i know i’m brief but this is all i know
it is a mass of existance which isn’t made up of atoms.
i know it isn’t an exact science but could somebody help me on understanding what it is or where it came from?
Its all the mass out there in the Universe that scientists predict should be there but that we can’t see. Least thats my Discovery Channel take on it.
-XT
Physicists can calculate how stars, planets, etc. should all move based on their understanding of the universe. However, when they do their calculations, the numbers don’t quite match up to what we actually see. Either they don’t understand the universe as well as they think they do (which is quite possible) or there’s a bunch of matter out there that we can’t see which is screwing up the equations. Since we can’t see it, we’ll call it dark matter.
Exactly what it is or where it came from isn’t known at this point. Right now it’s just a fudge factor way of making the equations work. It may not really exist.
To be a bit more precise, when they examine the motions of stars in a typical galaxy, they realized that the sum total of the visible starts, dust, whatever that they could see did not produce enough gravitational attraction to hold those galaxies together. So they drew the conclusion that there is something out there that does not interact with photons (hence dark, although invisible would be a better term since actual dark matter would absorb photons) and seems to interact with ordinary matter only via gravity. I don’t know if you could show that it doesn’t feel the weak or strong nuclear forces but they are very short distance forces active only over distances the size of a nucleus. It also seems (I am not sure why) that the stuff moves slowly so that it is not only dark, it is cold. Hence the phrase “cold dark matter”. I believe it is also the case that galactic clusters require dark matter to hang together.
Not to complicate things any, it also seems that the universal expansion is increasing, not slowing as you would expect from gravity. This is explained by something called dark energy. On the basis of measures of expansion (which is measured by counting supernovas) it is now thought that of the mass in the unverse, around 67% is dark energy, 28% is dark matter and a mere 5% is ordinary matter. And so we fade into cosmic insignificance. Except in Kansas where it can now all be explained as god’s whim.
There are dozens, possibly hundreds, of hypotheses on what might make up dark matter. Some of the possibilities are certainly made up of atoms. These include all the various speculations about huge numbers of planets, non-luminous stars, and similar massive but non-light-emitting bodies. These are collectively known as MACHOs - MAssive Compact Halo Objects.
Suggestions for dark matter that fall into non-baryonic particles, i.e., aren’t made of the parts that constitute normal everyday atoms, are collectively called WIMPs - Weakly Interacting Massive Particles.
There are suggestions that fall into neither category, like an abundance of black holes.
Of course, if we knew what dark matter was, we wouldn’t call it “dark matter” any more. 
dark matter is simply matter that isn’t giving off light (matter that is not burning in a star, for example). the earth is “dark matter”. humans are made of “dark matter”.
we can see the gravitational pull it exerts, but since dark matter isn’t emitting light or other radiation, we don’t know exactly what it is.
thanks
This is true and a very important point (one I would have raised myself). But it’s not the whole story. Undoubtedly, some dark matter is baryonic matter (the ordinary sort of matter with which we’re familiar). But it can’t all be, or even most of it. If there were that much baryonic matter in the Universe, then the abundances of the light nuclei (various isotopes of hydrogen, helium, and lithium) would be vastly different than what we observe. So most of the dark matter is non-baryonic. This still doesn’t tell us much about what it is, though, and every time a particle physicist hypothesizes some new particle for some reason or another, there’s always speculation that that new particle might make up the dark matter. Fact is, we don’t know.
Can you explain this a bit more?
If the dark matter is all, say, Iron, that would mean that the overall distribution of matter in the universe is not the same as that in our solar system, but it wouldn’t actually violate anything fundamental about our observations, would it?
It’s not so much how much matter we observe, but the various proportions of it. For instance, we can measure the proportion of deuterium to ordinary hydrogen in (our part of) the Universe, or of helium-3 to helium-4. It is, I suppose, hypothetically possible that the proportions of various isotopes varies with place in the Universe. But I have a hard time thinking of any mechanism which could preferentially segregate, say, helium-3 from helium-4. And we have perhaps a half-dozen different independant ratios we can measure, all of which imply the same initial baryon density for the Universe, so if something is discriminating between the isotopes to cause a non-uniform distribution, it’s doing so in a manner which very freakily looks like it is uniform. Furthermore, for all objects we’ve detected in the Universe (even galaxies billions of light years away), these proportions seem to be the same, so it really doesn’t look like they vary much at all.