Therefore, there exists three worlds on our planet, the outer surface, where we live, the middle earth which purportedly is lined with many caverns, tunnels (made by someone), Inner Cities and people who live there and lastly the Inner Surface. How Gravity works then is the following. For the people who live on the outer surface, Gravity holds them down. For the people that live in the middle earth, the closer they get to the center of the crust (i.e. - 400 miles down), the less effect gravity will have upon them.