The Parachute Cities fall endlessly, ploughing their way downwards through an infinite blue sky.
The Big Blue is a universe of sorts. It certainly has no bottom, but it does have a concept of ‘down’. Objects, airships, people and whole islands plummet through the occasional clouds, permanently lit and heated by suns that float through the sky in the far distance.
But the air doesn’t move. Everything has a terminal velocity caused by air resistance, yet (as the famous philosopher Aristocralopholes points out) if the universe is endless, has no bottom, and everything is accelerating downwards, the air too should be moving downwards. The fact the air doesn’t move means the cities aren’t in freefall, so the residents feel gravity.
The question is why the air is still, or at least why the residents of the Parachute Cities can’t observe it’s movement through the universe.
For the sake of clarity: in this particular universe gravity is uniform (but not necessarily 1g) the universe is infinite, and all points are filled with breathable air (save those filled by something else). Don’t worry about habitability of the universe or how objects come to be there, the focus of this question is by what mechanism the atmosphere can be prevented from falling at the same rate as everything else, leading to the phenomenon of terminal velocity and hence ‘gravity’.