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In a model (in theoretical physics) of gravity coupled to other fields, the energy momentum tensor or stress energy tensor T is the variation of the matter part $S_{fields}$ in the Einstein-Hilbert action with respect to the metric, $\delta S_{fields} = T \delta g$.
It is a measure for the energy and momentum density of the matter contribution to the theory.
Since the variation of the Einstein-Hilbert action $S_{EH}$ is the Einstein tensor $G$, the equations of motion of gravity, hence Einstein's equations assert that (up to constant prefactors)
The renormalization freedom in perturbative quantization of gravity (perturbative quantum gravity) induces freedom in the choice of vacuum expectation value of the stress-energy tensor and hence in the cosmological constant.
For details see there.
Last revised on February 9, 2018 at 07:02:24. See the history of this page for a list of all contributions to it.