Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Dark Matter





I am wondering when/where/who the idea of "dark matter" in the universe came
about.

The rotation of galaxies does not follow what would be predicted by
gravitational interactions between only the visible pieces. In
particular, the outer portions seem to rotate too fast which suggests
that there is a great deal of invisible mass outside the visible
parts of galaxies.

A second argument comes from inflationary cosmology. All inflationary
theories, which solve so many nagging problems so neatly, predict
that the universe should be pretty nearly of a flat geometry. Iffy
observations of galaxy recession are consistent but there is a great
deal of error built in. However, there is nowhere near enough visible
stuff in the universe for the gravitational effect to produce a flat
geometry. Ergo, there must be a bunch of stuff we can't see.


And is any of it close to the Earth?

Is it "localized" or is it thought to permeate the universe?

Doesn't "dark" just mean that (whatever it is) it does not radiate in the
visible?

It means that it is either (a) very cold ordinary matter so it
doesn't emit much in any part of the spectrum or (b) exotic stuff
that behaves who knows how? There was recently a rather strict limit
placed on at least one form of ordinary matter, brown dwarfs, which
means that they are probably not a significant component of the dark
matter. The next most serious candidate is massive neutrinos. Who
knows?


Jim.Green@Snow.edu


Paul J. Camp "The Beauty of the Universe
Assistant Professor of Physics consists not only of unity
Coastal Carolina University in variety but also of
Conway, SC 29526 variety in unity.
pjcamp@csd1.coastal.edu --Umberto Eco
pjcamp@worldnet.att.org The Name of the Rose
(803)349-2227
fax: (803)349-2926