Original subtitles

(mysterious music)

Everything in our universe has its size.

Planets are big,

insects are small,

people are somewhere in between.

Everything has its place in the grand order.

But does it have to be this way?

Does size really matter?

Wouldn't it be better

if everything were bigger?

After all, big animals live longer than small ones

and studies show that tall people are more successful.

So why are things the size they are

and what if we could change that?

Using the latest science,

we are going to do the ultimate thought experiment.

We are going to increase the size of everything,

and that includes us,

to see whether a bigger world,

really is a better world.

We're going to discover just how much size matters,

how it defines everything.

You'll never look at yourself or your world

the same way again.

(dramatic music)

(gentle music)

You might think this looks like an ordinary house

on an ordinary sunny morning.

In fact, you are looking at a parallel universe.

One just like our own

but with one important difference.

(alarm beeping)

In this universe, we can change the size of things

just to see what happens.

We're going to follow a normal guy

going about his normal day

and see what happens to him

when we increase the size of stars, planets

and living things.

We'll find out if the way things are

is the only way they can be

and explore the consequences of a world

where things are bigger.

Call it a thought experiment, if you like.

Something scientists have always used

to explore the workings of the universe.

Thought experiments are vitally important for science

because with thought experiments

we have a way to quickly explore

the realm of possibilities

before we engage in very detailed calculations.

So whenever we start any question in science,

we begin with a thought experiment.

By changing the size of things,

we're going to explore the laws of nature

and find out if there are limits

to how big things can get.

It's a thought experiment

that will give us a deeper understanding

of how things work in the real world.

And we're going to begin

by changing the size of planet Earth itself.

With a mass of six billion trillion tons,

that's a six followed by 21 zeroes,

the planet Earth is only the fifth biggest

of the eight planets of the solar system.

Let's compare it with number one, mighty Jupiter.

Jupiter is 11 times the width of Earth

and has 318 times the mass.

What would life be like

on a Jupiter sized Earth

and would it even be possible?

We're going to take things slowly

and start by gradually making Earth bigger

until it is twice as wide as it was.

By growing the planet,

we are going to find out

how much its size really matters.

Our infrastructure,

roads, bridges and buildings,

are all tailor made to fit the current Earth.

So it's no surprise

they won't cope if the planet starts slowly growing

towards the size of Jupiter.

But they're more resilient than you might think.

Bridges at least

are designed to expand a little.

So it'll be a few moments

before everything falls apart.

Roads can be rebuilt

but the most important consequence

of changing the size of a planet

is far harder to work around

and that's gravity.

Gravity is the key force

that governs the universe and nature

on the largest scales.

And at very basic levels,

every object in the universe

is attracting every other object

according to its mass.

The more mass, the stronger the force of gravity.

As the planet continues to grow,

Earth's gravity will get stronger.

The first casualties

would be low Earth orbit satellites.

Even if their orbits

grow in proportion with the Earth,

the planet's higher gravity

would soon pull the closest down

into the upper atmosphere.

Then, atmospheric drag would do the rest.

Falling satellites are just the beginning.

But what does higher gravity mean for humanity?

What would be the effect on our bodies,

our health

and how much more gravity can we take?

As you will see,

higher gravity is a big challenge.

There are a few people

who actually know what life on a bigger planet feels like

because they've experienced

something just like higher gravity, G-force.

To do his job,

royal air force typhoon pilot Mark Long

has to deal with extreme G-force.

G-force is like an increase

in the gravitational effect.

Your arms feel heavier.

You find that breathing's a little bit more difficult

because you're working harder against the force

that you wouldn't normally be exposed to.

So it's like gravity but just more intense.

(dramatic music)

Today, he's flying a display routine

which will push him and his plane to their limits.

(dramatic music)

As the plane turns,

Mark is pushed into his seat by G-force.

Albert Einstein's equivalence principle

tells us that the effect on his body

is just like higher gravity.

So that what he experiences during some maneuvers

feels exactly the same

as being on a higher G planet.

So I've just bottomed down from a looping maneuver here

and I'm turning the jet into a barrel roll maneuver.

It's quite slow

so the G-force is around two and a half at this point.

And as I get towards the bottom maneuver,

it starts to increase.

Back in our parallel universe,

Earth is now twice as wide as it was.

That means the planet's circumference

and the gravity at the surface

have also doubled.

So two G actually feels alright.

You can look around fine,

you can move your head

but everything is just a bit more of an effort.

Moving around under two G conditions would be tiring.

Life would be very slow,

you'd be lethargic,

moving your legs would feel heavy.

You'd just take longer to do stuff

and you would feel tired at the end

of every activity you tried.

Our infrastructure destroyed,

humanity brought to its knees,

a mere doubling of the radius of the planet

could be the end of days.

But we're not finished yet.

As this is a thought experiment,

let's just say that everyone survives

and rebuilds to suit two G.

It's a world in which standing up

is to be avoided.

If I was lying down,

now the heart hasn't got to work so hard

and life would be a lot easier.

The distance between your heart and your head

is the most crucial thing in the vertical sense

because your heart has to pump the blood against gravity.

So the best physique

is actually fairly muscular, quite short.

It turns out the upright human design

doesn't deal well with higher gravity.

Had our planet been bigger,

we might never have evolved.

(mysterious music)

Unfortunately, two G world

has yet more pain in store.

Changing the size of Earth

upsets the cosmic apple cart.

Our moon sits in perfect equilibrium with the Earth.

If you make the Earth twice as large in radius

and eight times more massive,

it has a dramatic effect on the moon's orbit.

The moon would be pulled

into a strange new orbit

that would pass much, much nearer to the Earth.

Not close enough to hit

but you'd soon see the difference.

But this moon also has a dark side.

In its normal orbit,

the moon causes tides in our oceans

that are seldom more than 10 meters high.

If we had tides operating

with this moon coming very, very close to the Earth

then in fact, the heights of the tides

would be extremely high.

So obviously there are some cities around the world,

many cities in fact

which would become uninhabitable under those conditions

because you'd have these great big tidal waves

sweeping around the planet.

With the moon now passing so much closer,

tides could be up to 1,000 meters high.

But so far, we are nowhere near the size

of the largest planet in our solar system.

(dramatic music)

But just what is the limit

for the human body?

Doing 350 miles an hour at this point

with the jets accelerating all the time,

so I'm going through 4G, 5G, up to 6G

as I turn on to a crowd line.

At 6G I don't think the human body

would be able to function on a bigger planet.

It would be incapacitated.

You would just be spending your whole time

trying to fight against the G-force.

You wouldn't be able to do anything.

In fact, you'd probably spend your entire life laying down.

But laying down

won't help with what happens next.

Because when the Earth reaches half the width of Jupiter,

something very strange happens.

The air itself becomes toxic.

As the increasing gravity of massive Earth

pulls the atmosphere closer to the surface,

the oxygen is more tightly packed in.

There are more and more oxygen molecules

inside every lungful.

That may sound like a good thing

but oxygen is a highly reactive element.

We are designed to cope with a certain amount.

Too much of it can cause violent seizures,

eye and breathing problems,

loss of consciousness,

and eventually death.

So even the air we breathe

depends on the size of the planet.

(dramatic music)

And we're not finished yet.

I'm preparing my body right now

for this onslaught of G's.

So as soon as I enter that turn, I'm at 9G.

I can barely move my head

so I'm forcing my body against the edge of the seat

to look 'round

with my reference point ready for pitching up for the loop.

When I pitch up for the loop,

I know this could be another 9G maneuver.

So I've pretensed my body.

And now as I get to the top of the loop

I'm relaxing into the G-force.

I've had the typhoon up to 10.4G

and it was painful

and I would hate to be on a plant that's 11G.

In fact, I'd look for a different planet.

As the planet nears the size of Jupiter,

insect and other invertebrates

will cope better with the higher gravity than humans.

But that won't help with that happens next.

With gravity now 11 times what it was,

the moon would be pulled from its orbit.

So if you make the Earth 11 times bigger

which is essentially the size of Jupiter,

the moon can no longer go around the Earth anymore.

It will crash into the Earth

and it'll crash into the Earth in about three hours

from the point

where you actually increase the mass of the Earth.

The Earth's gravity

is now just too strong for the moon to stay in orbit.

(moon exploding)

The result would be catastrophic.

Life as we know it could not survive

an Earth the size of Jupiter.

Size connects every part of our universe.

Changing the size of one thing

can affect almost everything.

So it's time to put the planet back

to the size it was.

If we can't change the size of the planet,

how about changing the size of life on the planet?

Living things come in a huge variety of sizes.

But can we make them bigger?

Will giant hearts and lungs still work?

Will giant legs still support us?

The answer is that it depends.

When it comes to living things,

size works in mysterious ways.

Take insects.

As animals go,

we think of them as small.

Even the very biggest insects,

weight no more than 115 grams

and have wingspans no greater than 28 centimeters.

But 300 million years ago

insects were much, much bigger.

Take meganeura,

a dragonfly-like insect

with a wing span of three quarters of a meter.

Is there a reason history can't repeat itself

and giant insects like Meganeura

take to the skies once more?

Well in fact, there is.

Insects don't have lungs like we do.

Insects breathe

through tiny little openings in their body,

so-called spiracles,

which connect to even finer tubes called tracheals

which permeate the entire body.

So this network transports oxygen

to each and every single cell

and removes carbon dioxide.

It's a system that works well

but only for small bodies.

You might think of the way that insects breathe

as letting oxygen sink in through their tissues.

Now that's fine for everything

that's very close to their body surface

but it becomes harder and harder

to reach structures that are deep inside the body.

And if you become larger and larger,

you have more and more volume relative to your surface area

and therefore it becomes harder and harder

to actually reach the structures

that are deep inside your body.

If the way that insects breathe

limits their size today,

why were they so much bigger in the past?

300 million years ago,

the oxygen content in the atmosphere was a lot higher,

around one and a half times as high as now.

So we now have about 21% oxygen concentration

and it used to be 32, 31 percent.

In today's atmosphere,

insects this big just can't get enough oxygen to function.

Insects today have to be small to thrive.

They have already reached their size limit.

But for other living things,

the rules are different.

And some people are already making giant happen.

My twin brother and I,

we live and breathe pumpkins.

We always have done.

These two men have devoted their lives

to making pumpkins into giants.

When he and I were little kids,

we took one of these seeds

and we planted it before we went on holiday.

And since thereabouts

we haven't stopped

and that's 42 years ago.

And it's just out of total passion really.

The seed is, they're like race horses.

We can look year to year

and you'll see that they get a pedigree

and then you know that this seed in particular

will grow lots of pumpkins to 2,000 pounds.

It's a competitive business

and the brothers put plenty of time and money

into their passion.

But however much work the brothers put in,

there's one thing that limits how big a pumpkin can get.

After around 100 days,

pumpkins are genetically programmed to stop growing

as their skins thicken and harden.

So growing the biggest pumpkin is all about speed.

It's physically got to grow that fast.

So next year, we'll be putting the heating up at night

to 22 degrees.

We need to get this thing growing

faster than 57 pounds a day.

So we need to get it going as fast as we can.

And it's just getting everything perfect

and speed, speed, speedy really.

It's a nerve wracking time for us.

That's a year and a massive amount of work.

It'll be the biggest one yet.

I told you.

That's good news.

Bit more.

Done.

Good job.

We need to get the world record

and we're getting close to it

and we've grown some big ones this year

so we'll see how we do.

Hopefully our season's gonna get rewarded

with something good.

(mysterious music)

If it works for pumpkins,

why can't people move up the scale

to challenge the blue whale,

the biggest animal of all time?

Perhaps giants of legend

could be made a reality.

(alarm beeping)

If two men can make a pumpkin

200 times as big as a pumpkin should be,

surely we can make a human

just three times normal size,

five meters tall.

Not a real giant,

but way taller than any human has ever been before.

A human being five meters tall may look possible

but they would be doomed to fail.

To find out why, we need to go to Turkey.

When I go to a hotel or to a friends,

the biggest problem is finding a bed I fit in.

The standard bed is just two meters.

I usually put two beds together.

As well as having oversized feet,

Sultan Kosen has an oversized pituitary gland

that has produced too much human growth hormone

throughout his life.

As a result, he is tall,

2.51 meters tall, to be specific

which makes him the world's tallest man.

Being this tall comes with perks

but also problems.

He keeps breaking his legs.

Sultan has traveled from his hometown to Ankara

to visit his doctor.

(speaking in foreign language)

This is the femoral fracture

that has occurred six years ago.

It was a midshaft fracture

which has replaced all the fragments

and this long rod plaque

has been inserted with nails

to stabilize the fragments.

It's a significant relationship

with the length of the bone

because you know that if you apply a force,

on a very long rod,

you can easily break it.

If it is relatively short,

it's not so easy to break it

because of the physical properties of the bone.

Sultan's other problem is more practical.

Like our five meter human,

he keeps falling over.

He cannot walk as we walk.

That's his basic problem.

That's why he's so prone to easy falls.

(speaking in foreign language)

Size doesn't matter.

What matters is health

and overcoming obstructions.

When obstructions are overcome,

it doesn't matter whether you're short or tall.

Sultan's health issues

reveal one of the main problems

faced by large living things.

Something we will need to understand

as we begin to make bigger humans.

A five meter human would be even more likely

to break their legs than Sultan, but why?

To find out, let's make this statue bigger

and see what happens.

You might think you just get a larger statue

but you'd be wrong.

There's something else going on.

Let's try again and find out what.

By the time it's double the size,

the arms weigh eight times what they did

but are only four times as strong.

Why is that?

The statue's weight depends on three dimensions.

So if you double the height,

the weight goes up eight times.

Strength depends on cross sectional area

which is just two dimensional.

So it doesn't increase as fast as weight.

The result?

Arms that fall off.

So if you want to double the size of a statue,

you'll have to reengineer it to be big.

Just ask Venus.

She knows all about it.

So if we're going to make bigger people

we'd better do the same

and reengineer the human body.

But how?

There are plenty of other living things

that have managed to make it

to the bigger end of the scale.

What can we learn from them

about building a giant human?

The tallest living things on the planet

are coast redwoods

to be found in California.

I love these trees because of their massive size,

their old age

and because of the way they build the forest that they do.

Professor Todd Dawson

and his team of scientists

have studied every inch of these trees

right to the very top.

If anyone knows why they're so tall, it's him.

So redwoods are a remarkably long lived tree

and the coast redwood can live more than 2,500 years.

Because they're plants, they're constantly growing.

And because they're very old,

as long as they keep growing and they have that old age,

they're just gonna keep

getting bigger and bigger and bigger.

So a tree like the one we're standing next to here,

it probably weighs thousands and thousands

and thousands of pounds, many tons.

One of the things that we notice about these trees

as they grow

is they begin to add more at the base.

So you go from a very small tree

that just goes right into the ground

like a carrot in the Earth

and as they grow larger,

they get heavier and heavier and heavier,

they begin to buttress,

they begin to add mass at the base

'cause they have to have a way to support themselves.

Eight meters, five centimeters,

nice sized tree.

They sort of built some sort of a structure

like an elephant's foot if you will at the base.

Remarkable set of compensation mechanisms.

So is this the limit

or could we imagine a parallel universe

where the biggest of living things

may be even bigger?

The redwood's strategy

of shape shifting,

getting more triangular as they grow taller,

means that their trunks

can support the weight of taller trees.

But they'd hit another problem.

So one of the factors

that limits how tall trees get

is their ability to get water

to the top of the tree itself.

And while a lot of trees may stop their growth,

redwoods have a special way of dealing

with that water limitation as they get taller.

For example, we've got leaves

that come from the lower part of the ground,

and ah,

these much smaller leaves,

they come from the very top of the tree.

And as the leaf area goes down,

the amount of water used goes down as well.

So they become more thrifty in their water use

at the top of the tree

than they do at the bottom of the tree.

Moving water upwards several hundred feet

needs pressure.

Fluid migrating into the roots

pushes water up

while at the leaves,

sunlight causes water to evaporate

leading to low pressure

which pulls water upwards.

The redwoods smaller leaves at the top

mean only a small amount of water

has to go all the way.

But grow a redwood too tall

and not even those special adaptations

can solve the water supply problem.

The leaves would dry out and die

and the tree would go no further.

Despite their problems getting water to the top,

trees still show us just how big you can get

if you change your shape as you grow.

That means that bigger creatures

can't just be scaled up version of smaller creatures.

They need profound adaptations

to overcome the challenges of size.

Take a dog for example.

This dog's skeleton makes up eight percent

of its total body weight.

But if we want to make it bigger

we'll have to beef it up a bit.

At three times the height,

thicker bones mean a skeleton

that weights 10% of its body weight.

But if we want to make it bigger still,

we've got to overcome yet another problem.

Big animals have less surface area per kilogram of weight

than small ones.

So they have proportionally less skin to lose heat from.

This means they can overheat.

Elephants evolved to be large

so that they could dominate their environment,

be safe from predators

and reach food more easily.

But they also needed a way

to avoid overheating in a hot environment.

Elephants don't just have large ears

because they look good.

They also help them to regulate heat.

Billy, our eight year old,

is being very energetic right now

but we're still seeing because of the colder temperatures

his ears are much colder than the rest of his body.

So it really shows how efficient they are

at controlling their body temperature

by using their ears.

In the summer times, we would see the opposite.

Their ears would be much warmer,

the veins would be full of blood

using it as an air conditioner

helping cool down the rest of the body temperature.

Maybe our giant dog could learn a lesson

from his elephant cousins.

Grow a pair of bigger ears

to increase surface area

and lose the fur,

since hair traps heat.

With stronger bones and a way to keep cool,

we can safely make an even bigger dog now.

But how big can we go?

How about as large as a medium size dinosaur?

Which is just big enough

to run into another problem.

It's just too slow.

Herve Bocherens is a paleontologist

who knows exactly why big animals are so slow.

Large animals have an issue with distance

the signal have to travel along the nerves.

Of course, if you are already about 20 meters long,

the signal has to be both ways

and therefore it's already significant fraction of a second

that takes time for the signal to travel.

And therefore the reaction time of big animals

will be slower than the reaction time of smaller animals

and this will make a difference in their life.

So today for instance,

the largest land animals are elephants

and it has been observed

that elephants have to be quite careful

when they walk

because the signal has to travel quite a long distance.

And when they hit something with their foot, for instance,

it takes a couple of milliseconds

to reach the brain.

And therefore, they hae to wait until the signal comes back

to know if they have hit something with their foot

before they make the next step.

Being slow is not good news for a dog

which needs to catch prey.

A giant dog might starve to death

unless it has someone to feed it.

We've managed a dog,

so it should be straight forward to scale up a human.

First thing to remember

is that a human just five times normal height

would weigh 125 times normal weight.

So he would need much thicker bones.

Then of course he'll need big ears like an elephant

to get rid of all that heat.

But before our giant gets any bigger,

we have to face one challenge that most big animals don't.

Humans walk on two legs.

Herve Bocherens is studying another primate

that tried to get giant in the past.

It's a story that begins in an unusual place.

It started in a Chinese pharmacy in Hong Kong

where a paleontologist

was looking at what is called dragon teeth.

And among these fossil material,

there were some fossil human teeth

but also teeth that were much bigger,

looked like humans.

And these were the first discoveries

of Gigantopithecus.

They weren't dragon's teeth.

They were teeth from the biggest ape to ever live,

Gigantopithecus.

Estimating the size of an animal

based on just teeth and lower jaw

is a difficult thing

but we can say that at least it was twice as heavy

as a gorilla.

So the weight could be up to 500 kilogram

which is a maximum estimate.

That makes it the largest primate

that has ever existed.

But estimating its height is even harder.

Most probably,

it was not standing so much

because with such a heavy weight,

it was probably essentially quadrupedal.

And therefore, it's more a comparison with a gorilla

who is mostly walking on four legs

rather than walking erect.

Gigantopithecus was just too big

to stand tall like a human.

We have many examples of in the past

of animals that started bipedal

and had to go back to their four legs.

And when they grew bigger,

it means that they had to carry their weight

on four legs

and not anymore on two legs.

So as we continue to grow our giant human,

should he walk on all fours like a Gigantopithecus?

Perhaps not.

If it's going to be a giant human,

it has to be bipedal

because bipedalism is the thing, the one major thing,

that sets our genus or our group, the hominids,

off from al of the other primates.

We are habitually bipedal.

Being bipedal has upsides.

Your head is raised

so you can see danger further away.

And you can reach higher to get food.

But for humans,

perhaps the biggest evolutionary advantage

is that it keeps your hands free for other things.

But the bottom line

is if it's not on two legs

it's just not a human.

So if we're going to make a giant bipedal human,

that means we hae to support all that weight

on just two legs.

If you're a giant

and you're really, really tall,

well you've got to get that blood pumped away from the heart

and up to the brain, very important.

So you need a big pump,

a big heart,

and that means a big chest

to put the heart in

and it's gotta go uphill.

And so I might put the heart higher up within the chest.

The heart is just a simple

pump that has to get blood around the body.

And pumping uphill is harder work.

So a giant human needs as short a distance

between heart and brain as possible.

The chances are, however large his heart,

our giant human would be lonely

and not just because to he way he looks.

Another consequence of being large

is that the population will be small

because each one need a lot of food.

And so giants would probably not be very numerous.

Even with a four-legged friend,

life as a giant would be no fairytale.

It would have to be a very strange creature indeed

to overcome all the problems

that being big creates for a human being.

That's because size is intrinsic to everything.

Your size determines what shape you are,

how you live, what you eat.

Change it too much

and you simply get a different species.

So let's put things back to how they were.

(alarm beeping)

We've changed the size of the Earth and everything on it

and it really didn't work

but there's one last thought experiment we can try.

Because if we're going to change the size of things,

we can't miss out something massive

that lies at the very heart of our solar system,

the sun, our nearest star.

But when it comes to stars,

does size matter?

Size is crucial to the work of astrophysicist Volker Bromm

because the size of a star

determines how it behaves.

When you think about stars,

then size is absolutely essential

because you could say that the size of a star,

or more precisely the mass of a star is destiny.

If a star's size is its destiny,

just how big is ours?

Well, it's 109 times wider than planet Earth

and 330,000 times as massive.

It accounts for 99.86 percent

of all mass in the solar system.

As it turns out,

just the right size for life on Earth.

The sun is, for us, the essential star.

The sun really provides us with a perfect cosmic environment

to enable life on Earth.

How do we know the sun is so perfect?

One way to find out

is to visit our parallel universe,

make the sun bigger

and see if the world survives.

Let's start by imagining our sun

but with exactly double the amount of gas.

You might imagine it would be twice as bright

but you'd be wrong.

How a star reacts to increasing the mass

is highly nonintuitive.

So you double the mass

and you increase the energy output tenfold.

On Earth,

the effects would be staggering.

The equilibrium temperature on Earth

would go up by a significant factor.

So we would have a much hotter Earth

which would then suddenly

become completely inhospitable.

First, the ice caps would melt.

Then the oceans and rivers would dry up.

The surface of the Earth would eventually stabilize

at over 200 degrees centigrade.

But all is not lost.

There is one way we could get things back to normal.

A key question in modern astronomy

is that we think about the region around any star

where life, in principle, could be sustained.

For life as we know it to exist,

the temperature of a planet needs to be right

for water to exist as a liquid.

The area around any star where this could happen

is called the goldilocks zone.

You basically have a very, very special region

around any star

and this goldilocks zone of not too hot, not too cold,

what we call the habitable zone

is a very precious, precarious zone

because if you play with the conditions in the central star

everything changes.

As a double mass sun burns so much hotter,

this means the goldilocks zone is now further away,

three times further away.

So we just need to move planet Earth

to its new resting place,

well past Mars,

450 million kilometers from the bigger sun.

Here, life would not be in immediate danger.

But it's far from ideal.

The new longer orbit means a year is much longer.

And so are the seasons.

In fact, winter would last 16 months

which would make growing crops very difficult.

So could Earth survive around an even bigger sun?

Before we can answer that,

we need to know just how big stars get.

(dramatic music)

Since mankind first invented the telescope,

we have wondered just how big the stars really are.

This is what we found.

We think of our sun as pretty big

but in the universe's hall of fame,

it's just a nobody.

The biggest star by radius

that mankind has every observed

is known as UY Scuti.

It's more than 1,700 times the width of our sun.

But there are stars even bigger

if we look far enough away.

Not just in distance but in time.

In astronomy,

we have a great privilege.

We can do something that historians and archeologists

only dream of.

We can directly take images of the distant past.

And we do this by looking at objects

that are far away in the universe.

Objects that are far away,

they have sent out the light

that we receive billions of years later

and light travels with a limit of speed,

the speed of light.

And therefore looking far out into space

means also looking far back into time.

When they looked far enough away

and far enough back in time,

scientists found that the biggest stars to ever exist

were born in the very early universe.

If one thinks about the early universe,

then you also discover possibilities

of really pushing star formation to the extreme.

Professor Volker Bromm

has built theoretical models

that show just how big

these early stars could've been.

His visualization lab

simulates how massive clouds of gas

in the early universe collapsed

to form giant stars.

So there are special regions in the universe

where conditions arrive

that you can have extraordinary large

clouds of primordial gas

collapsing in one go if you like.

So then we have a very, very extreme case

of visualized star formation.

A million solar mass cloud collapsing in one go.

And again, this is a very special condition

and we believe this only could've happened

in the early universe.

Volker's work tells us

that back in the early universe,

there may have been stars

a million times more massive than our own,

far, far bigger than anything around in the modern universe.

Our sun would just be speck compared with this.

The question is could the Earth

survive orbiting a star

that is possibly the biggest object

that has ever existed?

Let's find out.

As the sun grows to the size of a super massive early star,

it would envelope the inner planets.

So the Earth needs to move to a safe distance.

To the outer edge of our solar system,

far beyond Neptune.

Then we would have our planet

sitting our at this huge distance

and you can also ask then

how long would then one orbit take?

And then you would calculate

that one orbit would roughly take 30,000 years.

Not great for getting birthday presents.

And New Years Eve

would be something to be enjoyed

only once every 1,200 generations.

But there's a twist in this tale

that means none of that really matters.

The big problem then

that such a hypothetical planet would encounter

is that the host star,

the supermassive star would have a very short lifetime

because our sun lives for another five billion years.

But the total lifetime of the supermassive stars

is just a few hundred thousand years,

maybe up to a million years.

So this is in astronomical terms,

a blink of an eye.

Put simply,

if our sun had been a massive early star,

life as we know it would never have existed.

Before life had a chance to evolve,

the star would come to an end,

perhaps in a most spectacular way.

If these early super stars were to explode,

the supernova explosion,

then we could say that these would be the biggest explosions

ever to happen in the history of the universe

since the big bang.

The big bang, of course,

would still beat everything else.

But otherwise,

those would be truly colossal explosions.

In their lives and even in their deaths,

these giant early stars

were the limit,

the very end of the scale of big.

But they just don't work for planet Earth.

We've tried changing the size of the planet,

the size of our sun,

and even the size of living things

but nothing works quite as well

as what we started with.

We are our size.

Change it, and we risk changing who and what we are.

So does size matter?

What do you think?

It matters hugely

and it depends on what you're looking at.

If you're looking at the brain, yes.

If you're looking at bodies,

just sustaining life in different thermal habitats,

so size matters tremendously.

Size doesn't matter.

I've met the shortest people in the world

and also some of the tallest.

(speaking in foreign language)

I even once met something taller than me.

It was a giraffe.

Today, Ian and Stuart produced a pumpkin

weight 2,252.3 pounds.

That's a new UK record.

Woo!

Size is the only thing that matters.

Don't have to be pretty,

don't have to look nice.

Only thing that matters is size.

So size definitely matters for the redwood forest.

I think it really creates the structure, the scaffolding,

that makes the redwood forest

such a beautiful place to spend time.

So despite what some believe,

bigger isn't always better.

Bigger is hotter,

weaker,

more dangerous.

Bigger is grander,

slower,

and more fantastic.

And size really does matter.

(planet exploding)

(uplifting music)