Talk:Dark matter/Archive 5

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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)

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)

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 But a lecture from the '80s is quite out of date!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)

"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)

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)

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)

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)

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)

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)

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)

In supermassive black hole is discussed the evidence for the Milky Way supermassive black hole at centre. The star S2 is so close and moving so fast as to indeed require relativistic treatment of its velocity, which was done instead of Newtonian gravity. Stars near the edge of the galactic disk (and even further out) are moving so slowly in comparison that Newtonian gravity is an adequate approximation - corrections due to relativity would be absurdly small compared with measurement errors. All theories are approximate and you use the most appropriate one based on context. Puzl bustr (talk) 17:38, 18 March 2010 (UTC)

Bad example - they used Keplerian orbits for S2 (an even simpler approx. than Newton) when I checked. I may have been thinking of a documentary about this mentioning stars even closer in, which need the relativistic treatment. There are other examples like fast-moving close exoplanets and close binary systems. But the proper motion of most stars in most galaxies doesn't involve velocities which are a big enough fraction of the speed of light compared with measurement errors to make relativistic treatment necessary. Puzl bustr (talk) 17:58, 18 March 2010 (UTC)

If I remember that paper correctly, they did note that relativistic precession changed the axis of S2's orbit by a small amount, but that the perturbation was small enough not to cause problems with their conclusions. It's been a few weeks since I looked at it, though. --Christopher Thomas (talk) 19:09, 18 March 2010 (UTC)

The problem of dark matter has been completely solved

Archived self-published work.
The following discussion has been closed. Please do not modify it.
Mechanism-Revealed Physics (30/40) Completely solving the problem of dark matter (unveiling the mystery of dark matter): the problem of dark matter (i.e., essential understanding of the fundamental nature of dark matter) is widely recognized as one of the greatest challenges to science in the 21st century. The problem of dark matter has been completely solved by revealing the mechanism thus identifying the essence of dark matter with the newly established MRBHT (=Mechanism-Revealed Black Hole Theory, P. 541 ~ 548, 5.5, Ch.5B, reference #1). Be clarified, in solving the problem of dark matter, the concept and implication of black holes is based on MRBHT, rather than from current postulate-based black hole theory, i.e., mechanism-revealed black holes rather than postulate-based black holes. Based on MRBHT, when the mass of a hugely massive astronomical object is large enough up to the extent at which formation of Zhao’s black hole radius is required, the hugely massive astronomical object becomes a black hole, and the mass of the hugely massive astronomical object thereby becomes the mass in the black hole. While the huge mass itself residing in a black hole is invisible thus looks dark to the observers far away from the black hole, its existence generates two observable effects in its vastly affecting extending region. One is that it exerts tremendous gravity on those smaller astronomical objects orbiting the black hole--causing them orbiting much faster than if there were no the black hole. Another is that the inertia principle of photon traveling causes light rays bending when they are passing through the vastly extending region. These two effects exactly match and fully explain the two observed phenomena presently ascribed to the existence of dark matter. Therefore, the mechanism of dark matter is that the huge mass in a black hole increases the gravity and reduces the gravitational scales of space and time greatly in the vast extending region of the black hole, consequently in this region, stars orbit faster; light rays bend due to the inertial principle of photon traveling. The essence of dark matter is the mass in black holes. As a result, the concise definition is that: dark matter is the huge amount of mass residing in black holes, and it thereby generates significant gravitational effects in the vast extending regions surrounding these black holes, such as stars orbiting faster and light rays bending. In short, dark matter is the mass in black holes, and the mass in black holes is dark matter. As assisting helpful information, eight available clues supportive of or consistent with this conclusion that dark matter is the mass in black holes are provided and analyzed (P. 562 ~ 564, 5.7.2, Ch.5C, reference #1). The key to understanding of this solving the problem of dark matter: (i) as long as you have known the greatest equation in the history of science, which is Einstein’s famous mass-energy equation (E = mc2 or E0 = mc2), you will easily understand this solving the problem of dark matter, because the law of object’s mass doing work (OMDW) (P. 93 ~ 109, Ch.1A, reference #1), which is the root of this solving the problem of dark matter (P. 895, reference #2), has also revealed the mechanism behind the greatest equation (P. 114 ~ 118, Ch.1B, reference #1). (ii) The newly established MRBHT is the key to solving the fundamentally important problem of dark matter. Reference #1: 2009, Bingcheng Zhao, From Postulate-Based Modern Physics to Mechanism-Revealed Physics [Vol. 1(1/2)], ISBN: 978-1-4357-4913-9. Reference #2: 2009, Bingcheng Zhao, From Postulate-Based Modern Physics to Mechanism-Revealed Physics [Vol. 2(2/2)], ISBN: 978-1-4357-5033-3. Ph.D., Bingcheng Zhao, The author of “From Postulate-Based Modern Physics to Mechanism-Revealed Physics” 1401 NE Merman Dr. Apt. 703, Pullman, WA 99163 USA. Email: bczhao12@gmail.com or bzhao34@yahoo.com or bingcheng.zhao@gmail.com —Preceding unsigned comment added by 204.52.246.120 (talk) 17:47, 18 March 2010 (UTC)

Wikipedia is not the place to try to publish or popularize your own ideas. See WP:OR and WP:RS. --Christopher Thomas (talk) 19:04, 18 March 2010 (UTC)

Causality

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

Genesis?

75.166.243.209 (talk) 14:28, 12 March 2010 (UTC)

Sean7phil (talk) 14:27, 12 March 2010 (UTC)

It would have appeared during the Big Bang by the same mechanisms that created all other forms of matter. As long as the temperature was high enough, pair production would cause it to appear out of nowhere (along with particle/antiparticle pairs of all other types below the corresponding energy threshold). Particles that could decay to up/down quarks, electrons, neutrinos, and photons did so. Hypothetical particles that couldn't, would remain. Dark matter is usually proposed to be a particle of this type (with the "Lightest Supersymmetric Particle" being the most popular candidate). --Christopher Thomas (talk) 03:55, 1 April 2010 (UTC)

Measuring velocities of stars so far away

How exactly does one measure the velocity and position of a star in the Andromeda Galaxy at 2.54 million light years away (plus or minus 0.06 million light years), when it takes our sun a quarter of a billion years to even make one orbit around our similarly sized galaxy? That's quite a feat. How many quadrillionths of an arc length does a star that far take up, and are our telescopes that sensitive?98.165.15.98 (talk) 08:16, 11 May 2010 (UTC)

This does not seem to have anything to do with the article or improving it. I suggest asking your question at the reference desk. ScienceApologist (talk) 10:22, 11 May 2010 (UTC)

Actually, it has to do with the section "Galactic rotation curves", and Footnote 8 in it. Lars T. (talk) 17:09, 12 May 2010 (UTC)

Nowhere in the entire article is there any suggestion that people are measuring the velocities and positions of individual stars to determine galactic rotation curves. ScienceApologist (talk) 23:16, 12 May 2010 (UTC)

To actually answer the question, the "radial velocity" of stars (the speed at which they're receding or approaching Earth) is measured by looking at the doppler shift of various elemental emission lines in their atmospheres. The tangential velocity is found by combining the distance (found by parallax observations for nearby objects) with the proper motion (measured displacement over time of nearby objects). For distant objects, it's very difficult to measure tangential velocity. It's also difficult to resolve individual stars at intergalactic distances (though we can do so for some of our nearest neighbour galaxies).

As User:ScienceApologist alludes to above, for most galaxies other than our own, rotation curves are obtained by looking at the spectra for resolvable parts of them, which will contain many stars. As the average motion is what we're interested in, this still works quite well. The spectral lines will be smeared, because we're looking at the radial components for several different parts of the rotating disc, but the part we're interested in (where motion is as close as possible to directly towards or away from us) is easily found by looking for the endpoint of the smeared bands. To estimate the tangential component of the velocity, we need to make an educated guess as to how tilted the target galaxy's disc is compared to our line of sight. This is straightforward and reasonably accurate, so we get fairly accurate rotation curve values out.

For extremely distant objects, we can't resolve the disc well enough to do this. We can still get spectra, which tell us that parts of the disc of these very-distant galaxies are moving at least as fast as the half-width of the smeared spectral band (which will contain both red-shifted and blue-shifted components). This is mostly useful for placing constraints on the masses of supermassive black holes at the hearts of active galaxies, if I understand correctly (as they have brightly-glowing, easily-measured accretion discs). To the best of my knowledge, nobody's tried to get rotation curve data for a galaxy they couldn't resolve as an extended (non-pointlike) object.

For more details, I suggest searching for papers that perform rotation curve surveys and look at both the techniques they describe in the introduction to the paper, and the uncertainty values they claim on the various parameters they estimate.

I hope this answer is useful to you. --Christopher Thomas (talk) 03:11, 13 May 2010 (UTC)

Lead section too long, too technical

See also: comment in the preceeding post above by User:Chetvorno. I'm a regular Wikipedia editor (generally linguistics, wine, and settlements)., but I came here looking for a simple, encyclopedic explanation of dark matter, but gave up before even finishing the lead. Someone please reorganise the lead in compliance with MoS, (WP:LEAD), and put the ultra techno stuff into the relevant secvtions, leaving the lead as an introductory overview. I have tagged the article as needing the required attention. Thanks.--Kudpung (talk) 02:58, 1 July 2010 (UTC)

You are right - the second half of the lead dealt specifically with the difference between baryonic and nonbaryonic dark matter. I have split this out into a separate section, which shortens the lead to four paragraphs. Does this address your concerns ? Gandalf61 (talk) 09:38, 1 July 2010 (UTC)

That is much better Gandalf. Thanks. I wonder if it would be too unscientific to suggest somewhere that dark matter is what 'nothing' is made of. ;) --Kudpung (talk) 10:34, 1 July 2010 (UTC)

Neutrino section has been moved

The neutrino section that was previously under the Alternate Explanations section are now under Problems and Criticisms section! They were not lost in the shuffle! ykhan (talk) 08:56, 14 July 2010 (UTC)

Shadow matter

One possibility for part of dark matter is shadow matter. Shadow matter interacts with normal matter only through gravity. In effect, it is in a parallel universe which only shares the shape of spacetime with us. It could have its own set of non-gravitational forces and be just as complicated as normal matter or more so. JRSpriggs (talk) 12:40, 15 July 2010 (UTC)

Indeed, this needs to be included. Many M-theory proposals incorporate this, though the normal dilution of gravity across branes presents some problems for the overall density. ScienceApologist (talk) 17:29, 15 July 2010 (UTC)

afraid of counterexamples?

Who removed the section I put in about the Abell 520 Train Wreck cluster? ykhan (talk) 21:01, 13 July 2010 (UTC)

Me, mostly because it isn't considered a universal "counterexample" and is actually more confusing than it is enlightening with regards to dark matter. YMMV. The Bullet Cluster, on the other hand, is well heralded. There may be a bias in the sources, but Wikipedia cannot fight the outside world to provide inappropriate balance according to WP:WEIGHT. ScienceApologist (talk) 21:08, 13 July 2010 (UTC)

An encyclopedia article needs to be factual, and not an advocacy article, so all scientifically relevant data must be presented. If you thought it was confusing, and you were concerned about reader confusion, then you should've moved it off into a separate subsection (like "problems and criticisms") rather than deleting it completely and censoring relevant data from the reader. ykhan (talk) 03:54, 14 July 2010 (UTC)

I moved it to a more natural section. ScienceApologist (talk) 18:24, 14 July 2010 (UTC)

I see that you're coming around to my original point of view that these counterexamples belong within their own subjective sections rather than in a separate problems section. For consistency, you should consider removing the "neutrinos" subsection from under the "alternative explanations" subsection, and put it under the "hot dark matter" section, as neutrinos are not alternative to dark matter, they are dark matter. Also you should consider renaming the "alternative explanations" section to "alternative theories" and keep it strictly restricted to competing theories. I still have a lot of new data to add to this article, so I'll be busy dealing with that. I'll let you take care of sectional naming considerations. ykhan (talk) 05:17, 15 July 2010 (UTC)

You're absolutely right about the neutrinos. On it. ScienceApologist (talk) 17:18, 15 July 2010 (UTC)

The next bunch of sections that you should look at are under "Observational Evidence", specifically all of the sections from "Cosmic Microwave Background" through to "Lyman Alpha Forest" are all supporting evidence for the CMB, not of Dark Matter. In fact, the "Type Ia supernovas" has nothing to do with Dark Matter at all, it's the proof for Dark Energy. I'd suggest putting all of the sections after CMB, except "Structure Formation" as subsections of the CMB section.

In fact, there is way too much detailed discussion about the CMB in this article, they should all go into the CMB article itself. I suspect this is crap leftover from before there was a CMB article, but now that there is a separate CMB article, they just never bothered to clear out this stuff from here. There should only be a very concise section about the CMB in here, with only enough detail to show how it relates to dark matter. I can come in at some time later, analyze what I can move to the CMB article, and flush the rest of this stuff out. ykhan (talk) 20:40, 15 July 2010 (UTC)

Right again. These were actually put in fairly recently, though I think mentioning BAO and Type Ia data is relevant for constraining the kind of dark matter. The composition section is a bit more natural, perhaps. ScienceApologist (talk) 22:23, 15 July 2010 (UTC)

There is more than a whole paragraph for the Bullet Cluster, so yes, a single paragraph for the Train Wreck cluster is not excessive, plus there is plenty of physics about Dark matter explained in there. You are being obviously an advocate for the theory, trying to censor any negative information from readers. Putting in a single sentence about the Train Wreck cluster at the end of the last paragraph is completely ridiculous.ykhan (talk) 06:05, 19 July 2010 (UTC)

There is far more written about the Bullet Cluster in the literature than the Train Wreck Cluster. By all means, include the analysis at the article on the object, but it is not as relevant to the entire dark matter topic. ScienceApologist (talk) 14:49, 19 July 2010 (UTC)

Galaxy rotation curve: Spiral Galaxies vs Elliptical Galaxies

Could the presence of Spiral Arms in a Spiral Galaxy gravitationally extend the influence of the galaxy's central bulge explaining perhaps the observed higher than predicted velocities of stars far from the galaxy center, the absense of spiral arms in Elliptical Galaxies would have to be closer to the predicted velocity curve. Jalanp2 (talk) 18:54, 24 July 2010 (UTC)

This turns out not to be the case. The arms of spiral galaxies are regions where density waves have caused bursts of star formation, rather than particularly heavy structures (density is only increased by 10-20%). The mass of the galactic disc is already taken into account when predicting galaxy rotation curves based on visible matter. --Christopher Thomas (talk) 20:18, 24 July 2010 (UTC)

To Jalanp2: Perhaps you are thinking that gravity might be conducted or focused in certain directions in a way similar to magnetic lines of force preferentially following a rod of paramagnetic material. In Newton's theory of gravity (which is an adequate approximation in this case), no such phenomena occur. My understanding of general relativity is not sufficient to say whether or not it could occur to a very small degree in that theory. JRSpriggs (talk) 13:54, 25 July 2010 (UTC)

The spiral arms & leading edges of the spiral galaxies are also where most collisions occur with smaller galaxies (i.e. Large & Small Magallanic Clouds) as they are "consumed" by the growing larger spiral galaxy-would would this factor explain the faster than typical stars excessive speeds. Jalanp2 (talk) 16:09, 27 July 2010 (UTC)

There are two problems with that explanation. First, the stars in question are in reasonably stable, reasonably circular orbits, not collision-derived scattered orbits. Second, the galaxy rotation curve is very uniform; if it was derived from collisions at the rim, you'd see a dip in the middle, and a peak with a lot of velocity variation at the rim. We don't see this. As far as anyone has been able to tell, the entire galaxy has nice, orderly orbital motion at speeds that would cause it to immediately fly apart if stars and gas-clouds were the only matter in it. --Christopher Thomas (talk) 17:31, 27 July 2010 (UTC)

Certain Dark Fluid theories suggest that one problem with current Dark Matter theory is that it takes no account of time-dependent variables (this is also a criticism of modified certain gravity theories, btw). That is to say that when a dwarf galaxy crashes into a giant galaxy, the dwarf's dark matter content should become part of the giant's DM halo too. There should be a noticeable shift of the dwarf's DM halo towards the center of the giant's, but it won't happen instantaneously. While this dwarf DM is being integrated into the giant's DM, you should see a concentration of DM where the previous dwarf used to be, and you should see a disturbance in the stars of the giant galaxy as they are affected by the DM of the dwarf. DM theory doesn't take this effect into account. ykhan (talk) 23:37, 30 July 2010 (UTC)

Is Gravity the only force that can be involved?

To clarify, one of the underlying assumptions here (this article) is that the only force involved in holding a galaxy (or a larger object) together is gravity? Has that been generally proven? In particular, have claims from "Modified Newtonian Dynamics" (MOND) been disproven recently? Also, has there been a general disproof that other forces, such as electromagnetic forces (with reference here to "Plasma Cosmology") could not be responsible for holding galaxies together? Inquiring minds would like to know. Dmacgr 22 (talk) 05:58, 31 July 2010 (UTC)

See the section Dark matter#Alternative theories which includes mention of Modified Newtonian dynamics (MOND). MOND is usually considered to be a variant theory of gravity rather than a different force altogether. Generally, I think that it is easier to postulate new entities (e.g. dark matter) than to postulate more complex physical laws (e.g. MOND) which would have to be consistent with the many observations we have of normal matter.

As far as electromagnetism and plasma cosmology are concerned, if there were electric or magnetic fields in inter-stellar space strong enough to hold the galaxy together, they would have other observable effects, such as polarizing the astronomical electromagnetic radiation we see. No such effects have been detected as far as I am aware. JRSpriggs (talk) 14:41, 31 July 2010 (UTC)

Cont'd.

This is a response to an above comment. Question: Has MOND has "made a splash" at all in the physics community? -Stevertigo (w | t | e) 23:03, 16 August 2010 (UTC)

According to what definition of "splash"? MOND tends to show up a lot in the preprint servers but very little in the published journals. It's essentially fringe science at the present time, and hasn't been doing so well as of the last five years as the evidence for cold, non-baryonic dark matter has been piling up. Modified gravity in other realms has done marginally better, but it's usually invoked as an alternative to dark energy. ScienceApologist (talk) 23:20, 16 August 2010 (UTC)

Well, "splash" was Chris Thomas' term (above), the definition of which seemed vital to his rebuttal. The issue of that recent discussion was simple: If there are any viable or 'splash'-making candidates which are not matter, then saying 'dark matter is matter [that is inferred to exist]' is overstating what isn't all that obvious. The point again was to make the introduction more accessible, by dealing away with any possible tautology. -Stevertigo (w | t | e) 23:48, 16 August 2010 (UTC)

Most of the splash-worthy candidates right now are matter by any reasonable definition. However, it's certainly possible to imagine alternatives which are not matter. In spite of the weird tautology sound for the article, "dark matter is matter that..." seems like a good categorical definition to me. ScienceApologist (talk) 00:03, 17 August 2010 (UTC)

Allow me to highlight for you: "A "mainstream candidate" for dark matter would be anything that made enough of a splash in the scientific community for sources satisfying WP:RS to be found." The criterion for inclusion here is, was, and remains satisfaction of relevant Wikipedia policies (WP:RS and WP:UNDUE, for the most part). --Christopher Thomas (talk) 00:20, 17 August 2010 (UTC)

Which is why I asked if MOND itself had 'made a splash' in the scientific community. Is it a case where MOND 'made a splash' initially and then faded, or did it never really make such a 'splash' to begin with? -Stevertigo (w | t | e) 00:24, 17 August 2010 (UTC)

Milgrom's initial idea still holds some Ockham's razor-type appeal. While it takes as many as four distinct parameters to get dark matter models to give appropriate galaxy rotation curves, MOND allows for one parameter to reproduce all the curves. No one really has any good explanation for why this is yet. However, in the minds of most astrophysicists, this attractive feature is outweighed by a significant amount of evidence which seems to oppose MOND as an explanation. Attempts to get to relativistic MOND theories have generally been found to be unsatisfying by the GR-theorists to boot, leaving us with an underdeveloped model that was promising to begin with but then has since seemed to just, well, fizzle. ScienceApologist (talk) 00:41, 17 August 2010 (UTC)

Then I'm puzzled as to why you're asking about whether it's "made a splash", and claiming that "making a splash" is "vital to (my) rebuttal". Search for reliable sources in scientific literature. The citation/abstract databases are all freely accessible, even if you'd need to visit a library or buy electronic access to read the text of the articles in question. The citation counts, especially compared to articles about other alternatives, will tell you how much weight the scientific community as a whole puts on the concepts discussed in any given set of articles. --Christopher Thomas (talk) 00:57, 17 August 2010 (UTC)

(To SA) Thanks for that explanation. Was the "appeal" issue really one of just simplicity? I mean there is an element in these 'non-materialistic' theories that at least attempts to see DM from a different perspective. I understand that DM research has altered the standard view of matter itself, but it seems strange that DM has not made a similar impact on the standard view of spacetime. How, in a few words or less, is DM resolved in string theory? -Stevertigo (w | t | e) 01:03, 17 August 2010 (UTC)

(To CT) I didn't mean to suggest that your entire point rested or hinged on your term 'make a splash.' Various things 'make a splash' all the time, and thus I know you of course were referring more to the substantive issues of RS and WEIGHT. -Stevertigo (w | t | e) 01:03, 17 August 2010 (UTC)

AFAIU, the "appeal" was really just about simplicity. There are multiple ways to resolve DM in string theory. Supersymmetry may demand a dark matter particle. M-theory may provide for particles in next-door branes that act as dark matter particles. ScienceApologist (talk) 01:07, 17 August 2010 (UTC)

'Dark matter is matter consisting of 'feebly-interacting particles'...' seems to be more to the point than the current wording. Thanks to you both. -Stevertigo (w | t | e) 02:05, 17 August 2010 (UTC)

Is the "Dark Matter in Popular Culture" section really necessary?

It seems to me like it should either be expanded to provide relevant examples, or just deleted. A one sentence blurb complaining about the lack of accuracy in science fiction hardly exemplifies encyclopedic writing. —Preceding unsigned comment added by 71.101.229.45 (talk) 15:56, 24 August 2010 (UTC)

Additions by 97.103.48.87

I've moved this good-faith addition here to the talk page for vetting. My concerns are that a) this was in the wrong section (description of hot dark matter's properties, vs. observational evidence), b) this is an arxiv preprint, and so doesn't yet satisfy the requirements of WP:RS for scientific topics, and c) this may violate WP:UNDUE unless there are significant numbers of other papers talking about the proposed dark matter filament (otherwise it isn't yet ready for Wikipedia). Text is below. --Christopher Thomas (talk) 19:34, 12 September 2010 (UTC)

An elongated filament of hot dark matter might account for the observed rotation curves of disk galaxies <ref>Slovick, B., Rotation Curve of a Dark Matter Filament (2010) arXiv:1009.1113</ref>. From Gauss’ law, a cylindrical filament yields a flat rotation curve independent of the specific mass density distribution.

Doesn't seem to be all that useful for our article. Literally hundreds of articles are written about dark matter every month. It would be impossible for us to include them all. The idea is interesting, but I don't think it is entirely novel as many different distributions have been proposed to explain galaxy rotation curves. We do need to get our articles on structure formation and large scale structure up to par, but including singular references like this is not the best way to do it. ScienceApologist (talk) 05:14, 13 September 2010 (UTC)

Dubious lead sentence(s)

Is anyone bothered by the recently added lead sentence? "Dark matter is a conceptualization for observed physical mass at cosmological scales in space where matter itself does not exist" Besides being unnecessarily confusing, it seems to imply that dark matter is not matter, or that dark matter is only found in empty space. Comments? --Chetvorno^TALK 10:48, 19 June 2010 (UTC)

Chetvorno - I agree with you. I have restored the previous version of the lead sentence, before Stevertigo's changes of June 15, which is both clearer and more accurate. Gandalf61 (talk) 12:35, 19 June 2010 (UTC)

It's hard even to be sure what that sentence is intended to mean. The older lead sentence as restored by Gandalf is fine. --Amble (talk) 15:05, 19 June 2010 (UTC)

I disagree with the revert back to the version:

"..dark matter is matter that is inferred to exist from gravitational effects on visible matter and background radiation"

• The issue with the current version is that too much of the beginning definition rests co-dependently on the word "matter." Because the name of the concept uses "matter" in a special way, resting its definition on a common term "matter" is a tautology. Using this word "matter" here in this way presents unnecessary ambiguity.
• Conceptually speaking, the term is a conceptualization: The "matter" is not actually "matter" in the traditional sense, and its not actually "dark" either - its just of an unknown constitution. So the concept is not one of "invisible matter," but of localized "physical mass," not attributable to "visible matter".
• So if even light can cause curvature and thus be called "matter," then I think "matter" is too ambiguous to use is this blunt way. Some of these ambiguities are dealt with at matter. The "light" article for example, does not define "light" as "matter" or "a form of matter." Granted, the context here is cosmology, but should cosmologists suggest that "light" be redefined as "matter?" Resting on an special definition of "matter" doesn't make sense for an accessible article. You can look at my wording again and discern what about it is actually "bother[ing]":

"Dark matter is a conceptualization for observed physical mass at cosmological scales in space where matter itself does not exist"

-Stevertigo (w | t | e) 18:09, 19 June 2010 (UTC)

Dark matter is dominant on many astrophysical scales, so "at cosmological scales" is stuck in for no apparent reason. The final prepositional phrase "in space where matter itself does not exist" is entirely opaque to me. Finally, dark matter refers to the substance itself, and it would be quite idiosyncratic if the article tried to distinguish the term as referring only to the concept of the substance. --Amble (talk) 18:48, 19 June 2010 (UTC)

Fair enough. But your criticism itself seems opaque. For example you can substitute "astrophysical" for "cosmological," you can always rewrite relative clauses, and you can actually address the points above which deal with the word "matter." -Stevertigo (w | t | e) 19:22, 19 June 2010 (UTC)

(Edited:) I'm not sure there's a problem that needs to be solved here. Different definitions of matter should be covered at matter, and a wikilink from the lead sentence here is enough. If is is discussed here, it doesn't need to go in the lead. --Amble (talk) 21:33, 19 June 2010 (UTC)

Stevertigo - I have two main problems with your version. My main problem is with the phrase "... where matter itself does not exist". Matter is anything that has mass and occupies space i.e. its elementary particles are fermions rather than bosons (which is why light and other EM radiation is not matter). We know that dark matter has mass, and most dark matter candidates are fermionic. Therefore dark matter is, in most theories, very definitely matter in the scientific sense of the word - it is simply a form of matter that does not interact with electromagnetic or (probably) strong forces. So, yes, dark matter is invisible, but to write a lead sentence that implies that dark matter is not matter is simply wrong.

My second (and more minor) problem is with your word "conceptualization". I doubt that the average rader will understand that term. And whatever a "conceptualization" may be, it sounds much too vague and mysterious for this article. Wikipedia defines concept as "an abstract idea or a mental symbol whereas dark matter is a very concrete explanation for certain astronomical observations. Gandalf61 (talk) 19:31, 19 June 2010 (UTC)

"Where matter itself does not exist." - Certainly you are right about that most general definition of "matter" - a more general definition would be to say that its anything that causes spacetime curvature, and mass is simply a quantization of that property. But note the next sentence uses the term "visible matter," yet another term that does not itself have a rigorous definition, or even an article. I understand that the status quo is not bad, my issue again is its tautological usage of "matter." Of course the actual cause for the observed distortions is actually physical and has mass as a property, but the idea here is that the term was coined to contain the proposed culprit for an observed phenomenon - a culprit that stretches the concept of "matter" in important ways, but nevertheless uses a counterintuitive definition of "matter" - ie. for something that must be there, but isn't actually there, according to the typically-required evidence for "matter's" existence.

The primary noun "conceptualization" (concept-ual-ization) is simple enough in that it refers to a concept or term which contains an idea - particularly one in which the idea itself is not concrete and where the search evidence to support it is ongoing. The secondary noun "conceptualization" refers objectively to the process indicated by verb "conceptualization," which is cognitive encapsulation (cf. abstraction). -Stevertigo (w | t | e) 20:02, 19 June 2010 (UTC)

No, matter is not "anything that causes spacetime curvature" - light has mass and curves spacetime, but it is not matter because it is not fermionic. And there is noting "counterintuitive" about dark matter - it is simply matter that does not interact with the electromagnetic or strong forces. The neutrino - a very ordinary elementary particle that was first detected over 50 years ago - would be a good candidate for dark matter were it not for the fact that we do not think there are nearly enough neutrinos to explain the observed gravitational effects of dark matter. By using terms like "conceptualisation" and "cognitive encapsulation" you make dark matter sound rare, exotic and mysterious, which is entirely wrong and misleading - it is very common; no more exotic than neutrinos (just harder to detect); and its predicted properties are known in considerable detail. Gandalf61 (talk) 22:08, 19 June 2010 (UTC)

Neutrinos also move at near light speed, making them not ideal candidates for matter that ostensibly remains clustered and localized.

To say that "dark matter is a fermionic (ie. "matter") phenomenon would avoid the tautology of "dark matter is matter," but this too would be speculative - not all dark matter candidates propose strictly fermionic particles as the cause (cold dark matter). Most SUSY theories of course deal with fermionic superparticles like gravitinos and gauginos, but these rest on SUSY itself which posits how "matter" is generated under certain constraints. This generation aspect is not a part of the common colloquial concept of matter, which derives from the example of the atom and is generally static in structure. Hence "matter" itself isn't quite accurate, doesn't fit all definitions, and in reality the term "dark matter" is again just a container for what may best be defined as a rather non-material physical phenomenon.

I don't think "conceptualization" raises the issue of abundance or the otherwise lack thereof. It simply refers to the term as an encapsulation for a concept, which physicists then offer candidates to explain it. If 'abundance' of "dark matter" is something that needs upfront explaining, and I agree that it does, then that should be explained in overt language, not through preserving an implication encoded in the current language. -Stevertigo (w | t | e) 01:12, 20 June 2010 (UTC)

I think, at minimum, the new sentence would require a source saying that the consensus of the astrophysical community is that dark matter is not matter. Then it would require an additional sentence explaining why the astrophyical community named it "dark matter". --Chetvorno^TALK 08:26, 20 June 2010 (UTC)

Fair enough. The name is straightforward, and just as "black holes" aren't really "holes" - a name is a pointer or container for a concept. I don't object to the title or the object term "matter," as it was (as originally proposed in the 1930s) both 1) natural to think of "matter" as the cause for a mass or mass-like effect, and 2) useful to think of forms of matter which were novel and do not fit the typical definition. -Stevertigo (w | t | e) 15:14, 20 June 2010 (UTC)

Stevertigo - the current definition is not tautological - it says dark matter is "matter that is inferred to exist from gravitational effects on visible matter and background radiation, but is undetectable by emitted or scattered electromagnetic radiation" i.e. matter with very specific properties. This opening sentence is using "matter" in the scientific sense of the word. It is accurately and correctly describing the view of mainstream astrophysics. To import terms such as "conceptualization" and "non-material" would be both inaccurate and confusing, whereas "fermionic phenomenon", although technically correct, is needlessly verbose. I am done here. Gandalf61 (talk) 09:39, 20 June 2010 (UTC)

I think it is tautological, and I suggest a different approach not just to help break the tautology with "matter," but to break the assumption of fermionic phenomenon, such that it can accommodate the possibility of bosonic and other atypical candidates. It is not "technically correct" to say that only strictly fermionic explanations can explain what remains an elusive phenomenon open to discovery.

"Dark matter is matter that is inferred to exist [..]" - Forgetting the rationale for a moment ("[inferred] from.."), the concept of "matter" here is "matter that is inferred to exist", a relative object clause that itself is not defined. Is there a definition for "matter that is inferred to exist," or, for that matter "visible matter" or "invisible matter" or any other variant/qualified definition of matter used the article? Whether matter is visible or invisible is not the concept here - the concept here is the phenomenon, and explanations for it, which again are not confined to "matter." -Stevertigo (w | t | e) 15:14, 20 June 2010 (UTC)

PS: Dark matter is a theoretical substance of unknown composition suggested as the cause for a observed abundant ubiquitous mass-gravitational phenomenon [as observed by distortions [of space time spacetime] on large [astrophysical] scales]. -Stevertigo (w | t | e) 17:27, 20 June 2010 (UTC)

This has some serious problems. First, dark matter is motivated by observation, not theory. Second, "ubiquitous mass-gravitational phenomenon" is terribly awkward and unclear. Third, the evidence for dark matter is not primarily from spacetime geometry, except in the roundabout sense that gravitation acts through spacetime geometry. Fourth, it's not very clear what might be meant by "astrophysical scales" or "large astrophysical scales." The other changes had similar issues. --Amble (talk) 00:54, 24 June 2010 (UTC)

Agree completely with all Amble's points. Stevertigo's new opening sentence was not an improvement. Gandalf61 (talk) 07:11, 24 June 2010 (UTC)

I note that neither have said much with regard to my arguments against the current version, without actually defending the current or stating what is good about it. Hence the issues of tautology ("a black hole is a hole") resting on an unclearly-defined term ("dark matter is matter" but not "visible matter") inaccuracy (definition of "matter") excess precision (promoting a fermionic basis to the exclusion of non-fermionic candidates) and no-less terribly awkward language ("matter which is inferred to exist," "visible matter") remain.

As for Amble's critique, much appreciated. Some responses: 1) There is no "motivation" for dark matter, what you mean is perhaps that its investigations are "driven" by discovery and not theory. Putting aside the fact that my wording made no implication otherwise, your point here suggests an unnecessary preference for the observation/experimental side to the negation of the theoretical side. 2) There is nothing "terribly awkward and unclear" about "ubiquitous mass-gravitational phenomenon," though I understand this to be your view, without the required context stating it as your opinion. 3) Your third point is valid "not primarily from spacetime geometry" but is easily corrected to include cosmological anomalies. Keep in mind that the cosmological anomalies come from cosmological models which (while ostensibly representing material abundance) are not as compelling as more localized examples. This deals with your first point also, as cosmological evidence isn't explicitly observational either, as their actual basis is the model. Also, the editorial tendency to negate an entire series of edits based on a particular material issue is, at best, adversarial. 4) The issue of scale is relevant to the definition. -Stevertigo (w | t | e) 18:21, 25 June 2010 (UTC)

"Cosmological scale" is misleading, it leads one to think that this only happens at distances of z>0.1 or of regions encompassing hundreds of millions of light years. Yet, we encounter dark matter in the local dwarf galaxy population less than 1 million light years distant, over a scale of a thousands of light years. 76.66.195.196 (talk) 21:35, 25 June 2010 (UTC)

Well Gandalf suggested 'various astrophysical scales' which can be put simply as "astrophysical scales" and I thought that was sufficiently clear. -Stevertigo (w | t | e) 22:13, 25 June 2010 (UTC)

I found it confusing to lead with "but is undetectable by emitted or scattered electromagnetic radiation." First, it uses a lot of jargon to say something simple. Second, it seems to contradict evidence for dark matter that comes from gravitational lensing. I just changed it to "invisible". Roger (talk) 22:28, 25 June 2010 (UTC)

Well, gravitational lensing isn't really scattering in the usual sense. At the very least, it's not scattering off the dark matter itself, but off its gravitational field (or from the warp or bend in space-time, or however you want to think of this). Dark matter isn't just invisible, like gas, but if it doesn't interact with light, it's perfectly transparent. They really should really have called the part of dark matter that doesn't interact with light "transparent matter." SBHarris 23:59, 25 June 2010 (UTC)

I am also in support of changing it back. Air is "invisible" if you ask any layperson, but it is easily detectable by scattering and blackbody emission in non-visible wavelengths. I have changed it back. -RunningOnBrains^(talk) 06:22, 26 June 2010 (UTC)

(I came here through the post at WT:PHYS.) What about the current wording but with "is what is" instead of "is matter that is"? It retains all the advantages of the current wording, doesn't sound tautological, and can't be taken to exclude bosons. ― A._di_M.^{3rd Dramaout} (formerly Army1987) 11:20, 26 June 2010 (UTC)

You guys are thinking too hard. On the simplest level, we see the stars and the dark matter is what we don't see. We don't know for sure that the dark matter is undetectable, or fermionic, or consists of unknown particles. Any attempt at a very precise definition in terms of properties is going to have problems. Roger (talk) 19:02, 26 June 2010 (UTC)

I agree. Keep in mind that the vast majority of readers will be nontechnical people who merely want a simple, plain language definition. A wordy, overinclusive lead sentence that covers all the exotic possibilities is not appropriate for a general purpose encyclopedia. I have no objection to including a caveat in the introduction saying dark matter may turn out to be bosonic (if reliable sources say that is a significant possibility) but I think the word 'matter' should remain in the lead sentence. --Chetvorno^TALK 11:31, 28 June 2010 (UTC)

Again the definitive phrase "matter that is inferred to exist" does not have any meaningful definition, and in any case is simply too clumsy to leave as is. -Stevertigo (w | t | e) 23:47, 3 July 2010 (UTC)

Yes it does. If something cannot be inferred to exist at all, it doesn't exist, as far as such empirical sciences as astronomy and cosmology are concerned. If something can be inferred to exist but it doesn't shine, it's dark, by anybody's definition. The only problem is that among the possible meanings of matter there are some which are way too narrow for that sentence, which can be solved by replacing matter that with whatever. Let's try that... ― A._di_M.^{3rd Dramaout} (formerly Army1987) 10:56, 4 July 2010 (UTC)

Hmmm. I am afraid that "whatever" leaves the door open for Stevertigo's "theoretical substance"/"conceptualisation" nonsense. Is there a mainstream candidate for dark matter that is not a form of matter ? Our article on matter says not. So why should we pander to Stevertigo's mysticism here ? I appreciate that your edit was meant in good faith, but I have reverted it. Gandalf61 (talk) 12:06, 4 July 2010 (UTC)

Can conceptualisations bend spacetime? :-) More seriously, I see your point. (But I've noticed that while the matter article mentions the broad meaning of the term used by cosmologists in the lead, it doesn't expand on it in the article body and doesn't give a proper definition of it, e.g. "anything which causes spacetime curvature". But this is an issue of that article.) ― A._di_M.^{3rd Dramaout} (formerly Army1987) 14:42, 4 July 2010 (UTC)

What, Gandalf, do you mean by "mainstream candidate" such that would make you or anyone else expert enough to know at present date which candidates are valid and which aren't, to the exclusion of any non-"mainstream" alternatives? And what makes you suggest that staying open to these alternatives, and writing articles accordingly, equates to some kind of "mysticism" (which I understand to be a pejorative in this context) ? I don't see the good faith here on your part. -Stevertigo (w | t | e) 17:51, 9 July 2010 (UTC)

(Outdent, and outside response:) A "mainstream candidate" for dark matter would be anything that made enough of a splash in the scientific community for sources satisfying WP:RS to be found. To date, the proposed candidates in these sources are all matter (lightest supersymmetric particle, sterile neutrinos, a handful of other exotic proposals, and in the past things like normal neutrinos before "hot dark matter" was ruled out by observations). Proposals that do not involve matter involve modifying gravity instead. This is already covered in the mentions of MOND and similar within the article. If you have a source satisfying WP:RS that doesn't fall into either of these candidates, please cite it. Otherwise, calling "dark matter" "matter" seems appropriate, as that appears to be the consensus of the scientific community (with the minority dissenting view already expressed in the article). --Christopher Thomas (talk) 18:40, 9 July 2010 (UTC)

The above section

Please do not archive the above section, entitled "Dubious lead sentence(s)". I need to be able to refer to it for the time being. I will remove this section when I no longer need to refer to it, and leave a message over at WikiProject Physics talk. Your cooperation is greatly appreciated. ---- Steve Quinn (talk) 19:30, 10 October 2010 (UTC)

I suggest making a local copy if there's information in it you're referring to, or hardlinking the archived section if it gets auto-archived and you have to reference the original thread (at AN/I or what-have-you). In the meantime, I'll add a timestamp set for an absurdly distant future date, so that auto-archiving doesn't occur. No explicit deletion action would be needed; once you've finished, turn the "2099" timestamp back to "2010". --Christopher Thomas (talk) 00:03, 11 October 2010 (UTC)

Thanks Christopher. I now have a diff for the first statement which begins this page. I want to collect a few more. I am thinking those will access the page, archived or not. I am probably being overly concerned (due to lack of experience). In any case, I will turn the "2099" timestamp back to "2010", very soon. --- Steve Quinn (talk) 01:52, 11 October 2010 (UTC)

Diffs will work (and are the preferred form of evidence at AN/I and elsewhere, as they show specific statements instead of entire threads). Hard-links to specific versions of this page (the "&oldid=(numbers)" links from the article history) will also always work. Section headings work too; you just have to insert the "#(title)" bit into the URL manually. --Christopher Thomas (talk) 05:43, 11 October 2010 (UTC)

Thanks very much for the pointers, and your idea for the time-stamp. ---- Steve Quinn (talk) 06:55, 11 October 2010 (UTC)

Glad to help. Putting a bogus timestamp inside an HTML comment works too; I should have remembered that instead of altering my own, but it doesn't matter at this point. It came up at AN/I when a thread was getting prematurely archived. Usually I end up dealing with a different problem: A thread will not be archived if there are malformed or missing timestamps, so after setting up Miszabot it's usually necessary to come back a day or two later and fix timestamps in all of the old threads that stuck around after the first archiving pass. --Christopher Thomas (talk) 07:16, 11 October 2010 (UTC)

Neutrino flavors

There are three different flavors of neutrinos (i.e. the electron-, muon-, and tau-neutrinos), and their masses are thought to be very close to each other, but still slightly different.

The Wiki article on neutrinos gives a factor of 2 x 10⁶ between thw masses of electron and tauon neutrinos. I realise that relative to nucleons they are "massless" but as an interested outsider I am asking if the form of the line in quotes is really suitable?84.13.66.132 (talk) 13:53, 16 October 2010 (UTC)

Only the difference between squared masses is known. If absolute masses are sufficiently high (and they're claimed to be by one paragraph in the "mass" section at neutrino), then the masses may be nearly equal. The values you are referencing are likely the lower bound on the masses. I agree that this is murky enough that the sentence in question should be changed. --Christopher Thomas (talk) 00:46, 17 October 2010 (UTC)

Dark matter: cold gravitationally bound clumps of H and He?

(from the Reference Desk Ginger Conspiracy (talk) 18:18, 22 October 2010 (UTC))

Is there any reason dark matter isn't simply gravitaionally bound clumps of hydrogen and helium in the cold interstellar medium?

Gravitational clumps of cold interstellar hydrogen, helium, and other elements (with abundances in proportion to traditional nucleosynthesis ratios) would have the same spectra as many fewer individual molecules of the same substances because absorbed photons would be stored mechanically as heat and released as blackbody emissions at 50 down to 3 Kelvin and below in addition to much weaker spectral lines than in isolated gas molecules. This would explain why spectroscopy has detected much less cold interstellar media than would be consistent with thermodynamic cooling away from nearby stars as well. This would not require modification of any physical constants or cosmological principles. The spectra would be exactly the same for clumps of many more H and He molecules as for profoundly fewer individual molecules, except for the blackbody emission which is partially absorbed by our atmosphere and certainly overpowered by transmitted starlight through interstellar clouds.

Everyone admits that gravitationally bound clumps of interstellar gas are necessary for star formation, but after it's clumped, it's not really a gas so much as a mechanical fluid, is it?

My third question is: How many additional Daltons (AMUs) per interstellar medium molecule would be necessary to account for the 5.75 times as much mass as has been observed in non-dark matter?

[5] says we need accurate infrared spectrometry and imaging at 28.2, 17.0, 12.3 and 9.7 microns (the Earth's atmosphere is opaque at 9.7 microns) to be able to confirm the possibility. Ginger Conspiracy (talk) 06:50, 22 October 2010 (UTC)

The theoretical models of Big Bang nucleosynthesis predict the primordial abundances of ¹H, ²H, ³He, ⁴He, ⁷Li, etc. These models are only mutually consistent with the observations across all isotopes if you assume that total mass of all normal matter is about 1/6 of the total needed for all matter. As a result, the prediction is that 5/6 of the mass in the universe is in some non-baryonic (i.e. non-atomic) form. Presumably there is some unobserved mass in hydrogen and helium clumps, but the traditional nucleosynthesis arguments lead to the conclusion that most of the dark matter is in some other exotic form. Dragons flight (talk) 07:54, 22 October 2010 (UTC)

Gravitational microlensing is also used to set a limit on the number of dark "clumps" of mater, see Massive compact halo object, max 20% of the dark mater are MACHOs.

I am not shure that this rules out Robust associations of massive baryonic objects.

--Gr8xoz (talk) 09:13, 22 October 2010 (UTC)

This is already covered in the article, so I'm not sure why it's being posted here? What specific article changes are you asking for? --Christopher Thomas (talk) 19:24, 22 October 2010 (UTC)

Strange Edit Summary

Contains the following phrase: "Appears to OS". How is this phrase deciphered?Kmarinas86 (Expert Sectioneer of Wikipedia) ^{19+9+14 + karma = 19+9+14 + talk = 86} 00:55, 15 November 2010 (UTC)

Original synthesis: compare OR. Xxanthippe (talk) 01:16, 15 November 2010 (UTC).

WP:SYN is the relevant policy link (I was wondering about the acronym too). --Christopher Thomas (talk) 02:04, 15 November 2010 (UTC)

Process Physics in 'alternative theories' section

I reverted the edit which removed the paragraph on process physics under the alternative theories section, as I did not believe there was adequate justification for removing it. The reason given by Aknochel was that the journal Progress in Physics, in which some of the papers were published was "not a properly peer-reviewed journal". I consider this reasoning to be inadequate for several reasons:

- the journal actually describes itself as peer-reviewed, so I'm not sure where this "not peer-reviewed" misconception has come from.

- the publications are not limited to this journal (see reference in article), and include edited books, articles in publications such as New Scientist (including cover features), and a range of journals.

129.96.220.98 (talk) 04:18, 27 January 2011 (UTC)

Please see WP:RS for guidelines on what sources are generally acceptable (there's a section on sources for scientific works). WP:UNDUE and WP:FRINGE may also be useful reading.

While Process Physics is a concept that is known within the scientific community, right now it appears to be one researcher's pet project, so my own feeling is that it would violate WP:UNDUE to include it in this article. Given that you've had three unrelated editors tell you that it isn't appropriate to include it in this article, I'd suggest trying to convince people on this talk page before adding it again. --Christopher Thomas (talk) 06:58, 27 January 2011 (UTC)

I had a read of the articles you mentioned and as far as I can tell Process Physics seems to come under the classification of an alternative theory held by a significant minority.

Although the link I used as a reference gives a list of papers that clearly indicate the scientist in question focuses predominantly on this field of research, he is quite definitely not alone. I believe he's written a review or two which should be listed among his papers. They should hold a good list of references of the various work around the world.

If you can present specific reasons why this field of research does not merit inclusion I can perhaps present a better argument, but at this stage I don't really know what further information I need to present to argue in its favour, beyond just telling people to read the references.

129.96.220.98 (talk) 05:12, 28 January 2011 (UTC)

So, is it suitable for inclusion or not? 121.45.40.156 (talk) 15:00, 5 February 2011 (UTC)

No, because sources are substandard (for a new gravitation theory). In particular, Progress in Physics is a minor journal (no impact factor and other problems mentioned in the linked article) and is not a reliable source. Materialscientist (talk) 05:40, 11 February 2011 (UTC)

Finally! A justified argument, not just a contradiction! That's all I needed to hear. Based on this evidence I will concede that Progress In Physics does not appear to be sufficient to justify inclusion. However I am yet to hear anything against the other publications in which some of the listed articles appear. Could you address this point?

A list of all the other journals/books/etc I could find which publish these theories are summarised below. For completeness, I haven't excluded any from this list, although I will readily admit some would not meet Wikipedia's definition of a reliable source (e.g workshop proceedings).

• Relativity, Gravitation, Cosmology, - New Developments
• Ether Space-time and Cosmology: New Insights into a Key Physical Medium
• Apeiron
• Infinite Energy
• Einstein and Poincare: The Physical Vacuum
• Trends in Dark Matter Research
• Magister Botanicus
• Process Studies Supplement
• Workshop Proceedings of the 8th International Conference on the Simulation and Synthesis of Living Systems
• General Relativity and Gravitation
• The Physicist
• Physics Letters
• P.M. Magazin
• Adelaide Advertiser
• Flinders Journal
• New Scientist

129.96.220.98 (talk) 08:30, 18 February 2011 (UTC)

I am not an expert in this area and thus recognize above only two peer-reviewed journals with impact factor of around 2 or higher: Physics Letters (A or B?) and General Relativity and Gravitation (am I missing something?). Anyway, we need to see the full references. Materialscientist (talk) 08:49, 18 February 2011 (UTC)

Understood. References are below:

My original reference used in text:
http://www.flinders.edu.au/science_engineering/caps/our-school/staff-postgrads/academic-staff/cahill-reg/process-physics/home.cfm
This linked to a brief description of Process Physics, which also included links to pages containing many papers/books/etc related to the field.

R.T. Cahill, C.M. Klinger, "Pregeometric modelling of the spacetime phenomenology", Physics Letters A, vol 223, issue 5, p313-319, 1996.
DOI:10.1016/S0375-9601(96)00775-X

Four citations in Web of Science since 1996. Materialscientist (talk) 00:21, 21 February 2011 (UTC)

R.T. Cahill, C.M. Klinger, "Self-Referential Noise and the Synthesis of Three-Dimensional Space", General Relativity and Gravitation, vol 32, issue 3, p529-540, 2000.
DOI: 10.1023/A:1001984518976

Four citations in Web of Science since 2000, seem like self-citations. Materialscientist (talk) 00:21, 21 February 2011 (UTC)

R.T. Cahill, "Process Physics: Inertia, Gravity and the Quantum", General Relativity and Gravitation, vol 34, issue 10, p1637-1656, 2002.
DOI: 10.1023/A:1020120223326

Zero citations in Web of Science since 2002. Sorry, this theory does not seem widely accepted. Materialscientist (talk) 00:21, 21 February 2011 (UTC)

I don't know what you mean when you ask if you're missing something. If you could clarify your question I may be able to help. Also, the above list is just for the references from the original list, which were published in the journals you mentioned. There may be other relevant papers that I haven't included here.

121.45.92.247 (talk) 14:01, 18 February 2011 (UTC)— 121.45.92.247 (talk) has made few or no other edits outside this topic.

Before you make conclusions about the general acceptance of this theory, keep in mind that this is a very restricted search. If we extend the search to look at the most cited papers in the field we get much more numerous results. Listing them all here is impractical, so I've just selected a handful. Google Scholar will give you more extensive results for you to peruse at your leisure.

"Process Physics", 2003. (a review)
Cited by 62.

"Dynamical fractal 3-space and the generalised Schrodinger equation: Equivalence Principle and vorticity effects", 2005.
Cited by 25.

"Absolute motion and gravitational effects", 2003.
Cited by 39.

"'Dark Matter' as a Quantum Foam In-Flow Effect", 2004.
Cited by 26.

"Quantum foam, gravity and gravitational waves", 2003.
Cited by 24.

"Process physics: from quantum foam to general relativity", 2002.
Cited by 19.

Possibly also this:
TG Zlosnik et al, "Modifying gravity with the aether: An alternative to dark matter", 2007.
Cited by 72.

Your opinion?

129.96.220.98 (talk) 09:14, 21 February 2011 (UTC)

Any other citation index would give higher cites than Web of Science, because it would add less reliable sources like conferences, journals without IF, etc., but it does not matter - counts are still very low. Materialscientist (talk) 09:18, 21 February 2011 (UTC)

Low compared to what? Seems quite high for the field, and certainly a great deal more than any of the other papers referenced in the Alternatives to Dark Matter section of this article. If candidature for inclusion is this strict, perhaps a review of the entire Alternatives section is in order. Frankly I don't think you can reasonably expect any alternative theory to dark matter to be as highly cited as papers within the dark matter field, simply by definition of being an alternative to the most widely accepted theory, and hence everything should be viewed on a relative rather than absolute scale.

129.96.220.98 (talk) 05:23, 22 February 2011 (UTC)

Process Physics is one person's pet project which has been speedily deleted before (User talk:Danwills). It's not mainstream enough for this article. Another reference to it has also been added to Theory of Everything. Xxanthippe (talk) 06:01, 22 February 2011 (UTC).

I wish you would state your references. If I have to list dozens of papers and write an extensive debate just to justify a few sentences I don't see why its adequate for you to counter my arguments with vague statements and no references to back them up. 121.45.45.109 (talk) 14:32, 22 February 2011 (UTC)

MOND and variants are the main competitor to dark matter as an explanation for observations, and MOND has a far, far larger literature impact than process physics does. --Christopher Thomas (talk) 06:22, 22 February 2011 (UTC)

It's becoming increasingly evident that I have no idea what constitutes 'sufficiently notable' by Wikipedia standards. If the intuitive definition is not correct, then I am lost. It seems the editing of Wikipedia should be left to Wikipedians, rather than scientists. My mistake.

121.45.45.109 (talk) 14:32, 22 February 2011 (UTC)

"Written about by several unrelated research groups and cited by _many_ unrelated research groups" would be a good start. This applies both to the concept of "process physics" itself, and to its viability as an explanation for dark matter, separately. Please see WP:UNDUE for additional information about weight, and WP:RS for a description of what sources are and aren't considered to have weight in a scientific context. Also please take a glance at WP:COI, as your first IP address suggests that you might have a vested interest in having PP prominently mentioned. --Christopher Thomas (talk) 19:36, 22 February 2011 (UTC)

There is no conflict of interest. I am not a part of the research group, nor do I have anything to do with any research or study in the field of Process Physics. I gain nothing by having this information in the dark matter article. It is however, a subject which I regularly stumble across and when I couldn't find further information on Wikipedia I thought it could benefit from having some.

129.96.220.98 (talk) 04:01, 23 February 2011 (UTC)

I agree that Wikipedia would benefit from having an article about Process Physics. Unfortunately, the last time someone tried to write one, it was deleted due to not adequately establishing notability (per the archived discussion regarding deletion). It's possible that that might have changed in the interim, but you'd need sources from multiple unrelated research groups that talk about it to establish that it's known and at least a little bit relevant within the scientific community.

Including mention of PP anywhere other than a Process Physics article, though, would almost certainly violate WP:UNDUE, for the reasons mentioned above for this article. You'd have to show that people other than the model's creator and his group wrote papers in reputable journals mentioning this as a serious alternative. That's happened with MOND, but not with PP. --Christopher Thomas (talk) 04:48, 23 February 2011 (UTC)

Now we're getting somewhere. I was under the impression it was actually the other way around - a less notable subject could only justify a mention on merged articles incorporating multiple subjects within a related field, but not an entire article to itself. Thanks for the clarification.

The field which PP sits in is not a large one, so there's not a great deal of groups studying this sort of thing, be it PP or otherwise, but I have heard that there's experiments going on in Russia and a European country I can't remember (might be Belgium), which are definitely looking into components of PP but are not related to this other scientist's research group. I think the resources to establish notoriety are definitely out there, it's just a matter of tracking them down.

I think I've seen the former PP article and agree that its deletion was justified. It appears to be predominantly based on old information, and didn't give a particularly accurate summary to begin with. A significant update is definitely in order.

I'm afraid I'm quite new to Wikipedia and don't think I could manage a new article on my own. Would you be interested in collaborating on a PP article?

129.96.220.98 (talk) 07:39, 23 February 2011 (UTC)

I'm afraid I'm not in a position to do so (due to mostly being on sabbatical from Wikipedia). WT:PHYS would be one possible place to ask, but you'd have to take care in your approach. You have no idea how many people all of us see who say "X is important!"; this tends to get discounted as noise. You'll have a warmer reception with an approach along the lines of, "Process Physics was deleted a few years ago due to not adequately establishing notability; I think that this is changed, and can provide references, but I need mentoring on how to best write a properly-sourced article and how to go through the correct process to make sure it's not seen as duplicating deleted content". Another step that will help will be registering as a Wikipedia user. That gives you your own scratch-space to work on draft material, gives you a consistent identity no matter which machine you log in from, and will also get you a warmer reception (rightly or wrongly, quite a few people will assume that IP editors are troublemakers until proven otherwise). It'll also hide your "whois" information, which would otherwise be visible to anyone who clicks on the appropriate link, or manually invokes "whois" on their own machine.

I hope this advice is useful to you. Further discussion should probably either be at WT:PHYS or on your user account talk page (if you choose to register an account), as this is straying pretty far away from the topic of dark matter. Good luck! --Christopher Thomas (talk) 07:59, 23 February 2011 (UTC)

A worthwhile addition to the article?

Claims from Monash University in Melbourne, Australia.

It has been referenced in the new article Amelia Fraser-McKelvie, the name of the discoverer. HiLo48 (talk) 23:55, 28 May 2011 (UTC)

This press release is talking about baryonic matter that isn't in stars. It might be worth adding to baryonic dark matter or to galaxy filament, but the term "dark matter" usually refers to the non-baryonic type. Still a nifty observation report, of course. --Christopher Thomas (talk) 00:26, 29 May 2011 (UTC)

Filaments?

Apparently the missing mass has been found in the form of superhot filaments. How does that impact this article? The word "filament" doesn't even appear in it!

http://www.allvoices.com/s/event-9239517/aHR0cDovL3d3dy5zbWguY29tLmF1L3RlY2hub2xvZ3kvc2NpLXRlY2gvbW9uYXNoLXN0dWRlbnQtaGVscHMtc29sdmUtY29zbWljLW15c3Rlcnktb2YtbWFzc2l2ZS1kaW1lbnNpb25zLTIwMTEwNTI2LTFmNmZnLmh0bWwlMjNpeHp6MU5oYng1NWRM

--202.81.69.153 (talk) 02:22, 30 May 2011 (UTC)

See the previous comment section. This is baryonic matter (matter made from ordinary atoms that interacts with other matter), not the type of non-baryonic "dark matter" described in this article.

About 4-5% of the universe is normal matter. About a quarter of that is stars. The rest of it is primordial hydrogen and helium gas (and a bit of lithium), in galaxies and strung out in inter-galactic filaments following the large scale structure of the universe. The link you cite, and the links referenced in the previous section, are talking about an observation that confirms that there's gas in these filaments (we'd previously just seen the stars in them).

That covers 4%-5% of the universe's mass. Several un-related observations show that about 23% of the universe is matter but in a form that doesn't interact with normal atoms or with light. That's what scientists call "dark matter". --Christopher Thomas (talk) 02:58, 30 May 2011 (UTC)

The problem (with context) here is that at some point, "missing mass" got redirected/merged into this article, currently "dark matter". As such, there is really no place to discuss the progress of the research of missing matter in wikipedia without referring to the dark matter article. Perhaps a fork is needed, or a move back to missing matter and making dark matter a subsection. - Sangrolu (talk) 18:07, 31 May 2011 (UTC)

This is partially covered at baryonic dark matter, though that article could stand improvement. --Christopher Thomas (talk) 19:31, 31 May 2011 (UTC)

Role of Dark Matter/Energy in the Kuhnian development of physics

My strong sense is that dark matter/energy are a reification of fundamental problems in modern physics, i.e. gravity + the Standard Model. As I've put on Higgs Boson and it's never been challenged, dark matter/energy is not (except as a metonym for the observed discrepancy between that theory and observation) a part of any accepted (or FTM, SFAIK proposed) theory of physics, although there are various conjectures and speculations which fall short of same. This aspect doesn't seem to be fully enough developed in the article as it stands now nor do I see commentary in the talk archives about same but may have missed something. Lycurgus (talk) 16:08, 6 May 2011 (UTC)

Look up lightest supersymmetric particle. We have strong reasons for believing supersymmetry happens, and it predicts that there will be at least one new stable massive particle. That's a prediction of dark matter.

Also look up big bang nucleosynthesis. The fact that the element ratios come out right if and only if there's a lot of non-baryonic matter around also predicts the existence of dark matter.

You can make a stronger argument for dark energy being a label for an unknown rather than a specific thing, but dark matter - the subject of this article - is much better-understood. --Christopher Thomas (talk) 17:14, 6 May 2011 (UTC)

Yes, thanks for illustrating the issue, pieces parts that don't add up to anything. My point is that the article should show, more than it currently does, the thing for what it is and not commit the fallacy of assuming that it describes a physical reality rather than an artifact leading to a more complete understanding of nature in which it might or might not continue to be so regarded as for example in the classic cases such as phlogiston, the subliminiferous ether, etc.. Lycurgus (talk) 20:39, 6 May 2011 (UTC)

Most scientists consider the evidence for dark matter persuasive (and specific enough to greatly narrow down what it is). Alternatives are already noted in the article. Giving them more prominence would violate WP:UNDUE, as the vast majority of textbooks and scientific literature assumes a) that it exists and b) that it has certain properties (usually that it's massive particles that interact via the Weak force, sometimes that it's massive non-interacting particles). --Christopher Thomas (talk) 03:56, 7 May 2011 (UTC)

You're not getting my point which I've explained above. Wait for someone else to comment and respond to them (or not as you please). Lycurgus (talk) 08:06, 7 May 2011 (UTC)

The problem here is that your Kuhnian philosophy is considered crackpot stuff by others. Regardless of whether you are right or wrong, you need to find some published source that expresses the view, and then propose text that describe your view in terms of whoever is on the record with that view. Roger (talk) 17:38, 7 May 2011 (UTC)

One might think that you were Phyllis' son :) In any case the sociology of science established by Kuhn and others is the current received and mainstream, and more or less sole academically accepted approach to the subject. Lycurgus (talk) 23:57, 10 May 2011 (UTC)

Did you find any Kuhnian sources for your dark matter ideas? Yes, Kuhn has a following among academic non-scientists but a lot of astrophysicists think that he was a crackpot. Roger (talk) 21:10, 13 June 2011 (UTC)

Im certian someone's thought of this but i dont know where to look.

So, Im not a scientist. At all, in any sense of the word. But I was wondering if this effect could be compensated for, by surrounding the universe with void (which must fill) that pulls thigns in all directions, so gravity would increase toward the void at all times, because of how much matter would be shot continually into it, until heat death occurs.

I am almost definetly wrong and would be kinda astounded if I had any part of that even vaguely correct. So dont worry too much about that. What im really wondering is if theres any...simpler way to explain the effects of dark matter, that wouldnt be too abstract. It makes sense as a not-totally-correct way to visualize things for me, but I think others would have better views.

Additionally however, if someone HAS postulated my idea, id love to read about it. whether serious or mostly-disproven (cant disprove anything :( ) its still very interesting. Sorry for bringing this up here but I cant even figure out where to start googling for this sort of thing. 74.128.56.194 (talk) 20:09, 13 June 2011 (UTC)

Oh, Edit: I tend to take information, and compile it into a way that will have nothing to do really with the actual idea, but will still vaguely fit together. So feel free to criticize, as I cant always tell when when ive fallen off the deep end. The crazy pills are labelled poorly. 74.128.56.194 (talk) 20:13, 13 June 2011 (UTC) 74.128.56.194 (talk) 20:09, 13 June 2011 (UTC)

If all the light energy photons in transit from the 100,000,000,000 stars added together would equal to what?

Essay archived.
The following discussion has been closed. Please do not modify it.
Light cannot go round corners it is straight, a star looks like a dot in the sky but the light is emitted all around but cannot be seem from the side of the star only when looking direct we see the light. if we could see light from the side the night sky would be lit up as the light travels out from every star an crosses the universal plains. The universe is connected through mass ropes of light that can't be seen. What is the universal mass equation of all the light in transit? If all the masses plus the light that is in constant transit since the dawn of time from 100,000,000,000 plus stars. Would it equal the missing matter e.g.: if a star was spaced atom by atom in a straight line how far would it go before it was invisible to the eye meaning mass can appear missing when it is right under your nose. And as the visible universe is 92billion light years across and some say its bigger to the point that 92 billion light years is an atom size to its real size. That is a lot of light rays in transit, a lot, and this may add to filling in those numbers, and if it does. I will write some extra notes, Law of force every action is a reaction, The impact of light upon all other celestial bodies push everything away so creating and adding to a forever expanding universe. So who has worked out does light have a force when hitting matter, even if infinity small would it move an object with zero resistance? photons light described as rope in the shape that appears to be a series of very small multiple magnetic fields each one the size of the frequency that pulse another ant link maybe like coil induction effect to connect from A to B then even an X particle runs, pushed or pulled to its destination. —Preceding unsigned comment added by 77.99.29.196 (talk) 06:42, 9 March 2011 (UTC)

This is not the place to present your own views on how photons and dark matter work.

It's also very easy to place an upper bound on the mass of the photons stars emit over their lifetimes: Less than about 1% of the rest mass of the stars, as it's derived from fusion of the stars' fuel. The mass of dark matter is vastly greater than this, per the article. --Christopher Thomas (talk) 07:02, 9 March 2011 (UTC)

Remind you that according to the current standard model of particle physics photons are massless, that's why they travel at the speed of light, otherwise, according to general relativity, it would be necessary a lot more than a quanta pack of energy to move at that speed.Wcris (talk) 18:08, 25 June 2011 (UTC)

Lack of evidence for WIMPs

The weakly interacting massive particles article is replete with various failures to detect any evidence of the WIMPs, which involve a certain amount of wishful thinking about supersymmetry that might not be all that compatible with Occam's Razor. But Frampton says primordial intermediate mass black holes are consistent with halo rotation, isotope ratios, microlensing, and wide binary observations, and at least two of them have been detected so far. Would anyone object to listing the black holes before the WIMPs for the top two theories in the introduction? 99.39.5.103 (talk) 11:38, 18 May 2011 (UTC)

Yes, I would object, because despite the lack of evidence, WIMPS are still the favorite candidate. That's not something we can overrule here, no matter how good the argument against WIMPS is. Also, I remember reading some criticisms of Frampton's idea, so it's not that you have a DM candidate without problems here. Count Iblis (talk) 14:42, 18 May 2011 (UTC)

I'd be very interested in reading those criticisms. The idea that dark matter is black holes is not unique to Frampton (e.g. the NASA source about them doesn't mention him at all) he's just been taking the lead in pointing out that all observations are consistent with them. WIMPs, on the other hand, currently have exactly zero observational evidence. Just because a lot of people are looking for them doesn't necessarily mean they are anyone's favorites. 99.39.5.103 (talk) 16:28, 19 May 2011 (UTC)

My understanding is that black holes were ruled out as dark matter candidates by gravitational microlensing searches (along with most forms of massive compact halo object). Furthermore, Big Bang nucleosynthesis only produces the observed distribution of elements if you have quite a lot of dark matter that doesn't interact strongly with normal matter. Black holes, on the other hand, would interact with normal matter, so they don't address the BBNS problem. The fact that the amount of matter needed for nucleosynthesis to match observations is also very close to the amount needed to make galactic rotation curves and struture formation work is strong circumstantial evidence in favour of WIMPs or completely sterile particles as dark matter. --Christopher Thomas (talk) 00:29, 27 May 2011 (UTC)

Paul Frampton says microlensing observations are consistent with IMBHs, and if they are primordial then that addresses the BBNS deuterium-lithium ratio issue. Why would post-big bang interactions affect the nucleosynthesis ratios? I'm not sure that black holes aren't sterile, since they are equal opportunity gravitational attractors. I think we should start with the microlensing data. Where are the various scenario predictions compared with observations in the literature? 12.238.13.194 (talk) 01:51, 28 May 2011 (UTC)

I am referring to primordial black holes. Non-primordial holes would be composed of baryonic matter (not the non-interacting dark matter BBNS needs in order to work), and so don't address that part of the dark matter problem. During the BBNS, primordial black holes would act as strongly-interacting particles (large scattering cross-section if nothing else, and probably a substantial absorption cross-section), and the whole point of dark matter in BBNS is that some of the universe's energy density goes into matter that does not participate in BBNS interactions (not even by scattering).

With regards to microlensing, feel free to do your own literature search, as it's not a field I follow (I'd just seen the results of a couple of searches many years ago with statements about what they ruled out). The acid test of whether Frampton's view is considered plausible is the number of unrelated researchers citing his work (as with most other research). It's probably worth looking at those papers as well during your search, as some of them will be written by people who disagree with his assumptions or calculations. --Christopher Thomas (talk) 02:09, 28 May 2011 (UTC)

This article is worth reading Count Iblis (talk) 23:45, 21 June 2011 (UTC)

It makes serveral strong claims, but I don't see how it addresses the Big Bang nucleosynthesis requirement for dark matter. Claiming a critical density of stellar mass black holes really should have resulted in very obvious effects, too - that's about a hundred black holes for every star, and they'd be expected to follow the same distribution in galaxies as normal stars do! Particle-based dark matter, by contrast, isn't expected to clump on scales smaller than a galaxy, explaining why it's distributed as a more-or-less uniform halo rather than mingling with the disc. The halo distribution is important, as it's needed to solve the galaxy rotation problem; more star-like objects in the disc doesn't do it.

Long story short, I'd want to see other articles supporting this one before considering it evidence of a change in the prevailing view of the scientific community. By all means add it to the primordial black hole section, though. --Christopher Thomas (talk) 06:37, 22 June 2011 (UTC)

Hawkins (2011) discusses microlensing in great detail (and passed peer review so that cite is better than arxiv's). Is there any support for the idea that primordial black holes would influence nucleosynthesis ratios? My understanding is that they would not, which is why dark matter must be mostly primordial black holes if it is mostly black holes. Frampton et al (2010) agrees with you, contrary to Hawkins' assertion of entirely stellar mass black holes, with regard to the galaxy rotation problem, in that there was probably a uniform distribution of primordial black holes, the most massive of which formed galatic cores, and the majority of which are intermediate mass. Since Frampton also passed peer review I intend to replace your deletion, with black holes first, replacing his conference proceedings cite. 76.254.22.47 (talk) 20:29, 24 June 2011 (UTC)

Get agreement from other editors here before replacing it, as - both here and elsewhere - you seem to be the only editor pushing Frampton's work, with objections from others (here and at Talk:Gamma-ray burst). For the record, I do not feel such a change would be wise, as - from what I can tell - the vast majority of the scientific community considers new particles to be the most plausible explanation, with black holes already given sufficient weight as a hypothesis. --Christopher Thomas (talk) 20:53, 24 June 2011 (UTC)

On what sources do you base your opinion? All of the WIMP researchers say in all of their reports that they have no evidence for the new particles that they are looking for. Perhaps I am the only editor who has read Frampton and his distinguished co-authors' work. If you assert that the "vast majority" of scientists believe something, the burden is on you to provide sources supporting that assertion. 76.254.22.47 (talk) 23:18, 24 June 2011 (UTC)

Another important point to consider from Lacki and Beacom (2010) is that postulated WIMPs would gravitate towards and collect inside black holes, even if black holes were very rare. So, you can either believe there are black holes at the centers of galaxies, or more than a few percent of dark matter is composed of WIMPs, but not both. In hindsight it seems so simple, but a generation of cosmologists got hung up on a fanciful interpretation of a single data point from the very ambiguous bullet cluster. 76.254.22.47 (talk) 17:23, 25 June 2011 (UTC)

Dark vs transparent

section 2.0--"from background galaxies since Dark Matter has the ability to deflect light."

on the other hand we have in the introduction: "The largest part of dark matter, which does not interact with electromagnetic radiation, is not only "dark" but also, by definition, utterly transparent." This seems contradictory or at least needs explaining.24.7.28.186 (talk) 04:59, 21 June 2011 (UTC)

"Dark" in this case means "not emitting light", rather than absorbing light. I've updated the introduction to clarify this. As for deflecting light, that refers to gravitational lensing - bending of light by the gravity of a large amount of dark matter - rather than scattering events. I've attempted to make that text clearer, too. --Christopher Thomas (talk) 06:38, 21 June 2011 (UTC)

Don´t emit light? Do you mean visible light? Because this article says Dark Matter is believed to emit gama rays at specific frequencies, although elusive to detection so far. So, not to be confused with black holes darkness, derived form light being pulled to its event horizon due to the enormous gravitational field. Wcris (talk) 18:20, 25 June 2011 (UTC)

matter and antimatter as a source

From quantum mechanics we know that a perfect vacuum can not exist; particles and their anti versions popup into reality all the time and annihilate each when colliding. I dont know the frequency of this, but could it be enough on a grand scale to have a mass presence ?

All particles have mass even those particles that live shortly, on the large scale of light years together they could represent a large mass

Reason why posting this question here is because one should also ask how empty is empty; if space cannt be empty would that be enough for dark energy/mass, or is more mass needed ? (in an article like this the nature of empty space sohuld also be discused) 84.107.182.108 (talk) 21:43, 4 September 2011 (UTC)

What you are referring to is called vacuum energy, which can be thought of as the energy density of virtual particles in empty space. Because vacuum energy is tied to space itself, it doesn't move or clump the way dark matter does, and so cannot be dark matter. Vacuum energy is one of the possible explanations for dark energy, but bear in mind that the idea of virtual particles appearing and disappearing doesn't necessarily reflect what's actually happening - it's a mathematical artifact of perturbation theory. So it's possible to draw misleading conclusions from that idea.

Further questions about this should go to the science reference desk. This page is for discussing specific changes to the article, not general questions. --Christopher Thomas (talk) 22:23, 4 September 2011 (UTC)

baryonic?

In the section "Baryonic and nonbaryonic dark matter" the article refers to "primordial black holes". I dont see how a black hole could be classed either as either baryonic or not baryonic - a black hole is not composed of subatomic particles . To use a self referential justification the first sentence of baryonic in wikipedia is "A baryon is a composite particle made up of three quarks". Clearly this is not the case for a black hole, going beyond that I hit the wikipedia wall of justifying a claim that is so obvious that nobody writes it down.Mtpaley (talk) 20:45, 26 September 2011 (UTC)

I reworded it and removed "baryonic" Bhny (talk) 21:43, 26 September 2011 (UTC)

In this context, "baryonic dark matter" (which is arguably a misnomer) refers to matter that does participate in electromagnetic and strong force interactions, while "non-baryonic dark matter" refers to matter that only interacts via the weak force and gravity. I'd classify black holes as acting like baryonic dark matter in this context, but in practice it's best to just follow the conventions used by references that discuss them. --Christopher Thomas (talk) 23:49, 26 September 2011 (UTC)

There seems to be some variability in whether primordial black holes are considered to be baryonic or non-baryonic dark matter, depending on the context. They are non-baryonic in that they don't participate in Big Bang nucleosynthesis, but they may be included with baryonic dark matter for experimental / observational purposes because they are constrained by weak lensing like MACHOs. A quick search turns up at least one source Hawkins 1988 that classes them as non-baryonic, and one Bergstrom 2000 that classes them as baryonic. As Christopher Thomas correctly points out, the best thing is to follow the sources. In this case, the sources are at least somewhat mixed. It's not clear to me that there's a preponderance of usage one way or the other. --Amble (talk) 17:13, 28 September 2011 (UTC)

Molecular hydrogen as dark matter

I am not a cosmologist but I have a question that does not seem to be addressed in the article. The following two paragraphs are a preface to my question.

Hydrogen is the most common element in the universe. At the average temperature of 3K any hydrogen atoms which have interacted should end up as molecular hydrogen. Given an age of 14 billion years, most of the hydrogen in existence outside of stars and areas of intense radiation should have interacted and exist in the molecular form.

I understand that molecular hydrogen is very difficult to detect due to cancelling spins and a small or non-existent dipole moment. The seemingly obvious candidate for dark matter is large quantities of molecular hydrogen. This molecular hydrogen may reside in great quantities surrounding the luminous centers of galaxies and in intergalactic space and could well account for 95% of the matter in the universe.

Question: Why do cosmologists insist that the dark matter must be some unknown exotic form of matter that has never been directly detected instead of molecular hydrogen?

It seems to me that a very good reason is necessary to propose an exotic solution when molecular hydrogen seems to fill the requirements quite well. I think that ignoring this issue leaves the article incomplete. When discussing scientific matters, it is more important to understand why scientist believe what they do, than the fact itself that most scientist believe something.

I apologize if I have missed something that should be obvious. Carl Hitchon (talk) 16:36, 29 September 2011 (UTC)

This is already covered in the article. About 1% of the universe's mass is stars. About 4% is normal matter that is not stars. Most of that is primordial hydrogen and helium (the hydrogen may be atomic or molecular depending on whether it's dense enough to combine into molecules). The "Filaments" thread on this page describes the discovery of structures made of this.

The reasons why most dark matter (23% of the mass of the universe) cannot be normal matter are also outlined in the article. The big bang nucleosynthesis only gives the correct abundances of hydrogen, deuterium, helium, and lithium if some of the matter in the universe is an exotic, non-interacting type. Non-interacting dark matter also clumps differently than normal matter: normal matter in the galaxy is concentrated in the disc, whereas the dark matter halo has a more or less spherical distribution. Molecular hydrogen would follow the distribution of normal matter (the distribution happens because clouds of normal matter can collide with each other but dark matter passes through itself).

I hope this addresses your question. Further questions should probably go to the Reference Desk, as this page is mostly for requesting changes to the article itself. --Christopher Thomas (talk) 18:20, 29 September 2011 (UTC)

Thanks for your prompt response Christopher. I suspected that the BB theory's nuclear synthesis argument leads to the need for the exotic matter instead of ordinary cold hydrogen and you have confirmed that. This line of reasoning is not obvious in the article since molecular hydrogen is not mentioned, let alone the difficulty of detecting H2, if H2 is in fact the dark matter. It leaves the impression that we must look only for zebras without first eliminating the possibility of horses.

I think it's important for the public to understand the difference between inferences made from theory versus what is known more directly by observation. For example we can easily detect CO so it's existence cannot be denied but I don't think that is possible for H2. The chain of reasoning that leads to the requirement that dark matter is non-Byronic is complex and based on theory, not direct observation (as far as I know).

Does the BBNS-predicted abundance of lithium in fact match observation? I'm not trying to start a debate. I just believe the article could be a bit more upfront about it's suggestion that most of the matter in the universe is composed of mysterious non-interacting particles that have never been detected. It is a surprising proposal. Although the article does mention BB cosmology as a basis for the belief in a relatively small amount of ordinary matter, there are difficulties with that theory.

If there are observations that prove that the abundance of H2 is insignificant, then that material should be mentioned and referenced. Under "Alternative Theories" H2 is not mentioned. Does that mean it has been ruled out by observations? Other than this I think the article is fair in pointing out some of the problems with the exotic particle theory such as the "cuspy halo problem". Thanks again. Carl Hitchon (talk) 19:18, 30 September 2011 (UTC)

Molecular hydrogen, like neutral atomic hydrogen, can be detected from its absorption lines. Astronomers have been mapping the interstellar (and intergalactic) medium for quite some time, so the abundance is reasonably well known. Neither the big bang nucleosynthesis nor the galaxy rotation curve observations can be explained by normal matter, per above, and we already have direct observation of concentrations of non-interacting matter through gravitational lensing surveys.

The article as-written does not seem to mention BBNS arguments. This is very odd, as it's an important piece of evidence. It's described at Big Bang nucleosynthesis#Deuterium. If I have time, I'll add a sub-heading about it to the "observational evidence" section. Any of the other lurkers here are welcome to add it instead, as I'm rather busy at the moment. --Christopher Thomas (talk) 22:14, 30 September 2011 (UTC)

Can someone supply references which demonstrate that the abundance of H2 (particularly in halos) is reasonably well known through absorption line detection? Please exclude data derived from the CO proxy since it is based on complex assumptions. Carl Hitchon (talk) 15:44, 1 October 2011 (UTC)

You can check through the references at interstellar medium if you like, but the purpose of this page is to discuss improvements to the article, not to answer questions or to address your own conjectures about what dark matter is (per the banner at the top of this page). Questions normally go to the Reference Desk. --Christopher Thomas (talk) 18:48, 1 October 2011 (UTC)

The intro is way too long and the Composition section is way too short

According to WP:LEAD#Length we shouldn't have introductions over four paragraphs, and three should do fine for an article of this size. Why is the very brief Composition section all about WIMPs, sourced to a preprint, and doesn't mention the leading MACHO theories? Where is the mention that LHC has provided zero evidence of supersymmetry or WIMPs after almost two years now? Dualus (talk) 22:28, 24 October 2011 (UTC)

I created a new "Overview" section and moved most of the intro there. Bhny (talk) 16:53, 27 October 2011 (UTC)

(almost) incompatible

"though many scientists remain skeptical since negative results of other experiments are (almost) incompatible with the DAMA results if dark matter consists of neutralinos"

Someone want to explain just what the heck "almost incompatible" means? It's almost wrong (which means it's still right). Almost incompatible would still be compatible. Almost going fast means it's still going slow. Almost won means you still lost. So why is "almost incompatible" used as a reason to shoot something down? Sounds like the statement is almost right. — Preceding unsigned comment added by 220.248.48.66 (talk) 03:50, 29 October 2011 (UTC)

Contribution of Dark Matter to the mass of the Universe

In the first paragraph: "Dark matter is believed to constitute 83% of the matter in the universe.[2]"

This should read: "Dark matter is believed to constitute 23% of the matter in the universe.[2]" 130.88.173.52 (talk) 17:28, 21 November 2011 (UTC)

It's 23% of the mass, but 83% of the matter. Dark energy has mass, but does not count as matter. --Christopher Thomas (talk) 23:17, 21 November 2011 (UTC)

Matter not implicitly being equivalent to mass is a meaning that is sort of context specific to dark matter cosmology; in most instances when speaking of classical physics, I would consider mass and matter being equivalent. Perhaps we could end this little edit war some of you edit the paragraph to change terminology to be a bit more clear what everyone is talking about, such as "23% of the mass-energy"? - Sangrolu (talk) 13:28, 7 December 2011 (UTC)

I added "23% of the mass-energy", may as well put both since people seemed confused about the difference Bhny (talk) 15:37, 7 December 2011 (UTC)

Removing "Composition" section?

I suggest removing the "Composition" section. I don't agree that dark matter behaves as a perfect fluid; there is strong evidence from X-ray and lensing observations of clusters that dark matter does not behave as a fluid (http://adsabs.harvard.edu/abs/2004ApJ...606..819M , http://adsabs.harvard.edu/abs/2011ARA%26A..49..409A ). The title "Composition" is somewhat misleading, in my opinion, as "Composition" would imply, to me, knowledge of the particle responsible. I think that the useful information in this section can be incorporated into other sections. Craigheinke (talk) 22:33, 26 December 2011 (UTC)

I agree that the section is not terribly useful as-is; by all means fold its content in elsewhere. My understanding is that dark matter's self-interaction cross-section is still very low compared to normal matter, which is why a perfect fluid is sometimes used as a model for it (per the citation in that section). Your second citation provides a more realistic model, and would be a useful addition to wherever the section's content ends up. --Christopher Thomas (talk) 01:19, 27 December 2011 (UTC)

Ok, great. I think it might be best to fold the discussion of evidence against dark matter's self-interaction into the observational part, under galaxy clusters (where I see some is already), so I'll give that a try. I'm also thinking of moving the DAMA discussion under "Cold dark matter" down under "Detection". I also see that this page is labeled too technical. I'm not a very experienced Wikipedia editor, so don't know how that's defined exactly, but I'll see if I can make some headway on decreasing the technicality of the language. Craigheinke (talk) 18:38, 27 December 2011 (UTC)

There's been debate a few times in the past about the amount of technical language that's appropriate (here and elsewhere; there was a thread at WT:PHYS about it a month or so ago). It might be best to do this as two separate changes, to avoid entangling these topics. --Christopher Thomas (talk) 21:04, 27 December 2011 (UTC)

Thanks for adding all of the references, by the way; that was much-needed, and should reduce the amount of "fringe creep" in the article. --Christopher Thomas (talk) 21:24, 27 December 2011 (UTC)

Ok; it'll take me some time to get around to toning down the technical language. I changed the reference in Composition to a more recent, slightly more mainstream one referring to perfect fluid possibilities for dark matter, rewrote the section and put it into the Lensing section; see what you think. Craigheinke (talk) 01:08, 28 December 2011 (UTC)

The changes look fine to me; well done!

Regarding making the article "less technical", my main concern is that this often results in an article that's been "dumbed down" (less information, and descriptions that are often incorrect or misleading). By all means use your judgement regarding where to go with this; I only ask that you discuss anything you think might be problematic on the talk page first (in a new thread). If you think that you can improve readability without sacrificing correctness or losing anything important, by all means go for it.

Also, if you haven't already, please do check out the physics and astronomy wikiprojects (WP:PHYS, WP:AST, and WP:ASTRO for "astronomical objects"). The talk pages of those projects are used for coordinating editing of many astronomy and physics related articles, and you'd most definitely be welcomed there (editors who take the time to clean up sourcing are in short supply). --Christopher Thomas (talk) 02:12, 28 December 2011 (UTC)

Alternative theory on the composition of dark matter

Since I worked out this theory myself I could not add it to the main page

Another theory states that dark matter could be normal matter stripped of all its electrons due to interaction with positrons. This would mean that dark matter would not be able to interact with photons. This theory states that dark matter could be 'cold plasma', similar to normal plasma in that it has lost its electrons but dissimilar in the way it has lost its electrons and that normal plasma is energised with radiation and constant re-interaction with electrons. This theory further states that because dark matter has no electrons it cannot form bonds and exists as individual atoms.

Date 16/5/11 —Preceding unsigned comment added by Kishanparekh (talk • contribs) 13:27, 17 May 2011 (UTC)

This violates OR as noted in the talkheader. The place for this is in your userspace. There's no dearth of conjectures about the subject. That the observed universe is inside something and that the "dark matter" could be gravitation or other forces from that containing universe, although sourcable, isn't in either. Also it's false that matter stripped of electrons wouldn't interact with photons. Threads like this one are just exceptions to not touching talk space edits of others. Lycurgus (talk) 20:00, 18 May 2011 (UTC)

Sorry about that but I am just a 'slightly' over-average inteligence Fourteen year old, and I did watch a documentary about the origins of the universe wich said that the early universe had such high temperatures that atoms and electrons hadn't joined so the universe was a dark place because of that, I also read about plasma and about electrons forming bonds in atoms, so I used my common sense to put two and two together and got this theory. but I have put a copy on my userspace Kishanparekh (talk) 18:49, 22 May 2011 (UTC)

Normal matter stripped of electrons would be protons+neutrons which would strongly interact with photons. There is also the additional complication of where did these positrons come from and why positrons alone not positrons+protons. Mtpaley (talk) 01:27, 3 November 2011 (UTC)

It is entirely mass, right? What do photons and gravitons not have? Mass. It is a balance particle to photons and gravitons. It makes up for the mass they do not have.--74.79.248.160 (talk) 20:35, 23 January 2012 (UTC)

Cold / Warm / Hot dark matter - technical errors

The distinction between cold/warm/hot dark matter in the article is significantly flawed. It is not the velocities today which are relevant, but the "free streaming length" i.e. how far the particles could randomly move in the early universe.

In essence, collisionless particles move at speed near c while their total energies are much greater than the rest mass; particle momenta decrease as the inverse of the scale factor, and once the total energy becomes comparable to the rest mass, the velocities "redshift away" with expansion.

Therefore, the distance that particles can free-stream is approximately given by the horizon length back when the particles become non-relativistic, and any initial perturbations (e.g. from inflation) get "washed out" on a scale smaller than that (comoving) length.

This leads to the terms cold/warm/hot dark matter , depending on whether the free-streaming length is much smaller, similar, or much larger than a fluctuation which turned into a galaxy-scale object.

Hot dark matter (alone) is now excluded since it predicts supercluster-sized objects collapsing first and then (somehow) fragmenting into galaxies, which is clearly contrary to observation. Cold dark matter had "negligible" free-streaming length, but it acquires velocities of few hundred km/sec today as it falls into galaxy and cluster potential wells. Warm dark matter is of some interest since it may solve some problems relating to dwarf galaxies in CDM. 86.160.48.128 (talk) 23:47, 4 February 2012 (UTC) Will S.

Failed source verification on the acceptance of WIMPs

The following clause appeared in the "Cold dark matter" section. I moved it here because there is nothing in either of the sources cited, neither of which are peer reviewed let alone secondary, which remotely supports it:

in particular the most commonly accepted theory today is that dark matter appears to be composed solely of weakly interacting massive particles (WIMPs).(ref name="Halzen,Klein">F Halzen, S Klein, "The world’s biggest IceCube is ready for action," in CERN Courier: International Journal of High-Energy Physics. Feb 23, 2011, Vol. 51, Issue 1. IOP Publishing Limited, Bristol, UK.</ref>(ref name="Kaufmann">L Kaufmann, A Rubbia, The ArDM project: a Dark Matter Direct Detection Experiment based on Liquid Argon Abstract and Introduction, page 1.</ref>

67.6.170.33 (talk) 17:07, 5 February 2012 (UTC)

intermediate mass black holes

As I said in my edit comment, I think the idea that IMBHs can be dark matter is a fringe idea with very few adherents. By wiki's due weight policy, it shouldn't be mentioned, or at best mentioned just in passing. Waleswatcher (talk) 04:12, 6 February 2012 (UTC)

Why do you think that? Are there any sources which agree with your opinion about this? How do you measure the number of adherents? I replaced a conference proceeding supporting the idea with (Frampton and Ludwick (2011) "Number and Entropy of Halo Black Holes" Astropart. Phys. 34:617-9) which is peer reviewed in a prestigious journal. There are a large variety of candidate theories for dark matter and black holes are certainly the oldest. Do you have any specific reasons why they have "major problems" as you stated at Talk:Cold dark matter? 67.6.170.33 (talk) 07:49, 6 February 2012 (UTC)

I'll re-post my comment from our discussion on the cold dark matter tak page.

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

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

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

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

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

Find a reference text, or a list of prominent adherents, and you'll have an argument for inclusion. Waleswatcher (talk) 14:29, 6 February 2012 (UTC)

I've now checked two sources - a 2010 paper on black holes as dark matter, that says that they are ruled out over a huge range of masses, and one 2012 dark matter review, that says that particles are the only really plausible DM candidate (and also that black holes would require "funky physics" even to exist in the correct abundance). I've added both references. Waleswatcher (talk) 15:04, 6 February 2012 (UTC)

Thanks very much for those references. The 2012 review is a lecture note which has not been peer reviewed, and it cites the Carr et al. (2010) Phys. Rev. D paper in support of the statement you quote, which reads in full, "The only major non-particle candidate for dark matter is the primordial black hole, which would have collapsed directly from highly overdense regions of the early Universe, the existence of which requires funky physics." However, Frampton and Ludwick state that such black holes on the order of 100,000 solar masses, or about 2 × 10³⁸ grams, and Carr et al's conclusions in Figure 9 on page 33 show that mass region as excluded by the orbits of wide binaries (WB) which the subsequently peer reviewed Frampton and Ludwick (2011) paper says are consistent with such black holes. There have been a number of conflicting interpretations of wide binary orbits in the past decade, with substantial corrections of earlier results made only recently. Do you see, therefore, why intermediate mass black holes are the only viable dark matter theory with actual observational evidence? 67.6.175.184 (talk) 03:53, 7 February 2012 (UTC)

Well, we now have the author of an overall review of dark matter stating that new particles are the only serious candidates, and a very recent paper that reviews the evidence on black holes as dark matter candidates and says that intermediate mass black holes are excluded. On the other side, there are only papers by Frampton and collaborators. I think that establishes pretty firmly what I said - that IMBHs as dark matter are a fringe theory accepted by very few experts. As such, by wiki's policy of due weight they deserve at most a brief mention. (By the way, the same applies to "holeums".) Waleswatcher (talk) 13:32, 7 February 2012 (UTC)

Do you understand what I wrote about the wide binaries? Do you understand that the more recent peer reviewed source is in conflict with the one you found, saying that the orbits of wide binaries are consistent with IMBHs? Why do you think that IMBHs are not serious in the non-peer reviewed lecture notes review? The words from the passage you quoted are "the only major non-particle candidate." As for your question about the abundance of proponents, there are many and they are easy to find. This NASA report about a group at Stanford is already in the article. Here's another recent peer reviewed paper which says dark matter of any kind would accrete into intermediate mass black holes. Here's another peer reviewed paper which says the same thing. Here's a peer reviewed review of all candidates which calls IMBHs "promising" and seems to rule out everything else. Do you have any source saying, or any actual reason to believe that black holes as dark matter is some kind of a fringe theory? 67.6.175.184 (talk) 17:50, 7 February 2012 (UTC)

I've already given you two such sources. The existence of a peer-reviewed paper by a single researcher or group does not establish that any significant number of experts believe this is a serious option for dark matter, and the (more recent) direct quote of an expert in the field that says it's not a serious candidate proves otherwise. The papers you reference do not support what you say - just the opposite. For example, this paper http://arxiv.org/pdf/1003.3466v3.pdf says in its abstract that primordial black holes cannot form any significant fraction of dark matter (less than one part in 1,000). The paper http://arxiv.org/pdf/0711.4996v2.pdf says nothing about IMBHs as a dark matter candidate, it says that PARTICLE dark matter might be detectable from its annihilation near such holes.

Your own references disprove your assertions. I'm trying to take your comments as in good faith, but it's getting more difficult. The burden of proof here is entirely on you - find a reference to a current textbook that says that IMBHs are a DM candidate on the same level as WIMPs, for example. Waleswatcher (talk) 20:05, 7 February 2012 (UTC)

It does not seem that you are correctly representing those sources. The first, "Primordial Black Holes As Dark Matter: Almost All Or Almost Nothing," says that it eliminates the possibility, "for a vast range in PBH mass," but 100,000 solar masses is not part of that vast range, shown in their conclusions on Figure 2, page 4. But that paper does say -- as its title makes quite plain -- that if almost any dark matter is intermediate mass black holes, that almost all of it has to be. Perhaps you should consider the second paper's statements in light of that conclusion? And again, there is no shortage of confirmed empirical evidence of IMBHs while there is zero empirical evidence for WIMPs, other than one solitary lab's unconfirmed claims of a less than 3-sigma signal. If this recent peer reviewed WP:SECONDARY literature review doesn't convince you, I don't know what will: "The overall conclusion of the paper is that primordial black holes should be seen alongside elementary particles as viable dark matter candidates." (Preprint.) There are plenty more where those came from. Here's a peer reviewed paper published just this month: "results of experiment by the MACHO collaboration group have confirmed the presence of MACHOs in the galactic halo ... the 'most plausible' candidates for such MACHOs are being identified as primordial black holes ... It is concluded that the majority of the CDM mass of the galactic halo can be accounted for by MACHOs by using a reanalysis of the data, and by applying advances in black hole gravitational physics." 67.6.175.184 (talk) 22:16, 7 February 2012 (UTC)

"The first, "Primordial Black Holes As Dark Matter: Almost All Or Almost Nothing," says that it eliminates the possibility, "for a vast range in PBH mass," but 100,000 solar masses is not part of that vast range, shown in their conclusions on Figure 2, page 4." That's flat-out false. Figure 2 on page 4 of that paper DOES include 100,000 solar masses, that's the tick one to the left of the tick marked "6" on the horizontal axis, and it shows four differnt constraints at that mass, the tightest of which excludes black holes being more than 1 part in 100,000,000 of the dark matter. Not only that, the paper is written with the assumption that WIMPs are most of dark matter, it's about WIMP annihilation.

This conversation is over. You're either incapable of understanding this literature or deliberately distorting it. Either way, you've failed completely to establish any notability of this theory - in fact you've done exactly the opposite. Waleswatcher (talk) 05:36, 8 February 2012 (UTC)

Well! I suppose I should mention that the black-lined constraints were from earlier papers which have been addressed by the subsequent peer reviewed and WP:SECONDARY peer reviewed sources which I cited and quoted but you refused to address. The only constraints put forth in that paper are in the blue lines in that figure. Since you have refused to address the peer reviewed WP:SECONDARY literature review and more recent peer reviewed sources which I quoted and which contradict your assertions in plain language, I will be replacing the material you deleted with the addition of these newer, more reliable sources. 67.6.175.184 (talk) 07:47, 8 February 2012 (UTC)

Replacing the material I removed will be in direct violation of wikis due weight policy and will be reverted. Not one of the sources you've located say what you say they say. For example, the paper you asserted allowed black holes with mass 100,000 solar masses to be dark matter (a) was considering a scenario in which dark matter is WIMPs, and (2) showed a plot with four different constraints on 100,000 solar mass BHs, all of which restricted 100,000 solar mass BHs to be less than 1/10,000 of the dark matter.

More importantly, all your references - and those are your references, ones that you dug up to try to support your case - make very clear that black holes as dark matter is a possibility regarded as likely by few if any researchers. As such, that scenario should be accorded a significantly smaller amount of space in the article than WIMPs. The article can certainly have a section explaining why that is the case (along with all the other would-be possibilities) - that would be very good, actually. Waleswatcher (talk) 12:50, 8 February 2012 (UTC)

So, let's see whether we can agree on text to replace, but first I would like you to respond, please, to the quotations from [6] ("The overall conclusion of the paper is that primordial black holes should be seen alongside elementary particles as viable dark matter candidates") and [7] ("results of experiment by the MACHO collaboration group have confirmed the presence of MACHOs in the galactic halo ... the 'most plausible' candidates for such MACHOs are being identified as primordial black holes ... It is concluded that the majority of the CDM mass of the galactic halo can be accounted for by MACHOs by using a reanalysis of the data, and by applying advances in black hole gravitational physics") and whether you agree with the fact that the first of those sources is a peer reviewed literature review, as the second of those two sources refers to it, and is therefore a WP:SECONDARY peer reviewed source and accordingly the most authoritative of all possible sources per Wikipedia's reliable source criteria. Furthermore, if you believe that the authors of those sources and the sources they cite do not satisfy your request to "name prominent adherents" above, then please indicate how many additional prominent adherents you will require to be satisfied. Finally, are you willing to admit that all proponents of particle dark matter readily admit that they cannot explain the distribution of mass in the centers of galactic halos and dwarf galaxies, while black hole dark mater does not present such issues? 67.6.175.184 (talk) 19:50, 8 February 2012 (UTC)

The first reference is about stellar mass black holes, which differ in mass from the holes you mentioned in your last comment by a factor of 100,000. That has nothing to do with intermediate mass black holes, or with the material or references that was on this page, and it again undermines your position (unless you've abandoned the position that IMBHs can be dark matter). The second reference is published in a dubious journal I've never heard of that isn't specialized in astrophysics by an author with a non-academic address. Again, it is about stellar mass black holes, not intermediate black holes. Finally, it uses a theory of his own invention he calls "DNAg", which is some alternate theory to general relativity. As such, it's a fringe paper and utterly fails the notability test.

How many of the references you provided have I looked at, only to find that they say the opposite of what you assert they say? I'm losing my patience very rapidly. Waleswatcher (talk) 01:53, 9 February 2012 (UTC)

It seems to me we are making progress, as long as we don't get too hung up on the difference between "different by a factor of 100,000" and "the opposite." Do you agree that there are no particle dark matter hypotheses that can explain the relative lack of mass in the center of galactic halos and in dwarf galaxies? [8] may help you evaluate the journal you had questions about, and Worsley seems to be affiliated with Kings College London's Postgraduate Department. Presumably we should be deferring to a journal's editors and reviewers on questions of what is and is not fringe? You might have a look at WP:NNC on the question of whether notability has any bearing on what we include. I don't want to wear any more on your patience by proposing anything to include without giving you the opportunity to go first. How would you summarize the subset of the sources we have been discussing of which you approve in a sentence or three? 67.6.175.184 (talk) 07:02, 9 February 2012 (UTC)

So I see you have in fact abandoned your position entirely. Rather than assert that IMBHs are a serious dark matter candidate, you now want to assert that stellar mass BHs are. Is that correct?

As for stellar mass black holes, by due weight they cannot have a "line or three" unless WIMPs have much more. At the moment, both black holes and MACHOs are already mentioned in passing and should remain that way unless we extend that whole section. So I propose we delete the references to IMBHs that is in there now (since every single source you yourself provided either says they're excluded and doesn't mention them), and replace them with perhaps your first reference, followed by a phrase that indicates that most researchers believe BHs of any mass are excluded as DM candidate and a link to one of several references.

Ideally, there could be a section on cold dark matter candidates that outlines what properties they must have, and segues into the lensing and other evidence against MACHOs, with black holes listed as one of several MACHO candidates, that ends up explaining why almost everyone believes in WIMPs. Waleswatcher (talk) 12:41, 9 February 2012 (UTC)

No, I note that Frampton and Ludwick's (2011) paper on IMBH is cited approvingly in M.R.S. Hawkins' (2011) literature review. Frampton is also cited approvingly in, e.g., [9] and [10], so IMBHs are hardly fringe, and again, dozens of them have been confirmed in the last couple years. So I could not support such a deletion. I asked you about additional material to include. Do you intend to propose any? Do you intend to answer my question about whether there are any particle dark matter theories which can explain the mass density at galactic halo centers or in dwarf galaxies? 67.6.175.184 (talk) 18:34, 9 February 2012 (UTC)

The Hawkin's paper is about stellar mass BHs. The fact that IMBHs exist is not in dispute, what is in dispute is whether they can compose any significant fraction of DM. The answer, according you every reference thus far discussed, is "no". To reference the Frampton papers would by due weight require referencing just about every other fringe theory of dark matter, and then giving due space to the (literally) thousands of papers by hundreds or thousands of authors on more conventional models. I've said several times what I think should be included - a list of the properties DM needs to have, along with a list of candidates and how they fare. Black holes should be mentioned in that list, along with appropriately sourced statements showing that they are regarded as ruled out by the vast majority of experts. I don't see how IMBHs can be mentioned at all unless the list is very long and detailed, since there appears to be zero support for that idea outside of that one paper. Waleswatcher (talk) 19:38, 9 February 2012 (UTC)

Oh - and no, I'm not going to discuss WIMP physics with you here. IT's not the right place, it's not necessary, and it wouldn't be fruitful for either of us. Waleswatcher (talk) 19:40, 9 February 2012 (UTC)

You repeatedly contradict yourself. We've been discussing a paper which states in its title that if black holes comprise almost any dark matter, they comprise almost all of it. You say that "every reference thus far discussed" doesn't support that IMBHs are a substantial fraction of dark matter, and in the next breath you refer to Frampton and the several papers which cite him approvingly. And what reliable source says that black holes "are regarded as ruled out by the vast majority of experts"? You have had ample opportunity to provide such a source and have not done so.

And of course this is the place to discuss WIMP physics, as much as it's the place to discuss the physics of any dark matter candidate we are considering including in the article. But if you are so anxious to eliminate all mentions of black holes as dark matter, I can certainly see why you are unwilling to answer the questions about the fact that WIMPs can't even begin to explain the observations of mass distribution in galactic halo centers and dwarf galaxies. However, I fully agree with you that we need a list of candidates and how they fare. I would take it a step further and suggest what we really need is a table. 67.6.175.184 (talk) 21:36, 9 February 2012 (UTC)

Make up your mind. Are you talking about BHs with mass 100,000 times that of the sun, or are you talking about BHs with the mass of about the sun? Those are two totally different possibilities. Every single paper you listed discussed solar mass holes (for good reason), but even those are regarded as ruled out by the vast majority of experts, and the references I provided clearly show. The "approving reference" Hawkins gives is to a DIFFERENT Frampton paper (literally every single assertion of yours that I've checked has turned out to be false). That paper tries to make the case that some BH masses can evade limits, with 100,000 the upper limit even for them. Hawkins references it simply in the context of a theory that might be able to produce BHs in the necessary abundances, his paper is about STELLAR mass black holes.

As for the table or list, it should be based directly on a published review by a mainstream expert in the field. Waleswatcher (talk) 23:07, 9 February 2012 (UTC)

Indeed, Hawkins cites Frampton, Kawasakia, Takahashia and Yanagidaa (2010) "Primordial black holes as all dark matter" which suggests that micro black holes through IMBHs are all possibilities, and that the Planck satellite can test their mass, so I will not be taking an absolute position on the question, as you seem to have, until that data is in. With luck we will soon know for sure. Thank you for pointing out that Frampton et al (2010) was a different such paper. 67.6.175.184 (talk) 23:32, 9 February 2012 (UTC)