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hippy4christ
Skeptic Friend

193 Posts

Posted - 07/15/2004 :  12:50:51  Show Profile Send hippy4christ a Private Message
Hello,

I've been trying to understand the concept of dark matter recently, but I'm having trouble. So far it sounds like dark matter is something which hasn't actually been detected and is believed to exist because of unexplained gravitational effects. Some of my questions are: does dark matter take up space? Is dark matter anything more than a theory? Has there been any specific phenomenon which is believed to have been caused by dark matter, and why?

Hippy
[Moved to the Astronomy/UFOlogy Folder - Dave W.]

Stargirl
Skeptic Friend

USA
94 Posts

Posted - 07/15/2004 :  17:20:24   [Permalink]  Show Profile Send Stargirl a Private Message
Hippy

Dark matter was in fact discovered by its gravitational effects and has not been observed directly.
From what I've read its existence is accepted by all but a very small handful of scientists in the astronomical community. All the theories are about the composition of dark matter. The most extreme theory I've heard postulates that dark matter is composed of virtual particles that pop in and out of existence. Another is that dark matter is composed of brown dwarf stars and rogue planets, (planets not gravitationally bound to any star). Those are only two of the many, many theories and since dark matter does not give off any visible light, at least not enough that we can detect it may be a while before we know what actually constitutes the dark matter.

On a final note don't confuse dark matter with dark energy they are two separate things. Dark energy is the force that is causing the universe to accelerate its rate of expansion. Like dark matter dark energy is an observed fact. But like dark matter there are many, many theories to explain dark energy and none of them has an upper hand at this time.

By the way this topic may be better placed in the astronomy folder.

If God did not exist, it would be necessary to invent him - Voltaire
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Dave W.
Info Junkie

USA
26004 Posts

Posted - 07/15/2004 :  18:56:30   [Permalink]  Show Profile  Visit Dave W.'s Homepage Send Dave W. a Private Message
Stargirl wrote:
quote:
By the way this topic may be better placed in the astronomy folder.
Thanks for the reminder!

On with the thread...

- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too.
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Maverick
Skeptic Friend

Sweden
385 Posts

Posted - 07/16/2004 :  05:43:20   [Permalink]  Show Profile Send Maverick a Private Message
As far as I understand, brown dwarves, rogue planets and baryonic matter in other forms, still is not enough mass to be all the dark matter that should be there. Neutrinos could make up some fraction too, but I think more is "needed".

"Life is but a momentary glimpse of the wonder of this astonishing universe, and it is sad to see so many dreaming it away on spiritual fantasy." -- Carl Sagan
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chaloobi
SFN Regular

1620 Posts

Posted - 07/16/2004 :  08:07:57   [Permalink]  Show Profile  Send chaloobi a Yahoo! Message Send chaloobi a Private Message
Scientific American recently had a big article on Dark Matter. And it isn't matter that you simply cannot see with a telescope. It's much more bizarre than that. To understand Dark Matter, you have to understand a little about the nature of the matter we see.

Matter is composed mostly of empty space. An atom consists of a very tiny nucleus - where 99.9% of the mass is contained - and a difuse 'cloud' of electrons which inhabits 99.9% of the volume of the atom. What gives matter it's solid appearance, it's color, texture, etc, is the electormagnetic fields created by the electron cloud surrounding the nucleus. The electron clouds in the matter of your foot resist the electron clouds in the matter of the floor of your house and that's why you don't just pass right through the floor, and the ground, and get pulled by gravity to the center of the Earth.

The current theory on dark matter is that it is electromagnetically neutral. So it is not repulsed by the atoms of your hand, or the world, or anything else and it does not interact with light. So dark matter is all around us, indeed passes right through us all the time, but we can't see it or feel it or detect it in any way. However, Dark Matter IS affected by the force of gravity and DOES produce gravity by virtue of it's mass. It congregates around strong gravity wells like our star and the galactic center. The effects of it's pressence on the movement of objects is the only way it has been detected. By this theory we are in the midst of great clouds of dark matter which pass right through our bodies completely undetectable to us.

Neat theory, ain't it?

-Chaloobi

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furshur
SFN Regular

USA
1536 Posts

Posted - 07/16/2004 :  09:15:38   [Permalink]  Show Profile Send furshur a Private Message
Chaloobi,
Do you know how (if at all) dark matter relates to neutrinos. I know that these particles almost never react with matter, but I believe that it is still 'up in the air' if they have a rest mass. I think that neutrinos were theorized to exist to account for the conservation of momentum in some nuclear reactions. If that is true it is interesting that there are no theorized particles that could account for possible dark matter particles.

PS I thought when the Emperor was killed there was no longer any dark energy... Oh that was the dark force - never mind

If I knew then what I know now then I would know more now than I know.
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chaloobi
SFN Regular

1620 Posts

Posted - 07/16/2004 :  11:31:54   [Permalink]  Show Profile  Send chaloobi a Yahoo! Message Send chaloobi a Private Message
Neutrinos sound like they have more or less the same properties as Dark Matter - with the only possible difference being if neutrinos are massless. Dark matter, if nothing else, has mass, that being the only identifying characteristic.

Another point about Dark Matter - it doesn't interact via the strong and weak nuclear forces either. That's what separates it from neutrons, which are electromagnetically neutral but bind with the nuclear forces. (Anyone who's steeped in Physics please correct me if I'm wrong - I've not been in a physics class for over a decade and my memory sucks...)

EDIT: Didn't they build a neutrino detector that works essentially be detecting the occasional impact between a neutrino and the nuclei of atoms? If they are detectable this way, then dark matter MUST have different properties. If fully 90% of the matter in the universe is Dark Matter, and gravity wells are awash in the stuff, and dark matter has the same properties as neutrinos, one would expect to find a lot of nucleus impacts, no? Perhaps dark matter is some kind of subatomic particle that doesn't even bind into anything as large as a proton - or perhaps some property of atomic nuclei actually repels dark matter particles so no impacts ever occur...

-Chaloobi

Edited by - chaloobi on 07/16/2004 11:37:18
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furshur
SFN Regular

USA
1536 Posts

Posted - 07/16/2004 :  13:07:50   [Permalink]  Show Profile Send furshur a Private Message
When I said that a neutrino only weakly interacts with matter, I meant very weakly:
quote:
The mean free path of a neutrino in water would be on the order of 10x the distance from the Earth to the Sun.

If I knew then what I know now then I would know more now than I know.
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welshdean
Skeptic Friend

United Kingdom
172 Posts

Posted - 07/19/2004 :  03:58:57   [Permalink]  Show Profile Send welshdean a Private Message
I got as far as this;
quote:
Is dark matter anything more than a theory?

in the op and my woo woo, fundie alarm went nuts!!

"Frazier is so ugly he should donate his face to the US Bureau of Wild Life."

"I am America. I am the part you won't recognize, but get used to me. Black, confident, cocky. My name, not yours. My religion, not yours. My goals, my own. Get used to me."

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filthy
SFN Die Hard

USA
14408 Posts

Posted - 07/19/2004 :  04:45:50   [Permalink]  Show Profile Send filthy a Private Message
quote:
Originally posted by welshdean

I got as far as this;
<blockquote id="quote"><font size="1" face="Verdana,Arial,Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Is dark matter anything more than a theory?

quote:
in the op and my woo woo, fundie alarm went nuts!!



Hi Welsh. Hippy has been with us, off and on, for quite a while. He is indeed a YEC, but a YEC with a sense of curoisity, all too often absent in others. He asks good questions.


"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)

"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres


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Brother Boot Knife of Warm Humanitarianism,

and Crypto-Communist!

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Ricky
SFN Die Hard

USA
4907 Posts

Posted - 07/19/2004 :  05:44:52   [Permalink]  Show Profile  Send Ricky an AOL message Send Ricky a Private Message
"The effects of it's pressence on the movement of objects is the only way it has been detected."

Could it be possible that this is due to an unknown force and not unknown matter creating a gravity force? If there has been no observation of this dark matter besides its effects on objects, it seems like there is a vast number of ways to explain it. And with no evidence, how would you know which one is correct?

Why continue? Because we must. Because we have the call. Because it is nobler to fight for rationality without winning than to give up in the face of continued defeats. Because whatever true progress humanity makes is through the rationality of the occasional individual and because any one individual we may win for the cause may do more for humanity than a hundred thousand who hug their superstitions to their breast.
- Isaac Asimov
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Dave W.
Info Junkie

USA
26004 Posts

Posted - 07/19/2004 :  05:58:28   [Permalink]  Show Profile  Visit Dave W.'s Homepage Send Dave W. a Private Message
Ricky wrote:
quote:
Could it be possible that this is due to an unknown force and not unknown matter creating a gravity force? If there has been no observation of this dark matter besides its effects on objects, it seems like there is a vast number of ways to explain it. And with no evidence, how would you know which one is correct?
You go with the most parsimonious explanation that covers all the available data. If the effects look like they're due to gravity, then the simplest idea is that they are due to gravity, and some sort of hidden mass is required to create it. If other data comes along, which show that the effects of dark matter are subtley different than those of ordinary masses, then - perhaps - it would be more correct to describe it as a force all its own.

This kind of thing happens all the time. As far as I'm aware, nobody has ever seen what an actual electron looks like. The "tiny sphere" model works really well, but if we had microscopes with enough resolution, we might find that they actually look like tubby little leprechauns.

Have you ever played a game called "black box?"

- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too.
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Ricky
SFN Die Hard

USA
4907 Posts

Posted - 07/19/2004 :  10:09:40   [Permalink]  Show Profile  Send Ricky an AOL message Send Ricky a Private Message
"If the effects look like they're due to gravity, then the simplest idea is that they are due to gravity, and some sort of hidden mass is required to create it. If other data comes along, which show that the effects of dark matter are subtley different than those of ordinary masses, then - perhaps - it would be more correct to describe it as a force all its own."

But I don't see how the observation "It moves differently" could make it look more like gravity than some other force. I mean, it would move differently in the same way if there was more force acting on it (dark matter) and if some undiscovered force was acting on it. Each of these just add force to the object in question, so the object should (in theory) behave the same way under both. Both equally explain what has observed, and both introduce something new, so you can't use Occum's Razor.

I still fail to see why dark matter is a better explaination than an unknown force.

Why continue? Because we must. Because we have the call. Because it is nobler to fight for rationality without winning than to give up in the face of continued defeats. Because whatever true progress humanity makes is through the rationality of the occasional individual and because any one individual we may win for the cause may do more for humanity than a hundred thousand who hug their superstitions to their breast.
- Isaac Asimov
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Dude
SFN Die Hard

USA
6891 Posts

Posted - 07/19/2004 :  15:25:49   [Permalink]  Show Profile Send Dude a Private Message
Off the main topic, but somebody mentioned neutrinos....

There is some work being done now that has indicated neutrinos may be detectable by some rigid crystals.... and some work on creating a neutrino detector along these lines. (damned if I can find the journal where this work was mentioned.... no conclusive results, and nothing publised or peer-revied on the topic yet, but interesting none the less)

If this type of thing pans out... the possibilities for communications are pretty amazing.

A neutrino radio would not be limited by any kind of solid matter in the way, including the entire planet. Easy and very secure point-to-point communications systems, with no need for satellites.

Ignorance is preferable to error; and he is less remote from the truth who believes nothing, than he who believes what is wrong.
-- Thomas Jefferson

"god :: the last refuge of a man with no answers and no argument." - G. Carlin

Hope, n.
The handmaiden of desperation; the opiate of despair; the illegible signpost on the road to perdition. ~~ da filth
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chaloobi
SFN Regular

1620 Posts

Posted - 07/21/2004 :  06:29:34   [Permalink]  Show Profile  Send chaloobi a Yahoo! Message Send chaloobi a Private Message
quote:
Originally posted by Ricky
"If the effects look like they're due to gravity, then the simplest idea is that they are due to gravity, and some sort of hidden mass is required to create it. If other data comes along, which show that the effects of dark matter are subtley different than those of ordinary masses, then - perhaps - it would be more correct to describe it as a force all its own."

But I don't see how the observation "It moves differently" could make it look more like gravity than some other force. I mean, it would move differently in the same way if there was more force acting on it (dark matter) and if some undiscovered force was acting on it. Each of these just add force to the object in question, so the object should (in theory) behave the same way under both. Both equally explain what has observed, and both introduce something new, so you can't use Occum's Razor.

I still fail to see why dark matter is a better explaination than an unknown force.

It's simpler to postulate that the force in question is gravity - since it behaves just like gravity - and that the mass causing it is somehow 'undectected.' To postulate an entirely new, previously unknown force that acts exactly like gravity but does not originate in mass is a greater change in physics as we know it. While the second idea cannot be ruled out without further evidence, science tends to go with the least radical idea until more evidence is found.

-Chaloobi

Edited by - chaloobi on 07/21/2004 06:32:10
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tim10920
New Member

USA
1 Post

Posted - 07/21/2004 :  08:46:09   [Permalink]  Show Profile  Visit tim10920's Homepage  Send tim10920 a Yahoo! Message Send tim10920 a Private Message
I remembered reading something a while back about dark matter and dark energy possibly being seperate aspects of the same unknown force. I did a google on it and found something on this on newswire.

I hope it helps,

In the last few decades, scientists have discovered that there is a lot more to the universe than meets the eye: the cosmos appears to be filled with not just one, but two invisible constituents –dark matter and dark energy – whose existence has been proposed based solely on their gravitational effects on ordinary matter and energy.

Now, theoretical physicist Robert J. Scherrer has come up with a model that could cut the mystery in half by explaining dark matter and dark energy as two aspects of a single unknown force. His model is described in a paper titled “Purely Kinetic k Essence as Unified Dark Matter” published online by Physical Review Letters on June 30 and available online at http://arxiv.org/abs/astro-ph/0402316.


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