How come in the weak field approximation, where the metric is equal to, ds^2=-(1+2phi)dt^2 + dr^2(1-2phi). where of course dr is the three distance. why is phi multiplied by 2? I have two more stupid question regarding a different approach. please just explain it to me as i want to to see this through to end(in understand all the other parts of the chapter). first off i don't understand some of the steps here. http://www.mth.uct.ac.za/omei/gr/chap7/node3.html How do we derive the inverse of the perturbed metric(i know its silly). More precisely why is the unverse of the perturbed metric the inverse of the minkowski metric minus the inverse of the perturbation? Also why is the christoffel symbol in the weak field approximation equal to -1/2n^a0(h_00,0). where h is the perturbation and n is the minkowski metric. Seeing as how we are plugging in the metric itself, which is the sum of the perturbation and the minkowski metric, why isn't the christoffel symbol, equal to, -1/2g^a0(g_00,0). Please help me with this and write it out. I know that at this point gr is probably beyond me(at least without help from a mentor), but i'd like to reach einstein's equationa t the very least, especially since i'm so close. so please just explain this to me.