How simple ideas lead to scientific discoveries

Adam Savage walks through two spectacular examples of profound scientific discoveries that came from simple, creative methods anyone could have followed – Eratosthenes' calculation of the Earth's circumference around 200 BC and Hippolyte Fizeau's measurement of the speed of light in 1849.

One of the funny things about
owning a brain

is that you have no control over the things
that it gathers and holds onto,

the facts and the stories.

And as you get older, it only gets worse.

Things stick around for years sometimes

before you understand
why you're interested in them,

before you understand their import to you.

Here's three of mine.

When Richard Feynman
was a young boy in Queens,

he went for a walk with his dad
and his wagon and a ball.

And he noticed that
when he pulled the wagon,

the ball went to the back of the wagon.

And he asked his dad, "Why does the ball
go to the back of the wagon?"

And his dad said, "That's inertia."

He said, "What's inertia?"
And his dad said, "Ah.

Inertia is the name that scientists give

to the phenomenon of the ball
going to the back of the wagon.

But in truth, nobody really knows."

Feynman went on to earn degrees
at MIT, Princeton,

he solved the Challenger disaster,

he ended up winning the Nobel Prize
in Physics for his Feynman diagrams

describing the movement
of subatomic particles.

And he credits that conversation
with his father

as giving him a sense

that the simplest questions could carry you out
to the edge of human knowledge.

And that that's where he wanted to play.

And play he did.

Now Eratosthenes was the third librarian
at the great Library at Alexandria,

and he made many contributions to science.

But the one he is most remembered for

began in a letter that he received
as the librarian,

from the town of Swenet,
which was south of Alexandria.

The letter included this fact
that stuck in Eratosthenes' mind,

and the fact was that the writer said
at noon on the solstice,

when he looked down this deep well,

he could see his reflection at the bottom,
and he could also see that his head

was blocking the sun.

Now, I should tell you – the idea
that Christopher Columbus discovered

that the world is spherical is total bull.
It's not true at all.

In fact, everyone who was educated
understood

that the world was spherical
since Aristotle's time.

And Aristotle had proved it
with a simple observation.

He noticed that every time you saw

the Earth's shadow on the Moon
it was circular.

And the only shape that constantly creates
a circular shadow is a sphere –

Q.E.D. the Earth is round.

But nobody knew how big it was

until Eratosthenes got this letter
with this fact.

So he understood that the sun was directly
above the city of Swenet,

because looking down a well,
it was a straight line

all the way down the well,
right past the guy's head up to the sun.

Eratosthenes knew another fact.

He knew that a stick
stuck in the ground in Alexandria

at the same time and the same day,

at noon – the sun's zenith,
on the solstice.

The sun cast a shadow that showed
that it was 7.2 degrees off-axis.

Now, if you know the circumference
of this circle,

and you have two points on it,

all you need to know is the distance
between those two points,

and you can extrapolate the circumference.

Three hundred and sixty degrees
divided by 7.2 equals 50.

I know it's a little bit of a round number,

and it makes me suspicious of this story too,

but it's a good story,
so we'll continue with it.

He needed to know the distance
between Swenet and Alexandria,

which is good, because Eratosthenes
was good at geography.

In fact, he invented the word geography.

The road between Swenet and Alexandria
was a road of commerce,

and commerce needed to know
how long it took to get there.

It needed to know the exact distance.

So he knew, very precisely, that the distance
between the two cities was 500 miles.

Multiply that times 50, you get 25,000,

which is within one percent
of the actual diameter of the Earth.

He did this 2,200 years ago.

Now, we live in an age where
multi-billion-dollar pieces of machinery

are looking for the Higgs boson.

We're discovering particles that may travel
faster than the speed of light,

and all of these discoveries
are made possible

by technology that's been developed
in the last few decades.

But for most of human history,

we had to discover these things
using our eyes,

and our ears, and our minds.

Armand Fizeau was an experimental
physicist in Paris.

His speciality was actually refining
and confirming other people's results,

and this might sound like a bit
of an also-ran,

but in fact this is the soul of science,

because there is no such thing as a fact
that cannot be independently corroborated.

And he was familiar
with Galileo's experiments

in trying to determine whether or not
light had a speed.

So, Galileo had worked out
this really wonderful experiment

where he and his assistant had a lamp,
each one of them was holding a lamp,

and Galileo would open his lamp,
and his assistant would open his lamp.

And they got the timing down really good.

They just knew their timing.

And then they stood at two hilltops,
two miles distant,

and they did the same thing,
on the assumption from Galileo

that if light had a discernible speed,

he'd notice a delay in the light
coming back from his assistant's lamp.

But light was too fast for Galileo.

He was off by several orders of magnitude
when he assumed

that light was roughly 10 times
as fast as the speed of sound.

Fizeau was aware of this experiment.

He lived in Paris, and he set up
two experimental stations,

roughly five and a half miles distant,
in Paris.

And he solved this problem of Galileo's,

and he did it with a really relatively
trivial piece of equipment.

He did it with one of these.

I'm going to put away the clicker
for a second

because I want to engage
your brains in this.

So this is a toothed wheel.
It's got a bunch of notches

and it's got a bunch of teeth.

This was Fizeau's solution
to sending discrete pulses of light.

He put a beam
behind one of these notches.

If I point a beam through this notch
at a mirror, five miles away,

that beam is bouncing off the mirror
and coming back to me through this notch.

But something interesting happens
as he spins the wheel faster.

He notices that it seems like
a door is starting to close

on the light beam
that's coming back to his eye.

Why is that?

It's because the pulse of light,

it's not coming back through
the same notch.

It's actually hitting a tooth.

And he spins the wheel fast enough

and he fully occludes the light.

And then, based on the distance
between the two stations,

and the speed of his wheel,
and the number of notches in the wheel,

he calculates the speed of light
to within two percent of its actual value.

And he does this in 1849.

This is what really gets me going
about science.

Whenever I'm having trouble
understanding a concept,

I go back and I research the people
that discovered that concept.

I look at the story of how
they came to understand it.

And what happens when you look at
what the discoverers were thinking about,

when they made their discoveries,
is you understand

that they are not so different from us.

We are all bags of meat and water.

We all start with the same tools.

I love the idea that different branches
of science are called fields of study.

Most people think of science
as a closed, black box,

when in fact it is an open field.

And we are all explorers.

The people that made these discoveries
just thought a little bit harder

about what they were looking at,
and they were a little bit more curious.

And their curiosity changed the way
people thought about the world,

and thus it changed the world.

They changed the world,
and so can you.

Thank you.

(Applause)