Hey everyone, I have a question about the math involving gravitational time dilation. I have become very confused over this now and i need someone to clear this up. I know the formula for gravitational time dilation, which is- t'=t x square root of(1-(2GM/rc^2)) t'= the time of an observer within the gravitational field of a mass t= the time for someone who is not in a gravitational field G= gravitational constant M=mass c=speed of light r=??? I am really confused on what r is. I thought it was suppose to be the distance from the center of a mass. Then i looked on wikipedia and it says that r is "the radial coordinate of the observer (which is analogous to the classical distance from the center of the object, but is actually a Schwarzschild coordinate)" I have no clue what that is. Then searching this forum i found this thread. Saying that r= 2GM/c^2. This is really confusing me. Can someone please clarify what r is? Thanks.