[carapace]

You're absolutely right, above a certain ratio of surface area to mass it becomes downright hard to keep a structure on the ground.

I'm experimenting with kites and the Magnus effect to eventually build exactly what you describe: infrastructure in the sky. (Note the absence of "cloud" puns, that is deliberate.) With computer control I see no reason why we couldn't have flying buildings.

My concern is that we will need to be able to fly to pass through the current mass extinction. I was looking at birds one day and realized that the dinosaurs that made it could fly. One way or another we are going to need to move lots of people and things rapidly over great distances.

I want to make swarms of cellular kite robots that can reconfigure themselves and combine to create vast lifting bodies.

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Should mention Bucky Fuller's discovery: An aluminium geodesic sphere of one-half mile or greater diameter will float.

Sunlight reflecting internally from the metal heats the air which expands. Above the critical size the mass of the air displaced from the sphere by thermal expansion exceeds the mass of the aluminium shell. If you sealed the sphere (even if it leaked a bit) it would remain aloft overnight.

Bucky called them "Cloud Nine" and wanted to build cities in them.