Imagine a ball rolling down a huge basin. Very deep, ball gets a terminal velocity, rolls down at constant speed. Then the basin shallows, and finally the ball

Imagine a ball rolling down a huge basin. Very deep, ball gets a terminal velocity, rolls down at constant speed. Then the basin shallows, and finally the ball reaches the bottom. From the ball's point of view, "downnwardness", an ineluctable constant, has ceased to exist.