I have been reading GR but I have these gaps in understanding. Can someone help clear them? 1) SR has a transformation to new co ordinate system that is a linear one. When GR is described, the textbooks mainly discuss Geodesic and distance but I ave not seen the transformation from old to new coordinate system. I understand that it is non linear but where can I find the transformation from system such as (say) Cartesian? Is it even possible? As I see it, even if space is curved, Cartesian system should be defined. For example we can define 2D curved surface in 3D Cartesian frame, correct? 2) In GR, I see Geodesic equation and Einstein's equation derived from it. The derivation looks logical until a point where suddenly Energy Momentum tensor is introduced in the equation from no where. Where did that come from? What is the basis to add it out of no where? That adds confusion. It looks as it there is conspiracy to make the equation work (sorry, J Kidding) 3) Curvature is based on Riemann tensor which looks logical but then all of a sudden this tensor is shrunk (contracted) to Ricci tensor. I do not see any explanation why it is done and what is the logic behind it or how it affects 4 dimension surface in higher dimension calculation. If our intention was not to get it Riemann, why is it there in first place, can be get to Ricci directly from equation? Appreciate response.