- Hey, smart people.

Joe here.

If your science education was anything like mine, you probably learned about the scientific method.

The way it's taught to us, you make an observation and you come up with a guess about what's going on, and then you test that idea with an experiment to figure out if you're right or wrong.

Rinse, repeat, Newton's your uncle, and hopefully you end up with a better picture of reality than you had yesterday.

But that hasn't always been a thing.

Humans invented science.

The scientific method?

We invented that too.

And I wanna tell you a story about how that happened.

(bright music) Just follow me in here.

(footsteps crunching) (plastic crinkling) Okay, guys, I think I'm too old for this.

This is the inside of a bouncy castle and we turned it into a camera obscura.

(playful music) A camera obscura is basically just a dark room with a tiny hole at one end that lets an image of the outside be projected onto this back wall.

Now, it takes a lot of light for this to work but luckily the sun has us covered there, and it takes a really sensitive camera to make this shot even possible.

But, to the naked eye, in here, I gotta tell you, this is an incredible experience.

It's amazing that this works.

What you're seeing happening behind me here is not a trick, whatever Thomas is doing.

(jaunty music) This is the direct technological ancestor of the cameras that we use today.

It's one of the oldest methods of projecting images.

And the reason that we're in here is because around a thousand years ago a mathematician named Al-Hassan Ibn al-Haytham made a promise to the ruler of Egypt that he'd build a dam across the Nile River to stop its catastrophic floods.

Problem was, Ibn al-Haytham had never seen the Nile river.

And when he got to Egypt, it was way bigger than he expected, and suddenly he was in a little bit of trouble because the ruler of Egypt was famous for killing or banishing anything he didn't like.

Legend has it, he even banished a vegetable once.

(melancholic music) So to cover his mistake, Ibn al-Haytham decided to fake insanity and go into house arrest rather than lose his head.

And he's sitting in his dark room, and the only thing he had to entertain him was light beaming in through a tiny hole.

His room likely acted as a camera obscura, just like this one.

In a camera obscura, the image projected from the outside world is flipped upside down, which must have looked pretty strange to somebody a thousand years ago.

In fact, it looks pretty strange today too.

But as Ibn al-Haytham studied this light beaming into his little dark chamber, what he found was going to change science forever.

Ibn al-Haytham emerged from his imprisonment with all sorts of new ideas about light.

He showed how it travels in a straight line, how it bounces off of different surfaces in different ways, how it makes an image in the eye hundreds of years before thinkers in Europe re-figured those things out.

Eventually, he wrote a book that laid the whole foundation for what we know about the physics of light today.

But all of this wasn't even the biggest impact of Ibn al-Haytham's work.

In the process of revolutionizing optics, he pioneered what's perhaps the first version of the scientific method as we know it today.

Born in that dark room over a thousand years ago, today the backbone of modern science.

But what is the scientific method, really?

Back when he was studying that light hitting the wall of his room, there was no such thing as the scientific method but there were other ways of making sense of the world.

For example, for as long as humans have been humans, they've observed patterns in nature.

Cycles like seasons and years, what plants made them feel better when they were sick, which seeds would grow into the biggest grains.

That let them make calendars, medicines, and invent agriculture.

Not bad.

What these ancient humans were doing was a key piece of science.

They were using observations from the past to make predictions about the future.

And ancient people built up tons of knowledge about the natural world this way.

But what those ancient people didn't ask is why things are the way they are.

Ask an ancient Maya, Babylonian, Egyptian why the sun comes up or the wind blows, they'd probably point to a myth or a god, not to astronomy or physics.

Then the Greeks showed up.

Ancient Greek philosophy dudes were some of the first people that we know of who started looking for natural explanations to things in a really organized way.

The Greeks were masters at this thing called reasoning, basically using logic to explain things.

For instance, the Greek philosopher Pythagoras noticed that if you pluck a string, the sound that it makes depends on how long or short it is.

And he figured out that the notes in a musical scale aren't random, they're mathematically related to each other.

So, if scales are defined by math, and music is made by scales, he reasoned that math was the basis of all music.

These philosophers believed the truth was out there and reason and logic were the way to uncover it.

Those are important ingredients for how science is done today.

But there's one key thing that those philosophers didn't do very much of: experiments.

Eventually, some Greeks began dabbling with experiments.

Like one summer day, Eratosthenes observed shadows in different Egyptian cities so that he could calculate the size of the Earth.

A physician named Galen was setting fire to his own skin so he could test different burn remedies.

That's commitment.

Experiments let these scholars actually test their ideas about how the world works.

Ideas couldn't just stick around because they were good enough anymore.

They had to be right.

Now, some historians argue that these experiments were actually the seeds of the modern scientific method.

But by the 2nd century, the Orthodox Church was getting big in Greece.

And the church wasn't that into science, so the experimentation party fizzled out before it really got going.

Then around the 7th century, science was about to have another big moment, this time in the Islamic Empire.

It was the largest empire on Earth at the time, stretching all the way from Spain to India.

Islamic scholars read the works of the Greeks and others, and built off of their knowledge, making lots of new discoveries and inventions.

Ever heard of algebra?

That's theirs.

But the scientific method, as we know, didn't get its start until Ibn al-Haytham got stuck in that dark room.

So remember, one thing he noticed about the camera obscura is that images from out here in the outside world are flipped upside down.

So why does that happen?

Ibn al-Haytham reasoned that light had to travel in a straight line from every point on the object outside.

So the light rays coming from the top and the bottom cross as they enter the dark room, so that when they hit the wall, they're flipped.

But that was just a logical guess, and guessing isn't science.

It's what he did next that would end up changing the course of history.

He put his guess, his hypothesis to the test.

He placed lanterns in different positions outside the room and looked where the light from each one struck the wall.

If you cover one, it disappears over here.

Sure enough, the spot on the wall always made a perfectly straight line through the hole to the lamp.

So, light travels in a straight line.

Check.

Ibn al-Haytham performed a lot of other experiments in that dark room with a hole in it.

The size of the hole, how the moon and solar eclipses looked, how lenses and mirrors bent and bounced light.

And he wrote up these ideas about light in what's known as the "Book of Optics."

He explained all of the experiments that he did in meticulous detail so that others could adopt his method and reproduce his work.

He showed that science wasn't just reason, or logic, or even observation wasn't enough on its own.

It took experiments to find the truth.

And after him, there was no going back.

Now, Ibn al-Haytham didn't change the way science was done instantaneously.

The modern scientific method came together over centuries.

And things really got going after a Latin translation of his book began making the rounds in Europe.

One of the people to read that was an Englishman named Roger Bacon in the 13th century.

Bacon really loved that stuff about optics and light just fine, but what he really latched onto were Ibn al-Haytham ideas about how to do science.

Bacon helped popularize this idea that science was about experimentation and checking each other's work in order to establish one single scientific truth.

Which sounds pretty familiar, doesn't it?

Plenty of scientists from the time of the Scientific Revolution have direct or indirect links to Ibn al-Haytham.

We know that Kepler and Galileo read his book, and they made a few important discoveries thanks to science.

We associate names like Newton and Snell with the origin of the physics of light, but we know Ibn al-Haytham's work was being passed around their circle of friends so I have to wonder if even the great Newton got some of his ideas from somewhere else.

Today, a lot of that old science wouldn't pass peer review, but all of these characters were doing something that at least looks a lot like science as we know it.

Each of them uncovered fundamental observations about why the universe works the way that it does.

And it's probably no coincidence that many of them had Ibn al-Haytham's book on their shelves.

It would be wrong to say that one person invented science because, well, that isn't how science works.

But Ibn al-Haytham gave those who came after him a whole new way to explore the world and get closer to truth by making predictions, doing experiments, and most importantly, challenging existing ideas and being willing to replace those ideas with new ones.

Today, these are the key parts of what we universally call the scientific method.

Although different types of scientists have different ways of uncovering new knowledge, they all trace their roots to this story, this shift in how we seek to explain the world.

Science is often looked at and often taught like it's a collection of facts, but that's not really what it is.

Science, as a practice, as a verb, asks us to be enemies of facts.

One thing Ibn al-Haytham seemed to just get was that what we don't know is as important as what we know.

Because knowing what we don't know can tell us where we should be looking.

I mean, in a way, all scientists are sitting in the dark looking at the little bit of light let in from the outside world, and Ibn al-Haytham gave us a way to examine that light and get a little bit closer to the truth.

Stay curious - And as El.

(blows lips) His name every time.

Alright, one thing Ibn al-Haytham seemed to just get was that we don't.

(groans)