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So Tell me about.....

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Dark Matter, is it the fabric of the universe?

Why is it invisible and yet it's being looked for underground? If you cannot see Dark matter without specialized laboratory equipment what's the point looking under ground?


Do the answers to the universe lie in dark matter?
Or is it cods wallop?

Views?
 
There are a couple of different reasons physicists think dark matter must exist. One is that galaxies spin at a rate that should rip them apart based on the amount of visible matter. Physicists assume that there must be more matter that we don't see to provide enough gravitational attraction to hold them together.

There are also aspects of the large scale structure of the universe that seem to argue for the existence of dark matter although I don't really understand that part of it.

As to what dark matter is, that is still a matter for debate. One possible source of additional mass would be neutrinos provided neutrinos have mass. Neutrino detectors are essentially large underground tanks of pure water surrounded by light sensors. Neutrinos pass right through matter (they can fly right though the entire earth) and only rarely interact with it. Such rare interactions produce flashes of light which is what the neutrino detectors are looking for. The evidence seems to suggest that neutrinos do possess mass although I don’t think the amount of mass they contribute is sufficient to account for all the dark matter that current observations require. So there must be other things as well (true dark matter - whatever that is).

If you want to know more about this stuff, you’ll have to wait for a reply from someone like Stimpson J. Cat or Tez who actually knows something about the subject. :)
 
espritch pretty much got it.

We believe in dark matter primarily from watching the dynamics of stars in galaxies (the far outer stars/hydrogen have a reasonably constant velocity i.e. independent of how far they are from the center), and also from clusters of galaxies. We can also see gravitational lensing by dark matter "halos" - the blobs of dark matter which are (we conjecture) centered on the luminous matter but extend out about 10 times further.

In the last couple of years the story has gotten a lot weirder - we now also measure the effects of "dark energy" - a different kind of stuff which is actually causing a repulsive gravitational effect (see the thread "Cosmological Anthropocentrism" I started). Initially most peoople's reaction is "why two mysteries not one" - and many attempts have been made to show that the effects we attribute to dark matter and dark energy could all be caused by one "dark mystery field". These have failed - and recently a paper was published which pretty much nipped in the bud almost any attempt one might make in this direction.
 
Pie, why don't you ever do any of your own research? All you seem to do is post open-ended questions to people on an Internet message board. :rolleyes:

Your entire series of "tell me about..." threads is really irritating.
 
Hazelip said:
Pie, why don't you ever do any of your own research? All you seem to do is post open-ended questions to people on an Internet message board. :rolleyes:

Your entire series of "tell me about..." threads is really irritating.
Click to expand...

Then don't respond to them.

If you are irritated by people asking good-natured open questions on a public internet forum then you have a problem.

:(
 
Hazelip said:
Pie, why don't you ever do any of your own research? All you seem to do is post open-ended questions to people on an Internet message board. :rolleyes:

Your entire series of "tell me about..." threads is really irritating.
Click to expand...

You irrate me, but thats another open ended question for another day :D


Open ended because I was interested on what are the curent views on dark matter.



Is it a crime now and against the rules to learn more about things now on this forum?:rolleyes:
 
UndercoverElephant said:


Then don't respond to them.

If you are irritated by people asking good-natured open questions on a public internet forum then you have a problem.

:(
Click to expand...
;) thanks UCE.
Well said that big blue elephant. A well echoed sentiment.
 
Problem is, there is turd-carts full of stuff on the internet and only about 1% is true/usefull/accurate. The great thing about the Science forum is that if someone has a question about something they are not an expert in, they can post here and get expert input.

Its also interesting for others to follow the thread and add to our knowledge which otherwise might not happen.

So there!

:cool:
 
Tez said:
espritch pretty much got it.

We believe in dark matter primarily from watching the dynamics of stars in galaxies (the far outer stars/hydrogen have a reasonably constant velocity i.e. independent of how far they are from the center), and also from clusters of galaxies. We can also see gravitational lensing by dark matter "halos" - the blobs of dark matter which are (we conjecture) centered on the luminous matter but extend out about 10 times further.

In the last couple of years the story has gotten a lot weirder - we now also measure the effects of "dark energy" - a different kind of stuff which is actually causing a repulsive gravitational effect (see the thread "Cosmological Anthropocentric" I started). Initially most people's reaction is "why two mysteries not one" - and many attempts have been made to show that the effects we attribute to dark matter and dark energy could all be caused by one "dark mystery field". These have failed - and recently a paper was published which pretty much nipped in the bud almost any attempt one might make in this direction.
Click to expand...
Thanks Tez,

I just read or watched(?) about dark matter and probably watched it. They used a special device to view the dark matter, then they went on about looking for it underground in the earths bowels and that didn't seem to make any sense to me it was being investigate at the Boulby Mines. Then it just became confusing because they started on about *wimps(Weakly Interacting Massive Particles) *that make up the heavy particles of dark matter and thats how they can see it(?)

I know it was discussed how starlight was distorted by the gravitational effects of dark matter but that was not discussed at any length.

All in all it was short and very briefly mentioned.

Is it supposed to be that, 90% of the universe is made up of the invisible dark matter?


I am currently reading
here and
here

Are these any good ?
 
Pretty much everything that we can see in the universe, we see due to starlight.
Within galaxies, we see hugh dust lanes--streaks of dust partially blocking the light of stars behind them. These dust lanes are big--really big--and messy-looking. Have a look at http://antwrp.gsfc.nasa.gov/apod/ap010203.html and http://antwrp.gsfc.nasa.gov/apod/ap980116.html to get an idea what a dust lane looks like.

What would happen if there were a bunch of dust spread just thinly enough to not clump together and form stars? Well, it would still, as a whole, exert a gravitational force on things far away from it. More interestingly, if any strong gravitational center, like a heavy star, were to come sweeping through the middle of it, the resulting gravitational disturbance might cause some of it to start clumping together and forming stars in the wake of the intruder.

In general, information about astronomy and astrophysics which comes from the NASA.GOV domain is reliable. Others may be, as well, but I haven't checked them out.
 
As a kid, I was usually the one who asked the dumb question revealing that I didn't understand what was going on. For this I was mocked by my classmates. Who would later get me alone in the playground and ask me to explain it to THEM!

I now encourage anyone I train to appoint one of the group to ask "dumb" questions- even if he DOES understand. Noone laughs at him, or they get asked to explain.That way we don't get people who turn out to be ignorant when we are in a serious situation where understanding may save someone getting hurt.

Keep asking the questions, PIE, I'm learning from them too. I'd agree with Hazelip that it's also worth checking other sites. Much of what you see on JREF comes from widely read generalists, rather than true specialists. Some of whom are kids. Above average bright kids, mostly, but still kids. No one is guaranteeing to be 100% right or up to date. It's usually a great place to start though.
 
DrMatt said:
Pretty much everything that we can see in the universe, we see due to starlight.
Within galaxies, we see hugh dust lanes--streaks of dust partially blocking the light of stars behind them. These dust lanes are big--really big--and messy-looking. Have a look at http://antwrp.gsfc.nasa.gov/apod/ap010203.html and http://antwrp.gsfc.nasa.gov/apod/ap980116.html to get an idea what a dust lane looks like.

What would happen if there were a bunch of dust spread just thinly enough to not clump together and form stars? Well, it would still, as a whole, exert a gravitational force on things far away from it. More interestingly, if any strong gravitational center, like a heavy star, were to come sweeping through the middle of it, the resulting gravitational disturbance might cause some of it to start clumping together and forming stars in the wake of the intruder.

In general, information about astronomy and astrophysics which comes from the NASA.GOV domain is reliable. Others may be, as well, but I haven't checked them out.
Click to expand...

Ty :D will add the sites to the many I have already accumulated.

Now that latter part sounds scary.
By heavy star do you mean a black hole?

Looking at the dust lanes it strikes me they resemble something along the likes of our clouds. that has got me thinking is there weather in space? I know there is solar wind, but is there anything else?
 
Jon_in_london said:
Problem is, there is turd-carts full of stuff on the internet and only about 1% is true/usefull/accurate. The great thing about the Science forum is that if someone has a question about something they are not an expert in, they can post here and get expert input.

Its also interesting for others to follow the thread and add to our knowledge which otherwise might not happen.

So there!

:cool:
Click to expand...

There are these places, you might have heard of them, they actually pre-date the Internet... They're called LIBRARIES! :rolleyes:
 
Why they look underground.

With respect to looking dark matter in the bowels of the earth, it is due to the way certain types of dark matter interact.

Their are two types of dark matter.

MACHOs - massive compact hallo objects

MACHOs or really big but don't emit much radiation. A black hole that is not acreting any matter doesn't give off x-ray bursts and as such is barely detectable. So to find a MACHO one needs to see it obscur stars behind, or in the case of some black holes they notice the lensing effect of gravity.

WIMPs - weakly interacting matter particles

This is the type they look for underground. These particles don't interact with other things that much. They have no charge, and the ability to pass through damn near anything. By looking for them underground, the earth acts like a filter to everything except the WIMPs. Thus the detectors don't have to be worried about be overwhelmed by all the other radiation at the surface of the earth.

A search on "neutrino observatory" turned up The Sudbury Neutrino Observatory.

Walt
 
Thanks Walter Wayne I will read that link later.


Hazelip you mean touch dirty books eugh:eek:.

My library is so outdated it hasn't even got a copy of that new fangled book Romeo and Juliet by the rising star Shakespeare:D

Small libraries like my local one, does not supply books like that it caters for the elderly with romance, knitting patterns and gardening books.

The Internet is the only source I have available locally unless I blow a fortune at Amazon. So I ask learn and then either assimilate information or move on to something else(providing I recall what I learnt in the first place):p
 
Two of the three 2002 Nobel Prize in Physics recipients,
Raymond Davis and Masatoshi Koshiba, received the prize for their work on the "Solar Neutrino Problem".

The neutrino flux has been measured to see if it agrees with theoretical calculations based upon our understanding of the workings of the Sun and the details of the Standard Model of particle physics. The measured flux is roughly one-half of that expected from theory.... This discrepancy between theory and observation is the "Solar Neutrino Problem."

Thanks to recent measurements, particularly those with the Super-Kamiokande detector in Japan and the Sudbury Neutrino Observatory in Canada, there is probably an answer...the neutrinos themselves seem to behave in a way unexpected by the Standard Model of particle physics.
Click to expand...

More here:
http://www.gsfc.nasa.gov/scienceques2002/20030117.htm
 
Voob said:
Two of the three 2002 Nobel Prize in Physics recipients,
Raymond Davis and Masatoshi Koshiba, received the prize for their work on the "Solar Neutrino Problem".



More here:
http://www.gsfc.nasa.gov/scienceques2002/20030117.htm
Click to expand...

Thanks voob and thanks for the birthday greet :D

Interesting it does say in that link, that solving one problem opens up another this one being is how to redefine particle psychics to include the neutrinos results. I must say that is a first I have seen in a long while that is actually going to alter a previous used formulation or theory etc.
 
From DrMatt's link:

The Radio Plasma Imager instrument provides a three-dimensional view of the plasmasphere by sounding it with radio pulses, like an ultrasound image of the human body. To accomplish this, it uses the longest antennas ever deployed in space, longer than the height of the Empire State Building.
Click to expand...

:eek:

I hadn't heard about this before. That's an interesting article.
 
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