free debate

July 28, 2009

Scientific Unknowns: Dark Matter (Yes, it Really Exists)

When I teach astronomy, one of the most common questions I hear is "Is dark matter real?" In order to answer this question let me give an example.

Let's say that you are riding your bike and suddenly you start to hear a grinding sound. You start to slow down and the sound goes away. Let's call this Dark Sound. What you could do is try to describe the sound. If you have a speedometer on your bike, you may be able to say that it only happens when you are going faster than 10 miles per hour. You might try changing gears and find that it only happens when you are on your second rear gear. By doing this you can describe the problem, but you may still not know what the problem is. Dark Sound is a place holder name until you take it to a mechanic and they can tell you what's wrong.

Dark matter (and dark energy which I will talk about later) is a place holder name. The problem is with galaxies. When we look at a galaxy we can estimate how much stuff there is in that galaxy. We can then figure out how much gravity that stuff should have. The problem is that there is five times more matter in galaxies than we can see. It is estimated that over 90% of the matter in the universe is dark matter.   Scientists are getting closer and closer to understanding what this dark stuff is, but the answer still isn't there. We have imaged the effects of dark matter on small galaxies, and now understand there to be halos of dark matter around large galaxies. Right now, many of the world's leading astronomers and cosmologists are trying to figure out what this dark stuff is; when they do I'm sure that the answer will change how we see the universe.

For more I recommend Astronomy Cast