You stick to the ground because you are exchanging particles called gravitons with the earth beneath you. In fact you're exchanging gravitons with all the other matter in the universe but the other bits have minimal impact by comparison. Yeah-right! Our little planet versus the entire Universe - doesn't add up does it?
There's another problem. Presumably as the number of aircraft flying increases there will be an ever increasing shortage of gravitons to service them all. You'll notice this if you get to TOD, idle the engines and then... 0 fpm on the VSI.
However, fear not.This cannot persist for very long because queuing superstring theory tells us that after a short pause a bunch of gravitons will arrive together like No 49 buses.
Which, of course, explains Clear Air Turbulence, so always keep your seat belt nicely tightened.