what is dark matter?

Answer 1

In astrophysics and cosmology, dark matter is matter, not directly observed and of unknown composition, that does not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter.
see here:http://en.wikipedia.org/wiki/Dark_matter

Answer 2

Yeah, all that that Crisi wrote...but there's more.

First, dark matter was theoretically constructed to explain why spinning galaxies did not fly apart under their own cetrifugal forces. There had to be more mass than was observed to create the kind of gravity needed to offset the centrifugal forces. In fact, the observed masses accounted for only about 4% of the mass needed to keep the galaxies from flying apart.

Second, dark matter is no longer theoretical. It has been observed recently (2006) by a Stanford U. group as they watched two galaxies collide. The enormous energy from those ongoing collisions was sufficient to cause the dark matter to glow...to become visible. [See source.]

Answer 3

dark matter is supposedly some kind of mass in the universe that causes the galaxies to rotate.. or something..

but in the animated series Futurama, dark matter is Nibbler's (their alien pet) waste matter.. which also doubles as fuel.. and each pound of it weighs a thousand pounds (which doesn't make sense)

but for the real dark matter (pertaining to physics), just click here:
http://en.wikipedia.org/wiki/Dark_matter

Answer 4

Dark matter is a scientific-sounding name given to a set of properties that might produce an otherwise unexplainable set of phenomenon. In other words, it is a placeholder theory until something more useful comes along.