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Observations that are not explained by the ΛCDM model

  * The Hubble tension: 9% disagreement at 4.4σ significance

- There is a tension between the Hubble constant determined by Planck and by the cosmological distance ladder (

  * Axis of Evil

- Multipoles of the CMB are aligned with the solar system.

- Anomalies in the CMB (alignment quadrupole/octopole, insufficient lens effect in clusters, etc.)

  * CMBR: The σ8 tension

- A problem of the ΛCDM model is the tension between the relatively high level of clustering, as quantified by the parameter σ8, found in cosmic microwave background experiments and the smaller one obtained from large-scale observations in the late Universe. (

- Reionization epoch different from CMBR and QSO observations.

  * Dark matter is not observed in the laboratory

- The exotic, weakly interacting particles envisaged as candidates for the dark matter component are still undetected in the laboratory

- Discovery of baryonic matter with more sensitive instruments decreases the needed amount of dark matter.  The estimated amount of dark matter in the Coma cluster is now a factor of 4 to 5 larger than baryonic matter.  Due to the discovery of hot gas in rich galaxy clusters it is ∼100 less than when Zwicky first discovered it.

  * Missing Baryon problem

- The observed amount of baryonic matter does not match theoretical predictions, yielding about 50% of the expected baryonic density.  There is not enough matter to produce large galaxies in a time period not exceeding the age of the universe.
"Hot baryons within the virial radius of massive galaxy halos are insufficient to explain the ''missing baryons.'' " ApJL 2018.

   The ‘missing baryons problem’, McGaugh 2008, "The Halo by Halo Missing Baryon Problem. In: Dark Galaxies and Lost Baryons," Proceedings of the International Astronomical Union, Vol. 244, p. 136

  * Matter-antimatter asymmetry

  There is as of yet no consensus theory to explain the baryon asymmetry problem.   There is no observation of antimatter or evidence for CP violation.

  * Redshift anomalies

- The K-Trumpler effect: an excess of redshift observed on the more luminous stars of a cluster.  "Redshifts of high-luminosity stars - the K effect, the Trumpler effect and mass-loss corrections," Mon. Not. R. astr. Soc. 258, 800-810, 1992.

- Spatial correlations between objects at low redshift and objects at high redshift, galaxy-quasar associations:
"Physical association and periodicity in quasar families with SDSS and 2MRS," Astrophysics and Space Science, July 2018, 363:134

- Periodicity of redshifts

- Intrinsic and anomalous redshifts

- Quasars don't show time dilation with redshift
  "Time Dilation and Quasar Variability," The Astrophysical Journal Letters 553, No. 2, L97 (2010), arXiv:astro-ph/0105073.

  This work is often dismissed by citing a paper published two years later which claims to show time dilation in quasar light curves ["Using quasars as standard clocks for measuring cosmological redshift," Phys. Rev. Lett 108, 231302 (2012), arXiv:1204.5191 ].   However, the paper is not convincing for the reasons explained here.

  The luminous flux of quasars is analyzed manually: "We pick several straight line light curve segments [...] for more reliable identification (or rejection) of the observed patterns.  [...]  We identify five segments from its light curve that appear straight [...]  We take each of those segments, discarding the rest of the light curve [...]"  No criterion is given on how to pick the segments.  No rejection criterion is given concerning the patterns.  No objective definition of "appear straight" is given.  There is also no mention of the fraction of the data that was discarded.  Since the light curves patterns are never straight, this procedure is completely subjective and prone to cherry picking.

  Before they are overlapped and compared, light curves are normalized with three parameters: time offset, flux normalization and the time dilation factor.  However, no justification is given for a possible flux normalization by a negative factor.  The authors show that they can obtain a good match from only one pair of light curves (where they use this negative factor), but they fail to show that the choice of other possible parameters would never produce good matches.

  This subjective approach does not offer the robustness of a formal analysis.  Although this work is cited in arguments against the absence of time dilation, it does not convincingly show time dilation in quasar light curves.

- ΛCDM fails the Tolman test: the surface brightness signal does not follow (1 + z)-4: Lubin and Sandage, "The Tolman Surface Brightness Test for the Reality of the Expansion. IV. A Measurement of the Tolman Signal and the Luminosity Evolution of Early-Type Galaxies," The Astronomical Journal 122, no. 3, p. 1084, Sep. 2001, arXiv:astro-ph/0106566

  * Nucleosynthesis

- The ‘Lithium problem’ (B.D. Fields, "The primordial lithium problem" Annual Review of Nuclear and Particle Science, 61 (2011), p. 47)

- Galaxies with 4He< 24%

- Ill-understood deuterium abundances, failure in the predictions of Li, Be, 3He

- Higher metallicity and dust content at high redshift than expected

  * Failure to detect the Transverse Proximity Effect with a foreground quasar

- Contrived explanations are necessary to explain the absence of a transverse proximity effect in hundreds of observations of projected quasar pairs: arXiv:0809.2277 and arXiv:1809.04614 .  Observations are explained if QSOs have had their current UV luminosities for less than approximately a million years (coincidentally, we always observe just after an increase of the UV luminosity), or an anisotropic emission from a QSO located within an obscuring torus of gas and dust (always conveniently producing a very narrow emission angle).

- More:

- The missing satellites problem (B. Moore, et al., "Dark matter substructure within galactic halos" The Astrophysical Journal Letters, 524 (1999), pp. L19-L22)

- Satellite planes (unanticipated correlations in phase space)

- Excessive cluster densities

- The emptiness of voids

- The extreme evolution of galaxy sizes is poorly understood.

- The early formation of structure  (see section 4 of Famaey & McGaugh )

- Inhomogeneities at scales > 200 Mpc

- Intergalactic medium temperature independent of redshift

- The ‘too big to fail problem’ (M. Boylan-Kolchin, J.S. Bullock, M. Kaplinghat, "Too big to fail? The puzzling darkness of massive milky way subhaloes" Monthly Notices of the Royal Astronomical Society, 415 (2011), p. L40)

From Astronomy & Geophysics, Volume 51, Issue 5, October 2010, Pages 5.14–5.16

- The inclusion of a cosmological constant means that the ratio of the vacuum energy density to the radiation energy density after inflation is 1 part in 10100, a fine-tuning coincidence which leads to appeals to the anthropic principle for an explanation

- Even if fine-tuning arguments are regarded as unsatisfactory, the problem is that inflation was set up to get rid of fine-tuning in terms of the “flatness” problem and so the introduction of more fine-tuning with the cosmological constant appears circular

- Astrophysically, any cold-dark-matter (CDM) model in the first instance predicts a featureless mass function for galaxies, whereas the galaxy luminosity function shows a sharp “knee”

- CDM models predict that large structures should form last and therefore should be young whereas, observationally, the largest galaxies and clusters appear old

- To fix the above two problems, large amounts of feedback are invoked which results in more energy being used to prevent stars forming early than in forming them under gravity at later times.

- Milky Way Galaxy not well understood:
  The Fermi Galactic Center GeV Excess (arxiv:1704.03910) and the Fermi Bubbles (arXiv:1802.03890)

From:, "Non-standard models and the sociology of cosmology", M. López-Corredoira

- Much higher abundance of very massive galaxies at high redshift than expected

- Wrong predictions at galactic scales (no cusped halos, excessive angular momentum, insufficient number of satellites, etc.)
  The cuspy core problem (W.J.G. de Blok, "The core-cusp problem" Advances in Astronomy, 2010 (2010), p. 789293)

- Flows of large-scale structure matter with excessive velocity

- Dark energy in excess of theoretical models by a factor 10120.

- Problems in understanding inflation

Updated 2019-5-17

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