As is well known, the gravitational force between two masses is dependent on the spatial distance between them. Therefore, even at vast distances, the masses exert equal and opposite forces on one another. I know that our theories need for this to be the case (to derive things such as escape velocity, which calls the force at r = $\infty$ to be zero (by utilizing a limit where the distance approaches infinity)), yet the universe is so vast and complex (with an unimaginable number of masses). With so many masses in space, it seems as though this could make a huge difference (over a large distance, such as special relativity's involvement in magnetism) . Also, say there is a supernova 400 light years away from earth. The time independent theory states that we should immediately notice a difference in the net forces acting on us, yet that would mean information travelled faster than light, correct? My main point is this: Is it absolutely imperative that there is still a force infinitely far away? Would the universe still function if we were to cut it off at something like a light year? *(This is my main point) Does the infinite reach of the gravitational force have anything to do with the scaffolding of the universe as a whole ?
Yes, the Newtonian theory says that we would instantly notice a difference in the gravitational field but that contradicts special relativity. To resolve this we use general relativity. In GR a massive body will still give a gravitational field that only vanishes at infinity. To resolve the point about escape velocities, this model is idealized but it works to a good approximation. The gravity of other stars has very very very little influence on the trajectory of rockets we launch from Earth, because they're so far away that we can basically neglect their gravitational fields.