If their is a sight, second curvature in the vacuum

 The vacuum has to have a band limit, a limit on M the dimensionality it supports.  Assume that is 4. We think it is 3.

Then when we look straight out, we compute we are finding a central point of infinity, when there is an unknown slight curvature in that path. The more centrally backward looking, the more obscure the separation on the fourth axis. We see a closed system of a reverberating sphere, when there is relative motion unobserved.

Now change the assumption. Assume a cluster of blackholes are along an unobserved curve, assume 4. Then look for entropy maximizing rearrangements of the blackholes that might stabilize about a toroidal curve.  Invent a possible term for dark matter, then use that to predict a collapse from 4 to 3. It is like collapsing the salad bowl onto the flat Lie paper.  There is information loss, but strong hints remain.

My thinking tells me we do indeed bump up against the band limit of the vacuum, its expectation value. That is the only way the universe can track a closed system. That aliasing term becomes dominant in certain configurations, but aliasing provides a kinetic axis.   Quasars would be places where 4D spin collides.  The effect is to lock into the vacuum a slight drift along some curvature in 3D.