value of the stress energy tensor could be specified in some way, but as was mentioned before, the most likely candidate for such a state, the invariant state, doesn’t exist (at least not as a state fulfilling the microlocal spectrum condition). This means that apparently the setting of local covariant quantum field theory does not, at least without using further ingrediences, specify intrinsically the absolute value of the local stress energy content of a quantum field state, since the ambiguity of being able to add a difference term $C_{\boldsymbol{M}ab}$ always remains. In fact, this difference term ambiguity has the character of a renormalization ambiguity since it occurs in the process of renormalization (by means of discarding the singularities of a Hadamard parametrix), as is typical in quantum field theory. The fact that local covariant quantum field theory does not fix the local stress energy content may come as a surprise — and disappointment — since it differs from what one would be inclined to expect from quantum field theory on Minkowski spacetime with a distinguished vacuum state. This just goes to show that one cannot too naively transfer concepts from quantum field theory on Minkowski spacetime to local covariant quantum 