It should be noted that the same argument could be used for electromagnetic fields that are infinitely negative when attractive. Also, Maxwell suggested that the sign change, repulsive and negative fields for electrostatics presented a problem with regard to the ether. A Gedanken experiment simply suggests that the fields cannot be differentiated as they are both the action of a force on a body. The body can be of electrostatic (charged) nature or gravitational (mass). As both have the same limiting form they cannot be distinguished without independent experimental determination. Indeed, in his summary, Sattinger states that; "Maxwell's equations couple to Einstein's field equations of general relativity using Hilbert's variational method. The energy-momentum tensor is uniquely determined, and the theory of general relativity can be formulated in terms of Maxwellian fields, rather than specific force fields." Furthermore, electromagnetism and gravitation are simply two specific cases of fields that are relevant to GR. Furthermore, Sattinger states that GR is relevant where the electromagnetic fields are intense such as in the interior of stars or the early Universe. The electromagnetic fields are of significant magnitude in atoms.