what does dark matter look like?

[gib65]

If I had a clump of dark matter in my hand, what would it look like? Would it be black or invisible?

[Fred56]

A. You would be unable to 'hold' such a thing. Dark matter does not interact with the EMR spectrum, so there's no electric or magnetic device we can use to 'see' it. You are probably surrounded by some though. How much, and 'where' it is exactly are kind of meaningless, because there's a big problem observing or measuring it. It doesn't interact with ordinary matter, except, presumably, it has mass, and therefore inertia. If you could build a hand-held gravity wave detector, your chances might go up a bit. It's a theoretical explanation for some observed behaviour of distant gravity-bound objects (galaxies and galaxy clusters).

[Mr Skeptic]

It would be invisible and go through your hand.

[Severian]

It doesn't interact with ordinary matter, except, presumably, it has mass, and therefore inertia.

 

Not necessarily. It could very well have a weak interaction, like neutrinos have.

[gib65]

So do you mean to tell me that this stuff is like "heavy ghosts"? It doesn't interact with ordinary matter yet it succumbs to the force of gravity? So what would a handful of this stuff do if it was near the surface of the Earth? Would it plummet right through the ground and head straight for the center of the Earth?

[Fred56]

What sort of detector would be needed assuming there's a weak interaction? I haven't really looked all that hard at dark matter/energy 'cause they aren't part of any consistent theory yet are they?

[Severian]

gib65: In principle, yes. If you had a handful of dark matter and 'let go' then it would fall to the centre of the Earth.

 

Fred56: Most new theories building on the Standard Model have a dark matter candidate. In the minimal supersymmetric standard model for example, the dark matter is a stable 'neutralino' - a spin-half particle which has only weak interactions and gravity. Models of clumping predict the dark matter to be about 100GeV/c² in mass, so we might see it when we turn on the LHC.

 

There are also direct searches going on, e.g. http://cdms.berkeley.edu/ and http://xenon.astro.columbia.edu/

[Mr Skeptic]

gib65: In principle, yes. If you had a handful of dark matter and 'let go' then it would fall to the centre of the Earth.

 

Or stay in orbit at ground level?

[swansont]

Or stay in orbit at ground level?

 

That would depend on its original velocity. But "letting go" implies it's at rest WRT the earth's surface, so, no orbit. It should do a good approximation of the "drill a hole in the earth and drop a stone" thought experiment, since there would be no electromagnetic forces (or strong nuclear ones) to act on it. Basically, no friction.

[Mr Skeptic]

That would depend on its original velocity. But "letting go" implies it's at rest WRT the earth's surface, so, no orbit. It should do a good approximation of the "drill a hole in the earth and drop a stone" thought experiment, since there would be no electromagnetic forces (or strong nuclear ones) to act on it. Basically, no friction.

 

You're right, I got confused. It would be a hugely elongated orbit, most of which would be far below ground level. It would have a funny shape too, because it would get less gravitational attraction the deeper it went. I suppose it probably couldn't even be called an orbit if it is mostly inside the earth.

[foodchain]

You're right, I got confused. It would be a hugely elongated orbit, most of which would be far below ground level. It would have a funny shape too, because it would get less gravitational attraction the deeper it went. I suppose it probably couldn't even be called an orbit if it is mostly inside the earth.

 

It seems like you understand this stuff so I would like to ask you a question which I think pertains to the thread greatly, if not sorry.

 

Say you had the ability to make a BEC like the size of the earths moon for instance. If you would or could do that would it by itself interact with dark matter to any more visible degree or even a different then normal degree?

[swansont]

Say you had the ability to make a BEC like the size of the earths moon for instance. If you would or could do that would it by itself interact with dark matter to any more visible degree or even a different then normal degree?

 

No, there's nothing gravitationally special about a BEC.

[Master-Zarex]

To find out more about dark matter, you must solve this:

 

x/2{y2-x~2}xy/3 2x=9u.0[y73.9+x78.0u]

[swansont]

To find out more about dark matter, you must solve this:

 

x/2{y2-x~2}xy/3 2x=9u.0[y73.9+x78.0u]

 

Oh, please. The Trompp conjecture has been thoroughly discredited by BG Gruff.

[CPL.Luke]

tromp conjecture?

 

 

dark matter has to exist in order to account for the age of the universe, if it didn't then the universe would be alot older (younger?)

[thedarkshade]

If I had a clump of dark matter in my hand, what would it look like? Would it be black or invisible?

Invisible and unable to be hold or touched. The adjective dark has been given to it just because we no so little about the issue, so it's still in dark "frames".

[timo]

The adjective dark has been given to it just because we know so little about the issue, so it's still in dark "frames".

That is not the usually given reason for giving it that adjective.

[thedarkshade]

That is not the usually given reason for giving it that adjective.

Something that you don't know anything about it seems dark and gloomy to everyone. It's one reason to name dark.

http://youtube.com/watch?v=WhmO1nrRtsI

even this California University professor names something dark because they yet don't know what causes it!

[swansont]

But it's already been pointed out that dark matter doesn't use the EM interaction. It emits or absorbs no light, hence it is dark.

[timo]

a) He doesn't name it dark because of that but because that's the name of it (although in the case of dark energy it might be true that it's got that name because we don't know much about it - I dunno).

b) He's talking about "dark energy" and one of the first things he sais is that it shouldn't be confused with dark matter.

c) I just spent 10 minutes (and some additional minutes rewatching the parts where he could have said what you claimed he did) watching someone giving a pop-science talk about standard cosmology in the early universe, just to find out a) and b). Please don't post random might-be-related videos claiming someone said X, without properly quoting it.

[thedarkshade]

b) He's talking about "dark energy" and one of the first things he sais is that it shouldn't be confused with dark matter.

I know that they're two different things, but when he's talking about dark energy, he says it's dark because we don't completely know what is causing the expansion of the universe (he clearly knew about Big Bang)!

It's wasn't much for the dark energy or dark matter that I posted that but because of the way he's naming it DARK.

[Norman Albers]

Ii prefer to call it "the search for complete vacuum physics".

 

What exactly do we mean by this term, 'dark matter'? Can I say that we need to account for a gravitational interaction in the large from a field which does not couple to the E&M or mass-fields in the strong force (or weak)? Can I say further that it is characterized by velocities less than c, because it is associated with the large-scale structures of mass? Could it be a nonlinear expression of the gravity fields we deal with?