I know, it’s just a theoretical construct right now - but are there any thoughts about how dark matter is structured? it won’t have the tradtional proton-neutron-electron combinations? it’ll have some entirely different structure? have there been any attempts to figure this out yet?
Nobody knows for certain; we don’t really have any solid guesses as to what dark matter is made of, let alone a solid hypothesis amenable to testing. However, most of the time when physicists propose dark matter models, they only contain one type of particle, and it’d be hard to get any more complicated structures (like atoms) out of such a model. (Why not more than one type of particle? Occam’s razor, mostly. The only way we can currently “observe” dark matter is via its gravitational interaction, so as long as you get the matter density right, you don’t need to add further complications.)
As we get more observational data about dark matter and about the particles that might make it up, we might discover that the dark matter “sector” is more complicated than it seems today, and then we might be able to hypothesize about more complicated dark-matter structures. But given our current understanding of dark matter, trying to hypothesize about such things right now would be like a caveman trying to figure out what the Sun is made of.
I believe that I’ve read some articles where certain things have been said that they “might explain X percent of dark matter.”
MikeS seems to know more on the subject than I, but still the point is that “Dark Matter” doesn’t really represent anything but a catchy name for something we don’t know what is. So it might be one thing, it might be eighty different things. You can speculate about “The Furniture in the Room Over There”, but outside of being relatively sure that it’s furniture (or in the case of Dark Matter, matter), there’s no use guessing what any of it looks like until you have a way to confirm it.
Why would you assume that 90% of the stuff of the universe is homogeneous when the 10% we know is so varied?
My vote: a significant amount of dark matter (for certain values of ‘significant’) is Matrioshka Brains. Bingo, the dark matter problem and the Fermi paradox, solved in one stroke! 
Of the 4% (not 10%) of the Universe that’s directly observable, 98% of it is hydrogen and helium (74% and 24%, respectively.) It’s not terribly varied at all.
PossiblyNeutralino
I’d never heard of the conccept before, but taking a look at that Wiki page… If there were even one such structure in the observable Universe, I’d consider that pretty darn significant, regardless of its mass.
And strictly speaking, we know that the dark matter isn’t all of one type. We know with absolute certainty that at least some of it is normal baryonic (that is, protons and neutrons) matter. Everything I can see outside my window right now is dark matter: The ground, the snow, the other buildings, the clouds, all of it. And on a larger scale, there are objects like Jupiter, both in solar systems and (presumably) outside of them. Collectively, these Jupiter-like objects are referred to as MaCHOs (Massive Compact Halo Objects), and some estimates say they may account for as much as 30% of the galactic dark matter. Then there are also neutrinos: I think they’ve been ruled out as the sole form of darm matter (or at least, of the non-baryonic dark matter), but they’re out there, and they have some mass, so they must account for some non-zero, and possibly non-negligible, portion of the dark matter.
true. I meant at the subatomic level, though. And that some of the particles are so much more prevalent than others doesn’t take from the fact that there are many flavours of them.
Most dark matter, you probably couldn’t see or touch at all:
If it doesn’t interact with the electromagnetic force, it won’t interact with light, so you can’t see it. It would look like neutrinos do- they don’t interact electromagnetically, so they’re invisible. You could feel its gravitational pull, so you could orbit around it (but you couldn’t stand on it- a solid surface requires electromagnetic interactions of the electrons in the material repelling the electrons in your feet), but there would have to be a lot of it around in one place for you to notice its gravitational pull.
Some dark matter might be made up of “traditional proton-neutron-electron combinations”- that would be a subset of what is called baryonic dark matter. You can calculate how much baryonic dark matter there can be from big bang nucleosynthesis (basically, looking at the abundances of elements created in the Big Bang), and that rules out most dark matter being baryonic. So we think most dark matter isn’t made up of protons, neutrons, and electrons like normal everyday matter.
I suspect that the egos of physicists actually have some mass composed of something non-baryonic, and that’s what makes up the non-baryonic dark matter.
I also think that a fair portion of baryonic dark matter is made up of sock stars. The socks that get lost in your dryer somehow teleport to the outer reaches of the galaxy, where they meet up with other lost socks. When enough socks get together, gravity pulls the collection of socks into a sphere, which I call a sock star.
Maybe I’m just totally ignorant of atronomy here, but I suspect that a lot of the “dark matter” will turn out to be burned-out stars that no longer give off any significant amount of energy. Because they’re not luminous, and not really really close to earth, astronomers can’t detect them yet.
That’s my theory, at least.
I’m going to take a wild flyer of a guess and accept $1 bets on it from any takers, but I just have a feeling about this:
“Dark matter” is baloney. A fundamental mistake is being made. It will end up being the “lumiferous ether” of the modern age: stuff every physicist was convinced existed that, as it will turn out, doesn’t.
That could account for the baryonic dark matter, but we know that a significant percentage of dark matter is non-baryonic.
That is, of course, entirely possible. If that turns out to be right, I hope that Mr. Neville figures out the new theory of the universe, so he would get a Nobel Prize in Physics. 'Cos then he’d probably let me touch it, and I could go to bed with a Nobel Prize winner
Diceman, burned-out stars would be baryonic matter, and the total amount of that is limited (as Anne Neville stated) by big bang nucleosynthesis. Of the portion of dark matter which is baryonic, sure, at least some of it is dead stars, and it wouldn’t exactly be crackpot to say that it’s a pretty big chunk. But there’s still significantly more non-baryonic dark matter than baryonic.
RickJay, I’ll personally place one of those bets, but you’re not alone in thinking that. One Mordehai Milgrom has been pushing a theory called MOND, which would explain intragalactic dynamics without resort to dark matter. Personally, I don’t think it holds water (recent results on interactions between galaxies in clusters seem to back up dark matter but not MOND, and I think MOND has some consistency problems with binary clusters), but even I will admit that he’s apparently stumbled upon some interesting phenomena (he’s found some patterns among the rotation curves of many galaxies which would, in fact, be accounted for by his theory).
Could it look like this thing?
an ignorant’s question: If dark matter is so prevalent, wouldn’t that mean that we are surrounded by it? that my laptop and my nose are also 90-95% dark matter? If it isn’t, what determines where it goes and where it doesn’t? Why are we in a bubble of non-dark matter?
Exactly. To explain for those who somehow haven’t seen this yet:
There are two big clusters of galaxies colliding. They’ve each got a bunch of dust floating around them. The stars don’t tend to hit each other, but the dust clouds – and anything else made of baryonic (“normal”) matter that doesn’t normally glow – rub up against each other, heat up, and start glowing. The red patches mark where the glowing gas is.
However, we can also study how light from sources behind the clusters is slightly tweaked by passing through their gravitational field. This tells us where stuff is gravitating. The blue patches are where that stuff is. The one on the left, for instance, is the cloud of dark matter from the cluster on the right that didn’t get slowed down and just kept going on through the other cluster, and vice versa.
Just to be clear, those clouds cannot be dead stars, planets, dust, or any other normal matter. If they had been they would have slowed down and heated up like everything else did.
Your laptop and your nose are baryonic dark matter- they don’t emit enough light for astronomers in other galaxies to observe them directly.
Neutrinos, which are one form of non-baryonic dark matter, go right through us all the time. Wikipedia says more than 50 trillion of them go through you every second.
If something doesn’t interact with the electromagnetic force, it’s more likely to go through you than to make up a part of you- you and your laptop are held together by electromagnetic forces.
Okay, you’re on.
I bet you $1 that the theory of “Dark matter” comprising the majority of matter in the universe will be almost wholly rejected by January 1, 2037.
Woo hoo, I’m already planning how to spend my dollar!