So, rather than causality and time travel paradoxes and the like that are usually discussed about relativity, I'm curious about something else. On one side of the Einstein Field Equations is the Stress-Energy Tensor, along with some constant coefficients (G, c^-4, etc), which essentially describes the distribution of mass-energy. On the other side, is the tensors and such that describe the curvature of spacetime. Typically, people picture spacetime curvature with the rubber sheet analogy - a mass sitting on the rubber sheet causes the rubber sheet to curve. But an equal sign doesn't have an arrow pointing in the direction of causality. So wouldn't it make just as much sense to say that spacetime curvature causes stress-energy, as it would be to say that stress-energy causes spacetime curvature?