Hi, the following two views appear inconsistent to me: In the infinite perfectly homogeneous universe: a) the net force of gravity is zero everywhere, so no energy is being exchanged and no particle is pulled in any direction whatsoever. b) the net force of gravity within a spherical cavity is zero, therefore particles put into the cavity will (only) attract each other, therefore force of gravity on these particles is non-zero and directed to the center of the sphere on average. Applied to arbitrary spheres it implies that the net force of gravity on any particle in the universe must be non-zero. I like a) better than b) but the latter is mainstream. So what's wrong with a)? Is this subject being treated anywhere?