What is Dark Matter, and why does it matter to me?

Well, first, why does it matter to you, I don't know. I am not a psychic. But I will wager a guess. You were playing cards, and dark matter cheated and stole all your money. Now you want to know how to kill the dark matter, probably using a clever line like: "My name is anonymous, you stole my money, prepare to die."

First of all I would like to say that your story of the stolen money is rather far fetched. There is no evidence to suggest that dark matter is any more intelligent than a rock. You probably got drunk and someone stole your money while you were sleeping. Then you made up this dark matter story as a cover for explaining to your wife where all the money went.

Regardless of your reason, here is your answer.

The universe is composed of both light and dark matter. Light matter is the matter which we can see, dark matter we only see through its gravitational effects on light matter. Dark matter was first noticed in 1933 by Fritz Zwicky, who gets bonus points for having a name in which the letter 'z' appears twice. Zwicky noticed that some galaxies were spinning to fast. He reported this to his local police chief, but the local police responded that it was out of their jurisdiction. When he published his results he claimed that there was non-visible matter in the universe, and that as a precaution we should never be too careful with our money at poker games. His claims were largely uncorroborated for 40 years, with exceptions in a few saloons Then in the 1960's and 70's astronomers studying galaxy rotation curves. Vera Rubin studied the curves of these galaxies and found them to be disappointingly flat, and not curved at all. As astronomers grew depressed upon realizing that galaxies weren't curvy after all, they began researching dark matter more intensely. It may be they also hope to kill the dark matter, to get them curves back.

Dark matter is difficult to study, but current theories feel that there are several different types of dark matter. These types are divided into two catagories, Baryonic and non-Baryonic dark matter. Non-Baryonic dark matter is sub classified as Hot, Cold, or Tepid.

Baryonic dark matter includes MACHOs (massively compact halo objects). These are similar to captains of your high school football team. They are dense, are not too bright, and every thing revolves around them. These may actually be brown dwarf stars, or neutron stars, or unassociated planets. But it is generally accepted that they are only a small percentage of the total dark matter in the universe.

Hot dark matter is most likely composed of neutrinos. They are briefly discussed at the end of this post here. Neutrinos are not clumpy however, and dark matter is suppose to be clumpy; this is obviously wrong, so moving on.

Cold dark matter is clumpy. It is composed of WIMPs (weakly interacting massive particles). WIMPs only interact through the weak nuclear force and gravity. They also have large masses compared to neutrons and protons (which really isn't a great benchmark to call something massive). Wimps however are purely hypothetical, so also not a good candidate for reality.

Tepid dark matter is a combination of hot and cold dark matter. Most astrophysicists don't believe it exists, but as we learned from Goldilocks; if it's not too hot, or too cold, it must be just right; I'm betting the farm on this one.


Note 1: Some reports indicate that there are dark matter beings trying to destroy our galaxy; but I have it on good authority that the good guys won .