The physics keeping Star Wars' Cloud City afloat

Star Wars provides us with a perfect example of a science fiction floating city: Cloud City. Cloud City has an atypical backstory. Floating above the surface of the planet Bespin, the city was specifically designed to harvest tibanna gas rather than to house a displaced population. Tibanna gas is used in all kinds of technology in the Star Wars galaxy, including, but not limited to, blasters and repulsorlifts. Being one of the few sources of the gas, Cloud City enjoys financial success from its mining operations.