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Nerdman20
2005-Mar-04, 07:47 PM
I have been getting the newsletter for something like 2 years now and there has been a lot of talk about Dark Matter and muons. What exactly are these things, in laymans terms. I consider my self a smart person but whenever I see dark matter or anti-matter it goes right over my head. If someone could explain this in say... High School Terms then it would be a big help for me.

antoniseb
2005-Mar-04, 08:48 PM
Dark Matter in say... High School Terms

We don't know what dark matter is, but it seems to be there, based on gravitational influence.

Currently the best guess as to what it is involves particles that are very heavy, which we haven't seen in the lab yet, becuase our particle accelerators don't get up to energies that high [but they will soon]. The idea is that there may be some kind of particle that doesn't interact much at all with any of the particles that are still left in the universe. There may be many Earth-mass Solar-System-sized self gravitating clouds of these things [called neutralinos] orbiting the galaxy collectively causing enough gravitational attraction to make the spiral arms move much faster than they would if the only matter around was the matter we can detect becuase it gives off light.

If you want more details I can give them, but it stops being so dumbed down.

Nyrath
2005-Mar-04, 09:37 PM
When you have objects in space orbiting each other, you can use Newton's Laws to calculate the mass of both objects. So astronomers can measure the rotation rate of stars composing a galaxy and calculate the masss of that galaxy. And they can measure the orbits of galaxies around each other and measure their masses that way.

The trouble is, you can also estimate the mass by counting the stars and nebulae composing a galaxy. And when you do, you get a different number than using Newton. A lower number.

So obviously there is a lot of matter there we cannot see. "Dark" matter. What is giving the astronomers fits is that there does not seem to be anything that could generate all that gravity yet still not be seen. That is why they are clutching at straws with wild hypothesis about neutrinos and other exotic particles.

alainprice
2005-Mar-05, 03:16 AM
Anti-matter is a different story. We have observed anti-matter in particle accelerators. We have even created anti-matter atoms, anti-hydrogen.

Anti-matter is the same as normal matter, except it has opposite charge. Anti-matter does also touch other quantum properties, but not anything important to us. So an anti-electron(called a positron) is a positive electron. An anti-proton is a negative proton. A photon is its own anti-particle. When a particle comes into contact with its antimatter equivalent, annihilation occurs, and both are transformed into energy.
A PET scan detects positrons in order to map the internal structure of the body.

nomadicdemon
2005-Mar-05, 10:31 PM
Thx antoniseb.....I hae been wonderin that too, thx for dumbing it down...lol

astromark
2005-Mar-06, 10:32 PM
;) All good answers, and then me....
Looking in your own back yard answers this question. I often wonder why these things are not so obviouse to the rest of humanity. Yes thats a good description of anti-mater, but I take exeption to the notion that it is of no concern to us. Uninportant. I can not agree. It may be the way we are going to cross the universes vast distancess quickly. If the comming together of these particals producess nothing but energy. . . . :rolleyes: Its going to be frought with danger, and I want them to try this some place else. :blink:
As for dark matter. . . If it is any material that does not radiate visable light. thats simple enuff. Look across this solar system, only our sun is radiating enuff energy to be seen from any distance away. So all the planets, asteriods, comets gases, and dust are invisable. That area containing the ort cloud, invisable.... but,
With very sencitive equipment can we measure the energy out flow from Jupiter, or even the heat generated from this earths core? It may not be so dark as our equipment becommes more sencitive. If we could turn on the lights, it wont be so dark. Enlightning even. Look at how we can now see exo-planets, unherd of sencativaty and more to come... Mark.

Nyrath
2005-Mar-07, 12:34 AM
Originally posted by astromark@Mar 6 2005, 10:32 PM
As for dark matter. . . If it is any material that does not radiate visable light. thats simple enuff. Look across this solar system, only our sun is radiating enuff energy to be seen from any distance away. So all the planets, asteriods, comets gases, and dust are invisable. That area containing the ort cloud, invisable.... but,
With very sencitive equipment can we measure the energy out flow from Jupiter, or even the heat generated from this earths core? It may not be so dark as our equipment becommes more sencitive. If we could turn on the lights, it wont be so dark. Enlightning even. Look at how we can now see exo-planets, unherd of sencativaty and more to come... Mark.
I fear that you do not understand.

Dark matter apparently does not radiate visible light, infared, ultraviolet, radio, x-rays, gamma-rays or any other electromagnetic radiation. Which is sort of impossible for normal matter to do.

astromark
2005-Mar-07, 02:50 AM
Is'ent that what I said; I am not missing the point here. Do I need to spell it all out ( pun intended ). If we cant see it, its dark matter. And allthough you could go on about all sorts of egsotic things in our universe that cant be seen. For this 'Dumb it Down Dark Matter' I stand by what I said.

vet
2005-Mar-07, 03:17 AM
this nasty issue may be saved, simply by permitting 'multiverse equals'---able to 'interract'---'boundry areas of equal quanta of multiverse'---not the best of ideas, but it certainly tracks history.

Nyrath
2005-Mar-07, 03:35 AM
Originally posted by astromark@Mar 7 2005, 02:50 AM
Is'ent that what I said; I am not missing the point here. Do I need to spell it all out ( pun intended ). If we cant see it, its dark matter. And allthough you could go on about all sorts of egsotic things in our universe that cant be seen. For this 'Dumb it Down Dark Matter' I stand by what I said.
I sort of see what you mean. ;)
But the point is Dark Matter is probably not ordinary garden-variety matter that we don't happen to see. Much as it pains scientists, Dark Matter apparently is some kind of weird new matter not previously encountered.

Planetwatcher
2005-Mar-07, 04:45 AM
Dark matter apparently does not radiate visible light, infared, ultraviolet, radio, x-rays, gamma-rays or any other electromagnetic radiation. Which is sort of impossible for normal matter to do.
What if dark matter is dark simply because it absorbs light and energy rather then reflecting it. There are types of material which can do that.

That would explain why we can't see or detect it. And there can be any amount of it out there. But I suppose that is too simple to consider. ;)

antoniseb
2005-Mar-07, 11:58 AM
Originally posted by Planetwatcher@Mar 7 2005, 04:45 AM
What if dark matter is dark simply because it absorbs light and energy rather then reflecting it.
If it absorbed light, it would get warm and give off some lower frequency (infrared) light. It also needs to be something that doesn't interact with other matter much, so that it doesn't get trapped into the disk parts of galaxies.

Moseley
2005-Mar-07, 02:56 PM
Nice topic and useful to those of us who want to learn but not cosmologists. The recent discovery of a 'dark' galaxy would seem to indicate that dark matter clumps together (see no technical terms here) in a similar fashion to normal matter, although I appreciate we do not know how this galaxy formed or why there is no normal matter there, as yet.
Do we know if the mass of our galaxy is accounted for entirely by normal matter or is there a 'dark' portion?

Nyrath
2005-Mar-07, 04:24 PM
Originally posted by Moseley@Mar 7 2005, 02:56 PM
Nice topic and useful to those of us who want to learn but not cosmologists. The recent discovery of a 'dark' galaxy would seem to indicate that dark matter clumps together (see no technical terms here) in a similar fashion to normal matter, although I appreciate we do not know how this galaxy formed or why there is no normal matter there, as yet.
Do we know if the mass of our galaxy is accounted for entirely by normal matter or is there a 'dark' portion?
Well, yes, dark matter has to clump together. This is because it is subject to gravity. If it was not subject to gravity, we would not have all these galaxies misbehaving and we wouldn't be worrying about dark matter in the first place.

The last I heard, Yes, our galaxy is also misbehaving and must be full of dark matter.

sirius0
2005-Mar-08, 03:46 AM
Hello my first post!
i seem to recall that our galaxy is misbehaving because the stars orbiting the centre of our galaxy do so at the same angular velocity as those closer in. This requires more gravity ie matter than is visibly available. In other words our galaxy is more like a wheel than the solar system. i mean that all points in a wheel complete a revolution in the same time the hub spins slowest. Whilst a solar system has bodies orbiting a centre of gravity the sun. The slowest are actually further out. Dark matter is seen as an explabnation as to why the galaxy is 'sticky' enough to act like a wheel.

I have tried to touch on dark matter by explaining an effect that can be seen i.e. a spiral galaxy would not maintain the spiral look if the stars did'nt all maintain the same revolution rate. Perhaps we blame somthing we haven't seen yet to explain our ignorance of some different kinds of space that may be out there. Sort of like the old mythologies.

mike Dark Matter
2005-Mar-08, 09:05 AM
As I understand it, there is more gravity in the universe than the visible matter accounts for.
My prposition is that if, as we are being led to believe, we are only one of a multitude of universes existing at the same time, could it not be that the gravity exerted could come from these other but unseen galaxies in a parrallel universe?
The parralell universe maybe smaller than our own. The other thought could be that we are between a number of parallel universes, all of equal size and their gravitational influence is what we percieve as 'Dark Matter'.

I rest my nutrino's

astromark
2005-Mar-08, 11:35 AM
Where is the evadance that other universess evan exist.

jsc248
2005-Mar-08, 03:58 PM
:( Hi Gang,
I think that we are missing a very simple point here.
Nobody, layman or scientist, knows what dark matter really is.
We know that it exists and that it exerts a gravitational force on "ordinary matter" but the simple fact is we don't know what it is.
Exotic particles,muons or neitrinos-we are still not certain and it could be a while before we find out. Maybe us amateurs cpould put a coherent theory forward, any takers?
jsc248.

sirius0
2005-Mar-08, 09:31 PM
Originally posted by sirius0@Mar 8 2005, 03:46 AM
Perhaps we blame somthing we haven't seen yet to explain our ignorance of some different kinds of space that may be out there. Sort of like the old mythologies.
Perhaps the space around galaxys like ours are different. It was recently demonstrated that the earthwarps space as it rotates. i have often thought that spiral galaxys like ours are reminisent of drain turbulence, quite ordered like a rotating wave with a period and nodes and antinodes. What if the rotation of the galaxy, including the dense centre, causes a distortion in space that is responsible for the spiral form? The antinodes could then be a place of matter concentration. In other words gravuty or some other effect could in this situation have an angular dependancy allowing it to have a greater concentration to a greater distance than if it is uniform for a given radius. Could this explain the apparent lack of matter? Doesanyone know exactly how they do there calculatuions presently? Or a text?

Guest_mnj
2005-Mar-09, 12:57 AM
Dear all,

As far as I have understood, there is two way of determinig mass of a
galaxy
1) from its orbital motion using laws of mechanics (is ther any
correction due to general theory of relativity?)
2) calculating the mass of all the stars from observational data and
then summing up.
the mass 1 is greater than mass 2 and so we conclude that some mass is
observationally undetectable--this corresponds to the dark matter.

Am I right ? But my question is what is the dark matter actually ?
Are the comprised of any new particle instead of baryons, mesons,
leptons etc.
of our known visible world?
OR the are simply our known matter in an extremely condensed form i.e.
Black Hole?

astromark
2005-Mar-09, 05:00 AM
:rolleyes: Guest, I agree with your thoughts here, but expect to be blowen out of the water for this view. As I said befor, If we cant see it, its dark matter. I dont understand why some believe its some egsotic sort of mater. . . no proof for this balief . . . Not hidden mater, Not parallel univers, just dark mater, ( unseen ).

400poundgorilla
2005-Mar-09, 11:03 PM
Guest, Astro...

I wouldn't be one to blow either of you out of the water for those views. I don't think we really have the estimates of mass anywhere near correct even for what we CAN see. But if we are fairly accurate, then I would speculate that this Dark Matter is much less exotic than some would lead us to believe. I particularly like the analogy to the wave ripples "drain turbulance" the drain that Sirius proposed. I'd like to hear more point/counterpoint on that. :huh: