What is the relationship between dark matter and gravity?

[confused????]

dark matter and gravity?

can anyone help? been wondering ... gravity is the weakest of the 4 fundamental forces and no one knows why...10x weaker than it should be. there is 10x more dark matter than light emitting matter in the universe. i was wondering if dark matter is maybe a part of the gravity rather than a particle no one has discovered? i appologise if this seems daft but am v curious

 

[mdmaaz]

Well dark matter can be a part of gravity, because every mass has a gravitational pull. So the mass of dark matter will have a gravitational pull as well. Since dark matter is all around us, there is the gravitational pull everywhere. It may not be true, but this is what I think.
Sorry for going off-topic, but tell me how to start a thread on physics forums.

 

[confused????]

but is dark matter a particle or just part of gravity. am a layman at this. it just seems to me that the numbers seems too coincidental ... confused

 

[confused????]

re postin new threads. there is a new threads button that's what i used

 

[confused????]

in your answer you are assuming that dark matter is a particle. my argument is that it is a part of the force of gravity rather than a particle with mass.

 

[phinds]

but is dark matter a particle or just part of gravity. am a layman at this. it just seems to me that the numbers seems too coincidental ... confused

I'm not sure your question quite makes sense. What do you mean by "part of gravity" ?

Dark matter is, as far as is currently known, MATTER. It therefor has a gravitational effect the same way normal matter does. What it does NOT do is emit or reflect radiation of any kind, thus the name "dark". It is assumed to be a particle or bound groups of subatomic particles, of some sort. WHAT sort isn't at all known, thus another reason for the "dark".

 

[confused????]

what confuses me is that no one knows what dark matter is. we don't know that it is a particle, that is speculation. what i was wondering is whether it is a elemental force rather than a particle

 

[bcrowell]

can anyone help? been wondering ... gravity is the weakest of the 4 fundamental forces and no one knows why...10x weaker than it should be. there is 10x more dark matter than light emitting matter in the universe.

I don't think the 10x figure is right -- where did you get it?

 

[bapowell]

Dark matter was originally proposed to explain the fact that observed galaxy rotation curves were not in agreement with those derived from theory under the assumption that all galactic mass was visible. Dark matter -- a hypothetical entity that gravitated but was not electromagnetically interactive -- was suggested as an explanation. An alternative hypothesis was that rather than introduce new forms of matter, what really needed to be looked at was the gravitational theory itself. Modified Newtonian Dynamics (MOND) grew out of this line of inquiry to explain galactic rotation curves.

In the past few decades, evidence for dark matter has cropped up in many more places than only galaxy rotation. For example, the acoustic oscillations seen in the cosmic microwave background lend strong support to the existence of dark matter as a weakly interacting massive particle. Other individual pieces of indirect evidence, like the Bullet Cluster, also strongly suggest particulate dark matter. MOND, and its relativistic cousin, TeVes, have struggled to accommodate these new data, and are quickly falling out of the main stream.

It sounds to me that when you suggest that dark matter is an elemental force, you're really talking about modified gravity. Afterall, dark matter is needed to explain discrepancies in gravitational systems. So, to answer your question, it's looking less and less likely that modified gravity is the answer here.

It's true that we don't yet know what dark matter is, but that's not the same as saying that we have no idea. We have some good theoretical traction on the phenomenon, and cosmological observations have greatly shaped our understanding of what dark matter might and might not be.

 

[confused????]

so if i get this right, the current thinking is that darkmatter is a wimp? sorry if these questions seem stupid but not got a degree in cosmology. i appreciate the answers... i need to do more reading

 

[phinds]

so if i get this right, the current thinking is that darkmatter is a wimp? sorry if these questions seem stupid but not got a degree in cosmology. i appreciate the answers... i need to do more reading

I think it's closer to say that we still don't know what it is, but WIMPs are currently the leading contender for likely explanations. So I don't think many folks are saying it IS WIMPs but rather that it seems likely to be WIMPs. The jury is still out and scientists tend to avoid definitive statements with no proof.

 

[confused????]

why is it so hard to detect dark matter? is it because it moves so slow that it does not shine or interact with ordinary matter??

 

[Ryan_m_b]

You might be interested in this little video put together by some physics PhDs

http://www.phdcomics.com/comics/archive.php?comicid=1430

 

[Janus]

why is it so hard to detect dark matter? is it because it moves so slow that it does not shine or interact with ordinary matter??

It has nothing to do with its speed, but the fact that it doesn't interact electromagnetically. It doesn't emit, absorb, reflect or refract light. Neither does it form any bonds with itself or ordinary matter. In this way it would be a "ghost particle" much like the neutrino.

It does have mass, and therefore gravity, so we can "detect" it this way. However, since it wouldn't interact electromagnetically, it wouldn't form small compact bodies (there would be no "dark matter planets"), and so we can only detect it at large scales in this manner. It is also spread so thin, that even in a volume the size of our solar system, there would be very little of it. (I know that this seems strange, considering that there is supposed to be much more DM than ordinary matter, but ordinary matter is for the most part contained to the galactic disk while DM is in a larger spherical volume that engulfs the galactic disk. Also the average density of ordinary matter within the confines of the solar system is higher than the average density of the ordinary matter in the galactic disk)

 

[confused????]

so dark matter has no charge, pos or neg?

 

[mayflow]

Dark matter has never been seen by us, but observations especially on large scales (enabled by Hubble telescope pics) imply it has the opposite effect that gravity does. It is really on the leading edge of being explored by us...

http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/

The thing is "confused" We are ALL confused. Fun stuff, isn't it? i

 

[Chalnoth]

can anyone help? been wondering ... gravity is the weakest of the 4 fundamental forces and no one knows why...10x weaker than it should be. there is 10x more dark matter than light emitting matter in the universe. i was wondering if dark matter is maybe a part of the gravity rather than a particle no one has discovered? i appologise if this seems daft but am v curious

Well, right, many people have surmised that what we interpret as "dark matter" may just be a change in the gravitational law.

These attempts, however, have ultimately failed. Basically, if you propose a weakly-interacting massive particle, that particle rather easily explains a tremendous variety of observations. It turns out that this isn't so easy with modified gravity.

But if you want a relatively clear explanation for why we can be so sure dark matter exists, see this blog post as an example:
http://blogs.discovermagazine.com/cosmicvariance/2006/08/21/dark-matter-exists/

Now, if you ask me, this isn't even the strongest evidence in favor of dark matter. It is, however, the easiest to explain.

 

[confused????]

with brane theory and multiverse theory is it poss that dark matter is ordinary matter on another brane?

 

[Chalnoth]

with brane theory and multiverse theory is it poss that dark matter is ordinary matter on another brane?

Nope, because not only does dark matter not interact much with normal matter, but it also doesn't interact much with itself. Normal matter on another brane would interact pretty strongly with itself (as normal matter does here), and would thus behave very differently.

 

[phinds]

with brane theory and multiverse theory is it poss that dark matter is ordinary matter on another brane?

I saw Michio Kaku on TV recently saying that there is speculation that if the multiverse exists it is possible that some effect from another universe (he did not say brane) is leaking over into ours and causing the effect we see as dark matter.

I am PURELY passing on information here, not commenting on it.

 

[confused????]

i didnt explain very well... i know dark matter does not interact with ordinary matter. my point is... we only know about dark matter because we can see gravitational lensing from deep space pictures and because of galaxy rotational speeds. could it be that it is not dark matter at all but the gravity from matter on another brane. i am thinkin this because gravity is weaker than it should be.

 

[Ryan_m_b]

i didnt explain very well... i know dark matter does not interact with ordinary matter. my point is... we only know about dark matter because we can see gravitational lensing from deep space pictures and because of galaxy rotational speeds. could it be that it is not dark matter at all but the gravity from matter on another brane. i am thinkin this because gravity is weaker than it should be.

Are you trying to ask if this is gravity from another universe? I'm not really sure I understand. Gravity isn't "weaker than it should be". It's just the weakest of the fundamental forces (check the relative strength part of the table here http://en.wikipedia.org/wiki/Fundamental_interaction)

 

[confused????]

is dark matter gravity from another universe? that's what i am asking

 

[IsometricPion]

Dark matter has never been seen by us, but observations especially on large scales (enabled by Hubble telescope pics) imply it has the opposite effect that gravity does.

I think you are referring to http://en.wikipedia.org/wiki/Dark_energy" than it is to normal matter (except in that relatively little is known about the properties of either).

is dark matter gravity from another universe?

I don't think there is any way to tell without knowing more about it. If it is, as Chalnoth said, it would be nothing like our universe. On a different note, can it really be part of a different universe if it can interact with us? (this is a purely semantic, mostly rhetorical question with no bearing on the essence of your question)

 

[narrator]

Not sure about my recollection/understanding here. Just before Planck Time, the universe was made up of subatomic particles or some precursor to them. Could it be that a small percentage of these particles fused in the Planck Time heat to become regular particles, leaving behind most of the mass as subatomic particles? Or perhaps some of the subatomic particles did fuse into wimps and other exotic matter. Just reading between the lines - I know, not always good to do.. lol

 

[slooper2112]

I keep thinking about Flatland and the cube rotating and interacting with the two dimensional world. If there is a 'rotating' five dimensional object intersecting our four dimensional world, what would that look like?

If all we can 'see' is the effect in our four dimensional world then the phenomenon would look 'spooky'.