If you had an infinite universe filled with a static, homogeneous, electrically neutral dust, the same in all directions, so that there are no forces to consider other than gravity, what would happen? Would it remain in that static state? I have two ways of thinking about it that lead to different answers. First, the obvious: if the universe is the same in every direction, then the force of attraction on any dust particle is the same in all directions. So there is no net force on any particle, and the universe remains static. Second: Pick any arbitrary point in the universe (call it O). Then every dust particle is attracted to point O. The dust particle (call it P) lies on a sphere S centered at O. The dust particles inside the sphere attract P towards O as if their total mass were concentrated at O. On the other hand, the dust particles in any spherical shell outside the sphere S do not have any net attractive force on P. So there is no net force on P coming from particles outside S. Which one of these arguments is flawed? Or maybe both are? My apologies if this is an old puzzle that has been worked out many times. I just thought of it a few minutes ago.