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This is Columbia, the city featured in the video game Bioshock: Infinite. It stands out in that this city floats in Earth's atmosphere. How? Some sci-fi handwavium called "the Lutece Particle". This sounded like the sort of thing we'd associate the future with, except that in the game, Columbia was afloat in 1893. Considering the limited technology, knowledge and resource access of the time, this is completely unlikely, and the Lutece handwavium I can dismiss as "anachronistic cheating".

Before I ask as to how to create such an atmospheric city realistically, my first question is this--what point of departure must happen to make floating cities like Columbia a reality? Could be any time period, not just 19th century like in Columbia.

  • $\begingroup$ A half baked idea. Can't you just make an element up that if utilized correctly has anti gravity depending on the utilization? Say if you expose it to a current, just an example, it just start to move upwards into the sky. So gather enough. Do the calculation. Then just set up generators to constantly keep the city floating. Heck with being so high up maybe even solar panels can be easier. Honestly anything else is too impractical. Sure a sort of flying military base can make military sense, they have a lot of money, but city sized propulsion even with futuristic ways is too expensive. $\endgroup$ – Seallussus Sep 25 '20 at 1:49
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    $\begingroup$ The answer depends entirely on how levitation is achieved, which could be anything since you haven't specified its nature. $\endgroup$ – rek Sep 25 '20 at 4:36
  • $\begingroup$ This sort of stuff is 100% Impossible without Giant Air Ballons. Filled with Hydrogen which by itself is a VERY BAD idea. The city is just way to heavy for this to ever work on earth. It could however work on Venus or other Planets with a very Co² rich Atmosphere. $\endgroup$ – Erik Hall Sep 25 '20 at 16:27