Thank you, friend. For me it is easy. 1) The Einstein's Relativity has matched perfectly the many observations. The observations could be any, but they are accidentally matching the Einstein's Philosophy. (A theory is inseparable from Philosophy). Therefore probability of such luck of Einstein is total zero. But we have such happy event. Therefore, it is Transcendental Being has blessed him with right knowledge.
2) Now is simple: In Einstein's Relativity the photon moves with c between the reactions (absorption, emission). Gravity waves do exist. We have 3 spatial and 1 temporal dimensions.