Does Dark Matter imply Dark Gravity?

[mothythewso]

Normal gravity exerts an attractive force between masses of ordinary matter, or a bending of space-time resulting in the same effect. Just because dark matter and dark energy don't interact with ordinary matter or energy, this has nothing to say regarding how these phenomena interact amongst themselves. It defies common sense (at least mine) that they don't interact. Could there be "dark" analogues to the fundamental particles, fundamental forces that we encounter in our realm? And, if there is dark matter, does "dark gravity" logically follow? Would it exert a repulsive, rather than an attractive, force between whatever constitutes dark matter, a sort of bending outward of space-time? And, again positing the preponderance of dark matter over ordinary matter, if there is a "dark gravity", shouldn't it overwhelm the effects of normal gravity, and possibly be responsible for the observed expansion of our universe?

Amazing the thoughts that a good glass of Malbec in the morning can elicit!

mothythewso

[Strange]

While there may be some sort of unknown "dark force" interaction between dark matter, it cannot be equivalent to or as strong as the interactions between normal matter. If it were, then dark matter would intereact like normal matter does an collapse to form objects equivalent to planets and so on. The fact it exists in diffuse clouds supports the idea that it only interacts gravitationally.

 

 

It defies common sense (at least mine) that they don't interact.

 

Neutrinos don't interact with anything much, either. (But they don't have enough mass to be dark matter).

[Mordred]

These concepts get everyone just learning.

 

Let's start with dark matter. First off most people don't fully realize that not all particles have the same interactions with the four forces. A primary example is the neutrino. It doesn't interact with the strong force nor the electromagnetic. Photons only interact with the electromagnetic. Each force carrying boson has limitted interactions.

 

Dark matter only interacts with gravity as far as we know. This makes direct detection extremely problematic. However this isn't as ususual as people think. After all we ran into the same problem with neutrinos.

 

Dark energy is another matter. The universe is expanding isn't surprising. Cosmology is based upon GR and the ideal gas laws. So it's incorrect to think of dark energy as anti gravity. An accurate way to describe dark energy is positive vacuum , gravity being one of the influences in the negative vacuum.

 

The FLRW metric reflects this detail in the relation

 

[latex]w=\frac{p}{\rho}[/latex]

 

P is pressure

[latex]\rho[/latex] is energy density

w is the dimensionless number reflecting this relation.

 

The equations of state show the particle relations in their energy/mass density to pressure relations.

http://en.m.wikipedia.org/wiki/Equation_of_state_(cosmology)

 

The main problem with dark energy is why is it constant. As well as what mechanism keeps it constant.

 

here is a good article

 

http://arxiv.org/abs/1002.3966"why the prejudice against a constant"

 

on the geometry relations due to pressure distributions here is a starting article

 

http://cosmology101.wikidot.com/universe-geometry

Page 2

 

http://cosmology101.wikidot.com/geometry-flrw-metric/

 

Though page two is more on distance measures of the three geometries.

The cosmological constant aka dark energy has an equation of state roughly

w=-1

Edited January 12, 2015 by Mordred

[mothythewso]

Strange:

Can't figure out how to cut&paste your quote. I got D's in physics, on my second attempt. Go Figure!

I think the point that dark matter does exist in diffuse clouds, that it doesn't clump, supports my premise. If you accept the existence of gravitons, can you conceptualize "dark gravitons", mediating a sort of dark repulsive force. And because the dark matter is diffuse, dark gravitation isn't necessarily less powerful, but the distance between individual particles tends to lessen its effect. I know that dark matter is theorized to constitute most of the mass of the universe, to affect the spin rate of observed galaxies, implying an attractive force between normal and dark matter. But I point out that most of the observable universe is empty space, clumps of galaxies clustered in a large scale web-like framework. So the overall effect of dark matter would be minimal. And the Universe IS expanding. Why?

Sorry for the unscientific phrasing, I lack the formal education to properly express my thoughts.

mothythewso

[Mordred]

Dark matter and regular baryonic matter are effected by gravity in the same way. The difference is where the two are distributed.

 

The density of dark matter is less than baryonic matter due to not having a strong force interaction.

 

Take two dark matter particles, moving toward each other. The force of gravity between particles is negligible. As the two dark matter particles do not have a strong force they will drift by each other without interaction.

 

If this were two baryonic particles if they drifted close enough the strong force interaction will take effect. This will continue as more particles are collected. Causing mass

Edited January 13, 2015 by Mordred

[Strange]

Can't figure out how to cut&paste your quote. I got D's in physics, on my second attempt. Go Figure!

I think the point that dark matter does exist in diffuse clouds, that it doesn't clump, supports my premise.

 

The thing is, the "non-clumped" nature of dark matter is pretty much what would be expected for "stuff" that doesn't interact much. It doesn't need a new, unknown repulsive force to explain it.

 

 

But I point out that most of the observable universe is empty space, clumps of galaxies clustered in a large scale web-like framework.

 

And that large-scale structure is largely created by gravity - including dark matter.

 

 

And the Universe IS expanding.

 

Expanding is just a natural consequence of the same description of space-time (General Relativity) that explains gravity. Mordred posted a nice link to a (relatively) non-mathematical explanation of this, in another thread.

 

 

Sorry for the unscientific phrasing, I lack the formal education to properly express my thoughts.

 

No problem. Hope the answers make sense!

[mothythewso]

Strange ;

Thanks for your info. I've gotten intellectually lazy, I should have researched this topic myself. Actually got a lot of good info. Thanks for helping me get my stuff back together. One thing I still can't wrap my 2 remaining brain cells around. Dark matter particles don't even react to each other, in fact they pass thru/by each other without any effect (according to what I've read). But they do interact with gravity, I guess through some type of boson, a graviton I suppose. Is it because they have such a vanishingly small mass that their individual gravity pulls are effectively 0,but their preponderance over normal matter in the universe is so large, that their cumulative effect is enough to shape the macro-structure of the universe?

mothythewso

[swansont]

Strange ;

Thanks for your info. I've gotten intellectually lazy, I should have researched this topic myself. Actually got a lot of good info. Thanks for helping me get my stuff back together. One thing I still can't wrap my 2 remaining brain cells around. Dark matter particles don't even react to each other, in fact they pass thru/by each other without any effect (according to what I've read). But they do interact with gravity, I guess through some type of boson, a graviton I suppose. Is it because they have such a vanishingly small mass that their individual gravity pulls are effectively 0,but their preponderance over normal matter in the universe is so large, that their cumulative effect is enough to shape the macro-structure of the universe?

mothythewso

 

Dark matter should interact gravitationally with other dark matter. Do you have a citation that says it doesn't?

[Robittybob1]

 

Dark matter should interact gravitationally with other dark matter. Do you have a citation that says it doesn't?

The more I read this thread the more I realize I don't understand how Dark Matter operates.

[Mordred]

The more I read this thread the more I realize I don't understand how Dark Matter operates.

You wouldn't be alone in this..

[Strange]

The more I read this thread the more I realize I don't understand how Dark Matter operates.

 

That's a good thing... Think how much more exciting stuff there is to learn! That is what makes science so great.

[mothythewso]

I misspoke in my Jan 13 post when I said that dark matter particles pass by/thru each other with no effect. I think I should have said that they pass by each other with negligible effect. But what kind of dark matter are we talking about? I've seen references to cold DM, warm DM, hot DM, clumping DM, non-clumping DM(in reference to DM distribution in dwarf galaxies), etc. How boring our baryonic universe seems in comparison? Perhaps we're just some kind of impurity in the grand scheme of things. How humbling.

[Mordred]

Our model LCDM model supports cold dark matter

[Curiousabout]

So if I understand your conversation on dark matter and gravity. it would be safe to say that dark matter would be swallowed up by a black hole like everything else? I thought dark matter would occupy a black hole, but would move freely in and out of the host black hole. much like our atmosphere occupies a cup sitting on your counter.

[Strange]

So if I understand your conversation on dark matter and gravity. it would be safe to say that dark matter would be swallowed up by a black hole like everything else? I thought dark matter would occupy a black hole, but would move freely in and out of the host black hole. much like our atmosphere occupies a cup sitting on your counter.

 

Nothing can leave a black hole.