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In 1852, clockmaker Edward Dent set out | 0:00:01 | 0:00:05 | |
to construct the largest and most accurate public clock in the world. | 0:00:05 | 0:00:10 | |
It took seven years to build. | 0:00:11 | 0:00:13 | |
CLOCK STRIKES | 0:00:13 | 0:00:16 | |
A testament to a very human need. | 0:00:16 | 0:00:18 | |
Our modern day lives are completely driven by precise measurement. | 0:00:20 | 0:00:23 | |
Take Big Ben. For over 150 years it's been ringing out | 0:00:23 | 0:00:27 | |
the correct time to the people of London. | 0:00:27 | 0:00:30 | |
When built, it was an engineering marvel | 0:00:30 | 0:00:33 | |
accurate to an incredible one second an hour. | 0:00:33 | 0:00:36 | |
But times have changed. | 0:00:36 | 0:00:38 | |
Today we can build clocks which lose one second in 138 million years. | 0:00:41 | 0:00:48 | |
And now there are plans for a clock accurate to within one second | 0:00:49 | 0:00:53 | |
over the lifetime of the universe. | 0:00:53 | 0:00:57 | |
What is it that drives us to such extremes of ever greater precision? | 0:00:57 | 0:01:02 | |
Why do we feel the need to quantify and measure, | 0:01:02 | 0:01:05 | |
to impose order on the world around us. | 0:01:05 | 0:01:09 | |
Since our ancestors first began to count the passing of the seasons, | 0:01:09 | 0:01:14 | |
successive civilisations have used measurement | 0:01:14 | 0:01:16 | |
to help master the world around them. | 0:01:16 | 0:01:20 | |
It's taken us to the moon and split the atom. | 0:01:20 | 0:01:24 | |
And it fascinates me. | 0:01:24 | 0:01:27 | |
Ever since I was young, I've been obsessed with measuring things, | 0:01:27 | 0:01:30 | |
trying to make sense of the world around me. | 0:01:30 | 0:01:34 | |
But where did these measurements come from? | 0:01:34 | 0:01:36 | |
I mean, who decided a kilo was a kilo, and a second a second? | 0:01:36 | 0:01:42 | |
What we measure, how we measure it, | 0:01:42 | 0:01:44 | |
and how accurately we can measure it are surprisingly complex questions. | 0:01:44 | 0:01:50 | |
Questions which have obsessed generations of great minds, | 0:01:50 | 0:01:53 | |
and created a system that describes everything in our world with | 0:01:53 | 0:01:58 | |
just seven fundamental units of measurement. | 0:01:58 | 0:02:02 | |
And the quest to define those seven units with ever greater precision | 0:02:02 | 0:02:05 | |
has changed our world. | 0:02:05 | 0:02:08 | |
In this series, I want to explore why we measure. | 0:02:22 | 0:02:26 | |
What drives us to try and reduce the chaos | 0:02:26 | 0:02:28 | |
and complexity of the world to just a handful of elementary units. | 0:02:28 | 0:02:33 | |
In this first programme, I'm going to be looking at two of the most | 0:02:33 | 0:02:36 | |
fundamental measurements, namely the metre and the second. | 0:02:36 | 0:02:41 | |
It's likely that time and distance | 0:02:42 | 0:02:44 | |
were the first things people ever tried to measure. | 0:02:44 | 0:02:46 | |
They seem closely linked in our minds. | 0:02:48 | 0:02:51 | |
We even talk about length of time. | 0:02:51 | 0:02:54 | |
And, as we'll see, time and distance | 0:02:57 | 0:02:59 | |
are inextricably connected by modern science. | 0:02:59 | 0:03:03 | |
Being able to measure time actually means spotting patterns and | 0:03:04 | 0:03:07 | |
that's actually a very mathematical way of looking at the world. | 0:03:07 | 0:03:10 | |
In fact, measuring time is an incredibly sophisticated act. | 0:03:10 | 0:03:15 | |
So where did it all begin? | 0:03:15 | 0:03:19 | |
Our ancestors would have first picked up | 0:03:19 | 0:03:21 | |
on the patterns of the seasons. | 0:03:21 | 0:03:23 | |
Marking time as the leaves turned brown, or the days got shorter, | 0:03:26 | 0:03:30 | |
when rivers flooded, or berries ripened. | 0:03:30 | 0:03:33 | |
These very practical observations would have helped them | 0:03:33 | 0:03:37 | |
in their daily struggle to survive. | 0:03:37 | 0:03:39 | |
One of the first examples of humans' attempts to measure | 0:03:42 | 0:03:45 | |
was discovered here in Southern France by four teenagers | 0:03:45 | 0:03:49 | |
and their dog called Robot. | 0:03:49 | 0:03:50 | |
It was 1940 and the 18-year-old Marcel Ravidat | 0:03:51 | 0:03:56 | |
was exploring these woods | 0:03:56 | 0:03:57 | |
when he came across a hole where a tree had been uprooted by a storm. | 0:03:57 | 0:04:02 | |
He needed some tools to make the hole bigger | 0:04:02 | 0:04:05 | |
so he came back four days later with his three friends, | 0:04:05 | 0:04:08 | |
and they uncovered the entrance to a huge system of unexplored caves. | 0:04:08 | 0:04:14 | |
But what they discovered inside was even more exciting. | 0:04:14 | 0:04:17 | |
Wow! | 0:04:30 | 0:04:32 | |
The boys must have been absolutely staggered to have come here | 0:04:33 | 0:04:37 | |
and see these images painted on the wall. | 0:04:37 | 0:04:40 | |
I mean, these are some of the oldest cave paintings. | 0:04:40 | 0:04:42 | |
Oh, look at this! | 0:04:42 | 0:04:44 | |
All over the wall! | 0:04:44 | 0:04:46 | |
Marcel and his friends had discovered | 0:04:54 | 0:04:57 | |
some of the earliest cave paintings ever found. | 0:04:57 | 0:04:59 | |
These date back 17,000 years and were painted by Cro-Magnon man. | 0:04:59 | 0:05:04 | |
It's beautiful! | 0:05:06 | 0:05:09 | |
You can really feel the energy of these animals | 0:05:09 | 0:05:12 | |
rushing across the walls. | 0:05:12 | 0:05:14 | |
This cave is a replica of the original | 0:05:20 | 0:05:22 | |
which is a few hundred metres from here and is now carefully preserved. | 0:05:22 | 0:05:27 | |
Dr Michael Rappenglueck believes that these paintings | 0:05:33 | 0:05:36 | |
are evidence of man's first attempt to measure time. | 0:05:36 | 0:05:41 | |
This one is very, very beautiful. | 0:05:41 | 0:05:44 | |
To him, this is a giant calendar. | 0:05:45 | 0:05:48 | |
The clues lie in these strange patterns of dots. | 0:05:49 | 0:05:53 | |
Each dot represents a week. | 0:05:53 | 0:05:55 | |
13 dots represent one quarter of the year. | 0:05:55 | 0:05:58 | |
His theory is that each seven day phase of the moon, | 0:06:00 | 0:06:04 | |
what today we'd call a week, | 0:06:04 | 0:06:06 | |
is marked with a dot on the wall to chart the passing of time. | 0:06:06 | 0:06:10 | |
It was a distinctively-shaped cluster of dots | 0:06:17 | 0:06:20 | |
that eventually allowed him to unlock | 0:06:20 | 0:06:22 | |
the full meaning of the paintings. | 0:06:22 | 0:06:24 | |
Look up to the ceiling. You see six dots. | 0:06:26 | 0:06:30 | |
It reminds a little dipper, | 0:06:30 | 0:06:33 | |
and I think this is the star pattern of the Pleiades. | 0:06:33 | 0:06:36 | |
Oh, so these dots are not representing weeks any more, | 0:06:36 | 0:06:38 | |
these are stars up there? | 0:06:38 | 0:06:40 | |
Yes. These are stars, and they serve to start the year. | 0:06:40 | 0:06:45 | |
When our ancestors saw the stars form this same alignment in the sky, | 0:06:48 | 0:06:53 | |
it would mark the start of their year. | 0:06:53 | 0:06:56 | |
Dr Rappenglueck believes the animals have meaning too. | 0:06:57 | 0:07:01 | |
The stag represents autumn equinox | 0:07:01 | 0:07:05 | |
and it's starting a time cycle to the horse. | 0:07:05 | 0:07:08 | |
The horse represents spring time | 0:07:08 | 0:07:11 | |
and you see the horse is pregnant, highly pregnant, | 0:07:11 | 0:07:15 | |
so three-quarters of the year are represented on the wall. | 0:07:15 | 0:07:18 | |
So, it's the star calendar | 0:07:18 | 0:07:20 | |
followed by the calendar marking the weeks that allows them to know | 0:07:20 | 0:07:23 | |
when the stags are rutting, or pregnant animals... | 0:07:23 | 0:07:27 | |
Yes, they synchronised biological rhythms of animals | 0:07:27 | 0:07:30 | |
with astronomical rhythms. | 0:07:30 | 0:07:32 | |
-It's an extraordinarily sophisticated system... -Yes, it is. | 0:07:32 | 0:07:36 | |
-..for 17,000 years ago. -It is. | 0:07:36 | 0:07:37 | |
It's amazing! | 0:07:37 | 0:07:39 | |
With the aid of this basic calendar, for the first time, | 0:07:44 | 0:07:47 | |
our ancestors could start to predict what would happen, and when. | 0:07:47 | 0:07:52 | |
They could prepare to hunt when animals migrated close by | 0:07:52 | 0:07:56 | |
or, as agriculture developed, determine the best time to plant crops. | 0:07:56 | 0:08:00 | |
Measurement was making life easier. | 0:08:03 | 0:08:05 | |
But as communities grew, so did the need for more precise timekeeping | 0:08:12 | 0:08:17 | |
beyond the cycles of the moon, the stars and the seasons. | 0:08:17 | 0:08:22 | |
13,000 years after our ancestors painted the caves in Lascaux, | 0:08:22 | 0:08:26 | |
first the Mesopotamians and then the Egyptians | 0:08:26 | 0:08:29 | |
started to tackle the problem of dividing up the day. | 0:08:29 | 0:08:32 | |
And they took their inspiration from the sun. | 0:08:32 | 0:08:35 | |
By observing how the length of a shadow changed through the day, | 0:08:42 | 0:08:45 | |
they found an easy way to measure time. | 0:08:45 | 0:08:49 | |
And they used a device just like this. | 0:08:49 | 0:08:51 | |
This is a replica of an Ancient Egyptian sundial. | 0:08:54 | 0:08:58 | |
It's one of the first instruments ever created to measure time. | 0:08:58 | 0:09:02 | |
Now at midday, this stone here would have cast no shadow. | 0:09:02 | 0:09:06 | |
But, as the day went on, the shadow would get longer and longer, | 0:09:06 | 0:09:10 | |
so the Ancient Egyptians decided to divide the day up into 12 units. | 0:09:10 | 0:09:15 | |
You can see the lines here - we've got one, two, three... | 0:09:15 | 0:09:19 | |
We've got six lines for the afternoon, and six for the morning. | 0:09:19 | 0:09:22 | |
It's just coming up to three o'clock. | 0:09:22 | 0:09:25 | |
By linking time and distance, they could reliably measure | 0:09:26 | 0:09:30 | |
shorter periods of time. | 0:09:30 | 0:09:32 | |
Telling the time, by measuring the length of a shadow. | 0:09:32 | 0:09:35 | |
Although the sundial was a brilliant invention, | 0:09:46 | 0:09:48 | |
it was fundamentally flawed. | 0:09:48 | 0:09:50 | |
It didn't work at night. | 0:09:53 | 0:09:55 | |
Like the cavemen of Lascaux, who used stars to mark the seasons, | 0:09:59 | 0:10:03 | |
the Egyptians went one step further. | 0:10:03 | 0:10:05 | |
They used them to divide up the hours of darkness. | 0:10:07 | 0:10:10 | |
But on a cloudy night, just as on a cloudy day, | 0:10:10 | 0:10:12 | |
they still had no way of telling the time, | 0:10:12 | 0:10:15 | |
and this is where they made a conceptual leap. | 0:10:15 | 0:10:19 | |
This is a water clock. | 0:10:23 | 0:10:25 | |
It's a very simple idea. | 0:10:28 | 0:10:30 | |
Basically, what they did was to take a bucket | 0:10:30 | 0:10:32 | |
and make a hole in the bottom. | 0:10:32 | 0:10:35 | |
Then as night fell, they would fill the bucket with water. | 0:10:35 | 0:10:38 | |
Now, as the water drips out, | 0:10:45 | 0:10:47 | |
they can use lines marked on the side of the bucket | 0:10:47 | 0:10:50 | |
to tell how much time has passed through the night. | 0:10:50 | 0:10:53 | |
They could measure 12 hours | 0:10:58 | 0:11:00 | |
independently of the sun or the stars. | 0:11:00 | 0:11:02 | |
But why count 12 hours at all? | 0:11:04 | 0:11:05 | |
The answer lies in how business was done thousands of years ago. | 0:11:11 | 0:11:15 | |
Throughout the Middle East, | 0:11:15 | 0:11:17 | |
the number 12 and the number 60 were important in commerce. | 0:11:17 | 0:11:21 | |
They're numbers that were familiar to traders in markets just like this. | 0:11:21 | 0:11:27 | |
And the reason they use them is all to do with arithmetic. | 0:11:27 | 0:11:30 | |
As a mathematician, I love the answer | 0:11:32 | 0:11:35 | |
because it's about the mathematical properties of these two numbers. | 0:11:35 | 0:11:38 | |
They're highly divisible. | 0:11:38 | 0:11:40 | |
Take the number 60. | 0:11:48 | 0:11:50 | |
I can divide 60 beans in to 6 groups of 10 beans, | 0:11:50 | 0:11:54 | |
5 groups of 12 beans... | 0:11:54 | 0:11:58 | |
..4 groups of 15 beans... | 0:11:59 | 0:12:03 | |
3 groups of 20 beans. | 0:12:03 | 0:12:05 | |
Five, there. | 0:12:05 | 0:12:07 | |
2 groups of 30 beans... | 0:12:07 | 0:12:09 | |
..or 1 group of 60 beans. | 0:12:10 | 0:12:13 | |
But take 100 beans, how can I divide that? | 0:12:15 | 0:12:18 | |
I can divide it into 2 groups of 50 | 0:12:18 | 0:12:21 | |
but divide by three and I've got to start cutting a bean! | 0:12:21 | 0:12:23 | |
Because the numbers 12 and 60 were so familiar to the Egyptians, | 0:12:25 | 0:12:28 | |
it was perhaps no great conceptual leap | 0:12:28 | 0:12:31 | |
for them to come up with a 12-hour night and day. | 0:12:31 | 0:12:34 | |
So the idea stuck. | 0:12:34 | 0:12:36 | |
It wasn't just the measurement of time that the Egyptians needed to tackle. | 0:12:43 | 0:12:47 | |
They also needed to find better ways to measure distance. | 0:12:49 | 0:12:52 | |
Every year the Nile would flood, | 0:12:52 | 0:12:55 | |
bringing great fertility to the land. | 0:12:55 | 0:12:57 | |
But with each flood, | 0:12:59 | 0:13:01 | |
the borders of the farmers' land would be washed away. | 0:13:01 | 0:13:05 | |
So when the waters receded, an accurate way of measuring | 0:13:05 | 0:13:08 | |
field size and re-establishing boundaries was critical. | 0:13:08 | 0:13:12 | |
They needed a reliable and uniform measure of length. | 0:13:12 | 0:13:17 | |
And their solution was this. | 0:13:17 | 0:13:20 | |
It's a cubit rod and it's the Egyptian equivalent of a ruler. | 0:13:20 | 0:13:25 | |
Its length was the distance of the pharaoh's cubit, | 0:13:25 | 0:13:28 | |
which was the length from his elbow to the tip of his middle finger. | 0:13:28 | 0:13:32 | |
So actually, my cubit is slightly shorter than the pharaoh's. | 0:13:32 | 0:13:36 | |
But this led to the Egyptians creating some of the most remarkable buildings the world has ever seen. | 0:13:36 | 0:13:42 | |
This is the great pyramid of Cheops, | 0:13:46 | 0:13:49 | |
built over 4,500 years ago for the fourth dynasty pharaoh, Khufu. | 0:13:49 | 0:13:54 | |
It is said 20,000 men took 20 years to build it, | 0:13:57 | 0:14:00 | |
using over two million limestone blocks, | 0:14:00 | 0:14:04 | |
all meticulously aligned and measured with the cubit rod. | 0:14:04 | 0:14:09 | |
This is a miraculous building. | 0:14:09 | 0:14:11 | |
The length of the side is 440 cubits exactly. | 0:14:11 | 0:14:16 | |
-Exactly? -Exactly. | 0:14:16 | 0:14:18 | |
And the height is 280 cubits exactly. | 0:14:18 | 0:14:20 | |
Also it is very square. | 0:14:20 | 0:14:22 | |
It has perfection in every part of it. | 0:14:22 | 0:14:25 | |
Absolutely, and with so many people working on it, | 0:14:25 | 0:14:27 | |
spread over, I guess, a large area and a large amount of time, | 0:14:27 | 0:14:32 | |
I mean, actually having a standard unit of measurement | 0:14:32 | 0:14:34 | |
must have been absolutely essential. | 0:14:34 | 0:14:36 | |
Exactly. They had a rope which is 100 times this | 0:14:36 | 0:14:40 | |
that has knots in it every one cubit or every ten cubits, | 0:14:40 | 0:14:45 | |
which is called khet. | 0:14:45 | 0:14:46 | |
OK. We want to measure 440 so we need to take the corner stone | 0:14:46 | 0:14:50 | |
-as our starting point, so if you start measuring. -Yes. | 0:14:50 | 0:14:55 | |
The original cornerstones are no longer visible | 0:14:57 | 0:15:00 | |
but the foundations are still here for all to see. | 0:15:00 | 0:15:04 | |
I think I chose the easy job. | 0:15:04 | 0:15:05 | |
430... | 0:15:16 | 0:15:18 | |
Wow! | 0:15:18 | 0:15:20 | |
-440 cubits, pretty much on the knot! -Exactly! | 0:15:20 | 0:15:24 | |
What's so remarkable about the Egyptian system is that they | 0:15:36 | 0:15:39 | |
were one of the first to standardise length measurement. | 0:15:39 | 0:15:42 | |
It's said that every full moon, | 0:15:42 | 0:15:44 | |
the surveyors across the land would gather | 0:15:44 | 0:15:46 | |
and compare their wooden cubit rod against the royal master cubit. | 0:15:46 | 0:15:51 | |
Made of granite, this was held by the royal surveyor. | 0:15:51 | 0:15:55 | |
Failure to maintain an accurate cubit was punishable by death. | 0:15:55 | 0:15:59 | |
It was a very simple and efficient way | 0:15:59 | 0:16:02 | |
to standardise length measurement across the land. | 0:16:02 | 0:16:05 | |
And it enabled the Egyptians to measure things with phenomenal accuracy. | 0:16:05 | 0:16:09 | |
Mastering and standardising time and length measurement | 0:16:15 | 0:16:18 | |
was really key to the success of the ancient Egyptian empire. | 0:16:18 | 0:16:22 | |
The power of measurement is that it created order out of chaos | 0:16:31 | 0:16:35 | |
and allowed civilisation to flourish. | 0:16:35 | 0:16:37 | |
The standardisation of measurement which began here in Egypt | 0:16:53 | 0:16:57 | |
several millennia ago is now central to all our lives. | 0:16:57 | 0:17:00 | |
Nearly every country in the world has a national measurement body | 0:17:00 | 0:17:05 | |
whose master lengths and weights are calibrated | 0:17:05 | 0:17:08 | |
by one international body, | 0:17:08 | 0:17:10 | |
a little bit like the modern day pharaohs, | 0:17:10 | 0:17:13 | |
trying to bring standardisation of measurement across the globe. | 0:17:13 | 0:17:17 | |
But despite the obvious logic of having one international system, | 0:17:17 | 0:17:22 | |
it hasn't been completely embraced. | 0:17:22 | 0:17:24 | |
Take me, for example. | 0:17:24 | 0:17:26 | |
I'm going to the airport in this cab which measures its speed | 0:17:26 | 0:17:29 | |
in kilometres per hour and miles per hour. | 0:17:29 | 0:17:32 | |
When I'm up in the air, they'll be measuring their altitude in feet. | 0:17:32 | 0:17:37 | |
My clothes are measured in inches and my shoes are measured in... | 0:17:37 | 0:17:40 | |
..well, frankly I've never quite understood | 0:17:41 | 0:17:44 | |
what the unit of measurement for shoe size is! | 0:17:44 | 0:17:47 | |
Shoe sizes aside, | 0:17:49 | 0:17:51 | |
standardisation of measurement underpins all modern science. | 0:17:51 | 0:17:55 | |
Though the route to standardisation has not been an easy one. | 0:17:55 | 0:17:59 | |
Throughout history, | 0:18:13 | 0:18:15 | |
rulers had a nasty habit of ripping up measurement systems | 0:18:15 | 0:18:18 | |
and demanding that they be replaced by lengths based on their own body parts. | 0:18:18 | 0:18:23 | |
In 12th century England | 0:18:30 | 0:18:31 | |
the yard was defined as the length from the tip of the King's nose | 0:18:31 | 0:18:35 | |
to the top of his outstretched thumb. | 0:18:35 | 0:18:38 | |
But as each new reign came in, so things changed. | 0:18:38 | 0:18:41 | |
Henry VII, he defined a yard as the length of his arm. | 0:18:41 | 0:18:44 | |
Elizabeth I, not to be outdone by her male predecessors, | 0:18:47 | 0:18:50 | |
added a few more inches. | 0:18:50 | 0:18:53 | |
And so the chaos continued. | 0:18:53 | 0:18:56 | |
Lack of standardisation was a problem on the Continent, too. | 0:19:08 | 0:19:12 | |
If you thought the British had it bad, | 0:19:14 | 0:19:16 | |
then spare a thought for the French. | 0:19:16 | 0:19:18 | |
On the eve of the French Revolution, | 0:19:18 | 0:19:20 | |
the Ancien Regime had over 250,000 different weights and measures, | 0:19:20 | 0:19:23 | |
including several thousand for length. | 0:19:23 | 0:19:26 | |
By the end of the 18th century, | 0:19:36 | 0:19:37 | |
people realised that something needed to be done. | 0:19:37 | 0:19:40 | |
Trade was impossible and open to fraud, navigation was treacherous | 0:19:40 | 0:19:44 | |
and building plans made by an architect in one city | 0:19:44 | 0:19:46 | |
couldn't be reproduced in the other | 0:19:46 | 0:19:48 | |
cos they didn't have the same measurements. | 0:19:48 | 0:19:50 | |
The mess was finally sorted out by the French Academy of Sciences. | 0:20:00 | 0:20:05 | |
It was the last few days of the French monarchy, | 0:20:05 | 0:20:07 | |
and buoyed by the revolutionary spirit of the time, | 0:20:07 | 0:20:09 | |
a sense of egalite and rationalism, | 0:20:09 | 0:20:12 | |
France's best scientists decided to form | 0:20:12 | 0:20:14 | |
a ground-breaking and revolutionary plan of their own. | 0:20:14 | 0:20:18 | |
No longer would measurement be based on the human body, | 0:20:18 | 0:20:21 | |
or the vanity of kings and queens. | 0:20:21 | 0:20:24 | |
They decided that it should be based | 0:20:24 | 0:20:26 | |
on something permanent and unchanging. They chose the Earth. | 0:20:26 | 0:20:30 | |
It's really exciting to be here. | 0:20:50 | 0:20:52 | |
This is really one of the great scientific centres in the whole of the world. | 0:20:52 | 0:20:57 | |
And this is where the modern story of measurement really began. | 0:20:57 | 0:21:01 | |
Where a new standardised unit of length was introduced. | 0:21:01 | 0:21:04 | |
One that is familiar to us all today. | 0:21:04 | 0:21:07 | |
On the 26th March 1791, the Academy here decided to call | 0:21:09 | 0:21:13 | |
this new length measurement the metre. | 0:21:13 | 0:21:15 | |
Named after the Greek word "metron", meaning measure, | 0:21:15 | 0:21:19 | |
they decided it should be one ten millionth of the distance | 0:21:19 | 0:21:22 | |
between the North Pole and the equator. | 0:21:22 | 0:21:25 | |
It was very clever. | 0:21:27 | 0:21:28 | |
The Academy knew that a French colloquial measure | 0:21:28 | 0:21:31 | |
would never be accepted by the rest of the world. | 0:21:31 | 0:21:34 | |
By basing the metre on the planet itself, | 0:21:35 | 0:21:38 | |
no-one country could argue for their own measure. | 0:21:38 | 0:21:42 | |
They had transcended the politics of nations. | 0:21:42 | 0:21:46 | |
"This is a system for all people for all time", | 0:21:47 | 0:21:50 | |
announced the Revolutionary government. | 0:21:50 | 0:21:53 | |
There was one problem, though. | 0:21:53 | 0:21:55 | |
Nobody knew accurately what the distance between the North Pole and the equator actually was. | 0:21:55 | 0:22:00 | |
Getting an accurate figure would mean embarking on the most | 0:22:03 | 0:22:07 | |
ambitious and complex large-scale measurement project ever attempted. | 0:22:07 | 0:22:11 | |
Two scientists were tasked with turning the theory into reality. | 0:22:14 | 0:22:19 | |
They were Pierre Mechain and Jean Baptiste Delambre. | 0:22:19 | 0:22:23 | |
Their task was to measure the distance between two points on a meridian, or line of longitude. | 0:22:25 | 0:22:31 | |
Then using fairly simple mathematics, | 0:22:32 | 0:22:35 | |
and knowing the latitude of each point, | 0:22:35 | 0:22:37 | |
they could extrapolate and calculate the distance. | 0:22:37 | 0:22:40 | |
from the Pole to the equator. | 0:22:40 | 0:22:42 | |
This experiment would be difficult enough under normal conditions | 0:22:48 | 0:22:52 | |
but France was in the middle of a revolution. | 0:22:52 | 0:22:55 | |
It was a dangerous time to have big ideas that were not | 0:22:58 | 0:23:02 | |
necessarily easy for the new order to understand. | 0:23:02 | 0:23:04 | |
Nevertheless, undaunted, the scientists pushed ahead. | 0:23:08 | 0:23:12 | |
It was here in 1793, from this bell tower in Dunkirk, | 0:23:16 | 0:23:21 | |
that Jean Baptiste Delambre started the northernmost part | 0:23:21 | 0:23:24 | |
of his epic quest to measure the Earth. | 0:23:24 | 0:23:26 | |
While 800 miles to the south, | 0:23:33 | 0:23:35 | |
Barcelona was chosen for Pierre Mechain. | 0:23:35 | 0:23:38 | |
Their plan was to work towards each other | 0:23:41 | 0:23:44 | |
and meet in Rodez in southern France. | 0:23:44 | 0:23:46 | |
You can imagine Delambre's excitement as he stood up here | 0:23:51 | 0:23:54 | |
200 years ago, ready to start his journey. | 0:23:54 | 0:23:57 | |
A journey that would take him seven years to complete. | 0:23:57 | 0:24:00 | |
And the rather splendid piece of equipment they used was this, | 0:24:04 | 0:24:07 | |
a repeating circle. | 0:24:07 | 0:24:10 | |
A device that measure angles extremely accurately | 0:24:10 | 0:24:13 | |
and as good today as the day it was made. | 0:24:13 | 0:24:17 | |
Now, obviously, Delambre wouldn't measure every distance from here to Barcelona | 0:24:17 | 0:24:20 | |
but what he can do is use a method called triangulation. | 0:24:20 | 0:24:23 | |
So, the first point of the triangle is the top of this belfry. | 0:24:23 | 0:24:27 | |
Then Delambre would have looked across the countryside, trying to find two high points. | 0:24:27 | 0:24:31 | |
And he would use this piece of equipment to line up the telescopes | 0:24:31 | 0:24:35 | |
on those two other points. | 0:24:35 | 0:24:37 | |
Then all he had to do was measure the angle between the two points | 0:24:37 | 0:24:41 | |
and measure the distance to the closest one. | 0:24:41 | 0:24:43 | |
By then moving to the next high point | 0:24:45 | 0:24:47 | |
and measuring the angles again, | 0:24:47 | 0:24:50 | |
simple geometry gave him the distances between all three. | 0:24:50 | 0:24:53 | |
So it's an amazing principle because just one measurement of distance | 0:24:57 | 0:25:01 | |
and then it's triangles all the way to Barcelona. | 0:25:01 | 0:25:03 | |
Delambre had a number of close scrapes along the way. | 0:25:11 | 0:25:14 | |
He was arrested several times, accused of being a spy. | 0:25:15 | 0:25:19 | |
Why else would he be scaling towers carrying strange equipment? | 0:25:21 | 0:25:25 | |
He tried to explain that he was measuring the size | 0:25:26 | 0:25:29 | |
of the Earth for the Academy of Sciences | 0:25:29 | 0:25:32 | |
but a drunk militiaman interrupted, | 0:25:32 | 0:25:35 | |
"There is no more Academy. We are all equal now. You'll come with us." | 0:25:35 | 0:25:40 | |
But in general, they were literally above it all. | 0:25:47 | 0:25:50 | |
On roof tops, towers and church spires they carried out their quest. | 0:25:50 | 0:25:56 | |
It was an extraordinary feat. | 0:25:57 | 0:25:59 | |
Seven long years later, the two men had measured the exact distance | 0:25:59 | 0:26:04 | |
between Dunkirk and Barcelona. | 0:26:04 | 0:26:07 | |
Now the metre was just a simple calculation. | 0:26:08 | 0:26:11 | |
The result of all Mechain and Delambre's hard labour, the prototype metre bar, | 0:26:27 | 0:26:32 | |
is held here at the French National Archives in Paris. | 0:26:32 | 0:26:36 | |
Made in 1799 of pure platinum, it's meant to represent | 0:26:38 | 0:26:41 | |
one ten millionth of the distance | 0:26:41 | 0:26:44 | |
between the North Pole and the equator. | 0:26:44 | 0:26:46 | |
In fact, due to errors that Mechain made early on | 0:26:46 | 0:26:49 | |
in his survey, it's fractionally wrong. | 0:26:49 | 0:26:51 | |
The errors that Mechain made were pretty much irrelevant | 0:26:58 | 0:27:01 | |
because for the first time, | 0:27:01 | 0:27:02 | |
the world had a unit of length | 0:27:02 | 0:27:05 | |
that was based on something they believed was permanent and unchanging, the Earth. | 0:27:05 | 0:27:11 | |
There it is. The metre. | 0:27:14 | 0:27:16 | |
A thing of beauty. | 0:27:20 | 0:27:22 | |
Not so much the object but the idea it represents. | 0:27:22 | 0:27:26 | |
This metre bar ushered in the era of metrification. | 0:27:29 | 0:27:32 | |
And the achievement is immense. | 0:27:32 | 0:27:34 | |
Even Napoleon, in a moment of humility, admitted that, | 0:27:34 | 0:27:36 | |
"Conquests come and go, but this work will endure." | 0:27:36 | 0:27:39 | |
And he was right, | 0:27:39 | 0:27:41 | |
this lump of metal really represents a change in our thinking. | 0:27:41 | 0:27:45 | |
For the first time, | 0:27:45 | 0:27:47 | |
we had measurement based on something fundamental and universal. | 0:27:47 | 0:27:51 | |
The concept was brilliant, | 0:28:03 | 0:28:05 | |
but the metre's triumphant arrival | 0:28:05 | 0:28:07 | |
was not embraced with universal enthusiasm. | 0:28:07 | 0:28:11 | |
In fact, it took several decades before the metre was finally | 0:28:11 | 0:28:14 | |
accepted as a standard international unit of measurement. | 0:28:14 | 0:28:18 | |
It was on a spring day in 1875 that it all became official. | 0:28:23 | 0:28:28 | |
The historic Metre Convention was signed | 0:28:29 | 0:28:32 | |
and metre clones sent out around the world. | 0:28:32 | 0:28:35 | |
It was the beginning of our global system of precision and accuracy. | 0:28:37 | 0:28:41 | |
17 countries signed the convention to form the BIPM, | 0:28:41 | 0:28:46 | |
the Bureau International des Poids et Mesures. | 0:28:46 | 0:28:49 | |
The custodians of international weight and measurement. | 0:28:50 | 0:28:55 | |
It's a role they still perform today. | 0:28:55 | 0:28:58 | |
Metrication was to be the basis for a new system of measurement, | 0:28:58 | 0:29:02 | |
the System Internationale or SI. | 0:29:02 | 0:29:06 | |
It even led to a new science, metrology, | 0:29:07 | 0:29:10 | |
the study and refinement of measurement. | 0:29:10 | 0:29:13 | |
The metre had united the world. At least, in theory. | 0:29:13 | 0:29:18 | |
Alongside the metre, seismic changes had happened in how we measured time. | 0:29:31 | 0:29:36 | |
For more than 3,000 years, | 0:29:38 | 0:29:40 | |
the sundial was the timekeeper of choice across the world. | 0:29:40 | 0:29:44 | |
But it was not without its problems. | 0:29:45 | 0:29:47 | |
And the reason is it's just not possible to fix the exact | 0:29:49 | 0:29:52 | |
length of an hour because the shadow cast on the dial | 0:29:52 | 0:29:56 | |
alters daily throughout the seasons. | 0:29:56 | 0:29:58 | |
The Greek astronomer Hipparchus was the first to notice | 0:30:04 | 0:30:08 | |
the equal length of day and night at the spring and autumn equinoxes | 0:30:08 | 0:30:13 | |
and that this could give us a standard for setting a fixed length of hour. | 0:30:13 | 0:30:17 | |
But up until the 14th century, we had no practical way of doing this. | 0:30:26 | 0:30:31 | |
It took the invention of the mechanical clock to change everything. | 0:30:33 | 0:30:38 | |
This is the Salisbury Cathedral clock. | 0:31:00 | 0:31:04 | |
It dates back to 1386 and it's believed to be the oldest surviving mechanical clock in the world. | 0:31:04 | 0:31:11 | |
For me this is an absolutely staggering achievement, | 0:31:14 | 0:31:17 | |
I mean, this is the 14th century, | 0:31:17 | 0:31:19 | |
the medieval time, | 0:31:19 | 0:31:21 | |
and here a blacksmith and a stonemason have created something | 0:31:21 | 0:31:25 | |
that is able to regulate time. | 0:31:25 | 0:31:29 | |
Now, it isn't driven by a pendulum, | 0:31:29 | 0:31:31 | |
those sort of clocks wouldn't be invented until the 17th century. | 0:31:31 | 0:31:34 | |
Instead it's these weights at the back | 0:31:34 | 0:31:37 | |
which are controlling the clock. | 0:31:37 | 0:31:38 | |
And as the weights fall they unwind the ropes around these barrels. | 0:31:38 | 0:31:43 | |
It's gravity that drives the clock. | 0:31:47 | 0:31:50 | |
and all you need to power it is some muscle to raise the weights. | 0:31:50 | 0:31:55 | |
The intriguing thing is there isn't any clock face on this clock. | 0:32:05 | 0:32:10 | |
It was already quite an achievement in that time | 0:32:10 | 0:32:12 | |
just to get that bell to bong every hour. | 0:32:12 | 0:32:15 | |
BELL RINGS | 0:32:23 | 0:32:26 | |
By the end of the 14th century many cathedrals across Europe | 0:32:32 | 0:32:36 | |
had built clock towers, towering up to the heavens, glorifying God, | 0:32:36 | 0:32:40 | |
but perhaps more importantly, | 0:32:40 | 0:32:42 | |
controlling the lives of us mere mortals down below. | 0:32:42 | 0:32:45 | |
The clocks weren't terribly accurate, | 0:32:45 | 0:32:47 | |
probably the best ones lost 15 minutes a day, | 0:32:47 | 0:32:50 | |
but they began to irrevocably change people's lives. | 0:32:50 | 0:32:54 | |
No longer dependent on the sun, | 0:32:54 | 0:32:56 | |
we were tied to the chimes of man-made clocks. | 0:32:56 | 0:32:58 | |
In the 15th and 16th centuries, as the mechanisms became more accurate, | 0:33:03 | 0:33:07 | |
the clock face itself appeared, something we now take for granted. | 0:33:07 | 0:33:12 | |
It then became possible to break down our day | 0:33:13 | 0:33:16 | |
into even smaller units. | 0:33:16 | 0:33:18 | |
For the first time, the hour could be divided | 0:33:19 | 0:33:22 | |
into minutes and seconds. | 0:33:22 | 0:33:24 | |
The idea came from the Greek mathematician Ptolemy | 0:33:27 | 0:33:30 | |
who divided a circle into 360 equal parts called degrees. | 0:33:30 | 0:33:36 | |
He then split each degree into 60 minutes | 0:33:36 | 0:33:40 | |
and each minute into 60 second minutes... | 0:33:40 | 0:33:43 | |
..which gave us the words we use today. | 0:33:50 | 0:33:53 | |
The relationship between time and length was getting closer. | 0:33:56 | 0:34:00 | |
We now measured the passage of time by the distance the hand | 0:34:01 | 0:34:04 | |
travelled around the clock face. | 0:34:04 | 0:34:07 | |
Mechanical clocks gave us a fixed hour. | 0:34:11 | 0:34:14 | |
But actually setting them to the right time was still a problem. | 0:34:14 | 0:34:18 | |
We still looked to the sun and set our clocks and watches to noon | 0:34:20 | 0:34:23 | |
when the sun was directly overhead. | 0:34:23 | 0:34:26 | |
But that meant that each town had its own different time. | 0:34:26 | 0:34:30 | |
For example, here in Salisbury, | 0:34:30 | 0:34:32 | |
the clocks were over seven minutes later than the clocks in London. | 0:34:32 | 0:34:36 | |
The reason? | 0:34:36 | 0:34:38 | |
Well, we're further west here, so the sun arrives overhead later. | 0:34:38 | 0:34:41 | |
But with the development of steam power in the early 19th century, | 0:34:52 | 0:34:56 | |
things had to change because it was impossible | 0:34:56 | 0:35:00 | |
to set busy train timetables | 0:35:00 | 0:35:02 | |
if every town had its own different time. | 0:35:02 | 0:35:05 | |
A single national time was urgently needed. | 0:35:08 | 0:35:11 | |
Under the unswerving leadership of Sir George Airy, | 0:35:11 | 0:35:15 | |
the Astronomer Royal at the Greenwich Observatory, | 0:35:15 | 0:35:17 | |
Greenwich time became THE time for Great Britain. | 0:35:17 | 0:35:20 | |
The railways were the first to switch their entire timetable | 0:35:28 | 0:35:32 | |
to this new time. | 0:35:32 | 0:35:34 | |
And they did it by sending the correct time to virtually | 0:35:36 | 0:35:39 | |
every station in the country by the new telegraph lines | 0:35:39 | 0:35:43 | |
which often ran alongside the railways. | 0:35:43 | 0:35:45 | |
Gradually, national and international time | 0:35:50 | 0:35:53 | |
became essential for business and in 1884, | 0:35:53 | 0:35:57 | |
Greenwich time was universally adopted as the basis | 0:35:57 | 0:36:00 | |
for a new system of international time zones. | 0:36:00 | 0:36:02 | |
The reason for its enthusiastic adoption was because | 0:36:06 | 0:36:10 | |
the Greenwich Observatory produced the most accurate | 0:36:10 | 0:36:13 | |
nautical almanacs used by mariners throughout the world. | 0:36:13 | 0:36:17 | |
And as these almanacs were all set with Greenwich lying on zero degrees of longitude, | 0:36:18 | 0:36:22 | |
the prime meridian, at a stroke, | 0:36:22 | 0:36:24 | |
Great Britain became the centre of the world. | 0:36:24 | 0:36:28 | |
Time was no longer calibrated locally | 0:36:31 | 0:36:33 | |
by when the sun was at its highest, | 0:36:33 | 0:36:35 | |
it was set astronomically at Greenwich. | 0:36:35 | 0:36:39 | |
But while Greenwich time had gone international, | 0:36:48 | 0:36:50 | |
for most people, actually getting your hands on the correct time | 0:36:50 | 0:36:54 | |
was still a challenge. | 0:36:54 | 0:36:56 | |
And for businesses, this was fast becoming a problem. | 0:36:56 | 0:36:59 | |
And one family realised a cunning way to exploit this need. | 0:37:01 | 0:37:05 | |
Every week, John Henry Belville would come up the hill | 0:37:05 | 0:37:08 | |
here to Greenwich and set his chronometer to the correct time. | 0:37:08 | 0:37:12 | |
And then he'd go back down to London. | 0:37:15 | 0:37:17 | |
to sell the right time to watchmakers and businesses. | 0:37:17 | 0:37:20 | |
By the 1940s, thanks to the radio and cheap clocks and watches... | 0:37:24 | 0:37:28 | |
..we could all run on time. | 0:37:30 | 0:37:32 | |
Time was money. | 0:37:35 | 0:37:37 | |
International trade, business and travel were all thriving. | 0:37:37 | 0:37:40 | |
As the world embraced Greenwich time, | 0:37:42 | 0:37:44 | |
our journey towards globalisation started. | 0:37:44 | 0:37:47 | |
While universal time was transforming our world | 0:37:55 | 0:37:58 | |
the same could not be said for the metre. | 0:37:58 | 0:38:01 | |
17 countries had enthusiastically signed up to the historic | 0:38:02 | 0:38:06 | |
metre convention but, in practice, few had enforced it. | 0:38:06 | 0:38:11 | |
And the muddle of different measurements continued, | 0:38:11 | 0:38:14 | |
with standards and gauges differing from town to town, | 0:38:14 | 0:38:18 | |
and even factory to factory, | 0:38:18 | 0:38:20 | |
which was to have dire consequences, here in the United States. | 0:38:20 | 0:38:24 | |
When a huge fire ripped through the American city of Baltimore in 1904, | 0:38:28 | 0:38:33 | |
a disaster of epic proportions was unfolding. | 0:38:33 | 0:38:36 | |
As fire crews from the nearby cities of Washington | 0:38:40 | 0:38:44 | |
and New York rushed to the scene, all they could do was sit | 0:38:44 | 0:38:47 | |
and watch the inferno engulf the city. | 0:38:47 | 0:38:49 | |
None of their fire hoses would fit Baltimore's fire hydrants. | 0:38:50 | 0:38:55 | |
Despite being less than 200 miles apart, | 0:38:55 | 0:38:59 | |
all the fire crews were using different sized equipment. | 0:38:59 | 0:39:02 | |
The fire raged out of control for two days, destroying 1,500 homes. | 0:39:02 | 0:39:08 | |
Length measurement needed to be standardised and fast. | 0:39:16 | 0:39:20 | |
NIST, America's measurement body, | 0:39:20 | 0:39:22 | |
started campaigning for better standards. | 0:39:22 | 0:39:24 | |
Spurred on by the NIST campaign, | 0:39:34 | 0:39:37 | |
American industrialists soon realised | 0:39:37 | 0:39:39 | |
that they could capitalise on improvements in accuracy. | 0:39:39 | 0:39:43 | |
Henry Ford started commissioning increasingly accurate gauges and measures. | 0:39:44 | 0:39:48 | |
Precise and standardised measurement | 0:39:54 | 0:39:57 | |
meant that mass production was possible. | 0:39:57 | 0:39:59 | |
At the same time, strict patterns of shift work tied their workforces to the clock. | 0:39:59 | 0:40:04 | |
It was the dawn of the modern age. | 0:40:10 | 0:40:12 | |
For the first time, millions of identical parts | 0:40:12 | 0:40:15 | |
could be produced at rapid speed and minimal cost. | 0:40:15 | 0:40:18 | |
The American boom was under way. | 0:40:18 | 0:40:20 | |
And when you see inspectors checking parts for accuracy | 0:40:20 | 0:40:24 | |
to dimensions measured in 10,000th of an inch, | 0:40:24 | 0:40:27 | |
you see where quantity production of quality products | 0:40:27 | 0:40:31 | |
actually begins because parts must fit together perfectly. | 0:40:31 | 0:40:35 | |
It would provide a profound lesson to the world. | 0:40:35 | 0:40:39 | |
Precise measurement had the power to change the fortunes of a nation. | 0:40:39 | 0:40:44 | |
But the problem with any technological breakthrough | 0:40:51 | 0:40:55 | |
is no-one quite knows where it will lead. | 0:40:55 | 0:40:57 | |
It took the paranoia of the Cold War and the resulting arms race | 0:40:57 | 0:41:02 | |
to trigger the next big leap in length measurement. | 0:41:02 | 0:41:06 | |
And it led us further than we ever thought possible. | 0:41:06 | 0:41:09 | |
But history and our own conscience will judge us harshly, | 0:41:11 | 0:41:16 | |
if we do not now make every effort to test our hopes by action. | 0:41:16 | 0:41:21 | |
The stakes were rising but our level of accuracy | 0:41:22 | 0:41:25 | |
was failing to keep up with our aspirations. | 0:41:25 | 0:41:28 | |
Up to the 1960s, | 0:41:30 | 0:41:32 | |
we could measure with an accuracy of one ten millionth of a metre. | 0:41:32 | 0:41:36 | |
But an error of this magnitude in the components of a rocket navigation system | 0:41:36 | 0:41:41 | |
would mean missing the moon by 4,000 miles. | 0:41:41 | 0:41:45 | |
Now the challenge was to improve the accuracy a hundredfold. | 0:41:47 | 0:41:50 | |
We choose to go to the moon in this decade and do the other things, | 0:41:52 | 0:41:57 | |
not because they are easy but because they are hard. | 0:41:57 | 0:42:01 | |
Because that goal will serve to organise | 0:42:01 | 0:42:03 | |
and measure the best of our energies and skills. | 0:42:03 | 0:42:08 | |
The metre bar was no longer accurate enough. | 0:42:09 | 0:42:12 | |
A new and more precise way of measuring length was needed. | 0:42:12 | 0:42:17 | |
The answer lay in the fundamental properties of the universe. | 0:42:17 | 0:42:21 | |
It was the dawn of the quantum age. | 0:42:21 | 0:42:24 | |
Since the 1870s, | 0:42:52 | 0:42:54 | |
there had been a growing desire to take measurement away from earthly | 0:42:54 | 0:42:57 | |
constants like circumference of the globe or the length of the day... | 0:42:57 | 0:43:01 | |
..and to tie measurement to the fundamental and unchanging laws of nature. | 0:43:03 | 0:43:08 | |
Things like the speed of light or the charge on a single electron. | 0:43:08 | 0:43:12 | |
It was a Scottish genius, James Clerk Maxwell, | 0:43:15 | 0:43:18 | |
who first suggested that these universal constants | 0:43:18 | 0:43:22 | |
could hold the key to more precise measurement. | 0:43:22 | 0:43:25 | |
Considered by many to be the 19th century's most influential physicist, | 0:43:27 | 0:43:31 | |
Maxwell's theories would change the course of measurement history. | 0:43:31 | 0:43:36 | |
He said at the time, | 0:43:36 | 0:43:38 | |
"If then we wish to obtain standards which shall be absolutely permanent, | 0:43:38 | 0:43:42 | |
"we must seek them not in the dimensions or motion of our planet, | 0:43:42 | 0:43:46 | |
"but in the wavelength, the period of vibration | 0:43:46 | 0:43:49 | |
"and the absolute mass of these imperishable and unalterable | 0:43:49 | 0:43:53 | |
"and perfectly similar molecules." | 0:43:53 | 0:43:56 | |
Maxwell's idea was as revolutionary as the decision a century earlier | 0:43:58 | 0:44:02 | |
to take length measurement away from the human body and base it on the Earth. | 0:44:02 | 0:44:07 | |
Maxwell changed the direction of the science of measurement. | 0:44:07 | 0:44:11 | |
Maxwell, it's hard to overestimate the influence he had | 0:44:13 | 0:44:18 | |
on scientific thought in the 19th century. | 0:44:18 | 0:44:20 | |
It was a very influential idea he had and he said, | 0:44:20 | 0:44:24 | |
"We should be measuring length | 0:44:24 | 0:44:26 | |
"in terms of the wavelength of a colour of light." | 0:44:26 | 0:44:29 | |
But even he couldn't figure out how to really do it | 0:44:29 | 0:44:33 | |
to the accuracy that would be required to replace the, sort of, | 0:44:33 | 0:44:38 | |
metre definition. | 0:44:38 | 0:44:40 | |
Maxwell was never able to turn his dream of using | 0:44:41 | 0:44:44 | |
the wavelength of light to measure distance into reality | 0:44:44 | 0:44:48 | |
because the technology to achieve it simply didn't exist. | 0:44:48 | 0:44:51 | |
But his ideas were revolutionary. | 0:44:53 | 0:44:56 | |
It wasn't until decades later, a scientist at the BIPM, | 0:45:02 | 0:45:06 | |
the same place where the world's master metre bar is held, | 0:45:06 | 0:45:09 | |
would start to bring Maxwell's vision to life. | 0:45:09 | 0:45:12 | |
Albert Michaelson began to design | 0:45:16 | 0:45:18 | |
and build machines called interferometers | 0:45:18 | 0:45:21 | |
that could actually measure the wavelength of different light sources. | 0:45:21 | 0:45:24 | |
So this is one of Michaelson's original interferometers. | 0:45:28 | 0:45:32 | |
What was he using it for and how did he use it? | 0:45:32 | 0:45:35 | |
Well, he wanted to demonstrate that it would be possible | 0:45:35 | 0:45:39 | |
to measure a wavelength of light, because light travels in waves, | 0:45:39 | 0:45:44 | |
and then in a future time, | 0:45:44 | 0:45:46 | |
define the metre in terms of this wavelength of light. | 0:45:46 | 0:45:51 | |
Wavelengths of light are invisible to the human eye. | 0:45:51 | 0:45:54 | |
Michaelson's genius was realising that when light is split | 0:45:54 | 0:45:58 | |
and then recombined, it forms a unique pattern called interference | 0:45:58 | 0:46:03 | |
that can be used to count wavelengths. | 0:46:03 | 0:46:06 | |
So by counting how many, going from light to dark, light to dark, | 0:46:06 | 0:46:10 | |
take a metre, divide by the number of those, | 0:46:10 | 0:46:12 | |
you'll get the wavelength of light, | 0:46:12 | 0:46:14 | |
-something you can't see with your naked eye. -Right. | 0:46:14 | 0:46:17 | |
What he had to do was build up from a wavelength of light to a metre. | 0:46:17 | 0:46:21 | |
And in a half a millimetre, | 0:46:21 | 0:46:23 | |
-there are about more than 1,000 wavelengths. -Extraordinary. | 0:46:23 | 0:46:28 | |
It was the breakthrough that was to change the destiny of the metre. | 0:46:32 | 0:46:36 | |
After over half a century of laborious research, | 0:46:40 | 0:46:43 | |
scientists were ready. | 0:46:43 | 0:46:45 | |
Maxwell's dream was about to become a reality. | 0:46:45 | 0:46:48 | |
On Friday the 14th of October 1960, delegates from across the globe, | 0:46:48 | 0:46:53 | |
from Russian and America, gathered here in the grounds of the BIPM. | 0:46:53 | 0:46:57 | |
The fate of the metre was in the balance. | 0:46:57 | 0:47:00 | |
At six o'clock that evening, to much applause, | 0:47:03 | 0:47:06 | |
the metre was redefined in terms of the number | 0:47:06 | 0:47:10 | |
of wavelengths of light emitted by a special krypton lamp. | 0:47:10 | 0:47:13 | |
Finally, the metre bar was consigned to history. | 0:47:14 | 0:47:17 | |
But I don't think those French Revolutionaries | 0:47:17 | 0:47:20 | |
who first came up with the idea of the metre would be too disappointed | 0:47:20 | 0:47:25 | |
because it was really realising their dream of tying | 0:47:25 | 0:47:27 | |
the metre to something unchanging and universal. | 0:47:27 | 0:47:31 | |
Distance could be measured accurately | 0:47:37 | 0:47:39 | |
using a universal constant, the wavelength of light. | 0:47:39 | 0:47:43 | |
But how could we put this new science into practice? | 0:47:44 | 0:47:47 | |
That would need the help of a project codenamed Laser. | 0:47:59 | 0:48:03 | |
It was the brainchild of Californian Theodore Maiman. | 0:48:07 | 0:48:11 | |
Well, this device happens to be the original laser. | 0:48:13 | 0:48:19 | |
The beauty of the laser, is that it is light of a precise, | 0:48:20 | 0:48:23 | |
fixed wavelength. | 0:48:23 | 0:48:26 | |
By bouncing this beam off an object, | 0:48:26 | 0:48:28 | |
and precisely measuring the time it takes to bounce back, | 0:48:28 | 0:48:32 | |
suddenly we could measure distances with incredible precision. | 0:48:32 | 0:48:36 | |
Within years, the laser was helping us | 0:48:36 | 0:48:39 | |
to measure our world in ways we never thought possible. | 0:48:39 | 0:48:42 | |
And there was no better illustration of this | 0:48:42 | 0:48:45 | |
than the Apollo 11 lunar landings. | 0:48:45 | 0:48:47 | |
One small step for man, one giant leap for mankind. | 0:49:06 | 0:49:11 | |
When Neil Armstrong and Buzz Aldrin | 0:49:13 | 0:49:16 | |
landed on the Sea of Tranquillity more than 40 years ago | 0:49:16 | 0:49:19 | |
on the 21st July 1969, | 0:49:19 | 0:49:22 | |
they left a mirror on the moon's surface. | 0:49:22 | 0:49:24 | |
When astronomers later fired a laser pulse at it, | 0:49:30 | 0:49:33 | |
Maiman's invention was also about to make history. | 0:49:33 | 0:49:36 | |
The beam took 2.5 seconds to reflect back to Earth. | 0:49:38 | 0:49:42 | |
For the first time, scientists could calculate the distance | 0:49:44 | 0:49:48 | |
to the moon at any phase of its orbit | 0:49:48 | 0:49:50 | |
to an accuracy of three centimetres. | 0:49:50 | 0:49:52 | |
Lasers changed everything. | 0:49:58 | 0:50:01 | |
They made scientists rethink what was possible. | 0:50:01 | 0:50:04 | |
We could measure distance with extraordinary precision. | 0:50:04 | 0:50:08 | |
Distance was tied to a universal, unchanging constant | 0:50:26 | 0:50:30 | |
but time was not. | 0:50:30 | 0:50:32 | |
The second was still based on the rotation of the Earth, | 0:50:33 | 0:50:36 | |
which is actually rather variable. | 0:50:36 | 0:50:39 | |
Finding a better way of defining time | 0:50:46 | 0:50:48 | |
was to come from an unexpected quarter. | 0:50:48 | 0:50:51 | |
Just a few years before that landmark 1960 meeting in Paris, | 0:50:56 | 0:51:00 | |
an English scientist called Louis Essen | 0:51:00 | 0:51:03 | |
was working here at the UK's National Physical Laboratory. | 0:51:03 | 0:51:07 | |
His passion was precision timekeeping, | 0:51:07 | 0:51:10 | |
and he was beginning work on a new generation of clock, | 0:51:10 | 0:51:13 | |
the atomic clock. | 0:51:13 | 0:51:16 | |
We set our quartz clocks to keep time with the rotation of the Earth. | 0:51:17 | 0:51:21 | |
But for some of our modern problems, this is not quite accurate enough, | 0:51:21 | 0:51:24 | |
and now we're setting our quartz to keep time | 0:51:24 | 0:51:28 | |
with the vibrations of the atom. | 0:51:28 | 0:51:31 | |
The theory was to define time | 0:51:33 | 0:51:35 | |
through the vibration of individual atoms. | 0:51:35 | 0:51:38 | |
Across the Atlantic, the Americans, at their national laboratory, | 0:51:38 | 0:51:42 | |
were already pushing forward with a well-funded programme. | 0:51:42 | 0:51:46 | |
Back in Britain, Essen was struggling. | 0:51:46 | 0:51:50 | |
There was little enthusiasm for his clock project | 0:51:50 | 0:51:53 | |
and funding was always a problem. | 0:51:53 | 0:51:55 | |
His first experiment imploded, destroying much of his equipment. | 0:51:55 | 0:52:00 | |
But in a classic story of the underdog winning through, | 0:52:01 | 0:52:04 | |
Essen eventually created the world's first working atomic clock. | 0:52:04 | 0:52:10 | |
It was called the Caesium One. | 0:52:10 | 0:52:12 | |
And it was accurate to 1 second in 300 years. | 0:52:12 | 0:52:17 | |
The second was no longer based on the movement of our planet. | 0:52:17 | 0:52:21 | |
Time was now locked to the beating heart of a caesium atom. | 0:52:21 | 0:52:26 | |
A movement that was unchanging and fundamental across the universe. | 0:52:26 | 0:52:31 | |
In Britain, the latest incarnation of Essen's atomic clock is the CSF2. | 0:52:37 | 0:52:43 | |
It's one of a global network of atomic clocks that sets our time. | 0:52:45 | 0:52:49 | |
To most people this doesn't look like a clock at all, | 0:52:53 | 0:52:55 | |
so how does it actually measure time? | 0:52:55 | 0:52:57 | |
Well, what we're doing here is using lasers | 0:52:57 | 0:53:00 | |
to slow down the caesium atoms. | 0:53:00 | 0:53:02 | |
We form a cloud of very slowly moving caesium atoms | 0:53:02 | 0:53:04 | |
and we use the lasers to throw that cloud upwards through | 0:53:04 | 0:53:07 | |
an enclosure containing microwaves. | 0:53:07 | 0:53:09 | |
Then they fall back through it a second time under gravity. | 0:53:09 | 0:53:12 | |
When the atoms change from one energy level to another, | 0:53:12 | 0:53:15 | |
they emit or absorb one very precise frequency, | 0:53:15 | 0:53:18 | |
and we can use that frequency to keep track of time. | 0:53:18 | 0:53:21 | |
We simply count up the oscillations. | 0:53:21 | 0:53:23 | |
So it's the number of oscillations that will define the length of a second. | 0:53:26 | 0:53:30 | |
Those oscillations are a particular property of that caesium atom. | 0:53:30 | 0:53:33 | |
That's right, yes. | 0:53:33 | 0:53:35 | |
So, any caesium atom always has the same number | 0:53:35 | 0:53:38 | |
of oscillations per second. | 0:53:38 | 0:53:40 | |
The oscillations of these caesium atoms are the ticking of the clock. | 0:53:42 | 0:53:47 | |
and they give the CSF2 accuracy to 1 second in 138 million years. | 0:53:47 | 0:53:54 | |
It's a degree of precision our ancestors could never have imagined. | 0:53:57 | 0:54:01 | |
The genius of Maxwell, Michaelson | 0:54:03 | 0:54:06 | |
and Essen now touch every part of our lives. | 0:54:06 | 0:54:09 | |
They could never have guessed their work would one day | 0:54:16 | 0:54:19 | |
be at the centre of everything from our banking systems to phones, | 0:54:19 | 0:54:22 | |
GPS and the internet. | 0:54:22 | 0:54:25 | |
These only exist because of the accuracy of atomic clocks | 0:54:27 | 0:54:31 | |
and their ability to synchronise time across the planet. | 0:54:31 | 0:54:35 | |
Measurement has taken us in directions we could never have dreamt possible. | 0:54:36 | 0:54:40 | |
But the story doesn't end there. | 0:54:50 | 0:54:53 | |
In one last twist, scientists looked at the metre again... | 0:54:53 | 0:54:57 | |
..and realised that they could now redefine length | 0:54:58 | 0:55:02 | |
using the new accuracy of the second. | 0:55:02 | 0:55:04 | |
It was 1983 and in a collaboration between different measurement labs | 0:55:09 | 0:55:14 | |
across the world, atomic clocks measured the speed of light | 0:55:14 | 0:55:18 | |
with incredible precision. | 0:55:18 | 0:55:20 | |
The metre could finally be defined by how far light | 0:55:22 | 0:55:25 | |
travels in a tiny fraction of a second. | 0:55:25 | 0:55:29 | |
Time and length were intimately intertwined. | 0:55:29 | 0:55:32 | |
We've come a long way since the days of the pharaohs, | 0:55:41 | 0:55:43 | |
when time was defined by the length of a shadow. | 0:55:43 | 0:55:46 | |
After 3,000 years, time and distance are once again linked, | 0:55:46 | 0:55:52 | |
joined together by one of the most fundamental | 0:55:52 | 0:55:55 | |
and universal constants of nature, the speed of light. | 0:55:55 | 0:55:59 | |
Despite all the great advances in time and length measurement, | 0:56:25 | 0:56:28 | |
the quest is still on. | 0:56:28 | 0:56:31 | |
Scientists are trying to create ever more accurate clocks. | 0:56:31 | 0:56:34 | |
Clocks that will only lose one second | 0:56:34 | 0:56:36 | |
in the lifetime of the universe. | 0:56:36 | 0:56:38 | |
And once they're deployed we can only begin to imagine how it's going to change our world. | 0:56:40 | 0:56:44 | |
Instant communication, quantum computers, | 0:56:44 | 0:56:48 | |
planes that can land themselves. | 0:56:48 | 0:56:50 | |
Science fiction will become a reality. | 0:56:50 | 0:56:53 | |
And that's the beauty of measurement. | 0:56:53 | 0:56:55 | |
Every leap in precision, from the cubit rod to the atomic clock, | 0:56:55 | 0:56:59 | |
has led to a technological revolution. | 0:56:59 | 0:57:01 | |
Through history measurement has changed every aspect of our lives... | 0:57:04 | 0:57:08 | |
..splitting the year into seasons and lunar cycles | 0:57:10 | 0:57:13 | |
allowed man to plan ahead for the first time | 0:57:13 | 0:57:16 | |
and gain advantage over the rest of nature. | 0:57:16 | 0:57:19 | |
Dividing the day still further into 24 hours | 0:57:22 | 0:57:25 | |
was the bedrock for civilisation. | 0:57:25 | 0:57:28 | |
The fixed hour controlled the working day. | 0:57:28 | 0:57:31 | |
And uniform national and international time | 0:57:35 | 0:57:37 | |
allowed the globalisation of industry. | 0:57:37 | 0:57:40 | |
The world would never be the same. | 0:57:41 | 0:57:43 | |
The story of measurement has shaped and changed our history. | 0:57:47 | 0:57:51 | |
And will continue to do so as we delve deeper in to the atomic | 0:57:51 | 0:57:54 | |
fabric of the universe in search of greater precision. | 0:57:54 | 0:57:58 | |
Next time, I meet the biggest problem in measurement, the kilogram. | 0:58:03 | 0:58:09 | |
This 19th-century artefact is the world's master kilo, | 0:58:09 | 0:58:14 | |
and it's losing weight. | 0:58:14 | 0:58:16 | |
Now, a head-to-head race is on to replace it... | 0:58:17 | 0:58:20 | |
..as the best minds in measurement science fight it out, | 0:58:22 | 0:58:25 | |
there can only be one winner. | 0:58:25 | 0:58:27 |