(mysterious music)
Mark: 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.
Mark: 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.
Mark: 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)
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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)
Mark: 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.
Translator: 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.
Mark: 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.
Mark: 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)
Translator: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Volker: If one thinks about the early universe,
then you also discover possibilities
of really pushing star formation to the extreme.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Mark: 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.
Translator: 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.
Mark: 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)