1. TGD view of large voids
I have considered the problem of cosmic voids in the TGD framework for decades. I assumed that voids involve cosmic strings going through their center. At that time I did not realize that TGD allows us to consider a considerably simpler solution, which is not possible in general relativity.
In the TGD Universe, space-time consists of 4-D surfaces in H= M4×CP2. Einsteinian space corresponds to space-time surface with 4-D M4 projections, I call them space-time sheets and they can be connected by extremely tiny wormhole contacts, which are in the simplest situation isometric with a region of CP2 having 1-D light-like geodesic as M4 projection. Wormhole contacts serve as basic building bricks of elementary particles. Space-time surfaces or at least their M4 projections have outer boundaries. The boundaries of physical objects correspond to boundaries of 3-surfaces or of their M4 projections so that we can see the TGD space-time directly with our bare eyes!
Also other kinds of space-time surfaces, such as cosmic strings with 2-D M4 and CP2 projections, are predicted and play a fundamental role in the TGD inspired view of the formation of astrophysical objects.
Concerning the problem of large voids, the key point is that it is possible to have voids in M4 as regions of M4 (or E3) which contain very few or no 3-surfaces. Gravitational attraction could have drawn the 3-surfaces inside the voids to the boundaries of the voids. Could it be that we have been seeing TGD space-time directly for decades?
Also tessellations at the cosmic time= constant hyperboloids would be in a key role and one can imagine that they give rise to tessellations of voids with matter near the walls of the voids. There are 4 regular tessellations involving either cubes, icosahedron of dodecahedron (in E3 only a cubic regular tessellation is possible) plus the icosa-tetrahedral tessellation consisting of tetrahedrons, octahedrons, and icosahedrons. This tessellation is completely unique and plays a key role in the TGD inspired model of the genetic code, which raises the question whether genetic code could be universal and realized in all scales at the level of the magnetic body (see this).
2. Could CMB could spot be a super void?
There was also another interesting link to a popular article (see this) with the title "Our Universe is normal! Its biggest anomaly, the CMB cold spot, is now explained!" CMB cold spot is a huge region inside which the temperature of CMB background is about 70 μKelvin below the average temperature. What adds to the mystery is that it is surrounded by a hotter region. The idea is that the CMB cold spot corresponds to an expanding supervoid. I am however not at all sure whether our Universe is normal in the sense of general relativity.
Consider first the Sachs-Wolfe effect. Assume that a photon arrives at a gravitational well due to a mass distribution. The presence of matter induces first a blueshift as the photon falls in the gravitational potential of the region and then a redshift as it climbs out of it. The expansion however flattens the potential that there is a net reduction of the overall redshift due the average density of matter.
Since the local temperature depends on the local matter density, the low density region corresponds to a cold spot. If the cold spot corresponds to a region, which has a small density and expands during the period that photon uses to go through the cold spot, the redshift inside the region vanishes and is smaller than the redshift caused by the average region. The region appears to have lower density and lower temperature. There are a lot of these kinds of hot and cold spots and they induce fluctuations of the CMB temperature. But there is also a really big cold spot surrounded by hotter regions. This cold spot has been problematic.
The idea is that the CMB cold spot could correspond to an expanding supervoid. It is not however obvious to me how this explains the higher temperature at the boundaries of the supervoid. In the TGD framework, one can however ask whether the supervoid could correspond to a magnetic bubble caused by a local big bang, which has feeded energy to the boundaries of the resulting void forming a magnetic bubble so that the temperature at the boundaries would be higher than inside the void. One can even consider the possibility that the supervoid is in a reasonable approximation a void in M4 sense so that very few 4-D space-time surfaces would exist in that region.
3. Could M4 voids allow to test the TGD view of space-time?
The existence of M4 voids might allow to test TGD view of space-time. The physics predicted by TGD is extremely simple in the case of a single-sheeted space-time sheet. The observed space-time is however many-sheeted. One can think using analogy with extremely thin glass plates with M4 corresponding to the 2-D plane and CP2 corresponding to its thickness. Einsteinian space-time sheets correspond to 2-D surfaces inside the plate, which are slightly curved and are connected by wormhole contacts. At the QFT limit one must replace the many-sheeted structure with a region of M4 and define gauge and gravitational fields as sums of the induced fields associated with various sheets (and determined by the surface geometry alone). The extreme simplicity is lost.
However, if M4 vacua exists one could test TGD at the single-sheeted limit to see the predicted fundamental physics in its extreme simplicity. Things would indeed be simple. Not only are the induced fields determined by the minimal surface property of the space-time region but also holography holds and is realized in terms of a generalization of the 2-D holomorphy to 4-D case.
For a summary of earlier postings see Latest progress in TGD.
For the lists of articles (most of them published in journals founded by Huping Hu) and books about TGD see this.