““Insofar as the general theory of relativity follows Mach's ideas, it can be seen as expressing the distribution of masses in terms of properties of space itself. It all boils down to geometry-to the web of shortest distance between points in space-time. Here, all that exists can be expressed in terms of geometry. It is the motions occurring under the influence of all the masses of the universe that make up the elements of the geometrical web. The identity and the location of those masses can be read off the curvature of space-that is, off a geometrical quantity. Seen in this way, the general theory of relativity is a model for other, nongeometrical theories where the fields are added to space, just as we might add colors to a blank canvas; this is the way we treat electric or magnetic fields. But let us recall that those latter field theories were more realistic insofar as they quantize the field. It is only through the quantum effects that our hypothetical empty space becomes the physical vacuum.””
