The universe comprises mainly of dark matter. What is dark matter?

Answer 1

There are two different things here. One is dark matter, the other is dark energy. Dark matter makes up about 23% of the mass of the universe and dark energy makes up about 73%. Ordinary matter (protons, neutrons, atome, etc) make up the rest.

When models are made of how galaxies rotate, or galaxy clusters move, it turns out that the material we actually see is not enough to explain the motions that we see. Because of this, it was postulated that there is an extra bunch of mass out there to make up for the difference. Up to this point, we have not been able to detect this stuff except for the gravitational effects that it has, although we have been able to map out where it is using these effects. For the most part, dark matter and ordinary matter are closely associated (which led some to think that we simply had the amount of the grvaitational effect of ordinary matter wrong), but a recent study where two clusters were colliding gave an example where the matter and dark matter are *not* in the same places. So we do know that there is something else out there; we know about how much there is; but we don't know what it is made out of. As one poster mentioned, neutrinos are one part of it (possibly), but not all. This is one of the BIG open questions in physics right now.

Dark energy is even more unusual. It comes about from an extra term in Einstein's equations when applied to the universe. This term is needed to match the observations we have made, but almost nothing else is known about it. One effect it has is to accelerate the expansion of the universe. Without it, the rate of expansion would be slowing down and we now know it isn't. This alone was a HUGE surprise.

So, to answer your question, nobody knows at this point.

Answer 2

If I could answer that one I would be up for the Noble Prize!

You see the thing is that the stars in galaxies whip round far too quickly for the gravity of the galaxy to held them in - big problem. So there must be a lot of matter which we can't see - ie it doesn't interact with photons, that lies outside the visible part of a galaxy holding the stars in. We can't see it, it's dark, hence dark matter.

If this is the case there is about 10 times more dark matter than light matter.

Lots of strange things have been put forward. Neutrino's could account for about 10%, then there is black holes and strange and yet unproven particles such as aixons just to name a few.

There is also work work trying to find out if there problem is with gravity itself - which would also solve this problem without needing dark matter.

There are a number of Dark matter detectors currently being built which may solve this problem. These is also a recent paper published that suggests that dark matter has been detected by the effect it is having on colliding galaxies. Visit
http://home.slac.stanford.edu/pressreleases/2006/20060821.htm

Addition

I noticed that somebody suggested that black holes in the centre of galaxies could account for the massing mass. Sorry you are so wrong. It doesn't have the right properties and we have already taken them into account.

Answer 3

In layman's terms (and I'm not a physicist) here's the jist of dark matter:

Matter cannot be created or destroyed. But, it can shift form. The whole e=mc^2 thing describes the interchangability of matter and energy. Whenever there are astronomical "explosions" that create matter from energy or vice versa, there is a byproduct of this process. It is dark matter. Dark matter is sort of the interim between matter and energy. It doesn't really behave like either one, but it is there, nonetheless. It may not register as a physical object, but it possesses the elements (i.e. neutrons, electrons, protons) of matter. And, it possesses a large degree of gravitational force, showing us that it is there. Astrophysicists believe that when the "big bang" occurred, most of the matter/energy that went from being highly compressed to being the universe we know now was transfered into this dark matter state. This explains the "gaps" that exist when we try to find things that should be there, but aren't. For instance, if a galaxy is revolving around SOMETHING, but we don't have a physical counterpoint for this revolution. we deduce that the "something" is dark matter. It balances the first part of the equasion with the end result, in a sense.

My take on all of this: I'm not a huge proponent of Big Bang, but the universe is a really big place. Dark matter may exist, but how it got there, who knows? It's one of things we may think we understand now, but 100 years from now, our theories may seem under-educated. Enjoy the mystery and the process of discovery.

Answer 4

Nobody knows and it might not even exist. It has been well determined that galaxies are not moving in a way consistent with known laws of physics unless there is loads of mass that is not being seen by telescopes. Clearly there are 2 possibilities:
1) The relevant laws of physics need updating
2) There is unseen mass
So far nobody has been able to determine which of these possibilities it is. Dark matter sounds crazy in day to day terms but in terms of physics it is entirely reasonable, there are loads of forms of dark matter already known (E.G. the neutrino) but none of them quite fits the observations. Given that our knowledge of physics is partial there is plenty scope for either new forms of mass or changes to the laws.
Dark matter is not a problem - it is a challenge!

Additional note, zack is wrong. A central black hole has the wrong properties to be the dark matter.

Answer 5

Dark matter is required to explain several phenomenon.

One is that the galaxies we have observed spin (like our own solar system). Only the galaxies outer portions spin just as fast as the inner portions (unlike the solar system where the planets closest to the sun orbit the fastest).

To account for this either there has to be a lot of additional gravity in the galaxies we are observing (dark matter) or the laws of physics (gravity) as we know them are wrong.

Answer 6

The physicists come up with a theory about the universe. Then they find there's not enough matter in the universe to support the theory. So what do they do? Some of them go away and think up a new theory. The rest insist there is enough matter - it's just invisible.

I wouldn't worry about it. In a few year's time there'll be an even more far-fetched theory.

Answer 7

Okay, so everything that you think of as a vaccuum is actually dark matter. Dark matter is a type of particle that originates in one or more of the six dimensions you can't perceive. While dark energy is the force that causes everything to move away from everything else, dark matter is the pseudo-matter (I don't think that's a real word) that fills what we perceive as the empty space between.

Answer 8

Energy

Answer 9

dark matter>>>>>the stuff you flush down the john

Answer 10

Dark Matter might not even exist.
The galaxies swirling around, could be spriraling around a supermasive black hole.