Horizon (1964–…): Season 46, Episode 6 - How Long Is a Piece of String? - full transcript
VARIOUS VOICES
FADE IN AND OUT
'I'm Alan Davies...
'And this is a piece of string.
'All I was asked to do
is find out how long it is.
'You'd think that would be
a piece of cake.'
You can only measure
shiny flat things?
'But little did I know that,
by the end of the week,
'a centimetre would hold a new
meaning and I'd be starting
to question the fabric of reality.'
That piece of string
could actually be infinite.
Strings can be in more
than one place at a time.
Your string does not
actually possess a length.
Somehow, by measuring it,
we create a length for the string.
THEY LAUGH
'All because
I tried to measure string.
VARIOUS VOICES
FADE IN AND OUT
'It doesn't look a length
till you measure the length.
'The more you measure it,
the longer it gets.'
How long is a piece of string?
Should be simple.
'Now, I was never
a great science enthusiast.
'In fact, at school,
I wasn't very good at it.
'But measuring a piece of string,
that's something
'I can do. It's just one step up
from colouring in, isn't it?
'That's always been
a skill of mine.'
I wonder if you can help.
I need a piece of string.
A piece of string? Yeah, just
a piece. A piece? Say when.
That's good, that is good.
A piece of string.
Have you got a ruler?
Yeah, 32 centimetres.
32 centimetres.
That'll be the end
of the programme, then.
Thanks for solving that.
That's pretty good.
32 centimetres.
Thanks a lot, see you, bye.
Thank you. Bye.
Unfortunately, I suspect
it won't be that simple,
as I am now about to visit
the professor of mathematics.
'Professor Marcus du Sautoy is
a maths genius
'but also rather foolish.'
OK, Alan, let me take you
into the fourth dimension.
'Last year, he took it upon himself
to try to teach me
'some really complicated
mathematics.'
LAUGHTER
You've sold me, Marcus.
You've changed my view
of the universe.
That's fantastic!
'So who better to help me solve
a simple question about string?'
Professor! Hello! Great to see you.
How the devil are you? I'm good.
How about you? I'm very well.
All I want you to do for me is
a simple task this time,
shouldn't take long.
OK. I just need to know how long
is this piece of string.
Oh... OK, you want the
one-minute version? Yeah.
Or the 60-minute version?
Well, I've measured it, I know
it's 32 centimetres long.
You used a ruler where you bought
this? Where did you buy this?
The hardware shop. OK.
They had a ruler on the desk, it's
been measuring things for years.
And what about this ruler? Do you
think it's the same length?
It's got centimetres on it, yeah.
You want it in centimetres or inches
or cubits? Centimetres, please.
I'm... Or stadia?
LAUGHTER
The problem about measuring things
and putting them against...
'I knew he'd be like this. To me,
it's a short piece of string.
'But for Marcus,
it's a major mathematical problem.'
..measure and make it standard.
Measurement is really
the beginning of mathematics.
And new numbers arise out of trying
to measure things like this,
and the Greeks,
they were obsessed...
'Good god, he's giving me
the history of geometry.'
Your piece of string is really
a fundamental mathematical object.
I've spent the whole morning
trying to measure things.
This little Greek symbol here
stands for measurement
and it's measuring the size
of this double coset - GSP 2 N QP.
OK, tiger. Can I...? Hold on there.
MARCUS LAUGHS
I just need to how long this piece
of string is. Go back to the string.
There's interesting maths and
physics behind the question
of how long this piece of string is.
It isn't just 32 centimetres.
You're beginning a journey
that mathematicians started
5,000 years ago.
'I knew this wouldn't be
as simple as it first appeared,
'but things were going well
at this point.
'As far as I was concerned,
32 centimetres was close enough.
'But Marcus wanted to take me
somewhere very special,
'a place that's dedicated to
just one thing - measurement.'
And that's why we're going to
the National Physics Laboratory.
Bits of the bodies were first used
as a form of measurement,
so the Egyptians, for example,
they had something called a cubit -
the distance from your elbow
to the tip of your middle finger.
It's quite a nice distance.
Let's measure ours and see...
Look, you've got a huge cubit.
Famous for the size of my cubit.
That's no good for measuring,
because your house will be
bigger or smaller than my house.
It'll be bigger and that's fine.
What will it be? Bigger or smaller?
If we have the same number of
cubits? It'll be bigger. You'll say,
"My house is six cubits high and
it'll be longer." Six cubits high!
I won't be able to get in the door.
Whatever. We need something which
is gonna be the same for everybody.
You don't really want it depending
on whether people are tall or small,
or how big things are.
You want something which is
gonna be standard.
Do you mind if I ask you a question?
Yeah, sure.
How long is that piece of string?
Nine inches.
No, no, it's just 12 and a bit.
Good guess, though, it's not bad.
Nine inches.
Cheers. Thank you.
He's quite tall,
so I bet his cubit is probably
a bit bigger than our cubit.
No way you can rely
on anything that he says.
Go and ask him
how far it is to London.
He thinks that's nine inches,
he's 25% out! Yeah.
'Body parts and Egyptian cubits
are all very well,
'but they aren't exactly
what I had in mind for my string.'
What's needed is some science,
and that's what brings us
to the National Physical Laboratory,
the scientific home of measurement.
'This is a place filled
with priceless treasures
carefully locked away.'
It's got this special
feet-cleaning sticky floor.
We need to get this for home.
We have to keep the room
very, very clean.
'They are the country's
measurement standards,
'objects that define the units
we use to measure every day.'
This is the UK's
primary mass standard.
'That's a kilo to you and me.'
It's quite small.
Yes, this little cylinder in here,
that's a kilo? Yes.
The size minimises the surface area.
There's less to get contaminated. Ah.
'Got them all here,
replicas of the cubit.' Wow!
You are an Egyptian man!
LAUGHTER
'The definitive yard.'
It's 36 inches at 68 Fahrenheit.
'And a 200-year-old
original metre bar.'
How do they decide which metal
to make it from?
Well, they commissioned a study
to find out the most stable metal
and, after a lot of experiments,
decided that a mixture
of 90% platinum and 10% iridium
was the most stable material.
This is 90% platinum! 90% platinum.
That's quite valuable.
I don't think you'll get that
in your trousers. Watch me!
'For hundreds of years,
we defined measurements with
rods of stone and metal.'
18 fingers. 18 fingers.
Your answer. Happy with that.
It's quite cute. How long's
a piece of string? 18 fingers.
'But platinum is old hat
when it comes to defining length.
'At the NPL, the metre is defined
by the speed of light.'
I tell you, this is where
we want, the Length Bar
Interferometry department.
Let's run out screaming.
LAUGHTER
MACHINE HISSES
MARCUS LAUGHS
This is really... I love the sound.
I feel like Q in James Bond.
Yeah... "Don't touch it, Bond."
One of the problems when you want
to measure things very accurately
is keeping them still enough and
that's why we have to minimise
the vibration levels
that we get in the room.
So this table is floating on air and
shining throughout this instrument
is the laser beam that actually
performs the measurement.
'A laser! That's the kind of
measurement technology I need.'
So I think the amazing thing is
that, today, a metre isn't defined
by a piece of metal, but it's
defined by light and in particular
how far light will travel
in a fraction of a second,
and it's 1 over 299 million.
792458. There you go. Of a second.
Of a second, yeah. Yeah.
In that fraction of a second, light
will have travelled exactly a metre.
OK.
'If a metre is
the distance light travels in
three billionths of a second,
'how long is my string
in light speed?'
So, Andrew, I was wondering
if I can measure my string here
in your interferometer?
It would be a little bit difficult.
I would need to have the ends of the
string polished nice and shiny flat
and so I don't think we could
measure it in here...
You only measure shiny flat things?
In this particular instrument,
but we have got something else which
could have a go at measuring it.
A stringometer? A stringometer.
'When they say stringometer, what
they mean is this little fellow -
'the fully-automated
tracking laser.'
Are you interested in the length
of a piece of string?
Do you want us to go?
LAUGHTER
So what you're going to have
to do is take your ball,
position it accurately on the end
of the piece of string, about there.
Hold it stationary on that end,
and tell Andrew when you're ready,
he'll record the point.
OK, Andrew. I'm ready.
MACHINE BEEPS
Move to the other end of the piece
of string. I'll get out of the way.
MACHINE BEEPS
If he says 320 millimetres,
I'm leaving.
Well, according to the laser tracker,
the distance between those two points
you just selected is 319 millimetres
and 442 micrometres.
It's 319 and a half millimetres?
Just a touch under.
And do you know why it wasn't 320?
I didn't add the little bit of fray.
'I thought that was it.
'319.442 millimetres seems
a pretty definite length to me.
'But Marcus doesn't agree.
'He thinks we can get
an even better measurement,
'something more accurate
than the laser can produce.'
It's that long. Yes.
'So we travelled
132.4 miles to the west,
'because Marcus says
that my string is actually
a famous mathematical conundrum
'and he seems to think
that the way to solve it
lies in measuring Cornwall.'
Five...six... This could take a
while, this is really complicated.
You can do it a bit rough and ready
to start with. Do it wrong?
No, it's just quite hard to get
inside of all of the little inlets.
I'm prepared to make the effort.
I can see you're trying.
This might be the best bit
of the show if I get this right.
It could. On the other hand... You
deliberately made me lose my place.
Right start again, start again.
133, 143...
'What Marcus wants to demonstrate
is that
'how I go about measuring something
can change the result.
'With a ruler, from Black Head
to Looe is 42 centimetres.'
Down to Looe...
It's 42 centimetres.
Now of course the problem
you are finding using this is
with a flat edge, it's really
difficult to get into all of the
inlets and things like that.
What about using
your piece of string?
'My string was somewhat better,
but produced a different result...'
47 centimetres.
Right, let's do 47.
Seems to be growing.
'Finally, a map measuring wheel.'
Gosh, OK! Whoa!
Look, this is, this is...
centimetres round
the side here. 65.
We've got up to 65 centimetres
using this one. So...
with a ruler,
we had 42 centimetres.
With your piece of string,
47 centimetres.
If we had an even more accurate way
to measure the length here,
we'd probably get the coast
going up even more,
because you'd be able to get into
all the nooks and crannies.
Each measuring device is
effectively zooming in on the coast
looking at in greater detail,
and that reveals
more twists and turns.
Each new cove or inlet
increases the overall length
all the way down
to individual grains of sand.
And the more detail you reveal,
the longer the length becomes.
This'll have serious implications
for measuring your piece of string,
because this isn't
a smooth piece of string.
It's actually also got
lots of crinkly bits inside it,
so the length of this piece of
string is going to depend on how
accurately we measure it.
Oh, boy!
I knew this would happen.
LAUGHTER
So make sure he gets
a good night's sleep,
because tomorrow, we're going
to find out how long he really is.
'Studying Britain's
crinkly coastline
'has actually resulted in
a whole new field of mathematics.'
What I want to do is
to measure out nine metres.
That's the side of our triangle.
'It's the maths of fractals.'
Excellent.
Brilliant, so this triangle
that we're building is
a third the size
of the larger triangle.
Now we're going to add
even smaller triangles on,
we're going to make it even
more complicated. Right.
'Now I was wondering what on earth
a fractal looked like.
'But I wish
I'd never asked Marcus,
'because he has me drawing triangles
in the sand over and over again.'
Brilliant. The sticks
are getting a little bit big,
so I think it's chopsticks now.
Come on, then. Race you? Race you!
Nice little triangle.
Wow, there you go! OK, shall we do
another set of triangles? No.
You got the point? OK.
That's enough triangles!
So what we have here is
the beginning of a fractal
and does it remind you
of anything? Um...
Ice... Dust... Snow. Snow.
It's like a snow flake and in fact
this is called the Koch snow flake.
Nice(!) Yes, exactly!
It's the name of the German
who discovered the...
EMPHASISING THE END OF THE WORD:
The Koch! The Koch, yes, exactly.
All this drawing is so Marcus
can show me that fractals
are mathematical shapes
that look the same
no matter
how zoomed in on they are.
Their shape is repeated over
and over and over again.
And he thinks
it's the same for my string.
The closer you look at it,
the more crinkles appear.
That makes calculating the length
of the string a little tricky.
How long do you think the fractal
is that we drew here?
How long was the triangle, the big
triangle we drew at the beginning?
27 metres. Three times nine.
Yeah, nine metres each side,
so we had a triangle
which was 27 metres long
and then what we did was to add
a smaller triangle on the side
so actually, the length of this
has gone up by four-thirds
by adding these new triangles,
so every time I add on more
triangles, each time, the length
increases by four-thirds.
You add one third, but to do
the sum, you have to multiply by
four and divide by three. Yes.
You've got 27, the original length,
and we're adding a third on again
each time we add another triangle.
Multiply by four-thirds.
Exactly. Now do that again,
add an extra third on by
adding more triangles, so maybe
you can see what's happening.
Every time I add smaller and smaller
triangles on, the length increases
by another factor of four-thirds,
and potentially,
the lengths of this fractal...
will actually be infinite.
So we've drawn an infinite line
in the sand
and because your piece of string is
a bit crinkly, a bit fractal-like,
that piece of string could
actually be infinite in length.
Right. You've been carrying
around infinity in your pocket
all these days without knowing it.
Well, you say that, but look there's
the beginning and there's the end.
This is quite theoretical,
if you ask me!
You're right, I mean, this is
a shape in the beautiful, pure world
of mathematics and you're right.
If we kept on adding triangles
into the sand, at some point, you're
going to hit a grain of sand,
the atom, and you won't be able to
divide any further. Yeah, yeah, so!
OK, you're right, but I love this
pure world of mathematic where
you can just keep on dividing off
into infinity and produce
this beautiful fractal thing.
'When I asked Marcus to help me
measure my string,
'I thought he would definitely
have an answer.
'Instead, he proposes fractals,
'theoretical objects
that are infinite.
'But I want a length that works
in the real world and that means
'I'm gonna have to leave Marcus
and his equations behind.'
My watch says 8:52.
What time's it going down?
Doesn't this say
when the sun sets?
Yeah, this is the
classic 21st-century life.
We're so busy looking at what time
the sun sets, we missed the sunset.
LAUGHTER
We actually... Oh, it's gone.
It says it's still up at the moment.
Oh, does it?! Good, good.
Beautiful sunset. Yeah.
'I've still got my measurement
of 319.442 millimetres,
'which is pretty good, but I must be
able to do better than that.
'What I need to do is measure it
in the smallest units possible
'and surely, that means
measuring in atoms.
'So...I guess I'll have to get
to grips with some physics.
'Just one problem.
'When it comes to physics,
I have a little secret.'
I've been sent back to school
to do physics,
which I'm not proud to admit
that I deliberately
failed my mock O-level
to get a U,
so that I could drop it.
I've been slightly anxious
about a physics teacher,
but got my string and actually
I'm finding it quite comforting.
SCHOOL BELL RINGS
'This is
the Simon Langton School for Boys
'and I'm here to meet one of the
country's best physics teachers -
'Becky Parker.'
Hi there! Hi! Are you Becky?
Yeah, welcome to the Langton. Nice
to meet you. Lovely to meet you.
I've got a bit of a problem -
I've been trying to measure
the length of this piece of string.
Right, and you want a
straightforward simple answer to
this one? Wow! Is there one?
When you get down to the really
tiny scale, things get complicated
and that's why your problem
of measuring really accurately
that length of string
is not just straightforward.
I need to take you on
a bit of a journey through
lots of quite wonderful ideas,
which I think you'll find
quite mind-blowing.
I had a feeling
there'd be a journey.
'This is exactly
what I was afraid of -
'being locked in a dark room
with a physics teacher.'
'Any minute now,
she'll ask me for my homework.'
There you go, just need
to get it completely dark...
Oh, now, hold on a minute.
SHE IMITATES A FANFARE
AND PRESSES A SWITCH
Bang...
Oh! Electricity,
that's what you need.
Hey, hey, we have light!
Now we're going to
try and do some experiments
to understand what's going to
happen and it is quite amazing,
almost magical in a way, to see
the weird effects which happen
down in this atomic world, but what
do you understand the atom as being?
I bet you've probably done
that at school? I have a vague
recollection of it, yes.
Have you got any picture of
what that atom might look like?
Something might come to me.
Would you like to draw a model
of the atom on the board?
Why certainly!
Draw an atom. Yeah.
Right...
Well, all I really remember,
I remember from school,
I remember there was...
There's something very, very
small in the middle. Yeah.
And then, is there not something
going round and round it?
Yeah, definitely.
Spinning round and round.
So, in the middle,
there's protons. Yeah.
And neutrons.
Yeah, absolutely brilliant.
And then, what's the thing that's
going round? Electrons. Electrons.
That's it.
That's all I remember. Yeah.
I mean, this is how
the atom is portrayed,
a bit like a little mini solar
system that you've got this thing
which is pulling the electrons.
An orbit thing. Yeah yeah.
It gives an idea of how tiny this
nucleus is with the protons and
neutrons compared to the electron.
Most of the atom is nothing. So if
you collapsed - here's a question -
if you collapsed,
all of what you are as matter,
the whole of the human race
into just the massive stuff,
which is the protons and neutrons,
what would be the size of...?
If you just took the actual stuff
that we're made of
and took the space out,
we'd shrink down dramatically.
I mean, I'd come down to just a
little bit of... Yeah. ..a crumb.
You be careful, cos you wouldn't
see you, you'd be microscopic.
The whole of the human race would be
in the volume of a sugar cube.
Everybody? Yeah.
So the matter of everybody in
the world amounts to one sugar cube?
Yeah, if you got rid of...
The rest is just space? Yeah.
And so, we're all made up of these
just tiny little fundamental things.
'Talk about making
someone feel inadequate!
'We're all made up of space,
of nothing at all.
'At least I've managed to
pass my first physics test.
'Quite pleased with my atom.'
The only trouble is,
if the atom was like that,
then the actual electrons,
if they were accelerating round
orbiting the protons and neutrons,
they would lose energy
and so they would actually
spiral into the nucleus
and that would mean that
all matter would just collapse.
Now we know that matter doesn't.
So that's wrong?
The only thing I remember.
I know, because that's what
you've always been taught
then you have to re-learn it and
think that's not a very good model
cos it doesn't work at all.
So sorry about that!
That's what often happens.
You have to sort of, you know,
refine your thinking as
you understand more and more.
Atoms aren't what
I thought they were,
not neat little solar systems
with particle planets.
According to Becky,
they're much weirder than that.
So weird, they have their own branch
of physics - quantum mechanics.
'And that is a big problem,
because in quantum physics,
'the particles in my string
can be in two places at once.
'And that makes working out
where they are really hard.'
So...the thing about
why actually it's important is
when it comes to footballs,
for example, which, obviously,
are particle-like... Mm-hm.
..they're smeared out,
so in the quantum world,
they wouldn't just be here.
It'd be all over the place and
around and you wouldn't necessarily
be able to tell where it was.
So if I throw it at you, in
the quantum world, you wouldn't
be actually sure where...
A bit like somebody trying
to save a penalty, you wouldn't
know which way to go.
Oh, there you are, you see.
But that was a terrible penalty.
But say, in the quantum world,
we wouldn't know exactly
in which position the ball was.
It could even be behind me
or over your head.
So is this ball that ball?
Yeah, exactly. It can be
in two places at once? Yeah.
'This is a fundamental
tenet of quantum physics.
It's not a weird by-product,
but a reality that explains how
the smallest objects behave.
The whole question of actually
defining where the atoms,
where the footballs are becomes
quite a serious measurement problem.
That's the last thing I wanted was
a serious measurement problem. It's
the nature of the quantum world.
I wanted a simple measurement
solution. It's not straightforward,
because you can never be exactly
sure at what point your string ends.
Oh, no!
LAUGHTER
'I find it hard to accept
'that particles can be
in two places at once,
'not just two places at once,
but many places at once.
'Unfortunately, to see
this miraculous behaviour
'takes a lot more than
a bag of footballs.
'To prove to me that my string
can be in many places at once,
we need a real physics lab.
'At Imperial College in London,
they have the equipment
'to see individual particles
and watch how they behave.'
All these flashing lights...
A centre for cold matters.
Is that the fridge?
SHE LAUGHS
Johnny! Hi, great to see you.
Hi. Thanks for seeing us.
Dr Johnny Hudson, Alan Davis.
Hello! Hi, good to meet you.
'Becky and Johnny have chosen
one of the most common things
in the universe
'to provide evidence that objects
can be in two places at once.
'It's something that surrounds us
all the time - light.'
We'll shine a laser beam through two
very narrow slits. Can you see them?
Can you see two? OK.
Just. Yes, yes, I can.
They're about the size of a human
hair each and they're spaced by
about the same amount. OK.
What you can see
over on the far wall
are the stripes from the waves
coming from each slit interfering.
'Right, let's just stop it there.
'In a minute,
I will to see something that was
to turn my world upside down.
'But to properly understand it,
Becky needed to explain
a simple concept.
'It's all to do
with how light works.'
Firing laser light at two slits
doesn't create two shafts of light,
as you'd think.
It creates stripes.
That's because light is a wave.
The waves of light
pass through both slits
and then interfere with each other.
Some add up to give bright bands,
others cancel out, leaving darkness.
Becky calls this
an interference pattern
and she says it's telltale
evidence that the light
has passed through both slits
at the same time.
But Johnny is only
going to send through
a single particle of light,
called a photon, at a time.
Of course, you'd have thought
that would just create a dot,
but that wouldn't be quantum.
OK. So what we can see here
is each of these
little green splodges of light
is a single photon.
OK, so this is now averaging
those successive frames together,
laying them on each other as if you
printed them and put them in a stack
then held them up to the light.
Where you get more photon impacts,
you see a brighter green colour.
Where there are fewer, you see a
darker colour. And you can see that?
It's amazing. Stripes. Completely
amazing. It's definitely stripes.
'If only one photon at a time
goes through the slits,
'how does it create
an interference pattern?'
So you've got your photons,
they're going through two slits.
And they, they're passing through
them, one photon goes through both,
it has to go through both
to create the wave effect. Yeah.
But it's one photon. Yes. So it has
to be in two places at once? Yes.
It has to be in both slits at once?
Yeah, effectively.
It's adding up to a bright band,
cancelling out to give nothing...
But the photon's something that...
That's as small as you can get.
You can't split it in half
and re-form it?
Well, that's because
you can't then have that picture
of it being a single particle.
It seems to then act as a wave
when it goes through the slits.
The thing is, position isn't
a good idea any more.
Position is something that's
useful for big things.
But when you talk about
the smallest things, position is
not a good idea any more.
You mean where things are?
Yeah, they're not in a place.
They don't really have a position
as such, which is surprising, right?
'I thought that Johnny would have
a big fancy machine that would count
the atoms in the string.
'It's a tricky task,
but at least understandable.
'Alas, the real world
just isn't like that.
'It turns out, in reality,
the fundamental building blocks
'of the universe
don't have a fixed position.
'Well, if that's the case, how am
I ever going to measure my string?'
I think the philosophical
understanding
of how we understand reality has
got a long way to go, I think.
Really, we probably need a whole new
way of thinking about the world.
Yeah, it's quite difficult
to get your head round,
except it turns out out it is
possible to get your head round it,
because your head could be
in two places at once. Ha-ha!
Yes, so your head could be here
and then it would understand.
Yeah, it's getting your head round
the fact that you could get your
head round it. That's the trouble.
Wow, this whole measuring
thing turned out to be
so much more complicated
than I thought.
FAIRGROUND MUSIC PLAYS
'Measurement should be easy.
I do it all the time
'but according to quantum mechanics,
it's an almost impossible challenge.
'Worse than that,
it's a science that declares
'that the world is
mysterious and confusing.
'I knew that already.'
It sounds like a cop-out to
have a theory which says
that you can't work out the answer.
Well, Alan, yeah, like you, Einstein
grappled with this and never...
I like that sentence.
Yeah, you and Einstein.
Like me, Einstein grappled with
the laws of physics. No, you did!
Einstein and I have many
of the same concerns.
Yeah. You know,
people like you and Einstein
expect to be able to understand
the world and have it...
We do, we both do.
Yeah, have it completely clear
exactly what reality is.
You...
You don't get an absolute,
definitive answer.
You get probabilities
and likely to be here,
and most probable to be there.
I'm gonna go back
to 320 millimetres.
'Becky has been trying to help...
'But I think she might've
scrambled my mind.'
'Position is not a good idea...'
'I thought she'd give me
real world answers,'
'Turns out the real world is
stranger than I imagined.
'Now I'm more confused than ever.
'But what does this mean
for me and my string?
'We're all made of atoms
and particles.
'Does that mean we're
also blurry at the edges?
'Can I be in many places at once?
VOICE ECHOES
'If I'm here, where else am I?
VOICE ECHOES
'I want answers.'
'Quite an amazing journey right
right down into the tiniest stuff
'which I think you'll
find quite mind-blowing.'
'To find them, I've arranged to meet
a professor of quantum physics,
'a man called Seth Lloyd.
'Seth is a master of the quantum.
'He works with particles
and atoms all the time and can
bend them to his will.
'Seth's the man to bring sense
to this quantum madness.
'But I'm not entirely sure
why he wants to meet me
in a taxidermist's.'
Seth! Oh, Alan! Hello.
Good to meet you.
Nice to meet you too. Thanks
for inviting me to this place.
You're probably wondering
why I asked you down here today.
It has crossed my mind.
You have nothing to fear. Good!
LAUGHTER
In fact, I brought you here
to introduce you to Fluffy.
What a beautiful cat.
She WAS a beautiful cat.
LAUGHTER
First, let me ask you a question.
Do you think this cat is alive?
No, I think, I think it's stuffed.
You think it's stuffed? Yeah.
Now it may not seem to begin with
that cats have much to do
with measuring string,
but in fact, they have everything
to do with measuring string.
About 70 years ago, the German
physicist, Erwin Schrodinger,
came up with a thought experiment
about a cat,
a thought experiment which I'm now
going to ask you to go through.
OK. I'm ready. OK.
So Schrodinger imagined
that you had a cat.
But then, as a result
of a radioactive decay,
where an atom would decay
and emit a photon,
this photon would be absorbed by
a detector and, if the photon was
absorbed by the detector,
then a small amount of poison
would be put in the cat's milk.
The cat would drink the milk
and then die.
Right. At the level of
quantum mechanics,
a particle isn't
in one place or another,
so the photon in some funny sense
is both detected and it's somewhere
else where it's not detected
and that means that the poison is
being put in the milk and not being
put in the milk at the same time.
So if a photon can be here and there
at the same time, then a cat
can be alive and dead
at the same time.
'I was hoping Seth would
make things seem less weird,
'but now, things aren't just
in two places at once.
'They're also dead
and alive at the same time.'
I'm picking up the thought
experiment and I get the theory,
but in reality,
we're alive, the cat's dead.
The string is a certain length.
Well, that's what Einstein
would've liked to have thought.
This is why Einstein
didn't like quantum mechanics.
Right. So what's going on?
How can a cat be alive and dead?
We never see the cat alive and dead.
This has to do with observation,
crucially.
Looking at the cat is an act
of measurement and if the cat is,
in this funny sense,
alive and dead at the same time,
and we look at it or measure it,
it effectively has to have
become either alive or dead,
but not both.
LAUGHTER
I'm getting it, but I just feel
as though, even if I don't see it,
it's still dead.
Yeah, so it's important here to,
to think about what
we mean by observation.
Most human beings when they say,
"We observe something,"
it means we're there to see it.
But you have to think that,
as every particle of light
bounces off this cat,
it's effectively observing it, so
if there's anything there to detect
whether the cat is alive or dead,
then it's either alive or dead and
not alive and dead at the same time.
CAT PURRS
So big things don't show up
being two places at once
or cats don't show up being
dead and alive at the same time,
cos they're big and interact
with their surroundings.
Every interaction with the
surroundings is effectively
an observation.
The environment observes the cat.
And this is very important
for your length of string,
because, just in the same way
the photons can be here
and there at the same time,
the string can have
multiple lengths at one time.
'This isn't the news
I was hoping for.
'In fact, it's an utter disaster.'
Your string does not
actually possess a length.
Somehow, by measuring it,
we create a length for the string.
It hasn't got a length
till you measure the length?
It doesn't, and then its length
is what you measure it to be.
Then it goes back to not having
a length again? It's not even really
there until you measure it.
That's what Einstein hated
about quantum mechanics,
that things aren't there
until you actually look at them.
So reality, in some sense,
doesn't exist unless
we're actually observing it
and it's our act of observation
that makes things real.
Oh, no!
'Right, so let me get this straight.
'My string doesn't have a length
until it's observed,
and then its length is created.
'But it IS observed,
it's in my pocket.
'The last time I looked,
it was about 320 millimetres.'
I'm enjoying the theory
and the thought experiments.
I can see things and where things
are and I'm not really getting
the relevance to the real world.
It doesn't really matter.
This is all just theory
that isn't really relevant,
because we are observed by
the environment, so does it...?
Who are you - Einstein?!
Does it really matter?
What's your problem(?)
I feel more and more like Einstein
every day, which I previously
thought was a good thing.
You think that quantum mechanics
doesn't matter in a really
important way for living things.
Come with me,
I'll show you how it matters.
Don't knock quantum mechanics, baby!
LAUGHTER
'Seth doesn't need a laser
or a lab to demonstrate
'that quantum mechanics isn't only
relevant to invisible particles.
'All he needs is a greenhouse.
'He's brought me to Kew Gardens,
cos the latest scientific research
'has uncovered a surprising truth.
'That all life on Earth
relies on quantum physics.'
You say you don't believe
that quantum mechanics is really
important at a basic scale.
So what would you say if I told you
that every single plant here
is using quantum mechanics
in a fundamental fashion in order
to turn light into energy, and
to build itself up from scratch?
Nature effectively discovered
how to use the same kind of
quantum weirdness that allows
particles to be in two places at once
and that underlies Schrodinger's cat
in order to make all this happen.
Things have to be in two places
at once or there's no plant life?
That's right, exactly.
How do the plants know that?
Even I know that plants turn
sunlight, air and water into food
in a process called photosynthesis,
but according to Seth,
this relies on quantum physics.
The way that photosynthesis works
is that a photon particle of
light from the sun comes in,
gets absorbed in a gigantic molecule
like a chlorophyll and it creates
an energy state called an exciton,
an excited state of electron.
Now this exciton has got to get
from this side of the molecule
where it's been created
to this side of the molecule where it
can be turned into chemical energy
and photosynthesis is incredibly
efficient in this energy transfer
process, like 99% efficient.
And that's very hard to understand
because you can understand if it were
maybe, like, 50% efficient,
so if half the energy got there,
but it's quite crazy that 99% of the
energy gets from where it's absorbed
to where it actually gets
turned into chemical energy.
And the way that these organisms
figured out how to make it efficient
is by using this wacky quantum state
where you go through all possible
paths at once of the molecule
so it's in many, many, many
different places at once.
That way it can do it without
dissipating all this energy
that it's got.
We've gone past two places at once.
We've gone into thousands,
millions of places.
Millions of places at once, yeah.
Hey! Hey.
It's almost like this
quantum process
is trying to find a
path through a maze,
and the energy takes every
possible path at the same time
but having arrived at the centre,
it appears to have only
taken the quickest route.
Without this quantum weirdness
that allows plants to be so
energy-efficient,
life on earth
would be very different.
So without plant life discovering
this ability to transfer energy
in that way, there's no dinner on
the table, there's no anything?
There's no barley for the beer.
I have new respect for plants now.
The question really is
do they have new respect for you?
THEY LAUGH
Quantum physics
isn't restricted just to plant life.
It's everywhere. It's even in me.
Apparently quantum physics
is going on between my ears.
Alas, not in my brain
but up my nose.
Smell that. Very nice.
You couldn't smell if quantum
mechanics weren't there to help you.
The role of quantum mechanics
in the way we smell
is not yet fully understood,
but a research group,
led by Professor Marshall Stoneham,
are just beginning to uncover it.
Dr Simon Gain. Hi, there.
The question is what happens
when you actually get a smell.
But what we believe is happening is
the smell molecule has to pass
through various mucus layers
and so forth and it ends up
at a receptor, and you have
350 different receptors.
And they're all sitting there
waiting to be triggered?
That's right, and only perhaps a
dozen of those will be triggered by
any one scent molecule, and then the
mixture of those signals is what
tells your brain which smell it is.
And if it was a bad egg that
you've just opened, then you'd get
that effect of the bad egg smell
about a millisecond,
about a thousandth of a second
after things had gone in.
We can show you because it doesn't
happen everywhere in your nose.
It only happens in a specific bit
right up at the top between your eyes
and in,
just behind the bones of your nose.
So if you're interested, we can put
a camera up there and have a look.
And what does this camera look like?
This is the camera.
Holy smoke!
Better you than me, is all I can say.
Yeah, yeah.
To see where the quantum physics
is happening, required numbing
my nose and face.
And placing a camera
just below my brain.
So that's called the nasal
vestibule, the hair-bearing part.
Looking into the nose now
with the septum on the
right of the picture, we're looking
right up just below your brain.
Right here at the top of my
nose is a gap in the skull
that allows the smell receptors
to connect directly to my brain.
And that's where the lining
of your nose changes from
the respiratory mucosa
to the olfactory mucosa
which has the nerve endings
that bear the receptor that we think
works by quantum methods.
Just seeing if you left any
equipment.
THEY ALL LAUGH
Thank you!
As a scent molecule travels
up the nose, it finds its way
to a receptor.
To distinguish different smells,
the receptors have to send a signal
to the brain.
That signal
is triggered by an electron.
The only way for the electron
to signal the brain
is to go through
the solid scent molecule
though this should be an
impenetrable barrier,
but when the right molecule
hits the right receptor,
the electron can magically
pass through the molecule
and begin its journey to the brain.
This seemingly impossible process
is called quantum tunnelling.
What's remarkable, I think,
about this is that,
we've known about quantum
mechanics for 100 years now
but only in the last few years
has it become clear
that nature actually
discovered all this quantum weirdness
a billion years before
human beings even came on the scene.
You would expect it to be very
interesting to go from what
seemed to be a purely theoretical
experimental side to something
that's actually day to day life.
So are you willing to accept now that
quantum mechanics is more important
to life than just dead cats?
Yes, I can accept that.
The smell of success!
Yes, I get it.
Quantum physics underlies everything
in the world,
and gives us a glimpse
of what reality is actually like.
It's amazing and I'm very pleased
that smart people like Seth
are working all this stuff out
but I just think
we've taken a bit of a detour.
I set out to measure a piece of
string
and I can't believe that 0.442
of a millimetre
is as accurate as I can get.
Surely, there's a way to go
beyond that to get a better length.
So Seth,
come on!
You've shown me a lot of
particles and waves and...
I know a bit about quantum mechanics
now but I don't know the length
of my piece of string.
Fair enough.
Isn't science always like that?
It's turning out that way.
It answers lots of
questions but not the one you
want to know the answer to.
How long is a piece of string?
Absolutely.
Well, let's look
at how accurately you could possibly
measure your string. Yes, let's.
All right, so you know that
if you can measure your string very
accurately within a millionth of a
metre by counting the number of wave
lengths of light that go along it.
And then you say hey, I can measure
it more accurately
by putting in light with a shorter
wavelength, so if the light
has half the wavelength, I can
measure it to twice the accuracy.
This is what they were talking about
at the National Physical Laboratory,
using the wavelength of laser light
to measure my string.
Despite the uncertainties
of quantum physics,
it's the best way to measure length.
Theoretically, there is almost no
limit to how well you can measure
with it.
In principle you could actually
by making a light wiggle up and down
really, really, really, really fast,
you would think, "I can measure my
string to any degree of accuracy
I want."
Which would make you happy. Yes.
But there's one slight hitch.
Yeah, I thought there'd be a "but"
after it.
Yeah, yeah, I know.
I know. It's always this way, right?
Yeah. So... Go on then, what is it?
OK, the hitch is that if the light
is wiggling up and down faster,
each photon has more and more energy
so if it wiggles up and down
twice as fast, you double
the energy of the photon.
That's OK, we just put in
more energy but we get a better
measurement of your piece of string.
But what Einstein taught us is that
energy effectively has mass,
and mass gives us gravity,
but there's actually a limit
to how densely you can pack a
bunch of energy into a sub-class.
What's the limit?
Do the words, "Black hole"
ring a bell?
I can make a black hole with
my string? Well, you can.
Measuring leads to black holes?
To measure you need to put in energy.
Energy causes gravitation.
Excess of gravitation
causes black holes.
Oh, that's a terrible
disappointment.
I'm going with the black hole, Seth.
You wanted to know the answer.
I don't care any more.
Thanks for everything but...
kaboom!
THEY LAUGH
I've learnt something.
I just thought at the beginning of
this, a group of men in white coats
would point a laser at the string
and da-da, you'd get a length.
But it turns out
that trying to measure
something as simple as string
is actually a philosophical journey.
'The whole of the human race would
be in the volume of a sugar cube.'
'Everybody in the world?'
It's led me to discover the
fundamental building blocks
of everything defy reality.
We're only scratching the surface of
what's really going on in the world.
'The length of this piece of
string is going to depend....'
'It's a simple task, this time,
shouldn't take long.'
'The more you measure
it, the longer it gets.'
How long is this piece of string?
Right, and you want a simple answer
to this one?
319 millimetres and 442 micrometers.
That piece of string could actually
be infinite in length.
'Things aren't there until you
actually look at them.'
VOICES ECHO
32 centimetres.
That'll be the end of
the programme, then.
But after all this
maths and physics,
how long is my piece of string?
Well, I promised
to tell Marcus the answer.
Hello, how are you!
I'm good, how about you?
I'm fine, I'm fine.
My head is full of string now.
So ultimately what's the answer? How
long is your piece of string, Alan?
It's 320 millimetres.
That's what you said
right at the beginning.
But every time I asked someone
how long is it, they took me
further and further
down into it and they said,
really you can't measure it.
How long's a piece of string?
We just don't know.
I think your piece of string
might deserve a drink after
its long journey.
Shall we take it for a pint? OK.
I still don't really know, though,
why I had a six inch needle
stuffed up my nose.
I still don't really understand
that bit.
FADE IN AND OUT
'I'm Alan Davies...
'And this is a piece of string.
'All I was asked to do
is find out how long it is.
'You'd think that would be
a piece of cake.'
You can only measure
shiny flat things?
'But little did I know that,
by the end of the week,
'a centimetre would hold a new
meaning and I'd be starting
to question the fabric of reality.'
That piece of string
could actually be infinite.
Strings can be in more
than one place at a time.
Your string does not
actually possess a length.
Somehow, by measuring it,
we create a length for the string.
THEY LAUGH
'All because
I tried to measure string.
VARIOUS VOICES
FADE IN AND OUT
'It doesn't look a length
till you measure the length.
'The more you measure it,
the longer it gets.'
How long is a piece of string?
Should be simple.
'Now, I was never
a great science enthusiast.
'In fact, at school,
I wasn't very good at it.
'But measuring a piece of string,
that's something
'I can do. It's just one step up
from colouring in, isn't it?
'That's always been
a skill of mine.'
I wonder if you can help.
I need a piece of string.
A piece of string? Yeah, just
a piece. A piece? Say when.
That's good, that is good.
A piece of string.
Have you got a ruler?
Yeah, 32 centimetres.
32 centimetres.
That'll be the end
of the programme, then.
Thanks for solving that.
That's pretty good.
32 centimetres.
Thanks a lot, see you, bye.
Thank you. Bye.
Unfortunately, I suspect
it won't be that simple,
as I am now about to visit
the professor of mathematics.
'Professor Marcus du Sautoy is
a maths genius
'but also rather foolish.'
OK, Alan, let me take you
into the fourth dimension.
'Last year, he took it upon himself
to try to teach me
'some really complicated
mathematics.'
LAUGHTER
You've sold me, Marcus.
You've changed my view
of the universe.
That's fantastic!
'So who better to help me solve
a simple question about string?'
Professor! Hello! Great to see you.
How the devil are you? I'm good.
How about you? I'm very well.
All I want you to do for me is
a simple task this time,
shouldn't take long.
OK. I just need to know how long
is this piece of string.
Oh... OK, you want the
one-minute version? Yeah.
Or the 60-minute version?
Well, I've measured it, I know
it's 32 centimetres long.
You used a ruler where you bought
this? Where did you buy this?
The hardware shop. OK.
They had a ruler on the desk, it's
been measuring things for years.
And what about this ruler? Do you
think it's the same length?
It's got centimetres on it, yeah.
You want it in centimetres or inches
or cubits? Centimetres, please.
I'm... Or stadia?
LAUGHTER
The problem about measuring things
and putting them against...
'I knew he'd be like this. To me,
it's a short piece of string.
'But for Marcus,
it's a major mathematical problem.'
..measure and make it standard.
Measurement is really
the beginning of mathematics.
And new numbers arise out of trying
to measure things like this,
and the Greeks,
they were obsessed...
'Good god, he's giving me
the history of geometry.'
Your piece of string is really
a fundamental mathematical object.
I've spent the whole morning
trying to measure things.
This little Greek symbol here
stands for measurement
and it's measuring the size
of this double coset - GSP 2 N QP.
OK, tiger. Can I...? Hold on there.
MARCUS LAUGHS
I just need to how long this piece
of string is. Go back to the string.
There's interesting maths and
physics behind the question
of how long this piece of string is.
It isn't just 32 centimetres.
You're beginning a journey
that mathematicians started
5,000 years ago.
'I knew this wouldn't be
as simple as it first appeared,
'but things were going well
at this point.
'As far as I was concerned,
32 centimetres was close enough.
'But Marcus wanted to take me
somewhere very special,
'a place that's dedicated to
just one thing - measurement.'
And that's why we're going to
the National Physics Laboratory.
Bits of the bodies were first used
as a form of measurement,
so the Egyptians, for example,
they had something called a cubit -
the distance from your elbow
to the tip of your middle finger.
It's quite a nice distance.
Let's measure ours and see...
Look, you've got a huge cubit.
Famous for the size of my cubit.
That's no good for measuring,
because your house will be
bigger or smaller than my house.
It'll be bigger and that's fine.
What will it be? Bigger or smaller?
If we have the same number of
cubits? It'll be bigger. You'll say,
"My house is six cubits high and
it'll be longer." Six cubits high!
I won't be able to get in the door.
Whatever. We need something which
is gonna be the same for everybody.
You don't really want it depending
on whether people are tall or small,
or how big things are.
You want something which is
gonna be standard.
Do you mind if I ask you a question?
Yeah, sure.
How long is that piece of string?
Nine inches.
No, no, it's just 12 and a bit.
Good guess, though, it's not bad.
Nine inches.
Cheers. Thank you.
He's quite tall,
so I bet his cubit is probably
a bit bigger than our cubit.
No way you can rely
on anything that he says.
Go and ask him
how far it is to London.
He thinks that's nine inches,
he's 25% out! Yeah.
'Body parts and Egyptian cubits
are all very well,
'but they aren't exactly
what I had in mind for my string.'
What's needed is some science,
and that's what brings us
to the National Physical Laboratory,
the scientific home of measurement.
'This is a place filled
with priceless treasures
carefully locked away.'
It's got this special
feet-cleaning sticky floor.
We need to get this for home.
We have to keep the room
very, very clean.
'They are the country's
measurement standards,
'objects that define the units
we use to measure every day.'
This is the UK's
primary mass standard.
'That's a kilo to you and me.'
It's quite small.
Yes, this little cylinder in here,
that's a kilo? Yes.
The size minimises the surface area.
There's less to get contaminated. Ah.
'Got them all here,
replicas of the cubit.' Wow!
You are an Egyptian man!
LAUGHTER
'The definitive yard.'
It's 36 inches at 68 Fahrenheit.
'And a 200-year-old
original metre bar.'
How do they decide which metal
to make it from?
Well, they commissioned a study
to find out the most stable metal
and, after a lot of experiments,
decided that a mixture
of 90% platinum and 10% iridium
was the most stable material.
This is 90% platinum! 90% platinum.
That's quite valuable.
I don't think you'll get that
in your trousers. Watch me!
'For hundreds of years,
we defined measurements with
rods of stone and metal.'
18 fingers. 18 fingers.
Your answer. Happy with that.
It's quite cute. How long's
a piece of string? 18 fingers.
'But platinum is old hat
when it comes to defining length.
'At the NPL, the metre is defined
by the speed of light.'
I tell you, this is where
we want, the Length Bar
Interferometry department.
Let's run out screaming.
LAUGHTER
MACHINE HISSES
MARCUS LAUGHS
This is really... I love the sound.
I feel like Q in James Bond.
Yeah... "Don't touch it, Bond."
One of the problems when you want
to measure things very accurately
is keeping them still enough and
that's why we have to minimise
the vibration levels
that we get in the room.
So this table is floating on air and
shining throughout this instrument
is the laser beam that actually
performs the measurement.
'A laser! That's the kind of
measurement technology I need.'
So I think the amazing thing is
that, today, a metre isn't defined
by a piece of metal, but it's
defined by light and in particular
how far light will travel
in a fraction of a second,
and it's 1 over 299 million.
792458. There you go. Of a second.
Of a second, yeah. Yeah.
In that fraction of a second, light
will have travelled exactly a metre.
OK.
'If a metre is
the distance light travels in
three billionths of a second,
'how long is my string
in light speed?'
So, Andrew, I was wondering
if I can measure my string here
in your interferometer?
It would be a little bit difficult.
I would need to have the ends of the
string polished nice and shiny flat
and so I don't think we could
measure it in here...
You only measure shiny flat things?
In this particular instrument,
but we have got something else which
could have a go at measuring it.
A stringometer? A stringometer.
'When they say stringometer, what
they mean is this little fellow -
'the fully-automated
tracking laser.'
Are you interested in the length
of a piece of string?
Do you want us to go?
LAUGHTER
So what you're going to have
to do is take your ball,
position it accurately on the end
of the piece of string, about there.
Hold it stationary on that end,
and tell Andrew when you're ready,
he'll record the point.
OK, Andrew. I'm ready.
MACHINE BEEPS
Move to the other end of the piece
of string. I'll get out of the way.
MACHINE BEEPS
If he says 320 millimetres,
I'm leaving.
Well, according to the laser tracker,
the distance between those two points
you just selected is 319 millimetres
and 442 micrometres.
It's 319 and a half millimetres?
Just a touch under.
And do you know why it wasn't 320?
I didn't add the little bit of fray.
'I thought that was it.
'319.442 millimetres seems
a pretty definite length to me.
'But Marcus doesn't agree.
'He thinks we can get
an even better measurement,
'something more accurate
than the laser can produce.'
It's that long. Yes.
'So we travelled
132.4 miles to the west,
'because Marcus says
that my string is actually
a famous mathematical conundrum
'and he seems to think
that the way to solve it
lies in measuring Cornwall.'
Five...six... This could take a
while, this is really complicated.
You can do it a bit rough and ready
to start with. Do it wrong?
No, it's just quite hard to get
inside of all of the little inlets.
I'm prepared to make the effort.
I can see you're trying.
This might be the best bit
of the show if I get this right.
It could. On the other hand... You
deliberately made me lose my place.
Right start again, start again.
133, 143...
'What Marcus wants to demonstrate
is that
'how I go about measuring something
can change the result.
'With a ruler, from Black Head
to Looe is 42 centimetres.'
Down to Looe...
It's 42 centimetres.
Now of course the problem
you are finding using this is
with a flat edge, it's really
difficult to get into all of the
inlets and things like that.
What about using
your piece of string?
'My string was somewhat better,
but produced a different result...'
47 centimetres.
Right, let's do 47.
Seems to be growing.
'Finally, a map measuring wheel.'
Gosh, OK! Whoa!
Look, this is, this is...
centimetres round
the side here. 65.
We've got up to 65 centimetres
using this one. So...
with a ruler,
we had 42 centimetres.
With your piece of string,
47 centimetres.
If we had an even more accurate way
to measure the length here,
we'd probably get the coast
going up even more,
because you'd be able to get into
all the nooks and crannies.
Each measuring device is
effectively zooming in on the coast
looking at in greater detail,
and that reveals
more twists and turns.
Each new cove or inlet
increases the overall length
all the way down
to individual grains of sand.
And the more detail you reveal,
the longer the length becomes.
This'll have serious implications
for measuring your piece of string,
because this isn't
a smooth piece of string.
It's actually also got
lots of crinkly bits inside it,
so the length of this piece of
string is going to depend on how
accurately we measure it.
Oh, boy!
I knew this would happen.
LAUGHTER
So make sure he gets
a good night's sleep,
because tomorrow, we're going
to find out how long he really is.
'Studying Britain's
crinkly coastline
'has actually resulted in
a whole new field of mathematics.'
What I want to do is
to measure out nine metres.
That's the side of our triangle.
'It's the maths of fractals.'
Excellent.
Brilliant, so this triangle
that we're building is
a third the size
of the larger triangle.
Now we're going to add
even smaller triangles on,
we're going to make it even
more complicated. Right.
'Now I was wondering what on earth
a fractal looked like.
'But I wish
I'd never asked Marcus,
'because he has me drawing triangles
in the sand over and over again.'
Brilliant. The sticks
are getting a little bit big,
so I think it's chopsticks now.
Come on, then. Race you? Race you!
Nice little triangle.
Wow, there you go! OK, shall we do
another set of triangles? No.
You got the point? OK.
That's enough triangles!
So what we have here is
the beginning of a fractal
and does it remind you
of anything? Um...
Ice... Dust... Snow. Snow.
It's like a snow flake and in fact
this is called the Koch snow flake.
Nice(!) Yes, exactly!
It's the name of the German
who discovered the...
EMPHASISING THE END OF THE WORD:
The Koch! The Koch, yes, exactly.
All this drawing is so Marcus
can show me that fractals
are mathematical shapes
that look the same
no matter
how zoomed in on they are.
Their shape is repeated over
and over and over again.
And he thinks
it's the same for my string.
The closer you look at it,
the more crinkles appear.
That makes calculating the length
of the string a little tricky.
How long do you think the fractal
is that we drew here?
How long was the triangle, the big
triangle we drew at the beginning?
27 metres. Three times nine.
Yeah, nine metres each side,
so we had a triangle
which was 27 metres long
and then what we did was to add
a smaller triangle on the side
so actually, the length of this
has gone up by four-thirds
by adding these new triangles,
so every time I add on more
triangles, each time, the length
increases by four-thirds.
You add one third, but to do
the sum, you have to multiply by
four and divide by three. Yes.
You've got 27, the original length,
and we're adding a third on again
each time we add another triangle.
Multiply by four-thirds.
Exactly. Now do that again,
add an extra third on by
adding more triangles, so maybe
you can see what's happening.
Every time I add smaller and smaller
triangles on, the length increases
by another factor of four-thirds,
and potentially,
the lengths of this fractal...
will actually be infinite.
So we've drawn an infinite line
in the sand
and because your piece of string is
a bit crinkly, a bit fractal-like,
that piece of string could
actually be infinite in length.
Right. You've been carrying
around infinity in your pocket
all these days without knowing it.
Well, you say that, but look there's
the beginning and there's the end.
This is quite theoretical,
if you ask me!
You're right, I mean, this is
a shape in the beautiful, pure world
of mathematics and you're right.
If we kept on adding triangles
into the sand, at some point, you're
going to hit a grain of sand,
the atom, and you won't be able to
divide any further. Yeah, yeah, so!
OK, you're right, but I love this
pure world of mathematic where
you can just keep on dividing off
into infinity and produce
this beautiful fractal thing.
'When I asked Marcus to help me
measure my string,
'I thought he would definitely
have an answer.
'Instead, he proposes fractals,
'theoretical objects
that are infinite.
'But I want a length that works
in the real world and that means
'I'm gonna have to leave Marcus
and his equations behind.'
My watch says 8:52.
What time's it going down?
Doesn't this say
when the sun sets?
Yeah, this is the
classic 21st-century life.
We're so busy looking at what time
the sun sets, we missed the sunset.
LAUGHTER
We actually... Oh, it's gone.
It says it's still up at the moment.
Oh, does it?! Good, good.
Beautiful sunset. Yeah.
'I've still got my measurement
of 319.442 millimetres,
'which is pretty good, but I must be
able to do better than that.
'What I need to do is measure it
in the smallest units possible
'and surely, that means
measuring in atoms.
'So...I guess I'll have to get
to grips with some physics.
'Just one problem.
'When it comes to physics,
I have a little secret.'
I've been sent back to school
to do physics,
which I'm not proud to admit
that I deliberately
failed my mock O-level
to get a U,
so that I could drop it.
I've been slightly anxious
about a physics teacher,
but got my string and actually
I'm finding it quite comforting.
SCHOOL BELL RINGS
'This is
the Simon Langton School for Boys
'and I'm here to meet one of the
country's best physics teachers -
'Becky Parker.'
Hi there! Hi! Are you Becky?
Yeah, welcome to the Langton. Nice
to meet you. Lovely to meet you.
I've got a bit of a problem -
I've been trying to measure
the length of this piece of string.
Right, and you want a
straightforward simple answer to
this one? Wow! Is there one?
When you get down to the really
tiny scale, things get complicated
and that's why your problem
of measuring really accurately
that length of string
is not just straightforward.
I need to take you on
a bit of a journey through
lots of quite wonderful ideas,
which I think you'll find
quite mind-blowing.
I had a feeling
there'd be a journey.
'This is exactly
what I was afraid of -
'being locked in a dark room
with a physics teacher.'
'Any minute now,
she'll ask me for my homework.'
There you go, just need
to get it completely dark...
Oh, now, hold on a minute.
SHE IMITATES A FANFARE
AND PRESSES A SWITCH
Bang...
Oh! Electricity,
that's what you need.
Hey, hey, we have light!
Now we're going to
try and do some experiments
to understand what's going to
happen and it is quite amazing,
almost magical in a way, to see
the weird effects which happen
down in this atomic world, but what
do you understand the atom as being?
I bet you've probably done
that at school? I have a vague
recollection of it, yes.
Have you got any picture of
what that atom might look like?
Something might come to me.
Would you like to draw a model
of the atom on the board?
Why certainly!
Draw an atom. Yeah.
Right...
Well, all I really remember,
I remember from school,
I remember there was...
There's something very, very
small in the middle. Yeah.
And then, is there not something
going round and round it?
Yeah, definitely.
Spinning round and round.
So, in the middle,
there's protons. Yeah.
And neutrons.
Yeah, absolutely brilliant.
And then, what's the thing that's
going round? Electrons. Electrons.
That's it.
That's all I remember. Yeah.
I mean, this is how
the atom is portrayed,
a bit like a little mini solar
system that you've got this thing
which is pulling the electrons.
An orbit thing. Yeah yeah.
It gives an idea of how tiny this
nucleus is with the protons and
neutrons compared to the electron.
Most of the atom is nothing. So if
you collapsed - here's a question -
if you collapsed,
all of what you are as matter,
the whole of the human race
into just the massive stuff,
which is the protons and neutrons,
what would be the size of...?
If you just took the actual stuff
that we're made of
and took the space out,
we'd shrink down dramatically.
I mean, I'd come down to just a
little bit of... Yeah. ..a crumb.
You be careful, cos you wouldn't
see you, you'd be microscopic.
The whole of the human race would be
in the volume of a sugar cube.
Everybody? Yeah.
So the matter of everybody in
the world amounts to one sugar cube?
Yeah, if you got rid of...
The rest is just space? Yeah.
And so, we're all made up of these
just tiny little fundamental things.
'Talk about making
someone feel inadequate!
'We're all made up of space,
of nothing at all.
'At least I've managed to
pass my first physics test.
'Quite pleased with my atom.'
The only trouble is,
if the atom was like that,
then the actual electrons,
if they were accelerating round
orbiting the protons and neutrons,
they would lose energy
and so they would actually
spiral into the nucleus
and that would mean that
all matter would just collapse.
Now we know that matter doesn't.
So that's wrong?
The only thing I remember.
I know, because that's what
you've always been taught
then you have to re-learn it and
think that's not a very good model
cos it doesn't work at all.
So sorry about that!
That's what often happens.
You have to sort of, you know,
refine your thinking as
you understand more and more.
Atoms aren't what
I thought they were,
not neat little solar systems
with particle planets.
According to Becky,
they're much weirder than that.
So weird, they have their own branch
of physics - quantum mechanics.
'And that is a big problem,
because in quantum physics,
'the particles in my string
can be in two places at once.
'And that makes working out
where they are really hard.'
So...the thing about
why actually it's important is
when it comes to footballs,
for example, which, obviously,
are particle-like... Mm-hm.
..they're smeared out,
so in the quantum world,
they wouldn't just be here.
It'd be all over the place and
around and you wouldn't necessarily
be able to tell where it was.
So if I throw it at you, in
the quantum world, you wouldn't
be actually sure where...
A bit like somebody trying
to save a penalty, you wouldn't
know which way to go.
Oh, there you are, you see.
But that was a terrible penalty.
But say, in the quantum world,
we wouldn't know exactly
in which position the ball was.
It could even be behind me
or over your head.
So is this ball that ball?
Yeah, exactly. It can be
in two places at once? Yeah.
'This is a fundamental
tenet of quantum physics.
It's not a weird by-product,
but a reality that explains how
the smallest objects behave.
The whole question of actually
defining where the atoms,
where the footballs are becomes
quite a serious measurement problem.
That's the last thing I wanted was
a serious measurement problem. It's
the nature of the quantum world.
I wanted a simple measurement
solution. It's not straightforward,
because you can never be exactly
sure at what point your string ends.
Oh, no!
LAUGHTER
'I find it hard to accept
'that particles can be
in two places at once,
'not just two places at once,
but many places at once.
'Unfortunately, to see
this miraculous behaviour
'takes a lot more than
a bag of footballs.
'To prove to me that my string
can be in many places at once,
we need a real physics lab.
'At Imperial College in London,
they have the equipment
'to see individual particles
and watch how they behave.'
All these flashing lights...
A centre for cold matters.
Is that the fridge?
SHE LAUGHS
Johnny! Hi, great to see you.
Hi. Thanks for seeing us.
Dr Johnny Hudson, Alan Davis.
Hello! Hi, good to meet you.
'Becky and Johnny have chosen
one of the most common things
in the universe
'to provide evidence that objects
can be in two places at once.
'It's something that surrounds us
all the time - light.'
We'll shine a laser beam through two
very narrow slits. Can you see them?
Can you see two? OK.
Just. Yes, yes, I can.
They're about the size of a human
hair each and they're spaced by
about the same amount. OK.
What you can see
over on the far wall
are the stripes from the waves
coming from each slit interfering.
'Right, let's just stop it there.
'In a minute,
I will to see something that was
to turn my world upside down.
'But to properly understand it,
Becky needed to explain
a simple concept.
'It's all to do
with how light works.'
Firing laser light at two slits
doesn't create two shafts of light,
as you'd think.
It creates stripes.
That's because light is a wave.
The waves of light
pass through both slits
and then interfere with each other.
Some add up to give bright bands,
others cancel out, leaving darkness.
Becky calls this
an interference pattern
and she says it's telltale
evidence that the light
has passed through both slits
at the same time.
But Johnny is only
going to send through
a single particle of light,
called a photon, at a time.
Of course, you'd have thought
that would just create a dot,
but that wouldn't be quantum.
OK. So what we can see here
is each of these
little green splodges of light
is a single photon.
OK, so this is now averaging
those successive frames together,
laying them on each other as if you
printed them and put them in a stack
then held them up to the light.
Where you get more photon impacts,
you see a brighter green colour.
Where there are fewer, you see a
darker colour. And you can see that?
It's amazing. Stripes. Completely
amazing. It's definitely stripes.
'If only one photon at a time
goes through the slits,
'how does it create
an interference pattern?'
So you've got your photons,
they're going through two slits.
And they, they're passing through
them, one photon goes through both,
it has to go through both
to create the wave effect. Yeah.
But it's one photon. Yes. So it has
to be in two places at once? Yes.
It has to be in both slits at once?
Yeah, effectively.
It's adding up to a bright band,
cancelling out to give nothing...
But the photon's something that...
That's as small as you can get.
You can't split it in half
and re-form it?
Well, that's because
you can't then have that picture
of it being a single particle.
It seems to then act as a wave
when it goes through the slits.
The thing is, position isn't
a good idea any more.
Position is something that's
useful for big things.
But when you talk about
the smallest things, position is
not a good idea any more.
You mean where things are?
Yeah, they're not in a place.
They don't really have a position
as such, which is surprising, right?
'I thought that Johnny would have
a big fancy machine that would count
the atoms in the string.
'It's a tricky task,
but at least understandable.
'Alas, the real world
just isn't like that.
'It turns out, in reality,
the fundamental building blocks
'of the universe
don't have a fixed position.
'Well, if that's the case, how am
I ever going to measure my string?'
I think the philosophical
understanding
of how we understand reality has
got a long way to go, I think.
Really, we probably need a whole new
way of thinking about the world.
Yeah, it's quite difficult
to get your head round,
except it turns out out it is
possible to get your head round it,
because your head could be
in two places at once. Ha-ha!
Yes, so your head could be here
and then it would understand.
Yeah, it's getting your head round
the fact that you could get your
head round it. That's the trouble.
Wow, this whole measuring
thing turned out to be
so much more complicated
than I thought.
FAIRGROUND MUSIC PLAYS
'Measurement should be easy.
I do it all the time
'but according to quantum mechanics,
it's an almost impossible challenge.
'Worse than that,
it's a science that declares
'that the world is
mysterious and confusing.
'I knew that already.'
It sounds like a cop-out to
have a theory which says
that you can't work out the answer.
Well, Alan, yeah, like you, Einstein
grappled with this and never...
I like that sentence.
Yeah, you and Einstein.
Like me, Einstein grappled with
the laws of physics. No, you did!
Einstein and I have many
of the same concerns.
Yeah. You know,
people like you and Einstein
expect to be able to understand
the world and have it...
We do, we both do.
Yeah, have it completely clear
exactly what reality is.
You...
You don't get an absolute,
definitive answer.
You get probabilities
and likely to be here,
and most probable to be there.
I'm gonna go back
to 320 millimetres.
'Becky has been trying to help...
'But I think she might've
scrambled my mind.'
'Position is not a good idea...'
'I thought she'd give me
real world answers,'
'Turns out the real world is
stranger than I imagined.
'Now I'm more confused than ever.
'But what does this mean
for me and my string?
'We're all made of atoms
and particles.
'Does that mean we're
also blurry at the edges?
'Can I be in many places at once?
VOICE ECHOES
'If I'm here, where else am I?
VOICE ECHOES
'I want answers.'
'Quite an amazing journey right
right down into the tiniest stuff
'which I think you'll
find quite mind-blowing.'
'To find them, I've arranged to meet
a professor of quantum physics,
'a man called Seth Lloyd.
'Seth is a master of the quantum.
'He works with particles
and atoms all the time and can
bend them to his will.
'Seth's the man to bring sense
to this quantum madness.
'But I'm not entirely sure
why he wants to meet me
in a taxidermist's.'
Seth! Oh, Alan! Hello.
Good to meet you.
Nice to meet you too. Thanks
for inviting me to this place.
You're probably wondering
why I asked you down here today.
It has crossed my mind.
You have nothing to fear. Good!
LAUGHTER
In fact, I brought you here
to introduce you to Fluffy.
What a beautiful cat.
She WAS a beautiful cat.
LAUGHTER
First, let me ask you a question.
Do you think this cat is alive?
No, I think, I think it's stuffed.
You think it's stuffed? Yeah.
Now it may not seem to begin with
that cats have much to do
with measuring string,
but in fact, they have everything
to do with measuring string.
About 70 years ago, the German
physicist, Erwin Schrodinger,
came up with a thought experiment
about a cat,
a thought experiment which I'm now
going to ask you to go through.
OK. I'm ready. OK.
So Schrodinger imagined
that you had a cat.
But then, as a result
of a radioactive decay,
where an atom would decay
and emit a photon,
this photon would be absorbed by
a detector and, if the photon was
absorbed by the detector,
then a small amount of poison
would be put in the cat's milk.
The cat would drink the milk
and then die.
Right. At the level of
quantum mechanics,
a particle isn't
in one place or another,
so the photon in some funny sense
is both detected and it's somewhere
else where it's not detected
and that means that the poison is
being put in the milk and not being
put in the milk at the same time.
So if a photon can be here and there
at the same time, then a cat
can be alive and dead
at the same time.
'I was hoping Seth would
make things seem less weird,
'but now, things aren't just
in two places at once.
'They're also dead
and alive at the same time.'
I'm picking up the thought
experiment and I get the theory,
but in reality,
we're alive, the cat's dead.
The string is a certain length.
Well, that's what Einstein
would've liked to have thought.
This is why Einstein
didn't like quantum mechanics.
Right. So what's going on?
How can a cat be alive and dead?
We never see the cat alive and dead.
This has to do with observation,
crucially.
Looking at the cat is an act
of measurement and if the cat is,
in this funny sense,
alive and dead at the same time,
and we look at it or measure it,
it effectively has to have
become either alive or dead,
but not both.
LAUGHTER
I'm getting it, but I just feel
as though, even if I don't see it,
it's still dead.
Yeah, so it's important here to,
to think about what
we mean by observation.
Most human beings when they say,
"We observe something,"
it means we're there to see it.
But you have to think that,
as every particle of light
bounces off this cat,
it's effectively observing it, so
if there's anything there to detect
whether the cat is alive or dead,
then it's either alive or dead and
not alive and dead at the same time.
CAT PURRS
So big things don't show up
being two places at once
or cats don't show up being
dead and alive at the same time,
cos they're big and interact
with their surroundings.
Every interaction with the
surroundings is effectively
an observation.
The environment observes the cat.
And this is very important
for your length of string,
because, just in the same way
the photons can be here
and there at the same time,
the string can have
multiple lengths at one time.
'This isn't the news
I was hoping for.
'In fact, it's an utter disaster.'
Your string does not
actually possess a length.
Somehow, by measuring it,
we create a length for the string.
It hasn't got a length
till you measure the length?
It doesn't, and then its length
is what you measure it to be.
Then it goes back to not having
a length again? It's not even really
there until you measure it.
That's what Einstein hated
about quantum mechanics,
that things aren't there
until you actually look at them.
So reality, in some sense,
doesn't exist unless
we're actually observing it
and it's our act of observation
that makes things real.
Oh, no!
'Right, so let me get this straight.
'My string doesn't have a length
until it's observed,
and then its length is created.
'But it IS observed,
it's in my pocket.
'The last time I looked,
it was about 320 millimetres.'
I'm enjoying the theory
and the thought experiments.
I can see things and where things
are and I'm not really getting
the relevance to the real world.
It doesn't really matter.
This is all just theory
that isn't really relevant,
because we are observed by
the environment, so does it...?
Who are you - Einstein?!
Does it really matter?
What's your problem(?)
I feel more and more like Einstein
every day, which I previously
thought was a good thing.
You think that quantum mechanics
doesn't matter in a really
important way for living things.
Come with me,
I'll show you how it matters.
Don't knock quantum mechanics, baby!
LAUGHTER
'Seth doesn't need a laser
or a lab to demonstrate
'that quantum mechanics isn't only
relevant to invisible particles.
'All he needs is a greenhouse.
'He's brought me to Kew Gardens,
cos the latest scientific research
'has uncovered a surprising truth.
'That all life on Earth
relies on quantum physics.'
You say you don't believe
that quantum mechanics is really
important at a basic scale.
So what would you say if I told you
that every single plant here
is using quantum mechanics
in a fundamental fashion in order
to turn light into energy, and
to build itself up from scratch?
Nature effectively discovered
how to use the same kind of
quantum weirdness that allows
particles to be in two places at once
and that underlies Schrodinger's cat
in order to make all this happen.
Things have to be in two places
at once or there's no plant life?
That's right, exactly.
How do the plants know that?
Even I know that plants turn
sunlight, air and water into food
in a process called photosynthesis,
but according to Seth,
this relies on quantum physics.
The way that photosynthesis works
is that a photon particle of
light from the sun comes in,
gets absorbed in a gigantic molecule
like a chlorophyll and it creates
an energy state called an exciton,
an excited state of electron.
Now this exciton has got to get
from this side of the molecule
where it's been created
to this side of the molecule where it
can be turned into chemical energy
and photosynthesis is incredibly
efficient in this energy transfer
process, like 99% efficient.
And that's very hard to understand
because you can understand if it were
maybe, like, 50% efficient,
so if half the energy got there,
but it's quite crazy that 99% of the
energy gets from where it's absorbed
to where it actually gets
turned into chemical energy.
And the way that these organisms
figured out how to make it efficient
is by using this wacky quantum state
where you go through all possible
paths at once of the molecule
so it's in many, many, many
different places at once.
That way it can do it without
dissipating all this energy
that it's got.
We've gone past two places at once.
We've gone into thousands,
millions of places.
Millions of places at once, yeah.
Hey! Hey.
It's almost like this
quantum process
is trying to find a
path through a maze,
and the energy takes every
possible path at the same time
but having arrived at the centre,
it appears to have only
taken the quickest route.
Without this quantum weirdness
that allows plants to be so
energy-efficient,
life on earth
would be very different.
So without plant life discovering
this ability to transfer energy
in that way, there's no dinner on
the table, there's no anything?
There's no barley for the beer.
I have new respect for plants now.
The question really is
do they have new respect for you?
THEY LAUGH
Quantum physics
isn't restricted just to plant life.
It's everywhere. It's even in me.
Apparently quantum physics
is going on between my ears.
Alas, not in my brain
but up my nose.
Smell that. Very nice.
You couldn't smell if quantum
mechanics weren't there to help you.
The role of quantum mechanics
in the way we smell
is not yet fully understood,
but a research group,
led by Professor Marshall Stoneham,
are just beginning to uncover it.
Dr Simon Gain. Hi, there.
The question is what happens
when you actually get a smell.
But what we believe is happening is
the smell molecule has to pass
through various mucus layers
and so forth and it ends up
at a receptor, and you have
350 different receptors.
And they're all sitting there
waiting to be triggered?
That's right, and only perhaps a
dozen of those will be triggered by
any one scent molecule, and then the
mixture of those signals is what
tells your brain which smell it is.
And if it was a bad egg that
you've just opened, then you'd get
that effect of the bad egg smell
about a millisecond,
about a thousandth of a second
after things had gone in.
We can show you because it doesn't
happen everywhere in your nose.
It only happens in a specific bit
right up at the top between your eyes
and in,
just behind the bones of your nose.
So if you're interested, we can put
a camera up there and have a look.
And what does this camera look like?
This is the camera.
Holy smoke!
Better you than me, is all I can say.
Yeah, yeah.
To see where the quantum physics
is happening, required numbing
my nose and face.
And placing a camera
just below my brain.
So that's called the nasal
vestibule, the hair-bearing part.
Looking into the nose now
with the septum on the
right of the picture, we're looking
right up just below your brain.
Right here at the top of my
nose is a gap in the skull
that allows the smell receptors
to connect directly to my brain.
And that's where the lining
of your nose changes from
the respiratory mucosa
to the olfactory mucosa
which has the nerve endings
that bear the receptor that we think
works by quantum methods.
Just seeing if you left any
equipment.
THEY ALL LAUGH
Thank you!
As a scent molecule travels
up the nose, it finds its way
to a receptor.
To distinguish different smells,
the receptors have to send a signal
to the brain.
That signal
is triggered by an electron.
The only way for the electron
to signal the brain
is to go through
the solid scent molecule
though this should be an
impenetrable barrier,
but when the right molecule
hits the right receptor,
the electron can magically
pass through the molecule
and begin its journey to the brain.
This seemingly impossible process
is called quantum tunnelling.
What's remarkable, I think,
about this is that,
we've known about quantum
mechanics for 100 years now
but only in the last few years
has it become clear
that nature actually
discovered all this quantum weirdness
a billion years before
human beings even came on the scene.
You would expect it to be very
interesting to go from what
seemed to be a purely theoretical
experimental side to something
that's actually day to day life.
So are you willing to accept now that
quantum mechanics is more important
to life than just dead cats?
Yes, I can accept that.
The smell of success!
Yes, I get it.
Quantum physics underlies everything
in the world,
and gives us a glimpse
of what reality is actually like.
It's amazing and I'm very pleased
that smart people like Seth
are working all this stuff out
but I just think
we've taken a bit of a detour.
I set out to measure a piece of
string
and I can't believe that 0.442
of a millimetre
is as accurate as I can get.
Surely, there's a way to go
beyond that to get a better length.
So Seth,
come on!
You've shown me a lot of
particles and waves and...
I know a bit about quantum mechanics
now but I don't know the length
of my piece of string.
Fair enough.
Isn't science always like that?
It's turning out that way.
It answers lots of
questions but not the one you
want to know the answer to.
How long is a piece of string?
Absolutely.
Well, let's look
at how accurately you could possibly
measure your string. Yes, let's.
All right, so you know that
if you can measure your string very
accurately within a millionth of a
metre by counting the number of wave
lengths of light that go along it.
And then you say hey, I can measure
it more accurately
by putting in light with a shorter
wavelength, so if the light
has half the wavelength, I can
measure it to twice the accuracy.
This is what they were talking about
at the National Physical Laboratory,
using the wavelength of laser light
to measure my string.
Despite the uncertainties
of quantum physics,
it's the best way to measure length.
Theoretically, there is almost no
limit to how well you can measure
with it.
In principle you could actually
by making a light wiggle up and down
really, really, really, really fast,
you would think, "I can measure my
string to any degree of accuracy
I want."
Which would make you happy. Yes.
But there's one slight hitch.
Yeah, I thought there'd be a "but"
after it.
Yeah, yeah, I know.
I know. It's always this way, right?
Yeah. So... Go on then, what is it?
OK, the hitch is that if the light
is wiggling up and down faster,
each photon has more and more energy
so if it wiggles up and down
twice as fast, you double
the energy of the photon.
That's OK, we just put in
more energy but we get a better
measurement of your piece of string.
But what Einstein taught us is that
energy effectively has mass,
and mass gives us gravity,
but there's actually a limit
to how densely you can pack a
bunch of energy into a sub-class.
What's the limit?
Do the words, "Black hole"
ring a bell?
I can make a black hole with
my string? Well, you can.
Measuring leads to black holes?
To measure you need to put in energy.
Energy causes gravitation.
Excess of gravitation
causes black holes.
Oh, that's a terrible
disappointment.
I'm going with the black hole, Seth.
You wanted to know the answer.
I don't care any more.
Thanks for everything but...
kaboom!
THEY LAUGH
I've learnt something.
I just thought at the beginning of
this, a group of men in white coats
would point a laser at the string
and da-da, you'd get a length.
But it turns out
that trying to measure
something as simple as string
is actually a philosophical journey.
'The whole of the human race would
be in the volume of a sugar cube.'
'Everybody in the world?'
It's led me to discover the
fundamental building blocks
of everything defy reality.
We're only scratching the surface of
what's really going on in the world.
'The length of this piece of
string is going to depend....'
'It's a simple task, this time,
shouldn't take long.'
'The more you measure
it, the longer it gets.'
How long is this piece of string?
Right, and you want a simple answer
to this one?
319 millimetres and 442 micrometers.
That piece of string could actually
be infinite in length.
'Things aren't there until you
actually look at them.'
VOICES ECHO
32 centimetres.
That'll be the end of
the programme, then.
But after all this
maths and physics,
how long is my piece of string?
Well, I promised
to tell Marcus the answer.
Hello, how are you!
I'm good, how about you?
I'm fine, I'm fine.
My head is full of string now.
So ultimately what's the answer? How
long is your piece of string, Alan?
It's 320 millimetres.
That's what you said
right at the beginning.
But every time I asked someone
how long is it, they took me
further and further
down into it and they said,
really you can't measure it.
How long's a piece of string?
We just don't know.
I think your piece of string
might deserve a drink after
its long journey.
Shall we take it for a pint? OK.
I still don't really know, though,
why I had a six inch needle
stuffed up my nose.
I still don't really understand
that bit.