Talk:Dark matter/Archive 1

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Archived discussion please do not edit, post in Talk:Dark matter instead...

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Removed statement that existence or non-existence of dark matter contradicts big bang. Dark matter actually has very little to do with whether big bang is true or not.

The article at Big Bang theory speaks of a dark matter problem; you may want to correct that if you're better informed than the author. Mkweise 13:05 Feb 16, 2003 (UTC)

Did so. What I suspect that the author was referring to is the fact that dark matter *helps* the big bang theory. During the 1970's, there were a number of problems (mostly deuterium abundances) that have been nicely resolved by assuming that dark matter exists.

I vaguely remember that some time in the 1990s, new observations led to the stunning (at the time) conclusion that more than 90% of the universe's matter is dark. IIRC, some previously favored theories were essentially scrapped due to that - I don't remember specifically what theories, but I think it led to a change in the estimated age of the universe by many orders of magnitude. Mkweise 16:26 Feb 16, 2003 (UTC)

Having a description of Hot Dark Matter there doesn't fit, there should be accompanying descriptions of cold and baryonic.

new content

The following content was put on the page and was very hard to read. We can try to work it in, but in the meantime I've put it here and reverted the page. --zandperl 01:45, 18 Mar 2004 (UTC)

I have just worked it over, chopping it up into paragraphs and also into sections that I think might be better suited to other articles. If nobody objects to what I did with it, I'll merge them into their final destinations tomorrow. Bryan 19:06, 20 Mar 2004 (UTC)

I just moved all the text to the various articles I'd proposed moving it to (except for the dark energy section, which was entirely redundant with the stuff already in the dark energy article; I just deleted that one). Bryan 06:04, 25 Mar 2004 (UTC)

I did not see any mention in the article about what portion of dark matter is accounted for by the cumulative relativistic mass of all the photons that have been spewing out of all the stars in all the galaxies for the past several billion years. Should that be added? David Battle

Photons don't have any rest mass, and we usually just talk about "energy" instead of "relativistic mass." The energy of the photons goes into the energy budget of the universe as radiation, not dark matter - because you can see them. reuben

Mirror Matter

211.28.213.93 has been making statements about mirror matter being the solution to the dark matter problem and about the success of the DAMA experiment. I do not believe that these statements reflect the opinions of the majority of practicing physicists. Since an encyclopedia needs balanced coverage without overstating a minority view, I have been editting / reverting the statements made by 211.28.213.93. While I am an active physicist, I am not a dark matter scientist, and am certainly willing to listen to discussion if something has changed in this arena.

The DAMA group does report a persistent annual modulation in their NaI detector. I certainly respect their opinion and believe they have worked in good faith to validate these results. While their results are certainly consistent with expectations, it is also true that they report a summer-winter modulation in their detector. Even in a climate controlled vault in the bottom of a mine, it is hard rule out possible climate effects. For example, is the effectiveness of screening cosmic rays influenced by environmental conditions on the surface? We really need to see independent confirming results before the scientific community should accept this as the smoking gun of dark matter. Not unexpectedly, there are scientists working to provide those confirmations

As I am sure 211.28.213.93 knows, the DAMA results are inconsistent with dark matter made of particles usually considered. This has led a small industry of people championing mirror matter since it does appear to be consistent with the DAMA results. The traditional alternatives are just as theoretical as mirror matter, though their implications probably have been more thoroughly studied. Also, if mirror matter does exist, there is no reason that I am aware of for it make up such a large portion of all matter (an order of magnitude greater than the baryonic matter component). The consensus view among physicists has been that supersymmetric WIMPs are the most likely dark matter candidate. This is obviously a value judgement about the underlying theory, but an encyclopedia should respect that value judgment. Unless and until strong confirmation of the DAMA results have been provided, it seems unlikely that this consensus is going to change.

Dragons flight 03:54, Oct 9, 2004 (UTC)

What should be done is to write about experiments that have been performed. I haven't encountered anything about that here! Then one can discuss the various candidates (Mirror Matter, Kaluza Klein dark matter, Strongly Interacting Massive Particles (SIMPs), etc. etc. ) in a neutral way. E.g. what are the signatures of mirror matter compared to WIMPs?

If most physicists favour WIMPs then that should be mentioned. A reader of this encyclopedia should get an impression of the value judgement about dark matter of physicists. However, the reader should also be able to get an overview of the various dark matter candidates as published in peer reviewed journals, explained in plain english.

An overview of candidates and experiments can be found here.

Fixed link to arXiv

There was a problem with the link to arXiv. It only linked to articles posted on the physics archive. Most physicist posting preprints on dark matter put their articles on the astro-ph or hep-ph archive and don't cross link to physics. Now you get all the dark matter preprints on arXiv.

Changed arXiv.org to the mirror xxx.lanl.gov (there is a bug in the search facility at arXiv). Now you really get all the preprints that have in the title or abstract the phrase dark matter.

Added internal link to Strongly Interacting Massive Particles

I just made a new page on Simps. It is a bit short, but it can be easily improved using the references I gave there. Specific Simp candidates, such as gluon-gluino bound states should be mentioned.

There is a lack of dark matter candidates mentioned on this page. An encyclopedia should be as complete as is reasonably possible. Of course, WIMPs are the most popular candidates, but that should be made clear by mentioning that in the text, not by limiting the dark matter candidate list to only WIMPs and a few other candidates.

Other candidates that must be mentioned:

WIMPZILLAs (Supermassive WIMPs),

Kaluza Klein dark matter,

Heavy right handed neutrinos,

Q-Balls,

Cosmic Strings and other topological defects,

Monopoles,

Mirror matter in the form of invisible mirror stars, both in the broken and unbroken mirror matter model. The mirror matter page is far from complete.

And many other things...

Created a page on DAMA/NaI experiment and linked to that page

Unfortunately someone has voted to remove the DAMA/NaI page. He thinks it's original research. I doubt if he knows what original research is. It is true that the article is technical. However, it is easier to write the article this way and to improve it later. I give some references that can be used to expand the article and make it less technical.

Meteorites

Reading from Vera Rubin's work, I see that she does not rule out dark matter as something as simple as iron ash from a burned-out star etc. Why is this not mentioned in the article. Obviously we have not been to the outer sections of the galaxy, but why shouldn't the composition of meteorites give a clue about dark matter? Has no one else invented a crucial experimental setup to answer this? Is it because the ash would clump together, and heat up, like the earth? Ancheta Wis 17:19, 5 Nov 2004 (UTC)

The consensus in the scientific community is that this cannot be the case. The case for baryonic dark matter (i.e. dark matter consisting of ordinary matter in the form of dust, brown dwarfs, etc) is reviewed in these two articles:

[1]

[2]

I think that it could be mentioned here that till the 1990s baryonic dark matter was a viable possibility (the scientific community was split about this issue), but that observations and arguments mentioned in the articles by Freese et al. have convinced most astrophysicists that dark matter must largely be non-baryonic.

I deleted white matter and gray matter

The removed sentence added nothing. It was obvious from the context that the article was not about tissue. RPellessier 01:31, 24 Jan 2005 (UTC)

Two categories merged

I dont see a reason why we need two categories explaining the same thing, evidence/discovery are basicaly the same thing. --Cool Cat| My Talk 15:19, 28 Feb 2005 (UTC)