Why no Direct Dark Matter Observation

Most recent answer: 10/07/2014

Q:
Is it possible that detection of dark matter has been impossible because it exists in a weird quantum state that prevents its observation?
- Tim Cardella (age 63)
Marana, AZ USA
A:

Since, so far as we know, all properties of the micro world and perhaps of everything are quantum properties, I'll just take your question as being about what feature of dark matter might make it especially hard to detect. The basic reason it's called dark is that it isn't involved in the electromagnetic interaction, so it has no direct interaction with electromagnetic waves such as visible light. When you think about it, there's no obvious reason why the various ingredients of the world should all have to interact strongly with the same fields as us, so having some of the matter be dark is not all that surprising. (Gravity is special, in that any form of energy-momentum must give rise to gravity, and thus the existence of dark matter is inferred from gravitational effects.)

So why do people have such strong hopes that dark matter will show up also via some sort of weak interaction with familiar matter, at least a little bit? As I understand it, the argument runs roughly as follows. The ratio of the average density of dark matter to the average density of familiar matter is around 6, a smallish number. It's not 1,000,000 or 0.000001. Now that similarity of densities could be some sort of coincidence, but it's more natural to explain it by some process in the early universe by which the different types of matter could inter-convert. For that to happen in the brief interval allowed, you'd need some minimum value for some dark-matter/familiar-matter interactions. That's why there's hope that with slightly better detection methods evidence of such interactions should be found.

Mike W.

There is a nice Wikipedia article on dark-matter candidates called WIMPs or Weakly Interacting Massive Particles.      LeeH

 


(published on 10/07/2014)