and found that Kansas is in fact literally flatter than a pancake.

Of course, the Earth is not flat, the Earth is round.

Otherwise travellers would be falling off the edge all the time.

Right?

Wrong.

If the Earth was not a ball shaped, but was instead a flat disk, like this plate, well

with the weight, density and thickness, living in the middle could feel pretty normal.

But as you move toward the edge, gravity on a disk Earth would slightly skew, pushing

at a greater and greater angle back toward the centre.

My friend Nick from 'yeti dynamics' put together this great simulation.

The person and buildings obviously aren't to scale but check out how such increasingly

diagonal gravity would work. Although this is a flat disk, it would feel

to a runner headed toward the edge, like they were fighting to climb up a steeper and steeper

hill.

The building foundations behind the runner

reflect how you would have to build structures, closer and closer to the edge, so that people

living in them always felt like down was at right angles to the floor - the way we feel

it on our big, round Earth. As you approach the edge, things would get

scary.

Remember, this is a flat Earth, but it would

feel like a sheer drop off.

What's really cool is that contrary to the

"don't fall off the edge" fear, on a flat world because of gravity, the scary risk would

actually be falling away from the edge and rolling all the way back to the centre.

Once you stepped over the edge, instead of falling off into space, you'd be able to relax.

It would be a nice level place.

This model, of course, neglects the fact that such

a planet shape would be impossible.

Anything as massive as the Earth, shaped like

a flat disc, would, under its own gravity, naturally collapse back into a ball.

This is why in outer space everything more than few hundred miles in diameter is round.

Or so we've been told. What if gravity isn't real?

What if the Earth is, in fact, flat and science has been wrong all along?

It's a misconception that Christopher Columbus discovered that the Earth is round.

Virtually every scholar and major religion in the West accepted Earth's rotundity, since

at least the time of the Ancient Greeks, who, for instance, had noticed that boats disappear

bottom first when sailing away. And, as you walk north and south, stars pop

in and out of the view.

The misconception that only a few hundred

years ago lots and lots of people believed the Earth was flat likely began in the modern

era, as a sort of insult. Well, your people recently thought the Earth

was flat, so why should we believe you now? The smear was repeated and published so often

it became accepted as historical fact. "Flat-Earther" became synonymous with "Anti-science".

It might seem flat over short distances, but over longer ones, well the Earth is pretty

darn curvy.

The Verrazano–Narrows Bridge, connecting

Staten Island and Brooklyn, had to be designed with Earth's roundness in mind.

Its 2 towers, separated by 1300 metres, and perfectly vertical, are nonetheless 41 milimetres

further apart at the top than at the bottom

because of Earth's curvature.

In the 3rd century BC, Eratosthenes measured the differences between shadows cast by poles

in Syene and Alexandria to calculate, more than 2000 years before rockets and space travel,

the circumference of the entire globular Earth, with, for the time, impressive accuracy.

Word got around that the Earth was a round shape after that.

But in 1906, Wilbur Glenn Voliva became head of a slightly bizarre religious sect that

pretty much ran the city of Zion, Illinois.

Voliva believed that the Earth was actually

flat and he enforced flat Earth's teachings in schools in Zion.

He also enforced that belief on really anyone who entered the city.

Voliva believed not only that the Earth was flat, but that the sun was only few thousand

miles away from Earth. Not 93 million.

He also believed that the sun was only 32 miles across, not 860 000.

He sounds crazy, or does he? You see, the same phenomenon Eratosthenes

measured could be explained by a flat Earth, if the sun were only few thousand miles away

and 32 miles across - the math would work out the same.

Today, with the power of the Internet, modern day flat Earthers have picked up where Voliva

left off.

They have quite good explanations for any

evidence you throw at them that the Earth is round.

Circumnavigation is really just a flat circle path.

The round shadow Earth casts on the Moon during a lunar eclipse could also be made by a flat

disc. Time zones are caused by spotlight sun, and

remember how gravity would be totally different on a disc-shaped planet?

Well, they argue that gravity, as we know it, simply doesn't exist.

The flat disc of Earth is merely accelerating up at 9.8 metres per second.

As for all of the photos and video evidence we now have that the Earth is round, thanks

to space exploration, well all of that material is completely fabricated.

A hoax, perpetrated by Big Globe. Space agencies, airlines, globe manufacturers.

They are reaping the rewards of our ignorant belief that the Earth is actually round.

They know, of course, that it's flat. And they're hiding that truth from us.

Is it merely a coincidence that the logo used by the Flat Earth Society is a projection

of Earth, centred on the North Pole, and also happens to be the projection used by the United

Nations?

Are these people for real?

Probably not most of them. But this is the crocks of Poe's Law.

An adage that states that at their extremes, parody of extremism and sincere extremism

are difficult to distinguish.

Although clever, flat Earth theories are predominantly

ad hoc explanations - excuses made up on the spot that only address one issue and don't

fit all the evidence.

Science, of course, rejects a theory if a

better one fits more of our observations, but why the egoistical obsession with OUR

observations?

A cosmic ray particle could use the very same

scientific method we use and conclude that the Earth was, in fact, flat.

You see, at speeds near the speeds of light, time slows down and lengths contract.

One way we know this is that unstable muons, created in the upper atmosphere by the collision

of cosmic rays with the atmosphere, should mostly decay before reaching Earth's surface.

But yet, we detect a lot of them down here, because they're crazy fast speed literally

means that, from our perspective, their physics runs according to a slower clock; and to them,

the distance they have to cover to the surface during their short lives is, from their perspective,

much much shorter than it appears to us. If you're a cosmic ray proton travelling at

99.9999999999991% the speed of light, Earth would appear to be only 17 metres thick in

the direction you travel.

So Earth is flat to them, but round to us.

It is ball shaped to some observers and flat to others.

There doesn't appear to be a single most correct-est, in all circumstances, answer.

Susan Haack compares knowledge to a crossword puzzle.

New answers interweave with old ones, they all reinforce one another.

The clues are the questions we ask, and the way the answers fall into a predetermined

grid, well, that's our confidence that we're on the right track.

But that doesn't mean one day there will be a finished puzzle - a complete answer.

Recall The New York Times famous 1996 crossword puzzle that came out the day before the US

election between Bill Clinton and Bob Dole. The clue for 39 across was pretty crazy.

You seemed to need to be able to tell the future to answer it correctly.

It simply said,

"Lead story in tomorrow's newspaper

(blank) elected".

Well that blank could be Clinton or Bob Dole and who's to say which one until tomorrow?

There's no way to know. But, as it turned out, the answer was Clinton,

or Bob Dole. No matter which you wrote in, all the other

clues fit. For instance, a "black Halloween animal" could

either be a cat or a bat.

Our knowledge about the outside world might

be the same.

A puzzle with no answer key, just the reassurance

that the answers we think we know fit together, so they're probably correct.

Though there's always the possibility that the answer to one clue, or all of them, will

fundamentally not have a single definite satisfying answer.

The puzzle may be playable forever.

I like what Richard Feynman says about this.

"Some people say 'How can you live without knowing?' I do not know what they mean. I

always live without knowing - that is easy. How you get to know is what I want to know."

You know?

And as always,

thanks for watching.