What is energy in GR. My professor has mentioned several times that GR introduces a manifold in place of Euclidean space. He goes on to say that on a manifold it is not possible to add vectors anymore and that the notion of mass, energy and velocity become hazy.
If that it is the case that I can't compare energy of two points on my manifold, what the heck is energy in GR. Is it at all useful anymore? Does it get discarded?
Please also consider my parallel question Where is energy in the standard model?
