How do we know dark matter is out there?

Question

Is the only evidence we have for dark matter the fact that there is a lack of "visible" matter we can detect to account for the gravity holding galaxies etc together? Is there any other evidence?

If there is none is it not possible that we have something fundamentally wrong with our understanding of gravity itself?

Answer 1

Dark Matter is the term astronomers, astrophysicists, and physicists use to describe the type of material out there that we cannot see.

We know that there is dark matter in the galaxy initially by studying the rotation rate of our galaxy. Basically, by comparing the empirical results to what the rotation rate should be for the stuff we can see, we notice that theory and observation does not match. In order to be able to explain the observed rotation rate of the galaxy one needs to have more material in the galaxy than observed, hence dark matter.

The source below shows a good summary.

Answer 2

You've got it turned around.

We know enough about how gravity works to know that the measurements are correct--that's the first thing scientists checked.

But--here's how the whole dark matter thing came about. Scientists found that there was more gravity in the universe than could be accounted for by the observed matter in the universe--even after they checked and double-checked everything we know. So they knew there was SOMETHING out there--even though they had no clue as to what it might be.

This isn't actually unusual in science--and finding "anomalies" like this is how some of the greatest discovries are made. Now--when this happens, there's a specific way that scientists deal with it.

What they did was postulte an "unknown entity"--a fancy way of saying what I already said: "We know something's out there--even though we don't know what it is."

And--for conveniience (and no other reason) they gave this unknown a label: "dark matter." But they made no assumptions about what it was--the term is jsut a easy shorthand that makes it easier to talk about the topic.

Fast forward to today. We have not learned a whole lot about dark matter. We do know it appears to be in two forms that are analogous to matter and energy--labeled dark matter and dark energy. And we know it (whatever it is) makes up most of the mass of theuniverse.

We do know its real. recently (late last year and this year) astronomers observed a region ( at the edge of a distant galaxy) where light rays are being bent-and only gravity can do that. But--there's no matter where it would have to be to account for the bending. Scientists are fairly sure the cause is dark matter.

But again--re your question--we know "something" is out there. "Dark matter" is jsut the label we stuck on that soething for convienience.

Answer 3

Actually, there's more evidence than that, a prime example is of two colliding galaxies - the momentum of dark matter is far greater than that of 'normal' matter, and it takes more force to slow down and/or curve it's path. Here's a description and a picture:
http://www.abc.net.au/science/news/stories/s1720848.htm

Science feels we have a good understanding of the force of gravity - **as long as it behaves the same everywhere in the universe as it does here.** That's an important statement, because we assume that anything that we see nearby is the same as it is far away.

If Gravity behaves differently "there" than it does "here", then our definition of the universe will need to change.

Answer 4

Yeah, I think that's the main reason - they need more mass to account for gravity, and so they came up with the dark matter theory. They might be able to measure it also by the way that light comes from far away stars, but I can't remember.

Answer 5

Both dark energy and dark matter are just place holders to account for certain gravitational movements. Both might be already observed constructs such as black holes, atomic particles and even hydrogen atoms, but there is no way yet to detect the missing matter and energy from where these objects are in the universe with the systems we have now.

Answer 6

It's always possible that we do not understand gravity. But "dark matter" explains the observations -- why bring in something more complicated? It's a general principle of science, that the simplest explanations are the best. Explanation should be just complicated enough to explain what we observe, but not more complicated than that.

Answer 7

Dark matter is sci-fi nonsense. Do you mean to say antimatter?

We cannot see most of our universe because it is so far away. We would not be able to see, using light, what holds the universe, or even the Milky Way together, because those objects are super massive black holes (in theory). That means that their gravitational pull is so immense that light itself cannot escape it.

Answer 8

Dark matter is really a blanket term for stuff that doesn't do anything but theroetically should be there.

Dark matter is so calle because it doesn't react with anything (yet). CERN's LHC should enlighten us a little more, as soe of their work is very involved with dark matter.

Answer 9

black matter is probably detected by waves given off when light makes contact with it. depending on how many angles you have of the area in question, the pattern will show its movement and sized.