Talk:Dark matter

Adding results of Cooperstock and Tieu

The article should mention the results in these papers (I'll add the references later):

http://xxx.lanl.gov/abs/astro-ph/0507619

http://arxiv.org/abs/astro-ph/0508377

http://xxx.lanl.gov/abs/astro-ph/0610370

http://xxx.lanl.gov/abs/0712.0019

Jan Bielawski (talk) 23:11, 12 October 2009 (UTC)

Hearty agreement - this is a viewpoint from a very well-known relativist of long-standing in the GR community, with a sterling publication record and a long career behind him. It is a simple viewpoint - namely that the non-linearity of GR is essential, as it is with fluid mechanics (Navier Stokes equations). You cannot linearize GR without tossing out important physical phenomena. This idea definitely should be represented in the article. Antimatter33 (talk) 12:05, 20 December 2009 (UTC)

GA Sweeps: On hold

This article has been reviewed as part of Wikipedia:WikiProject Good articles/Project quality task force in an effort to ensure all listed Good articles continue to meet the Good article criteria. In reviewing the article, I have found there are some issues that may need to be addressed, listed below. I will check back in seven days. If these issues are addressed, the article will remain listed as a Good article. Otherwise, it may be delisted (such a decision may be challenged through WP:GAR). If improved after it has been delisted, it may be nominated at WP:GAN. Feel free to drop a message on my talk page if you have any questions, and many thanks for all the hard work that has gone into this article thus far.

• The references need to be tightened substantially. I count 16 paragraphs with no references whatsoever. There are a few specific instances of unsourced, possibly contestable statements that definitely need a citation; there may be still more that I have missed:
  • "In the Bullet Cluster, lensing observations show that much of the lensing mass is separated from the X-ray-emitting baryonic mass."
  • "For 40 years after Zwicky's initial observations, no other corroborating observations indicated that the mass to light ratio was anything other than unity (a high mass-to-light ratio indicates the presence of dark matter)."
  • The first four paragraphs of the "Galactic rotation curves" section are full of uncited assertions
  • "In the dozens of cases where this has been done, the mass-to-light ratios obtained correspond to the dynamical dark matter measurements of clusters."
  • "The correspondence of the two gravitational lens techniques to other dark matter measurements has convinced almost all astrophysicists that dark matter actually exists as a major component of the universe's composition"
  • The entire section: "Structure formation"
  • "Hot dark matter cannot explain how individual galaxies formed from the Big Bang."
  • "At present, the most common view is that dark matter is primarily non-baryonic, made of one or more elementary particles other than the usual electrons, protons, neutrons, and known neutrinos"
  • "Experiments with the Large Hadron Collider near Geneva may be able to detect the WIMPs."

Ref added. Puzl bustr (talk) 20:06, 1 December 2009 (UTC)

• • "The PAMELA payload (launched 2006) may find evidence of dark matter annihilation."
  • "The Fermi space telescope, launched June 11, 2008, searching gammawave events, may also detect WIMPs."
  • "In 2014 the LSST will be operational, one of the main goals of the telescope is to discover and learn more about dark matter."
  • "An experiment planned to be carried out deep within a formerly abandoned mine in or near Sioux Falls, ND in 2016 hopes to further prove the existence of dark matter using a process called LUX (or Large Underground Xenon) detection."
  • "A proposed alternative to physical dark matter particles has been to suppose that the observed inconsistencies are due to an incomplete understanding of gravitation."
  • "Some M-Theory cosmologists also propose that multi-dimensional forces from outside the visible universe have gravitational effects on the visible universe meaning that dark matter is not necessary for a unified theory of cosmology."
• The references should be in a consistent format, using {{cite web}} and similar templates if possible. Specifically, bare links such as ref #29 are unacceptable, and online sources should include information on the access date (in case the links go dead).
• Stub sections such as "Popular culture" need to be expanded.
• "These cosmological models predict that if WIMPs are what make up dark matter...." What cosmological models?
• The second paragraph of "Structure formation" alternates between past and present tense.

These are minor concerns to be addressed, I will still likely pass this article without these changes, but they should be fixed before going up for Featured Article candidacy:

• There are several instances of Words to avoid, such as "claimed," "however," "although," etc. Not all of these are necessarily bad, but look to avoid them in certain instances.
• Single-sentence paragraphs in the "Detection" section should be merged into larger paragraphs.
• The lead section is quite long; try to shorten it, possibly by introducing a new section below. The lead should also not contain any information not contained in the main article; it should be a summary, not a tease (see WP:LEDE)

I will leave a notice at the appropriate WikiProjects/userpages to hopefully get attention to these problems. This article should be fixed, or substantial, ongoing progress be made, by July 9. I plan on adding more problems later; I will extend the deadline if need be.-RunningOnBrains^{(talk page)} 17:13, 2 July 2009 (UTC)

Unfortunately, while a few improvements have been made, as of July 11, 2009, this article fails to satisfy the Good Article criteria. For that reason, the article has been delisted from WP:GA. However, if improvements are made bringing the article up to standards, the article may be nominated again at WP:GAN. If you feel this decision has been made in error, you may seek remediation at WP:GAR. -RunningOnBrains^{(talk page)} 07:03, 11 July 2009 (UTC)

A matter of style and mathematical correctness needs be addressed. In the article I find this: "there are 10 to 100 times fewer." It seems to me that "one time less" would be zero. If I have 5 widgets, one times five is five which, when subtracted from the original number of widgets leaves zero. So "there are 10 to 100 times fewer" leaves some kind of large negative number. It would be more precise to say that there are "one-tenth to one-one hundreth as many" or "1/10 to 1/100 as many" or "fewer by a factor between 10 and 100." 24.125.58.26 (talk) 20:20, 20 October 2009 (UTC)kjdamrau

Dark matter is a Theory

Isn't Dark matter more of a theory than anything else? Shouldn't we be talking about the Theory of Dark matter? I'm concerned about sentences like "Dark matter also plays a central role in structure formation and galaxy evolution". Shouldn't we say "The theory of Dark matter plays..." ?? Here's another one: "The dark matter component has much more mass than the 'visible' component...". Or even "The vast majority of dark matter in the universe is believed to be nonbaryonic..." which should probably read "Dark matter theory posits that the vast majority of dark matter in the universe is nonbaryonic..."

We have no direct evidence that any dark matter exists (no one has detected dark matter). So shouldn't this article be about Dark matter theory and not about Dark matter itself which may not exist at all? —Preceding unsigned comment added by 71.235.51.239 (talk) 18:52, 2 August 2009 (UTC)

Indeed, as most of the current actual data available supports MOND over Dark Matter, it would be highly misleading to imply the existence of Dark Matter, the article should make plain that dark matter is a hypothesis, yet to be borne out by experimental data. It would be like the article on a god stating everything attributed to them as fact, when no evidence exists for their existence. —Preceding unsigned comment added by 77.98.210.64 (talk) 12:32, 14 August 2009 (UTC)

There is nothing but theories in science. F.ex. there are no God-given truths, although a few theories come near. Some theories are well attested, some are weaker, some are speculative and some are fringe. ... said: Rursus (^mbork³) 07:27, 6 October 2009 (UTC)

"Indeed, as most of the current actual data available supports MOND over Dark Matter..." What are you talking about? MOND has been excluded by observation for years. Nice try (and many wish it was so), but it's just a statistical approximation for dark matter distribution in typical massive galaxies. The scientific consensus should follow "actual data available", lagging by a few months to account for repeatability and review. So your statement is tantamount to a conspiracy theory. In any case, this page should cover any evidence that would go against the theory as well. Długosz (talk) 23:05, 26 October 2009 (UTC)

It is, however, worth pointing out that the power spectrum appears to contradict the predictions of the LambdaCDM model (the predicted second peak that isn't there) as per Stacy McGough et al. The total failure to detect DM so far combined with the prediction failure of models like LambdaCDM do present a real problem for DM theory (and, for that matter, the Bullet cluster interactions aren't a slam dunk for DM as these interactions don't obviate other explanations). That doesn't mean its dead (and nor does that necessarily invert into support for MOND which has its own issues) but I too felt that the flavour of this article was a little too confident about the veracity of DM. It may be worth having a flaws or criticisms section to highlight that DM still has significant gaps as a theoretical model. Jimjmoore (talk) 04:53, 25 February 2010 (UTC)

I think you're slightly confused and about 10 years out of date. The second acoustic peak in the CMB certainly is there, and McGaugh based his argument on the detection of this second peak by BOOMERanG. So you're mistaken in saying it isn't there. McGaugh assumed values for various cosmological parameters. These were reasonable guesses before precision CMB data were available, but they were only guesses. Replace them with values based on observational constraints, and there's no problem: Lambda-CDM fits the CMB spectrum exquisitely. And it can't be made to fit McGaugh's baryon-only model from 10 years ago. This is not to criticize McGaugh; his analysis was valuable work at the time, but the field has not stood still in the last decade. --Amble (talk) 08:35, 25 February 2010 (UTC)

See for example p. 10 in Tegmark et al., Cosmological parameters from SDSS and WMAP. --Amble (talk) 08:40, 25 February 2010 (UTC)

The direction of rotation of the Milky Way Galaxy was only observed a little over a hundred years ago, and concepts of mass beyond the visible stars were either nonexistent or completely unresolved before then in terms of galactic rotation. Indeed, human beings thought that the more distant stars were fixed in place in some kind of 'firmament'.

It seems possible that now the massive and numerous exterior objects, which are largely galaxies outside the Milky Way, are being resolved in terms of the symmetry-hand of Galactic rotation. First perceptions, by those adapting to the correct direction of rotation of the Milky Way Galaxy, of mass and matter would be that mass beyond our galaxy seems to consist of a familiar kind of matter and an unfamiliar kind of matter. Moreover, in an entire 220 million year orbit of our solar system around the Milky Way, the exterior objects, moving slowly, will in most cases not appear displaced in position relative to each other, more than their own diameters.

Familiar distant mass is consistent with a sense of the mass of exterior objects perceived by persons who have adapted to or accommodated the correct direction of rotation of the Milky Way Galaxy.

The seemingly unfamiliar, unresolved mass or "dark matter" could be that sense of exterior mass that comes from not considering the rotation of the Milky Way at all. It is not consistent with any other concept of right such as ecliptic and equatorial.

Encouraging those who profess the existence of dark matter to get a sense of galactic rotation for themselves would help resolve the issue, as their before-and-after opinions would be valuable.SyntheticET (talk) 23:09, 20 December 2009 (UTC)

Unsoundness and extreme POVvyness

About VIRGOHI21 in section Velocity dispersions of galaxies:

Models of the Big Bang and structure formation have suggested that such dark galaxies should be very common in the universe, but none had previously been detected. If the existence of this dark galaxy is confirmed, it provides strong evidence for the theory of galaxy formation and poses problems for alternative explanations of dark matter.

No, that's not the natural clause to draw! The natural conclusion to draw from the statements in the text is quite the opposite: the theory of dark matter actually hangs by a single thread that any moment will snap: the lack of a multitude of dark galaxies is a great obstacle for the theory of dark matter, and it is only saved for a short while by one single alleged dark matter galaxy. (Although it has no real place here: the main weaknesses of Big Bang is today the lack of a coherent explanation of the missing matter and the weaknesses of the Standard Model of particle physics). ... said: Rursus (^mbork³) 19:14, 5 October 2009 (UTC)

In this regard see Dwarf galaxy problem particularly the "Keck observations in 2007 of eight newly discovered ultra-faint Milky Way dwarf satellites showed that six were around 99.9% dark matter". This is strong evidence (my POV) for a continuum of dwarf galaxies with increasing proportion of DM. <tongue-in-cheek>Perhaps it is unreasonable to expect many observations of DM-only galaxies - there's nothing to see!</tongue-in-cheek>. More seriously, the technical problems in "observing" DM-only galaxies must be considerable. Time will tell as to whether the observations of ultra-faint dwarf galaxies can be replicated further afield - are they a feature of other nearby large galaxies e.g. Andromeda? Puzl bustr (talk) 11:11, 28 January 2010 (UTC)

Lord Kelvin's Dark Matter

See [1] - apparently there was a concept of non-luminous matter required to keep the stars in proper motion due to gravitation attraction in the 19th century...

76.66.197.2 (talk) 11:32, 12 November 2009 (UTC)

Needs a simple summary paragraph

Article needs a simple statement defining the term 'dark matter' and why it's important in cosmology. For example, there is no mention of big crunch anywhere in the English or simple English versions.Cyberplasm (talk) 10:13, 2 December 2009 (UTC)

Why would the big crunch be especially relevant here? The introduction does define dark matter and explain its importance in cosmology. Since it plays a number of important roles, it's difficult to condense it to a single sentence. Could you be more specific about what changes you believe are needed, and why big crunch should be included? --Amble (talk) 22:46, 2 December 2009 (UTC)

Lectures I attended in the 80's at slac... Dark matter, if it exists, could cause the universe to eventually collapse instead of expand forever --- it would provide the 'missing mass' required for a critical tipping point. Dark matter speculated to be neutrinos, but I don't know what the science is now. There are zillions of articles on this. The article here is written for less than 1% of readers.Cyberplasm (talk) 10:36, 4 December 2009 (UTC)

Ok, thanks - I see where you're coming from now. But a lecture from the '80s is quite out of date! At that time it was believed that dark matter would make up most of the critical density of the universe, and that the ultimate fate of the universe was directly tied to its curvature. (So a universe with less density would have negative curvature and would expand forever, a universe with more density would have positive curvature and would collapse again in a big crunch, and a universe with exactly the critical density would be spatially flat and also expand forever). This all changed in the late '90s with the discovery of accelerating expansion, a.k.a. "dark energy." This has positive energy density but negative pressure, and makes up the majority of the energy density of the universe (about 73%). So spatial flatness is no longer closely tied to dark matter, and it appears that our universe will not have a big crunch even if the energy density is a little about critical. --Amble (talk) 20:07, 4 December 2009 (UTC)

References needed

The main reason for the loss of good article status was the lack of references in new material. I plan to work thru' and add references, but must add the disclaimer that I'm far from being an expert. Puzl bustr (talk) 16:38, 3 December 2009 (UTC)

"Nonbaryonic dark matter": RfC

Apparently, back in September someone resurrected the nonbaryonic dark matter article and the "Nonbaryonic dark matter" heading/section in this article. It is common (if arguably less than entirely correct) for the term "dark matter" to be used to refer to the nonbaryonic dark matter, and in any case the vast majority of the dark matter (assuming it exists) is nonbaryonic; thus it seems pretty clear to me that (1) there should not be a separate article on nonbaryonic dark matter, since anything there is to be said on that subject should be in this article, and (2) there should not be a section in this article called "nonbaryonic dark matter", since that is what the majority of the article is/should be about. However, perhaps I am missing something, since no one reverted the change when it was made, and I am not actually a cosmologist. Does anyone who is a cosmologist disagree with me? If so, it's about time I got straightened out; if not, I'd appreciate some moral support before I change the article again. False vacuum (talk) 04:52, 14 December 2009 (UTC)

Incidentally, I just merged back into this article the material that had been moved, back in September, to nonbaryonic dark matter, which I effectively deleted several hours ago (mea culpa—I wasn't paying enough attention). This incidentally makes the introduction a bit longer again, which I see has been a point of contention, or at least criticism. Someday perhaps this article will be good, although perhaps dark matter is too controversial a subject for Wikipedia to handle reliably </sarcasm>, but I think it is widely agreed, and in any case it is true, that the introduction to an article such as this one, which gets quite technical and probably cannot (or will not) be read in its entirety by most, should provide an accurate and complete synopsis of the topic. Not that the present introduction does that, but it's closer to that ideal than when it had had a couple of its paragraphs arbitrarily deleted (moved elsewhere, strictly speaking) to make it shorter. False vacuum (talk) 17:51, 14 December 2009 (UTC)

Backwards Traveling Higgs Boson Alerts to Dark Matter Discovery

A time traveling higgs boson has alerted me to Dark Matter's detection. This will become apparent tomorrow 5 pm eastern time. Hopefully wikipedia can begin including information from the future now? Please excuse —Preceding unsigned comment added by Ultima821 (talk • contribs) 01:09, 17 December 2009 (UTC)

This post is GARBAGE gadfly46 21:33, 10 March 2010 (UTC)

Added section on cosmic microwave background with refs, to help explain the observation background to the structure formation section

This section has several wikilinks and refs to help explain the observations which led to the particular cosmological model with dark matter in it, which helps (I hope) to explain the more technical structure formation section. I couldn't find precise refs for the CBI and DASI results. If I find them I'll add them. Puzl bustr (talk) 18:22, 21 December 2009 (UTC)

From the Big Bang article:

"The earliest and most direct kinds of observational evidence are the Hubble-type expansion seen in the redshifts of galaxies, the detailed

measurements of the cosmic microwave background, the abundance of light elements (see Big Bang nucleosynthesis), and today also the large scale

distribution and apparent evolution of galaxies which are predicted to occur due to gravitational growth of structure in the standard theory.

These are sometimes called "the four pillars of the Big Bang theory"."

It looks to me (standard warning that I'm no expert) that the observations supporting the existence of dark matter whose references are missing from the current article are taken from these four pillars (or at least include some of them). I'll do some more reading and see how this pans out. If others want to comment here, please do. Puzl bustr (talk) 19:35, 21 December 2009 (UTC)

Note that there are seven major (long, technical!) papers analysing the five-year WMAP data of which I've only skimmed two. These two seem to have a great bearing on this article, and the one on dark energy. The Hinshaw ref I added (one of the seven) mentions the other six. They seem to act as survey articles of a sort. Similar papers from several years ago (the one and three year WMAP data) are right at the top of the "Super Hot Papers in Science Since 2003" list, so it seems a good starting point (for my learning!). Puzl bustr (talk) 19:52, 21 December 2009 (UTC)

Hi Puzl bustr - you're doing really great work on this page. The CMB section is well done, but it is really discussing the concordance cosmology rather than dark matter specifically (and this is correct, since CMB provides information on dark matter indirectly). I think it would be useful to make the connection back from concordance cosmology to dark matter by describing how CMB constrains dark matter. --Amble (talk) 21:16, 22 December 2009 (UTC)

Thanks - and I agree about your comments on concordance, was thinking along the same lines. I added refs for the CBI and DASI results, and a ref for simulations of large scale structure. Puzl bustr (talk) 21:32, 22 December 2009 (UTC)

Added a summary with refs explaining the link between CMB and dark matter as I understand it, wikilinking the CMB article and referencing the Nobel Prize 2006 physics lecture by Smoot. The latter is a press release so should be replaced with a proper citation at some point.Puzl bustr (talk) 07:04, 23 December 2009 (UTC)

Replaced the Smoot press release with a proper reference. Puzl bustr (talk) 18:49, 24 December 2009 (UTC)

Added new sections on Sky surveys and BAO and on Type Ia supernovae

I put in referenced sections (working from the WMAP refs) to explain very briefly how sky survey and supernovae data have been used to constrain cosmological models. I haven't tracked down the Lyman alpha forest stuff as yet - but what I've added now provides references for and expands on the structure formation section, which is becoming a summary of the material I added with more explanatory info.Puzl bustr (talk) 18:47, 24 December 2009 (UTC)

Added Lyman alpha section with a recent reference I found myself. If any expert has a better ref, please add it.Puzl bustr (talk) 19:42, 24 December 2009 (UTC)

Added more references - plea for help

Added recent Nature ref for dwarf galaxy dark matter simulation which resolves the discrepancy between observations (constant density core, shallow profile, bulgeless) and previous larger-scale Lambda CDM simulations (cusped profile).

Added refs and wikilink for the Dwarf galaxy problem.

Unable to find precise refs for the assertion about galaxies being virialized up to ten times their visible radius. My impression is that the non-optical astronomy involved is radio astronomy, observing the ISM, but I find radio astronomy articles impenetrable. Other non-optical astronomy observations may be relevant closer to the galactic centre and as a consistency check on the radio ones. The following are links and refs I've found but not included in the main article.

Found 2001 paper [2] applying radio observations (HI and H alpha) of five spiral galaxies which mentions a figure of three visible radii. An earlier original paper would be a better ref. Have seen papers applying radio observations of HII, e.g. [3], also others at the scale of galaxy clusters.

Found the original ref [4] for the NFW profile of dark matter (authors' initials) which is much discussed in the literature - this gives the cuspy profile of DM.

Found Dark matter halo article with book refs (none of which I have). A wikilink should be worked in to the present article.

An editor with knowledge of radio astronomy is requested to take this further. Puzl bustr (talk) 10:35, 28 January 2010 (UTC)

clarification

just wondering there, about the galactic rotation section, where it says that oh no Newtonian gravitation could be wrong

does this mean that the nice figure showing the predicted (A) galactic rotation curve is based on Newtonian gravitation?

has anybody bothered to calculate what it would look like (B perhaps?) if we used Einstein's equations instead of Newton's?

No offence but Newtonian gravitation actually IS wrong and does this mean Dark Matter depends on Newton being right? —Preceding unsigned comment added by 128.231.213.25 (talk) 15:24, 5 March 2010 (UTC)

In normal galaxies, rotation velocities, matter/energy densities and gravitational gradients will not be large enough to require relativistic corrections. Newtonian gravity is a good enough approximation in such cases. Gandalf61 (talk) 16:46, 5 March 2010 (UTC)

Normal galaxies probably have 1 million solar-mass black holes in their centres. Sounds like you need Einstein to me. You didn't answer the question. Has a simulation been done using Einstein's Equations, which we know are correct, as opposed to Newton's Equations, which we know are wrong. You say you need unobservable dark matter to explain galactic rotation, I say you haven't done the correct model simulation. —Preceding unsigned comment added by 128.231.213.25 (talk) 20:31, 5 March 2010 (UTC)

My point was that I doubt any physicist would bother applying relativistic corrections to the Newtonian rotation curve because there are clear a priori reasons to think that this would not make any significant difference. But if you know enough to be convinced otherwise then you know enough to do the calculations for yourself, so go ahead. Gandalf61 (talk) 23:42, 5 March 2010 (UTC)

Causality

There is nothing in artcile to explain occurance / genesis of dark matter. gadfly46 21:34, 10 March 2010 (UTC)