Talk:Dark matter/Archive 7

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Archive 7

Archive 8

Does not interact with light, but still detectable through gravitational lensing? Apparent contradiction needs clarification

In the article it is stated:

"Although dark matter cannot be directly observed with conventional electromagnetic telescopes, its existence and properties are inferred from its various gravitational effects such as the motions of visible matter, via gravitational lensing..."

And in the Gravitational Lensing article, GL is defined as "a distribution of matter (such as a cluster of galaxies) between a distant source and an observer, that is capable of bending the light from the source."

Please clarify what "the motions of visible matter, via gravitational lensing" means, if not the bending of light. — Preceding unsigned comment added by TheRealJoeWiki (talk • contribs) 17:52, 2 June 2016 (UTC)

"Matter" article says Dark Matter = 23% of Universe, this article says 27%

The "Matter" article repeatedly says that Dark Matter composes 23% of the mass of the universe, whereas this article repeatedly says Dark Matter composes 27% of the mass of the universe. Please resolve. — Preceding unsigned comment added by TheRealJoeWiki (talk • contribs) 18:05, 2 June 2016 (UTC)

that isn't a major functional change, neither a mechanism.

Indirect detection

The section Indirect detection mentions the LIGO detection of gravitational waves in February 2016. This date is the public release of a detection which took place in September 2015, not February 2016, so I would be inclined to think September 2015 would be a better time stamp when signaling the detection event. Would this make sense? --66.185.60.38 (talk) 17:13, 20 June 2016 (UTC)

Good call! Want to clean that up? - Parejkoj (talk) 18:35, 20 June 2016 (UTC)

Done. Hope two persons agreeing was enough... --66.185.60.38 (talk) 01:07, 22 June 2016 (UTC)

we are way more than two pal... — Preceding unsigned comment added by 2A02:587:4103:CA00:F029:A0D8:F21E:BA07 (talk) 20:51, 22 June 2016 (UTC)

Bosonic spin of galactic photon regions aligned as fermionic via spatiotemporal curvature (compound supersymmetry)

Bosons like to pile on top of each other. The bosonic spin is always an integer. At galactic scales space curves. Some polarized stellar photons prefer to align in fermionic lines at the galactic level (thus neither straight nor random), generating dark matter patches, fewer non initially polarized or depolarized photons also contribute. Can photons that are bosons due to polarization groupings produce virtual femions? Photons propagate extremely fast, so in order to bend their polarity enough to produce the effect demand galactic scale regions, the effect is negligible at lab set-up scales. What bends? Initially only polarity, not the directivity of motion, but as the virtual fermionic galactic patch gains mass, even the directivity of motion is affected due to gravity. Stellar heliopauses act as "particle grains". A single star has a negligible effect, but stellar clusters shepherd the fermionically aligned photons. Why we don't observe extreme photonic polarization then? Because a. that polarization is not extreme at stellar level, only at galactic level becomes significant, most photons aren't polarized fermionically, b. the termination shock of stellar heliospheres distort and arbitrarily stir most of the phenomenon.

. why the hot gas Bullet cluster region doesnt generate enough lensing? it's photons are disturbed and don't form the huge fermionic regions, dark matter evolves gradually. Also we should evolve a more generic endo-feynmanian alternative. In some rare cases dark matter of colliding clusters not only it doesn't correspond to the gas regions that include most of the galactic mass, but also (dark matter) may continue to travel a bit more afar than the stellar region. That fermionic huge shape has inertia and the lines evolve and move with their own pace so need time to adjust to rapid changes?

Sounds promising. I guess is simply a bullshit but we might extract some parts of that theory and try to test them via observations, calculations and formulations.

that will help you. consider galaxies and clusters as machines that generate gravity, I do not mean the gravity of the unplugged device. if you turn on that galactic device generates more gravity. way more than the original mass. galaxies and clusters seem to control some potential flow of quantum jittering, and make it seem not random. but mass like. 1. what is the particle(s) "current" inside the machine? all the endo-feynmanic (inside Feynman diagrams) virtual particles? prefer to use only discovered particles in your model, if you use non existent particles you will conclude at a dead end. 2 what is the mechanism a. main components b. pathways of that current/ field/galactic sized pseudo-particle . Analyse discovered particles that have mass and try to solve their equations at the galactic scale. Dark matter isn't a perfect particle but many and noisy in shape so we don't need solutions for a huge hyperparticle but for a grouping of huge particles.

also in the same context fermionic (classic) matter at larger scales likes to act as huge bosons that like to pile on top of each other thus we have gravity

A very moronic proposition. — Preceding unsigned comment added by 2A02:587:4103:AE00:D47:B687:8172:7D1E (talk) 13:16, 2 July 2016 (UTC)

Darkmatterion's name is Dark Matter Particle

Darkmatterion's name is Dark Matter Particle. Although many scientists believe it's a mechanism and not a particle. Others believe that many dark matter particles exist the darkmatterions act as fermions and the darkmatterons are bosonic. Dark Matter seems to be a time correction among large scaled group formations that acts as gravity. We have no indication of gravitons, darkmatterions and darkmatterons but because all particles are grouping mechanisms of the quantum noise of the Silverman grid we could name them particles. — Preceding unsigned comment added by 2.84.212.208 (talk) 19:41, 18 July 2016 (UTC)

Dark matter and black holes

I am a novice but would WIMPS interact with the gravity of black holes or possibly observed around the sun? Even Jupiter with the mass and gravity it has? — Preceding unsigned comment added by Redindiny50 (talk • contribs) 18:11, 8 July 2016 (UTC)

If they exist they would. Perhaps a black hole gets heavier and heavier as it takes on more WIMPs. Perhaps a flow of WIMPs could be focused to a point, or small regions by the gravity of an object, but unless we have a good reference that talks about it it won't be written about here. Graeme Bartlett (talk) 00:08, 24 July 2016 (UTC)

Neutron Groups as a dark matter candidate

I have added some information about the neutron group as a candidate for dark matter. I am new to editing Wikipedia so I am not sure how to proceed. The addition that I put in was deleted from the page after a few seconds and I am not sure what I need to do to get it accepted. The change was in the composition section: The composition of dark matter remains uncertain. Possibilities include dense baryonic (interacts with electromagnetic force) matter and non-baryonic matter (interacts with its surroundings only through gravity). There is one further candidate which is baryonic matter in the form of neutron groups. These are neutrons bonded together and are like an atomic nucleus but without the protons. The neutrons in neutron groups do not readily decay and have no interaction with photons.

The referenced paper which describes neutron groups can be found by searching Google for Richard Lewis The Evolution of the Universe and looking at Appendix 6.

I feel that this is a valid dark matter candidate which may be helpful to researchers in this area. How do I proceed to get this post accepted?

Richard RichardLewis41 (talk) 17:06, 25 July 2016 (UTC)

Hi Richard, Please take a look at WP:OR which explains our policy on original research. --agr (talk) 22:50, 25 July 2016 (UTC)

Dark matter: Hypothetical or not?

This user's edit caught my attention. In fact, Dark matter is not hypothetical, what is hypothesized is what it is, not the fact it exists. To me that seems true, but two persons attempted to add that word back there again. What do we do? EeeveeeFrost (talk) 15:05, 23 July 2016 (UTC)

I agree with you, but I'm not an expert on the subject. Bubba73 ^{You talkin' to me?} 16:45, 23 July 2016 (UTC)

I'm could take it either way: one could certainly argue that it remains hypothetical until we actually discover or create some dark matter particles, so I'm not too concerned about that edit (though the recent IP editor's edit summary is rather hyperbolic). - Parejkoj (talk) 18:10, 23 July 2016 (UTC)

This is similar to the (recent) detection of gravitational waves, where it was deducted and indirectly inferred -but not hypothetical. So yes, I would remove "hypothetical". Cheers, BatteryIncluded (talk)

University of Oregon: "When these measurements were performed, it was found that up to 95% of the mass in clusters is not seen, i.e. dark. Since the physics of the motions of galaxies is so basic (pure Newtonian physics), there is no escaping the conclusion that a majority of the matter in the Universe has not been identified, and that the matter around us that we call `normal' is special. The question that remains is whether dark matter is baryonic (normal) or a new substance, non-baryonic." [1] Cheers, BatteryIncluded (talk)

I reverted your edit: unexplained is worse than hypothetical here. If you don't like hypothetical, maybe "...is a not-yet directly detected..." (though that's rather verbose for the lede)? To your quote above: from cosmological measurements (e.g. WMAP), we're certain that dark matter cannot be baryonic. We know more about what DM cannot be than what it is. One could convincingly make the case that gravitational waves were hypothetical until their recent direct detection. For GW the case was even stronger than for DM, considering the binary pulsar spin-down measurements which had no other explanation, whereas there are a handful of somewhat plausible alternative hypotheses (e.g. MOND) for the various measurements of large scale gravitational effects. - Parejkoj (talk) 17:42, 25 July 2016 (UTC)

"Since the physics of the motions of galaxies is so basic (pure Newtonian physics), there is no escaping the conclusion that a majority of the matter in the Universe has not been identified". Key word: unidentified.How about that? Cheers, BatteryIncluded (talk) 22:59, 25 July 2016 (UTC)

Unidentified definitely sounds good. I will edit it in. The current word is "undescribed", which is a really bad choice in my opinion, so I have an urge to replace it. Extra suggestions for words are: "invisible", "non-baryonic", or simply no word at all. But still, "unidentified" seems to be the most adequate. EeeveeeFrost (talk) 04:52, 26 July 2016 (UTC)

I can get on board with "unidentified". - Parejkoj (talk) 17:44, 26 July 2016 (UTC)

I will not indulge in an edit war, or long arguments and I will leave it be, but some editors are still confused on what aspect of dark matter is hypothetical. Dark matter is in known to exist, there is no escaping the fundamental conclusion that it is there as it can be measured; what is hypothetical is the nature of its particles. See the difference? Cheers, BatteryIncluded (talk) 14:52, 28 July 2016 (UTC)

Table?

Maybe this has been discussed before, but I feel it would be beneficial to have a table listing various dark matter candidates, and some key parameters for comparison. Key parameters could include things like FSL and categorizations according to hot, warm, cold dark matter (even potentially under different schemes). This might make the hot/warm/cold more intuitive, and bring more info directly to the fore. To me, it would also make sense to include a reference to the theory which originated each candidate. 70.247.163.128 (talk) 05:17, 20 August 2016 (UTC)

Sounds good to me. How many "top" hypotheses are there? If created, we'd need to be vigilant the table doesn't mutate into a list of speculations. Cheers, BatteryIncluded (talk) 06:17, 20 August 2016 (UTC)

Summary Contains Outdated Information

Specifically the discussion of WIMPS and their explanatory power is from an article dated over 20 years ago Bergmanucsd (talk) 22:16, 9 September 2016 (UTC)Bergmanucsd

This article could mention ultracompact minihalos

Not sure where to mention ultracompact minihalos (UCMH) - discussed since 2003 according to Cosmic Clues from Mini Clumps of Dark Matter - Rod57 (talk) 19:17, 4 October 2016 (UTC)

Is this the same as Ultracompact dwarf, as we have no article titled ultracompact minihalo? Graeme Bartlett (talk) 20:30, 4 October 2016 (UTC)

dark matter as a partial (imperfect) renormalization side-effect

not mentioned here — Preceding unsigned comment added by 2A02:587:4107:9B00:FD1D:4570:446D:E240 (talk) 08:19, 29 October 2016 (UTC)

Question

Why some people combine the dark matter problem with the missing antimatter problem? — Preceding unsigned comment added by 2A02:587:4114:C800:2871:4943:BCD5:341C (talk) 06:15, 26 December 2016 (UTC)

Questions at our wp:reference desk/science—see wp:TPG. - DVdm (talk) 09:12, 26 December 2016 (UTC)

Emergent gravity - Is it a figment?

Should this view (https://www.quantamagazine.org/20161129-verlinde-gravity-dark-matter/ be mentioned? Some-one who is knowledgeable on the topic and not biased should decide. Kdammers (talk) 05:40, 4 December 2016 (UTC)

As with any very recent publication, it's best if Wikipedia waits to see what the research consensus is: so far, there are no peer reviewed responses to it. It might merit a short note, but no more. - Parejkoj (talk) 18:40, 4 December 2016 (UTC)

Now New Scientist reports on an experimental test of EG and says it passes without resorting to free parameters. EG: Emergent Gravity and the Dark Universe Verlinde 2016, Brouwers test : First test of Verlinde's theory of Emergent Gravity using Weak Gravitational Lensing measurements Brouwer 2016, NS news item : First test of rival to Einstein’s gravity kills off dark matter. Whereas MOND explains galactic rotations, EG seems to also explain galactic clusters that MOND had problems with (and provides an explanation/mechanism for MOND). - Rod57 (talk) 09:54, 9 January 2017 (UTC)

Observational evidence section

I greatly rewrote this section because I felt that it's grown out of hand. The ideal section, in my opinion, is one which describes in general terms how all the different strands of evidence lead to dark matter. This is what I did. There are important cases such as the Bullet Cluster as well. I propose to move them to an "individual cases" section, which is not in the article (yet).

Opinions on this welcome. Stable link to the article before I removed large swathes of the article is here: [2] If anyone feels parts of the removed material should be inserted back to the article, or have better references to use, etc, please do so. Banedon (talk) 11:59, 18 February 2017 (UTC)

Alternative theories section

I think this section is badly written as it is and practically invites people to add more and more alternative theories. Since there are a bajillion alternative theories out there this is also an invitation to trouble. I suggest writing here that there are a lot of alternative theories, and source to a review on the topic, and leave it at that. If any specific theories are at all mentioned, I'd mention only MOND and TeVeS, possibly f(R) gravity as well. Banedon (talk) 02:37, 13 February 2017 (UTC)

Agreed. Feel free to have a go at it. - Parejkoj (talk) 19:13, 13 February 2017 (UTC)

Yes good idea. It would make sense to have a short section with some links to the most popular alternatives you mentioned, along the lines of "other theories are available". JonHMDavis (talk) 20:02, 13 February 2017 (UTC)

I went ahead and gave it a try. Here's the version before I rewrote the section: [3]. The new section was not easy to write; by now the topic is so big that I don't think anyone will be brave (or crazy) enough to attempt a comprehensive review. I don't think all alternatives to dark matter rely on modifying GR either, and these other alternatives aren't covered. I am also a bit concerned about citing Sean Carroll as the "prevailing opinion" of "most astrophysicists". I don't doubt that most astrophysicists will agree with Sean Carroll, but still the reference does not back up the claim very well. If anyone has better references to cite, both for this and other issues with the section, feel free suggest or just to add it into the article. Banedon (talk) 06:57, 14 February 2017 (UTC)

To be honest, given how large the rest of the article is, I think now this section requires expansion. It just needs expansion in a way that doesn't encourage constant addition of new text. I am not sure how to do it however. The section could say that given the multiple independent lines of reasoning that leads to dark matter, any alternative theory necessarily has a high standard to meet. It could cite some examples like the bullet cluster. It could say that some alternative theories (like emergent gravity) have nonetheless scored some successes. Any suggestions? Banedon (talk) 02:23, 20 February 2017 (UTC)

Embedded lists

Do we need the tag's stated purpose? I think the See also section work fine. Having a list of topics with maybe a subtitle added to a few seems okay. Do we need the See also section turned into prose? El_C 08:24, 17 March 2017 (UTC)

The see-also section is fine. I'm not sure what the tag is proposing, that we have a long sentence listing all the items in the list? If so, that doesn't seem very sensible. Isambard Kingdom (talk) 13:00, 17 March 2017 (UTC)

I took out the list tag. It's not appropriate for a See also section, which is typically in list format. If someone wants to create a new prose section incorporating some of the See also links, they can discuss it here or be bold and produce one.--agr (talk) 14:14, 17 March 2017 (UTC)

Did anyone bother to read the guidelines from the MOS that the tag indicates? Apparently not, as otherwise I wouldn't be getting some of these responses. Honestly, I'm pretty annoyed with the fact that I'm have to defend this at all, as this is a huge waste of my time. Whereas a simple tag should have sufficed to encourage a real discussion, it clearly hasn't. So I'll point out some obvious things that have happened to attempt to shine a light on the dysfunction that is happening here.

I started initially by adding an editing tag to the article. 8 Characters. No fundamental changes to the article itself. What is the point of the tag? It's to highlight areas for improvement, such as excessively long lists, that could be discussed in an article, but aren't. (But you knew that right, because you read all that background info, right?) Articles that have excessively long lists don't really help the reader. They are often just a grab bag of unrelated topics, with little helpful context.
I was reverted after 5 minutes, with the explanation "seems unnecessary". So, let me get this straight. After five minutes, all the background information had been read (or previously read) and taken onboard. Having considered fully whether or not I might have a point, it was decided:
- it's safe to ignore the guidelines for removing the tag
- a revert can unilaterally be made without discussion
- it's safe to ignore the obviously differing opinion I indicated
- the best explanation that can be provided is just an opinion — Preceding unsigned comment added by 75.139.254.117 (talk) 07:50, 18 March 2017 (UTC)
I decided to undo the revert. Surely that would make it clear that it wasn't an unintentional use of the tag.
Reverted again. This time with a comment was included about discussion. HUH? A discussion would have been nice before the first revert. That was the point of the tag, to point out an area that needed discussion. Does not compute! Surely he's not insisting that I have to be personally involved in every trifling edit, to the point where I have to defend pointing out weak parts of an article. Again--8 characters. Self-explanatory background material. Why am I being hounded over this?
I undid the revert again, pointing out that the tag explained it's own purpose.
Reverted. This time, a little bit more helpful, indicating that the tag might not be appropriate for a See Also section. I disagree, See Also sections can also be bloated and better explained with sensible article prose.
I reinstated the tag, explaining this.
Finally a discussion ensues. There's one comment that just chooses to ignore the issue, a second that puts up a strawman, insisting that surely I meant that one sentence for each one was the appropriate solution (don't feel it is, BTW). And then there's another unilateral decision that it's not appropriate. Yet again, I'm told my good faith effort is flat out wrong and unwanted, and cannot be tolerated within the article itself (for its intended purpose of pointing out an area of improvement). The change is reverted again.
So now, here I am, having to defend 8 injurious characters in this silly rant. I'm putting the tag back in, and hoping that someone will bother to try to see things from my point of view, and have an honest discussion about how to improve the article.

It probably doesn't matter to you, but it sure as heck matters to me. You see, if I can't even point out the areas where Wikipedia needs improvement with a fairly innocuous 8 character edit, without having my good faith questioned twice, and having to defend my actions by writing unnecessary responses that waste my time, then what can I actually do to help? Everyone seems to assume that I want to discuss ad nauseum. I don't.

I never wanted to write this, but I feel that many people like me have already been alienated from Wikipedia, so that maybe the interest of of improving the articles isn't well-represented any more. But I'm at a crossroads. I've steadily reduced my contributions here because it's become increasingly hostile to do anything against the status quo without being goaded into becoming a wikilawyer. Now, apparently 8 characters is enough to do it. I will likely be gone once my edit is reverted again, because what's the point? I certainly won't feel like contributing on a scale of less than 8 characters at a time, and I won't feel like there's a meaningful amount of good faith left to depend upon.

WIKIPEDIA HAS JUMPED THE SHARK. I'll just kick back and relax, waiting for all the responses which will continue to miss the point. We'll still have the old times. 75.139.254.117 (talk) 07:40, 18 March 2017 (UTC)

If you know about the Manual of Style than you ought to know about the Three revert rule, which you have violated. El_C 07:54, 18 March 2017 (UTC)

Why not spend the time it took you to write the above just making the improvements yourself? Myself, and my colleagues above disagree that it's needed (and Wikipedia works on consensus—not one person forcing their position through edit warring), but still: why not do it yourself? It's a fair question. El_C 08:21, 18 March 2017 (UTC)

It is a fair question, and as I've explained above, I didn't feel a 8 character edit warranted extensive discussion. Also, as I've mentioned above, the welcome I got did not seem to signal that my concerns were being taken seriously. There's no sense in wasting effort when it will just be reverted reflexively because it's inconvenient. 75.139.254.117 (talk) 17:21, 18 March 2017 (UTC)

I'm having a hard time imagining what the IP editor wants changed. Is it to develop a paragraph that gives, in sentence form, a long list of stuff? If so, I don't see how that would be better than, nor would it seem to be different in terms of content from, the column-formatted list of stuff that we already have. So, I support the IP jumping in and showing us what he/she has in mind. Thanks. Isambard Kingdom (talk) 13:20, 18 March 2017 (UTC)

Can you think of no other ways to convert some of that list to prose? I certainly wouldn't expect one paragraph to capture a set of unrelated ideas. A paragraph usually expresses a set of related ideas. Why couldn't these links fit somewhere within the existing text? 75.139.254.117 (talk) 17:22, 18 March 2017 (UTC)

I'm of opinion that if you want something done, go ahead and do it (WP:BOLD). That immediately makes what you are proposing clear. If you just tag it, then if people don't really understand what you want to do then the edit is more likely to be challenged. Banedon (talk) 04:29, 19 March 2017 (UTC)

Yes, I wanted something done. I wanted this page to be cleaned up. I was BOLD, and inserted a tag that said as much. I thought it was pretty clear. I mean if it's not clear, then why is there such a tag? I'll be honest, I didn't create that tag, but it does seem to speak to the concerns I had. 75.139.254.117 (talk) 21:00, 19 March 2017 (UTC)

The tag doesn't show what you want to be done. It only says you think there's a problem. As for "if it's not clear why is there such a tag" - if it is clear, why are so many people uncertain about what you want to do? You'll also note that the tag starts with "this ARTICLE ...", not "this SECTION". Banedon (talk) 00:47, 20 March 2017 (UTC)

Yes, point out what you think is problematic with the list, that's something that can be addressed. The tag is too vague for a list which everyone else thinks does what it's supposed to. El_C 07:51, 19 March 2017 (UTC)

I pointed out that the list is excessively long, did I not? 75.139.254.117 (talk) 21:00, 19 March 2017 (UTC)

It's a rather lengthy and complex article, to boot, so having a substantive list of related terms seems topical. But if you have the inclination, by all means integrate some into prose like the tag suggested. El_C 21:03, 19 March 2017 (UTC)

So is there a consensus way of doing that, or do I have to invest all my time into trial and error? — Preceding unsigned comment added by 75.139.254.117 (talk) 21:11, 19 March 2017 (UTC)

Just be bold—and try not to take differences of opinion as a personal affront. If you're familiar with the material, it's likely to be worthwhile. El_C 21:15, 19 March 2017 (UTC)

I was bold. I put in a tag. That tag is no longer in the article. I wasn't allowed to make the observation that the article needed improvement. I was told there was consensus it didn't. The tag was removed. I don't see how that solved the problem. — Preceding unsigned comment added by 75.139.254.117 (talk) 21:21, 19 March 2017 (UTC)

I'm done commenting on the tag—it's someone else's turn to discuss that with you. El_C 21:25, 19 March 2017 (UTC)

I would like to put the tag back into the article. The article still needs immprovement. I think the tag speaks to that. I don't see what the harm of having the tag in the article is. I think it encourages improving the article, rather than accepting the status quo. — Preceding unsigned comment added by 75.139.254.117 (talk) 21:33, 19 March 2017 (UTC)

I and everyone else disagree with that, so you best put your energy more constructively elsewhere. Like improving the article concretely, without the use of any tags, even—by sharing your knowledge directly. El_C 21:37, 19 March 2017 (UTC)

Right. You've successfully upped the stakes. Now in order to help, I can't just point out that a problem exists, I have to solve it. On my own. And I suppose I can't point out that world hunger is a problem either, because then I would have to solve it. All by myself. 75.139.254.117 (talk) 21:45, 19 March 2017 (UTC)

No comment with respect to IP address(es). El_C 21:53, 19 March 2017 (UTC)

The Structure of Scientific Revolutions: sometimes we go down dead ends

I object to the first sentence of this article: "Dark matter is an unidentified type of matter." No, "dark matter" is the name we have given to a set of phenomenological anomalies in physics, most prominently the discrepancy between the rotation rates of galaxies vs. the strength of the gravitational force that we predict from the estimated amount of baryonic matter. We do not know what causes this anomaly. Dr. Tyson agrees: https://www.youtube.com/watch?v=N4x6N0uAkTQ "We don't know if it's made of matter. It could be a profound misnomer, sending people off into thought directions that might not be the right path." Yes, that is what this Wikipedia article is helping to do by espousing a specific hypothesized solution to this anomaly. There is no concrete scientific basis for claiming, as this article does in its first sentence, that dark matter is, in fact, a type of matter and not something else entirely. And the source for this claim is a New York Times article. — Preceding unsigned comment added by 2607:F140:6000:8:8071:4A74:7593:7A8A (talk) 03:00, 3 March 2017 (UTC)

I think it is more correct to say that "dark matter" refers to a set of explanations for the phenomenological anomalies, not the anomalies themselves. There are other possible explanations for the anomalies - such as Modified Newtonian dynamics - that do not require additional matter. Some of these are mentioned in the "Alternative theories" section, and several alternatives are described in separate articles. Gandalf61 (talk) 11:55, 3 March 2017 (UTC)

I've added "whose existence would explain a number of otherwise puzzling astronomical observations" to the lede. The article does cover alternative theories.--agr (talk) 14:18, 3 March 2017 (UTC)

Yes, perhaps since there are alternative theories, the heading should clearly state this is a theory with some observations that support it. — Preceding unsigned comment added by 73.20.10.219 (talk) 06:42, 3 April 2017 (UTC)

Suggestion re the lede...i.e. Date of Discovery!

The lede says nothing about the date that Dark Matter was discovered, which is a basic fact that readers who aren't post-graduate physics students might like to know. (The article is generally very good, and this isn't a major complaint.) Reading further into the article, the first section indicates that the idea of Dark Matter surfaced gradually over decades, but nevertheless has this: "An influential paper presented Rubin's results in 1980.[35] Rubin found that most galaxies must contain about six times as much dark as visible mass;[36] thus, by around 1980 the apparent need for dark matter was widely recognized as a major unsolved problem in astronomy."

I am not going to edit the article myself, because every edit I have ever made on wikipedia has been immediately reverted on some flimsy pretext, but my suggestion is that the lede itself should contain a statement to the effect that (rephrasing the statement quoted above) "The apparent need for dark matter was widely recognized as a major unsolved problem in astronomy by around 1980." (Otherwise, a very informative article.)77Mike77 (talk) 01:16, 14 April 2017 (UTC)

Support removal of reference Sharpe, Dan (2017)

Banedon (talk · contribs) removed the reference Sharpe, Dan (2017). "Exploring Composite Dark Matter with SIDM and CDM". UK: International Research Journal of Pure and Applied Physics. ISBN 1520306318. ISSN 2055-009X. {{cite journal}}: Cite journal requires |journal= (help) from the article, and this removal was reverted by Plantsurfer (talk · contribs). Reading the reference, I tend to agree with Banedon - it is a very poor quality, uninformative and misleading reference. Some quotes will illustrate this:

"... all it takes is kinetic energy and pressure to achieve cold fusion with protons"

"... it’s important to recognize that negative energy is not photons (possibly a dark photon) ..."

"A proton with a negative polarity potential would have similar poles reversed, such as negative energy, negative thermodynamics and negative electrodynamics, without a full inversion that results in an antiproton."

"Therefore, negative atoms (dark proton variants) would pass through ordinary matter with little to no resistance"

All nonsense. I agree with the removal of the reference, so I have removed it again. Gandalf61 (talk) 10:33, 7 June 2017 (UTC)

POV check needed

Per Wikipedia's guidelines that one peson's opinion that an article has a non-neutral POV doean't warrant a POV tagging of the article, I am instead bringing this up in Talk, per guidelines.

I noticed that banedon made a drive-by edit that removed content added by another user without relocating it in the article, including four or five references. There is a section in the article labelled Alternative Theories. Banedon should have made an effort to incorporate those changes into the appropritate section. Wiping it out seems to support a non-neutral POV.

References the other editor included would seem to counter banedon's claims that "it is the current paradigm" and that dark matter is still as mainstream as it once was. Removing the references that refute those claims is self-serving censorship in favor of a single viewpoint.

He should have moved the content into "Alternative theories"

As long as the subject is "dark matter" versus something like "anomolous rotational momentum of outer galaxy stars", this article is focused on the dark matter discussion. However, I think effort should be made to make the POV in this article more neutral. Additionally, removing content, regardless of the age of the original content, by someone simply because they don't agree with the POV amounts to sabotage that supports a non-neutral POV and should not occur.

I am sorry for picking on one edit, but the edits the previous day were better and more neutral than whole-scale sabotage. I suspect that history of the article edits, however, support a non-neutral POV.

Edit in question: [ https://en.m.wikipedia.org/wiki/Special:MobileDiff/790938006 ]

Netdragon (talk) 22:53, 17 July 2017 (UTC) Netdragon (talk) 22:53, 17 July 2017 (UTC)

On a side note, I added these references to the appropriate section Netdragon (talk) 23:02, 17 July 2017 (UTC)

I completely disagree with Netdragon. The case for dark matter has been getting stronger, not weaker (most authoritative would be the latest Planck data, and also DM is more standard now than it was in 1980). Statements arguing otherwise are fringe and should not be in the first paragraph. I stand by my original edit.

I have no objections to keeping some of the references later reinserted by Netdragon, although I see no value in doing so - statements such as "MOND is an alternative to explain observations without invoking dark matter" has a bajillion of sources, so adding another one is not a big deal. I am skeptical about the inertial mass reference however, since there are also a bajillion alternative theories out there, and there should be some indication of notability before adding each one. Banedon (talk) 00:38, 18 July 2017 (UTC)

I agree with UserBanedon: we should mention one or two prominent dark matter alternatives (likely variations on MOND), and that's it. - Parejkoj (talk) 16:58, 18 July 2017 (UTC)

Dark matter no more?

Should this news article be reflected in this page? I am not a subject expert, no idea how credible it is. --Yurik (talk) 08:19, 10 October 2017 (UTC)

It's reliable (it's from New Scientist after all) but the missing baryon problem isn't the same as the dark matter problem. They're both matter, but the evidence is that a large part of dark matter is not made of baryons (Dark_matter#Composition_of_dark_matter:_baryonic_vs._nonbaryonic). I would not add it to this article. Oddly enough we don't appear to have an article on the missing baryon problem as well, which is where this would best slot into. Banedon (talk) 20:35, 10 October 2017 (UTC)

Missing baryon problem is now a blue link - the information should go there. Banedon (talk) 22:17, 12 October 2017 (UTC)

Inaccuracy in Galaxy Rotation Curves

I noticed an appearing imprecision and the beginning of the Galaxy Rotation Curves subsection. There is written that

"If luminous mass were all the matter, then we can model the galaxy as a point mass in the centre and test masses orbiting around it (similar to the solar system)."

It seems to me not to be like that, in fact in the case of large bodies as galaxies you can not schematize all of the mass collocated in the centre, because you have to account for all of the gravitational effects of all the single bodies as they are not concentrated in the centre. This way, when "testing masses around it", these masses would be interacting strongly with the bodies in their neighbourood, collocated at different distances from it. In fact, following the link to the main article, one can read that:

"The rotational/orbital speeds of galaxies/stars do not follow the rules found in other orbital systems such as stars/planets and planets/moons that have most of their mass at the centre. Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances. In contrast, the orbital velocities of planets in solar systems and moons orbiting planets decline with distance. In the latter cases, this reflects the mass distributions within those systems."

Which seems to be in contrast with the previous quote.

I could easily be wrong, but noticing what seems like an inconsistency in an important article I wanted to report it.

There is a well-known theorem (the shell theorem) in classical mechanics that for a spherically symmetric body, one can treat all the mass interior to the orbit as a point mass in the center + all the mass exterior to the orbit has no effect. Galaxies are to a large extent spherically symmetric (spiral galaxies are also spherically symmetric, but in 2D), which is why we can model the galaxy as a point mass in the centre. The link you gave actually says the same thing: it's because the rotational / orbital speeds do not follow the rules in other orbital systems that we infer that dark matter exists. I will see what can be done about it. Banedon (talk) 21:15, 26 October 2017 (UTC)

Gravitational microlensing and Circumstellar disks

Astronomical searches for gravitational microlensing in the Milky Way found that at most a small fraction of the dark matter may be in dark, compact, conventional objects (MACHOs, etc.); the excluded range of object masses is from half the Earth's mass up to 30 solar masses, which covers nearly all the plausible candidates.

The MACHO collaboration ended in 1999. Their data refuted the hypothesis that 100% of the dark halo comprises MACHOs, but they found a significant unexplained excess of roughly 20% of the halo mass, which might be due to MACHOs or to lenses within the Large Magellanic Cloud itself.

So 80% of the expected MACHO's were not detected. Maybe 80% of brown dwarfs have such extensive gas and dust discs that they block the light being lensed. They would only need to block the light within 1 au of the brown dwarf. 70-80 au is typical for a disc.

This would also explain why we haven't detected all these Brown dwarfs directly.

UKIRT_Infrared_Deep_Sky_Survey#Large_Area_Survey_(LAS)

Just granpa (talk) 15:50, 7 December 2017 (UTC)

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Lede misleads: dark matter may or may not be baryonic

Currently the lede begins: "Dark matter is a hypothetical type of matter distinct from ordinary matter such as protons, neutrons, electrons, and neutrinos." It is a fact that there is a continuing debate around whether or not dark matter is distinct from ordinary matter. Indeed, the body of the article discusses this debate. To "pick a side" in the opening line of the lede seems non-encyclopedic. Ordinary Person (talk) 04:36, 3 February 2018 (UTC)

The rest of the article states though that "multiple lines of evidence suggest the majority of dark matter is not made of baryons". Banedon (talk) 12:21, 3 February 2018 (UTC)

That's fine, and it would be fine if the lede represented that, but at the moment it equates dark matter with non-baryonic matter. Ordinary Person (talk) 11:31, 4 February 2018 (UTC)

Article issues

4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. Thus, dark matter constitutes 84.5% of total mass, while dark energy plus dark matter constitute 95.1% of total mass–energy content.

1. The numbers above don't seem to add up. Please either fix or explain.

2a. There seems to be no discussion of dark matter within our own solar system. What is the explanation for this? Is it possible that we are surrounded by it now and it's affecting our measurements? Is it possible that it's here now and hasn't been in the past, or vice versa? I'd expect these to be hot topics.

2b. The article discusses distribution of dark matter, but doesn't seem to explain why the distribution seems to be significantly different from the distribution of "normal" matter.

--Scott McNay (talk) 14:55, 3 March 2018 (UTC)

The numbers add up perfectly. Just granpa (talk) 16:05, 3 March 2018 (UTC)

2a see http://cdms.berkeley.edu/Education/DMpages/FAQ/question36.html but perhaps we can find a better source. Someone might have looked rather than speculated. Graeme Bartlett (talk) 04:01, 8 March 2018 (UTC)

Lede

The lede is a bit weaselly.

eg. The lede sentence: "Dark matter is a type of matter that has not yet been directly observed, but is thought[by whom?] to form a fundamental part of the universe"

It is bad form to introduce something with a "not" statement. Who first, or most prominently, proposes that it forms a fundamental part of the universe? The word "fundamental" is often a grandiose claim to cover a weak assertion. Is there a list of proposed fundamentals of the universe? --SmokeyJoe (talk) 23:34, 29 March 2018 (UTC)

this is not philosophy where there is a debate. or are you challenging the consensus in physics? 184.158.82.42 (talk) 00:16, 30 March 2018 (UTC)

Fix what you perceive as "weasel". If you want to fix the 'what', don't demand 'whom'. Don't throw spurious tags demanding the names of all the researchers that published on all the different lines of evidence. It is supposed to be a summary and you are demanding names on people that work a wide range of approaches! BatteryIncluded (talk) 23:55, 29 March 2018 (UTC)

I see the issue has been fixed. The tags weren’t spurious. SmokeyJoe (talk) 01:09, 6 April 2018 (UTC)

You mean somebody added an extensive list with names? BatteryIncluded (talk) 01:35, 6 April 2018 (UTC)

No. It was rewritten to not include reference to unnamed people. —SmokeyJoe (talk) 07:43, 6 April 2018 (UTC)

There is a statement that "it does not appear to interact with observable electromagnetic radiation, such as light, and is thus invisible " but in the next paragraph there is a mention that "Dark matter's properties are inferred from observations in gravitational lensing", these statement dont seem to reconcile as gravitational lensing is actually because of the "Dark Matter" bending light. — Preceding unsigned comment added by Solo-man (talk • contribs) 10:02, 2 April 2018 (UTC)

I think user Solo-man comment regarding gravitational lensing is legitimate. I am not that knowledgeable in physics to edit that entry in the intro, but further explanation may needed to clarify this apparent contradiction. Cheers, BatteryIncluded (talk) 00:22, 6 April 2018 (UTC)

DM does not bend light itself. It bends space. Light follows the curvature of space; this gives lensing effect. So there is no contradiction.UbedJunejo (talk•cont) 00:44, 6 April 2018 (UTC)

Great. The article section "Gravitational lensing" mentions bending light, but not bending space. Would you mind mentioning this in the article? Thank you. BatteryIncluded (talk) 01:33, 6 April 2018 (UTC)

No, I won't do that since link to related arricle does the job.UbedJunejo (talk•cont) 02:37, 6 April 2018 (UTC)

What related article? The gravitational lensing article mentions nothing about dark matter bending spacetime and therefore light, so no, that link is not "doing the job." A reader should not be stumbled at this point and go chasing for a third or more links. I'm not picking a fight here, just agreeing with user Solo-man on an apparent contradiction because there is an incomplete explanation. I am happy this is self-evident to an expert, but there is another opportunity to improve this article further and explain to the reader what you admit is missing. Cheers, BatteryIncluded (talk) 06:58, 6 April 2018 (UTC)

The related article does have explanation Gravitational lensing#Explanation in terms of space–time curvature. Secondly, term gravitational lensing is self evident in the fact that bending of light is due to gravity of DM and not electromagnetic in nature. As anything else feels gravity, so does light. It being electromagnetic radiation doesn't alter the fact that it can experience gravity due to energy-mass equivalence. You can edit the article if you see it fitting. I don't see it necessary so I will not. And, I'm not expert in the field. Thanks.--UbedJunejo (talk•cont) 11:43, 6 April 2018 (UTC)

This article fails criteria "Neutral point of view"

The article fails the neutral point of view criteria: "It has not been directly observed, but its gravitational effects are evident in a variety of astrophysical measurements" suggests that dark matter is a proven fact and not a prevailing theory to explain observations. "generally accepted by most of the astronomical community, a minority of astronomers", clearly biased language. Please stop rolling back this poor article or fix it yourself. — Preceding unsigned comment added by 202.159.142.103 (talk) 10:20, 5 April 2018 (UTC)

Thanks for your comment. According to our rules, the language you cite does NOT violate our Neutral Point Of View guidelines (WP:NPOV), PROVIDED that it correctly reflects the balance of reliable sources (WP:RS) on the matter and does not give undue weight (relative to the afore-mentioned balance of reliable sources) to one viewpoint (which would be contrary to WP:UNDUE). Indeed these guidelines explicitly oblige us to indicate clearly to our readers which is the majority view and which isn't, where this is reasonably clear from the balance of RS (unsurprizingly, as otherwise we would end up having to give equal weight to the views that the earth is round, flat, cubic, square, rectangular, etc, and that the moon is made of green cheese, blue cheese, yellow cheese, red cheese, not cheese, etc). If, having examined the matter, you still think that some of the language does violate that balance, there are a number of ways of pointing this out, including discussing it here, and, if necessary, flagging relevant bits of text with various suitable templates, etc. However it is usually not too easy to get WP:CONSENSUS for major changes to long-established text (which tends to be assumed to enjoy broad consensus as a result of being long-established). There are also special guidelines regarding the article's lead paragraph(s), in WP:LEAD (and possibly elsewhere too). Incidentally I think your viewpoint will probably carry more weight in practice if you get yourself a user account (it's free - all you need is an e-mail address, and then click Create Account at the top of the page). Thanks again, and regards. Tlhslobus (talk) 11:23, 5 April 2018 (UTC)

Is science a popularity contest? There's no argument that dark matter isn't the prevalent accepted theory and I fail to see where that was drawn in my reverted edits, but the theory remains a theory until dark matter is actually described. Indeed it's ironic that in implying a comparison between alternative gravitic theories such as MOND with some sort of crank theory like flat-earth in context of dark matter. In context of my edits, they were a cleanup of running changes to text which are being reverted as some sort of crank edit; I made a fair effort remediate the page but it seems destined to languish as delisted.202.159.142.103 (talk) 12:55, 5 April 2018 (UTC)

Sorry, I did not intend to imply that MOND was equivalent to flat-earth, I was simply trying to say what would ultimately happen if our rules didn't require us to say which theory has majority support among RS. If you could show that the majority of RS don't support dark matter, and persuade a consensus of editors that this is so, then the article would have to be changed to reflect this, but not otherwise. But in fact you accept above that "There's no argument that dark matter isn't the prevalent accepted theory", while your original assertion was that "generally accepted by most of the astronomical community, a minority of astronomers" was "clearly biased language" and made this article POV, when it's actually just another way of saying what you have just said, that dark matter is the prevalent accepted theory. However I really don't have time to argue this seemingly (at least to me) rather self-evident point any further (all the more so as I'm not even one of the editors who reverted you). Regards, Tlhslobus (talk) 14:23, 5 April 2018 (UTC)

Afterthoughts: The other point you originally made was that our language "suggests that dark matter is a proven fact and not a prevailing theory". I'm a somewhat fundamentalist skeptic myself (as far as I'm concerned there are at least arguably no proven facts anywhere - how can one prove that an alleged proof has no flaws too subtle for humans to be able to spot?). So I'm inclined to agree with you. But then that is true of all our language. Humans always speak as if there were proven facts (seemingly unavoidably so, partly because it's not practical to say something like "at least arguably" in every sentence), etc, as inevitably also do our RS, so we seem stuck with this kind of language. So if you want to try to modify the language of fact in this instance you won't find it easy. However if you get yourself a User Account, unless things have changed since I started years ago, somebody should soon thereafter contact you to offer you advice as a newcomer if you want it, and you could ask that person how best to proceed in this instance, and they would almost certainly be able to give you far better advice than I ever could, as well as being more willing to spend the time to do so. Anyway, good luck and regards.Tlhslobus (talk) 16:38, 5 April 2018 (UTC)

MOND is an interesting alternative, but far less important than DM as measured by (say) quantity of articles about it, or number of researchers working on it. And in fact MOND's trajectory as a viable idea has been steadily declining due to observations that it cannot accommodate (like the Bullet cluster, or perhaps the recent observation of a galaxy without DM). There really are no good alternatives to DM, and the article reflects that fairly accurately. Waleswatcher (talk) 15:21, 5 April 2018 (UTC)

I don't see how the language I used promoted MOND at the expense of dark matter. MOND is a serious, good-faith published scientific theory with at least some supporting evidence, but that's not the point I was making. Language like "Although the existence of dark matter is generally accepted by most of the astronomical community" is loaded, implying not just acceptance of the DM theory but that the existence of the same is certain. Dark matter is a placeholder term for a possible undescribed substance, not a factual description. The lack of a compelling alternative theory is not proof in itself for DM; as already pointed out science is not a popularity contest. DM still has some serious faults itself and there are good-faith attempts to provide a credible scientific alternative, I think my edits highlighted this fact.202.159.142.103 (talk) 21:47, 5 April 2018 (UTC)

By the way the edit you keep trying to make is inaccurate for a number of reasons, one of which is that DM could be responsible for "80% of the total gravitic effects observed in the universe". To the extent that makes sense at all, it's badly wrong (more than 70% of the energy budget of the universe is dark energy, only 25% or so is dark matter). No offense intended, but clearly you are not knowledgeable on this topic. Waleswatcher (talk) 15:25, 5 April 2018 (UTC)

I think he is right in saying that "80% of the total gravitic effects observed in the universe", because DE was introduced to account for accelerated expansion and there are no known gravitational effects of DE (due to vanishingly small local densities) as opposed to DM. But the problem with his edits is that, as mentioned above, these edits try to give undue weight to DM alternatives. Wikipedia is not a research platform. Overwhelming consensus among the experts is that DM is real. We can not say it otherwise, even if we personally believe that DM doesn't exist.UbedJunejo (talk•cont) 20:39, 5 April 2018 (UTC)

That of course is not true. The accelerated expansion IS the gravitational effect of DE, as you can easily see by solving Einstein's equations in the presence of DE. But anyway, this is not very relevant since that edit was reverted. Waleswatcher (talk) 02:43, 6 April 2018 (UTC)

Not that it matters much, but I think s/he is only 'right' because of the word 'may', which can cover almost anything no matter how implausible. I don't know how many reliable sources would state that DE has no observed gravitational effects given that it supposedly accounts for 75% of the mass of the observable universe; the most that seems logical to say is that we don't know about such effects, but s/he has not said 'known' gravitational effects (note that just because they aren't known doesn't necessarily mean they haven't been observed - for instance the observed accelerated expansion is at least arguably an observed gravitational effect if it just happens to be the result of some currently unknown but DE-related aspect of Quantum Gravity, which would not be particularly surprising). But in any case being 'right' in that sense is just OR and thus can't be used in our article (so it doesn't matter much, as already mentioned).Tlhslobus (talk) 22:02, 5 April 2018 (UTC)

OOPS. I should have said 'not that it matters as things currently stand'. Because if s/he or anybody else can find Reliable Sources that say that DM accounts for 80% of observed gravitational effects (with or without the word 'known'), then it would no longer be OR, and might well end up having to be used (tho that might depend on other matters such as WP:UNDUE, etc). I just might even eventually look for some such RSs myself (tho almost certainly not anytime soon as it's all a distraction from more urgent stuff); but I probably won't for fear that it would prove more hassle than it's worth.Tlhslobus (talk) 22:32, 5 April 2018 (UTC)

I was referring only to the comment that since DE makes 75% of energy density of universe so DM can't account for 80% of gravitational effects. DM is roughly 80% of "matter density" and so the claim of gravitational effects is not OR in that sense. The thing that the editor implies, though, in saying "80% of gravitic effects" is that "what is observed is just unaccounted for gravitational phenomena (i.e modified gravity), and as such DM is just an unproven hypothesis to explain the phenomena and hence should not be called a real thing", and is OR (or POV); you are right in that. But "80% of gravitic effects" thing can not be rendered incorrect on DE grounds.UbedJunejo (talk•cont) 22:55, 5 April 2018 (UTC)

Lambda-CDM is the current standard model of cosmology, and it includes dark matter. I'm pretty confident a poll of all astronomers will find that the large majority, maybe as much as 90%, believe in dark matter. It's not proven, and until it's proven the alternatives must be explored, but there are few astronomers who actively believe that dark matter does not exist. Alternative theories have their own section, which is kept intentionally small, because it's fringe. It's not as fringe as flat earth theory, but it's still fringe. Having said that, I can agree that the lede is not very good right now. Maybe I'll amend it later. Banedon (talk) 22:40, 5 April 2018 (UTC)

Belief doesn't come into it. An appeal to authority isn't an actual scientific proof and while there is scientific merit in consensus on theory, the theory of DM is not conclusive. The validity of competing theories isn't the point here, but the motivation behind them certainly is. A disingenuous relation to an obvious crank theory implies bias and hence this discussion.202.159.142.103 (talk) 07:13, 6 April 2018 (UTC)

Improving lead language

The introduction to dark matter does look a bit absolutist for non-specialists, so that concerns of NPOV have merit. The language replaced by IP 202 may need work, but some of it is clearer than the previous one. Let's work here to improve it. — JFG ^talk 23:35, 5 April 2018 (UTC)

Intro paragraph - before

Dark matter is a type of unidentified matter that may constitute about 80% of the total matter in the universe. It has not been directly observed, but its gravitational effects are evident in a variety of astrophysical measurements. For this reason there is a broad scientific consensus that dark matter is ubiquitous in the universe and has strongly affected its structure and evolution.

Intro paragraph - IP 202

Dark matter is a theorized non-baryonic form of matter that may constitute about 80% of the total gravitic effects observed in the universe. It has not been directly observed, but its gravitational effects are implied in a variety of astrophysical measurements, in context of accounting for a discrepancy between observable matter and current understanding of gravity. For this reason there is a widely-known and popular scientific theory that dark matter is ubiquitous in the universe and has strongly affected its structure and evolution.

Intro paragraph - Proposal A (changes in bold)

Dark matter is a theorized non-baryonic form of matter that may account for 80% of the total mass of the universe. It has not been directly observed, but its presence is implied in a variety of astrophysical measurements, notably when observing gravitational effects that cannot be explained by visible matter alone. For this reason most scientists consider that dark matter is ubiquitous in the universe and has strongly affected its structure and evolution.

Last paragraph of lead - before

Although the existence of dark matter is generally accepted by most of the astronomical community, a minority of astronomers, motivated by the lack of conclusive identification of dark matter, or by observations that do not fit the model, argue for various modifications of the standard laws of general relativity, such as MOND, TeVeS, and conformal gravity that attempt to account for the observations without invoking additional matter.

Last paragraph of lead - IP 202

Although the theory of dark matter is generally prevalent within the astronomical community and popular science, some astronomers, motivated by the lack of any theory which explains dark matter, or by discrepancies in observation, argue for various modifications of the standard laws of general relativity, such as MOND, TeVeS, and conformal gravity that attempt to account for the observations without requiring unknown and unexplained non-baryonic matter.

Last paragraph - Proposal A (changes in bold)

Although the existence of dark matter is generally accepted by the astronomical community, some astronomers, motivated by the lack of explanations for dark matter, or by observations that do not fit the dark matter theory, argue for various modifications of the standard laws of general relativity, such as MOND, TeVeS, and conformal gravity, that attempt to account for the observations without invoking unexplained non-baryonic matter.

Comments and suggestions welcome. — JFG ^talk 23:35, 5 April 2018 (UTC)

Seems reasonable. I would suggest keeping "may constitute about" instead of "account for" in first paragraph proposal. Inclusion of "non-baryonic" is also fitting. "most scientists" may be replaced with something stronger to reflect the fact that only a few scientists think it doesn't exist, "most" is too weak to express the reality in this case. "observations that don't fit..." in last paragraph proposal should be made "some observations that do not fit..." as there are only a few.UbedJunejo (talk•cont) 23:54, 5 April 2018 (UTC)

@Ubed junejo: I think that "most" is strong enough to denote general acceptance by the scientific community, and I agree that we should qualify the quantity of observations under scrutiny; I would suggest writing "certain observations" rather than "some observations", which sounds a bit vague. Readers can discover the precise observations we refer to in the body of the article. — JFG ^talk 06:21, 6 April 2018 (UTC)

I think both proposed changes by JFG are reasonable, and take into account some of the improved language introduced by the IP but without the POV. Cheers, BatteryIncluded (talk) 00:15, 6 April 2018 (UTC)

Support suggested change, except for:

"that may account for 80% of the total mass of the universe."
This must be changed as follows: ... that may account for about 80% of the total matter of the universe.
2 reasons: 1) 'about' is necessary because the figure is often given as 5 to 1, which is 83%
2) It's matter, not mass, because about 75% of the mass of the universe is Dark Energy, leaving only 20% of the mass as Dark Matter, and about 4% as ordinary matter (this adds to 99% due rounding).
So you might also say: ... that may account for about 80% of the total matter of the universe, and about 20% of its total mass (with the rest being about 75% Dark Energy and about 4% ordinary matter). (But you might want to check a reliable source for the 75/20/4 figures).

Regards, Tlhslobus (talk) 01:42, 6 April 2018 (UTC)

PS: When the change is made we should all thank IP 202 here for helping to improve the article. Cheers, Tlhslobus (talk) 01:55, 6 April 2018 (UTC)

@Tlhslobus: I think we should not confuse readers with dark energy, when they may be already struggling to grasp what this dark matter is all about. However I agree with you that we must remain precise. Certainly the total observed mass/energy distribution is dominated by dark energy at intergalactic scales, but we should focus here on the distinction between observable matter and the "missing mass" in galaxies, which has led to posit the existence of dark matter. I would suggest writing "that may account for about 80% of the total mass of matter in the universe". This neatly sidesteps the mass/energy contribution of dark energy, while remaining scientifically accurate.

Thanks, and sorry for the delay in replying, JFG. If necessary I can go along with your above-suggested amendment as technically correct, but I think it likely to mislead many of our readers (as the current lead may also do) into thinking that DM is 80% of the universe when it isn't. So I suggest "that may account for about 80% of the total mass of matter in the universe (and about 25% of the total mass in the universe)". I've wikilinked 'total mass in the universe' to Universe#Composition, which currently gives DM=26.8%, DE=68.3%, ordinary matter=4.9%, with citations variously dated 2003 to 2015. My suggested change gives the reader the correct picture without misleading them and without mentioning DE, while making it easy for them to check what's missing if they wish to do so. Regards, Tlhslobus (talk) 10:10, 6 April 2018 (UTC)

in or of?: In the above, I've said "total mass in the universe" solely for consistency with "total mass of matter in the universe", but it is more usual and arguably better to say "total mass of the universe". Tlhslobus (talk) 10:23, 6 April 2018 (UTC)

@Tlhslobus: Thanks for your support and further suggestion. I would shorten it to "(and a quarter of its total mass)". Perhaps even without parentheses: "roughly 80% of the mass of matter in the universe, and a quarter of its total mass." Would you approve this? — JFG ^talk 10:42, 6 April 2018 (UTC)

Thanks, JFG. Add in 'about' (or 'roughly' or 'approximately', etc), as in "(and about a quarter of its total mass)" or "roughly 80% of the mass of matter in the universe, and roughly a quarter of its total mass.", etc, and whichever of those versions you prefer will have my support.Tlhslobus (talk) 10:54, 6 April 2018 (UTC)

"lack of explanations for dark matter" ... "unexplained non-baryonic matter" - these don't really make sense. There are a plethora of explanations for and models of dark matter, that isn't the issue. The issue is which one (if any) is correct. Better just to say "that attempt to account for the observations without invoking non-baryonic matter" at the end, and maybe leave out the speculation on motivations at the beginning. Waleswatcher (talk) 02:49, 6 April 2018 (UTC)

@Waleswatcher: Indeed "unexplained" sounds wrong, as several competing explanations for dark matter are available. Perhaps we could say "supplemental" instead? I have cut down the "speculation on motivations", leaving just the key driver of experimental discrepancies. — JFG ^talk 06:45, 6 April 2018 (UTC)

Here is my updated proposal B, taking into account remarks above. I have split the long run-in sentence in the last paragraph, and added the important attempt of alternative models to do away with arbitrary free parameters that allow us to "tweak" characteristics of dark matter to fit the observations. I have also replaced "scientists" by "astrophysicists" in the first paragraph, and "astronomical community" by "scientific community" in the last one, to avoid the awkward "astronomical" repetition. Also added entropic gravity, whose predictions have been tested recently. — JFG ^talk 06:45, 6 April 2018 (UTC)

Intro paragraph - Proposal B (changes in bold)

Dark matter is a theorized non-baryonic form of matter that may account for roughly 80% of the total mass of matter in the universe. Dark matter has not been directly observed, but its presence is implied in a variety of astrophysical measurements, notably when observing gravitational effects that cannot be explained by visible matter alone. For this reason most astrophysicists consider that dark matter is ubiquitous in the universe and has strongly affected its structure and evolution.

Last paragraph - Proposal B (changes in bold)

Although the existence of dark matter is generally accepted by the scientific community, some astrophysicists, intrigued by certain observations that do not fit the dark matter theory, argue for various modifications of the standard laws of general relativity, such as MOND, TeVeS, conformal gravity, or entropic gravity. These models attempt to account for the observations without invoking supplemental non-baryonic matter or arbitrary free parameters.

Hi thank you for your constructive edit. I am satisfied the edit addresses some of the concerns with this otherwise comprehensive article.202.159.142.103 (talk) 07:13, 6 April 2018 (UTC)

And thanks for getting this useful discussion started, 202.159.142.103. Tlhslobus (talk) 10:17, 6 April 2018 (UTC)

Please note my above reply to JFG, with its reservations on the subject of mass of matter.Tlhslobus (talk) 10:17, 6 April 2018 (UTC)

Amended in proposal C. — JFG ^talk 11:01, 6 April 2018 (UTC)

Intro paragraph - Proposal C (changes in bold)

Dark matter is a theorized non-baryonic form of matter that may account for roughly 80% of the mass of matter in the universe, and about a quarter of its total mass. Dark matter has not been directly observed, but its presence is implied in a variety of astrophysical measurements, notably when observing gravitational effects that cannot be explained by visible matter alone. For this reason most astrophysicists consider that dark matter is ubiquitous in the universe and has strongly affected its structure and evolution.

Thanks, JFG. That's now basically fine by me. But I do have a none-too-important afterthought: Since you mentioned 'a quarter', I was thinking that 'five sixths' was better than 'roughly 80%', before concluding that 'roughly 85%' seems best. 'roughly 80%' is four fifths, which seems inconsistent with the bit of our text which says 5 to 1. I know that has a CN on it, but a citation is easily found - I saw one somewhere or other just yesterday. But the current 'best' figure is seemingly about 26.8/(26.8 + 4.9), which is about 84.54%, so 'roughly 85%', with a rounding error of 0.46%, would seem best, and it is also better than five sixths (83.33%, rounding error 1.21%) or six sevenths (85.71429%, rounding error 1.17%, which thus seems the closest simple fraction, but which I've never seen in a citation). However, as already mentioned, this is none-too-important, because 84.54% can also be correctly described as 'roughly 80%', so I certainly won't be objecting if people prefer it. Tlhslobus (talk) 11:40, 6 April 2018 (UTC)

Yeah, measurements and estimates are all over the place, that's why I used "roughly", so 80±5% does not "matter".

— JFG ^talk 11:44, 6 April 2018 (UTC)

No problem, JFG. But I wish somebody could stop me having none-too-important afterthoughts

. My latest is that 'the observable universe' is better (more accurate) than 'the universe', because we know little or nothing about the matter and mass beyond the observable part of our universe. It's not too important because in practice 'universe' is often used as shorthand for 'observable universe', so it arguably isn't really 'wrong'. But it's not ideal either.Tlhslobus (talk) 12:39, 6 April 2018 (UTC)

PS: Incidentally, again none-too-important, but there's also a case for wikilinking the word mass.Tlhslobus (talk) 12:51, 6 April 2018 (UTC)

PPS: And astrophysical? Tlhslobus (talk) 12:55, 6 April 2018 (UTC)

But maybe we can worry about such additional wikilinks (measurements? gravitational? structure? evolution or perhaps evolution?) later, as they don't usually cause major rows, and we may not want to risk a row now about actual or alleged overlinking, and we can do without possible lengthy debates now about the right targets for things like 'structure of the universe' and 'evolution of the universe'. Tlhslobus (talk) 13:00, 6 April 2018 (UTC)

I would object to writing "observable universe" in the first sentence, because the second sentence asserts that dark matter cannot be directly observed. Hence a naive reader might be confused, thinking "how can a thing can cannot be observed be deemed to make up a quarter of all observable things???" As for the suggestions to link "mass" or other topics, we should really leave this to general editing after the text is altered. I'm not too keen on overlinking generally, but perhaps one link to "astrophysical" or "astrophysicists" may be warranted. — JFG ^talk 13:55, 6 April 2018 (UTC)

If wikilinking, 'Astrophysical' rather than 'Astrophysicists' because it comes first in the text, and because others below are disputing 'astrophysicists'. But, as already mentioned by both of us, wikilinking can always be left until later. As for 'observable universe' I'm actually a lot more worried about the reader, whether naive or not, who correctly deduces that there's something 'wrong' (or at least 'not-quite-right') about saying 'universe' instead of 'observable universe', so I definitely prefer 'observable universe'. But, as already mentioned, I can live with it (or perhaps try to get it changed later, long after you've made the more important changes) because it's at least arguably commonly-used shorthand and thus at least arguably 'not really wrong'.Tlhslobus (talk) 16:31, 6 April 2018 (UTC)

But anyway, thanks for all the excellent hard work that you've been putting into this.Tlhslobus (talk) 16:35, 6 April 2018 (UTC)

Regarding the last paragraph: "without invoking...arbitrary free parameters" is not correct. TeVeS has at least one entire continuous function's worth of free parameters (so, continuously infinitely many), and MOND has at least one. Conformal gravity is nonsense (it is unstable instantaneously due to what are called "ghosts"), but the way it's used it effectively has several free parameters. Entropic gravity is barely developed at all. So, in my view the phrase about parameters should just be deleted. Waleswatcher (talk) 13:51, 6 April 2018 (UTC)

The lede section is a necessarily brief summary of the main points. The phrase I added does not purport to imply that the alternative theories have no free parameters whatsoever, but that their emergence was partly motivated by the presence of several such parameters in the dominant Lambda-CDM model. I'm happy to remove conformal gravity if it's indeed considered nonsense by experts. Entropic gravity is indeed young, but the recent encouraging attempts to test its predictive powers do warrant inclusion imho. — JFG ^talk 14:06, 6 April 2018 (UTC)

It's true that all DM models have parameters. My point is that so do the alternatives listed, but the language as you have it makes it sound as though that's not the case. Waleswatcher (talk) 15:36, 6 April 2018 (UTC)

OK, how about "or with fewer free parameters"? — JFG ^talk 16:21, 6 April 2018 (UTC)

Comment: "mass of matter" seems dubious to me. I can't see what is wrong with "matter". "Most astrophysicists" is also not okay. Particle physicists and cosmologists also belive DM. UbedJunejo (talk•cont) 14:18, 6 April 2018 (UTC)

We were trying to express that the apparent "missing mass" in astronomic observations was the impetus behind the dark matter theory; this is lost if we talk only about matter and not about mass. Tlhslobus prompted me to distinguish the share of mass within matter variants and the share of mass/energy in the total contents of the universe, which led to the phrasing in Proposal C. Regarding "astrophysicists", you are correct and I'd happily replace this with "specialists" or "experts". — JFG ^talk 17:21, 6 April 2018 (UTC)

New proposals, taking into account latest remarks:

Intro paragraph - Proposal D (changes in bold)

Dark matter is a theorized non-baryonic form of matter that may account for roughly 80% of the mass of matter in the universe, and about a quarter of its total mass. Dark matter has not been directly observed, but its presence is implied in a variety of astrophysical measurements, notably when observing gravitational effects that cannot be explained by visible matter alone. For this reason most experts consider that dark matter is ubiquitous in the universe and has strongly affected its structure and evolution.

Last paragraph - Proposal D (changes in bold)

(There was no proposal C for this one.)

Although the existence of dark matter is generally accepted by the scientific community, some astrophysicists, intrigued by certain observations that do not fit the dark matter theory, argue for various modifications of the standard laws of general relativity, such as MOND, TeVeS, or entropic gravity. These models attempt to account for the observations without invoking supplemental non-baryonic matter, or with fewer free parameters.

Do we have consensus yet? — JFG ^talk 17:26, 6 April 2018 (UTC)

No. It's not true that those models have fewer free parameters. In fact, TeVeS has vastly more free parameters than any DM model I've every seen. Waleswatcher (talk) 00:04, 7 April 2018 (UTC)

Lambda-CDM has at least 6 free parameters, MOND has one a₀ parameter and an interpolating function, TeVeS has plenty of stuff, and entropic gravity claims to have no free parameters. We may explain as much in the article body, not in the lead. The proposed wording says "or fewer free parameters", so that this assertion does not need to apply to all cited alternative theories. — JFG ^talk 06:53, 7 April 2018 (UTC)

None of those other theories are theories of cosmology, so they cannot actually be compared to Lambda-CDM. MOND is non-relativistic and can't even handle gravitational lensing, let alone cosmology. Same for entropic gravity. TeVeS is a total mess with many functions (and by the way, even one interpolating function is infinitely many parameters, to the extent parameter-counting is defined at all). In other words, the parameters of Lambda-CDM you refer to are not really parameters of DM, they are parameters of a theory that describes many features of the universe. This is part of the problem we are having - you immediately have difficulty when trying to put these alternatives on anything close to the level of Lambda-CDM, because they are very different. Waleswatcher (talk) 11:56, 7 April 2018 (UTC)

Well, that's too much detail, better addressed in the article about the various theories. Let's drop it from here. — JFG ^talk 12:08, 7 April 2018 (UTC)

Last paragraph - Proposal D2 (changes in bold)

Although the existence of dark matter is generally accepted by the scientific community, some astrophysicists, intrigued by certain observations that do not fit the dark matter theory, argue for various modifications of the standard laws of general relativity, such as MOND, TeVeS, or entropic gravity. These models attempt to account for ~~the~~ all observations without invoking supplemental non-baryonic matter.

Good to go? — JFG ^talk 12:08, 7 April 2018 (UTC)

I'd delete "the" in the last sentence (they seek to fit observations that fit DM as well as those that don't). I'm still slightly unhappy with the motivations - it's not just that there are observations that don't fit DM, which is what you were trying to get at with the parameters stuff - but I think it's good enough. Waleswatcher (talk) 12:16, 7 April 2018 (UTC)

OK, I'll replace "the observations" with "all observations", because after all, that's how good theories get vindicated. Thanks! — JFG ^talk 12:42, 7 April 2018 (UTC)

Done. Thanks everyone for your comments and help in shaping this improved wording. — JFG ^talk 18:12, 7 April 2018 (UTC)

Electrons are leptons not baryons

The section "Composition of dark matter: baryonic vs. nonbaryonic" currently states: "Dark matter can refer to any substance that interacts predominantly via gravity with visible matter (e.g., stars and planets). Hence in principle it need not be composed of a new type of fundamental particle but could, at least in part, be made up of standard baryonic matter, such as protons or electrons." The last word "electron" should be changed, e.g. into "neutrons". 7. April 2018 146.198.14.85 (talk) 18:15, 7 April 2018 (UTC)

In astronomy, "baryonic matter" is generally used to refer to both actual baryons and the electrons that are bound to them. [4] In other words, it includes all the stuff made out of atoms. So the sentence is correct, as used in astronomy, but there probably is a better way to convey this without seeming confusing. Dragons flight (talk) 18:32, 7 April 2018 (UTC)

Thanks, Dragons flight. The simplest way to do this is perhaps to add a footnote beside baryonic explaining this, and citing your source~~, and leaving the wikilink in that footnote instead of in the lead where it will just cause confusion~~. I may try to do this myself shortly if somebody else hasn't already done it by then. (Unfortunately we presumably can't add that astronomers should probably say 'atomic' instead, unless somebody can find a Reliable Source that says this. Similarly we probably can't or shouldn't add that some astronomers at least allegedly also use 'metals' to refer to elements heavier than helium

). Tlhslobus (talk) 02:34, 9 April 2018 (UTC)

Actually 'atomic' wouldn't do either since the source mentions that astronomers' use of baryonic includes black holes (which are neither atomic nor baryonic) and neutron stars (which are baryonic but not atomic).Tlhslobus (talk) 02:58, 9 April 2018 (UTC)

~~Done~~. OOPS, I misread some of the above and put the footnote in the wrong place, so I've self-reverted before checking whether a footnote is still needed and, if so, where. Tlhslobus (talk) 03:48, 9 April 2018 (UTC)

I've now put the footnote where it belongs (and crossed out the mistaken part of my above suggestion).Tlhslobus (talk) 04:07, 9 April 2018 (UTC)

Mass-energy + observable

In view of an earlier edit by Banedon and the edit description of its revert by Waleswatcher, I've tried replacing mass by mass-energy in the lead as a fix, and then I've also changed universe to observable universe to try to be consistently accurate. But if this is felt to be unsatisfactory, then an alternative may be to restore the original text and add an explanatory footnote (or two) instead. Tlhslobus (talk) 21:02, 9 April 2018 (UTC)

Galaxy without dark matter

I'm not sure if this discovery merits mention in this article: Ghostly galaxy may be missing dark matter. Research paper: A galaxy lacking dark matter. Cheers, BatteryIncluded (talk) 18:39, 28 March 2018 (UTC)

The mass media picked it up, but NASA just published an outreach page with an extensive explanation of the research paper in plain language,[5], as well as images from Hubble ST: [6]. Cheers, BatteryIncluded (talk) 13:49, 29 March 2018 (UTC)

I think if we were to discuss it, we'd need a section on UDGs in general (since some have a lot of dark matter, and some have not so much). Probably best to wait for a overview article? - Parejkoj (talk) 17:11, 29 March 2018 (UTC)

I think it's too soon to add this, and it's unclear how it's related to dark matter. If it's confirmed, it could be used to test modified gravity models, and we can add it then. Otherwise it seems more related to galaxy formation than dark matter. Banedon (talk) 21:42, 29 March 2018 (UTC)

That's not how it's being reported, at least by the BBC, and the NASA article also has the van Dokkum quote "... and it shows that dark matter is real: it has its own separate existence apart from other components of galaxies.", so I fail to see how it doesn't relate to Dark Matter (there's nothing to stop us adding it to Galaxy Formation articles as well - I've now linked the two articles in both directions). Per WP:NOTCENSORED, WP:IAR, WP:5P5, etc, it belongs here, probably with the above NASA link added (which I've now done). But it may well be better in some Recent Developments section (or as a stand-alone section, or whatever), though there's also a lot to be said for leaving it under Observational Evidence, since it clearly is observational evidence (whether weak or strong is for others to say) that dark matter is real. Meanwhile I've added it back so readers attracted by the news can find out more about it. Tlhslobus (talk) 17:12, 2 April 2018 (UTC)

I also think this development can be mentioned in this article; it is related and it is relevant. BatteryIncluded (talk) 18:11, 2 April 2018 (UTC)

I think you misunderstood van Dokkum's quote. He's saying that if the findings are confirmed, dark matter is separate from ordinary matter. In other words when modelling galaxy formation, one has to model dark matter and ordinary matter separately. Note he also focuses not on dark matter, but on galaxy formation. That is where this finding is most relevant: galaxy formation. Let me try spelling out the implications from this observation, because it's understandable to a layperson.

Standard galaxy formation models predict that galaxies form with ordinary matter and dark matter. You should not be able to find a galaxy with only ordinary matter, just as much as you should not find a galaxy with only dark matter (but see Dark_matter#Dark_matter_aggregation_and_dense_dark_matter_objects).
Now we find a galaxy with only ordinary matter. Note this isn't the first time it's happened. This is clearly a problem for galaxy formation models, and it's got little to do with dark matter (note that the dark matter article covers a lot of material other than galaxy formation).
What is more related to dark matter is how this acts as a testing ground for modified gravity theories. If a modified gravity theory is correct, it should be able to match observations both for galaxies with dark matter and for galaxies without it. These theories have parameters that are tuned to match observations of galaxies with dark matter. The challenge is if these theories can also fit observations of this galaxy, which does not have dark matter. If changing the parameters becomes necessary, then we have a problem, because it'll fail to match observations of galaxies with dark matter.
Note that nowhere in this analysis does this observation prove that dark matter is "real". The most that can be done is disprove our most popular modified gravity theories. This doesn't mean that other modified gravity theories do not work. The only way to really confirm dark matter is to directly detect it, and this is not a detection.

I think this doesn't deserve to be in the article. Maybe it's worth mentioning in a few months' time if there's a change to the status of modified gravity, but it would go into the alternatives section, not where it currently is. Banedon (talk) 23:27, 2 April 2018 (UTC)

I largely disagree, but I don't have time to respond in much detail. So I will just briefly say:

1) I do not think I am misunderstanding van Dokkum. He says "it shows that dark matter is real." I fail to see how that somehow means that he doesn't mean that "it shows that dark matter is real", all the more so when his colleague Mack says the same in the BBC article, and when what they are both saying, whether rightly or wrongly, is easily understood by most people. However some slight rewording such as "according to van Dokkum[cite Nasa] and Mack[cite BBC]" may well be desirable.
2) The fact that one or more similar galaxies have been reported as long ago as 2008 may mean that some more rewording is needed, but, at least at first glance, it also seemingly makes it all the more necessary to include this, given that we have arguably been keeping our readers in the dark for 10 years, which seems all the more reason for not keeping them in the dark any longer (per WP:NOTCENSORED, WP:IAR, WP:5P5, etc, as already mentioned).
3) As mentioned before, I don't have any great problem with shifting the item to some other location, at least at first glance, but probably not the above-suggested Alternatives section, since that is about dark matter not existing, whereas this is ostensibly claiming to possibly lead to proof that dark matter exists.
4) I may well try a more detailed and considered response if and when I have time at a later date.

Regards, Tlhslobus (talk) 03:36, 3 April 2018 (UTC)

Having now had time to give the matter some further thought, I am largely satisfied with most or all of what I've said above (and saying too much more at this stage might risk unnecessarily aggravating the disagreement), but I will add the following:

5) Mack is not in fact a colleague of Van Dorren, and is not a co-author of the paper. That seems useful as it makes her a secondary source (tho NASA and the BBC arguably already count as secondary sources anyway).
6) If and when I get round to trying to amend this section, as partly already indicated in my items 1 and 2 above (probably not for another couple of weeks or so, as I expect to be mostly tied up with other matters), I will probably be looking for other such RS secondary sources, and for any RS secondary sources that dispute this view (in Wikipedia we report both sides, suitably weighted, when the RS show there is a dispute).
7) I think it may be useful to at least consider turning our present subsection into a lower-level subsection of a new subsection within 'Evidence', which would be called something like 'Evidence that amending the Theory of Gravity is not enough' (tho the exact wording of this title seems bound to be a little messy). This would include an introductory explanatory sentence or two, then our subsection, then one or more other such subsections for other such evidence

7b) I know of at least one instance (there may be more) of the above-mentioned 'other such evidence' : Professor Jim Al-Khalili discusses a photograph of (if I remember right) a particular instance of Gravitational lensing in his BBC4 documentary about Dark Matter, where he descibes that photograph as something like the best evidence of which he is aware that Dark Matter is not just an illusion caused by the need to amend our current Theory of Gravity. But finding the details of Al-Khalili's view may be a bit difficult unless his programme can be found and watched on Youtube
7c) incidentally we know that some amendment to our current Theory of Gravity seems needed for other reasons, because we need a proper theory of Quantum Gravity as Quantum Theory and our current theory of Gravity (General Relativity) are mutually incompatible, but that doesn't necessarily mean that Dark matter is just an illusion. I don't know whether or not this should be briefly mentioned in our article (assuming suitable supporting RS can be found, though there should be dozens to thousands of those, or at least for the parts of the above that says that a theory of Quantum Gravity is needed).

8) Any delay by me will probably give more time for sources for contrary views to emerge, but there's nothing to stop other editors trying to make most or all of the suggested amendments long before I get around to trying to do so (always assuming that I actually do eventually get around to this).

Regards, Tlhslobus (talk) 10:47, 5 April 2018 (UTC)

The problem is you're relying on secondary sources to understand what van Dokkum is saying. Let's try it this way. How can the discovery of a galaxy without dark matter prove that dark matter exists? You quote Prof. Jim Al-Khalili as asserting that gravitational lensing as evidence for the existence of dark matter, which is true. Gravitational lensing (+GR) lets us infer the mass distribution, which we can compare to the luminous mass (aka stars galaxies etc), from which we can calculate the mass-to-luminosity ratio. We get very high results, too high to be consistent with known astrophysical sources, from which we infer that dark matter must exist (note this line of reasoning doesn't exclude dark matter as being baryonic in nature). All this is already in the article.

So now the question: how does the existence of a galaxy without dark matter serve as evidence that dark matter exists? Give me an answer similar to the one I gave for gravitational lensing being evidence for dark matter above. Don't appeal to authority with "van Dokkum said so, therefore it must be so". I'm pretty confident that if I talk to van Dokkum personally, he will agree that this is not direct evidence for the existence of dark matter.

PS: The inconsistency between quantum mechanics and general relativity is not directly related to dark matter. You will note in the alternatives section that the leading candidates for alternative theories without dark matter are all classical in nature. Banedon (talk) 22:33, 5 April 2018 (UTC)

@Tlhslobus: this still needs to be resolved. If no objections, I'll remove it from the article. Banedon (talk) 07:44, 11 April 2018 (UTC)

@Banedon: Yes, I know it still needs to be resolved. I plan to reply at some length, either later this week or some time next week, and then probably withdraw from this (at-least-to-me intolerably tedious, stressful, and exhausting) discussion and leave it up to others to decide what to do about it. Meanwhile I would object to you removing it before then, unless somehow I unexpectedly don't reply by the end of next week (say, by midnight Friday 20th, although I hope to have replied a good deal sooner than that). Regards, Tlhslobus (talk) 12:26, 11 April 2018 (UTC)

In some sense the existence of a galaxy without DM does indeed serve as evidence that dark matter exists, but in any case that is not the standard for inclusion in this article. This article is not a list of evidence for dark matter, it is an encyclopedia article about dark matter. To me it is obvious that this observation is relevant to such an article, both because it illustrates an important aspect of DM (that different galaxies have very different ratios, so DM and ordinary matter are distinct), and because it bears directly on the alternative theories that have been proposed. The only question then is how notable this specific discovery is, whether it would be undue to discuss it now. I lean towards the view that it is sufficiently notable, but I could perhaps be convinced otherwise. Waleswatcher (talk) 18:00, 12 April 2018 (UTC)

Compare Bullet Cluster. The Bullet Cluster's existence doesn't prove dark matter, it just provides evidence against modified gravity. The same applies here, although AFAIK the studies on whether / how much this galaxy impacts modified gravity have yet to be completed. The Bullet Cluster is already mentioned in passing in the article, arguably it deserves more; if so then that section would be where to mention this new galaxy. Banedon (talk) 23:01, 12 April 2018 (UTC)

I'd rather see the section moved and not deleted. Cheers, BatteryIncluded (talk) 23:19, 12 April 2018 (UTC)

In view of this, this and this I change my mind and think that we should remove mention of this entirely, and the sooner the better. Meanwhile, the bullet cluster could be promoted to its own section. Banedon (talk) 02:51, 16 April 2018 (UTC)

DM in Universe v/s Observable Universe

Dark matter is a theorized non-baryonic form of matter that may account for approximately 80% of the mass-energy of matter in the "universe". Tlhslobus has changed "universe" in this sentence to "observable universe" on the grounds that "otherwise it becomes confusing/misleading". To my mind, it is incorrect. Universe is homogeneous and isotropic. We believe properties of universe are same even beyond observation limit. This goes with DM, DE, Baryonic matter, gravity, quantum mechanics etc. It is incorrect, for example, to say that "matter curves spacetime in observable universe (since we don't see beyond)". In my view, it should be made "universe", as it was before. Thanks --UbedJunejo (talk•cont) 01:01, 11 April 2018 (UTC)

I don't want to get into another long argument about this, so I'll just give a brief (OOPS, not all that brief

) reply here and then leave it to others to decide what, if anything, to do about it.

1) It's perhaps a minor point, but "matter curves spacetime in the observable universe" is not a very similar example. Normally we would simply say "matter curves spacetime" and we would not have to mention the universe, whether observable or not. By contrast we can't avoid mentioning the universe when we are talking about things like the total mass of the observable universe (which is reasonably well known) or of the universe (which is only reasonably well known if we are using universe as shorthand for observable universe)
1.1) The example also compares two very different things, a necessary consequence of our currently understood Laws of Physics ('matter curves spacetime' is a necessary consequence of General Relativity) and an observation about the observable universe which is not a requirement of our Laws of Physics, a difference which is very relevant to how likely it is to remain true in the unobservable part of the universe.
1.2) The example you give does not seem "incorrect" (your chosen word). It is not "incorrect" (tho arguably inconvenient) to say "matter curves spacetime in the observable universe". On the other hand it may well be arguably convenient but at least technically "incorrect" (and perhaps also confusing and/or misleading) to drop the word "observable".
1.3) And whatever about your example, it is certainly NOT "incorrect" to use "observable" as I have done, whereas it may well be at least technically "incorrect" (and perhaps also confusing and/or misleading) to drop it.
1.4) In both cases the statements appear 'true' about the observable universe (at least to the extent that Science is 'true', which is what matters here since we go by 'reliable sources'). But whether they are similarly 'true' about the unobservable part of the universe is far more debatable (as incidentally implicitly indicated by your expression 'we believe')
2) I'm not clear who 'we' is in 'we believe'. I have certainly seen scientists writing that the observable universe may be a homogeneous part of a much larger inhomogeneous Universe.
2.1) It may or may not also be relevant to mention that Max Tegmark sometimes compares the horizon of the observable universe to the horizon you see if you are in the middle of a seemingly homogeneous ocean (this is of course a homogeneous part of a larger inhomogeneous whole, the surface of the Earth)
2.2) Statements like 'we believe' are arguably unscientific, especially when they concern something which can seemingly never be verified or falsified on any humanly practical timescale (which may well mean that in practice most scientists don't have any 'beliefs' about it, and may even strongly object to such 'beliefs' being described as 'science')
2.3) There is presumably also a difference between what scientists 'believe' and what they may occasionally use as a convenient working assumption on the rare occasions when they have to make working assumptions about the unobservable part of the universe.
3) I don't know what, if anything, the majority of reliable sources say on the subject of the homogeneity or otherwise of the unobservable part of the universe.
4) Investigating what reliable sources say on the subject is also greatly complicated because, as already mentioned elsewhere, scientists (and others) routinely use 'the universe' as convenient shorthand for 'the observable universe', just as they use 'baryonic matter' as convenient shorthand for something that includes much that is non-baryonic (and some astronomers allegedly use 'metals' as convenient shorthand for any element heavier than helium)
5) Such shorthand can be confusing/misleading to both readers and editors.
5.1) For instance, yesterday I put in an explanatory footnote because somebody objected to including electrons as part of baryonic matter (see 2 sections above this one)
5.2) I put in 'mass-energy' because edits and edit descriptions by Banedon and Waleswatcher seemingly indicated dissatisfaction with what can at least arguably be described as the use of 'mass' as shorthand for 'mass-energy' (see the section above this one). (I then added, both there and in my original edit description (here), that "I've also changed universe to observable universe to try to be consistently accurate." - I later added it a second time for consistency and to avoid confusion after "its" got changed to "the universe's" by Waleswatcher to avoid another possible source of confusion)
5.3) I have already said that it may well be better to keep the original text and perhaps use one or two explanatory footnotes (see the section above this one).
5.3.1) Others may be far better able than I am to find citations to help support such footnotes, if any (just as another editor found the supporting citation that lead to the baryonic matter footnote, see 2 sections above this one)
6) So, having said my bit, as already mentioned, I am now going to withdraw from this discussion, per WP:NOTCOMPULSORY, and leave it to others to decide what if anything to do about it.

Regards, Tlhslobus (talk) 02:09, 11 April 2018 (UTC)

(Afterthought:) I should perhaps have added that as a community we have, probably wisely, just gone through a major collective exercise to remove from the lead the implication that DM is factual rather than hypothetical, despite the vast amount of evidence supporting DM. Yet it is in effect now being demanded that we leave in the same lead as apparent 'fact' something for which there is (and can be) no evidence whatsoever, seemingly purely on the basis that this is allegedly something that 'we believe' (whoever 'we' is). Tlhslobus (talk) 12:36, 11 April 2018 (UTC)

By we believe it is meant humans/scientists in the field who believe that. Inflation cosmology is based just on that and you can not just deny that with your personal views on universe which are not substantiated by any published sources. What you say is OR. You mention Max Tegmak's conjectures that it may well be different. Well then may be dark matter glows pink beyond hubble sphere, one can say anything one wants. Do DM experts specifically say that in their publications that it is only "observable universe" or that by universe they actually mean observable universe? Nevertheless, I have no interest in engaging with you in your long war of exhaustion. Banedon is good match for that. So, have fun with mass of matter in your observable universe.UbedJunejo (talk•cont) 10:33, 12 April 2018 (UTC)

Homogeneity and isotropy are simplifying assumptions; there is no harm in stating "observable universe" because, following the scientific method, 1) disregards beliefs, and 2) uses required caution such as "as far as we can tell". Cheers, BatteryIncluded (talk) 02:55, 11 April 2018 (UTC)

Just cited today's report from ESA at http://www.niquette.com/puzzles/tobillos.html#epilog, which provides newly discovered evidence from XMM Newton Space Observatory for a form of ordinary intergalactic matter that may be deductable from the DM 'ledger'. Paul Niquette (talk) 13:28, 21 June 2018 (UTC)

theory

There seems to be a question as to dark matter being theory, or not. As well as I know it, the important thing about a theory is that it can be proven wrong. Most often, one can never be proven right. If it explains (most of) the physics, and there are tests that can show it wrong, it is fine as a theory. Gah4 (talk) 18:36, 29 June 2018 (UTC)

OK, more discussion here, and less reverts there. The statement Dark matter is that component of the universe that is not ordinary matter but still obeys ρ ∝ a⁻³. seems to reasonably define dark matter, in theory. Next there are varying hypotheses to explain such matter. As well as I know it, the alternative to dark matter would be gross violations of Newton's laws, such as action without reaction. Gah4 (talk) 19:23, 6 July 2018 (UTC)

Missing source

Randall 2015 is cited several times but the source is not given. Does anyone know whether it is Lisa Randall's Dark Matter and the Dinosaurs? Dudley Miles (talk) 19:21, 12 August 2018 (UTC)

See Randall, Lisa (2015). Dark matter and the dinosaurs: The astounding interconnectedness of the universe. Harper Collins Publishers. pp. 67–68. ISBN 978-0-06-232847-2. [7] by user:Huntster, this user reorganised but did not introduce the cite. Graeme Bartlett (talk) 07:25, 13 August 2018 (UTC)

Dudley Miles, look under the section header "Bibliography", below the References list. I've restored the citation; it was apparently removed in this series of edits by someone replacing it with some random, apparently unconnected article. — Huntster (t @ c) 07:28, 13 August 2018 (UTC)

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Sylvain Ribault (talk) 19:18, 27 October 2018 (UTC)

Shear modulus of the void at large orders of magnitude

https://www.youtube.com/watch?v=gcI-bkr7ilg

Even if it's wrong in this case, we should mention it. — Preceding unsigned comment added by 2A02:587:4104:F000:D4F4:9054:C9DC:E410 (talk) 18:33, 26 December 2018 (UTC)

The void is more plastic at large orders of magnitude than it should be. That can explain dark matter and dark energy (but dark energy is more fundamental, because at its peak is a big bang).

Kepler's third law, not second

In the Observational evidence section under Galaxy rotation curves, shouldn't it be Kepler's Third Law? The second law is for a single planet. The third law says that the square of the period is proportional to the cube of the radius of the orbit (or more precisely, the semi-major axis). And we are talking about the orbital speed vs. distance. The orbital speed determines the period. Am I missing something? — Preceding unsigned comment added by Betaneptune (talk • contribs) 13:46, 12 December 2018 (UTC)

Kepler's second law says "a line joining a planet and the Sun sweeps out equal areas during equal intervals of time". In this context it means a line joining a star and the galactic center sweeps out equal areas during equal intervals of time, i.e. the closer a star is to the galactic center, the faster it moves. Banedon (talk) 21:51, 26 December 2018 (UTC)

Dark matter attempted detection using network of atomic clocks

Reported in Science Advances and brief news item in Nature.

Wcislo P, Ablewski P, Beloy K, Bilicki S, Bober M, Brown, R, Fasano R, Ciurylo R, Hachisu H, Ito T, Lodewyck J, Ludlow A, McGres W, Morzyński P, Nicolodi D, Schioppo M, Sekido M, Le Targat R, Wolf P, Zhang X, Zjawin B, Zawada M (December 7, 2018). "New bounds on dark matter coupling from a global network of optical atomic clocks". Science Advances. 4 (12). doi:10.1126/sciadv.aau4869.
"The search for dark matter that runs on time". Nature. December 11, 2018.

--User:Ceyockey (talk to me) 19:16, 29 December 2018 (UTC)

I hope they detect these anomalies. By the way, 85% of the matter in the universe can hardly be called an "artefact". Cheers, Rowan Forest (talk) 19:55, 29 December 2018 (UTC)

Clarification of sentence in section Dark matter aggregation and dense dark matter objects

The last sentence in the section Dark matter aggregation and dense dark matter objects reads: “These were again ruled out in December 2017,[98] but research and theories based on these still continue as at 2018, including approaches to dark matter cooling,[99][100] and the question is by no means settled.”

It is not clear what “These” and “these” refers to. The sentence needs to be elaborated.

Domandologo (talk) 20:40, 6 January 2019 (UTC)

I edited this sentence. Banedon (talk) 00:20, 7 January 2019 (UTC)

I rewrote the whole paragraph on primordial black holes to give some background on the debate (as is done for other proposals in this section trying to account for dark matter). I also replaced the New Scientist reference which refutes the primordial black hole hypothesis with one in Astronomy.com because New Scientist had a paywall & this way readers can follow up to read the reference if they wish.

Domandologo (talk) 15:32, 7 January 2019 (UTC)

Clarification of sentence in CMB section

In the section "Cosmic microwave background" the last sentence of the 2nd Paragraph reads: “The first peak mostly shows the density of baryonic matter, while the third peak relates mostly to the density of dark matter, measuring the density of matter and the density of atoms.[62]”

I found the closing phrase of this sentence confusing: What is “measuring the density of matter and the density of atoms” referring to? If it refers to the second item in the previous sentence (third peak) then I find this confusing since atoms are not dark matter, they are baryonic matter. Also “density of matter” would appear to include both baryonic and dark matter, so it also does not make sense if one assumes that “respectively” should be added at the end of the sentence, which would indicate that “measuring” means that the first peak measures “density of matter” and to the 3rd peak measures the density of atoms.

Domandologo (talk) 20:40, 6 January 2019 (UTC)

Did you check the reference? Measuring the density of matter would be measuring the total amount of all matter (including both baryonic and non-baryonic), while the density of atoms would be only baryonic matter. If you still find it confusing, feel free to edit the sentence. Banedon (talk) 00:17, 7 January 2019 (UTC)

Yes, I checked the reference. The first part of that sentence is clear. My proposal is to drop the second part ", measuring the density of matter and the density of atoms" which I think repeats the first part of the sentence.

Also, I think a second reference is needed for the assertion "The series of peaks can be predicted for any assumed set of cosmological parameters by modern computer codes such as CMBFast and CAMB," since this not mentioned anywhere in the referenced intermediate internet tutorial on CMB [62]. I assume that the curves shown were obtained with these programs, but it is not stated anywhere in the tutorial. Domandologo (talk) 21:12, 7 January 2019 (UTC)

Include results from study of Dark matter heating in dwarf galaxies?

There was a study published recently showing movement of dark matter can be caused by active star formation in dwarf galaxies. They refer to this as "heating up" of dark matter. I assume that this a different kind of temperature than the one discussed in the section of the wikipedia article on temperature catagories of dark matter, which are related to free streaming length in very early part evolution of the universe, but could the heating up referred to in the study still be relevant, since it might obscure the temperature behaviour expected? Anyway it seems to be an important observation but I am not sure where to place it. Possibly at the end of the section on temperature catagories? Here is some text I wrote on the article. Maybe someone else can decide if/where it fits into the wikipedia article:

Evidence that changes in the temperature of dark matter can be affected by gravitational interaction with baryonic matter were provided by a study of dwarf galaxies which showed that dark matter was driven to the periphery in those galaxies which maintained active star formation where as those which stopped forming stars early in their evolution showed evidence that dark matter was more concentrated at their centers. This was interpreted as due to radiation pressure from star formation driving baryonic mass into the periphery, with the dark matter following it by gravitational interaction.^[1]

Domandologo (talk) 22:26, 7 January 2019 (UTC)

References

^ "Dark matter on the move". ras.ac.uk. 28 December 2018. Retrieved 6 January 2019.

Lyman alpha forest subsection of section Type Ia supernova distance measurements needs expansion

The subsection of Lyman alpha forest, in the section Type Ia supernova distance measurements is very cursory. It does not explain how one arrives at evidence supporting dark matter as is done for the other headings of this section, and needs some expansion.

Domandologo (talk) 20:40, 6 January 2019 (UTC)

No such thing as can't be explained or probability or not, explain, can explain any by any no matter what and any is perfect. — Preceding unsigned comment added by Cioxikl (talk • contribs) 16:23, 12 February 2019 (UTC)

Why remove section on Galaxies with less or more evidence of DM

There was a section here on Galaxies with less DM - sounds like a useful subtopic - but its been removed - not sure why or when. It could say what the current view on NGC 1052-DF2 (an ultra-diffuse galaxy) is. [8] also mentions DF4 and shows the topic is of interest and relevance. Reasons for/against this section ? - Rod57 (talk) 09:24, 29 March 2019 (UTC)

A new study suggests that the results showing no/little dark matter for NGC 1052-DF2 were likely due to error in analysis of the distance to the galaxy. LewriBaedi (talk) 22:01, 16 June 2019 (UTC)

Assumption

"The effect is not detectable for any one structure since the true shape is not known, but can be measured by averaging over many structures assuming Earth is not at a special location in the Universe."

Do we have evidence that the Earth is not in a special location? If so, then this sentence should be changed to remove the word "assuming" and instead invoke the evidence.

If we don't have such evidence, then a sentence should be added to this which considers the possibility that the Earth is in a special location. — Preceding unsigned comment added by 157.14.234.194 (talk) 03:40, 26 May 2019 (UTC)

The assumption that Earth and the Solar System are not special is implicit in all current astronomical research, and has been corroborated by virtually all evidence across centuries of observation. Accordingly we should simply remove this part of the sentence. — JFG ^talk 09:09, 26 May 2019 (UTC)

I agree that the assumption that Earth and the Solar System are not special is implicit in all current astronomical research, but there has never been any evidence for it. For example, the fact that we observe all galaxies accelerating away from the Earth is evidence that we are in the center of an expanding universe. But all current astronomical research assume that cannot be true and so re-interprets the data any other way that they can to avoid that conclusion. A sentence should be added which considers the possibility that the Earth(or the solar system) is in the center, and that observations from any other solar system would not seem to be in the center. — Preceding unsigned comment added by 222.230.133.24 (talk) 14:49, 31 May 2019 (UTC)

No, writing that is as accurate as writing "Earth may be flat" in the article on Earth. "We in the center" would require "static we", which is false. Earth moves around sun, sun moves around galactic center, and son on. AhmadLX-)¯\_(ツ)_/¯) 15:56, 31 May 2019 (UTC)

About "the fact that we observe all galaxies accelerating away from the Earth is evidence that we are in the center of an expanding universe", see [9]. That statement is untrue, the fact that we observe all galaxies accelerating away from the Earth is NOT evidence that we are at the center of the Universe. Banedon (talk) 07:11, 1 June 2019 (UTC)

Uh, not all galaxies are moving away from us. The vast majority of them are moving away from us, but there are some that are blue-shifted, most notably the Andromeda Galaxy, which is set to collide with us roughly 4.5 billion years from now. SmallMossie (talk) 00:59, 26 June 2019 (UTC)

Spekkenian dark matter: axioms don't exist. axioms are a silly mistake.

Simple wave functions with few components, are easily disturbed. It's easy to distort the entanglement of two electrons. At larger orders of magnitude, many micro-arrangements exist, and even if we disturb a puny part of the "quantum [spin-alignment] network", most of our network maintains its overall characteristics. At even larger orders of magnitude though, even the overall system does have an extra level of generalized uncertainty. Thus generalized uncertainty does exist and has a measurable anti-Newtonian impact, and it appears in steps at larger orders of magnitude.

I live in Spekkensville and on our central plaza we have a statute of Robert Spekkens. The bronze figure is friendly and teaching; elaborating and pondering. It's not a strict/static statue. It has a natural pose. — Preceding unsigned comment added by 2A02:587:410B:9500:D156:EDB1:378E:2F4 (talk) 10:40, 30 June 2019 (UTC)

We have an article on Spekkens toy model but not on Robert Spekkens or Spekkensville -- is that a real place or totally bogus? Also "Spekkenian dark matter" seems to have no writings on it. Are there any publications on that topic? Graeme Bartlett (talk) 11:11, 30 June 2019 (UTC)

Hypothesis

It seems to me that with the "thought to be", that the paragraph is fine without mentioning hypothesis. More references for the first paragraph might be nice, though. It is inconvenient that DM is so hard to detect, though. Gah4 (talk) 14:09, 7 June 2019 (UTC)

The sentence states definitively that Dark Matter is a form of matter. Whether or not Dark Matter is actually a form of matter remains a scientific debate. — Preceding unsigned comment added by 2604:2d80:dd10:6700:e020:26b8:ad6e:85cb (talk) 08:23, 8 July 2019‎ (UTC)

Dark matter definitely is a form of matter - its density scales as a^-3 (see the technical definition section). Banedon (talk) 21:27, 8 July 2019 (UTC)

I would favor keeping the intro sentence as "Dark matter is a hypothetical form of matter, […]" It clarifies to the general public that dark matter has not yet been isolated or directly observed. Its existence is inferred from various astronomical observations and from our current understanding of gravity, and that is well-explained further in the intro. Saying it's a "form of matter" would imply that we know a lot more about it. — JFG ^talk 20:43, 10 July 2019 (UTC)

How about something to the effect that it is a type of matter of unknown nature. As JFG stated, its existence is inferred from various lines of observations, but we still ignore its nature or composition. Its existence does not seem hypothetical, but its substance/composition/nature. Rowan Forest (talk) 22:15, 10 July 2019 (UTC)

I spoke to a cosmologist recently who said that the evidence for dark matter was now so extensive that when he gives public-level talks, he simply says dark matter exists. I'm also certain that dark matter is a form of matter given how matter is defined by cosmologists (explained above). However I am ambivalent on whether to say it's a "hypothetical" form of matter; it seems like a minor matter and both having it or not is fine. Banedon (talk) 23:32, 10 July 2019 (UTC)Neil deGrasse Tyson has on multiple occasions called Dark Matter an unfortunate misnomer, as the term Dark Matter falsely conveys a conclusion science has not reached.

"Dark" means unexplained, not "hypothetical". Just like dark energy is defined as an unknown form of energy. Rowan Forest (talk) 01:22, 14 July 2019 (UTC)

That's certainly not true, see dark fluid. Banedon (talk) 10:00, 14 July 2019 (UTC)

85% should be 27% (see referenced CERN article)

It turns out that roughly 68% of the universe is dark energy. Dark matter makes up about 27%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the universe." (source https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy). ~/~ NASA & the CERN article PROVE that Wiki's "85%" is wrong. "Dark matter is a form of matter that is thought to account for approximately 85% of the matter in the universe...." ~ So the dude that reversed my correction should reverse his mistaking. — Preceding unsigned comment added by Kreematismos (talk • contribs) 20:10, 18 July 2019 (UTC)

The dude will respond here. CERN article says that DM is 27% of the contents (energy+matter) of the universe. Our article says that it is 85% of total matter (not matter+energy). So there is no contradiction. AhmadLX-)¯\_(ツ)_/¯) 20:48, 18 July 2019 (UTC)

Per AhmadLX, there's no error. If you're measuring by energy content then Dark Matter is about 27%. If it's by matter content then it's 85%. The article right now says "approximately 85% of the matter in the universe and about a quarter of its total energy density", which is correct. Banedon (talk) 22:27, 18 July 2019 (UTC)

The wording about the 85% is technically correct but leaves readers thinking the Wiki article is incorrect. 20:59, 19 July 2019 (UTC) — Preceding unsigned comment added by Kreematismos (talk • contribs)

The reader must be patient and read the whole sentence, which, as Banedon has mentioned above, says it is "approximately 85% of the matter in the universe and about a quarter of its total energy density". AhmadLX-)¯\_(ツ)_/¯) 21:30, 19 July 2019 (UTC)

Move discussion in progress

There is a move discussion in progress on Talk:Dark Matter (disambiguation) which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 09:01, 11 September 2019 (UTC)

Radial Acceleration Relation

I would like to insert the new paragraph "Radial Acceleration Relation":

"The dark matter contribution to the total acceleration of a galaxy can be seen as the difference between the total acceleration of a galaxy g and the contribution due only to the baryonic matter gb. In the first analyses it was thought that g, and therefore the dark matter contribution to it, was a universal function of gb only. However a later work and 72 Low Surface Brightness (LSB) galaxies determined a relation, called GGBX relation. The GGBX makes evident how the total acceleration of a galaxy g depends, not only on the baryonic acceleration gb, but also on other quantities that differ from galaxy to galaxy. These quantities are the baryonic fraction, the Hubble type of the galaxy and the normalised radius with respect to the optical radius Ropt. The GGBX deviates from the Newtonian relation at larger galactocentric distance and from the previous result at smaller galactocentric distance."

under the section "Observational Evidences". I think this paragraph add new material even if the discrepancy between theoretical and experimental galaxy velocity was already mentioned. Infact was first thought (S. McGaugh, Stacy; Lelli, Federico; M. Schombert, James (19 September 2016). "The Radial Acceleration Relation in Rotationally Supported Galaxies". Phys. Rev. Lett. 117, 201101 (2016).) that the dark matter contribution to the total acceleration of a galaxy was a universal function of the baryons therein present, while the recent article (Di Paolo, Chiara; Salucci, Paolo; Fontaine, Jean Philippe (17 January 2019). "The Radial Acceleration Relation (RAR): the crucial cases of Dwarf Discs and of Low Surface Brightness galaxies". The Astrophysical Journal 873(2) March 2019.) evidences how the dark matter contributes to the acceleration in a far more complex way than previously thought. I think it is good to mention recent results to give the idea of how things are proceeding in the study of dark matter and that things are far less simple than thought. Istudentphysics (talk) 09:48, 17 November 2019 (UTC)

[1] "Dark matter on the move". ras.ac.uk. 28 December 2018. Retrieved 6 January 2019.

[1]

Does not interact with light, but still detectable through gravitational lensing? Apparent contradiction needs clarification

"Matter" article says Dark Matter = 23% of Universe, this article says 27%

Indirect detection

Bosonic spin of galactic photon regions aligned as fermionic via spatiotemporal curvature (compound supersymmetry)

Darkmatterion's name is Dark Matter Particle

Dark matter and black holes

Neutron Groups as a dark matter candidate

Dark matter: Hypothetical or not?

Table?

Summary Contains Outdated Information

This article could mention ultracompact minihalos

dark matter as a partial (imperfect) renormalization side-effect

Question

Emergent gravity - Is it a figment?

Observational evidence section

Alternative theories section

Embedded lists

See Also list could be shorter

List divided into subheading

The Structure of Scientific Revolutions: sometimes we go down dead ends

Suggestion re the lede...i.e. Date of Discovery!

Support removal of reference Sharpe, Dan (2017)

POV check needed

Dark matter no more?

Inaccuracy in Galaxy Rotation Curves

Gravitational microlensing and Circumstellar disks

External links modified

Lede misleads: dark matter may or may not be baryonic

Article issues

Lede

This article fails criteria "Neutral point of view"

Improving lead language

Electrons are leptons not baryons

Mass-energy + observable

Galaxy without dark matter

DM in Universe v/s Observable Universe

theory

Missing source

Invitation to submit to the WikiJournal of Science

Reasons for submitting

What we need

How to submit

Why this article

Shear modulus of the void at large orders of magnitude

Kepler's third law, not second

Dark matter attempted detection using network of atomic clocks

Clarification of sentence in section Dark matter aggregation and dense dark matter objects

Clarification of sentence in CMB section

Include results from study of Dark matter heating in dwarf galaxies?

Lyman alpha forest subsection of section Type Ia supernova distance measurements needs expansion

Why remove section on Galaxies with less or more evidence of DM

Assumption

Spekkenian dark matter: axioms don't exist. axioms are a silly mistake.

Hypothesis

85% should be 27% (see referenced CERN article)

Move discussion in progress

Radial Acceleration Relation