A very bad analogy is air pressure. Because air pressure is really not a force in of itself, it's just the presence of air at certain measures, but we observe t

A very bad analogy is air pressure. Because air pressure is really not a force in of itself, it's just the presence of air at certain measures, but we observe the effects of air pressure as we move through the atmosphere. That drag coefficient changes depending on air pressure, and influences the aerodynamics..... you get the idea. In orbit around earth the drag of upper atmosphere is enough to decay orbits, even though it's so minute it's practically a near vacuum. That is something like gravity's inverse square law, or put another ways we have been obsessing on the measured effects of gravity, but not truely understanding.... like we used to not understand air pressure centuries ago. Anyways, it goes without saying air pressure emerges from lots of air concentrated in a space, just like gravity emerges from the presence of mass in a concentrated space. Gravity is the air of the universe.