The BBC On "Cracks In Cosmology"

A January 13, 2021 article in issue 358 of BBC Science Focus Magazine entitled "The Cracks in Cosmology: Why Our Universe Doesn't Add Up?" by Marcus Chown nicely sums of the LambdaCDM Standard Model of Cosmology and some key lines of observational evidence indicating that it is flaws.

The model, in his simplified terms in which he explains it, consists of the Big Bang, plus inflation, plus dark matter, plus dark energy. Inflation smooths out the universe, dark energy speeds its expansion, dark matter shapes the cosmic background radiation patterns, aids in galaxy formation, and leads to phenomena like galactic rotation curves that aren't Keplerian and galactic clusters that are much heavier than their visible matter.

He identifies three notable recent flaws in this model in observations newly made in 2020.

First, he points to the gravitational lensing of subhalos in galactic clusters recently observed to be much more compact and less "puffy" than LambdaCDM would predict.

Secondly, he points to a KIDS telescope observation of very large scale structure which shows it to be 8.3% smoother (i.e. less clumpy) than predicted by LambdaCDM.

Third, he points to the Hubble tension (see, e.g., here) that shows that Hubble's constant, which is a measure of the expansion rate of the universe, is about 10% smaller when measured via cosmic microwave background radiation (with a small margin of error) than when measured by a wide variety of measures at times much more removed from the Big Bang that the time at which the cosmic microwave background came into being.

He then provides a laundry list of ways that the model or the data collection could be flawed.

Other Problems With LambdaCDM

Honestly, these aren't even necessarily the most serious of the problems, and many of the big problems have been known for a long time. Among problems with the Cold Dark Matter model, especially at the galaxy and galactic cluster scale. 

* The halo shapes are usually wrong (too cuspy and not in the NFW distribution predicted by the theory). 

* The correspondence between the distribution of ordinary matter and inferred dark matter in galaxies is too tight; truly collisionless dark matter should have less of a tight fit in its distribution to ordinary matter distributions than is observed. This is also the case in galaxy clusters. 

* It doesn't explain systemic variation in the amount of apparent dark matter in elliptical galaxies, or why spiral galaxies have smaller proportions of ordinary matter than elliptical galaxies in same sized inferred dark matter halos, or why thick spiral galaxies have more inferred dark matter than thin ones.

* It doesn't explain why satellite galaxies are consistently located in a two dimensional plane relative to the core galaxy. 

* Not as many satellite galaxies are observed as predicted, or why the number of satellite galaxies is related to budge mass in spiral galaxies.

* The aggregate statistical distribution of galaxy types and shapes, called the "halo mass function" is wrong.

* Galaxies are observed sooner after the Big Bang than expected (see also here).

* The temperature of the universe measured by 21cm background radio signals is consistent with no dark matter and inconsistent with sufficient dark matter for LambdaCDM to work. 

* It doesn't explain strong statistical evidence of an external field effect that violates the strong equivalence principle. 

* Observations are inconsistent with the "Cosmological principle" that LambdaCDM predicts, which is "the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale.

* It doesn't do a good job of explaining the rare dwarf galaxies (that are usually dark matter dominated) that seem to have no dark matter. 

* It doesn't explain deficits of X-ray emissions in low surface brightness galaxies.

* It predicts too few galaxy clusters.

* It gets globular cluster formation wrong (see also here).

* It doesn't explain evidence of stronger than expected gravitational effects in wide binary stars.

* There are too many galaxy clusters colliding at speeds that are too high relative to each other. 

* It doesn't explain the "cosmic coincidence" problem (that the amount of ordinary matter, dark matter and dark energy are of the same order of magnitude at this moment in the history of the Universe since the Big Bang).

* There are potential unresolved system problems in current dark energy measurements.

* Every measure of detecting it directly has come up empty (including not just dedicated direct detection experiments but particle collider searches, searches for cosmic ray signals of dark matter annihilation, and indirect searches combined with direct searches and also here). But it requires particles and forces of types not present in the Standard Model or general relativity to fit what is observed.

* It has made very few ex ante predictions and those it has made have often been wrong, while MOND has a much better track record despite being far simpler (which should matter).

* There are alternative modified gravity theories to toy model MOND that explain pretty much everything that dark matter particle theories do (including, e.g., the cosmic coincidence problem, clusters, the Bullet Cluster, galaxy formation, the cosmic background radiation pattern observed), with fewer problems and anomalies.