Talk:Dark matter/Archive 2

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Archive 5

Evidence

I didn't feel that the sections on evidence for dark matter and composition of dark matter explained it enough to understand well. How do we know that it's not just regular matter that's not illuminated for various reasons? Like dust particles in interstellar space; planets, astreroids, and dust particles in star systems; or just electrons or photons or whatever floating around in space? Or maybe I'm not following, and those are likely candidates. --Booch 20:01, 6 September 2005 (UTC)

I added half a paragraph. Some references were given earlier in the Discussion, now archived. —Długosz

That's something that always bothered me about dark matter. I've read many sources that state that it simply can not be 'normal' matter, and this seems to be common enough that there must be some reason, but I've yet to find anything or anyone who can give me the mechanics that rule out 'normal' matter. Granted, it's probably a complex reason, but I have phylisophical issues with dark matter anyway, so I'm somewhat demanding in such regards. ;) --70.242.163.65 22:09, 15 October 2005 (UTC)

(Disclaimer: I'm not an astrophysicist.) Well, suppose, as you say, that the dark matter is composed of clumps of "normal matter", such as clouds of hydrogen atoms. Judging by the gravitational effects, these clouds would have to be pretty dense. But the denser they are, (i) the more blackbody radiation they emit, (ii) the more starlight they absorb, and (iii) the more likely they are to simply clump together to form stars. All three effects ought to be observable, which means they wouldn't be dark matter anymore. Astronomers do see hydrogen gas clouds floating around in space, but these clouds are dilute. -- CYD

How can you have philisophical issues about a scientific discovery? All physicists are saying is that there's stuff out there, and it acts like matter, but we can't see it. (And so, as CYD says, it can't be normal matter--because if it were, we could.) Then we start throwing out ideas about what it might be, one of which might be right and most of which will have to be wrong. -- SCZenz 00:25, 16 October 2005 (UTC)

Well, it would be more accurate to say I have philisophical issues with the universe being fated to heat death, which is an outcome of dark matter. But that's another discussion entirely. As for CYD's points, they are better than most I've seen, but I have issues with the idea that the matter has to be so dense that detection is nesesitated. But I'm not an astophysicist either, so I couldn't say anything about the details of the observations that give rise to the need for some kind of dark matter. --70.242.163.65 18:58, 16 October 2005 (UTC)

The stuff that appears to be dooming the universe to heat death is Dark Energy, which is different. As for whether invisible ordinary matter would reflect/emit enough light or not, CYD gave the ideas; to prove they work we'd need to do some laborious calculations. I don't know how to do 'em either, but I trust the experts; whenever I learn enough to calculate something I'd only been told as a fact before, it turns out the fact is right. -- SCZenz 20:08, 16 October 2005 (UTC)

Silk damping

Well, i'm not an astrophysicist either (so i don't consider myself adept enough to contribute to this article directly), but recently i heard about an effect known as 'Silk damping', which is said to be a very strong evidence for the existence of dark matter. It says that radiation in the early universe was too strong for baryonic matter to lump, and whenever some baryonic particles aggregated, the electromagnetic radiation, which was just everywhere, tore them apart again. Therefore, compaction of baryonic matter was only possible when the universe was about 380.000 years old, at the time when radiation decoupled from matter and the universe became 'transparent'. We have a souvenir photo of this point of time, which is known as the cosmic microwave background and it shows density fluctuations, which can only be explained by matter which must have aggregated much earlier, and which must not have interacted with radiation at all, or it would'nt have been able to lump because of the radiation. I'm not able to describe this process in a scientifically accurate way (nor am i a native English speaker), but maybe someone else knows more about Silk damping and is able to add it as evidence to the article (?) --82.141.54.30 07:33, 13 December 2005 (UTC). .

galaxy disintegration?

I have fixed a mistake in the article which is unfortunately widespread. Dark energy is accounted for the universe acceleration whereas dark matter is accounted for the prevention of galaxies disintegration.

--Tomer Ish Shalom 02:26, 9 Jun 2005 (UTC)

I have never heard of this disintegration stuff before. Could you provide references? --Philipum 07:05, 9 Jun 2005 (UTC) www.groklaw.net/article.php?story=2005061901241583

---

I would be glad to. A popular explanation can be found at dark matter tutorial Note in particular the concept of rotation curves for galaxies.

--Tomer Ish Shalom 10:30, 9 Jun 2005 (UTC)

Dark energy does indeed account for the acceleration of the universe. The reason that confusing element was in the article is that it was once thought, before measurements of dark energy, that precise measurements of the amount of matter in the universe would decide the ultimate fate of the universe. It is now thought that the universe is geometrically flat, so this is not such an issue any more.

This galactic disintegration stuff is misleading. It is true that if all the dark matter in galaxies spontaneously disappeared, the outer reaches of these galaxies would probably disintegrate. (The central part of the halo, where most of the visible matter is – and indeed where we are – actually contains relatively little dark matter and would be largely unaffected.) But it is not as though dark matter is what keeps galaxies from disintegrating, as they never would have formed in the first place without it! I have tried to revise the article to make this a little clearer. –Joke137 20:48, 9 Jun 2005 (UTC)

Jaan Einasto

What exactly is Jaan Einasto supposed to have done? This page and the article under his name call him "one of the discoverers of dark matter," but there are no more details. According to the article under his name, Einasto has been active in physics long after the dark matter problem was discovered, so it doesn't really make sense as it is. If this claim is true in some sense, it requires some elucidation. -- Reuben 04:00, 20 Jun 2005 (UTC)

I agree. It makes no sense to have a people section without a clear idea of what each person contributed and in which the people seem chosen at random. And while I don't doubt that Einasto has worked on the dark matter problem, his major interest seems to be superclusters and voids: the formation and morphology of structure on the very largest scales. He seems to have contributed quite a bit to this. –Joke137 13:38, 20 Jun 2005 (UTC)

Dennis Sciama

OK, so now somebody's claiming Dennis Sciama as "generally credited" with introducing the idea of dark matter. Fritz Zwicky inferred the existence of dark matter and apparently coined the term in 1933, when Sciama was seven years old! I'm removing the claim and the link to Sciama. See for instance this review article: [1]. --Reuben 04:55, 16 August 2005 (UTC)

Yes, that was me. I agree that I was probably wrong, shouldn't have put those claims in, and I am glad you took them out. I replied at greater length in Talk:Dennis_William_Sciama. Sorry, I won't be that careless again!

If anyone reading this is interested in obtaining some oral history regarding the Golden Age of General Relativity (1960-1975) (an article yet to be written), please comment at User_talk:Hillman/Wikiproject_GTR_draft. TIA---CH (talk) 07:33, 16 August 2005 (UTC)

Popular culture

Almost all the popular culture references need toi be removed. They are about matter which is dark, not about dark matter. Ken Arromdee 02:06, 22 August 2005 (UTC)

Even if one finds the section 'Popular culture' appropriate, it should be moved elsewhere, because it is becomming too large compared to the main DM article. A new article should be written and one should give one link to that article from here. Count Iblis 11:56, 22 August 2005 (UTC)

Cooperstock and Tieu preprint

The pre-print by Cooperstock and Tieu is featured on Slashdot [2], so naturally it has to be important, so naturally we have to mention it in the article...

Actually, it doesn't, and we don't. The consensus of workers in the field seem to be that Cooperstock and Tieu are wrong (see [3], [4], and the lack of citations for C&T [5]). Given that we don't feature other pre-prints from astro-ph in this article, I'd suggest removing the reference from the article, until such time as it gets accepted by the mainstream astro community. It's not encyclopaedic. -- CYD

One critical article does not a "consensus" make. -- Anonymous

If the astrophysics community felt that C&T are on the right track, there would be a deluge of follow-up articles. It's the wrong articles that tend to be ignored; in this case, the existence of even one debunking article is plenty. -- CYD

The article is still fairly recent. I wouldn't use the "lack of citations" argument for recent articles. But in this case the fact that you have one citation debunking it speaks volumes. Alternatives to dark matter, even if they are viable, are not very popular anyway. Such articles will probably attract a few citations per year, like the Phys. Rev D article I quoted below.Count Iblis 22:00, 11 October 2005 (UTC)

I agree. This can be mentioned in the section about alternative explanations. This particular explanation is problematic as you rightly point out. Still, it is instructive to mention it together with the comment by Korzynski, just to illustrate that explaining the (apparent) dark matter isn't very easy! The introduction now mentions dark matter as a fudge factor, but it is a non trivial fudge factor because it has to be consistent with so many other things as well.

There are some other recent articles that can also be mentioned there. A few weeks ago I saw an article in arXiv suggesting that the renormalization group running of the gravitational constant could also explain rotation curves, see here and here. Count Iblis 22:50, 10 October 2005 (UTC)

Alternative Explanations

Yes, I would like to see more in this section, including an explanation of Cooperstock and Tieu and what the problems are with their theory, sicne I haven't really been able to find that information reliably elsewhere. I have also read some (unreliable sources which say that electromagnetic forces on plasma may explain galaxtic rotation. See here which is where I first saw that idea. I don't know about it's validity, but I think the alternative explanations section needs to be expanded in general. -NMB

The page you link argues with most of modern physics, for often trivially fallacious reasons. Like the relativistic addition of velocities "obviously doesn't apply for material objects". I am rather disinclined to set a precedent of writing down, and then arguing with, every silly little thing they say. As for why Cooperstock and Tieu are wrong, the abstract of the one paper disagreeing with them says it pretty well:

Recently a new model of galactic gravitational field, based on ordinary General Relativity, has been proposed by Cooperstock and Tieu in which no exotic dark matter is needed to fit the observed rotation curve to a reasonable ordinary matter distribution. We argue that in this model the gravitational field is generated not only by the galaxy matter, but by a thin, singular disk as well. The model should therefore be considered unphysical.

What that means is, their model had a disk of zero-thickness and non-zero mass that was producing the rotation curves, and they didn't realize it. I guess that's worth half a sentence, which I'll add now.

My point is, we should certainly include plausible alternative explanations, but not ones which aren't. -- SCZenz 19:34, 15 October 2005 (UTC)

Hi SCZenz! If you have time then perhaps you can put some stuff in from this article and this one. These ideas seem to be less problematic than the Cooperstock/Tieu stuff. Count Iblis 01:13, 16 October 2005 (UTC)

Cooperstock and Tieu now have a new preprint out. The paper included a modified solution that no longer requires the singular disc.

In alternative proposals, I think there is something missing about scalar-tensor theories. There are many of them so at least the name should be pronounced in the text. And some of them are interesting, especially, since they are popular for explaining inflation and since Higgs fields (which are scalar fields) couple in a gravitation-like manner to the particles that get mass through them (Dehnen, Frommert: Int.J. of Th. Phys. 29(4):361 (1990), 30(7):985 (1991)). --141.70.111.178 15:20, 29 October 2005 (UTC).N.M.B.R.

With regard to the removal of references to Plasma Cosmology: Could the authors at least put in a link to Non-standard cosmologies somewhere on this page. Now I'm off to Wiki research instead. Bye. Alex.

Plasma physics edits

Count Iblis deleted the following: The role of electrical and magnetic interactions may explain missing mass. Electromagnetism can impart force between masses up to 10 to the power of 39 greater than that of gravity, over vast distances. Gravitational effects would be overwhelmed. See Plasma cosmology.

with the comment Plasma cosmology is not serious science. But conventional cosmology has a big problem: We know there are large coherent magnetic fields by observing spectral line splitting: Inference: There are large coherent charge flows occuring: Inference: There are large electric currents in space. We have laboratory experiments showing plasma naturally forms current-carrying filaments. We know 99% of the visible universe is plasma. And we know electrical forces are far more powerful than gravitational forces. eg in a proton-proton interaction the repulsive force is approx 10 to the power of 37 times greater than the gravitational attraction. So why is conventional cosmology so focussed on gravitational interactions? Why isn't there space here for even *mentioning* Plasma Cosmology? How can such censorship be scientifically justified?

Your comment has several parts that need to be responded to individually. I'll try to separate the points out for clarity.

1. Please sign your comments. It's easier to come to a consensus that way, and it can be a useful token of good faith.

2. It's fair enough to ask Count Iblis to justify his edit on the discussion page (that is, right here). If you haven't already, I suggest you put a note on his talk page - not an argument, just a polite request that he explain his edit. It's likely that some reference to plasma cosmology would be acceptable.

3. Arguing for or against the correctness of a scientific idea in Wikipedia discussion pages doesn't tend to be very productive. Although some individual participants may be very knowledgeable, it's not for Wikipedia to decide whether plasma cosmology has anything to it or not. To say it another way, a Wikipedia article is not science, even one that's about science. The content of the article is justified encyclopedically, not scientifically - Wikipedia doesn't follow the scientific method.

4. Using the word "censorship" can only be inflammatory. It won't help get the article to a state you can be happy with.

--Reuben 04:25, 19 December 2005 (UTC)

Basically, per Wikipedia:No original research and Wikipedia:Reputable sources, we only use scientific information from cited, peer-reviewed journals or other reputable sources. Does that help explain it? -- SCZenz 04:29, 19 December 2005 (UTC)

Sure, that's part of what I was trying to express. (The original formatting in my comment may have left it unclear who wrote what; I've tried to fix that). --Reuben 04:38, 19 December 2005 (UTC)

Image necessary?

That image in "Alternative explanations" is too small for the text to be readable, ugly, and does not provide any information to supplement the text of the article. I suggest removing it. -- CYD

I'm inclined to concur. Any objections? -- SCZenz 18:13, 29 October 2005 (UTC)

I agree. This looks more like an advertisement for isracast than useful information. It would be nice to replace this by an overview of dark matter candidates containing links to wikipages. Also Dark matter in popular culture should be moved to a different location.Count Iblis 21:22, 29 October 2005 (UTC)

Lack of clarity

Concerning this passage in the beginning "If dark matter does exist, it vastly outmasses the "visible" part of the universe [1]. Only about 4% of the total mass in the universe (as inferred from gravitational effects) can be accounted for. About 23% is thought to be composed of dark matter. The remaining 73% is thought to consist of dark energy, an even stranger component, distributed diffusely in space, that probably cannot be thought of as ordinary particles."

First off, "the remaining 73%" does not make sense because it is 77% that remains. If the number 73 is correct, then it should not be designated as "the remaining". If the number 77 is correct then it should be changed to this.

And also, what is meant by "Only about 4%...can be accounted for."? Only 4% can be accounted for by what exactly? I assume this means that only 4% can be accounted for by "visible matter"..but this is not clear.

• Your second point is right, that sentence should be clarified; I'll fix it now. Your first point is wrong: 4% for visible, 23% for dark matter, and 73% for whatever-it-is, adds up to 100%. -- SCZenz 22:21, 13 November 2005 (UTC)

What's 'dark'? VIRGOHI21 is reportedly made of visible hydrogen, right? So then it's not dark? Or is it made visible by its absorption spectrum, not through its radiation spectrum, and that's why it's considered 'dark'? Is interstellar hydrogen (which is made of regular baryons) dark or not? An astrophysicist recently told me that black holes, and interstellar hydrogen and helium are all NOT dark matter. Please update the article to clarify if you know the answers... Thanks. - Elvey, ex-physics student. If there are multiple widely used definitions, and/or one that's dominant, an explanation would be great. (I wonder if the (probably insignificant) mass of the photons flying about are already factored in to calculations as non-dark matter.)

Cooperstock and Tieu

The Cooperstock and Tieu papers are great and fascinating to people following the field, but seeing as how we're updating the page every week or so as one side launches a challenge on the other, perhaps it is not yet "encyclopedic" knowledge. Why not just clip it from the article until the community decides whether the work is important and correct? -- Xerxes 16:35, 27 December 2005 (UTC)

Hi Xerxes, my preference would be to replace that paragraph by one or two sentences, saying that Cooperstock and Tieu have formulated a model that seems to predict a thin disk of (possibly exotic) matter at the symmetry plane of the galaxy.Count Iblis 16:54, 27 December 2005 (UTC)

Actually, C&T make some very compelling arguments that the alleged disk of matter is simply a mathematical curiosity, with no physical significance. The singularity arises from their use of the absolute value function on the z coordinate, which works everywhere else, but produces a discontinuity with the derivatives at z=0. I'd prefer a statement about the disputed nature of the C&T model, but leave out specific criticisms, especially those that require a fairly detailed understanding of the C&T model to understand.70.168.137.34 03:28, 18 July 2006 (UTC)

anti-Dark matter?

Is it possible that there exists some type of anti-Dark matter that balances the effect of Dark matter on the universe? If there isn't, could it be created? --Guthrie 20:42, 5 January 2006 (UTC)

I'm not a scientist, but I'm sure the honest answer is: show me some dark matter first, and then we'll know more about its properties. Art LaPella 21:13, 5 January 2006 (UTC)

Matter and antimatter behave identically with respect to gravity, since there is a strong symmetry (CPT) that insists that antiparticles have exactly the same mass as particles. So anti-(dark matter) could not be distinguished from dark matter observationally (via lensing or rotation curves or whatever). -- Xerxes 21:57, 5 January 2006 (UTC)

It depends on what the dark matter actually is. Some dark matter candidates have distinct antiparticles, and some don't (like neutralinos). However, if they do exist, they would not balance out the effect of the dark matter; the particles and antiparticles would interact with gravity in the same way, like Xerxes said. In fact, we only know about dark matter through its gravitational effects, so if anything did cancel out those effects, we would not know it was there! You might be thinking of something like dark energy. It doesn't cancel out the effects of dark matter that we see in galaxies or galaxy clusters, but it does dominate the dynamics of the universe on the largest scales, making it expand faster and faster. This acceleration is the opposite of what you would see if the universe contained only matter (including dark matter). You can find out more in the dark energy article. --Reuben 04:44, 6 January 2006 (UTC)

It's possible that dark matter is a third party when compared to the relationship between matter and anti-matter, and may be the only type of matter that won't experiance anhillation.--Dansanman 06:26, 3 February 2006 (UTC)}

Dark matter creating more questions than answers?

It seems to me Dark matter creates so many questions, it violates Occam's Razor. I will list some of these:

1) Dark matter is hypothesised to counter discrepancies in observed gravitational phenomena. Dark matter must by definition interact with ordinary matter gravitationally but not electrically, magnetically or through nuclear forces. In other words, pass straight through ordinary matter. Given that dark matter must interact with ordinary matter gravitationally, there will necessarily be energy transfer between dark matter and ordinary matter domains. If dark matter were to travel through the earth, a mass which interacted with ordinary matter only through gravity would experience a damping effect. The movement of a gravitational point in matter will create movement in ordinary matter, resulting in a conversion of dark matter kinetic energy into heat in ordinary matter. In other words, if dark matter itself were itself subject to newtonian laws, it would be snared by the gravitational and damping effects of ordinary matter, and vice versa. Ordinary matter would be damped by the effects of dark matter. Dark matter would gradually accumulate at the centers of gravity of ordinary matter. For example, a proportion of dark matter would accumulate at the earth's core, the Sun or any other ordinary matter massive body.

Assuming dark matter interacts with dark matter in a similar manner to ordinary matter interacts with ordinary matter: Further dark matter passing in the direction of earth would increasingly be stopped by dark matter within the earth. The earth's gravity would then be much higher than expected for it's density calculating for ordinary matter alone. A large accumulation of such dark matter may exceed the mass of the earth, leading to dark matter extending beyond the earth's crust, creating a measurable damping to the movement of ordinary matter at the earth's surface. If a large amount of dark matter accumulated centered around the earth's core, a dark matter meteor could destroy the earth through an enormous shift of the center of gravity of the dark matter, and the energy coupling which would accompany such a shift of centers of gravity.

If on the other hand, dark matter did not interact with dark matter other than through gravitation, just like it is supposed to interact with ordinary matter, I hypothesise that dark matter would tend to accumulate into extremely intense gravitational points, such as black holes. Without the interaction and pressure caused by ordinary matter, such dark matter would possibly have disappeared into a dark matter induced black hole early in the universe, taking much ordinary matter with it. Any gravitation-only interacting dark matter still in the universe would still tend to accumulate at the centers of any mass, and tend to induce black holes through extreme point gravity. The notion of dark matter appears to me to create more questions than answers. Given that dark matter is itself a hypothesis without evidence, i think it appropriate to offer my counter hypothesis and speculation.

If we have evidence that most celestial bodies appear much more massive than they should be, and detect gravitational damping around the earth which doesn't appear in deep space, this would provide evidence of dark matter. Nick R Hill 23:19, 11 February 2006 (UTC)

Hi Nick, excellent questions. The points you raise are absolutely things that have to be taken into consideration when deciding which dark matter models are viable candidates for describing the real world. These considerations can rule out some models, but none of them is a killer for particle dark matter in general. One note on terminology: dark matter that interacts weakly with ordinary matter (through gravity and perhaps weak force) but more strongly with other dark matter particles is called "self-interacting dark matter" (and the alternative is "non-self-interacting dark matter").

Exotic particle dark matter such as WIMPs can indeed be captured at the center of the Earth or the Sun as you suggest, or at the galactic center. However, the cross-section for this kind of capture in ordinary WIMP models is not large. If the WIMPs interact only gravitationally, the energy lost by a WIMP passing through teh Earth or the Sun would be totally negligible (although I agree it's nonzero). With some other interactions, like the weak force, you can get some significant population of captured WIMPs at the center of the Earth or the Sun. This is something that's actively searched for in indirect dark matter searches that look for signs of WIMP-WIMP annihilations in the Earth, the Sun, or the galactic center. Any model with high enough cross sections that most of the dark matter gets trapped would be ruled out, but I don't think this is a very stringent constraint.

It's very hard to make non-self-interacting dark matter collapse on small enough scales to make something like a black hole. In order to get such a collapsed object, you need some way to get rid of the extra energy and angular momentum of the particles. WIMPs don't have any good way to do this, so basic WIMPs are expected to be more or less uniform on the scale of a galaxy. You can add some self interactions to make them clump on various smaller scales, but any theory where they disappear into black holes is ruled out. If you read about black hole accretion disks, you will see that it's actually harder than you may think to get stuff to fall into a black hole.

So in summary, your questions are important ones to ask about any given dark matter model. There are lots of viable models that pass these tests, though. --Reuben 08:13, 12 February 2006 (UTC)

Dark Matter Hypothesis for Mercury Perihelion Precession

Hello,

This is an excellent article. Does anyone agree that it might benefit from mentioning that a century ago, unknown "dark matter" near the sun was proposed as a model to explain the precession of the orbit of Mercury, which was later completely explained by Einstein's General Relativity. I find it interesting that today is not the first time in history that dark matter was proposed to exist to explain an anomoly in astronomy. There are interesting (if superficial) parallels between the situation we now face, and that faced by scientists a hundred years ago. Spebudmak 16:14, 25 April 2006 (UTC)

Sounds good. What journal references are there? One might also mention that precession of the perhelions sets an upper bound on the density of dark matter in the Solar System. The bound is in agreement but pretty far above the expected value. -- Xerxes 16:23, 25 April 2006 (UTC)

This is a bad idea and would make casual readers link dark matter to the precession of Mercury's orbit. And besides, nothing like dark matter was invoked to describe Mercury's orbital motion in the first place. I challenge you to find an article that invokes dark matter to describe Mercury's orbit User:Astroceltica.

I´m not simply trying to invert the burden of proof here, as if in defense of Spebudmak, but just for curiosity, how was the history then? They´ve just left it unexplained, it was never a problem, some hypotheses were made, but none with anything vaguely labelable "dark matter" (since it was presumably not labelled so at that time, as I guess the quotation marks imply) or what? --Extremophile 01:04, 11 May 2006 (UTC)

molecular hydrogen hypothesis

I think that maybe something in this sense could be added. Paul Marmet proposes that molecular hydrogen could fit the role of mysterious dark matter, as it is the most common element in the universe, and also, is more stable in the molecular form than as a atom, but also harder to detect. Here is a text for people more knowledgeable and better writers than me to analyse and eventually add something to the article:

• Discovery of H2, in Space Explains Dark Matter and Redshift

--Extremophile 00:54, 11 May 2006 (UTC)

Please don't. This is fringe stuff. The link is to an article from 21st Century Science and Technology, which is Lyndon LaRouche's magazine of fringe science. If you read this and Marmet's other articles, you can eventually trace everything back to Marmet's rejection of GR and SR on philosophical grounds. --Reuben 01:38, 11 May 2006 (UTC)

I would not do anything myself, but I would find interesting and even desirable, despite of being fringe stuff. Much of actual mainstream was once fringe. Wikipedia has things that, at least in my opinion, are far less encyclopedic than fringe science, such as whole categories about pokemon and articles such as "towel". And since these fringes are not just plain crackpots like that timecube guy, I think that at least some brief mentioning/linking to main articles would be interesting. --Extremophile 20:17, 11 May 2006 (UTC)

"When light passes through normal molecular gases, such as oxygen, nitrogen, and others, radiation excites the resulting electric dipole in the molecule, and some energy is scattered or absorbed. However, in the case of molecular hydrogen, there is no dipole moment, so that no radiation can be absorbed or emitted. "*Discovery of H2, in Space Explains Dark Matter and Redshift This is not accurate. Hydrogen molecules DO radiate in their rovibrational states, but they must be heated to temperatures of about 100 K. But interstellar space is usually colder than this, so thats why they are not seen to radiate much. Even so, electromagnetic radiation from the visible portion of the spectrum up to higher energies is enough to dissociate hydrogen molecules, so thats why hydrogen in its molecular form only exists in large quantities in dark clouds. These clouds are rare and not very massive, so hydrogen molecules cannot account for the missing mass. The universe contains much more atomic hydrogen, which is easily detectable and has been accounted for. 01:55, 11 May 2006 (UTC)User:Astroceltica

COOUP project

Is it real or is it vandalism? I couldn't find it on Google or Google Scholar, but maybe it's misspelled. Art LaPella 01:44, 11 May 2006 (UTC)

I think the editor was confused. From the heavy water reference, it sounds like he might be thinking of SNO. The name is similar to COUPP, which is a really cool WIMP detection project using bubble chambers. So maybe it's the result of confusion between COUPP and SNO. --Reuben 01:51, 11 May 2006 (UTC)

EGRET data

Somebody knowledgeable should include the findings by Wim de Boer and his team - they found traces of Dark Matter Annihilation in the data of the EGRET (telescope). http://www.edpsciences.org/articles/aa/abs/2005/46/aa3726-05/aa3726-05.html --217.236.226.31 08:40, 12 May 2006 (UTC)

Certainly an exciting claim, but their model seems pretty dodgy. See, for example, criticisms in Is the dark matter interpretation of the EGRET gamma excess compatible with antiproton measurements?. There is no need to include every recent extraordinary claim without substantial proof in Wikipedia; let history sort things out for a bit. -- Xerxes 16:21, 12 May 2006 (UTC)

//I disagree with Proffesor Shanel, on her views of Dark Matter. What she says about dark matter being 80% of the universes matter is totaly wrong and she is a weirdo!!!

Dark matter rewrite

The page was in need of some cleanup/rewrite, and so I took it upon myself. I think that the "alternative explanation" part needs to be paired down especially since MOND is somewhat fringe. It doesn't need to be removed, just contextualized. We also need some more references, but I think this page has improved substantially. --ScienceApologist 12:09, 19 May 2006 (UTC)

Nice edits. This page had been drifting for a while, and your cleanup has done a lot to bring it back into line. Perhaps it would be good to think about how to organize dark matter articles overall: as it is, the same topic is often covered several times in different articles, without any consistent scheme. There are a lot of different ways to divide the topic: hot vs. cold, theory vs. experiment, direct vs. indirect detection, baryonic vs. nonbaryonic, by candidate, by experiment... --Reuben 18:09, 20 May 2006 (UTC)

Dark matter explains several anomalous astronomical observations

Isn't dark matter inferred from several anomalous astronomical observation, in which case it may explain them, but to suggest that "Dark matter explains them" is a truth which I don't think has yet been met? --Iantresman 17:35, 28 May 2006 (UTC)

Dark matter is a catch-all term that refers to the explanations for concomitant observations listed in the article just as much as it refers to the particles themselves. Even if dark matter turns out to be epicyclic in nature (and there's pretty good evidence that this probably isn't the case), it still will be able to explain the observations. --ScienceApologist 19:30, 28 May 2006 (UTC)

I think that Iantresman means that we don't know for sure that dark matter exists and that any explanations based on it (even if it is not epicyclic in nature) could turn out to be incorrect. This is a matter of language. You could say that dark matter does explain certain phenomena even if in reality dark matter has nothing to do with them. The fact that a ceetain theory explains certain phenomena doesn't rule out other theories explaining these phenomena. Count Iblis 21:57, 28 May 2006 (UTC)

The fact that a ceetain theory explains certain phenomena doesn't rule out other theories explaining these phenomena. --> Precisely correct, which is why the wording needs to stay as written that dark matter explains phenomena. It doesn't preclude other explanations! --ScienceApologist 22:01, 28 May 2006 (UTC)

So although it may not be relevent to this article, by writting, for example, that "interacting parallel Birekland currents explains anomalous galaxy rotation curves without the need for dark matter", because it doesn't rule out other theories, is a fair wording? --Iantresman 00:48, 29 May 2006 (UTC)

Almost. The issue would be in what precisely "interacting parallel Birekland currents" means. Since these phenomena exist independent of galaxy rotation curves, it would be a requisite to explain a detailed observational argument for their existence (what the evidence is, why they haven't been observed directly, etc.) If an article that discussed such things contained these descriptions and if it is clear that the "interacting parallel Birkeland currents" in question refer directly to this postulate, then the wording would be fine. If you are interested in writing such a piece, I'm more than happy to help you. --ScienceApologist 03:16, 29 May 2006 (UTC)

Alternative theories

Regarding Alternative theories, can I suggest a one or two line introduction which perhaps categorises them type (if that's appropriate), or chronologically, as they all appear to run together. Unfortunately I do not enough knowledge of all the alternative theories to do this myself. --Iantresman 17:40, 28 May 2006 (UTC)

We do need to clean up this section. Take a crack at it, sure. --ScienceApologist 19:30, 28 May 2006 (UTC)

I've just trimmed down this section.Count Iblis 21:46, 28 May 2006 (UTC)

more alternative theories

how come this article takes a completly non-theistic aproach to explaining the forces that guide the universe? wouldn't it be better to show at least some more diverse alternative theories than this?--F.O.E. 13:38, 31 May 2006 (UTC)

This particular article is not really about force, and the Wiki article on force is about that force which can be measured qualitatively. However, you may find that the article on Force (disambiguation) is more relevant. --Iantresman 13:44, 31 May 2006 (UTC)