What is Dark Matter?

originally posted by: Toolman18
Come on. That's just a ridiculous thing to say. Dark matter can be anything we want it to be right now. I've yet to hear a good idea about what it is. But soon I believe we will know

There are lots of good ideas. Here are some of the dark matter candidates from a dark matter expert:

www.abovetopsecret.com...

originally posted by: ErosA433
a reply to: Arbitrageur

Nail on head there Arbitrageur, there are different forms of dark matter, and much close examination of space has been performed and lots of different theories with different shares of matter content. They point as you say to this unobserved fraction being about 75-80% of the matter content of the universe.

As for what it is, there are as many theories as you can think of, and an interesting interplay between what the theories are and how they behave. There is a great image that shows this...

That is not my picture, I grabbed it from a blog after I saw it presented by a theorist in a conference.... To say that dark matter theory is closed minded is to deny that theory didn't put all its eggs in one basket but actually many baskets hehe

It's almost certainly more than one thing. As bedlam suggested, some is probably neutrinos. One type of dark matter is what you're standing on, the Earth, and other planets. Brown dwarf stars can only be seen when they are relatively lose in cosmic terms, so we don't really know how many brown dwarfs there are and how much of the dark matter they make up but it's probably at least some.

The problem is even after we make our best guesstimates of all these obvious sources, it still doesn't add up to the effect we're seeing so that's why we have so many other ideas on that chart about what else might be involved, such as other types of particles we haven't detected yet for example.

By the way here's a good thread by the ATS dark matter expert on the experiment he's working on to detect to try to detect these particles:

Direct Dark Matter Detection [A review]

Can you see gravity? Me neither. I guess since we can't observe it gravity doesn't exist. Except black holes! We can see that gravitational effect. At the same time gravity should be smashing this universe together with all its mass. But not happening. These things can be measured and you look like a fool arguing otherwise

My personal hope is that whatever it's finally discovered to be is really off-scale quirky. A new equation of gravity, or cross-universe gravity shadows, or something that's much more unexpected and screwy than WIMPs or MACHOs with neutrinos and some rogue planetary bodies.

a reply to: Parthin

But what if this dark matter is ordinary matter?

There's a term for that: 'baryonic dark matter'. And yes, some 'dark' matter is indeed ordinary matter that absorbs electromagnetic radiation or is transparent to it, and is therefore invisible to us. Examples would include 'massive compact halo objects' or MACHOs, objects like unassociated planets, neutron stars and brown dwarfs.

However, we know that most dark matter is of a different kind entirely. It is not baryonic and does not form atoms. It is not electrically charged (it would be detectable if it were). See also this post by wildespace in a different thread. It explains why ordinary circumstellar debris (Oort cloud objects, etc.) cannot be dark matter.

Finally, the amount of baryonic matter is strictly limted according to current cosmological theory:

The theory of Big Bang nucleosynthesis, which predicts the observed abundance of the chemical elements, predicts that baryonic matter accounts for around 4–5 percent of the critical density of the universe. In contrast, evidence from large-scale structure and other observations indicates that the total matter density is about 30% of the critical density. Wikipedia

I was going to say Bill Cosby.

originally posted by: NthOther

originally posted by: Parthin

This would account for the mass that our telescopes cannot see.

I'm not much of a "science man", but to me it would seem that if we can't see it...

...it probably doesn't exist. At least that's what scientists say about everything else they can't observe and quantify.

But that would mean their equations are completely wrong and they really have no idea what they're talking about.

And we certainly can't have that now, can we?

Scientists do not say that. We cannot see particles and quantum effects but they are there and we hypothesised about their existance long before we could observe them or their effects. We could not see the Higgs (and still cant) but we know it exists and we thought it existed for 60 years.

But yes, scientists are thge bad man...boooo science!!! Bad science! How dare you make us live longer, give us better healthcare, better medecine, MRI machines, comet landings, better transport, fast computers, the internet....

You just cant trust scienctists can you...all a bunch of lying, cheating scumbags in the gubments pocket (sarcasm)

originally posted by: NthOther

originally posted by: Bedlam

But I agree, you're not much of a science man, or you'd understand a bit more of the process.

What "process"?

Making things up?

Oh dear.....i reserve a special place in my disdain corner for people who benefit every single day from science and yet hold said science/scientists in such low regard. Ignorance at it's finest.

a reply to: 3danimator2014

Reminds me of this:

originally posted by: GetHyped
a reply to: 3danimator2014

Reminds me of this:

Exactly.

Whats hilarious is these people are spewing their rubbish using computers, which use transistors. Cant exist without transitors. And transistors are a purely quantum mechanical device. And QM is WAY out there...yet undeniably correct. They have no concept of science being self correcting and scientists not being afraid of being wrong.

a reply to: Parthin

Nobody knows, hence the term.

originally posted by: NthOther

originally posted by: Parthin

This would account for the mass that our telescopes cannot see.

I'm not much of a "science man",

Right here. This is where a wise person would stop talking and open their ears.

a reply to: NthOther

I'm not much of a "science man", but to me it would seem that if we can't see it...

...it probably doesn't exist.

Can you see gamma rays? Do they exist? How about atoms? Do thoughts exist? I assume you were trying to be glib, but the way you say it is pretty naive. I would say you are definitely "not much of a science man."

V

originally posted by: NthOther
...But that would mean their equations are completely wrong and they really have no idea what they're talking about.

And we certainly can't have that now, can we?

"Science knows it doesn't know everything, or else it would stop"
--Dara Ó Briain


You can't see the wind, but you can see the effects of the wind. We can't see what "dark matter" is (if it is anything), but we can see that the large-scale structure of the universe is being affected gravitationally by something unknown. That "something" could be an unknown form of matter, which may be as "unseeable" as the wind, or it may be that our understanding of gravity is wrong.

Either way, science is embracing the fact that it knows that it doesn't know everything. One of the whole points of the scientific method is to attempt to poke holes in hypotheses in an attempt to prove that science does not know everything.

The idea that they will find out something they didn't know before -- INCLUDING learning that what they though they knew was incorrect -- is what keeps science going.

I'm not a "science man", but here's my uneducated criticisms of a scientific field of research.

originally posted by: Parthin
According to the estimated gravity due to the observed matter of our galaxy, it should fly apart as it rotates.
a reply to: intrptr

Because of gravity, it can't "fly apart". Thats why objects form and stay together, because of gravity.

I didn't find the post by wildespace convincing. Saying all objects are detectable doesn't mean we can detect them. We can detect only the largest Kuiper Belt objects, yet we assume most of these relatively close objects are undetected, due to their small size. I like your some of this, some of that theory. The gravitons from another dimension idea of wildespace involves a physics we do not have yet, yet it is in-line with the idea that gravitons, whatever they are, exist partly in another dimension. Mbrane thoery includes 11 dimensions.
a reply to: Astyanax

With the observed motion of our galaxy , the observed matter it contains is insufficient to keep it together. The star systems should be spinning off into intergalactic space. Yes, there's gravity, but there must be MORE gravity than we can account for, thus, "dark matter" to generate that gravity.
a reply to: intrptr

Photons have no mass.
a reply to: Toolman18

originally posted by: Parthin
Photons have no mass.
a reply to: Toolman18

And yet they are affected by gravity. Im not sure that photons are massless...i think we will find out that they do mingle with the Higgs field in soime way. but this is just a guess from what i have learned.

EDIT: i know they say that its the space time that is affected by gravity and hence the photos, but i have a feeling there is more to it than that.

a reply to: Parthin

Saying all objects are detectable doesn't mean we can detect them.

You're not detecting individual objects. You're seeing infrared light in galactic halos, and you know that comes from, essentially, baryonic matter losing heat. You don't have to see each individual rock and pebble (and gas molecule).

The main point of my post is that we know that most dark matter isn't the same as 'ordinary matter'.