m.e.h.

<a href="http://news.bbc.co.uk/2/hi/science/nature/2165878.stm" target="_blank">http://news.bbc.co.uk/2/hi/science/nature/2165878.stm</a>

gregw

Actually, this month's Scientific American has an article about the possible non-existence of dark matter. (I can't link to the story...one must "buy" it! Oh well...)

I guess the debate will continue until someone actually picks up a lump of some black stuff and says "That's it!" :-)

Hey...you don't think that coal...nah...

Friar Bellows

Another thing to know is that there's different kinds of dark stuff. A recent paper I read (forget the title) breaks it down into the following components (by percentage):

Dark Energy: 67% (cosmological constant term, possibly the vaccum energy, postulated to account for the observed accelerated exapnsion of the universe)

Non-Baryonic Dark Matter: 28% (cold dark matter, moving slowly so it can't be neutrinos, not much interaction with baryonic matter apart from gravitational, the key to the formation of structure in the universe)

Baryonic Dark Matter: 4% (some of it has been identified as hot x-ray emitting gas around clusters, but we're not sure about the rest of it, maybe intergalactic, maybe some of it is in and around galaxies, we don't know)

And then there's the directly detectable stuff:

Baryonic Visible Matter: 0.5% (the stuff we see, stars, molecular gas clouds, kittens)

Neutrinos: 0.3%

These percentages are estimates and subject to frequent change.

Starboy

That article in SA was very interesting. It was about a theory that has been floating around since the early 80's called MOND - Modification Of Newtonian Dynamics. It fits most of the observed data very well, better than dark matter theories. The only hitch is that it postulates a change that would effect general relativity, but no one has been able to figure out how to incoporate it.

<a href="http://www.astro.umd.edu/~ssm/mond/" target="_blank">The MOND pages</a>

Starboy

[ August 02, 2002: Message edited by: Starboy ]</p>