Not worrying about the term DE exactly - my question really is, why is the CC described as an energy density, instead of just a nonlocal quantity ? Why bother with a constant scalar field when a constant would do ? After all we do not hear talk of a local gravitational strength density which by the way happens to be constant - so what is the fundamental difference between the two cases? Or is is just convention / usage, with no deep meaning ? Then, if this is indeed necessary, how should we interpret this in a relational view of spacetime ? Thanks Edit : I realize this allows an identification with QFT vacuum energy, but with 120 orders of magnitude to cross, this isn't really compelling - or is it ?