tall, making them the tallest things humans had ever built. And they remained that way

for nearly 4,000 years. It wasn't even until the 1300's that we finally got around to making

something taller, a cathedral in England. So, does that mean that the Great Pyramids

of Giza are the "Best tallest structures Of All Time?"

Well, to find out more, all aboard the BOAT.

So, what is a building? Well, technically, a building is a structure in which at least

50% of its height comes from floor plates where people can live, work, chill out- it

has to be habitable. Any less than that and it's not a building- it's a tower. After the

Lincoln Cathedral finally surpassed the height of the pyramids, a number of churches continued

to be built that kept breaking and setting new records. The next long-term record holder

was the Eiffel Tower. It was the tallest thing, ever in history,

that we had built, for about 40 years in a row. It was finally surpassed by the Chrysler

Building in New York, a personal favorite, which was then quickly bested by the Empire

State Building. Now, the Empire State Building is interesting in that it was the first structure

ever built by man that was so tall, were you to jump off the top of it, you would actually

reach terminal velocity before you hit the bottom. It was the first structure we'd ever

built that was so tall, rather than just continuing to accelerate as you fell, you would actually

stop accelerating because you would reach the fastest possible speed your limp body

could fall at. In the mid 1950's, something weird started to happen: Humans started to

build radio and TV towers. These things could be way taller than the buildings that we'd

made previously that had to be habitable. And, so, ever since the Empire State Building

had its record broken by a TV tower, all these other famously tall buildings, the Petronas

Towers, Tapei 101, the World Trade Center, the Willis Tower (formerly Sears Tower)- none

have them have ever, within their existence, actually held the title for being the tallest

"thing" we've ever built. There was always a radio or TV tower somewhere that was taller.

Up until quite recently, and for quite a while, the record for the tallest thing ever built

by humans went to the Warsaw radio mast in Poland. It's visually incredibly striking

because there aren't any other sky scrapers around it. It's all alone, being very tall.

Well, that was until 1991, where some workers exchanging guy-wires made a mistake, and the

whole thing started to bend and then snapped in the middle. There's no video of the event

happening, but it would have been similar to this collapse, though much, much taller.

After the Warsaw radio mast collapsed, the KVLY-TV mast in North Dakota became the tallest,

still standing, structure built by man. But, recently, buildings have made a comeback.

And, to check that out, we're going to have to travel to the Middle East. This is the

first time I've ever touched the Nile. Tadaaa. Ok, so that was me dipping my

waterproofed camera into the Nile. If you were to take

the entire length of the Nile River and stand it up on it's edge, perpendicular to the Earth,

it would reach into outer space about this far, which is pretty impressive. But, where

does the space shuttle orbit? And where does the International Space Station orbit? This

far away? This far away?? Maybe, this far away? Actually, if this pink, inflatable "Horrible

Bosses" ball was the Earth, the space shuttle would orbit about right there. It's incredible,

but it's possible because the shuttle, and the International Space Station, travels so

quickly. They travel so quickly around the Earth that, instead of seeing one sunrise

and sunset every 24 hours, they see 16. But, don't be jealous. You can easily see more

than one sunrise and/or sunset in a day by taking advantage of tall structures. So, let's

take a look at the tallest structure, the current record holder for the tallest thing

humans have ever built, the Burj Khalifa in Dubai. The height of this building blows my

mind. You can literally watch the sunset from the base of the building, and then take a

super-fast elevator all-the-way up to the top and watch the same sun set again. In fact,

the difference in timing between sunset at the base and the

top is so significant, the Dubai Islamic Affairs department actually had to make a ruling about

when you can start, and break, your fast during Ramadan inside the building. People above

floor 80 or higher have to actually wait to start eating 2-3 minutes after the people

at the base, because the sun hasn't yet set for those at the top. But, before you head

to Dubai to watch the sun rise, or set, twice in a day, keep in mind that the only height

you actually need to see two sunrises or sunsets is the height of your own body. Try this the

next time you're at a beach. Watch the sun rise, or set, over

the water. Water is important because it won't have the terrain or hill issues that land

does. Now, let's say you're watching a sunset- begin by laying on your stomach. Watch the

sun set, and, as soon as the last little bit of sun goes below the horizon, quickly pop

up into a standing position, and, voilá, you'll see the sun's back- part of it's back-

and it will set another time.

If you take a stopwatch and record the time between the first setting and the second setting

that you witness, and, measure the height of your eyes when you're laying down and when

you're standing, you can use those numbers to calculate the radius of the Earth.

XKCD took this a little bit further by proposing the "Double Sunset Date." Take your date out

to the beach in a cherry picker, and, sure enough, it was calculated, given the speed

of a cherry picker, all you have to is move about 6 feet up, and you can watch a beautiful

sunset all over again.

To put things in perspective, the Burj Khalifa is nowhere near as tall as Mount Everest.

But, the tallest structure that we could potentially build wouldn't be as tall as Mount Everest-

it would be way, way taller. Like, into space taller. Of course, the problem with building

things that are really tall is that they get heavier and heavier, and have to support their

own weight. But only up to a point.

If a structure was so tall that it wound up at the altitude of a geostationary orbit,

it would start to feel a new force, not just a gravitational force downward, but, all of

the sudden, this new, centrifugal force up, and outward.

And so, a building that tall could be stable through tension. And, more than 35,000 KM

high. This kind if structure is known as a "Space Elevator."

Unfortunately, there aren't any materials known to science today that are strong enough

to make building something that large feasable. With the exception, maybe, of Carbon Nanotubes,

or Boron-Nitrate Nanotubes. Of course, if we went to a smaller celestial body, like

the Moon, we could build one today out of stuff like Kevlar.

There are a lot of different things that we have to be wary of when we build a space elevator.

For instance, how do we dodge space debris? One solution is to attach the Earth side of

the cable to a boat in the ocean that can maneuver around and move the elevator away

from dangerous obstacles.

Another interesting point is that the taller the cable, the faster the far end of it will

be traveling. In fact, if the cable is more than 50,000 KM long, its far end will be travelling

near escape velocity, and simply walking outside could take you to the Moon. But, why build

a space elevator? Well, because it would be awesome. But also for better reasons too.

For instance, right now, in order to send a pound of material into orbit, it costs about

11,000 dollars. But with a space elevator, we could send the same amount of material

into orbit for only about 100 bucks. That difference is so significant that Philip Ragan

has said that the first country to deploy a space elevator will have a 95% cost advantage,

and will possibly be able to control all space related activities. Alright, so here you see,

in the mirror, Alex playing guitar while she holds a camera in

her mouth and records us. Impressive. I'm here with Kristen from Barely Political. She's

visiting London, and if you enjoyed this episode of BOAT, check out other episodes- I've got

them all up there. And, as always, thanks for watching. Oh, and check out Kristen's

channel right there. Bye! Bye.