In Einstein equation of general relativity, one side is stress-energy tensor and the other side is the Einstein tensor (functions of metric tensor). But the problem is in order to describe the matter field/stress-energy tensor, we have to use the space and time, which are determined by the metric tensor. So there is some circular reasoning here. Is the spacetime just some geometry or a real field carrying energy? In the string theory, a string exists in a 26 or 11 or 10 dimensional spacetime. But could the spacetime exists as some kind of container for the string? Is spacetime some kind of material or a priori notion of physics?