Dark Matter is dark. HA, good opening joke there... Yeah, I'm going to make this dark matter post as short as possible. I'm going to cut out all the glut you can find on Wikipedia, because really, who can't find just about everything they need to know there? Why? Because today is not my finest day for blogging. Seasonal allergies are kicking in and I'm pretty sure if have a haymaker of a hay fever, and I need to start feeling better before the weekend gets here. I also spent most of the day filling out application forms and those silly personality tests for a job offer I received. And answering questionnaires on the Life in the Universe Toolkit I've been working with. Plus, I think I am having withdrawal from my girlfriend going back to school after her short spring break visit. On the upside, I got Dragon Age 2 last night (an early birthday present), so I want to hurry up and get to playing that too.
So, the Wikipedia article on dark matter looks like a huge mess anyways. Good luck with that, and I might follow up on it another time with more detail. Pretty much I am going to go off the top of my head and give some of my ideas about dark matter.
Firstly, no, I don't know what it is. No one does. That's kind of the point of it. Dark matter is just a descriptive name given to this form of matter that does not emit or normally interact with electromagnetic radiation. Electromagnetic radiation being radio, x-ray, microwave, ultraviolet, and visible light. So, pretty much, with all our fancy telescopes, which look at light, we cannot see dark matter. It is visibly dark, picture related:
So how do we detect dark matter if we cant see? How do astronomer's know it is really there? It comes down to a matter of gravity. The concept of dark matter was born out of studying the physics of galaxies and the cosmic microwave background. There were problems with the math, the structures of galaxies and galaxy clusters didn't hold up with what was observed. The amount of mass observed in a galaxy wasn't enough to maintain their rotation. Something just looked fishy, there was missing matter.
Initially there were a few competing theories, and I remember in the 90s this being a hot topic of debate. I really don't know to much about what happened then, since I was a kid, and most of my knowledge is after the fact. But outside of the field, the debate made little sense, but sounded entirely cool. Some movements wanted to rip up all of physics and start over again, destroy the laws of Newton. Others just wanted to modify Newton's gravity laws. A few others wanted to create a special, separate, quantum gravity. But by far, the leader of the movement came to be dark matter.
Why dark matter? Because it made sense, the math worked out, the modeling worked out, and it was testable. These other theories just didn't have the evidence to back them up. It goes with the euphemism: extraordinary claims require extraordinary evidence. With larger, better, faster, stronger, daft punkier supercolliders, there was the actual ability to search for the particles that make up dark matter.
These particles come in a couple different forms, and there are a couple different ideas about them. The most prevalent and accepted for of dark matter being Weakly Interacting Massive Particles, also known as WIMPS. Think about that name, it completely applies to the situation, they have a weak interaction with baryonic (normal) matter, but have a large gravitational effect. But the weak part is a misnomer, because it actually means that they interact with the weak nuclear force. It still stands though that these are cold, massive, slow moving particles that bind the galaxy together. I don't know that they have been directly detected, I know there are massive research projects to search for their particles though. What I can tell you is that, in astronomy, the proof is there. These particles are responsible for an effect called gravitational lensing, where light can be bent around an galaxy.
Now, even though those particles, that make up what is thought to be the majority of dark matter, have not been directly observed, there is another kind where there has been great success. Neutrinos. Neutrinos are a form of dark matter, but are much smaller, faster, and hotter then their WIMP cousins. They have also been much easier to find and are an established particle of matter now. And they give us an idea of what to look for, where hopefully the IceCube Observatory in Antarctica will eventually discover them. IceCube being the most ambitious of these detection projects, drilling massive holes into the ice sheet and lining it with detectors.
There is almost no argument from the established community about the existence of dark matter. Its particles are all around us and scientists have even discovered some of these particles and their building blocks. The arguments against it may rise up here and there every once in awhile, but mostly its just someone trying to attract attention by 'shaking up' the community. I guess it makes for interesting news, but the alternative ideas also keep pressing scientists to search for more proof and settling it in peoples minds that dark matter is a real phenomenon. Dark matter is just a name for it, but as science sheds more light into the dark corners of the Universe, we will begin to have a better understanding of how this matter works, and it might be understood as something other then the placeholder name of dark matter.
Also, new poll time! I was going to do open questions, but not feeling quite up to it yet, perhaps next week.