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greenbdb
2005-Jan-26, 03:00 PM
It has been reported that up to 74% of the matter of which this universe consists is called "dark matter" for want of a better description. Could it be that this may turn out to be the mass of light (electromagnetic radiation)?

Betelgeuse
2005-Jan-26, 04:14 PM
Hello,

Dark matter is in fact theoretical non-luminous matter that has eluded detection by all present means, appart from through gravitational interaction with luminous objects. Astronomers and astrophysicists have calculated that dark matter comprises more than 90% of the universe, actually. It's possible that most of the universe exists as undetected clumps of interstellar dust and gas, and that cold dark stellar cores collapsed billions of years ago. Some other physicists have suggested an unknown form of matter, and a small mass for neutrinos (a fundamental particle produced in massive numbers by the nuclear reactions in stars. They are in fact very difficult to detect because there are so many of them passing completely through the Earth without interacting). Whatever the explanation, much of the universe has yet to be seen.

We know that dark matter must exist for many reasons - like spiral galaxies rotate so fast that if the light matter was all that was there, the galaxy would fly apart - there must be something else there, something must be holding it together.

Examples of dark matter include planets, black holes and white dwarfs all being because they have low luminosity. There are also more sort of "exotic" things like WIMPs (weakly interacting particles that are thought as dark matter jargon for Weakly Interacting Massive Particles - they include electrons, which have very little mass, and neutrinos (which I've explained), which may have zero mass. They're also refered to as nonbaryonic matter).

Hope this helps
Kind regards
Rigel

Svemir
2005-Jan-27, 09:41 AM
O.K. I must replay on this (on neutrino issue, again).
Neutrinos can not be WIM(assive)P with zero mass.
Photon has got zero mass (in rest), and moves by speed of light.
Since there are neutrino osilations (from muon to electron neutrino) according to the newest observations (in order to explain missing neutriono emmission from Sun), they must have a non-zero mass and must have speed lower then speed of light.
Their mass counts for ca. 10% mass of the Universe.
Here is an article (web is full of them) on Dark Matter issue.
http://csep10.phys.utk.edu/guidry/violence...darkmatter.html (http://csep10.phys.utk.edu/guidry/violence/darkmatter.html)

Guest
2005-Jan-27, 08:37 PM
they use it in futurama so it must be good.....!!!

Algenon the mouse
2005-Jan-28, 02:32 AM
There are three theories about what dark matter might be:


Baryonic matter(black holes, burnt out stars etc). The problem with this theory is that currently it can only account for 10% of dark matter.





Neutrinos( an invisible particle discovered by Pauli) The problem with this theory is we are not sure neutrinos have a mass.




A yet undiscovered particle or particles . I do not think I need to state what the problem with this theory is.

I know there was a discussion on the theories of dark matter somewhere in this forum, but I do not remember where.