 There is in fact no way to define a global energy–momentum vector in a general curved spacetime.In general relativity, the stress tensor is studied in the context of the Einstein field equations which are often written as

where formula_49 is the Ricci tensor, formula_50 is the Ricci scalar (the tensor contraction of the Ricci tensor), formula_51 is the metric tensor, is the cosmological constant (negligible at the scale of a galaxy or smaller), and formula_52 is the universal gravitational constant.In special relativity, the stress–energy of a non-interacting particle with rest mass "m" and trajectory formula_53 is