2/2 Some years ago there was no reason to think that the dust was diluting away with any driver other than some single impulse in the distant past. An initia

2/2 Some years ago there was no reason to think that the dust was diluting away with any driver other than some single impulse in the distant past. An initial acceleration, followed by an eternity of inertial motion. More recently evidence has tended to disfavour purely inertial motion, driving the study of possible mechanisms for (and expressions of) ongoing acceleration. A strong enough violation of the cosmological principle -- that there is something unexpected and atypical about the local neighbourhood our galaxy cluster is in -- might drive us back to a purely inertial expansion, if that atypicality is causing us to mistake a local gravitational acceleration for a cosmological one. This is the topic of the Hossenfelder blog entry. However, one possible result is that there is something unexpected about the gravitation in the local neighbourhood, but that it applies in other local neighbourhoods too, including those containing extremely bright sources like quasars, returning us to the problem of accelerated expansion. Real proposals that are under investigation include the dynamical outflow of gas and stars from galaxy clusters, driven by the internals of these clusters and the gravitational influence of neighbouring overdensities (our "local hole" is adjacent to several including the Shapley Supercluster, about 231 Mpc distant). Such processes over cosmological timescales may serve to drive galaxy clusters towards typicality. There are also many open questions about the intermediate regime between the cosmological scale and the galactic scale each of which can be studied with a much more easy to work with approximation of the full theory of General Relativity. z ~ 0.04-0.55 - ~ 100-250 Mpc is right in that intermediate regime. The growth of our theoretical toolbox may resolve some blurry problem at the length scales that are at the root of the arguments in several of the papers Hossenfelder's blog post refers to. The result might be that the allegedly unexpected local phenomenon ("the local hole") should have been expected after all. See https://astrobites.org/2021/09/01/gravity-on-all-scales/ https://astrobites.org/2021/09/01/gravity-on-all-scales/ for some details.