Talk:Cold dark matter

Untitled

Rather than move this article to Dark_matter, I believe it and Hot_dark_matter should be there...unless I'm missing something. BF

cold/slow

Does "cold" just mean "slow compared to the speed of light"? 124.168.192.129 (talk) 05:55, 23 November 2008 (UTC)

Yes, and also not blackbody hot above the background, e.g. less than about 25 Kelvin. And it also covers black holes, which don't really have a classical temperature or any meaningful outside temperature in the thermodynamic sense, but are considered blackbody cold by their radiation.[1] Dualus (talk) 02:54, 22 May 2011 (UTC)

MACHOs

Machos are not in this group, but in barionic dark matter.-Mazarin07 (talk) 13:11, 5 March 2010 (UTC)

Why not? I think they can be, if they are slow and cold. So I guess that does rule out some of them, like white dwarfs. Dualus (talk) 07:12, 22 May 2011 (UTC)

Thanks, and merci beaucoup

Thanks to you all, contributors to this article. It has now been translated into FR. Hop ! Kikuyu3 (talk) 20:23, 7 July 2011 (UTC)

intermediate mass black holes

I deleted that paragraph for two reasons:

(1) it was very unclear. It never said that the BHs are a dark matter candidate. As such, its meaning was quite obscure to a non-expert. Since the source it referenced does claim that, any such paragraph should mention the numerous major problems with the proposal.

(2) Due weight. This is a fringe idea that's accepted by very, very few cosmologists. It can't be discussed until the more mainstream ideas are. Waleswatcher (talk) 03:38, 6 February 2012 (UTC)

Certainly (1) can be corrected. What do you see as the major problems with the proposal? What are your sources for (2)? 67.6.170.33 (talk) 04:08, 6 February 2012 (UTC)

It's not my responsibility to demonstrate due weight - it's the responsibility of anyone that wants that material in the article. Considering that none of the other possibilities for CDM get more than a line or so, to give a paragraph to this you'd need to show that it's by far the most commonly accepted theory for CDM. To even mention it you'd need to argue that it's as widely accepted as (say) WIMPS.

From Jimbo Wales, paraphrased from this post from September 2003 on the mailing list:

If a viewpoint is in the majority, then it should be easy to substantiate it with reference to commonly accepted reference texts;

If a viewpoint is held by a significant minority, then it should be easy to name prominent adherents;

If a viewpoint is held by an extremely small (or vastly limited) minority, it does not belong in Wikipedia (except perhaps in some ancillary article) :::: regardless of whether it is true or not; and regardless of whether you can prove it or not.

Find a reference text, or a list of prominent adherents, and you'll have an argument for inclusion. Waleswatcher (talk) 06:09, 6 February 2012 (UTC)

I am not asking you to demonstrate anything other than the reasons you say the proposal has "major problems" and the reasons you say the idea is accepted by "very, very few cosmologists." Also, please correct me if I am wrong, but I believe there is no observational evidence for WIMPs, while there were nearly a dozen IMBHs either detected or confirmed in the past year alone. Is that not true? 67.6.170.33 (talk) 07:52, 6 February 2012 (UTC)

There are all sorts of problems with the idea that IMBHs are dark matter, but this talk page is not the place to discuss them, and our opinions of them are irrelevant. Every idea in the article must be given an amount of space in the article that's roughly commensurate to its acceptance in the scientific community. So if you want to put it back, you'll need to demonstrate that it is widely accepted (see my previous post). Thanks. Waleswatcher (talk) 14:26, 6 February 2012 (UTC)

I've added two references to the dark matter wiki that comment on this. Here's what I wrote on the talk page there: "I've now checked two sources - a 2010 paper on black holes as dark matter, that says that they are ruled out over a huge range of masses, and one 2012 dark matter review, that says that particles are the only really plausible DM candidate (and also that black holes would require "funky physics" even to exist in the correct abundance). I've added both references." Waleswatcher (talk) 15:06, 6 February 2012 (UTC)

(Let's continue and try to resolve this discussion in one place at Talk:Dark matter#intermediate mass black holes.) 67.6.175.184 (talk) 03:57, 7 February 2012 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Cold dark matter/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

The "Missing Galaxies Problem" may have been solved, basically astrophysicists have been able to observe new dwarf galaxies that are 99% dark matter using the Keck II telescope to follow up on objects found during the Sloan Digital Sky Survey. Ref: 'Missing Dwarf Galaxy' Problem May Be Solved

Last edited at 18:17, 15 September 2007 (UTC). Substituted at 12:00, 29 April 2016 (UTC)

Collisionless cold dark matter

There is a link from the DAB page CCDM to this article, claiming the acronym is used for collisionless cold dark matter. Having seen this in a number of published papers, I believe it correct, but there is no mention of the acronym in the article which could confuse visitors. Can it be shoe-horned in somewhere? Lithopsian (talk) 15:19, 12 March 2018 (UTC)

Please update with: "An excess of small-scale gravitational lenses observed in galaxy clusters"

Please add short info on this paper to the article – probably to section #Challenges. It's currently featured in 2020 in science like so (you could also edit the item there):

Scientists report that results of cold dark matter simulations – probability of strong gravitational lensing events due to dark-matter distributions in 11 galaxy clusters – based on current theories are substantially inconsistent with observational data.

--Prototyperspective (talk) 21:54, 22 October 2020 (UTC)

References

the particle cold dark matter paradigm in the Challenges §

This is the only occurrence of 'particle' in the article as an adjective connoting a type of 'cold dark matter paradigm'. Suggest it be deleted. Humanengr (talk) 14:55, 14 August 2021 (UTC)