All language subtitles for Precision.The.Measure.Of.All.Things - 2of3 - Mass.And.Moles

On the morning
of the 14th June, 1940,

several German tank
divisions rumbled

through the streets of Paris.

The impossible had happened.
Germany had invaded and France
had fallen.

But there was one building
on the outskirts of Paris that

the Nazis never occupied.

This chateau has the same
status as an independent territory.

Its contents are
so closely guarded,

I have to hand over my passport
to gain access.

Today, an eminent
group of scientists have

gathered from all over the world
to witness a very special event.

Security is tight, with key holders
arriving from three different
countries.

The vault holds one of the most
important artefacts in our world.

This is a real piece of measurement
history. Well, I suppose it's

not really history at all,
because this is the kilo.

Under three layers of protective
glass is the kilogram master

known as Le Grand K.

It's the weight on which all
weights have been based since 1889.

Its importance is
so great that neither the Nazis nor

the liberating American forces
dared set foot inside here.

And the reason we're here today?

Well, just to check it's still
here. But there's a problem.

Tests have revealed that Le Grand K,
this scientific celebrity,

is losing weight, creating
a crisis in the scientific world.

It's losing approximately 20
billionths of a gram every year.

But why on earth should such a tiny
change matter so much?

I'm on a journey to investigate the
world of measurement, and to see how

our drive for precision has really
changed the course of history.

Today we can describe the chaos

and complexity of the universe with
just seven fundamental units,

the building blocks of modern
science.

And science is obsessed with
defining these units with
ever-greater precision.

In this series, I want to understand
why such extreme

levels of precision are
so important,

how we define these units,

and how, through history, each step
forward has unleashed

a technological revolution.

In this programme, we'll explore why
being able to measure weight is

so important.

And how the race to replace
the ageing Grand K

might hold the key to a new
way of understanding our world.

This is the story
of how we mastered weight.

"How much do I have?" is a question
that has driven trade

and commerce
since the dawn of civilisation.

And today, weights are still
central to all our lives.

The reason we're
so reliant on weights and scales

is in part down to our own inability
to accurately gauge weight.

We tend to believe our eyes
rather than trusting

the weight in our hands.

And I've come to London's Borough
Market to prove the point.

Excuse me - wonder whether I could
get you to take part in a little
experiment? Of course, yes.

So, I've got a series of weights
here which I've just

put in order of height and what
I'd like you to do is to place

the heaviest weight here
and the lightest one at your end.

Have a go. See which one you
think is the heaviest.

That's....

This little guy, that's the
heaviest? OK. What about the next
heaviest?

I think this one... that's
the lightest.

The lightest of all? I think... OK!

The really surprising thing is
that the one you've put at this end,

which you think is the lightest,
is in fact the heaviest!

So you thought this one here
was the heaviest.

OK, I'm going to give you both of
these in your hand - this one is

actually heavier than that one.
Do you believe me?

Well, it doesn't feel like that.

No, it doesn't,
but let's use the scales.

So I am going to weigh the one that
you thought was the lightest,

so that comes out about 424 grams.

OK, let's put your one on.

You think this one is heavier.
It's only 345 grams!

Isn't that extraordinary?
Because even with that knowledge,

now try and weigh them
again. Which one is heavier...

This one. I know! And that's why
we need a set of weights

because we're so bad at perception.

Like any good scientist
I carried on with the testing.

How's that possible?

And my random shoppers,
to a man and a woman,

all chose the same two weights

and they all chose wrong.

OK. Wow!

Seeing if something is big or
small massively

skews our perception of how heavy
it is.

It is a problem our ancestors

first started grappling with more
than 5,000 years ago.

Our earliest evidence comes
from the Middle East and was driven

by the emergence of the first cities
in Mesopotamia around 3,000 BC.

As populations grew,

a way of fairly trading goods was
urgently needed.

People demanded a system of weight
that everyone could trust.

Taking their inspiration
from nature, they used grain.

Uniform in size and shape,
grain was available to all.

The world had its first weights.

Using simple beam balances,
which we continue to use today,

we started to trade goods
based on their weight in grains.

It wasn't perfect, but with grains
varying so little in weight,

the system worked.

It made the movement
and sale of goods possible,

enabling humans to live together in
bigger cities and allowing the first

economies to grow.

Empires were no
longer being built solely by armies.

They were being built by trade.

As commerce developed
across the ancient world, a faster

means of weighing produce
was needed.

After all,
if I wanted to buy something that

weighed 700 grains of barley,

I don't want to have to count out
700 grains each time.

So, gradually, a standardised
system of weights began to emerge.

First the Mesopotamians and then
the Ancient Egyptians developed

stones and things made out of metals

and brass in order to represent
different weights of grain.

It was such an efficient system
that it began to be

copied across the civilised world.
So here we have standard

weights from China.

These hexagons
are standard weights used in Sudan.

And the amazing thing is
that despite all of these

different weights and measures, they
were all related back to the weight

of a grain, because everyone trusted
how much a grain would weigh.

By Roman times, millions of
tonnes of produce were being

traded around the world every day.

The ability to compare the weights
or masses of two different

kinds of goods
so that you can work out how to

exchange between them,
that's the key to economic success.

And so it's the demand for economic
comparison that drives weight

standardisation throughout history.

By the end of the 13th century,
the world had hundreds of different

weights, and nearly all were
based on a fixed number of grains.

In England, we'd inherited
the pound from the Roman Empire.

It was initially made up of 12
ounces,

which were equivalent
to 437 grains of barley.

But the problem all rulers faced
was how to keep weight

standardised across a nation.

It was considered such a big issue
that even the Magna Carta, the most

celebrated legal document in English
history, tried to deal with it.

"Let there be one measure of wine
throughout our whole realm,

"and one measure of ale
and one measure of corn."

It all sounded great in theory
but in practice,

it was virtually impossible
to enforce.

Cheating was such a big problem,

regular trials were held to check
merchants' weights and measures.

Any found to be wrong were
immediately destroyed.

Accurate scales were the only way
cheats could be exposed.

Accuracy was power.

Scales were not
only a great measuring device.

They also came to symbolise
fairness, power,

the very legal system itself.

From Ancient Egypt's Feather
of Truth to the paintings

of the great Dutch Masters, scales
have featured throughout history.

As it was written in the Bible,
"By weight, measure and number,

"God made all things."

Measurement has always been
associated in culture with

justice and law and crime. Because
what it does is to establish the

equivalence between two things that
you otherwise could not compare.

That's what justice means,
so it's no coincidence that the

figure of Justice is shown carrying
scales, carrying balance pans.

And for centuries, when you made
a weight measurement, you had to

show your customers what you were
doing, partly to avoid

the possibility of deceit
but also to show how just you were -

to be just,
was precisely to use balance.

So, with all this moral weightiness
flying around, the punishment

for using false
measures could be severe.

In 1772 BC, the Code of Hammurabi
was introduced into Babylonian law,

which said that any taverner using
false weights could be served up
with a death penalty.

And in the 18th
century, bankers caught cheating

would have to stand in pillory,
and brewers... in the dung cart.

But despite the importance
we placed on weight

and getting it right, it took one
remarkable Englishman

to realise the measurement of
weight has a fundamental problem.

It was the great Sir Isaac Newton
who first realised that

weight changes depending on where
and when you are measuring it.

It was 1665 and Britain was
gripped by the Plague,

so Newton decided to
flee his college in Cambridge and

he came to the safety of his country
retreat here at Woolsthorpe Manor.

And here is the famous apple tree
that inspired his observations.

So much has been written about this
apple tree, it really has become

a symbol for the turning point in
our understanding of the universe.

Newton's eureka moment was
witnessed by a friend.

"After dinner,
the weather being warm,

"we went into the garden and drank
tea, under the shade
of some apple trees.

"The notion of gravitation came
into his mind.

"Why should that apple always
descend perpendicularly to the
ground?"

Newton realised there must be
a force acting on that apple,

pulling it to the ground, otherwise
why wouldn't it just

float in the air,
or move sideways or go upwards.

He named that force "gravity"
after the Latin word

"gravitas" for heaviness.

Newton's law of gravity was to
completely change the way

we think about weight.

We finally understood the subtle
but vital difference between weight

and mass and it paved the way for
modern measurement.

Now to show how important Newton's
discovery was, I've got a piece of
metal here

and an incredibly sensitive
set of scales.

Now, the scales say that this

piece of metal weighs 368.7025/4...

It's kind of flickering
between the two, it's so sensitive.

Now, let's take this
piece of metal to the top of this

block of flats
and see how much it weighs up there.

Now, up here, the metal
weighs 368.69 grams,

so I seem to have
lost ten milligrams.

But of course the mass
hasn't changed,

what's changed is the gravity.

I've got less gravity up here

than I have got down at the bottom
of the block of flats.

If I took this piece of metal
another 100,000 metres

up into space then it would weigh
hardly anything at all.

Simply put, mass is measuring the
amount of stuff there is inside
here,

and that doesn't change whether I'm
at sea level or out in space.

But the weight does.

In one simple equation,

Newton's genius revolutionised how
we thought about weight and mass.

But it would take a real revolution
in France, to finally create

the measure of mass that we all use
today - the kilogram.

By the middle of the 18th century,
weight measurement,

like length, was in a total mess and
nobody had it worse than the French.

People were supposed to use
the King's measures for pounds
and ounces.

But in reality, every village
and town had their own system,

all slightly different.

Disputes and arguments were so
commonplace that the village took

to chaining the weights and measures
to the wall of the local church.

Trade was painfully slow
and open to corruption,

and no-one could agree on whose
weight was right.

A new international system
of measurement was urgently needed.

Letters flew between the powers
of Europe.

"Too long have Great Britain
and France been at variance

"with each other, for empty honour
or guilty interests.

"It is time that the two free
nations should unite their exertions

"for the promotion of a discovery
that must be useful to mankind."

On the eve of the French
Revolution, the great and good

of the French scientific community
approached the doomed Louis XVI for

permission to create a new system of
length, mass and volume measurement.

The greatest minds of the day
gathered here at the

prestigious Academy of Sciences
in Paris to brainstorm a solution.

They decided to base their new
system on something universal

and unchanging - the Earth.

It was the birth of metrication.

The first unit they fixed was
the metre, basing it on one ten-

millionth of the distance between
the North Pole and the Equator.

The next was the kilogram,
and the task was given to the

father of modern chemistry,
Antoine-Laurent Lavoisier.

By day, he was a wealthy tax
collector. By night,

he was the greatest
chemist in the land.

The French visionaries behind the
metric system wanted all the new

measurements to be linked, so they
came up with an elegant solution.

The new kilogram was to be
equal to the weight of one perfect

cubic decimetre of water...

..a litre.

The idea was very simple.

Anybody with a metre ruler and some
water could create their own kilo.

But making a kilo based
on the weight of a cubic decimetre

of water turned out to be much more
difficult than they thought.

Now, I've got two perfect
decimetres of water here.

The trouble is that these don't
weigh the same amount.

The colder water weighs 998 grams
whilst the hotter water

is 957 grams.

Because the hotter water is,
the less dense it is.

And that's the trouble, the weight
depends on the temperature.

Not only that, it will depend
on what impurities are inside the

water, what the atmospheric pressure
is, how far I am above sea level.

There's a real problem with trying
to define the kilo

based on the weight of water.

Lavoisier came close to solving
the problem of how to accurately

weigh water.

But his brilliant career
met an abrupt end

at the hands of the guillotine
on the 8th May 1794.

His tax-collecting day job
was his downfall.

Next to take up the kilo
challenge were scientists

Louis Lef�vre-Gineau
and Giovanni Fabbroni.

Four years later, they finally
perfected how to measure

a cubit decimetre
of distilled water.

A master metal kilogram could
finally be cast.

And on the 22nd June, 1799,

they presented their prototype
kilogram to the nation.

Called the "kilogramme des Archives",
it was made out of the new

wonder metal, platinum.

Soon, kilogram clones,
as well as copies of the metre bar,

were being sent to villages
and towns across the nation

to bring uniformity to the
French Empire.

Their vision was brilliant.

But there was a flaw.

The trouble was that pure platinum,
although resistant to air

and water, is actually rather soft
and prone to damage.

And that meant bits were easily
knocked off,

gradually rendering the hundreds
of cloned kilos inaccurate.

The Academy's grand idea was
slowly being eroded.

It would take nearly 70 years
to realise a new,

more stable master kilo, and then
a set of clones would be needed.

London metallurgists Johnson
Matthey were given the order to

produce 250 kilograms of platinum
mixed with strength-giving iridium.

It was a big order, worth �2.2
million at today's prices.

The man in charge of production,
George Matthey,

the world's leading expert
in casting platinum, offered to

make the kilos at his
state-of-the-art furnaces

at Hatton Garden.

But French pride intervened,
insisting it happened here,

at the Conservatoire in Paris.

It was a disaster.

The platinum got contaminated
by iron, rendering the whole
consignment useless.

It was a huge embarrassment, both
for French pride and their pockets.

But it wasn't the death of the kilo
or the metric system.

With international trade booming,
the benefits of having one

common measurement system were
clear for all to see.

And in 1875, diplomats from 17
countries met here in Paris

and agreed to formally adopt
the metric system.

With great zeal,

a new kilogram master was
commissioned.

The order once again went to Johnson
Matthey and this time George Matthey
was finally

allowed to cast the most accurate
platinum and iridium kilo ever made.

Christened "Le Grand K", it was
consigned to a specially-made vault

at a newly established international
centre of measurement outside Paris.

And here it is - the Bureau
International des Poids et Mesures.

The BIPM. In English, the
International Bureau of Weights
and Measures.

And this is really
international territory.

It's kind of a mark of how
important measurement

is to the world that we've created
a UN of measurement.

From the beginning, the BIPM's
mission was to make sure

measurements were consistent
throughout the world.

This is the building that was once
home to all the world's master
measurements.

Today, most have been retired,

replaced by new definitions based
on the universal and unchanging

laws of nature,
like the speed of light

and the movement of atoms.

Le Grand K is in fact the
only artefact that is still in use.

A measurement dinosaur.

Today, here at the BIPM they're
still making clones of that Grand K.

Fabrice here is polishing this
until it exactly matches

the mass of the Grand K
sitting in the vault downstairs.

Over half the countries in the
world have one of these clones.

The next one he's working on is
clone number 103 that's going to go

to... well we're actually not
allowed to know where
it's going to go.

Without Le Grand K, our entire
global system of mass

and weight measurement
would crumble.

Unfortunately, "crumble"
is a little bit of a touchy word

inside this building because that's
what's happening to Le Grand K.

I mean, it's not literally
crumbling,

but despite the kid-glove treatment

it's received over the last 150
years, it's believed that it

has changed by the equivalent of one
grain of sand during its lifetime.

And that's bad news,

because it no longer matches
the weight of the world's clones.

A new way to define mass is
urgently needed.

Now the race is on to replace
the definition of the kilo with

something more
fitting for the 21st century,

something based on a universal
constant that can be measured

wherever you are in the universe.

We've done it for length - that's
now tied to the speed of light,

for time - that's related to the
movement of electrons in the atom.

Now we want to do it for the kilo.

It's a head-to-head race between
two international teams.

Each one taking a radically
different approach to solving

the kilo crisis.

In America, Team Watt Balance
are combining the power

of electricity with scales whose
principles date back 5,000 years.

Their dream? To redefine
the kilo based on energy.

6,000 kilometres
away in Germany, Team Silicon Sphere

are trying to count every single
atom in a perfect ball of silicon.

It's an immense task -
like covering the Earth in sand

and trying to count every
single granule.

As the best minds in measurement
science fight it out,

Le Grand K's long and illustrious
career could soon be over,

but its legacy has been
staggering.

From the moment it was
adopted, the movement

and sale of goods became much easier
and more efficient.

The scientific community
jumped on the new "metric" system,

loving its simplicity and the ease
they could split or multiply

the metre and the kilogram by ten.

But from the very beginning

of its life in the 18th century, the
public remained less convinced.

People were just not interested
in revolutionising their everyday

life, what they did when they went
shopping, how they exchanged

and bought, in the name
of revolutionary purity.

The kilo continues to divide
opinion.

In the UK it was only
adopted in the 1960s

and its arrival was met with
outright hostility.

'All we ask is the freedom of choice
to record in the native

'and still legal measures of this
country instead of these

'cock-eyed kilograms, which make
no sense at all.'

But despite the opposition,
today all

but three nations - the
United States, Liberia and Myanmar -

have embraced the kilo
and the metric system.

While the world was moving towards
a unified weight measurement

system, the actual technology of
weighing was now lagging behind.

Variations
on ancient Mesopotamian

and Egyptian beam balances
remained our scales of choice right

up to the 19th century.

The problem was they
took so long to use.

In the UK, weighing was made much
worse by the Turnpike Act of 1752.

Eager to tax the movement of goods,
the government ordered all towns

to "erect a crane machine or engine
for the weighing carts and wagons".

At each location,
carts had to be unloaded, weighed,

reloaded and weighed once again.

And to the add to the daily misery,
every key road demanded tolls, too.

All payable on the weight
you were carrying.

With the birth of the Industrial
Revolution, things had to change.

Factories to forges now needed raw
materials in unprecedented
quantities.

And they had to be weighed,

bought and transported with
ever-increasing speed and
precision.

A faster, more efficient means of
weighing was desperately needed.

The solution was the weighbridge.

A technological triumph,
the weighbridge,

with its balance scale
hidden beneath the floor, would play

a key role in driving our industrial
revolution onwards.

Now, loads could be
weighed in seconds as they rolled on

and off the bridge.

But it would take electricity to
drive the next big

breakthrough in weighing.

Inventor, Charles Wheatstone,
championed

the use of electricity in the 1840s.

Experimenting with simple
electrical circuits,

he devised a way of measuring
electrical resistance.

But it wasn't until a century later
that people realised this

very same technology could be
used to measure weight.

Today, the need for speedy mass
measurement drives our world.

This train is delivering coal to
Rugeley Power Station

and as it runs over the track,
it's being weighed by load cells,

which are underneath the track.

If we come in here, we can see
how much we've weighed so far.

So, hi, Andy. Hi.

So this is the first carriage
that's gone over,

so we've got 100 tonnes.

Yeah. So it's much more efficient
than weighing it all by hand.

Oh, yeah, very much so.

We can measure at
70 kilometres per hour

so we are talking less than
a second per wagon, probably.

Wow, that's extraordinary.

So how's this piece of track
actually weighing the train?

Well, underneath
the track are several of these.

They're called load cells.

And actually,

it's this little system of wires on
the rod which is doing the weighing.

But as soon as something runs
over the track,

it compresses the rod and the wires
get shorter and fatter.

The resistance goes down

and I get more electrical current
running through it.

And suddenly I'm getting a reading.

What's amazing is there's a direct
mathematical relationship between

the increase in electrical current
and the weight going over the wires.

So we're using the electricity to
weigh the train.

In fact, this thing is so sensitive
that even if I step on it,

I actually can get how much I weigh.

So let's see.

So how much do I weigh, Andy?

84.

84 kilos?! Yeah.

I don't weigh 84 kilos. Must be
the weight of this.

Today, load cells are used
the world over.

We've come a long way
since the days of the beam balance.

Now everywhere, from roadside weigh
stations

to supermarket checkouts use them.

Measuring mass with electricity
has changed our world.

We can now weigh, transport

and deliver billions of tonnes-worth
of produce with a speed and accuracy

our Victorian forefathers would
never have dreamt possible.

Precision mass measurement is key
to world commerce.

Now it's the turn of the very small
to push the limits of mass
measurement.

Here in America, I've come to meet
a team who've come up with

a unique approach to measuring
some of the smallest living

things on Earth... cells.

Project leader Scott Manalis

is using mass to monitor
the growth of cells.

His work could one day revolutionise
our fight against cancer.

In his lab, he has built the world's
smallest weighing station.

Here, inside a microchip just
millimetres in size,

cells are captured
and passed over a sensor.

The long, thin section
highlighted here,

acts a bit like a diving board.

When a cell passes over it,

it vibrates just like a diving board
moves after a diver jumps off it.

The speed of the vibration

is directly linked to the
weight of the cell.

So, using simple maths,

Scott can measure the cell with
incredible accuracy.

This cell is the equivalent
of like a white blood cell,

in terms of its size. OK.

And it weighs 100 picograms.

Picograms, so that's
ten... To the minus 12.

All right, OK. So that's
a lot of zeros.

So this is incredibly small.

So the cell doesn't weigh very much.

And the precision at which
we can weigh it with,

is four orders of magnitude
below that.

Wow, that's incredible.
So that's ten femtograms...

So a part in a thousand.

One part in 10,000. 10,000!

We care a lot about these things.

We're soon in the domain
of extreme numbers,

but what's amazing is Scott's
measuring the weight

of a single cell to within
a thousand-trillionth of a gram.

His work is revolutionising
our understanding of how cells grow.

And by measuring how cells respond
to a drug, it could lead to

personalised and far more
effective cancer treatment.

It's absolutely amazing, the limits
we are now pushing mass measurement.

But scientists are frustrated.

And it's because we're still trying
to tie mass back to that

ageing lump of metal in Paris,
Le Grand K.

And with Le Grand K's weight
unstable, there's a real

urgency to find a new, even more
accurate way to define mass.

Now a race is being fought across
two continents to retire Le Grand K.

20 miles north of Washington is
one of the world's most

accurate set of scales.

This whole area is a car-free zone,
and that's because the scales

that are being used here are
so sensitive that even the magnetic

field caused by the metal inside the
cars can affect the measurements.

Welcome to Team Watt Balance.

Most things in this strange-looking
building are made of wood,

and clad in vinyl to minimise
the effects of magnetism.

Everything from the power
lines to the plumbing

pipes are encased in shielded
plastic ducts.

And every single bit of metal that
enters the lab, down to this

tiny spare part has to be
checked for its levels of magnetism.

Stephan Schlamminger's project is
one of the longest-running

metrology experiments in the world.

Its founders have long
since retired,

but now the team here are close to
fulfilling their dream.

And this is their brainchild.
The watt balance.

Inside this cage of pure copper,
is a weighing scale whose

principles go back to the very
first balances 5,000 years ago.

And it's so sensitive it can
measure the kilo to eight decimal
places.

So here's our watt balance.

It is a thing of beauty.

It really is.

And you see up here this wheel is
like the beam in an old-fashioned
beam balance.

That's quite ancient
technology, isn't it?

Yeah, it's thousand-year-old
technology up on top,

but down here, you will

see the coil that's connected to
three rods and this will provide the

counterforce to the gravitational
force that this mass is providing.

On one side of the scales,

deep inside the mechanism sits
a clone of the Le Grand K.

What's so extraordinary about this
device is that on the other side,

instead of a weight, the team
are using electrical force

to counterbalance it.

The watt balance defines
the kilogram by linking

mechanical power to
electrical power.

That's why it's called
the watt balance. Right.

Their goal is to measure
the amount of electricity needed to

perfectly counterbalance
the kilo clone

and redefine the kilogram,
based on electrical power.

It sounds straightforward,

but when you are working with
one of the most sensitive

scales in the world, everything
from car engines to the movement

of the local deer population outside
can affect its readings.

Even tiny shifts in gravity,
like the phase of the moon

and the level of ground water,
need to be measured

and taken into account
when this experiment is running.

It seems you're
having to keep track of

so many different things in order
to pin down that kilo.

That is the art.

That's the art
and science of this! Amazing.

So we try to measure this kilo
to about four parts per 100 million,

and in order to do so,
we need to measure all these

auxiliary qualities like voltage,
resistance, gravity, metre,

second, to much better than four
parts per hundred million.

Now, after more than 30 years
of perfecting the scale's accuracy,

Team Watt Balance are very close to
achieving their holy grail -

a new electronic kilogram.

I left the watt balance team
realising I was witnessing

a potentially historic moment
in the life of the kilogram.

The days of the American kilo
making its transatlantic journey to

Paris to be compared against
Le Grand K are probably numbered.

But the watt balance team
have got a rival.

In Germany, Team Silicon Sphere have
got a completely different

approach to redefining the kilo.

And it involves counting
the number of atoms in a kilogram

of silicon crystal.

People often talk about counting the
number of grains of sand on a beach.

But what Team Silicon Sphere
are proposing to do

is in a completely different league.

It's like trying to cover
the whole globe in sand

and counting every grain.

But what are these atoms
they're trying to count?

It was the Ancient Greeks who first
came up with the word "atom"

to define the smallest indivisible
particle of matter.

But it took Englishman John Dalton
in the 19th century to shed

light on what atoms really are.

At the time, we knew that all
matter was made up of different

elements, like carbon and oxygen.

Dalton's brilliance was a radical
theory that each element must

consist of atoms of a single
unique type and mass.

Dalton would never have dreamt it
possible to see or count these
atoms.

But now, in a remote lab
in Northern Germany,

scientists are attempting
to do just that.

What Dalton didn't realise is the
sheer number of atoms inside things.

That there are trillion upon
trillion inside a single

kilo of silicon.

And it's by counting these atoms,

that the silicon sphere team hope
to redefine the kilo.

This is a perfect kilogram
sphere of pure silicon.

The culmination of 30 years' work.

It represents one of the most
ambitious challenges ever to

be undertaken
in measurement history.

Like the watt balance, the silicon
sphere project started
in the 1970s.

The goal was to measure
the atomic distances -

the distance between the atoms
in a very perfect crystal.

Silicon was at that time a material,
which was used for the semiconductor

industry and was the first very
perfect material for that use.

Silicon atoms line
up in an extremely rigid

and regular pattern, which in theory
makes them easier to count.

The idea was to create a perfect
sphere of silicon,

measure its dimensions with
extreme precision,

and then calculate
the spaces between the atoms,

using a technique called X-ray
crystallography.

Then, using simple maths,

they could work out the total
number of atoms in the sphere.

The project was supposed to take
a couple of years,

but they faced many challenges.

The first,
was how to create a perfect sphere.

The levels of perfection
the team were seeking

were beyond the capabilities
of any machine.

They scoured the globe and found
the only way to create a sphere

to the level of perfection
they needed, was to do it by hand.

And only one man was
capable of this.

Australian lens maker
Achim Leistner.

He literally used his hands to shape
the ball to such an incredible

level of perfection,
that if you likened it to the Earth,

the level of its surface would never
vary more than a few metres.

Using his extraordinary sense
of touch, it's said Achim could

feel silicon's atomic structure
with his fingertips.

You need really...

..a feeling how many atoms you have
to remove on that side or

on the other side of the sphere, so
he had atomic feeling in his hands.

It took months for Achim to
perfect his sphere.

Finally, the task of analysing
the space between the silicon

atoms could begin.

But on the cusp of realising
their dream, disaster struck.

There was a flaw in the very
makeup of the silicon.

In its natural state, silicon
consists of three different

forms called isotopes.

Now, each different atom has
a different mass.

Leistner's sphere contained all
three different types
of these atoms.

The team needed a pure source
of silicon or else the project

was over.

The solution came
from an unlikely source.

A nuclear weapons facility.

The Cold War was over and a lot
of centrifuge in Russia

were not running
for nuclear weapons,

so we were lucky to rent

some of these centrifuge to prepare
silicon for our purpose.

A new batch of silicon was
sent to Russia

and spun in the same centrifuge that
was formerly used to enrich uranium.

This forced out the wayward
extra isotopes,

producing pure silicon-28.

Then Leistner had to start
the job of polishing all over again.

Finally, after many years, the
scientists once again started
counting

the space between the atoms.

And trillions of atoms later,
they've nearly completed their task.

We hope that in two years,
we will have all the information

together for a new definition that
means we have a value

with a very small uncertainty -

let us say below two times ten
to minus eight.

And that's an accuracy to eight
decimal places.

It's the same level of

precision as Team Watt Balance
in America are striving for.

At the moment, we are in the pole
position to win this race.

Within a few years,
Le Grand K could be retired.

But the work here could
revolutionise

another of the seven fundamental
units we use to describe our world.

Ein Kaffee mit Milch, bitte? Danke.

If the silicon team are successful,
then they won't just redefine

the kilo, they could end up
redefining the SI unit most

feared by chemistry students
across the world - the mole.

It's a word which comes from Latin
meaning "massive heap of material".

Now, chemists probably
won't like this,

but consider this cup of coffee.

There's a certain ratio of milk to
coffee, say one part milk,

to nine parts coffee,
which combined,

makes one part perfect milky coffee.

Now the mole does a similar
thing for chemists,

but replace the coffee and the milk
with atoms and molecules.

Yep, perfect!

All this leads back to our friend,
Dalton,

and his work in the 19th century.

When he began his investigation
into atoms, he discovered that

atoms from different elements
weighed different amounts.

At the centre of every atom is
a nucleus containing protons
and neutrons.

Different elements have different
numbers of these protons

and neutrons, which is why
they weigh different amounts.

Throughout the 19th century,

the greatest chemists of the day
feverishly tried to work out

the atomic weights of all
the known elements.

It led to one of science's
greatest-ever achievements,

Dmitri Mendeleev's periodic table.

And if you look at each
element on that table,

you'll see their atomic mass
written just below them.

It was a huge breakthrough.

Chemists could finally mix

and manipulate elements
with new-found precision.

But atoms are far too small to
look at and manipulate individually.

What chemists needed was a way
of scaling up atomic weight into

something more tangible
they could weigh.

And the answer was the mole.

The mole is really just
a big number.

A huge number, in fact,

which, when you combine it with
the atomic weight of each element,

allows you to work out how many
atoms there are inside something.

It's the chemist's
way of scaling up the microscopic

world of the atom,
to our world of the gram.

It's really the bedrock of modern
chemistry, allowing us

to mix things from drugs to fuel
with such precision.

But it leaves open one big question.

Exactly how many
atoms are there inside a mole?

The number of atoms that we
have in a mole is what

we call Avogadro's number.

We can go back to
Einstein, for instance, in 1905.

He came up with one of the first
estimates of just how big

this number is from looking down
microscopes at pollen grains and

from that he was able to get one of
our first estimates of the number.

He got the first number right.

He got the six right
and he got the 23 zeros right.

While Einstein's groundbreaking
work got close to defining

the elusive Avogadro's number,
it's the silicon sphere team that

could not only solve the kilo
conundrum,

but also solve the centuries-old
question of how many atoms

there are in a mole...

..and once and for all,
define Avogadro's number.

If this happens,

it will be a remarkable
moment in measurement history.

In one astonishing experiment,

two golden units
of measurement could be redefined.

We've come a long way since the days
of using barley corn weights.

Our quest for ever-greater
precision,

has led us into the very fabric of
our universe, allowing us to weigh

and analyse things with incredible
speed, scale and precision.

In a few years' time,
all going well, the BIPM will

decide between atoms or electrical
force to redefine the kilo.

The winner is kind of irrelevant.

Both Team Watt Balance

and Silicon Ball have done what
seemed impossible,

to redefine the kilo based on the
unchanging laws of the universe.

In the pursuit of ever-greater
accuracy, these remarkable projects

have brought together thousands
of years of scientific endeavour.

But our quest for ever-greater
precision doesn't stop here.

The last great measurement
frontier will be to

journey inside atoms themselves,
to discover what mass really is.

100 metres under
the Swiss-French border,

at CERN's particle accelerator,
scientists think that

they have discovered a particle
that gives things mass - the Higgs
boson.

And one day, our human
desire for ever-greater precision

may even see mass redefined
once more,

and tied to Higgs itself.

If it happens, who knows what the
technological impacts will be?

And that's the beauty
of measurement.

Every leap in precision leads
to new scientific

and technological advances.

Measurement has shaped our history,

and will continue to
change our world.

Next, we explore
the world of energy.

And how the measurement of light,
heat and electricity

have transformed our lives

as I continue
my journey into measurement.