Not the state of rest, but the states of uniform translation form an objectively distinguished class of motions, and this puts an end to the substantial ether. Finally, and fourthly, the general relativity theory re-endows this metric world structure with the capacity of reacting to the forces of matter. Thus, in a sense, the circle is closed.

Philosophy of Mathematics and Natural Science, Part II, Chapter III (p. 176), Princeton University Press. 1949