At extragalactic distances, matter flows (co-moves?) with the expanding spacetime (i. e. vacuum energy?), thus experiencing little disparity in relative motion between the two. At distances less than the radius of one's neighborhood galaxy, however, the vacuum flows past significantly coherent (by definition, unaffected by the Hubble expansion) masses.
It seems to me that there should be a measurable difference between far field static vacuum-matter interactions and near field kinetic vacuum-matter interactions. This quasi-frictional effect would most likely manifest as a vacuum polarization, and may explain the quantum nature of dark energy.
What ideas do you all have on the possibility of this phenomenon?