Talk:Dark matter

Dark Matter is a new current event!

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

Ring of Dark Matter

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

Another question about dark matter

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

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

If gravity causes baryonic matter to get clumpy and ultimately condense into stars etc, why doesn't the same happen to dark matter? Qemist (talk) 12:37, 27 July 2008 (UTC)

How much gravity does dark matter produce?

With relation to galaxies, do we have any idea how much gravity is missing ( associated with dark matter ) in an average galaxy? Can this be worked into a linear or volume density? Like 1 light year ^ 2 produces x amount of gravity on average. --Tommac2

dark antimatter

the opposite of matter is antimatter...
but what is the opposite of dark matter? dark animatter?
or biuld the thee a triplett?

--hanmac —Preceding unsigned comment added by 89.61.67.218 (talk) 18:40, 11 April 2008 (UTC)

Not all matter has antimatter in the sense that they can enialate each other’s. When a particle is created, it is not created alone, but in a pair with another particle. That second particle is the 'anti-matter'. A proton and an anti-proton will enialate, but a photon which is its own antiparticle will not. It is possible that dark matter is made up by equal parts of some particles and their antiparticles coexisiting side by side. On the other hand, the big-bang left a universe with more normal matter than antimatter, so it is fully possible that this is the case for the dark matter as well. —Preceding unsigned comment added by 83.254.67.136 (talk) 17:39, 15 June 2008 (UTC)

It's one thing to understand all the complexities of this type of thing. It's quite another to be able to spell "annihilate" :-) —Preceding unsigned comment added by 79.74.73.242 (talk) 19:30, 26 June 2008 (UTC)

IANA scientist, so.......

Because this is out of my field, I simply point out this. Maybe worth some sort of development/mention in this article? Kaiwhakahaere (talk) 23:10, 24 April 2008 (UTC)

IANAS either, but it's already mentioned. Dark matter#Detection of dark matter says "In April 2008, researchers announced at a physics conference in Venice that dark matter had been detected at the Gran Sasso laboratory.[19]", linking the same article. Art LaPella (talk) 23:53, 24 April 2008 (UTC)

Aaaaarrrrgggghhhhh. Ok, it has a mention, but how about a development (like a little bit more info)? Or is it not as earth shattering as I think? Cheers. Kaiwhakahaere (talk) 00:13, 25 April 2008 (UTC)

It is actually the same DAMA/NaI team. They have done experiments with the successor of DAMA/NaI known as the DAMA/LIBRA detector and confirmed the result they found with DAMA/LIBRA. I agree that we should rewrite the paragraph about detection of dark mater. We should say that DAMA LIBRA has now confirmed the DAMA signal. Also the DAMA/NaI page should be updated, the red link to DAMA LiBRA can now be filled in.

The relevant preprints we should refer to are: http://arxiv.org/abs/0804.2741 and http://arxiv.org/abs/0804.2738 Count Iblis (talk) 00:19, 25 April 2008 (UTC)

Cooperstock and Tieu

The work of Cooperstock and Tieu, several papers that have been peer reviewed and published in reputable journals, and which amounts to a major ongoing research program with considerable interest in the community of relativists, should be mentioned in the "Alternatives" section. I added yesterday a short section to this effect, sticking only to the facts - a short description of the import of their work, its origin in general relativity, and its reception by the community. This was immediately deleted. It is a valid alternative explanation, open to debate, but real work by real physicsts, and should not be suppressed. Antimatter33 (talk) 14:26, 16 May 2008 (UTC)

I'm not taking sides, but you seem unaware of previous debate. Search Talk:Dark matter/Archive 2 for the word "Cooperstock" to find several discussions. Art LaPella (talk) 21:02, 16 May 2008 (UTC)

This argument against their work (abs z and all that) has been specifically addressed by C&T and shown to be fallacious. A similar argument in electrostatics would be equally wrong. Their work remains of fundamental importance and more or less demands to be mentioned! The criticism was launched by a Polish grad student. Cooperstock has been doing GR for decades and has a raft of publications. Who do you trust?Antimatter33 (talk) 18:56, 23 May 2008 (UTC)

That wouldn't proof C&T are right even if it were the only article saying they are wrong - it isn't. And even their refutation has been dealt with [1].

For that matter, I have not been able to find that the original paper has actually been published in The Astrophysical Journal as originally said. Lars T. (talk) 21:16, 23 May 2008 (UTC)

This paper is so off base it hardly needs refuting (again the example of the similar problem in electrostatics can be invoked without implying an infinite charge distribution). Apparently there is a large confusion among researchers about what is a potential and what is a field, because they keep making elementary blunders. In any case C&T have answered this "criticism" as well, long ago now. And again I would point out that Menzies has nowhere near the stature of Cooperstock as a researcher, so it is somewhat embarrassing to see him make a fool of himself with such a completely wrong-headed "argument" such as this one.

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=find+author+cooperstock

Antimatter33 (talk) 18:58, 3 June 2008 (UTC)

So in which issue of the Astrophysical Journal was this paper published? It says it was "Submitted to Astrophys.J.", but not that it was published - and I couldn't find it at http://www.journals.uchicago.edu/loi/apj either. Why do you think it wasn't published? Is there a vast conspiracy going on? Lars T. (talk) 23:47, 3 June 2008 (UTC)

I know nothing about this particular series of papers, but an ADS search for these two authors yields only arXiv preprints—nothing published in a peer reviewed journal. That makes them appear like fringe theories that do not belong on Wikipedia. ASHill (talk | contribs) 23:55, 3 June 2008 (UTC)

Just click the link to SPIRES provided so kindly by me, above. The latest paper will also will appear in Mod.Phys.Let.A. C&T have a large correspondence with other relativists, myself included, and interest in their work is very keen. That it gets banned from this public page is outrageous. This is not a "fringe idea" - it is a straight application of ordinary GR.Antimatter33 (talk) 07:28, 4 June 2008 (UTC)

Not so dark?

Should the conclusions drawn from Danforth/Shull (05/20/08 "The Low-z Intergalactic Medium. III. H i and Metal Absorbers at z < 0.4" http://www.journals.uchicago.edu/doi/abs/10.1086/587127) stating that they have detected up to ~40% of "missing" Baryonic matter be included somewhere in this article? (Basically this supports the hypothesis that DM is made up of baryons that we have not observed) --Hyperion2010 (talk) 00:36, 21 May 2008 (UTC)

That article is about the missing ordinary baryonic matter, not dark matter. Of the matter in ordinary baryonic form, mainly hydrogen, that we know is out there, a lot is very hard to detect. Count Iblis (talk) 00:45, 21 May 2008 (UTC)

LSP?

In the introductory section several candidates for the possible dark matter component are put forward, but notably no mention is made of the lightest super partner (LSP). This candidate is certainly one of the likely favourites amongst scientists and should be mentioned accordingly. I would edit the article but I've just returned home from my 8th exam this month and am too tired to think about supersymmetry in any detail right now! Unfortunately the mass spectrum of SUSY particles does not necessarily have to resemble that of ordinary baryonic matter so there is no concensus as to what particle the LSP actually is, although, as I say, it is certainly a favoured candidate for the dark matter. Dazza79 (talk) 23:55, 29 May 2008 (UTC)

Is it silly to think...

...that as the universe expands large amounts of mass could slowly begin to move in behaviour similar to wavelengths, but on a macro scale? And as those paths reach movement proportionate to light wavelength ranges the total rest mass of a system could begin to slowly lower? If some of our methods of measurement use mass relationships, a disparity may start to occur between parts of the universe moving at different wavelength-type paths and we may not see why because we would be a part of that disparity. --RedFeather1975 (talk) 05:32, 25 June 2008 (UTC)

Some ideas are so ill-formed that they are "not even wrong". See Mu. So to answer your question: yes, it is "silly". WAS 4.250 (talk) 17:32, 25 June 2008 (UTC)

I'm not entirely sure why I said that. D: I think at the time I was so tired and thinking that natural tendencies try to reach phase transitions that follow the path of least resistance. And I may have misread somewhere that the outer systems in spiral galaxies are accelerating faster than they should be. I don't know. I need sleep! :( --RedFeather1975 (talk) 10:10, 26 June 2008 (UTC)

I noticed too that I was using wavelengths in that post. I just don't know what the right words are to describe what I must have been thinking. --RedFeather1975 (talk) 11:11, 26 June 2008 (UTC)

The rate of rotation of the parts of our galaxy do not match what gravity theory predicts if there is no dark matter, but can match if there is dark matter.

Out of Control is an excellent online book (click the links on that page). Read it and you will find out why you "said that". There is no "you". Or rather, you are a "society of minds" as Marvin Minsky puts it. WAS 4.250 (talk) 15:55, 26 June 2008 (UTC)

Ohhh. That book looks interesting. Thanks for linking it. :D --RedFeather1975 (talk) 04:43, 27 June 2008 (UTC)

Could this be the answer?

I'm no astrophysicist or anything but please bare with me. We know that Neutrinos seem to be in a state that one could almost say they were phased partially out of our reality... I mean being that they travel at the speed of light and billions of billions of them pass thru us each second yet they hardly ever react with any matter.

Could Dark matter itself be a form of matter but on the atomic scale part of it be sort of phased out of our reality....in a sort of not quite totally in this reality but not totally out of it either. But at the same time, still a whole of its own and still able to react with other matter of our universe?

Think of those 2 dimensional graphs u see that represent space and how all matter we know of bends that space... What if there were an additional graph that blanketed the space we know of (overlapping our whole universe) and could react with it, but was in itself in a state of being that allowed it to sort of stay fixed between matter and anti-matter?

I know, you think i'm totally insane right? Well, think of it this way. We have 0 and 1 don't we... 0 being the neutral and 1 being a positive. But, we also have -1... Anti-matter would be -1, being only theoretically possible (and possibly catastrophic if ever exposed to matter) to us on the matter side of the universe... but dark matter being the 0 would be in a fixed place between the two... Never being quite a total part of either, yet able to react with both on some things like say gravity?

I know i could be just blowing smoke, but i hope this helps to further the discussion and maybe it'll at least eliminate 1 birdbrained idea from the mix.

PS: If someone wins the Nobel using my idea i better get a little recognition. :) Xeroz (talk) 17:20, 27 June 2008 (UTC)

Dark matter is known to interact with us gravitationally so if there was any concentrated form of it, say a dark matter planet in our solar system, we would know due to its gravity effects, but if there were dark matter aliens walking among us we would not. On the other hand, we know dark matter does not interact at all with our kind of matter through electromagnetic forces, so they could not "walk" with us as they would pass right through the Earth without even noticing it. All in all, it looks like dark matter, is something like neutrinos, that is a ghost particle that just does not interact with anything very much except for gravity, so the "real world" is the world we can see with most of its mass in a form we can not see (except though its gravitational effects) in the form of individual particles that do not form any kind of structure - they remain particles gravitationally trapped in orbits around galaxy centers but farther from the center than regular matter which slows when it collides. Dark matter does not collide - basically it just goes right through both dark matter and regular matter like it wasn't there. Since it can't even interact with itself enough to collide, it can't interact enough to form structures like atoms or molecules. WAS 4.250 (talk) 20:15, 27 June 2008 (UTC)

Maybe it's just a force which developed through enough interactions and permutations of existing forces layering over one another. And it persists because it's circumventing particular factors which would interfere with it's natural evolution. Circumvention is potent in potential for preservation. But it can require a complex course of processes to build up to such a state. I just wonder if understanding it, might lie in thinking big over thinking small. --RedFeather1975 (talk) 00:15, 29 June 2008 (UTC)

Understanding it lies in experiments and observations and equations that make predictions that can be tested. WAS 4.250 (talk) 18:44, 29 June 2008 (UTC)

If the observed phenomenon is the result of a cosmic scale system of systems behaviour, is there an avenue of experimentation we can explore at this time? I am worried there isn't as of yet, and we will have to be very patient and prudent in our search for answers. --RedFeather1975 (talk) 01:43, 30 June 2008 (UTC)

We are limited to mathematical modeling and observing whether or not predicted observations are in fact observed for emergent phenomenon on a cosmic scale. WAS 4.250 (talk) 13:55, 30 June 2008 (UTC)

Moved material relating to bullet cluster

I know very little about this subject, but it was clear that the material relating to the bullet cluster was out of place in the lead section on observational evidence. It's placement made the article less readable, and appeared to be a tangent from the question "how do we know that dark matter exists?" I have therefore relocated it to a separate section further down. Someone more familiar with the subject may find a better way to integrate it into the article without disrupting the logical flow.zadignose (talk) 09:04, 30 June 2008 (UTC)

Hey WAS, nice sloppy and lazy revert. Don't revert over two edits without bothering to compare them, and don't revert at all as a short cut to fixing the problem. If you think the bullet cluster needs to be mentioned in the lead of the section, then REWRITE IT to show how it's relevant to the question "how do we know that dark matter exists?" The description of the bullet cluster PRESUMES DARK MATTER EXISTS, and does not explain in what way it serves as EVIDENCE OF THE EXISTENCE OF DARK MATTER. That's why I asked, in clear language, for someone to "find a better way to integrate it into the article without disrupting the logical flow." The revert is NOT a solution. The fact that the earlier edit was also reverted, though it was a clear improvement in presentation without removing or relocating any substance from the article, highlights what's wrong with simply clicking "revert" when you disagree with an edit. Apparently it falls to me to rewrite the text, and I invite anyone with more knowledge of the subject to improve it... not REVERT it.zadignose (talk) 08:07, 3 July 2008 (UTC)

Okay, I probably should have toned down my heated response to the reversion, but in any case I've attempted an edit that will hopefully improve the article. I hope it is found satisfactory.zadignose (talk) 09:22, 3 July 2008 (UTC)

I've revised the rewritten version a bit, but I'm not sure that mentioning the Bullet Cluster in three places (the article lead, the "Observational Evidence" lead, and a separate subsection in "Observational Evidence" is necessary. I also added a transition sentence to the discussion of the Bullet Cluster in the "Observational Evidence" lead to (hopefully) make it more clear why this result is so important. ASHill (talk | contribs) 15:06, 3 July 2008 (UTC)

I agree that the additional section at the end is likely unnecessary. I hesitated to completely remove what may be pertinant, especially the linked references, but I expect another editor could integrate what's most important and remove the rest.

I'm not so sure about some of the most recent edits. Particularly, I question the change of language from electromagnetic interactions (as it is also described in the article on the bullet cluster) to "collisions." It may just be a semantic distinction... when gasses collide, what force, if not the electromagnetic force, will most effect the velocity of the gasses? I don't think a collision mainly occurs between atomic nuclei, but more importantly, the reference to electromagnetic interaction relates directly to the first sentence of the article which defines dark matter as "matter that does not interact with the electromagnetic force."

I'm also very confused by "This is held as direct evidence of the existence of dark matter, independent of Newtonian gravity," though perhaps it's meant to suggest that Newtonian gravity couldn't account for what is observed? I think what's most important is that it is evidence of dark matter. The use of the word "direct" also seems a bit loaded.zadignose (talk) 08:37, 4 July 2008 (UTC)

I've clarified the description a bit. "Collision" is the term normally used in the literature to describe interactions between particles, although in the case of a plasma, it is indeed the electromagnetic force that is responsible for the interactions. My earlier removal of the term "electromagnetic" was because, as it was worded before, I thought it sounded like "electromagnetic" referred to the emission of X-rays. I hope I've clarified this ambiguity.

To my reading, the fundamental thing that's exciting about the Bullet Cluster result is that it shows directly that dark matter does exist; these data can't be explained by modified Newtonian dynamics. That doesn't mean necessarily mean that Newtonian gravity is completely right on large scales, but it does mean that dark matter must exist. I tried to clarify that as well, without giving MOND much weight.

I've also merged the two separate sections back together in one subsection, now within the "Galaxy clusters and gravitational lensing" subsection, with a brief version in the lead of the "Observational evidence" section. This organization seems the most logical to me, but there may be a better way. ASHill (talk | contribs) 15:28, 4 July 2008 (UTC)

Illustration as Humor?

Alright, I get it. "Dark matter as it is currently understood." Big black square:

File:Dmatter square.jpg

An image used to represent Dark Matter as it is presently understood.

But is this page really intended for comedy? Or is this a post-post-modern riff on The Life And Opinions of Tristram Shandy? Nothing meaningful can be learned about dark matter from this. Maybe someone needs to make an article called "dark matter humor?" On second thought, no.zadignose (talk) 07:28, 12 July 2008 (UTC)

Archiving

This talk page is enormous, so I'll set User:MiszaBot to archive threads older than, say, 120 days unless there's objection. —Alex (ASHill | talk | contribs) 16:43, 27 July 2008 (UTC)

Alternative Explanations

I removed the statement: "However it is important to remember that if dark matter passes through matter freely, a detector created from matter has little or no chance of either proving or disproving the existence of dark matter or energy." This sounded a bit mystic! Dark matter may not be baryonic, but it is matter nevertheless and while it may interact weakly with baryonic matter, it will interact: the discusion on the DAMA experiment above discusses this. Perhaps the person who wanted to say this wanted to discuss the difficulty of detecting dark matter directly? If so, it should be phrased better.Perusnarpk (talk) 14:23, 28 July 2008 (UTC)

I changed the first line

Dark matter exists only within the Standard Model. We do NOT see effects. We see that the predicitions of the Big Bang are against observation, so if we use the Standard Model we have 2 ways: either the Standard Model is wrong, or there is something we do not see. Why don't you write that this simply?83.103.38.68 (talk) 09:57, 19 August 2008 (UTC)

WOW, nice rollback, completed with the request of explanations. Which are here and you didn't wrote a word here, only in the rollback action. All the netiquette got lost, when needed. But still no answers here. So what's the point of the message on the rollback?83.103.38.68 (talk) 13:30, 19 August 2008 (UTC)

You still haven't explained what this has to do with the Big Bang exactly. Lars T. (talk) 16:51, 19 August 2008 (UTC)

Introductory sentence

"In physics and cosmology, dark matter is matter". Are you sure? Wouldn't it be more fair to say the ONLY thing we know is that spacetime appears to be curved in ways we wouldn't expect? Perhaps it is something that resembles matter, but all we really know at this point is that our physics don't work. --Eleassar ^{my talk} 11:46, 28 August 2008 (UTC)

If it is not matter and the (apparant) extra gravity is caused by some other effect as suggesed by some theories, then we don't call that "dark matter". See e.g. the MOND theory mentioned in this article. Count Iblis (talk) 13:18, 28 August 2008 (UTC)

Perhaps it should say "is hypothetical matter", since it hasn't yet been proved to exist. And if it doesn't interact with electromagnetic radiation, how does it affect the cosmic background radiation?