posted on Feb, 3 2007 @ 02:04 PM
Originally posted by Mondogiwa
I hear a number of scientists speak of, "Dark Matter" but nobody can really explain it. Is it the new catch phrase for, "We have no idea what it
Well, yeah, actually. Physicists only know it exists because they can observe its effects throughout the universe. "Dark matter" is the place
holder of a name to explain the extra gravity required to keep galaxies like ours from falling apart because there's simply not enough normal matter
to create enough gravity to keep them together (as shown by computer simulations).
In spite of not knowing what it is, we can at least infer some amazing properties of dark matter, like that it rarely interacts with normal matter
beyond its gravitational effect. It also doesn't emit or reflect EM radiation (a.k.a. light) which makes the stuff even harder to study.
Physicists are very, very certain of existence because of recently observed phenomena in the Bullet
(amazing stuff, really). Two galaxies collided with each other in such a manner that matter got separated from dark matter, and
gravitational lensing could actually be seen
The name for "dark energy" has a similar story. Physicists are very, very certain it exists, but don't know what it is.
Alas, that's a different topic, and I'm tired. I might try to explain it later though.