Are large voids empty of dark matter and how to understand quiet Hubble flow

Are large voids empty of dark matter and how to understand quiet Hubble flow

Sabine Hossenfelder (see this) had a very interesting video about recent findings challenging the notion of the spherical dark matter halo and provides support for the TGD view. Hossenfelder crystallizes the findings to a statement "We live in between two huge dark matter voids".

The article discussed by Sabine Hossenfelder is published in Nature Astronomy by Wempe et al with title "The mass distribution inside the local group and around the local group" (see this). Here is the abstract of the article.

Modelling efforts have long struggled to reproduce the quiet Hubble flow around the Local Group, as they require unrealistically little mass beyond the haloes of the two main galaxies. Here we revisit this using ΛCDM simulations of Local Group analogues with initial conditions constrained to match the observed dynamics of the two main haloes and the surrounding flow. The observations are reconcilable within ΛCDM, but only if mass is strongly concentrated in a plane out to 10 Mpc, with the surface density rising away from the Local Group and with deep voids above and below. This configuration, dynamically inferred, mirrors known structures in the nearby galaxy distribution. The resulting Hubble flow is quiet yet strongly anisotropic, a fact obscured by the paucity of tracers at high supergalactic latitude. This flattened geometry reconciles the dynamical mass estimates of the Local Group with the surrounding velocity field, thus demonstrating full consistency within the standard cosmological model.

One of the motivations for the work of Wempe et al was the problem of quiet Hubble flow. Hubble flow corresponds to cosmic expansion. The gravitational interaction of astrophysical objects is expected to give rise to peculiar velocities as deviations from this flow. The scale for the deviations of these velocities from mean is however found to be too small, as if the local gravitational interactions had no effect.

The second challenge is to understand the generation of large voids with unrealistically low mass density.

1. In principle, dark matter as particles could have experienced gravitational condensation and have developed localized structures just like ordinary matter. The observed planar pancake structure between two large voids associated with the local Group containing the pair formed by the Milky Way and M31 at its center can be reproduced by choosing initial values suitably in the simulations of ΛCDM model. would explain also the quiet Hubble flow. The likelihood for this kind of configuration is reported to be between 1/100 or 1/1000 in ΛCDM.
2. In absence of any identified candidate for dark particles having only gravitational interactions, one is forced to challenge the notion of dark matter halo. A further motivation is that the ΛCDM model makes several problematic predictions. A cuspy galactic dark matter halo, too many small satellite galaxies and too slow growth of galaxies by gravitational condensation are predicted. These failures challenge not only the ΛCDM paradigm but also the view that gravitational condensation has formed galaxies.

Does dark matter really consist of exotic particles having only gravitational interactions?

What if dark matter is not realized as exotic particles and there is no halo of galactic dark matter?

1. The TGD based view of space-time is motivated by the energy problem of general relativity (see this and this) and differs dramatically from that of general relativity (see this). Space-time at the fundamental level corresponds to space-time surfaces in H=M⁴× CP₂ obeying holomorphy = holography principle and satisfying minimal surface equations irrespective of action except at 3-D singularities. Space-time surfaces are analogs of Bohr orbits for particles as 3-surfaces and are slightly non-deterministic although field equations are satisfied (see this).

   General Relativistic space-time follows at the quantum field theory limit when the many-sheeted space-time surface is approximated with single a slightly curved region of M⁴ and the induced gravitational and gauge fields associated with different space-time sheets are summed to give the standard model gauge fields and gravitational field in long length scales.

2. TGD predicts Russian doll cosmomology. This follows from a fractal hierarchy if causal diamonds CD=cd× CP₂, where cd is causal diamond of M⁴ identified as intersection of future and past directed light-cones. One could regard cd as an analog of perceptive field of a conscious entity or as quantization volume. cd is also analogous to an empty cosmology: big bang followed by big crunch. CDs contain space-time surfaces inside them. 4-D cosmologies are in TGD analogous to Bohr orbits of particles identified as 3-surfaces.
3. The weak failure of classical determinism forces what I call zero energy ontology (ZEO) (see this) and together with the number theoretic vision (see this, this and this) this leads to the prediction that quantum coherence is possible in all scales. Space-time surfaces can be regarded as quantum coherence regions. The notion of field body, in particular the predicted monopole flux tubes, means a rather radical modification of the Maxwellian view of classical fields and has far reaching implications in all scales.

TGD view of galactic dark matter

TGD predicts that galactic dark matter is actually analogous to dark energy and concentrated at long cosmic strings with thickness given by CP₂ length scale.

1. Cosmic strings generate 1/ρ gravitational potential predicting the flat velocity spectrum (see this). Both volume term and Kähler magnetic energy contribute to the string tension.
2. The cosmic string model bears a relation to the MOND model. At a certain radius the stringy 1/ρ contribution overcomes the ordinary 1/r² contribution from the galactic nucleus and this critical radius has critical acceleration as a counterpart in the MOND model. Already Zeldowich observed a long time ago (1982) that galaxies are located along linear structures at the boundaries of giant voids.
3. The model predicts a mechanism for the generation of ordinary matter via the decay of cosmic strings induced by some perturbation, say by their collision, inducing their thickening and reduction of string tension and the transformation of the energy to ordinary matter. This process would replace inflation in the TGD framework.

   No exponential expansion of the Universe is required since TGD predicts quantum coherence in arbitrarily long scales explaining the almost constant of the CMB temperature.

4. The cosmic strings were the first extremals found already during the first year of TGD after the emergence of the basic idea in 1977 and leading to my thesis 1982. In the discussion inspired by the the article of Sabine Hossenfelder (see this), I learned that I am not anymore the only physicist suggesting that string like objects could explain galactic dark matter. Also K. Zatrimaylov has proposed something similar (see this, this, this, this, this).

Going to the concretia, one can ask whether MW and M31 are associated with the same cosmic string connecting them in the plane between the voids, or whether there are also vertical cosmic strings orthogonal to the plane and going through MW and M31. The cosmic strings carry monopole flux and must be closed: could MW and M31 be associated with the same closed cosmic string? There is indeed evidence that MW is formed in a collision of two cosmic strings, which are bound to occur for cosmic strings glued to background 3-surfaces.

TGD view of voids explains the quiet Hubble flow

An entire hierarchy of voids have been observed. Besides the Local Void (or rather pair of voids having the pancake-like structure between them) there are other Large Voids such as KBC void, Böotes Void, and Giant Void appearing in various scales.

In standard view gravitational condensation would have led to the generation of voids. This could be the case also in TGD. Could TGD say something more detailed about them?

1. Poincare invariance and Lorentz invariance are exact symmetries of TGD. The preservation of these symmetries lost in GRT was the basic motivation of TGD. cd allows slicings by Lorentz invariant light-cone proper time constant hyperboloids of cd. The hyperbolic 3-space H³ as cosmic time constant 3-surface is therefore a fundamental object in TGD.

   H³ allows an infinite number of tessellations (see this and this) as analogs of lattices of E³ characterized by a symmetry group which is an infinite discrete subgroup of the Lorentz group SO(1,3). Simplest tessellations are honeycombs consisting of Platonic solids.

2. There are indications that astrophysical objects could be assigned with the vertices of these kinds of tessellations. The quantization of cosmic redshifts is one piece of evidence for this. The recent finding of unexpectedly strong gravitational radiation background (see this)could be understood in terms of diffraction of gravitational radiation in a tessellation having stars at its vertices.

   Could also galaxies tend to form this kind of tessellations? These tessellations have vertices, edges and sheets as basic building blocks. Could the 3-D cells correspond to voids? Could vertices correspond to galaxies and edges to cosmic strings? Could faces correspond to the regions between voids. Could the unavoidable collisions of the cosmic strings generate networks giving rise to these tessellations.

3. Could these tessellations dynamical equilibria emerge as correspond to gravitational bound states, in which the gravitational interactions with neighboring vertices are compensated. Could this be true also for the edges and matter at sheets. If so, the tessellations are quasi static in the sense that they only participate in cosmic expansion associated with the either half-cone of the cd. This would mean that virial motion.

   Planar sheets in E³ are minimal surfaces: could configurations M¹× E² × S¹ ⊂ M⁴× CP₂ are not allowed by holography= holomorphy principle in its basic form: could one combine M⁴ time coordinate and the geodesic coordinate of S¹ to a complex coordinate of H?

4. The icosa tetrahedral tessellation involved assigned to the TGD based model of genetic code (see this and this) is of special interest? Tetrahedra, octahedra, and icosahedra have triangular faces appearing as faces of this completely unique tessellation. Octahedra define however void regions, kind of holes in the tessellation formed by icosahedra and tetrahedra. Could this tessellation occur also in cosmic scales? Could octahedra correspond to regions of cd as geometric vacua in which there is no space-time as 4-surface. Could galaxies or larger units tend to be associated with the vertices and the faces of the tessellation.
5. This picture could solve the problem of quiet Hubble flow. The gravitational interactions of astrophysical objects should induce peculiar velocities so that the velocity field of astrophysical objects is expected to deviate from the smooth Hubble flow caused by the cosmic expansion. The peculiar velocities are however much smaller than expected. Apparently, the gravitational interactions have no effect on the Hubble flow. This finding actually motivated also the study of Wempe et al (see this) leading to a support for the view that there are two voids containing no dark matter. If the galaxies and larger structures form quasi static tessellations having cosmic strings as edges, this would be the case.

   See the article About the recent TGD based view concerning cosmology and astrophysics or the chapter with the same title.

   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.