Talk:Lambda-CDM model

That's not part of the model. It's an observation that the universe is close to flat, but the model will handle non-flat universes fine. — Preceding unsigned comment added by Roadrunner (talk • contribs) 05:16, 26 May 2012 (UTC)

• The model assumes a "flat" spatial geometry, which means that the interior angles of a triangle defined by three beams of light will sum to 180°; space is defined by straight lines. (Alternative geometries include a spherical or "closed universe" in which the interior angles of a triangle would sum to more than 180°, and a hyperbolic or "open universe", in which the angles would sum to less than 180°.) The current values of key parameters imply that the universe is either flat or slightly open, the universe will expand forever, and the expansion is accelerating.

The Challenges section is totally out of control. Is far too long given the length of the article, and gives total weight to fringe claims.

Some of the sections are just utterly inappropriate. In particular the section on Violations of the Strong Equivalence Principle, this section has no place in this article. The analysis which claims to detect evidence of the SEP violation did so assuming MOND. What they were really testing for is evidence of MOND’s external field effect, which violates SEP. Because the analysis assumes MOND, it tells you absolutely nothing if LCDM is the correct cosmology. The paper makes some offhand claim that they don’t believe LCDM could explain the data, but they do not test this. The paper does not use or compare to any LCDM simulations. So this paper has nothing to do with LCDM. It does not belong on this page. I vote to delete this section.

Furthermore there are some sections which are entirely based on one or two researchers. For example the claimed "High-velocity galaxy problem” is based on only two papers, with the same first author. The "Fast galaxy bar problem" has one citation with many of the same authors as the previous. Similarly with "Galaxy morphology problem”, "El Gordo”, and the "KBC void”. Someone seems to have gone through these MOND researchers papers and put a section for each claim. To be worthy of Wikipedia there has to be a lot more substance to the problem than this. The article as it is today gives more weight to these totally fringe claims than real problems like the missing satellites problem. Some of these claims consist of one paper, the missing satellites problem has hundreds written about it.

It’s also quite strange that in the middle of this section there is a point about Milgrom, McGaugh, and Kroupa criticizing LCDM, but has no citations at all.

The section also makes no distinction between real cosmological tension with LCDM, and claims which depend on assumptions about how galaxies form (usually through simulations). The missing satellites problem is an example of that.

The is also a lack of followup. The S8 section is a mess at the end listing values without any explanation. It also fails to mention that the most recent results have shown the tension has disappeared (e.g. KIDS). The high redshift galaxies section is also very outdated. It specifically mentions a galaxy candidate (CEERS-93316), which was debunked years ago and can be removed. It also doesn’t mention that the galaxies which were in tension with LCDM have been shown to be active galactic nuclei (Little Red Dots). This was not included the modeling or masses. None of the universe breaking galaxies have been confirmed. Also the other galaxy mentioned (JADES-GS-z13-0) is one of the ones which was consistent with simulations run before. Many of the other topics lack balance.

I propose removing the following sections. And updating some of the others. If people disagree then they can provide more substantial sources which demonstrate it is not fringe:

El Gordo galaxy cluster collision

KBC void

Violations of the strong equivalence principle

High-velocity galaxy problem

Fast galaxy bar problem

Small scale crisis [This a duplicate. If you open the one paper cited you will see it is referring to the missing satellites problem, and others already mentioned.]

I think the article would be greatly improved if this section was a lot more concise. The LCDM successes is short and to the point. The Challenges section is just way too long. LazyAstronomer (talk) 19:10, 23 July 2025 (UTC)

See also the topic "Is the Lambda-CDM Model a failure?" above. I worked on this problem, primarily by focusing on the successes part which was missing entirely.

I agree that only significant challenges need to be addressed. Any content based on a single primary source can be removed. (I don't like to characterize these as "fringe" because many of these papers are legit physics for a narrow point). Your list looks like a good start.

There are mainstream review articles which discuss many issues with LCDM and these are the sources we should summarize. Any items not in such a review can be removed. (I encourage you to work one at time with edit summaries for each). The result may still be "unbalanced" in terms of length but that can be improved with more discuss of successes. Johnjbarton (talk) 19:29, 23 July 2025 (UTC)

I've not looked into the sources, but I was surprised that "High redshift galaxies" under "Cold dark matter discrepancies". I think the content should explain this organization. Johnjbarton (talk) 23:40, 24 July 2025 (UTC)