes up through here...
..where it either pushes or pulls on a teeny tiny set of bellows
that then makes or breaks an electric circuit.
This is like a physical switch that is responding to the temperature
inside the fridge,
switching on or off the cooling system.
When you turn the dial, what you're doing
is you're physically changing
the point at which this circuit closes.
It's how you set just how cold you want the fridge to be,
simply by using the dial.
I mean, that's, like, just so delightful, isn't it?
So how did we come up with this little beauty
that automatically turns the cooling system on and off
to make sure that the temperature stays constant?
Well, it all started in a time before fridges,
when our diet was determined by the seasons
and if you're a fan of chicken, the friskiness of your fowl.
In about the 1600s, people realised that chickens had this potential
to be cheap and filling food for a lot of the population.
The only problem was that producing enough of them
proved to be quite a challenge.
Excuse me, girls.
Oh, she's lovely!
Look at that.
I feel like we're sort of matching.
Do you know what I mean?
For a fertilised egg to turn into a chicken you can eat,
it has to be sat on by a broody hen and kept perfectly warm
for 21 days straight.
Come on, girls.
Various ways to incubate eggs artificially had been tried.
Hello, girlie.
Oh! Is it OK if I have your eggs?
But on the whole, nothing beats what nature had intended.
Ideally, you want something that can replicate the precise
and constant temperature of a hen's bum.
Bear in mind that in the 1600s,
cutting-edge science was served up by royal court magicians...
..and there was none more famous than Cornelis Drebbel.
So this guy, Drebbel, he's a prolific inventor.
He comes up with a submarine, a perpetual motion machine,
and then he decides to take on the chicken production problem
by having a crack at the world's first thermostat.
And as if by magic...
..here it is.
Look at that!
We have created an...
HESITATING: ..exact replica of the thermostat mechanism that controlled
the temperature of Drebbel's ingenious egg incubating machine -
with just one slight difference.
So here we have a heat lamp.
Now, in Drebbel's case, obviously before the discovery of electricity,
this would have been a fire instead.
Let me just switch this on here.
This tube is filled with flammable alcohol,
so we decided to keep fire out of the mix this time.
Oh, that is nice and warm, isn't it?
You have to imagine, then, that you've got your eggs
in a little container just here,
and this tube here is monitoring the temperature.
Instead of a hen keeping them warm,
the eggs are surrounded by a water bath, warmed by the fire.
And the tube containing alcohol sits in the water too,
warming up alongside it.
Alcohol expands as it gets warmer, and so as it expands,
it pushes down this tube all the way round to the bottom here.
Sitting in the bottom of this U-bend is some mercury,
which feels the pressure from the alcohol.
In turn, the mercury moves through the tube,
and as it's so dense, it creates a lot of upwards force.
Now, here we have this sort of... It's like a cork, basically,
with a pin stuck in it.
And slowly, slowly, slowly,
as this bit here warms up and expands,
this pin is going to move upwards,
until eventually, the magnet stuck to it
is going to switch off the heat lamp.
In Drebbel's device,
the pin pushed up onto a damper
that controlled airflow needed for the fire to burn.
I sort of feel like it is moving very, very slowly.
Look, can you see now how it's slightly lower
on this side than that side?
The temperature rises, the alcohol expands
and pushes the mercury up.
Here we go.
It's getting super, super close.
It's going to switch.
Oh!
No boiled eggs for us.
In the same way, when Drebbel's incubator got too hot...
..the damper closed, quelling the flames
and cooling everything down a little.
The mercury would then fall until the damper opened again
and the fire was stoked.
This is now perfectly self-regulating.
It heats up, turns off, cools down, turns on.
You can leave this be and come back when your chickens are hatched.
Chicken problem?
What chicken problem?
Well, it wasn't quite solved,
because Drebbel's thermostatically-controlled incubator
was way ahead of its time.
And as far as we know, no-one ever managed to reproduce it.
You have to imagine, right, Drebbel was doing this at a time when
most of the physics of what's going on here
was yet to be discovered, right?
No idea about thermal expansion, no idea about hydraulics.
And then tune it perfectly
to the precise temperature of a chicken's bum.
It is absurd that he was able to successfully do this in the 1600s.
In fact, it took over 200 years
for a thermostat using the same principles to be patented.
The spectacularly-named Damper Flapper automatically controlled
the temperature in early home central heating systems.
And 100 years later, it inspired the design of the first
modern mechanical fridge thermostats,
like this one.
Today, the team in Bosch's development lab
are giving the thermostat a 21st-century upgrade.
The compressor is our heart
and the thermostat and our electronics are the brain.
Oh, nice. And they are connecting with each other.
That is Inaki Sola,
master of modern thermostatic magic.
This was state of the art, but 20 years ago. Mm-hm.
Now what's the state of the art?
Look at the size. Mm-hm.
This is the same function you see over there, in this big part. Yeah.
This electrical one.
And what happens, we have here, a resistance.
Yeah. And this is changing the electricity moving into this cable.
So, wait, this is just like a thermometer, is it? Yeah.
By detecting changes in the flow of electricity in this cable,
the temperature can be quickly and accurately measured
here at the top of the fridge and converted into a digital signal.
So you've gone from mechanical to digital.
Exactly.
But with a digital signal, this fridge's brainy thermostat
can do some cool new things.
Right, let's imagine... Yeah. ..that I come in and I'm like,
right, I've cooked a really big stew.
Yeah. Irish, thank you.
And I've just put it in there. Very irresponsible.
I've put it in there while it's still hot.
Yeah. The fridge can tell?
Yeah. It can tell?
Yes. You put the stuff here. It's really, really hot.
This warm air goes to the thermostat, to this. Yeah.
And this means, he's realised, "Oh, something changed." Mm-hm.
And it sends a signal to the brain, our electronic and say,
"Hey, compressor, start running."
The super smart bit is what happens next.
We are able to control the flow, the air flow circulation,
and then the cold air distributed by this fan unit
will start flowing all round... Mm-hm.
..ensuring that when you set here, for example, +6 degrees,
you have everywhere six degrees.
Oh! Yeah.
Bosch's robots test their smart thermostat
and airflow control to the max.
Whether it's shoving in warm leftovers
or keeping the door open for ages,
they simulate the lot to make sure the entire fridge
stays within 0.5 degrees of the temperature we choose...
..with one exception.
So you see here you can choose from two to eight degrees,
but here, it will always stay close to zero.
Why do you want that?
I will show it to you. Yeah, go on.
Same appliance. Touch this.
Oh, hello! Some stunt veg.
How long has that been in there?
That is a manky carrot! Almost four or five days.
Four or five days?!
Yeah. And now compare it with that.
Did you really put these in at the same time?
We bought them both the same day.
OK. And then, wait. But then there's also the salad.
Yeah, the salad is also here. It's also the same.
So you can compare them.
And people are not aware about that.
By varying the temperature in different sections of the fridge,
smart thermostats in many modern fridges
don't only save you from veg wilt,
they also allow the fridge to use less energy, saving us cash.
I've got to be honest with you, I have never once adhered
to the pictures on the drawers.
I know. It's our pain.
I thought it was just like, you know, hey, helpful suggestion!
This is, like, a cute-sized drawer.
I didn't realise you were designing the entire thing to be perfect.
But this is really important. You should really take care of that.
All right. I'm going to go rearrange my fridge when I get home.
Yeah.
THEY LAUGH
May we now consider ourselves officially schooled
in proper fridge usage.
With so many bits dedicated to hoofing heat out,
it's time for the component that stops it getting back in.
Quietly crucial,
hiding just beneath your fridge's shiny shell.
It's...
..the insulation.
Remember all that stuff I was hacking away at earlier on?
This is the insulation,
and it is not there to stop the cold from escaping.
No. We've spoken about this.
It is there to stop the heat from outside getting in.
If I take a little bit of this,
I can show you how it's able to do this under a microscope.
And it's only when you magnify a really thin slice...
Just a little bit of that there.
..and look at it with a powerful lens...
Look at that. Wow!
..that you can see just how insulation...
Oh, my gosh!
..does its insulating thing.
You really can see the plasticky strings that are just encasing
bubble after bubble after bubble after bubble.
And, like, layers and layers and layers of them.
This plasticky material, called a polymer,
is bad at transferring heat energy,
and so is good at insulating your fridge.
But what's more important...
It's, like, almost all bubble.
..is the unique foamy structure it creates.
All of these bubbles trap air, and when air is trapped,
it can't move heat.
It's almost all air.
That's what you don't realise.
And that is what makes it a good insulator.
And I'd love to show you just how well it keeps heat out of the fridge
by turning these on it.
But unfortunately...
..foam insulation is quite flammable, so, um, instead...
What, I have to do it?
..it's tidy-up time.
Have we got a dustpan?
There you go.
So how did we end up with this messy but quite miraculous material?
Well, the insulation used in early fridges was stuff like wool
that naturally trapped air.
ARCHIVE: The cabinet is insulated with pressed cork.
This makes any leakage of heat a very slow process.
Wool and cork were gradually replaced.
The latest insulation material is aluminium foil.
But this was as good as it got...
..until the 1930s, when the spectre of war...
Our defence programme will be no more than is sufficient.
..and an accidental experiment began a synthetic insulation revolution.
There are so many different combinations of chemicals
that you can add together to make surprising things.
Meet materials maestro Anna Ploszajski.
And what she doesn't know about these things
is frankly not worth knowing.
Back in the 1930s, World War II about to happen,
trade routes internationally are starting to break down.
Suddenly, lots of countries weren't able to get access
to materials that they're used to, particularly natural rubber.
So there's a big challenge, really, to the chemical community of,
can you make this stuff in the lab?
It's 1937, and at pharmaceutical giant IG Farben,
the challenge falls to a young scientist called Otto Bayer.
He's really interested in this problem of,
can we make a new synthetic rubber?
And one day, he added two chemicals together.
What we now know is that one of those chemicals had
a bit of contaminant in it, which he didn't realise. Oh!
And that contaminant actually made a big, bubbly, foamy mess. Ooh.
And he showed it to some colleagues and they said,
"Otto, we don't need a Swiss cheese."
THEY LAUGH
Oh, poor guy! "We need some rubber."
And so a lot of his colleagues were doubting him,
but he believed in his foams, and so he continued to work on them.
In honour of Bayer's tenacity...
Do I need to worry about my own kitchen here?
Not at this stage. OK.
THEY LAUGH
..we are going to recreate his accidental discovery
of what today is called polyurethane foam.
How much am I putting in? 35ml.
OK.
Our ingredients are two different liquids
that individually don't do much...
What we're going to do is pour both of these at the same time
into that beaker. OK.
You ready? Yep. Three, two, one.
..but when combined...
Very good. OK. Now you can stir, stir, stir. OK.
..it is a different story.
Ooh! It's getting bubbly. Right. So you can see it bubbling
straight away. Yeah. What, are we putting it in that one?
Yeah, it's going to go... Is that how big it's going to go? Yeah.
All right.
Sorry, yeah. Pour it?
OK. I don't believe you.
Oh! And now watch. Come on. It's growing.
HANNAH GASPS
Ta-da! Oh, my goodness.
It looks like when you've over-poured a beer.
Molecules in the two liquids are linking together
into long, stringy polymer chains that can build a solid.
And it is a bubbly one
because in the process, a gas is also released.
OK, I have a strong feeling this could go over the top.
THEY LAUGH
Here it goes. Oh, my gosh.
Oh, my gosh! Shall I catch it?
Yeah, go on.
Looks like... Oh, it's quite warm. HANNAH LAUGHS
It looks like something's being birthed. Oh!
Whoa!
OK, that is the weirdest thing.
THEY LAUGH
Weird, indeed.
And at first, not even Bayer quite knew what to do with it.
I have to be honest with you,
I'm just imagining that day in the lab when he's, like,
pulling out the streams of this stuff in front of his colleagues.
GERMAN ACCENT: "Look, it's a new invention!"
Yeah, I mean, it's fair enough they weren't that impressed. It is.
Just a couple of years later,
war broke out, and the company IG Farben
became a central participant in the Nazi killing machine.
It would be another ten years, long after the war...
..that the potential of Otto's discovery would be realised.
ARCHIVE: Science presents a new synthetic sensation.
It's the world's lightest solid.
In the early 1950s, polyurethane foam took off.
As an insulating material for houses,
refrigerators and aeroplanes.
With tweaks to the recipe, it could be mass manufactured.
This machine produces polyurethane foam.
In a soft and squishy form for home furnishings,
or light and rigid enough to hit the surf...
Clamped on either side are blocks of stiff polyurethane foam.
..its insulation powers were so good that it even took us to the moon.
Magnificent desolation.
As the cooling industry boomed,
it would become the only choice for fridge insulation.
And today, it's what beats the heat
in nearly all of the world's household fridges.
So where does the fridge go from here?
Well, the next big breakthrough
could change how its innards work forever,
because the future looks rather more magnetic.
For over 100 years, the humble fridge has been chugging away,
brilliantly keeping stuff cold.
But there is a cost.
The 200 million fridges bought worldwide each year
are big, resource-heavy beasts, and much of their materials,
from the insulation to the refrigerant,
take their toll on our rapidly warming planet.
So what if there was a greener way to chill?
There are three billion cooling appliances in operation today,
and that's going to grow to over ten billion by 2050.
So this is an enormous industry.
That is Neil Wilson.
From this unassuming workshop in Milton Keynes,
his company are developing a radical new fridge,
built from recyclable materials and, crucially, without
the most problematic component.
When we began the company,
we really were worried about the refrigerant gases.
They're a lot better than they used to be, though, aren't they?
Are they still problematic?
There's an enormous amount of HFC still used,
and that drives global warming.
And even many of the alternatives are flammable or explosive or toxic.
So you want to change that? We want to change that.
We want to bring in a new technology
that doesn't use refrigerant gases at all.
It might not look like the future of refrigeration,
but Neil's alternative is this small piece of metal on the end of a stick.
Now, this material has one special property.
When it goes into a magnetic field, it changes temperature.
I'm going to put it into the field.
It's gone up!
Oh, loads! A couple of degrees. So it warmed up. Yeah.
And now the heat that was generated, that's just now dissipating.
So now when you pull it out, what happens?
So now... It dropped! It's gone down.
You're cheating physics!
There's no cheating at all. Nothing's touched it,
and it's gone down in temperature.
It's not actually cheating.
The metal cools because of the way magnets affect the energy
of the tiny little electrons.
When we put it into the magnetic field,
the electrons, which were just buzzing around...
Having a nice old time. ..having a nice old time,
suddenly are in this ordered state.
A bit like a musical statue, they stop.
So that energy gets transferred into the metal,
and so the metal warms up.
And then when it comes out, the heat goes out into the room,
meaning that ends up getting colder. Precisely.
That is cool.
I'm extremely impressed by this, but you're only getting down to
about 20 degrees, and that is still too warm for milk to not go off.
Absolutely. So the material is key, but we need to engineer it
into a device that effectively amplifies the effect.
The solution is surprisingly simple -
take a bunch of these bits of magic metal, stack them up,
and get a great big magnet spinning around them.
This allows us to create a continuous cooling process.
Got you. So at any point in time, some of the materials are
going into the magnetic field,
and at the same time, some is coming out.
I see. So you're continuously driving
this heating and cooling of the material.
What we have flowing around our loop is essentially water.
So you've basically got the water doing kind of the same journey...
Kind of, yes. ..as the refrigerant gas does in a bog-standard fridge,
moving the energy around. Absolutely.
I can start the magnet spinning.
Then turn on the pump.
The cold loop that was sitting at room temperature,
that'll cool down to around four or five degrees.
Fridge temperature. Milk temperature, yes.
You should now be able to feel this loop getting cold.
Ooh!
If it was inside an insulated box,
it would cool the box down a bit colder.
Amazing.
Can you just pop this in the bottom of a fridge, then?
Yes. This has actually been designed to fit
into a standard mass-produced fridge.
It's still early days, but Neil has developed a commercial version
and is also working with a domestic fridge manufacturer.
It may be that soon the tech that makes our fridges tick
will look fundamentally different...
..but the fact that it has remained largely unchanged for 100 years
shows just what an extraordinary invention this is.
The thing I can't get over is this idea that
if you lived in a hot country before any of this happened,
you would never have experienced anything cold,
because there are strict rules to physics that cannot be broken.
You cannot move energy to where it does not want to be moved,
until someone worked out a way to do it.
And that, my friends, that is cool.
ARCHIVE: And there you have the secret of the refrigerator.
Next time - it's the roller-coaster.
Oh, my God!
It's the story of some dodgy French physics in the 19th century...
Basically a torture device that you pay to go on.
..NASA rocket scientists...
We can simulate the forces twirling the man round at a suitable rate.
..and the vast vision of a cartoonist called Walt.
He says, "Bobby, build this."
Build a mountain.
The Open University has produced a free poster
exploring what lies behind the genius of some everyday objects.
To order a copy, call...
..scan the QR code or go to...
..and follow the links to the Open University.