Question about Absolute gravitational potential energy?

You can't reduce the dimensionality of the gravitational problem from 3 dimensions to 1 and get meanignful results. First the force on an object has to be due to another m, so you have more than just the object at a point in space and a reference at infinity. Once you have two objects, you relaize that there is no preferred direction to call "x" (or y or z for that matter), so the problem has spherical symmetry. That being the case, only radial distances are inportant - and further, the origin of coordinates is at the center of the other m. SInce radial distances are alway greater than or equal to zero, the infinity is always positive.