I would like someone with more knowledge than me to poke holes in this, tell me I am a retard, or best case, acknowledge I am genius! :)
First off I am not up to speed on latest explanations of gravity. I am assuming for this thought experiment that however it arises, gravity is a still a property or aspect of mass.
The setup: an Earth-sized sphere of homogeneous matter, to eliminate variations in density. It could be a sphere of solid steel. There is a shaft opening at the surface, just wide enough for a person, and a ladder to climb down.
The experiment: I start to climb down into the shaft, toward the center of the sphere. At the surface, I feel the gravity of all the sphere's mass pulling on me. This pull is not just perpendicular toward the center, but also to some extent laterally, from all of the mass extending on all sides toward the horizon. As I descend further, more of the sphere's mass is to the sides and above me. The further down I descend, the more of the sphere's mass is above me and to the sides. When I finally reach the center of the sphere, all of the sphere's mass is "above" me, in all directions. This would appear to result in zero gravity at the center of the sphere, as total mass is pulling equally on anything at the center. If this inference is correct, then maximum gravity in such a sphere would be not at the center of it but in a spherical zone/shell somewhere between the center and the surface.
Well that's it. I would really like someone to shoot this full of holes because then I could finally file it under "dumb ideas".