Original subtitles

The human eye - one of the most powerful instruments on Earth.

On a clear day, we can spot the smallest detail in the widest view.

But what the eye sees is not the full picture.

Alongside the world we see is a very different world.

An invisible world of hidden forces and powers.

This shapes every aspect of life on Earth.

Now, technology can open a door on that hidden world,

revealing its mysteries, and showing us the true wonder of the world we live in.

In our vibrant, hectic world, we think we spot everything.

But right in the midst of this busy world, there's a whole other world going on,

it's just that we can't see it.

To us, it's invisible.

Our eyes are too slow to see everything that's really going on.

The world is full of things that happen too fast for us to notice.

Things we miss in the blink of an eye.

The blink of an eye takes about 15 milliseconds,

and it takes the human brain about 150 milliseconds to process what we see.

We're not aware of this time lag going on,

but in those few milliseconds, there are things happening,

extraordinary things that were never see.

This is the invisible world of speed...

..where thin air...

can shatter rock

and water can tear through metal.

Where the fastest thing on Earth is right beneath our feet.

And where we'd see spectacular events that some thought were UFOs.

If we could stretch time, we could solve some of the biggest mysteries of our planet.

Now, using the latest camera technology, we CAN stretch time, making the invisible visible.

We can overcome the limitations of our eyes to see whole new worlds.

Lightning. A billion volts and hotter than the sun.

But there's even more danger in what you CAN'T see.

This is Rapid City, South Dakota.

In the middle of America's lightning belt,

it gets hundreds of strikes every year.

But there is something strange about the lightning here...

..something that's becoming a bigger and bigger problem.

Something too fast to see.

Lightning travels at over 100,000 miles an hour.

So only with super slow-motion cameras can experts begin to understand what's going on.

When you view a flash in real time, it's like seeing a title of a book.

You can see that there was a flash there that reached the ground,

maybe it flickered a little bit, but that's all you know.

You come and record this same flash with these high-speed cameras,

it's like a novel.

It tells a unique story every time you play it back. Incredible.

In slow motion, we can see what gives lightning the shape that launched a thousand horror movies.

Fingers of electricity hunting for the ground.

And now, these high-speed cameras are allowing us to catch something

completely invisible to the naked eye.

The strange lightning that's found not in the plains, but right in the heart of Rapid City.

There's a storm brewing.

Specialist cameras set to record at nearly 300 times slow-motion are waiting to capture it.

And there it is.

At first it looks like a normal lightning strike

but the technology reveals something else.

Instead of lightning shooting downwards, this lightning is travelling upwards.

When I played this for the first time, I was just blown away.

It was just amazing to see it.

And this strange, upside-down lightning is powerful, it carries more charge than normal lightning.

But what's really extraordinary is that upward lightning is created by us.

Because it's these tall transmission towers that are triggering

the vast bolts of lightning firing up into the clouds.

Now, you might think that because it is going away from the town,

this lightning is harmless.

Unfortunately not.

When the upward bolt hits the storm clouds, it triggers more lightning

that fires straight back down to the city.

And it is not just here, in Rapid City.

As we build more tall buildings,

this new form of lightning is spreading across the world.

In this high-speed world, there are surprises hidden in even the most everyday things we think we know.

Take this, for example.

On the face of it, that's just one small firework designed to make people go, "Ahh!"

But in fact, there's an invisible force at work here,

one hidden in all explosions, and it's powerful enough

to destroy buildings or tear through solid rock.

Even this little candle unleashes a force too fast for us to see,

that reaches way beyond the pretty sparkle.

And that's what this special camera shows,

something our eyes can never see.

It's a shockwave -

super-fast, devastating, potentially deadly, and yet it's just thin air.

I want to take a closer look at this devastating force in action.

To do that, I need to blow something up.

So, this rock face, it's about 100 metres long.

That's what we're going to blow up,

which will mean shifting about 20,000 tons of rock.

Up here on the top, we're filling not one, but 20, separate holes with explosives.

You see, our experiment is a bit more sophisticated than just creating one massive explosion.

Each one of these 20 separate explosions needs to be

choreographed to go off at 25 millisecond intervals.

That way, each explosion will fragment the rock,

and open up a face that can then be hit by subsequent explosions.

At least, that's the theory.

This whole event is going to be over in about half a second.

So to stand a chance of seeing this,

we're going to need to film it at high-speed.

We're using a remote trigger with a short travel,

so I need to be 100 metres away from the explosion - in that.

Yeah, I know.

But it does mean I'll get to experience very much at first hand

the impact of 20 separate explosions detonating within half a second

of one another to try and shift 20,000 tons of rocks.

So in that sense, I'm lucky to be in there.

Nice!

Oh, yeah.

I feel safe.

So, I arm it with that. BEEP

That means it's now armed.

Counting down from five, four, three, two, one.

20,000 tons of rock, gone in a second.

And I'm still safe, which is a bonus.

That was quite a rumble.

I really felt that.

Yeah, just to actually feel the earth move

because of something you have just triggered, that's quite a sensation.

Yeah.

A little lie-down is needed.

But it's only when we slow down in the film 40 times that

we can see more of what just happened

and why I wasn't turned into mush.

There's a flash as the detonation cable ignites.

And now we can see the blast going off. One every 25 milliseconds.

But the real force is not the blast.

It's the shockwaves that each blast releases.

Deep in the quarry face, the shockwaves are forcing their way through sheer rock,

eventually erupting at the top.

The shockwaves keep on expanding outwards,

powerful enough to crumble the rock

and finally tear apart the entire face.

But thankfully, not mine.

By choreographing the explosions,

we were able to drive and steer the shockwaves through the rock,

rather than let them spill out into the air around,

which is why I was able to get so close.

Not sure I'd want to get much closer.

So, how can a shockwave cause such awesome destruction?

To find out, we're going to trigger one almighty explosion.

We're going to attempt to see a shockwave.

It'll be over in the blink of an eye,

but high-speed cameras will capture every millisecond.

At least, that's the plan.

First, thousands of pounds of gunpowder are loaded.

That's a lot of gunpowder.

The fuse is set.

To be safe, everyone needs to be over a mile away -

that's why they're running away in pick-up trucks.

Except for these guys -

the detonators.

They'll be less than half a mile from the blast zone,

which is why they get the armoured car.

Everybody ready? Are you ready, sir?

Range control to security checkpoint, are you clear? 'All clear.'

Obs one, are you clear? 'We're all clear.'

10/4, stand by for counting. I'll say it again, stand by for counting.

Five, four, three, two, one...

In an instant, thousands of pounds of gunpowder explode.

But the shockwave is completely invisible.

So we need to slow it down over 100 times,

and then watch it back repeatedly - from several angles.

Stand by for counting. I'll say it again, stand by for counting.

Five, four, three, two, one...

The fuse races towards the site.

In a thousandth of a second, the gunpowder ignites.

In one millionth of a second it changes from solid to gas.

And there it is. Finally, we can see the shockwave.

A wall of intense high pressure in the air.

It's travelling at over 300 metres every second.

So fast that anything in its path is punched aside.

And now we can see amazing detail.

The shockwave reignites unburnt fuel, triggering a secondary shockwave at the tip.

It's the shockwave, not the explosion itself, that causes devastation.

In the high-speed world, thin air can create brute force and destruction.

But it can also allow us to do some pretty amazing things.

OK, right, so go for the off, yeah.

A nice bit of back pressure as you take-off, plenty of left pedal.

And a bit more.

That's it.

There she goes.

Now, bear with me, I am still learning this.

Now, it's something that we take for granted, but essentially

nearly two tons of helicopter and me are being held up by air.

Just very, very fast-moving air.

The rotor above pushes air downwards, that creates the lift that keeps me up in the sky.

It's one of the basic principles of aerodynamics.

But step into the world of the invisible,

and this benign and useful force suddenly looks very different.

These planes are flying close to the speed of sound.

But at this speed, the air moves so fast

it's about to become a potentially dangerous force.

Slowed down by nearly 200 times, just watch what happens on the wing.

At these super high-speeds, the moisture in the air suddenly condenses into water.

A cloud forms.

I know that doesn't sound very scary - a cloud -

but that cloud is like suddenly dumping the weight of a car on the wings.

Only the most skilled pilots, like these, can cope.

We may think that we've conquered flight,

but compared to the natural world,

our mastery of the air is basically rubbish.

Engineers have been wrestling with the problem of flight

since the Wright brothers first got airborne 100 years ago.

But it is only now, with the advent of ultra-high-speed filming

that we can really begin to understand some of the secrets

of the natural world, which has, after all,

been working on the same problem for over 350 million years.

Now, come on, you've worked it out now.

It's a lot of practice, it's a lot of years.

Yep, got there in the end.

The first creatures to fly weren't birds,

they were insects.

For centuries, their secrets were invisible.

Wing movements lost in a blur of motion.

We're only now starting to get the full picture.

The hummingbird hawk-moth is revealed to be a model of flying finesse.

With amazing control, it can hover at a complete standstill,

perfectly poised to gather nectar.

But not all insects are quite so elegant.

The bumble bee is an aerodynamic mystery that had scientists baffled.

A big, fat body, supported only by tiny wings.

Now, how's that supposed to work?

The confusion started over 70 years ago, when a French entomologist

calculated that bee flight was aerodynamically impossible.

Ever since, scientists have struggled to understand just how

a bee's apparently random flapping can possibly keep it airborne.

And, at first, even seen in slow motion,

the mystery doesn't get any clearer.

Here she is, lurching through the air.

She even has to use her legs to balance herself -

elegant it's not.

The only way she's staying up is by furiously flapping

at an extraordinary 200 beats every second.

That's why she's so round,

her chest is a mass of muscle to power the wings.

No, I'm not trying to set fire to them,

this smoke should help us see what's happening.

As the bee beats its wings,

air, or in this case, smoke, is pulled downwards.

This generates lift,

but not enough to keep the stripy buffoon airborne.

Only in super slo-mo can we see she's actually rather clever.

At the end of each downstroke,

she twists her wings over.

So, even on the upstroke, the smoke is still pulled downwards,

giving her double the amount of lift.

And you don't get that with an aeroplane.

By looking into the invisible world of high-speed,

human engineers are discovering a range of animal secrets

they can use to develop even better flying machines.

So, why do we miss so much of what's around us,

when it's perfectly obvious to other creatures?

A fly, for example, can see 100 images a second,

allowing it to zoom around at top speed and not crash into things.

To a fly, our world appears incredibly slow...

..which is why, annoyingly, I'm never going to catch it.

But what the fly has in speed, it loses in detail.

Everything it sees is a blur.

We, on the other hand, have evolved to see very fine detail.

But there's a trade-off - our eyes can't do speed.

We process a lot of information in any one scene,

but it does take time. So much time, in fact, that the best we can do

effectively is take snapshots of the world around us.

We take a look, process the information,

take another look, process that information, and so on.

Each snapshot lasts just 100 milliseconds.

And unlike the fly, our snapshots are very detailed.

So it takes time to process each one.

Anything that happens in those milliseconds while we're processing information remains hidden.

It's as thought it's not there.

So, right now, everything's fine.

I can deal with all the information coming my way, I can see colour,

yellow track, I can see the curve, the shape of it.

I can even see the chain moving to pull my little cart long.

No problem...at normal speeds.

But it's surprising how quickly you reach the point beyond which

I can't process the information, because as things get faster,

so strange things begin to happen to our vision.

Now, it's not that I'm missing stuff

cos I'm looking the wrong way.

I just can't deal with the information as it comes in.

There's just too much going on!

I can't work out what's what.

My vision hasn't suddenly gone faulty, this is as good as it is.

The faster things move,

the less time we have to process all the detail in the picture.

But as things speed up, eventually the rate of incoming information

exceeds the speed of our neural processors, and you can't see!

I'm not too sure my stomach can process it either.

And when it gets too fast, we simply can't see it at all.

Did you spot this?

When we start to see the things that are usually invisible,

it shows us how extraordinary our world really is.

Water becomes thick, elastic.

It even contains a powerful force that can tear through sheet metal.

Nothing is quite what it seems, even stuff we think is familiar.

It's not exactly a rare thing for most of us, rain.

But venture into the invisible realm, and suddenly the world as we think we know it changes.

Take a simple raindrop, for example.

We all know that they form a tear-shape,

fall through the air, and then land on the ground.

Except they don't necessarily do any of those things.

Looking at this downpour with specialist cameras reveals the surprising story of rain.

Every raindrop begins as a perfect sphere.

As they fall, air resistance causes the drops to flatten.

Real footage slowed down

shows that they're really, well, wet hamburgers.

In fact, they never, ever form the classic teardrop we imagine.

So much for the raindrops' tear shape.

High-speed filming shows what happens next to these airborne hamburgers.

This rare sequence reveals something quite extraordinary -

rain that simply vanishes.

Bigger raindrops can swell and inflate like balloons

until they burst, exploding into smaller and smaller drops.

Some of these tiny drops never actually hit the ground,

they're just dispersed into the air.

But there are still enough big drops left to land on us.

In the high-speed world, water becomes thick...

..dense...

..an alien environment that we struggle to get through.

Over time, a strong swimmer can manage about two miles an hour.

But that's a crawl compared to other mammals, like this fella,

the dolphin, who speeds through five times faster.

But it's only in slow motion that we can see

why the dolphin is so much at home here...

..and why we aren't.

Water is 800 times thicker than air.

So thick that it pulls and distorts our soft bodies as we swim,

causing drag, which holds us back.

Now watch what happens to Mr Dolphin here.

The water doesn't distort his body at all, passing smoothly over it.

That's because the dolphin has much thicker skin, like rubber,

that stops his blubber flapping.

So, while we struggle to make headway,

a dolphin is barely trying.

And when it needs to swim even faster, the dolphin makes it look easy.

Slowed down 40 times,

we can suddenly see things invisible to the naked eye...

..like the way the water flows cleanly around its torpedo-shaped body

so the dolphin can speed through effortlessly,

saving his energy for, well, showing off, basically.

Yes, yes, very good.

Have a fish.

And if he can't be bothered with all this,

he can hitch a ride on the surf.

But there's something really strange about water,

and it's hiding beyond our sight.

Lurking in these warm, clear waters, is an invisible force...

..capable of tearing through metal.

A force that is, even now,

destroying this boat.

To see this force in action, we're going to need some help.

In this tank is a tiny creature,

but it's armed.

Hiding under the rock is a pistol shrimp,

and it's packing a lethal weapon.

This crab is heading into trouble.

Our shrimp is ready for a scrap.

At first sight, it looks like he's punching the intruder with his claw.

But, in fact, something much stranger is going on.

Its weapon isn't exactly the claw itself, not directly.

The weapon is invisible,

as I shall now demonstrate with this paint brush.

I'm not getting in there with it, it's armed.

Right...

Come on. SNAP!

Oh! Did you hear that?

SNAP!

That noise is a big clue as to what's going on.

It's too fast to see, so let's have a look at it again in slow motion.

The sound we hear is not from the claw itself

but from an amazing invisible force.

The claw snap happens so fast it causes a high-speed water jet

which shoots forward at almost 60 miles an hour,

fast enough to vaporise the water and form a bubble.

And that's a lot more dangerous than it sounds.

The temperature inside the bubble reaches over 4,000 degrees,

and, as it collapses, this massive energy is released

like a superheated shockwave, stunning, or even killing, its prey.

The knockout punch comes not from the claw

but from the super-hot power of a bubble.

This incredible force is called cavitation.

It happens whenever water is forced to move at extreme speeds,

and it can do a lot more than scare off a little crab.

Up to now, it's been completely invisible.

Using ultra high-speed cameras, we can finally see it in action.

This propeller is spinning so fast it vaporises the water around the tips of the blades...

..creating streams of super-hot bubbles.

As they collapse, they release a massive wave of energy...

..bombarding the propeller blades.

It's so powerful,

it can destroy the metal itself.

Cavitation ruined this propeller

after a single journey across the Atlantic.

Our everyday world, familiar, ordinary, even a bit boring.

But hidden beyond the timescale of our eyes

lie truly amazing phenomena.

And some of the fastest of all happen not in the air

or in the water, but right under our feet.

The plant world lives according to an entirely different time-frame to ours,

which is why this all looks very peaceful, calm, relaxing, even.

But, in fact, there's a war going on. It's just that we can't see it.

By squeezing weeks into seconds,

we see plants locked in a battle for survival,

competing for sunlight, space, and for the attention of insects.

But plants don't just do slow.

This timescale according to which the plant world lives is exactly that, a scale.

And plants can exploit the extremes at either end of it,

so when they need something to happen fast, they can do fast.

Watch this.

You see?

No, you won't have done, because it happens too fast to see.

We'll have to slow it down to see what's actually happening.

This Himalayan balsam is firing out seeds at an astonishing six metres a second.

Flinging them in all directions like a toddler with a plate of peas.

Sending them far enough to keep its own patch free from competition.

OK, so what do you think is the fastest accelerator on the planet?

A rocket?

A jet fighter?

A missile?

Nope. Thanks to the latest in high-speed cameras,

we now know it's something else entirely.

And it's found right here in the British countryside.

The fastest living thing on the planet is in this field right now.

It's not some supersonic species of falcon, or a cheetah.

We're in Herefordshire, they don't have them here anyway.

It's not those two, either. But it's got something to do with them.

What it is, is right here.

Down, it's smaller,

it's down...it's right here.

Yeah, this. Well, not actually this,

but this horse poo is home to hundreds of tiny fungi

and it is literally the speediest thing on the planet,

in there.

Well, not exactly the fungi themselves, but their spores.

Here they are, just starting to appear now.

When these grow up,

they will be capable of feats of acceleration that the mind can barely comprehend.

These little beauties, pilobolus,

can do 0-20 in two millionths of a second,

and pull 20,000G, which is a lot.

Astronauts on a space shuttle have to cope with four.

Get anything past five G, pretty much, and people start passing out.

Now watch the spores.

They're the black bits on the top.

At normal speed, they seem to simply vanish...

..because they have one of the speediest lift offs on the planet.

It's so fast that it's invisible.

It's only recently, with the development of ultra high-speed cameras,

that we've had any idea of the incredible high-speed performers hidden in humble horse poo.

Slowed down 10,000 times, we can see them hurtling through the air.

It's so fast, it's like us being catapulted to 100 times the speed of sound.

All of which begs the question, why?

Why does a fungi that lives in poo

need to be the speediest thing on the planet? Why?

Well, for our fungal family to survive,

their spores need to get gobbled up by a friendly grass eater.

This horse, for example.

But he won't eat grass from an area around any pile of poo,

known, rather charmingly, as, "the zone of repugnance".

Which it kind of is.

So the fungus has to launch spores beyond that,

which means clearing over two metres.

But there's a problem.

The air's too thick.

You see, the smaller you are, then, relatively speaking,

the thicker the air gets. Imagine this coin

were a tiny pilobolus spore.

There it goes.

But, to the tiny spore, the air is thick, like honey.

And would stop it in its tracks.

The only solution is to go fast enough

to power through the thick air into the fresh, poo-free grass beyond.

And that's exactly what the fungal spores do.

Underneath each tiny head, an explosive bubble of liquid pressure builds up

until, finally, it bursts,

launching the spore at its tip more than two metres away.

I know, it's impressive.

Yep, your head's really heavy.

Close-up, you're quite ugly, you know that, don't you? Get off.

By looking into the invisible world of high-speed,

we discover extraordinary events,

even in something as ordinary as a garden pond.

These little creatures, water striders,

had long been a bit of a mystery. Nobody could work out quite how

they could propel themselves across the surface of the water so quickly.

They can scoot forward nearly two metres every second.

And they're achieving something of biblical proportions,

actually walking on water, skating across the surface without sinking.

Only by seeing what time usually renders invisible to us

can we understand what's really going on,

and it's got something to do with what's about to happen here.

Normally, this is too fast to see.

But watch what happens in slow motion,

as the droplet of milk hits the water surface.

Instead of breaking, the water surface stretches,

bouncing the milk drop back up into the air.

The water behaves as if it has a thin elastic film on the surface.

It's called surface tension.

And it's this elastic membrane that allows the water strider

to stand on the water, rather than sinking into it.

He's also using that elastic surface tension

to catapult himself across the pond at the equivalent of about 600mph.

In coloured water, we can see the force

of the strider's legs as they push across the surface.

The high-speed artist of the invisible world.

To us, this is just a pond.

But to the water strider, it's a giant trampoline.

Now we're going even further, looking far above us

to reveal the invisible secrets on the very edges of our world.

At the edges of our world, high above our heads,

are even more astonishing events.

The night sky might look calm, tranquil, the silvery moon,

a few stars, all of that, but there are other things up there,

things so strange we weren't even sure they existed.

Our final journey takes us on the hunt

for one of the most elusive events of the invisible world.

We're attempting to find a spectacular lightning formation

50 miles wide, but so fast it's virtually invisible.

Centre 6775 with you at flight level 4-0-0.

'Take off from 6775 Centre.'

Brief glimpses have been mistaken for UFOs.

They're called sprites.

Now a team of scientists is heading high above the clouds, trying to

catch them in the air on high-speed cameras for the first time.

We're closer to the sprites, which is good,

but since we're closer and we don't know where they're going to happen,

that makes it a little harder.

Conditions have to be just right.

After years of planning, tonight is the night.

No pressure then(!)

1,000 miles away, a massive storm is brewing.

This little plane's flying right into it.

We're headed to Meridian, Mississippi now, and past that,

we're going to head over toward Little Rock, Arkansas, and then

we're going to go straight up toward Des Moines, Iowa.

About two hours to get there.

We'll have four hours to loiter around the storms

for the sprite pictures in the back, and then two hours back home.

So we'll be airborne about eight hours tonight.

The mission takes place in almost total darkness.

Any stray light makes it harder to detect sprites.

A low-light camera and image intensifiers will help us see in the dark.

I've also packed some carrots.

Sprites are electrical discharges like normal lightning,

but very different.

The real difference is how brief the sprites last.

Normal lightning can last,

if you count all the strokes together, maybe half a second.

Sprites are a lot shorter in duration.

The plane's flying higher and higher.

Now at 50,000 feet, close to the border with space.

See that? That's Jupiter.

With flying at this altitude, it's the clarity of the air.

The visibility is forever.

Getting close now.

There's a storm building way below.

It looks to me like we're getting all the lightning

on our back side right now, so is it possible to turn ten degrees to the left?

As the plane turns, the storm unleashes its fury.

These are perfect sprite conditions.

There's no time to lose.

Do you think we should go up? Don't know.

It won't hurt the intensifier.

The high-speed cameras and image intensifiers are prepared.

10,000 frames a second, 50 micro-second integration time.

They're fixed on an area just above the storm itself.

Gain is 60,500,

the aspect is zero, elevation is minus four. Do we go again?

Trying to catch one of the most elusive phenomena in the natural world.

A sprite. There's something.

I think that was probably outside the field of view, I'm not sure.

It could have been a sprite.

And the storm's about to die.

We're now at minus four degrees elevation.

And then... Sprite. We're looking. Yeah, we got it.

It looks like there's two of them. I think he got them.

A vast column of light, 20 miles tall.

It dwarfs the city below.

A spectacular formation, trailing globes of light.

Each one is as bright as Jupiter.

These amazing high-speed images have been captured from the air for the very first time.

You and I live on seconds or minutes or maybe even years of timescales.

And sprites are one one-thousandth of a second.

It makes you realise how different the world can be.

This vast display happens in our skies all over the world,

but we're completely unaware of it.

Although it is reckoned that some reports of UFOs

might actually be glimpses of these vast, super-bright round flashes.

Sprites aren't just spectacular.

They're also one of the greatest secrets of the invisible world.

Thanks to high-speed cameras, we've been able to see things we never even dreamed of.

But of course, that is not the end of the line.

Who knows what else is going on right now that we can't see - yet.

Subtitles by Red Bee Media Ltd

E-mail subtitling@bbc.co.uk