  I remark from an epistemological point of view: it is not correct to  say that space or the world [spacetime] is in itself, prior to any  material content, merely a formless continuous manifold in the sense  of analysis situs; the nature of the metric [its  infinitesimal Pythagorean-Riemannian character] is characteristic of  space in itself, only the mutual orientation of the metrics at the  various points is contingent, a posteriori and dependent on the  material content.