Is there a reason to believe in a limited variety of dark matter?

[mrspeedybob]

"Normal" matter makes up about 5% of the mass/energy content of the universe. From studying this 5% we have discovered 4 fundamental forces and numerous fundamental particles. When I read things about dark matter and dark energy it seems that each is assumed to be a single class of phenomena. This seems odd to me because I would expect the stuff we can't see to be just as diverse as the stuff we can.

Is there a reason that we expect fewer varieties of dark matter and dark energy then we observe of visible matter and energy? Or is it just because it's pointless to speculate about variety when we can't yet detect any of it.

 

[Nabeshin]

Or is it just because it's pointless to speculate about variety when we can't yet detect any of it.

Mainly this. Certainly some people have thought about the concept of a whole 'dark sector' comprising many different particles similar to our own, except that they interact only weakly with our own sector. The difficulty is that these models are so complicated and it's so difficult to measure anything about dark matter to begin with that it just confuses the matter. The natural direction is to propose the simplest explanation for the phenomena and then see if it fits the data (it seems to, so far).

 

[Haelfix]

That's a good question. There is no reason, other than simplicity. When scientists go up against unknown quantities, they look for the simplest most minimal possible model first. Unfortunately there are a lot of very simple models that could potentially work for new physics like dark matter, and there is absolutely no reason that there couldn't be a combination of them that are at work. We don't know, and nature hasn't given us enough clues to figure out.

Very likely, especially for dark matter, there is going to be some amount of give and take, even with older more established physics. For instance, it was speculated early on that normal garden variety astrophysics objects like pulsars, black holes and the like could potentially be a source of dark matter. People have done exhaustive searches (weak lensing etc) to try to 'count' these sources and while it seems like there is not enough of these objects to account for dark matter, we could be wrong by a few percent as well, and therefore the actual amount of missing 'matter' is less than what we currently suspect.