"The resemblance between the Coulomb force and Newton's gravitational force is very impressive. ...[T]he similarity between a planetary system and the electromagnetic structure of an atom... is due to the resemblance between their laws of interaction. ...After the creation of GTR, there followed attempts to reformulate electromagnetic theory in a similar way, attempts to construct a geometric theory of the , and attempts to create a unified field theory which would combine gravitation and electromagnetism. All... failed. The gravitational field acts universally; it imparts equal accelerations to all objects. This... permits one to describe gravity by a change in the properties of... spacetime... The electromagnetic field does not have such a universality; various bodies... have different ratios of charge to mass and experience different accelerations. ...Roughly speaking, the electromagnetic field has energy; and this energy has weight... [T]he equations of GTR for a spacetime which contains an electromagnetic field necessarily force the field to satisfy Maxwell's equations. ...The idea of defining all fields by varying the spacetime curvatures that they create is... ' Its most articulate exponent is... John Archibald Wheeler."