My limited understanding of relativity tells me that "gravitational forces" are really just due to the curvature of spacetime. That is, the reason why the earth orbits the sun is because the earth is following a "straight" line but the actual spacetime is curved so the "straight" line appears curved. Like an ant on a sphere, it walks straight but the sphere is curved so the path is curved. Anyways, when you hold an object in the air and then let go, it falls. Why? What's giving it the "push" to fall?