Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asked at the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and ad-free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

One day we may retire our rockets and instead reach the heavens by ascending towers

so tall they dwarf mountains and rise above the sky itself.

The tallest structure in the world, at over half a mile or 828 meters tall, is the

Burj Khalifa in Dubai.

It's not very far from the land of Shinal, the region of ancient Mesopotamia where it

has said the Tower of Babel was built, seeking to stretch the heavens themselves.

That story is typically associated with pride and hubris, and it's often been true of many

projects for constructing the tallest buildings or largest palaces or temples.

Even in modern times, these gems have often been financially absurd, and indeed the reason

the Bush-Khalifa is the tallest building isn't because we can't build taller, it's because there's no compelling reason to build so high.

It is easy to forget that even the biggest and grandest of cities like New York or Tokyo

only have a few hundred skyscrapers, while each place boasts over a million buildings, and

often even those values come only from using

the most generous lowest mark for skyscraper, which is unofficially viewed as being at

least somewhere between 100 to 150 meters tall or 40 to 50 stories or more.

The reasons to build that high is partially for maximizing super valuable real estate in

packed downtown regions,

where your cost per acre might run a few million dollars, compared to a few thousand

...