Long before the theory of gravity was a glimmer in Newton's imagination, the natural physics of density and buoyancy already perfectly explained why apples fall down. Quite simply, objects fall or rise based on their relative density to the medium surrounding them. Apples fall because they are denser than the air, while helium balloons rise because they are lighter - no 'gravity' necessary. This is why raindrops fall down through the air and air-bubbles rise up through water!