This question came from Keira, who at age four and a half wanted to build a billion-story building.
Actually, it came from Keira's dad, who wanted to help Keira appreciate how big and difficult such a project would be.
Keira, if you make a building too tall, the top part is heavy and it squishes the bottom part.
Until you make it really really tall, and then the top part will tear itself off and go into orbit near the moon.
But we're getting ahead of ourselves. Have you ever tried to make a tower out of jello?
It's easy to make a little tiny wobbly jello castle – in fact, some people like to serve fancy jello that way.
But if you try to build a really big jello castle, the whole thing smushes down on itself. The same thing happens with buildings – eventually.
The buildings we make are strong: the tallest are almost 1 kilometer tall, and we could probably make buildings 2 or even 3 kilometers tall if we wanted, and they would still be able to stand up under their own weight.
But too much higher and we'd run into the jello problem: the top part would squish the bottom part. There are other problems with a tall building, too. One is wind.
The wind up high is very strong, and buildings have to be very strong to stand up against the wind. Another problem is, surprisingly, elevators.
