Stressenergy tensor
The stressenergy tensor is a tensor quantity in relativity. It describes the flow of energy and momentum. It satisfies the continuity equation

The quantity

over a spacelike slice gives the energymomentum
vector. This tensor is the
Noether current associated with
spacetime translations. In
general relativity, this quantity acts as the source of spacetime
curvature. One thing to note is that in curved spacetime, the spacelike
integral now depends on the spacelike slice in general. This is simply the statement that there's no way to define a global energymomentum vector in a general curved spacetime.
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