Talk:Dark matter

Earlier reference to dark matter

The earliest reference to "dark matter" appears to be by Arthur Eddington in 1917: "Some of the regions are in the galactic plane, where obscuring matter is generally suspected -- and, indeed, is known to exist in certain parts. It would seem that the dark matter must be very local."; Eddington, A. S., "Researches on globular clusters" The Observatory, Vol. 40, p. 394-401 (1917) And by Henry Norris Russell in 1921: "In view of the great numbers of dwarf stars, which give out far less light in proportion to their masses, and the existence of unknown quantities of dark matter, it is probable that the radiation per unit mass for the Galaxy as a whole is much less than this"; Russell, H. N., "Radiation pressure and celestial motion" Astrophys. J., 53, 1-12 (1921)

So what does Zwicky write, which differentiates his "dark matter" from those of Eddington and Russell? I see that Eddington talks about an "obscuring" matter which is not necessarily the same as a "dark mass", but both Eddington and Russell would have been aware that dark obscuring matter must have mass. --Iantresman 08:32, 20 June 2006 (UTC)

It seems that Zwicky's contribution was not in identifying dark matter, but suggesting that in Nebulae, "the gravitational interactions of its component masses is so high as to cause it to rotate like a solid body".[1]. But earlier commentators suggest "dark matter" in relation to galactic rotation, eg.:

"Photos of the region in Sagittarius where the nucleus is supposed to exist, reveal sufficient dark matter to obscure a mass sufficient to account for the observed rotation." Harper, W. E., "Astronomical Research during 1929" (Retiring President's Annual Address), (1930) Journal of the Royal Astronomical Society of Canada, Vol. 24, p.97[2]

Isn't the development of "dark matter" something along these lines:

• Obsuring dark matter exists (Eddington/Russell)
• Dark matter affects nebular/galactic rotation (W. E. Harper, 1930)
• Dark matter affects rotation like a solid disk (Zwicky, 1933, 1937)
• Dark matter is non-Baryonic (attribution, date?)
• Differentiation of Cold Dark Matter and Hot Dark Matter (attribution, date?)

--Iantresman 09:23, 20 June 2006 (UTC)

Eddington, Russell, and Harper are talking about the dynamics of light obscuring matter which is really just gas and dust of the interstellar medium. What's more, Zwicky didn't measure the rotational velocities, but only velocity dispersions of clusters. The attribution to Zwicky for a "discovery" of dark matter is really something of an honorary title because no one would have remembered Zwicky's work if it hadn't been for Rubin and others finding other velocities that didn't match the mass-to-light ratios. There is sometimes some confusion about whether "dark matter" could just be normal matter that's "difficult" to see (for example MACHOs), but the determination of the non-baryonic nature of dark matter really happens when detailed CMB studies come out predicting that such material should be in the proportions that dark matter is supposed to be in. I hope this helps explain the sequence. --ScienceApologist 14:02, 20 June 2006 (UTC)

• So what's the difference between Baryonic dark matter and that of Eddington, Russell, and Harper?

Mostly context and the way in which it is observed. The "dark matter" of Eddington is observed to exist because of dark nebulae. Baryonic dark matter (if it exists as such) is observed to exist because of gravitational effects. --ScienceApologist 14:56, 20 June 2006 (UTC)

• What distinguishes Zwicky's dark matter from that of Eddington, Russell, and Harper? --Iantresman 14:46, 20 June 2006 (UTC)

The dark matter of Zwicky's is a gravitational mass while the dark matter of Eddington is a material that is obscuring light. --14:56, 20 June 2006 (UTC)

• Presumably, Zwicky's dark matter is not non-Baryonic matter, which I though is the most commonly thought of, type of dark matter? --Iantresman 14:46, 20 June 2006 (UTC)

Zwicky didn't inquire into the nature of the phenomena causing the observations, he just reported unusually high velocity dispersions for galaxy clusters. --14:56, 20 June 2006 (UTC)

In which case "dark matter" is all quite similar; it's method of observation is what distinguishes Zwicky from the others. Baryonic dark matter could be Eddington's... and Zwicky just proposed another way to try and detect it? --Iantresman 15:18, 20 June 2006 (UTC)

I'm not sure your characterization is exactly correct -- Zwicky didn't really make any claims on the kinds of matter doing the gravitating other than it was required by Newton's Law of Universal Gravitation, but it is true that to a certain extent baryonic matter could be the same type as that seen in dark nebula, except with improved techniques for observing these nebula in other wavebands, the matter in them is far from dark. CO emission, in fact, is rather bright in Eddington's "dark nebula". So it's not exactly baryonic "dark matter" in the usual sense of dark matter. --ScienceApologist 16:15, 20 June 2006 (UTC)

Didn't William James Sidis predict dark matter before Zwicky? In his book "The Animate and the Inanimate" and according to the wikipedia article on William James Sidis, he proposed the existance of dark matter. This book was published in 1925, and the article says Zwicky proposed its existence in 1933. Shouldn't this receive mention in this article? --Anonymous 17:09, 08 July 2006

From the Wikipedia article in question, I can only gather that The Sidis book where the "prediction" takes place is a)about cosmology, b) often (apparently erroneously) taken as a prediction of black holes, and c) according to the editor, a prediction of dark matter. I don't have the book here, so I cannot verify this, but if I understand from Sidis' biography correctly he was a theoretician and not an astronomer. Without reading the book itself, I suspect that he was probably referring to a dust solution of GR and applying it to the FRW metric which is often seen as the cosmological equivalent of a dark matter prediction, especially considering that the observable luminous matter density of the universe is lower than what is needed for closure. However, this is not a prediction of dark matter per se, it's actually a prediction of a closed universe and dark matter was the stuff that would allow for such a thing. Interestingly enough, we don't live in a closed universe so it is somewhat misleading to state that Sidis "predicted" the stuff, and even so, there were people before him who applied dust models to FRW. I'd also point out that this is probably based on the grander ideas of cosmological reversability, an idea that Sidis seems to have taken to heart, appears to be a major impetus for Sidis cosmology which does lead naturally to an insistence on universe closure, approach of the Big Crunch and an oscillating universe. While a viable solution to the Friedman equations, it just so happens that our universe is not such a place nor is cosmological reversability given much thought these days. I think the major issue is that Sidis' "prediction" was a fluke coincidence and although it does correspond in theory to dark matter's function in a matter dominated universe, it's entirely by accident that it worked out that this particular model has relevance to our universe. While there are differences, this is somewhat akin to using a atomistic alchemist's theories on how iron atoms can be "fused" to form gold as a basis for claiming that said alchemist "predicted" nuclear fusion. The superficial prediction is correct but the details of the science supporting it is only coincidental. --ScienceApologist 10:04, 9 July 2006 (UTC)

It seems to me that others did predict "dark matter" before Zwicky, whose only claim to fame was trying to quantify it. Zwicky's dark matter also bears little resemblance what dark matter is considered to be today. --Iantresman 12:55, 9 July 2006 (UTC)

Zwicky, of course, didn't "predict" dark matter -- he observed it. That's why he's famous. The measurements Zwicky made of the phenomena are actually very close to the accepted measurements today, so actually it does bear a remarkable resemblance. --ScienceApologist 15:34, 9 July 2006 (UTC)

• No, Zwicky observered the rotation of the galaxy, and infered viscosity caused by "dark matter". It seems to me he is well-known for applying "dark matter" to the galaxy rotation problem, which he thought could be due to "dust particles and gases". But he was not the first to suggest "dark matter".

This is a misinterpretation. Viscocity was what prevented the dynamics of the system from keeping the galaxy from flying apart. Zwicky is suggesting that dust and gases could serve as a glue of sorts, but his dark matter observations were much clearer with regards to the dynamics of clusters. --ScienceApologist 17:28, 9 July 2006 (UTC)

• While some of the "Earlier reference to dark matter"(above) are, as you correctly point out, in refernce to its obscuring properties, rather than mass, it is also clear that Birkeland preceeded them all when he wrote:

"It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system in evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in 'empty' space. [..]

This might be considered a prediction for the interstellar medium which is a very different thing than dark matter. However, Birkeland wasn't the first to make a prediction of this sort. There were others before him who opined that the ISM might have gaseous components. --ScienceApologist 17:28, 9 July 2006 (UTC)

"There is also another question which naturally presents itself for investigation : Will the assumed density of flying corpuscles in space bring about any appreciable resistance to the motion of the heavenly bodies?". Polar Magnetic Phenomena and Terrella Experiments, in The Norwegian Aurora Polaris Expedition 1902-1903 (publ. 1913, p.720)

Seems like a prediction of solar wind type of phenomena. Again, very different from dark matter. --ScienceApologist 17:28, 9 July 2006 (UTC)

It was pointed out to me by a colleague that Oort likely beat Zwicky by a year in proposing dark matter. He was looking at the orbits of stars at large scale heights out of the milky way disk and determined they needed much more matter than was present in the stars and gas clouds, and couldn't be dust because of the low extinction of the "extragalactic nebulae" (galaxies) in the area. The reference is Oort 1932, Bull. Astr. Inst. Neth., 6, 249 (http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1932BAN.....6..249O&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf for the article in ADS). It wasn't clear reading it if he was proposing that there had to be exotic dark matter, so I'll leave it up to the regulars to decide if it's worth including.

You should tell you colleague that Oort's suggestion for dark matter in the disk has been disputed by more recent papers. Oort's analysis has not really stood the test of time and shouldn't be considered an earlier observation than Zwicky's because of this. --ScienceApologist 15:02, 9 September 2006 (UTC)

Zwicky quote

"We must know how much dark matter is incorporated in nebulae in the form of cool and cold stars, macroscopic and microscopic solid bodies, and gases. [..] we infer that the cores of nebulae possess considerable internal viscosity. The problem of deducing theoretical values for this viscosity therefore arises. It will be interesting to see whether the gravitational interactions in dense stellar systems are sufficient to account for the fact that such systems rotate like solid bodies, or if it is necessary to introduce matter in the form of dust particles and gases.".

The quote Ian inserted is interesting, but turns out to be not directly related to the subject of dark matter. Zwicky was making some interesting observations regarding the dynamics of the "nebula" including that there wasn't a reliable measurement for the luminous mass of the objects. Zwicky was commenting that it would be important to measure the material that was difficult to detect. He wasn't really discussing dark matter per se. This might be a good quote to include on the Fritz Zwicky page because it illustrates his care in distinguishing between what was and wasn't observed. However, it doesn't really fit with the dark matter article. --ScienceApologist 17:28, 9 July 2006 (UTC)

In which case, why don't you provide the appropriate quote, because I can't find it. Or maybe Zwicky didn't didn't propose dark matter, as it is generally thought of. --Iantresman 17:32, 9 July 2006 (UTC)

Not everything can be boiled down to "appropriate quotes". Zwicky's writing is notoriously convoluted even while in hindsight his work is remarkably predictive. I am not opposed to including a quote that is succinct and helps the reader understand what he was doing, but Zwicky sort of prided himself in being an obscure read and difficult to comprehend (not exactly in line with Wikipedia:Style guide). There was a saying the gist of which went that everything that is discovered today in astronomy was already discovered by Zwicky, but wasn't paid attention to because no one could understand it. --ScienceApologist 17:38, 9 July 2006 (UTC)

These two quote suggest that Zwicky is credited with the first EVIDENCE or DISCOVERY of dark matter:

• "The first evidence of dark matter was found by the Swiss astronomer Fritz Zwicky" (my emphasis), Galactic Dynamics by James Binney, Scott Tremaine
• "The Swiss American astronomer Fritz Zwicky was the first who discovered dark matter in galaxy clusters" (Zwicky, 1933) Proceedings of an Issi Workshop, 19-23 March 2001, Bern, Switzerland by Philippe Jetzer, Rudolf Von Steiger, K Pretzl

These quotes suggest that dark matter is IMPLIED or INFERRED:

• "We use the term dark matter to denote any form of matter whose existance is inferred solely from gravitational effects" Galactic Dynamics, op cit.
• "This is the path that led Zwicky (1933) to infer the existence of dark matter" Merging Processes in Galaxy Clusters By L Feretti, I M Gioia, G Giovannini

We can see that those people who accept dark matter will see Zwicky as the discoverer, and those astronomers who are a little more cautious, that he provided evidence that infers dark matter.

One view is subjective, the other is accurate. There is NO DOUBT that Zwicky came up with the first evidence that infers dark matter.

Consquently, other people predicted dark matter before Zwicky. --Iantresman 18:14, 9 July 2006 (UTC)

I follow and agree with your analysis all the way up to the very last sentence. In science, inference and evidence are really all we ever go on. There are "strong" inferences and there are "weak" inferences. However, writing from this "accurate" perspective is cumbersome in the English language which deals exclusively with definitional forms that are nuanced mostly by means of adjective modification. It's just not reasonable to go through all science articles and change the statements that are absolutes into statements that accurately reflect the scientific method. For example, take a random science article like Geomagnetic reversal and look at the language that is used. Very first sentence: "A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged." It's actually inaccurate to say this. A more accurate statement would be: "An inferred geomagnetic reversal is an inferred change in the inferred orientation of the Earth's inferred magnetic field such that the inferred positions of inferred magnetic north and inferred magnetic south are inferred to become interchanged". Some of these inferences are strong, some of them are weak, but they are all inferences. Similarly Zwicky was making inferences which at the time to many astronomers appeared weak but have over the course of the years shown to be much stronger than one may have guessed in the 1930s. So we've come to a bit of a quandry here, in science writing it is not always best to have utter accuracy because relying on accuracy alone is too linguistically cumbersome.

Where does this leave us? Well, "dark matter" is a phrase that can be interpreted in a very broad sense ("matter that is dark"), and inasmuch as one wants to rely on this interpretation it is perfectly reasonable to state that various people made a "prediction" of dark matter in history. What we really are trying to decide is what the research origins of the phenomenological "dark matter" concept in physical cosmology are. I haven't seen any evidence that before Zwicky there were people who predicted that there was vast amounts of matter that would be so biased away from the properties of local astronomical objects (e.g. the Sun, the planets, the gas and debris of the solar system) that it would cause the observed dynamics of large objects to deviate substantially from Keplerian. If someone finds a source to such a claim, it would definitely be a prediction of "dark matter" in the strict sense of the term the article uses, but simply predicting that some of the matter in the universe isn't as bright as stellar objects as Birkeland pointed out, or proposing a matter-dominated cosmological model like Sidis did, is not really a prediction of "dark matter".

--ScienceApologist 18:57, 9 July 2006 (UTC)

• ScienceApologist wrote: I haven't seen any evidence that before Zwicky there were people who predicted that there was vast amounts of matter that would be so biased
• Reply: Birkeland wrote: "... it is not impossible that future investigations will show that without coming into conflict with experience in any way here mentioned, we may reckon that there are more than ten thousand times greater masses gathered as flying corpuscles in "empty" space than the masses in the stars and nebulae" --Iantresman 21:01, 9 July 2006 (UTC)

But this isn't light-biased mass, Ian. This is normal matter. It exhibits thermal radiation. It is detectable in ways other than dynamical measurements. Birkeland is predicting a massive component of the visible universe might be in the ISM, he's not predicting dark matter. --ScienceApologist 21:05, 9 July 2006 (UTC)

And Zwicky (quote above) was summising that it might be "necessary to introduce matter in the form of dust particles and gases." I don't see the difference. --Iantresman 21:52, 9 July 2006 (UTC)

The difference is that when Zwicky was proposing (as all good conservative scientists do) that given enough ISM material the discrepancies in dynamics could be avoided. Birkeland was discussing the components of the ISM, but made no reference to the dark matter dynamics. This all boils down to dark matter being different from the ISM. --ScienceApologist 22:28, 9 July 2006 (UTC)

• Birkeland says: "Will the assumed density of flying corpuscles in space bring about any appreciable resistance to the motion of the heavenly bodies?"
• He is indicating that the extra mass may cause an appreciable change in the motion of heavenly bodies. This is the prediction. Zwicky found it. --Iantresman 00:09, 10 July 2006 (UTC)

No. Birkeland's "resistance to the motion of heavenly bodies" is not the same thing as dynamical velocities exceeding Keplerian predictions based on mass-to-light assumptions. In fact, they're entirely different arguments. You can use this as a prediction of solar wind or similar phenomena, but it is not a prediction of dark matter. --ScienceApologist 17:51, 10 July 2006 (UTC)

And when Zwicky says, above, "..if it is necessary to introduce matter in the form of dust particles and gases", that surely isn't dark matter either? --Iantresman 20:43, 10 July 2006 (UTC)

As we currently understand dark matter, dust and gas is not dark matter, no. --ScienceApologist 20:45, 10 July 2006 (UTC)

Sidis

I've been looking through the web version of The Animate and the Inanimate at sidis.net, and I can't find anything corresponding to dark matter. He talks about dark sections of the universe where the second law of thermodynamics runs in reverse and stars absorb light (or emit darkons?). This idea, however, has no obvious connection to dark matter beyond the shared attribute "dark." If somebody can point me to a specific chapter that really does talk about dark matter, that would be much appreciated (and the chapter # should be added to the citated reference). Otherwise, I'm inclined to say that the claim should be removed. --Reuben 22:00, 5 August 2006 (UTC)

I have found several sections on the web that say that sidis was the first to predict dark matter. Anyone can look them up.

Anyway: Definition from dictionary.com, Dark matter - Physical objects or particles that emit little or no detectable radiation of their own and are postulated to exist because of unexplained gravitational forces observed on other astronomical objects. Dark matter is believed to be part of the missing mass.

He describes matter in his book that absorbs light (no not darkons!?!?!?) and other matter simple too dim to see. He predicted that 10 times more matter exists than we can see. One of the reasons apart from his prediction of the reversal of the 2nd law of thermodynamics was that the universe seemed to be gravitationally much larger than is visible through light. That seems to qualify as dark matter. Matter that is dark. Also since noone even knows what dark matter is made of today, I can't see why the claim is invalid. --Shane --t_a_y_l_o_s

• Fan web sites are not a very authoritative reference. One of the ones that was recently cited as a reference on the page goes on to claim that William Sidis "probably" coined the term libertarianism (link), which is patent nonsense (see Online Etymology Dictionary).
• No, being dark and made of matter doesn't make it dark matter. Dark matter is a technical term with a specific meeting that's not related to what Sidis was proposing. In fact, absorbing light is one of the properties that dark matter specifically must not have. The crux of Sidis's argument is the part about the second law of thermodynamics running backwards, and this has absolutely no analog in the idea of dark matter as we know it. It appears to me to be quite a stretch and a weak argument to draw such a connection.
• (Please feel free to ignore the darkons; that's just an old physics joke that came to mind.)
• Please provide a specific citation for the prediction of 10x more dark matter than visible matter. From what I can see, Sidis proposes approximately equal amounts of negative space and positive space. --Reuben 01:03, 6 August 2006 (UTC)

The Animate and the Inanimate chapter 13, last paragraph http://www.sidis.net/ANIM13.htm "If we take 18,000,000 as the approximate number of visible stars, and allow about 9 times as many that are dark or too faint to be seen..."

Yes he proposes equal ammount of positive and negetive space but that doesn't mean that every positive object(operating under the 2nd law) emits enough light that we can see it.

Where does it say that dark matter cannot absorb light? Wiki quote: "MACHOs- Massive Compact Halo Objects assumes that the dark matter consists of condensed objects such as black holes, neutron stars, white dwarfs, very faint stars, or non-luminous objects like planets. The search for these consists of using gravitational lensing to see the effect of these objects on background galaxies." It seems to me that black holes absorb light, and black holes are under the "potential explanation for part of dark matter" list. http://en.wikipedia.org/wiki/Cold_dark_matter

I have defined dark matter according to dictionary.com above, if you have another defintion could you please post it so that I can understand your arguement better. Thanks. --t_a_y_l_o_s 02:55, 6 August 2006 (UTC)

From Wikipedia, the Free Encyclopedia: "In cosmology, dark matter refers to matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation (light) to be detected directly, but whose presence may be inferred from gravitational effects on visible matter such as stars and galaxies." [3] In all seriousness, that should help you understand the argument; Sidis is not proposing modern dark matter at all. -- SCZenz 04:09, 6 August 2006 (UTC)

• Here's another one that may be useful. From Ned Wright at UCLA: Glossary of Astronomical and Cosmological Terms. One thing to understand is that when he says dark matter doesn't emit, doesn't absorb, and doesn't scatter light, that's an approximate, shorthand way of speaking. What's really meant is "very, very little." Although MACHOs should indeed absorb some light, it will be a very small amount; you would have a very hard time detecting them by their absorption, unlike some other famous objects such as the Horsehead Nebula. Sidis's negative space regions are supposed to absorb essentially all the light that enters them, so that they would hide whatever's behind them.
• Dark matter does indeed lens the light from background objects. That's been experimentally observed. So dark matter does lens light, but it doesn't significantly absorb, emit, or scatter it.
• Thanks for the chapter 13 citation. I'll check it out. It sounds like that refers to faint but ordinary stars, so that the 90% number is separate from his thesis about the negative space regions. --Reuben 04:16, 6 August 2006 (UTC)

SCZenz- yes it doesn't sound like the modern dark matter, but so what, when Fritz Zwicky proposed dark matter he didn't predict the modern version of dark matter either but we call what he predicted dark matter anyway.

Reuben- I see what you mean and I agree that sidis's negetive absorbing stars are not modern dark matter.

I don't think that every photon going into the negetive regions of space's of sidis would be absorbed because that would mean that all lines of sight had matter directly in the way, but you are right it would absorb a lot of light. Plus his dim stars could be dark matter.

Also the only thing i can find wrong in Sidis's logic in his book is time-symmetry, he assumes time-symmetry but in fact time is only very slightly time-asymmetrical, creating an arrow of time. --t_a_y_l_o_s 04:46, 6 August 2006

Actually, what Zwicky found is exactly dark matter in the modern sense. When people say that Zwicky was the first to discover dark matter, it's because his observations pointed to the phenomenon we still know today as "dark matter," and similar observations today continue to provide strong evidence for dark matter. --Reuben 18:37, 8 August 2006 (UTC)

I see. Well.. do you think that Sidis deserves credit for being the first to predict dark matter? I think he does. --t_a_y_l_o_s 20:41, 8 August 2006

Check the discussion in the section above. Dark matter != matter that is dark. --ScienceApologist 21:06, 8 August 2006 (UTC)

From looking at The Animate and the Inananimate, I would say no. What Sidis was talking about isn't related to what we now call "dark amtter." And if you take dark matter to mean just "matter that is dark," then the proposal of dark stars by John Michell in 1783 would be an earlier prediction of dark matter (among others). So either way, I don't think it's right to say that Sidis was the first to predict dark matter. --Reuben 21:35, 8 August 2006 (UTC)

Contradiction

From the article:

• Hot dark matter - nonbaryonic particles that move ultra-relativistically
• Warm dark matter - nonbaryonic particles that move relativistically
• Cold dark matter - nonbaryonic particles that move non-relativistically

But then in the next paragraph:

If the dark matter is composed of abundant light particles which remain relativistic until shortly before recombination, then it may be termed "hot". The best candidate for hot dark matter is a neutrino....

And Hot dark matter says:

Hot dark matter is a form of dark matter, which consists of particles that travel with relativistic velocities....

So, relativistic or ultra-relativistic? Which is it? Rangek 16:56, 15 August 2006 (UTC)

This is not a contradiction, although it could be made more clear. Ultra-relativistic is "really, really relativistic" not "beyond relativistic" so ultra-relativistic particles are a sub-set the relatavistic ones. Vondo 16 August 2006 (UTC)

The definition of "ultra" is beyond. Therefore, ultra-relativistic IS "beyond relativistic". I get what you are trying to say, but "ultra-relativistic" is not how you say it.

How about "at nearly the speed of light"? Rangek 02:33, 16 August 2006 (UTC)

According to Wiktionary:ultra- it can also mean excessively, to an extreme. So ultrarelativistic can also mean extremely relativistic. Besides, the word seems to be in common use (Google)Lars T. 16:20, 16 August 2006 (UTC)

Okay. Then I guess the issue is really with Hot dark matter and Warm dark matter Rangek 17:24, 16 August 2006 (UTC)

Intro Paragraph

I added the word "theoretical" in the opening sentence, and it was cited as 'weasly' and removed. I'm assuming the editor was referring to 'weasel words' as defined by Wikipedia. This article is about an unproven theory. This is unclear to the casual reader until later in the article. Theory/theoretical are only considered weasel words when used as synonyms for guess or speculation, which is clearly not how I am using it. I've reverted the article so that others can see how it reads for discussion purposes. Please review wikipedia's 'words to avoid' and provide input here so we can come to a consensus before modifying any further. CPitt76 02:02, 21 August 2006 (UTC)

All theories in science are "unproven" since science is inductive and doesn't rely on proof but rather observations. The problem with placing theoretical as an adjective here is that dark matter is an observationally driven phenomenological theory. It isn't "theoretical" in the same sense that general relativity is and was when it was proposed. Of course, dark matter "theory" exists, but it's not quite correct to consign the entire subject to this side of the theoretical/observational divide. --ScienceApologist 02:05, 21 August 2006 (UTC)

My point was that your argument that theory is a weasel word is not valid in this article since we are talking about a theory. I'm not discounting the theory, just making it clear to casual readers not familiar with the topic that we are discussing a theory. As it reads now, the layman will think this is a universal truth, which is not the case. CPitt76 02:36, 21 August 2006 (UTC)

"Universal truth"? What kind of philosophy of science are you spouting? On a more serious note, the problem with presenting dark matter as a "theory" for the causal reader is that, more than many other theories, it is based primarily on astronomical observations. Dark matter was driven by observational astrophysics as opposed to theoretical astrophysics. See the problem. In this particular subject, there are a few people who are adamantly, for one reason or another, opposed to the existence of dark matter. What they are arguing against is not just "theory" but the implications of a number of different observations. See the distinction? --ScienceApologist 02:43, 21 August 2006 (UTC)

There's substantial room to improve the intro, and if it's done well, it should be able to satisfy both of your concerns. As ScienceApologist said, the idea of dark matter is primarily driven by observation, not theory, so "theoretical" seems out of place in the definition. However, observation doesn't demand that dark matter be made up of some yet-undiscovered fundamental particle. That's just one type of (theoretical) dark matter candidate. I suggest that the definition be reworked to focus on the ways that we (indirectly) see the dark matter, instead of ideas about what it might be. Then, various dark matter candidates such as WIMPs, axions, etc. can be correctly described as theoretical later in the text. --Reuben 02:45, 21 August 2006 (UTC)

I agree with eliminating the speculation, and highlighting the observations. It's much more objective and will allow for a more unbiased interpretation by the reader. ScienceApologist, care to take a stab? You seem more passionate and knowledgeable about the subject than I am. Hopefully it won't interfere with your ability to come up with such zingers as "What kind of philosophy of science are you spouting?"

To respond (seriously) to your last post, SA, based on your last post, it seems that you assume I lack an understanding of the role observation played in recognizing dark matter, which isn't the case. I wasn't trying to get bogged down in a debate about the theory itself. Your initial comments on the edit page took issue with "theoretical" as "weasly". I took this to mean you thought it was considered a Wikipedia weasel word. The use of theoretical here did not meet that definition. If you weren't using weasly in that sense, I misunderstood and apologize. CPitt76 03:29, 21 August 2006 (UTC)

I do consider theoretical and theory to be words that are often misunderstood by the general public and so we must take extra care to use them only where they are 100% appropriate. The scientific community can play fast-and-loose with their terminology and jargon when they're h'yucking it up around the water cooler, but when writing an article that any random fop will find interesting, one misuse of the word "theory" will lead to 10,000 bulletin board posts saying "See? According to Wikipedia dark matter is only a theory." Yikes. --ScienceApologist 06:40, 21 August 2006 (UTC)

I have made a first stab at reworking the intro paragraph. Your comments are welcome. --Reuben 15:35, 21 August 2006 (UTC)

A vast improvement over the previous write, in my opinion. A more objective and well written presentation. Thanks for taking the time. CPitt76 01:45, 22 August 2006 (UTC)

Critique of Wikipedia's mishandling of Dark Matter entry.

The intro section (below) to wikipedia's "dark matter" is an erudite, technically accurate assemblage of words that acts as a filter to the casual reader, to (sub-consciously?) deny the basic fact that scientists do not know what makes up the majority of the universe, including our own galaxy, probably our own planet. and arguably even our own bodies. (By "majority" I am including "Dark Energy" as well.) Again, scientists do not know what it is that makes up the majority of our world. Deny eruditely all you will, but the mature thing would be to make this very, very clear from the get-go. (And yes, I did study the discussion on this subject.) To simply slide in there the word "inferred" and finish that lengthy intro with an above-average-education allusion to "terra incognita" denies the public of what the matter is. Pun intended. We must rise above writing in fear of how the readers might react to the truth. I strongly recommend that the wikipedia intro to dark matter be submitted to non-scientific, average-education members of the community, who would be asked to read it, and then "summarize" it, without letting them know what the issue of my critique is. If a majority of them clearly indicate in their summaries that scientists do not know what makes up the majority of the universe, including our own galaxy, then we have fixed the problem.

also, please note criteria n.2 from wikipedia's "good article guidelines:

"2. [...] factually accurate and verifiable."

The very first words of the "dark matter" article are:

"In astrophysics, dark matter is matter that [...] "

Please note: the phrase "dark matter is matter that" is not accurate and not verifiable. "Dark matter" is a ***name*** that astropyhiscs has given to account for something which they cannot explain, cannot identify, and ****do not know**** if it even exists. They have inferred that it exists to compensate for the fact without "it" and without "dark energy" (same problem) astophysics is unable to account for more than 95% of the universe, at least according to current astrophysics standards. 95% of the universe is either unexplained by astrophysics, or undescribeable by astrophysics. If astrophysics cannot explain what it is, or describe what it is, it cannot say that "it is," let alone that it is "matter" or, in the case of dark energy, that "it is energy." "Dark matter" is not ***verifiably*** matter, and "dark energy" is not verifiably energy. They are names for the unknown, unseen, undescribed, unexplained. Not accurate. Not verifiable. In direct conflict with scienctific description of the universe, and therefore "inferred" to exist. In order to be "accurate" and "verifiable," astophysics needs first to be able to describe it. (Not just describe its "effects," which are dependent on astrophysics theories, that is circular reasoning). If it states it "is" real, it must be able to describe "it." To claim that dark matter explains the majority of the universe is tantamount to claim that god exists. They are equally undetectable. And their "effects" are equally based on ***presuppositions.*** Faith is the (unverifiable) presupposition in explaining the evidence of god, and scientific theory is the (verifiable) presupposition in the case of ***inferring*** dark matter, which however is unverifiable itself! Dark matter is in conflict with verifiable theory, and thus to claim that it exists ***because*** of the theory, is circular reasoning. But neither faith nor astrophysics can detect each claims exists out there (god, or dark matter). FTR, I am an atheist. But astrophysicis still cannot claim that dark matter "is matter" -- it cannot verifiably claim that it exists. The aug. 2006 picture is a picture of what, exactly? A picture of what we cannot describe. Unacceptable to not start off article clearly saying "science does not know what makes up the majority of the universe, and it has called this unknown majority 'dark matter' and 'dark energy.'" Now, **that** statment would be accurate, **that** statement is verifiable. Again: astophysics does NOT know what makes up the majority of the universe, but presupposes that something does, and it has called that presupposed component "dark matter" and "dark energy." Ask most astrophysicists, truly, and accurately, and verifiably. Ask them. They do not know.

Have the courage to tell the readers the truth. Clearly. Right off the bat.

Passaggio 18:07, 9 January 2007 (UTC)

Please don't start new discussions in the middle of the talk page. As for your additions to the article, I don't think they serve to clarify anything. Your definition would include as dark matter a lot of things that aren't dark matter, such as dark energy, the Higgs boson, or neutronium. At the same time, it excludes subdominant forms of dark matter that are now directly observed and understood, like neutrinos. The existing wording, "The composition of dark matter is unknown," is much better. --Reuben 18:54, 9 January 2007 (UTC)

Another Wikipedia guideline is Wikipedia:Avoid self-reference, so I'm glad the "Critique of Wikipedia's mishandling of Dark Matter entry" is off the main article page. Art LaPella 21:41, 9 January 2007 (UTC)

Significant news?

"Cosmic smash-up provides proof of dark matter"; 21:50 21 August 2006; NewScientist.com news service; David Shiga; http://www.newscientistspace.com/article/dn9809-cosmic-smashup-provides-proof-of-dark-matter.html Mitchconquer 09:45, 22 August 2006 (UTC)

I know next ot nothing about dark matter, but Space.com has an article about it today, a big discovery about dark matter, and it seems like it's a really big deal, possibly throwing current ideas about gravity into question. So I thought I'd just post it so others can decide what to make of it. There's a picture as well. --Age234 20:22, 21 August 2006 (UTC)

The Bullet cluster is significant in that it may be impossible for MOND et al. to explain. However, it has been known for a while now. The Chandra results announced today appear to be just an incremental improvement in the characterization of the bullet cluster. Although it is being reported as "the first direct detection of dark matter," the dark matter is still detected indirectly through its gravitational effects, using weak lensing, which has been done before. The bullet cluster actually reinforces our current understanding of gravity, possibly ruling out some (very very clever and interesting) alternative ideas. --Reuben 01:18, 22 August 2006 (UTC)

Yes, and I was expecting to see new results on the DM-DM cross-section, but as you can read here they're still doing the simulations. The old result from 2004 is sigma\lesssim 1 cm^2 (m/gram). Count Iblis 01:27, 22 August 2006 (UTC)

Could you please add a sourced statement to Bullet cluster saying "... from 2004 is sigma\lesssim 1 cm^2 (m/gram)" and why this is important? (rules out most MOND?) (with wikilinks to the dimensions if you could) WAS 4.250 01:36, 22 August 2006 (UTC)

This particular result constrains self-interacting dark matter, not MOND. However, the limit on the self interaction cross section is not as strong as constraints from other observations. Count Iblis 12:34, 22 August 2006 (UTC)

B.t.w. what happened to the "research due to be fully published in spring 2006, researchers from the University of Cambridge Institute...". ???? Count Iblis 01:32, 22 August 2006 (UTC)

talk from Dark Matter 2006, paper in the arxiv --Reuben 01:40, 22 August 2006 (UTC)

Thanks! Count Iblis 12:34, 22 August 2006 (UTC)

"In research due to be fully published in spring 2006" <-- I hope this can be removed before it is 2007. --JWSchmidt 01:06, 10 December 2006 (UTC)

Nope, still there. I don't know enough about the topic to take care of this. Can someone? -- Netdragon 19:01, 23 September 2007 (UTC)

This paper in the arxiv seems to be more directly about it and is "in press in Nuclear Physics B" so should be published very soon. I'll give it a quick skim to see if there's anything different to / more specific than the original BBC story. Fwb22 13:42, 21 December 2006 (UTC)

Velocity vs angular Velocity?

The Galactic rotation curves section uses 'velocity' and 'speed' where it seems to me 'angular velocity' may be more appropriate; certainly it would help to explain the difference for those who aren't used to using both. 'Speed of rotation' will mean something like revs per second to many people. It might also be useful to include a brief explanation of how the Newtonian predicted curve is obtained, and what a rotating solid disc would look like on the graph. Davy p 05:11, 26 December 2006 (UTC)

Flat rotation curves in spiral galaxies

Came across this paper from 1972 which seems to already have shown flat rotation curves and an implied M/L of 20 in solar units. From the conclusions: "In addition, we confirm here the requirement for low-luminosity material in the outer regions of these galaxies (M/L ~ 20) ....". This is 3 years before the findings the article attributes to Vera Rubin. 132.235.24.91 22:42, 3 January 2007 (UTC)

What is the symbol of dark matter?

I'v seen lambda, omega, and many other symbols which deal with dark matter, but what is the actual symbol for plain old dark matter? —Preceding unsigned comment added by 96.232.156.197 (talk) 02:02, 29 January 2008 (UTC)

There are lots of different symbols depending on what candidate for dark matter you're talking about, and what properties you are talking about. The symbol for a neutralino is ${\tilde {\chi }}^{0}$, so that's one possibility. I think the closest thing to a generic symbol would be "dm," as in Ω_dm. Lambda specifically refers to a cosmological constant, and by extension to dark energy, not to dark matter. --Reuben (talk) 02:47, 29 January 2008 (UTC)

Is dark matter pseudoscience?

"NASA Finds Direct Proof of Dark Matter" (Aug 21, 2006). This seems to fail at least two important criteria as defined in the Pseudoscience article:

• "Evasion of peer review prior to publicizing them (called "science by press conference")". Sure, the material will be printed in The Astrophysical Journal Letters, but this does seem like science by press release.
• "Assertion of claims that a theory predicts something that it has not been shown to predict"; at best the observations is evidence that is consistent with the theory, which is FAR from being proof?

I also wonder whether (a) the observations were predicted, (b) the conclusions are testable. --Iantresman 08:54, 22 August 2006 (UTC)

Please see WP:Point, Ian. Jefffire 09:59, 22 August 2006 (UTC)

It says that "discussion .. is prefered", not "illustrative edits". My comment falls into the former, and you side-stepped the issue. --Iantresman 10:42, 22 August 2006 (UTC)

Can you find a reliable source calling dark matter a pseudoscience? Otherwise spare us the OR. If any of the page regulars would are curious as to what Ian's motives may be on this, take a scroll through the Pseudoscience talk page. Jefffire 10:47, 22 August 2006 (UTC)

I'm pleased to hear that you require a reliable source, and assume that a press release claiming "proof" is not one. Indeed, Wikipedia reliable sources tells us "In science, avoid citing the popular press"[4], and even "... arXiv (or similar) preprints and conference abstracts should be considered to be self-published"[5]. So let's wait to read the final article in The Astrophysical Journal Letters --Iantresman 11:04, 22 August 2006 (UTC)

Nice to see you sidesteping the question and forming strawmen already. I'll take this to mean that you can't find a reliable source to support your POV. Jefffire 11:13, 22 August 2006 (UTC)

I asked a legitimate question, not to be confused with whether we describe dark matter as pseudoscience, which indeed requires a reliable source. --Iantresman 13:57, 22 August 2006 (UTC)

The press conference was called only after two papers were accepted for publication in ApJ:

http://xxx.lanl.gov/abs/astro-ph/0608407

Comments: Accepted for publication in ApJL

http://xxx.lanl.gov/abs/astro-ph/0608408

Comments: Accepted for publication in ApJ

Count Iblis 12:40, 22 August 2006 (UTC)

Thanks for that, that covers the science by press release, though I still think that "proof" is preposterous. --Iantresman 13:57, 22 August 2006 (UTC)

No-one here is calling it "proof", it's evidence. Write a letter to NASA chiding them for exaggeration, but leave the good people here to get on with their business. Jefffire 14:11, 22 August 2006 (UTC)

The paper above, "A direct empirical proof of the existence of dark matter", as accepted by ApJL, says just that. Shall we chide ApJL too? --Iantresman 14:44, 22 August 2006 (UTC)

Yes, empirical proof which always comes with some small print. This is also true for well established theories. You can't be 100% sure that tomorrow the laws of physics will be completely different than what they are today. E.g. gravity could stop to exist and the Earth would float away from the Sun. There is no way to rule this out with 100% certainty. Count Iblis 15:02, 22 August 2006 (UTC)

I think it is a very powerful statement that the observation is consistent with dark matter, and not with any proposed alternative theory—especially since the folks with the alternative theories have been trying pretty hard. But yes, we can't ever say any theory is capitol-T True in any sense; we can only say that our models describe reality. When the proof stacks up, of course, it's easier just to say "we found dark matter," and in pratice that's what we do. The same thing has happened with many physics discoveries—you could argue we have no proof that electrons exist either. -- SCZenz 15:50, 22 August 2006 (UTC)

Iantresman, the recent observation of dark matter (see the SLAC Today reference in the new addition to the observation section in the main article) takes care of any arguments that dark matter is pseudoscience, and the article has been appropriately updated to reflect this. Your question was valid regarding prior observations in that they were not submitted at the time to peer reviewed journals. This new observation will be submitted to no less than two peer-reviewed astrophysical journals, and a variety of physics phenomena were cross-referenced to obtain a more complete understanding of the data. Since I work closely with this field, I will stay on top of this article. Cheers, Astrobayes 18:43, 23 August 2006 (UTC)

Thanks for that. But to suggest "proof" is a bit strong, and does seem to falled into the pseudoscience description above. --Iantresman 20:50, 23 August 2006 (UTC)

The recent observation does not fall under the category of pseudoscience. The dark matter was observed, not inferred (please see ref [6] in the article).

Sorry for the split paragraph. This is incorrect. If you could observe it it would not be dark matter. The articles demonstrate that the dark matter halo was massively inferred. Some articles (but not all) state 7000 distinct measurements. What kind of measurements you might ask?

http://climatesci.atmos.colostate.edu/

"In addition to the Chandra observation, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes were used to determine the location of the mass in the clusters. This was done by measuring the effect of gravitational lensing, where gravity from the clusters distorts light from background galaxies as predicted by Einstein's theory of general relativity."

So the dark matter halo was not observed, it's presence and shape was derived from gravitational lensing observations. For a simple system this might well be fairly precise, but I suggest that for a galaxy cluster, there is too much information and I don't expect results would be spot on.

One final note, looks to me like the blue halo is not mass (dark matter or otherwise) but rather it outlines where the cluster's gravitational field is strong enough to cause gravitational lensing. And gas that hot (emits x-rays) does not come from simple compression, but usually from hot new stars forming, some of which go supernova and heat the surrounding gas. At this distance their remnants would not be visible.

64.172.115.2Rich

The hot plasma in clusters of galaxies has very little to do with star formation. In fact, most of the hydrogen and helium in the plasma have never been processed through a star, but are primordial gas. This gas is heated up by falling into the potential well of the cluster, thermalizing to several million degrees Kelvin, which almost totally ionizes it and causes it to emit mostly in X-rays (thus why it's observed with X-ray observatories). Any atoms heavier than helium in the gas would be from supernovae, planetary nebluae, etc, but the metalicity of the plasmas is small compared to that of most stars.

What was overlayed in blue in the bullet cluster image on the main page is a weak lensing observable called the convergence (or really one step from a direct observable - you directly measure the shear then use a mathematical transform to obtain it). If gravity has a 1/r^2 force law, then the convergence is simply the surface density of matter scaled by a cosmological scaling constant, so the blue overlay really does show where the mass is. If gravity does not have a 1/r^2 force law then the convergence is a non-local function, and you have to take a given mass distribution and calculate the resulting shear and run it through the same transform to get what the kappa distribution of it would be (see the Angus paper in the refernces for an example). For all of the gravity laws, however, the convergence is a set of second derivatives of the surface potential, and as such the blue overlay does show where the surface gravity is located (and for anyone confused by the term "surface," it means an integrated 2-dimeinsional distribution).

So, is the bullet cluster observations a direct measurement of dark matter? The answer depends on what definition you're using for direct. To a particle physicist, the answer would be no, because it didn't measure an individual particle of dark matter. To an astronomer, the answer would be yes, because it was a measurement of a direct observable, instead of a result which depends on modeling of the data to determine (for instance, the relative height of the third peak to the second peak in the cosmic microwave background power spectrum shows good evidence that dark matter must exist, but the evidence relies on models fitting to the data).65.24.145.231 01:52, 19 November 2006 (UTC)

The hypothesis of the existence of dark matter is testable, was tested, was confirmed, and is now going to be published in two astrophysical peer-reviewed journals. According to we scientists, the word proof is appropriate here since we predicted something, then saw it - so the article now reflects that fact. Thanks to the hard work of astrophysicists and engineers, the issue of the existence of dark matter has been put to rest. The article will be updated regularly as new news comes in. Cheers, Astrobayes 21:30, 23 August 2006 (UTC)

Ian seems to be a troll, in my opinion. He has taken up similar issues on other pages, including on the pseudoscience page concerning evolution! Raistlin7000 19:01, 20 September 2006 (UTC)

Dark Matter is a new current event!

http://www.newscientistspace.com/article/dn9809-cosmic-smashup-provides-proof-of-dark-matter.html

Dark matter important?

Why is dark matter such a revelation? Why do people attempt to describe it with new particles such as neutrinos, and other as yet undiscovered matter? Why don't people just assume the obviously simple answer: dark matter is matter that doesn't emit light, and is therefore almost impossible to see.

It seems so obvious to me that dark matter is spacerock that aren't suns or hot nebulae. I'm not perporting to know a great deal about this, nor do I want to change the article in any way to reflect my view. What I'm looking for is a rational explanation as to why I'm wrong - because obviously plenty of physicists think I am. Am I alone in this confusion? Fresheneesz 18:35, 22 August 2006 (UTC)

This is covered in the article. MACHO's. Jefffire 18:39, 22 August 2006 (UTC)

In brief, thermal radiation ensures that all "normal matter" will emit electromagnetic radiation. --ScienceApologist 19:28, 22 August 2006 (UTC)

There's also measurements of the amount of mass in the universe that don't correspond to the amount of everyday (Cosmologists call it Baryonic) matter we predict. I think it'll be explained under big bang model or something similar. There is baryonic dark matter which you describe and the predicted non-baryonic dark matter (as well as dark energy!). I'll try and find the best article to link you too. Jameskeates 11:51, 25 August 2006 (UTC)

Try Lambda-CDM model and links contained on that page.Jameskeates 11:53, 25 August 2006 (UTC)

As for "normal matter" that will emit EM thermal radiation, thats simply not true. Matter needs be hot to emit thermal radiation, and even hot matter might not emit enough to be "directly detected" thus making it dark matter. But I'll look into the rest, thanks for the pointers. Fresheneesz 09:00, 3 September 2006 (UTC)

If an object has 0K temperature then it will not emit thermal radiation. Otherwise it will emit thermal radiation. Indeed, there is some question as to whether matter at very cold temperatures of space can be observed, but we have observed the infrared glow from cold gas clouds down to the temperature of the CMB (~3K). So the only far-reaching possibility is that there are some very compact objects holding the baryonic mass at low tempertures. These are the so-called MACHOs and there are a number of reasons that astrophysicists believe there cannot possibly be enough of them to solve the Dark Matter problem. First of all, there would have to be an enormous number of them and they should be observed through microlensing events such as those looked for by OGLE. Secondly, compact objects need time to cool down to low temperatures since a collapsin mass naturally heats up as the particles lose potential energy. To get cold compact objects in the right amount and distributed through the universe in this way just doesn't correspond to our observations. --ScienceApologist 18:20, 5 September 2006 (UTC)

Alright, some of that does make sense. However, I'd be interested to know how far away the 3K gas clouds are from us, and how they know the temperature solely based on its radiation. Fresheneesz 21:44, 5 September 2006 (UTC)

The details of infrared astrophysics isn't exactly germane to this discussion. If you are interested in looking at the components of the interstellar medium, I'd suggest starting at that article and doing research in this subject. The majority of objects in our galaxy are warmer than 30 K due to the fact that cooling processes are so difficult to come by. The higher the temperature, the easier to see. The background at 3 K is a subject of the foreground papers of WMAP and was very well-researched by astronomers on that observing team. --ScienceApologist 23:25, 5 September 2006 (UTC)

But see, I think this article should have that sorta explanation so people don't have to research it to understand dark matter. Fresheneesz 07:38, 6 September 2006 (UTC)

Fresheneesz, you commented that you didn't know "...how they know the temperature solely based on its radiation." The answer is that for any radiation wavelength there is a corresponding peak temperature with a predictable functional form off-peak. This is called a black-body curve. As far as any object needing to be "hot" to emit radiation, the word "hot" is a misnomer because if an object has a temperature above 0 Kelvin then it will emit radiation because the molecules making up that matter will either have rotational transitions or vibrational transitions or other atomic transitions. Although this information will not apply directly to this article, I hope it helps you. Cheers, Astrobayes 15:18, 6 September 2006 (UTC)

When I said "hot", I meant it needs to be hot to be able to be *detected*, not to emit. If you're looking into an abyss, and expect to see some rocks at 10K 100 light-years away, I wouldn't be surprised if you get disappointed. Also, when you're looking at far off objects, nothing you can see is really going to be close to a black-body - of course i'm just speculating.

When you say the information doesn't apply directly to this article, do you mean that it isn't an appropriate subject, or is shouldn't be linked to? Fresheneesz 19:47, 7 September 2006 (UTC)

The fact is, we know exactly how 10K rocks radiate; they actually do look more or less like a blackbody. We can thus estimate how many there could be 100 light-years away without noticing... The answer is: not enough. Astrophysicists have thought through these questions in great detail.

As for what's relevant for the article, Wikipedia is an encyclopedia rather than a FAQ. That is, we present the state of current research, not answers to every question anyone might ask about it. As discussed below, counting stars and gas clouds is an extraordinarily complex job done by very skilled professionals, and it is not at all easy to explain in detail—although perhaps we should have a Wikipedia article about it and link there from here when we mention the estimates of "ordinary"/"visible' matter. -- SCZenz 20:59, 7 September 2006 (UTC)

An encyclopedia should have an article that doesn't require a FAQ to understand. Fresheneesz 02:40, 17 October 2007 (UTC)

Dark Matter Observed - August 2006, Kavli Institute

Yesterday, I put in a reference to the SLAC Today article describing the observation of dark matter in the Bullet Cluster. I didn't have much time to make that addition very attractive other than to put in a sentence or two, and I really appreciate the individual(s) who made the last paragraph in the Observation section more descriptive after I logged off. The section looks great now, and I just have to say that it is exciting that such a new discovery could have such implications for current astrophysical models. Now that dark matter has been observed, any arguments that dark matter is pseudoscience in the article should be removed now as they have lost their steam. Thanks again for helping with this contribution. Cheers, Astrobayes 18:39, 23 August 2006 (UTC)

I disagree. If in fact the existance of dark matter is confirmed, wikipedia should still cover allegations, yet mention that those allegation may, or are, no longer valid. Fresheneesz 09:13, 3 September 2006 (UTC)

Comment on the Bullet Cluster http://www.astro.umd.edu/~ssm/mond/moti_bullet.html someone may wish to add this.

Also note that dark matter has not been "observed", despite anyone that might say so. The event is simply more evidence. Yet, this new evidence does almost nothing to tell us what makes up this dark matter - and its not at all unreasonable to cover legitimate critics when scientists are proposing any and every possible explanation for dark matter. Fresheneesz 09:16, 3 September 2006 (UTC)

I agree here - the ref 11 just says that the presence of dark matter is confirmed by grav lensing studies, it has not been "observed" or seen in any light - that is part of the DEFINITION of dark matter. Please get rid of that "has been observed" part, especially "optically" - the data was from xrays etc. varunbhalerao 18 October 2006

Go to this link. See the material highlighted in blue? That's dark matter - as has been confirmed by the hundreds of physicists working on the project using x-ray detectors of the matter in the region. I collaborate with the institute that was responsible for this discovery, and I can tell you that this direct observation of Dark Matter is indeed a milestone. And this observation, which the article now properly reflects, outdates the objections made in that arXiv paper which supplies only computer models as refutation of the observation of Dark Matter seperate from ordinary matter. This is exciting news and I'm glad that Wikipedia is able to bring this knowledge to the public by accurately reflecting it in the article. Cheers, Astrobayes 18:12, 5 September 2006 (UTC)

Well, I guess my point is that there are criticisms of *explanations* for dark matter. Also, when i said it hasn't been "observed" i meant in the physical sense. If we observed it, it wouldn't be dark - we merely infered its existance. So yea, my point is that much of dark matter theory is still legitimately under fire - for example, theorys about MACHOs and WIMPs (and now even super WIMPS). Fresheneesz 21:54, 5 September 2006 (UTC)

There is a difference between theories about what dark matter is and whether dark matter exists. There is (basically) no controversy that dark matter exists and that it is mostly non-baryonic. There is still controversy over the detailed composition of the stuff. When you say it hasn't been "observed" what you mean is in the "particle physics" sense, not the physical sense. Astrophysical observations are still physical. --ScienceApologist 23:28, 5 September 2006 (UTC)

I'd say there's no controversy about what it is, because we have no clue. ;) It's sure as heck been observed, about as directly as it can be. If people are really concerned about semantics, we could say "detected directly" instead or some such. -- SCZenz 01:50, 19 October 2006 (UTC)

That's not actually better: in the dark matter field, "direct detection" means DAMA/NaI, CDMS, etc., i.e. dark matter particles scattering in your detector. --Reuben 02:30, 19 October 2006 (UTC)

It is very wrong to say that the existence of Dark Matter has been proven.And for sure it still remains highly hypothetical.You can't prove something like that by observing a single image with supposed gravitational lensing in it,but you can always see what you want.

Critics comment in Observation section

I removed the phrase that "critics point to..." because the statement was sourced from a blog, not a scientist studying dark matter. And the source paper for the comments in that blog (found here) is on the LANL arXiv pre-print database, which is not a peer-reviewed source of scientific research (see also WP:OR), but is rather a database containing original research by numerous non-scientists in addition to scientists publishing research prior to submission to peer-reviewed journals. And the paper in question uses computer models as the basis for their criticism of dark matter theories, in contrast to and published prior to the recent observational discovery of dark matter seperate from matter by physicists in association with the Kavli institute at SLAC. While there are problems with dark matter, in the interest of the highest quality article standards at Wiki, the criticisms of dark matter ideas should come from much more credible sources than blogs and non peer-reviewed pre-prints, especially in light of the observational discovery of dark matter. This is why I made the edit. Astrobayes 19:25, 28 August 2006 (UTC)

I see my comments have since been reverted. I don't want to get into an edit-and-revert debaucle over something so simple so I'm calling for some perspective by individuals who regularly watch this article. Here's the situation: in August 2006, astrophysicists observed dark matter seperately from ordinary matter. This direct observation was confirmed by collaborators at institutions all over the USA and across the world. These results have by consensus been so convincing that the results are going to make it into no less than two peer-reviewed astrophysics journals. Thus far, any claims that this direct observation of dark matter doesn't prove its existence have not and according to their authors' comments thus far will not be published in scientific peer-reviewed journals. The article on the arXiv (which is a non-peer reviewed database that anyone, scientist or not, can upload to) that is used to refute the dark matter observations was actually published before the August 2006 observation of dark matter. It is therefore historically inaccurate to refute a more recent peer-reviewed observation with a historical non-peer reviewed paper using computer models. The language in the article as it currently stands does not therefore reflect the current status of observations of dark matter. How should we note this in the article so that we avoid endless reverts? Thanks for your perspective on this. Cheers, Astrobayes 22:28, 1 September 2006 (UTC)

One small correction: it's not quite right that the authors of the paper made their observations in August 2006. That's just when this paper was published. The observations that went into the paper were done well before this, and had been going on for many years already. In fact, very similar results had been reported in 2003 by some of the same researchers. The new feature of the August 2006 result is a much higher statistical significance (I think it was something like 8 sigma, compared to 3.4 sigma in 2003) for the claim that the centers of lensing are separated from the center of mass of the hot gas. But August 2006 is not when the observations or discovery were made, it's just when this particular announcement and paper came out. --Reuben 18:05, 21 January 2007 (UTC)

The paper said that they had proved the existance of dark matter, no dispute there. However, one would argue that proofs are never demonstrated, merely evidence that is consistent with the theory... which is far from a proof. Unfortunately most popular magazines and newspapers jumped on the soundbite, and reported the same. There is also no argument that others will accept the finding as proof, when what they really mean, is belief in the findings. Fortunately one paper does not make a scientific consensus, but we can report what one set of researchers has found --Iantresman 23:27, 5 September 2006 (UTC)

Thanks for your feedback. Language is a delicate art, and the art of semantics can often be a point of contention which in turn leads to troubled article improvements here at Wiki. I think that ScienceApologist made an appropriate and subtle correction to the wording in that section so that it reports rather than adopts a POV. Cheers, Astrobayes 05:47, 7 September 2006 (UTC)

More explanation

There are a couple things that would be very interesting to include in this article. One is how scientists estimate the expected mass of the universe, another is how scientists detect mass at a distance. Some of this may be implicit in the article, but since those are subjects that are so integral to the mystery of dark matter, I think it should be more explicit. Fresheneesz 09:11, 3 September 2006 (UTC)

The second question is answered in detail in the article, in the sections on rotation curves and gravitational lensing. For the first part, they basically count stars and gas and galaxies they can see; however, the details of this count are obscure to most people (including me), in large part I suspect because it is very tedious work. -- SCZenz 15:24, 6 September 2006 (UTC)

Fresheneesz, you ask some good questions and I sympathize with your point of view but the difficulty with answering explicitly the broad question (2nd) you've asked here is the same one that college physics and chemistry professors face when teaching a difficult subject. Higher subjects (say Quantum Field Theory or Cosmology) require an aptitude at their sub-disciplines (Electromagnetism, Celestial Mechanics, Optics, Relativity, etc.) that is not achievable in a short span of time, just as creating Wiki articles that answer in detail all of the possible questions that a complicated subject may inspire is likewise not possible in a short span of space on the article page. As SCZenz points out, it is true that the answer to your question lies in the years of tedious data acquisition and computer interpolation of the data, in synthesis with constantly updated models that must conform to the basic sub-disciplines of physics. We cannot possibly cover such things in this article past a mention in the appropriate section or appropriate links (which thus far the article does a fair job at, but you're welcome to put in new links if it would help). To inspire your curiosity further, here are some references which you may enjoy: NASA-GSFC Topics, The Planetary Mass Problem, The Universal Web, Stellar Mass Paper, The Initial Mass Function. I hope they help! Cheers, Astrobayes 05:44, 7 September 2006 (UTC)

"estimate the expected mass of the universe?" ... pointing to experiments measuring the cosmic microwave background would probably be what you are looking for (such as WMAP, COBE, VSA, etc). Also experiments such as Supernovae type Ia measure the Hubble constant which indirectly infer the mass density. By mass i mean non-relativistic mass. Baryon mass density can be found from the measuremnt of the light element abundance.

observing the dynamics of cluster and galaxies will give you an estimate (a bound more like it) on the total matter too. Theres been many observations and the current estimates of the matter density (based on particular models of course) is usually a best-fit analysis of combined data.

"how scientists detect mass at a distance" .... the real tricky part is measuring how far away the objects are from us. In a sense theres no real direct way to do this. It has quite an interesting history. Basically we look at specific objects which we know the mechanisms in which they radiate, and then measure the radiation that reaches us. Thats the jist of it although which objects we pick depends on what distances we are looking at: redshifts below or above one. Theres plenty of info on it that doesnt recquire much knowledge of physics except the basics.

I guess im trying to say is that the information is out there; not necessarily on wiki but its definatly out there. you just have to link to it. i dont think its necessary to have to put it in the article per se. that seems a little redundant. im sorry i dont have the references off the top of my head but you can find them easily these days like arxiv.org, prola.aps.org, etc ... or just try searching for it =) --Blckavnger 22:40, 15 November 2006 (UTC)

It seems to me that there are quite a number of misunderstandings of which I'll mention just two: 1) While some of the discussors treat dark matter as ordinary matter of which the light cannot be detected from Earth, others treat it as devoid of visible light, and still others treat it as devoid of any electromagnetic emision, absorption, deflection, diffusion, or diffraction (i.e., perfectly transparent). Of course, all of them may (and probably do) exist. It would be helpful to specify every time which dark matter is being discussed. 2) It is unfortunate that various types of dark matter are being DEFINED by the properties of the particles BELIEVED to constitute those dark matters! (It would be appropriate to ASSUME ...) Perry Mason mighht say "the assertor assumes facts not in evidence." The down side is that it precludes the consideration of a continuum constitution (as distinct from a particulate constitution) of dark matter. Fundamental skeptic 01:06, 11 October 2006 (UTC)

Dark matter is often misunderstood, in part because of the historical references discussed in the first section above where the term was originally used to mean dark clouds which absorbed light. In modern astronomy dark matter is anything which satisfies 5 criteria: 1) It does not interact with electromagnetic radiation (light) in any observed passband at a detectable level in any way (emission, absorption, deflection, etc) except through gravity. 2) It exerts a gravitational pull on its surroundings. 3) It reacts to the gravitational pull of its surroundings (i.e. overdense dark matter distributions pull additional dark matter into them). 4) It has a very low or non-existent collisional cross-section to both other dark matter particles (if it is particle in nature) and baryons (as compared to baryon-baryon cross-sections). 5) At the time of the last scattering surface of the CMB, the largest overdensities must be diffuse enough to only cause the observed fluctuations, and must be able to collapse fast enough to form the observed galaxies, clusters, and large-scale structure in later epochs. Because these are the 5 basic observations, any dark matter candidate must satisfy all of them to be considered a viable candidate. The reason why all of the discussed candidates are particles is because nobody (afaik) has come up with a way of creating a field based candidate that satisfies all 5 observations. 65.24.145.231 23:12, 21 October 2006 (UTC)

I agree, except with point 4. The cross section only has to be an order of magnitude lower than the baryon-baryon cross section, see here and here. Count Iblis 23:34, 21 October 2006 (UTC)

Here I mean the nuclear cross section not the electromagnetic. The electromagnetic cross section is actually not so relevant for the interstellar gas which is almost a collisionless plasma. Count Iblis 21:50, 24 October 2006 (UTC)

The reason it appears that "... nobody has come up with a way of creating a field based candidate that satisfies all five observations.", is because all such (fields-based) candidates are excluded from the literature. The gates to publication are held by scientists religiously devoted to the proposition that in the last analysis, anything ponderable IS CONSTITUTED OF PARTICLES, not necessarily baryonic but particles. Anything different is excluded at thosee gates. It does not allow the larger community of scientists to discuss such candidates. Such attitude seems very much like that of the Church against the Copernican system (for some centuries). On the other hands, errors that some Sophomores would not make are published (and remain unchallenged in print) when offered by "authorities." For example, about the consideration of dark matter (DM)as a possible explanation of the Pioneer Anomaly, one of the arguments against that explanation is that the presence of the needed amount of DM would disturb too much the Ephemeredes in the Solar system, ..." especially the Earth Ephemeredes, the most accurate ...". However, a good Sophomore student would realize that the argument is based on the error of inadvertently counting twice DM mass within the Earth trajectory: once in using those Ephemeredes to determine the total mass within the Earth trajectory (including DM),and then adding the DM mass a second time to make their argument. If instead they correct for the mass of the Sun (-140 ppb) to allow for the DM contribution to the total mass, then adding the DM (to recover the total mass) does not affect a bit the Earth Ephemeredes ("the most accurate!"). The other arguments against DM are also erroneous, but those errors are more subtle. My main point is that the gate keepers will allow only BIG NAMES in physics (whether right or wrong) to stray off the mainstream path, while others (again, right or wrong) are excluded. Therefore, while it would be correct to state that "a way of creating a field based candidate that satisfies all five observations has not been published," it is quite unjustified to state that "... nobody has come up with a way of creating a field based candidate that satisfies all five observations."Fundamental skeptic 21:40, 24 October 2006 (UTC)

All this doesn't matter. Wikipedia is not the place to publish original research, nor is it the place to advertise for your favorite fringe theory. If you want to be taken seriously, publish in a journal or argue at a conference. Wikipedia is not the place to spam for your favorite ideas and explanations. --ScienceApologist 22:33, 24 October 2006 (UTC)

Let me try to understand what you are writing: Are you accusing me of advertizing here for a favorite (fringe)theory just because I am pointing out the exclusion from discusion of a whole range of ideas (giving the impression that they do not exist)? Is it OK to discuss trends blessed by the establishment, but not OK to point out the proscription of other ideas? Are you saying that if the establishment proscribes a range of ideas, we are all to abide by it (because sending someone back to the locked gates achieves nothing)? How is this different from the attitude of the Church, for several centuries, towards the Copernican ideas? Fundamental skeptic 18:17, 25 October 2006 (UTC)

No, he's writing about Wikipedia policy: Wikipedia:No original research and Wikipedia:Fringe theories, and he might have added Wikipedia:Verifiability. If Wikipedia existed at the time of Copernicus, it would indeed say that the sun goes around the earth, citing religious authorities, and Copernicus might not have been notable enough to mention as a minority opinion. That may seem to be a strange choice, but it's policy because for every Copernicus there are a million snake oil promoters, and scientists should tell the difference, not us. If you want to argue that your theory is under-represented rather than arguing that it's true, we would then ask for Wikipedia:Reliable sources. Art LaPella 23:57, 25 October 2006 (UTC)

I had to go back and read carefully Wikipedia policy to realize that you are both right: pointing to a bias (suppression of a range of view points) in the official scientific literature is itself a point of view, which naturally is not voiced there and, therefore, has no place in Wikipedia. Mea culpa. Fundamental skeptic 22:24, 26 October 2006 (UTC)

Is there any theoretical underpinning to the idea that dark matter (and perhaps dark energy) could arise through infinitesimally small interactions between matter in our universe and matter in multiverses (sort of a "gravitational leakage")? Sammyj 21:21, 23 January 2007 (UTC)

Speculatively, M-theory and brane cosmology may be able to accomodate such phenomena. --ScienceApologist 21:45, 23 January 2007 (UTC)

Would you direct me to any papers that specifically disucss this possibility? Thank you. Sammyj 22:17, 23 January 2007 (UTC)

for starters --ScienceApologist 00:14, 24 January 2007 (UTC)

Thanks - I'll try to wade through this! Sammyj 01:11, 24 January 2007 (UTC)

New Mapping Information

I don't really know much on the technical side of dark-matter but there was an interesting article [ http://news.bbc.co.uk/2/hi/science/nature/6235751.stm ] on the bbc website that someone might want to incorporate into the wiki entry. You should check out the 3D graph anyway, its quite beautiful. Ironcorona 00:23, 8 January 2007 (UTC)

Dark matter isn't really my area either, but this seems like an exciting development. There's a good article on the Independent's website (it was front-page news!) that might help inform this article. [6] ▫ Urbane Legend ^chinwag 13:02, 8 January 2007 (UTC)

The first example of dark matter

It might be worthwhile including a paragraph or two on Le Verrier and his discovery of Neptune and non-discovery of Vulcan as examples of what is meant by dark matter. After Uranus was discovered, it was quickly realized that its orbit didn't follow Kepler's and Newton's laws. The two possible ways to solve this were to either put a new, unobserved gravitating body in a certain orbit (which were the calculations that Le Verrier did) or changing the way gravity worked (sound familiar?). It turns out that the planet Neptune was found, about 1 degree away from where Le Verrier had calculated it needed to be.

Fresh with success, Le Verrier turned to the other planet which didn't fit Kepler's Laws - Mercury. He created a new planet (Vulcan) interior to Mercury's orbit. In this case, it turns out the other solution (Newton's law of gravity was wrong) was correct, and Mercury's orbit was calculated using General Relativity without needing Vulcan. So we have the first example of dark matter (Neptune) being later made non-dark matter by being observed, and theoretical dark matter turning out to be non-existent (Vulcan) because we had the physics wrong. A lot of this is already in pages on Urbain Le Verrier, Neptune, and Vulcan, so the dark matter page would mostly need a discussion on why these were originally dark matter and why they're not now.132.235.24.91 21:16, 12 January 2007 (UTC)

Close, but no cigar. While Newtonian mechanics was famously verified by these observations to the point where scientists trust them, it is very different from dark matter. --ScienceApologist 15:53, 15 January 2007 (UTC)

I disagree - Until it was discovered, Neptune fit the description of dark matter exactly: 1) it's existence was detected by gravity, and 2) it did not emit, absorb, or interact with light at a level which was detectable. Once they figured out where it was and pointed a sufficiently large telescope at it, then they could detect the light it was reflecting, so it moved from being dark matter to regular matter. The same with Vulcan, it was an object which was postulated to exert a detectable level of gravity, but had never been seen. Once it was shown that our understanding of gravity was wrong, then it ceased to exist and went from being dark matter to non-existence. I guess the question is whether this article is about dark matter as a general astronomy term meaning "something that we know exists but can't see" or is restricted to dark matter as that particular particle which we think makes up the majority of matter mass in the universe. 132.235.24.91 21:09, 15 January 2007 (UTC)

Well, Neptune did not fit part 2) of the description (which you later point out) - it was reflective enough to be seen with equipment of the time, and somebody could have found it by accident. Quite unlike Dark Matter, which can't be seen even if we can tell pretty well were it should be found. Lars T. 00:29, 16 January 2007 (UTC)

For what it's worth, the article states: "dark matter ... may include ... dwarf stars, planets" which can be seen. Whatever. Art LaPella 00:48, 16 January 2007 (UTC)

Isn't Zwicky's "dark matter" also very different from our current understanding of dark matter? --Iantresman 22:15, 15 January 2007 (UTC)

Zwicky is a hard fellow to read. He enjoyed being crypic and rude to his fellow astronomers, and while he was often "right" sometimes he left interpretations so wide open that it would be hard not to be "right". --ScienceApologist 07:10, 16 January 2007 (UTC)

• But Zwicky's "dark matter" is very different from our current understanding of dark matter? --Iantresman 11:50, 16 January 2007 (UTC)

Not substantively. --ScienceApologist 12:30, 16 January 2007 (UTC)

While I agree Neptune does not qualify as the first detection of dark matter, it seems that Oort's discovery of excess mass in our galactic disk from measurements of star velocities should qualify. It predates Zwicky's far more famous result by a year. Easily found by googling for "dark matter 1932". If I hear no objection I'll add it to the main article. 99.231.137.234 (talk) 04:27, 24 December 2007 (UTC)

opening sentence

i'm not sure i understand the "it's only inferred" bit in the opening sentence.. i mean, isn't everything in physics "only inferred"?? do you mean that its existence is questionable? controversial? only a conjecture? surely if you can "infer" something's existence, then that's as good as you're going to get.. 131.111.8.98 10:38, 15 January 2007 (UTC)

Quite correct. It slipped through the watchlist radar. --ScienceApologist 15:52, 15 January 2007 (UTC)

• Incorrect. Dark matter is inferred in quite a different way to, for example, the way we infer a glass of liquid contains water. A glass of water, for example, can be tested, whereas dark matter can only be inferred by indirect observations. There is no comparison. --Iantresman 22:22, 15 January 2007 (UTC)

There is no such thing as an "inderect" observation as opposed to a "direct" observation. All observations are always inderect, but some are 'more indirect' than others. If you see or feel something then that's ultimately a calculation made by the neural network in your head. What really matters is the amount of information we get about the thing we want to know about. How much do our observations constrain the theories about what dark matter can be? This is the relevant question. Similarly if you "directly" observe an object, and you say that your observation constrains the size of the object in the range between 1 and 1.5 meters, then that statement contains the relevant information concerning the length of the object. The fact that you "directly" observed it adds nothing to that statement. Count Iblis 23:10, 15 January 2007 (UTC)

• There are no observations, indirect or otherwise, on dark matter. The temperature of a glass a water I can measure directly by sticking a thermometer into it. The gravitational force from a lump of metal I can measure directly by sticking another suspended mass next to it. "Infer", and "directly" or "indirectly" are all just words. But I'm sure there's a more accurate adjective to describe what we mean here. --Iantresman 23:24, 15 January 2007 (UTC)

It's just plain false to claim that there are no observations... on dark matter. There is some phenomenon which is "out there". That phenomenon is "observed". That phenomenon has a name: "dark matter". Therefore there are observations... on dark matter. --ScienceApologist 07:12, 16 January 2007 (UTC)

• And by the same logic, the observations support MOND. Or Peratt's interacting Birkeland currents. Or non-Baryonic Phlogiston.
• Dark matter is the name of a hypothesis. Hypotheses are not observed; they're inferred. --Iantresman 11:56, 16 January 2007 (UTC)

No, Ian. There is a difference between what you are describing and that scientific consensus-naming of an observed phenomenon. Dark matter is not just a "hypotheseis". Just like CO-cooling or Bok globules are not just hypotheses. --ScienceApologist 12:30, 16 January 2007 (UTC)

• The very first sentence of the article says that dark matter is matter; It does not say it is the name of a phenomenon. --Iantresman 13:26, 16 January 2007 (UTC)

Matter is a phenomenon just like everything else. So says Immanuel Kant, anyway. (And he was an astronomer!) --ScienceApologist 13:55, 16 January 2007 (UTC)

• Dark matter is not inferred in the same way that, for example, liquid in a glass is inferred to be water. --Iantresman 15:14, 16 January 2007 (UTC)

Have a cite for that one? --ScienceApologist 19:11, 16 January 2007 (UTC)

• Do you have a reference saying they are inferred in a similar way. I have references saying that dark matter is (a) inferred (b) observed indirectly (c) is a hypothesis. --Iantresman 19:23, 16 January 2007 (UTC)

Okay, so you don't have a cite for that one. Good, then this discussion can cease. --ScienceApologist 19:24, 16 January 2007 (UTC)

• And neither do you. --Iantresman 20:34, 16 January 2007 (UTC)

Don't know about the inferred part but it's still only an hypopthesis. Dark matter is not a phenomenon but hypothetical matter to explain a phenomenon. There are other explanations for the phenomenon and dark matter is not proven. The sentence gives the impression that it is matter somehow proven to exist when it is only matter hypothesised to exist. 212.100.250.230 (talk) 12:50, 18 December 2007 (UTC)

It's not just hypothetical matter: the properties of the dark matter are well understood from model comparisons in cosmology, for example. We know that something exists that has the properties of dark matter and that something, right now, is called "dark matter". ScienceApologist (talk) 15:38, 18 December 2007 (UTC)

You may think and believe there is something there but you don't know for sure. Even the article says there are other explanations besides dard matter like an incomplete understanding of gravity or quantum mechanical explanations. Calling it matter when it is only hypothetical implies that it exists when it may or may not exist. It's not non-hypothetical until it is shown to actually exist and exist where you need it to exist. 83.138.172.76 (talk) 15:32, 20 December 2007 (UTC)

Dark Energy Comes From Life Intelligence and Patterns

Everything is energy. Energy can not be created or destroyed. By defenition, the energy that life has and that intelligence contains and that patterns in general posses, has to be comming from somewhere. The universe is not expanding or getting bigger, it is just getting more organized and structured as life evolves and celestial bodies orient themselves and gain structure. The new energy that they embody came from a source the phisical mass and is thus observed as dark matter because we can not SEE patterns, we can only observe them, nevertheless they still have energy. This same energy was origionally sourced from massive objects when they were random and did not have much intellectual or structural energy. As matter takes shape or gains structure, patterns, intelligence it appears to become cold, more distant, bigger. The universe appears to be expanding, but it is not really, where there was once matter, the same energy is not manifested in intelligence as matter in between is disipitated. More energy in intelligence is contained, as a result, less physical matter as well as heat is observed. This theory also proves the existance of aliens and extraterestrial life forms because we can not see or detect them, but their energy from intelligence and the lack of energy in matter that they have converted is absorbed. It is predicted that the universe will continue to appear to be getting bigget and colder and the proportion of dark matter and dark energy is increased as more matter is converted into life.

The expansion of the universe is accelerating because life and civilization is evolving at an ever increasing pace as the build up of patterns is cululative as it is self replicatory.

Everything is energy. Patterns, structure or order is energy. Order in the universe is increasing. This energy has to come from somewhere, it is obserbed from physical energy or matter. Energy can not be created or destroyed. Structure must be obtaining it's energy from somewhere. Structure can't not have energy because it has potential and everything is energy. It is very simple. Dark energy is not alive, it is life. —The preceding unsigned comment was added by Nadyes (talk • contribs) 14:28, 26 January 2007 (UTC).

Luminosity is measured in units of energy per second so why is there so much energy in dark matter?--24.22.111.99 23:22, 26 January 2007 (UTC)Kyle McKenzie Street

Energy is required for the creation of life and intelligence. Life can not be seen. We can only see the physical things or the carriers of life. Life itself however is what contains the energy and that is why that energy is dark or invisible. The presence of so much dark matter and dark energy not only indicates that there is intelligent extraterestrial life, but that there are a lot of other things besides simple particles and atomical entities that we can not detect in the universe.

Dark energy comes from extraterrestrial alien influence to keep Hyperspace obscure for us. [7]

I don't think that the content, nor the scientific accuracy of anything be said here is correct. energy can't be destroyed yes, but please, no philosophy and no aliens. This is the discussions page not the aliens page.Tourskin 00:26, 26 February 2007 (UTC)

Nothing has a body. If you use a microscope to zoom into atoms, you'll see that there is nothing physical, it keeps breaking down into more particles and beans. Further it breaks into waves, vibrations, fields and mathematical patterns. There isn't a single thing in theis universe that we know of and can identify that has a real physical body. Everything we see and know of as matter is actually a cloud of patterns and vibrations that we can understand and identify as reas, and thus we call it matter. There are also patterns which we can not understand, but just happened to be able to measure the gravitational effects from. Thus we call it dark matter mecause we can not identify anything else about it. Presumably these patterns are more complicated then ourselves which is why we can not contain them. Since they are more complex than us, or more advanced than us it might just be what we would call higher life forms or extraterrestrials. We have to resort to more phylosophical or deductive reasoning. Obviously our scientific method has not given us the answers so we don't have a choise. Phylosophy and art is also part of science so we have to include it if we are to understand this universe as a whole.--Nadyes 10:56, 28 February 2007 (UTC)

1. Wikipedia:Attribution.

2. If we do need (properly attributed) philosophy, it belongs in articles like philosophy of science. Art LaPella 20:56, 28 February 2007 (UTC)

Dark matter proved unnecessary by frame-dragging effect(spinity)

I tried to modify the dark matter main page, but somebody deleted it. I am very diasppointed. But, I think I find out the truth. Dark matter is unnecessary!! Considering the frame-dragging effect derived by general relativity, dark matter is not neeeded. The frame-dragging force(I call it Spinity) is SJm/r^2, S=2G/c^2. If spinity is considered in deduction of virial mass, the newly modified virial mass will become 2RV^2/(G+SWr^2). The discrepancy of virial mass and mass estimated by light-to-mass ratio is greatly reduced. In Mily Way galaxy, newly modified virial mass is 10^6 less than original predicted virial mass. Thus, dark matter is unnecessary in the Milky Way galaxy. Please go the website Http://www.phy.ntnu.edu.tw/demolab/phpBB and type wanchung in search box. Or, please type frame-dragging and dark matter in google search box. You will find the title-dark matter proved unnecessary by spinity for detailed deduction. Wanchung Hu 15:37, 1 March 2007 (UTC)

I corrected a typo you made in your recent addition, but I can't otherwise comment on the content of your new text because I'm a non-expert. I have the article on my watchlist solely to watch out for blatant vandalism and/or mistakes in grammar. I'll leave it to the experts to debate the inclusion of this new information or not. - Itsfullofstars 17:46, 1 March 2007 (UTC)

I propose removing this, as it is clearly an advertisement for original and unvetted research. Speaking as a dark matter researcher I find the result pretty dubious, but that's irrelevant. If this work stands up to scrutiny it could be included in this article at some future date, but at least for now it doesn't fit in. —The preceding unsigned comment was added by JPFlip (talk • contribs) 18:25, 1 March 2007 (UTC).

Please see WP:OR. Wikipedia is not an appropriate place to publish your original research. --Reuben 20:00, 1 March 2007 (UTC)

Rewording last sentence (and other sentences in) the opening paragraph.

September 2007

Comment: this sentence:

"Fritz Zwicky used it for the first time to declare the observed phenomena consistent with dark matter observations as the rotational speeds of galaxies and orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies."

is confusing, in the normal English sense of being difficult to parse. I wish it could be reworded. My comment has nothing to do with the content. I don't feel qualified to edit this highly technical page, even in an attempt to clarify its use of language.

After comparing it to Fritz Zwicky#Dark matter, I think what the sentence means is: "Fritz Zwicky was the first to assert that dark matter accounts for observations of rotational speeds of galaxies..." continuing as before. But I'm not sure if that sentence would be true. Art LaPella 20:32, 16 September 2007 (UTC)

March 2007

"All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than is directly observable, indicating that the remainder is dark."

Any doubts about the evidence are covered by the word 'suggest' in the beginning of the sentence.

The last bit of the sentence could be stronger. "...observable, indicating that the remainder is dark." could be replaced with "...observable, making the remainder dark." Suggestions for other wording are welcome. Pukkie 10:43, 3 March 2007 (UTC)

That could work. It could also be "observable, and the remainder is dark" or "observable, and that the remainder is dark," so that the "remainder is dark" is already covered by the first "suggest." Right now the "remainder is dark" is sort of doubly-hedged, by "suggest" and "indicating," and I think you're right to try to change that. --Reuben 17:58, 3 March 2007 (UTC)

I changed it to "observable, and the remainder is dark". Pukkie 11:44, 7 March 2007 (UTC)

Question from a layman

Does this dark matter stuff relate in any way to the old Aether concept? —The preceding unsigned comment was added by 142.161.181.175 (talk) 20:00, 3 March 2007 (UTC).

There were several old Aether concepts, but Aether theories says "In physics there is no concept considered exactly analogous to the aether. However, dark energy is sometimes called quintessence due to its similarity to the classical aether." Dark energy is a lot like dark matter - neither can be created and studied in a laboratory. Enemies of dark matter enjoy comparing dark matter to aether or to any discredited theory, but of course that doesn't prove dark matter is real or unreal. Art LaPella 20:28, 3 March 2007 (UTC)

Yes. I believe that Dark matter is another Aether theory. Please see my above article(Dark matter proved unnecessary by frame-dragging effect). Dark matter is a wrong theory, especially in milky way galaxy. If dark matter really exists, it should exist in ellipical galaxies as well. But, there is no dark matter in ellipical galaxies from a research result in Science 2003,301(5640):1696 by Romanowsky AJ. Dark matter doesn't exist!!!!!!!Wanchung Hu 18:19, 6 March 2007 (UTC)

whether dark matter turns out to be another Aether theory is yet to be seen. however if you take out dark matter in cosmological models, its very hard to find good fits to cosmological data such as Sne IA and Cepheid red shift observations, cosmic microwave background, and matter distribution in the universe today. As you can imagine, these equations can be quite complex and often have degenerate consequences from changing variables such as the % of dark matter in the universe.

as of now, dark matter is just a word. there is no set definition; it is "defined" by its properties that it needs to have (i.e. nonrelativistic energy today) to not be detected and give the gravitational pull needed in spiral galaxies (or better worded , interpreted from observation). there is no particle in the standard model of particles that would fit this bill, although extensions do explain some of it like SUSY WIMPS or Axions. However, it might not exist at all and then we will have to look into General Relativity or Statistical Mechanics or experimental errors or etc etc. to explain this. This topic is current research, so we'll have to wait and see.

i believe that observational interpretation of some elliptical galaxies do show dark matter, although not at the level a lambdaCDM universe would like. NGC 3379 survey was the most recent one i believe; you can look it up on arxiv.org Wanchung, you have already presented you view along with a link. wikipedia is not a scientific forum as stated before. please write up a scientific paper and present it for publishing or pre-print online libraries such as arxiv.org so the scientific community can discuss you research. --Blckavnger 19:40, 6 March 2007 (UTC)

questions from a scientifically inclined laymen

Is it perhaps logical to think that dark matter/energy is perhaps only quasi real or maybe 1 dimension out of phase with our universe? —The preceding unsigned comment was added by Avatar of Nothing (talk • contribs) 23:01, 3 March 2007 (UTC).

Most any such Star Trek theory is arguable, as long as we can't catch the stuff and analyze it. Art LaPella 23:44, 3 March 2007 (UTC)

But isn't it to cover this sort of situation that Popper came up with his criterion of falsifiability. For any hypothesis to be given houseroom to start with it has to be open to falsification. If it's not falsifiable, it's not properly within the realm of science. Davy p 03:47, 4 March 2007 (UTC)

Sometimes lack of falsifiability is a function of lack of understanding. When Copernicus first penned De Revolutionibus he roughly proposed that there was no falsifiable way to distinguish between his model and Ptolemy. If strict Popperians had been around then, they would have roundly criticized him for being "extra-scientific". It was only after Kepler repositioned the Copernican model into the 3 laws of planetary motion and Galileo developed frame dynamics that people could see why the arguments used against heliocentrism were incomplete or based on misunderstanding of physics. Telescopic evidence that would falsify key-features of the geocentric model would follow only afterwards. --ScienceApologist 13:59, 4 March 2007 (UTC)

ok. So the concensus is I may be right, but at the current stage it must be assumed I am wrong because it can't be falsified, right? I wasn't originally thinking of ST but now that you mention it I am pretty sure they mentioned something about it a few times. Avatar of Nothing 15:26, 5 March 2007 (UTC)Avatar of Nothing

Dark matter 'proof' called in doubt

The Dark matter 'proof' has been called into doubt: http://space.newscientist.com/article/mg19125684.200-dark-matter-proof-called-into-doubt.html and http://www.eurekalert.org/pub_releases/2006-09/ns-dm090606.php Jazzman123 22:33, 23 April 2007 (UTC)

A few thoughts:

• New Scientist is not a very authoritative source. It tends to put a very positive spin on anything outside the scientific mainstream, uncritically overlooking even very serious flaws. It's not a science journal, it's a popular magazine about science, with a particular editorial bent.
• The Eurekalert link is just a copy of the article from New Scientist.
• John Moffat's work on the Bullet Cluster hasn't been published in a peer-reviewed journal as far as I know, so it's also hard to use that as an authoritative source.
• Moffat's work on MOG and other MOND-related work are good science, and are in no way "fringe" theories. Wikipedia should take them seriously.
• We do need to be careful about uncritically using phrases like "direct proof of dark matter."

--Reuben 23:17, 23 April 2007 (UTC)

This is just another round in the dark matter vs MOND debate. One method adds extra matter, the other modifies the laws of gravity to make it look like there is more matter. --h2g2bob 01:15, 24 April 2007 (UTC)

Moffat has written 2 articles on astro-ph, neither of which he appears to be submitting to journals. If you're going to quote a results of a researcher, you should quote the papers and not news coverage of the paper. You can see the history of this article about how these results have over time been added, deleted, added, modified, deleted, etc. Wikipedia does not cover original research, only reports on refereed, published results, and astro-ph by itself is not publishing a result. 132.235.24.91 21:03, 29 April 2007 (UTC)

Can this unknown huge mass in cluster of galaxies proceed from dark holes? or can this huge mass of universe attached to dark matter do not exist almost at all?

Sounds a little crazy(or an answer) but what if the number of dark holes are more spread in the universe that we are thinking, if it number in a galaxy is huge(relative of course), they are (invisible)hard detectable even in our milky way - in far off galaxy almost impossible(at this time). Their presence can explain the needy mass in galaxies and cluster of galaxies and no wonder that this can do so distortion of behind light.

So this effect is not so hard proof for existence of influence of dark matter's attraction(or dark matter's huge mass) in cluster galaxies.

When we want to count the mass of universe of course we need to take in consideration not only the mass of the galaxies (including this invisible black holes) but and the mass of small particles like all radiation kind - alpha, beta, gamma.... photons (not sure about radio wave influence to mass but .......)

But... If is a little funny about the big influence of so small particles like light (photons) to the mass of universe what to say about dark matter particles much smaller like neutrino... ???...

Let's take some example:

Supposing, that universe represent an aquarium and we are some kind of life being in that aquarium that has the technology of an optic microscope and we try to calculate the mass off universe.... Oh ! this explain ... the mass of water is huge to other things BUT... let's think again the water can't be seen but it is sensed...

Supposing, that universe represent in this case a greenhouse where in the place of water is air and we have the same life being with technology of optic microscope and they try to calculate the mass off universe ..... ???.. . this is not the same thing, in this case the mass of invisible air (less sensed) is not huge...

Let's return to our problem, with our technology we hardly hardly discovered neutrino that isn't sensed at all...... maybe this small particles don't contain this mass that we try to attach to something (in we don't find it in this undiscovered black holes) or maybe it don't exist almost at all => maybe this can explain Why galaxies are estrange(remove, go away) from each other with acceleration ! (this deficiency of gravitation may be the reason why it can't keep galaxies together so they are estrange with acceleration having their angular acceleration from moving) or do you think is more real the theorem of some kind of "dark forces" pushing them away.

I'm not a scientist, just a ordinary student :) but waiting comment from real scientist :)

sorry if there are grammatical mistakes, but I hope you understand me :) Mark md4 16:56, 18 May 2007 (UTC)

I'm not a real scientist, but I believe their answer would boil down to: We've thought about things like that, but we just don't know. This page is intended to help us improve the Dark matter article, which is intended to report prevailing scientific opinions, so a better place to discuss theories like yours would be at blogs like [8] [9] [10] etc. (Warning: In general, there are a lot more theories from newcomers, than interest in them from experts.) Art LaPella 17:50, 18 May 2007 (UTC)

Hi Mark, you can also ask questions like this at the Wikipedia:Reference desk, where there is a "Science" category. I've found that very obscure and strange questions will usually get an impressively quick and complete answer there. For a short answer to your questions, cosmologists try to be as thorough as possible in studying the mass and energy budget of the universe. This includes radiation (photons are currently a very small part of the total), neutrinos (constrained to < 10% or so, probably much less), black holes (which are not completely ruled out as dark matter if they have certain mass ranges, but I don't know of models where this happens), etc. Electrons (a.k.a betas) and helium nuclei (a.k.a. alphas) are found in cosmic rays, so they are up there. There just don't seem to be enough of them to solve the dark matter problem. There could be dark matter particles much lighter than neutrinos: axions. They are a very good candidate, in fact. --Reuben 18:29, 18 May 2007 (UTC)

Art LaPella you are right, but I saw there up a "discussion" tab(I didn't understand it in the right way), thanks for links ;Reuben, I understand question for the desk, no debate on wiki. Mark md4 19:30, 18 May 2007 (UTC)

Dark matter=Celestial ether?

Is dark matter just another name for the celestial ether that was thought up in the 1800's and early 1900's and was later proved to not exist by relativity theory? —Preceding unsigned comment added by 72.69.85.212 (talk) 12:55, 21 June 2007

No. the central features of Luminiferous aether was that it was an all-pervading backdrop to the universe that was thought to interact (i.e. transmit) light. Dark matter, however, is much more lumpy, and only interacts with other objects by gravity. Mike Peel 19:16, 21 June 2007 (UTC)

Yes. At least according to the modern theoretical research of the dynamic aether fluid crystal-like structure (compare to this recent discovery) that permeates all space, accounts for the creation of matter and regulation of quantum activity and, in the macro scale level, for observed cosmological phenomena that defies the constantly patched standard model and derived popular theories.

Should you perform an analysis to the historical of a few articles, i.e. aether theories, you will also notice that editors around have been deliberately opposing-erasing the addition of these type of current data-research into the articles (allowing only historical references to what all know to be misconceptions of the 19th century physicist about an [inexistent] static or luminiferous aether, obviously discarded through the 1887 MMX). The direct relation between the term Dark matter, as expression[s] of our ignorance (see source) and the dynamic Aether subtle medium/substance is established (see link) by researchers as Dr. Harold Aspden, a physicist and electrical engineer (see background) whose Aether theory and derived predicted values (of proton-electron mass ratio, alpha, muon g-factor, electrostatic spin, etc.) is recorded in some of the major peer-review journals (i.e. Lettere al Nuovo Cimento and Physics Letters A); however data about this researcher, as all current data about the dynamic aether, was also recently banished as "fringe" and "non-notable" by Wikipedia's relativists science editors (see deletion log).

Yet, in order to discard the Aether they would have to erase not only Dark matter but all that is already experimentally termed as the vacuum energy and related vacuum fluctuations, the zero-point energy and more or less related effects, such as the Casimir effect, Van der Waals force, etc., and all currently ongoing experimental research in these fields. Well, but these relativists, along with the majority of the world, and in spite of all the recent observational results, still fanatically [my pov] adhere to the space-time, the big bang and the expanding universe wild stories... Cheers, from a truly layman in these fields of science. —The preceding unsigned comment was added by 213.58.99.29 (talk • contribs) 22:10, 12 August 2007 (UTC).

Molecular Hydrogen hypothesis

An article here: http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/421111 appears to state that the authors detected large amounts of intergalactic(?) molecular hydrogen which they submit could constitute a significant part of the baryonic dark matter. I'm not able to look at it myself since it's behind a paywall, but I am wondering if this should be mentioned as one of the possible explanations of/sources for baryonic dark matter in the article.

I am aware that this hypothesis that dark matter is nothing more than H2 is promoted by various people who do not accept the Big Bang as a valid explanation for the origins of the universe (many of whom are cranks or else legitimate physicists who are clinging to old theories), but the article appears to be reporting on actual findings, rather than speculation... were those findings later found to be flawed? Glaurung quena 16:46, 24 August 2007 (UTC)

There's nothing wrong with those findings, and molecular hydrogen can be a big part (or the bulk) of the baryonic dark matter. There are also some people who claim that hydrogen clouds make up all the dark matter - and sometimes also claim that the same molecular clouds can explain away all kinds of other things, like cosmological redshifts. But leaving those theories aside, the finding that baryonic dark matter can be made up of molecular hydrogen clouds is perfectly real. Then we come to an issue of imprecise terminology. The term "dark matter" is often used to mean nonbaryonic dark matter in particular, since it's by far the most dominant component. The Wikipedia article is an example, as it only makes a few mentions of the baryonic kind. There's no separate article for baryonic dark matter, although there is a red link from this article. If you'd like to try clarifying the status of baryonic dark matter in this article, that would be great! --Reuben 18:30, 24 August 2007 (UTC)

Good reference?

I was recently pointed at this paper: Report on the Direct Detection and Study of Dark Matter, from "The Dark Matter Scientific Assessment Group (DMSAG), A Joint Sub-panel of HEPAP and AAAC." It looks like it would be a pretty good source for the article, as it summarizes many of the recent developments in the field. Since it is something of a funding recommendation, I suppose it might have a particular bias to it in that respect. --Starwed 09:28, 2 September 2007 (UTC)

Out of date? / Future events warning?

I found something that was out-of-date. Do you think we should tag this article as future events? Template:Future or something to indicate it needs constant updating, or perhaps keep a list of things that may be outdated very soon? How about moving all the discussions of potential future research and papers to a new section to make it easier to maintain? Or is just something generally accepted for this topic? Sentence in question: "In research due to be fully published in spring 2006, researchers from the University of Cambridge Institute of Astronomy claim to have calculated that dark matter only comes in clumps larger than about 1,000 light-years across, implying an average speed of dark matter particles of 9 km/s, a density of 20 amu/cm³, and temperature of 10,000 kelvins.[17]" -- Netdragon 19:14, 23 September 2007 (UTC)

As I understand it, scientific matters shouldn't be reported at all on Wikipedia until they've gone through peer review. It should be possible to find the publication and cite it properly in this case. If not, perhaps it should be deleted. That could apply to other preliminary results that have been announced but not published. Discussion of future experiments or research should be fine, but preliminary results are somewhat questionable. --Reuben 03:47, 24 September 2007 (UTC)

Here's one publication from Gilmore and others, covering part of the announcement. I haven't checked whether everything's there or not. astro-ph/0608528. This paper goes with their presentation from the 2006 UCLA dark matter conference, where Gilmore presented remotely. You can also find his slides here: gilmore.pdf. It will be published in Nuclear Physics B along with the rest of the conference proceedings, probably out ~ early 2008. --Reuben 04:01, 24 September 2007 (UTC)

Ring of Dark Matter

As far as I know, the community is rather certain that this ominous ring is an artifact, based on bad data analysis, namely circular correlations of noise. This assumption is also supported by the fact, that the group's description of their work in their paper was very fishy and partly self-contradicting. Therefore, I suggest to delete this part in the article.
--René 21:50, 17 October 2007 (CET)

Dark matter as Matrioshka Brains

It is equally reasonable, given the age of the universe and the possible evolution of civilizatiosn billions of years older than ours (see the work by Lineweaver's group), that there are many civilizations which have evolved to the Matrioshka Brain stage and which have decided to leave their galaxies, thus giving ruse to an abundance of "dark matter". Such civilizations which radiate energy at temperatures very close to the CMB temperature would be undetectable using current methods. Discussions of "dark matter" which do not take into account the end stage evolution of advanced technological civilizations (and what they would look like) are inherently incomplete.

Robert 11:07, 6 November 2007 (UTC)

Fourth Universal Field

I've removed (for a second time) a section that appears to be original research. The citation given was to a book published by a vanity publisher, rather than a peer-reviewed scientific journal. That is unacceptable for the purposes of Wikipedia. --131.215.123.98 20:32, 11 November 2007 (UTC)

Reply. I was the one who posted this topic. Being new to Wikipedia contributions, I was unaware of the policies upon which the removal was based. I now understand and I have no quarrel with the removal. Nonetheless, the topic is interesting to me and I would be pleased to see some talk related to it. The thesis that I had mentioned has a foundation in the writings of James Clerk Maxwell, but few researchers ever picked up that thread from him. If I posted a brief mention of the topic based on Maxwell's work and a few follow-ups from verifiable sources as a minority view, would the topic likely survive the editor's pen (assuming that the topic then appears relevant)? Ordovico 23:21, 11 November 2007 (UTC)

I still doubt that would pass the test. The equation you mentioned in the article looks a lot like gravitomagnetism to me (a low-order correction to Newtonian gravity which comes from General Relativity). Other scientists know about gravitomagnetism, but haven't suggested that that is an explanation for dark matter.

Nitpick: since this was put under "Alternative explanations", it would explain why DM need not exist. Lars T. 01:05, 12 November 2007 (UTC)

Granted. My point stands, however, in that scientists know about gravitomagnetism, but haven't suggested that it explains why dark matter need not exist. (Precision isn't always my strongest suit.) --131.215.123.98 01:22, 12 November 2007 (UTC)

All additions you make need to be based on material published in reputable sources -- e.g., Physical Review Letters, in this case. For example, a claim that it "obviates the need for QCD or string theory" is a pretty huge claim -- even for an unverified theory -- and would have to be explicitly stated in a very reputable source. Maybe you should introduce these kinds of edits on a talk page, and only move to an article after other editors have chimed in. --131.215.123.98 00:47, 12 November 2007 (UTC)

Orientation Question. Directed to the editor: why was I unable to detect the deletion of the article in the first place? My later changes were not an edit war but simply resulted from confusion about why the article was missing. I checked "related changes" where I expected to see entries disclosing my original addition of text and any later edits that removed my text, but I found neither. Should I have been looking elsewhere? Ordovico 23:26, 11 November 2007 (UTC)

"Related changes" is "a list of changes made recently to pages linked from a specified page". What you are looking for is the "watch" link on the top of the page. Lars T. 23:54, 11 November 2007 (UTC)

I think you want to go to the relevant article itself (not its talk page), then click "History", which is probably right at the very top center. Also, I'll note that I really don't think this was an edit war; I'm sure your edits were in good faith. Welcome to Wikipedia. --131.215.123.98 00:47, 12 November 2007 (UTC)

Small remark. You say that one should cite only reputable sources, well I agree on that. But why then there is still this picture of the ring-like dark matter structure in the article? There is no reputable source in the article. Furthermore, as far as I know, the results yielding this picture are not acknowledged and in wikipedia there should be only information that is correct for certain.
--René 21:17, 13 November 2007 (CET)

I thought it was gone. It shouldn't be replaced until it's cited. If you have a some evidence that it shouldn't be here, that might help convince whoever put it back. --131.215.123.98 01:49, 14 November 2007 (UTC)

Well, maybe the following link would suffice as citation: http://hubblesite.org/newscenter/archive/releases/2007/17/image/a/

However, of course there is no source stating that this is not accepted yet.

--René 08:45, 14 November 2007 (CET)

Are planets Dark matter?

"The composition of dark matter is unknown, but may include ordinary and heavy neutrinos, recently postulated elementary particles such as WIMPs and axions, astronomical bodies such as dwarf stars and planets (collectively called MACHOs), and clouds of nonluminous gas. Current evidence favors models in which the primary component of dark matter is new elementary particles, collectively called non-baryonic dark matter."

Are planets dark matter? Tyr Lord Of Combat (talk) 17:50, 13 January 2008 (UTC)

Look at the Wikipedia article for baryonic which will allow you to discern what non-baryonic means.--JEF (talk) 17:54, 13 January 2008 (UTC)

Planets would be classified as baryonic matter.--JEF (talk) 17:56, 13 January 2008 (UTC)

Well, I guess he knows and is trying to point out that "astronomical bodies such as dwarf stars and planets (collectively called MACHOs)" and also the following "and clouds of nonluminous gas" should be cut from the paragraph. Lars T. (talk) 20:43, 13 January 2008 (UTC)

Re new gravity model

Looks like this might be worth reading and mentioning in article:

"In a paper in the August 3 online edition of the Institute of Physics' peer-reviewed Journal of Cosmology and Astroparticle Physics, they put forth the idea that scientists were forced to propose the existence of dark energy and dark matter because they were, and still are, working with incorrect gravitational theory.

The group suggests an alternative theory of gravity in which dark energy and dark matter are effects – illusions, in a sense – created by the curvature of spacetime (the bending of space and time caused by extremely massive objects, like galaxies). Their theory does not require the existence of dark energy and dark matter.

“Our proposal implies that the 'correct' theory of gravity may be one based solely on directly observed astronomical data,” said lead author Salvatore Capozziello, a theoretical physicist at the University of Naples, to PhysOrg.com."

Dark Energy and Dark Matter – The Results of Flawed Physics? By Laura Mgrdichian, Copyright 2006 PhysOrg.com Discussion of J. Cosmol. Astropart. Phys. 08 (2006) 001.
http://www.physorg.com/news77190620.html

-- Writtenonsand (talk) 21:36, 31 January 2008 (UTC)

It could potentially be mentioned in the article, along with other modified gravity theories. The PhysOrg article is not a great source, though (and is from 2006). What would be needed is to show that this model has gained notability and been accepted by others in the field as a workable theory of gravity that's consistent with all observations in support of dark matter and dark energy. In particular, it would be good to see whether or not this modified gravity model is still in the running after the Bullet cluster observations. Unfortunately, I don't see a talk on non-Riemannian gravity at next month's UCLA conference [11], but there is one on observational tests of modified gravity theories in general, so perhaps it will come up. I encourage you to look for some current info on the status of the Capozziello et al. model. --Reuben (talk) 05:40, 1 February 2008 (UTC)

i believe this article already has a decent section on modified gravitational theories toward the end. i think its adequate considering the evidence for dark matter and the lack of success current alternative models of gravity have sofar. of course some day that may change, but i believe that the growing consesus is that dark matter is more plausible explanation than any modified theory so far. theoretical work will continue on modified gravity of course, and it could very well be that there is a needed modification as we explore large z>10, but at this point i think its fair to say that the majority of cosmologist agree on a mostly cold dark matter model--Blckavnger (talk) 16:16, 6 February 2008 (UTC)

Another question about dark matter

I was just wondering why dark matter, even if it exists as an exotic particle that is invisible to the electromagnetic spectrum, is not observed on Earth. I don't mean it like "why, if it's right in front of us, can't we see it", because the challenges of observing a truly invisible form of matter are obvious, but more like "why don't we see gravitational effects of this supposedly massive (in the strictest sense of the word, i.e. 'containing mass') substance in our everyday Earth-bound physics?" The mass of our planet is a known quantity, and we base that not on observed matter plus dark matter, but solely on observed matter. Same goes for our cars, our structures, and so on. Assuming there's more dark matter than observeable matter at a ratio of about 6:1, why doesn't this translate even a little bit (as I realize the argument I might be getting back would be something pertaining to the fact that dark matter is "lumpy") to what we can see? Goland (talk) 18:13, 6 February 2008 (UTC)

Great question! In a "standard" dark matter halo with dark matter made of exotic particles, the density of dark matter in the vicinity of Earth should be about 0.3 GeV / cm^3. According to google calculator, that's about 5x10^-25 times the density of water! So although the dark matter halo is more dense than the ordinary matter when you average over very large volumes (including mind-bogglingly huge empty spaces), it's far, far less dense than a planet. Actually, though, there's another, independent reason why we don't detect the dark matter in things like the mass of the Earth. Assuming the dark matter is not too clumpy, there's as much of it in any other Earth-sized volume as inside the Earth itself. This means that the gravitational tug of the dark matter in our neighborhood is pulling on you equally in all directions, and you can't detect it that way. On the scale of a galaxy, there's more of it in the direction of the galactic center than in the opposite direction, which has a huge effect on the orbits of stars (including the Sun) around the galactic center. --Reuben (talk) 01:29, 8 February 2008 (UTC)

Gravity

While we don't fully understand gravity we will not be able to understand dark matter, as the latter is so closely connected to first. For all we know gravity might work in a different way that we think and this will make up for the 'lack' of mass. —Preceding unsigned comment added by 195.204.65.2 (talk) 12:05, 7 March 2008 (UTC)

Is this a suggestion for how to change the article? Remember at Wikipedia, it doesn't matter what we fully understand here. Wikipedia is intended to reflect leading scientific opinions worldwide, not just ours. For more details see Wikipedia:No original research and Wikipedia:Verifiability. Art LaPella (talk) 21:13, 7 March 2008 (UTC)

dark matter and redshift?

Would dark matter or I guess any gravitational field create a redshift in the light that passes through it?

It seems that the farther light travels in space the greater red shift it has. Could this be from the amount black matter gravity that has effected the time space that it has travelled?

--Tommac2