Consider the following, fairly famous statement (amongst the cognoscenti of natural philosophy) of Minkowski, a collaborator of Einsteins on the new conception of space and time that Einsteins theory appeared to demand:
The views of space and time which I wish to place before you have spring from the soil of experimental science and therein lie their strength. they are radical.
Space by itself, and time by itself are doomed to fade away into mere shadows and only a kind of union of the two will preserve an independent reality.
Now, Schopenhauer (over a century earlier) writes in the first book of Die Welt:
But space and time are not only, each for itself, presupposed by matter, but a union of the two constitutes its essence, for this as we have seen consists of action ie causation
The consonance of these two remarks are remarkable; given that the first is meant in a definite and technical relation in physical science (physics) and the latter in terms of Kants Idealism; (or perhaps not so remarkable given the common intellectual soil from which both have sprung from; and it's admixture of various intellectual currents).
But it appears that Schopenhauers, in its generality, goes further than Minkowski: if we suppose its does not refer to space and time but matter; then it appears he conceives matter itself as the essence of the union of the two; and which he concieves as causation.
Is this reading confirmed by reference to Kants Critique of Pure Reason?