Explosions: How We Shook the World

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We see explosions all the time,

and during my career as an engineer, I've certainly made a few.

But actually understanding them and controlling all that power,

that's a whole different story and sometimes quite a surprising one.

It's a story that starts with the accidents of the medieval alchemists...

Don't try this at home.

Whoa!

..but eventually leads us to a fundamental understanding of the forces of nature...

..forces that we've mastered for good or evil.

Explosives revolutionised battlefields,

industry and engineering.

To uncover the story, I'll be reading the words of medieval scholars...

..going deep underground through ancient Cornish mines...

That looks like a lot of gunpowder to me.

..and making some of the most dangerous substances ever known.

It mustn't go above 18 degrees centigrade.

It's a journey that will take us right to the centre of matter.

- Is that a split atom?

- Oh, yes.

Wow!

And the power it can unleash.

This is the story of how we learnt to harness the forces that shook the world.

The very first record we have of people using explosions comes from

a Chinese document which could date from as far back as two centuries BC.

It describes how travellers in the mountain wilderness of the West

were threatened by shape-shifting creatures of the night.

To scare away these creatures,

they would lay lengths of bamboo on their campfires.

- BANG!

- The very first Chinese firecrackers.

CRACKING AND HISSING

The hissing noise we hear is moisture in the bamboo turning to steam,

but bamboo has a special structure to it.

It grows in sealed compartments.

Now, when the moisture in these sealed compartments

starts turning to steam, pressure builds up inside here.

It can't go anywhere.

- Water, when it turns to steam,

- BANG!

wants to expand hundreds of times, but there isn't room for it do that,

so pressure builds up.

Eventually the structure of the bamboo breaks down. Kcrrr!

It explodes,

scaring away shape-shifting creatures of the night.

Using simple natural explosions like this

was the first step of mankind's journey to harness explosive power,

starting to understand the process in order to control it.

It's easy enough to create an explosion.

Any explosion is simply the moment when gas tries to expand suddenly.

- LOUD BANG

- Oh!

And when that suddenly expanding air crashed into the air around it,

it created a pressure wave that then moves through the surroundings.

A sudden change in pressure forced a cloud of water droplets out of the air.

These allow us to see the wave.

The faster the gas is trying to expand,

the more powerful the explosion,

when that pressure wave hits your ear, you hear it as a bang.

An explosion relies on a lot of gas trying to expand.

Heat can make this happen, because heat, of course, makes things expand.

Introducing more gas can do the same thing,

but mankind discovered a way to create both heat and gas

by reacting chemicals together and this was the start

of our journey to really master explosive power.

In Europe, chemical explosions were unknown until the medieval period,

and the first time people came across them,

they were a bit shocked.

I've come to the Bodleian Library in Oxford

to see a manuscript that describes one of these early encounters.

It's one of the few copies of a book written in 1267

by the medieval scholar Roger Bacon,

who split his time between Oxford and Paris universities.

Now, this particular passage that starts "et experimentum"

describes his knowledge of man-made explosives at the time.

"There is a children's toy, something no bigger than one's thumb,

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