Talk:Dark matter

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)