What is the current evidence for dark matter?

[dryogeshd]

Hi all,

I was wondering, could the dark matter just be the particles that actually pop in and out of existence inside the protons and neutrons and all other matter or anti-matter?

Please enlighten me if my assumption is wrong somewhere.

 

[Simon Bridge]

If I have understood what you are getting at:
That's already accounted for as binding energy and mass for the protons and neutrons and etc.

 

[dryogeshd]

If I have understood what you are getting at:
That's already accounted for as binding energy and mass for the protons and neutrons and etc.

I don't think so, I do understand the binding force, but that's not what I am thinking about, I am thinking about the empty space between the quarks, and everywhere else for that matter. Maybe even outside of atoms. I am not so convinced about outside of atoms as yet

 

[Simon Bridge]

The particles popping in and our of existence in the "empty space" between quarks is taken into account as vacuum energy... it's one of the suggested constituents of dark energy.

According to the Planck mission team, and based on the standard model of cosmology, the total mass–energy of the known universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy.

http://arstechnica.com/science/2013...-the-universe-is-still-weird-and-interesting/
http://arxiv.org/abs/1303.5062

If you are referring to some other mechanism for particles popping in and out of existence inside nucleons ... then I'll need to see a reference.

 

[PAllen]

Dark matter has a distribution derived very directly from gravitational lensing observations and indirectly from the paths of stars in galaxies, galaxies in clusters. These imply most of it is where there are very few atoms or ordinary particles.

 

[Superposed_Cat]

Right now the leading theory is WIMPS although I heard something about LUX getting negative results on that?

 

[PAllen]

The best (by far) discussion of the LUX finding I've seen on the web so far is:

http://profmattstrassler.com/2013/10/31/questions-and-answers-about-dark-matter-post-lux/

 

[Chalnoth]

Hi all,

I was wondering, could the dark matter just be the particles that actually pop in and out of existence inside the protons and neutrons and all other matter or anti-matter?

Please enlighten me if my assumption is wrong somewhere.

Such particles wouldn't cluster like dark matter does. Clustering requires them to be persistent.

 

[ryanuser]

I was thinking that dark matter even isn't matter, its a force because apparently it might be interacting with gravity and gravity is a force.

 

[phinds]

I was thinking that dark matter even isn't matter, its a force because apparently it might be interacting with gravity and gravity is a force.

That is unsupportable personal speculation and as such it is not appropriate for this forum.

 

[ryanuser]

Dryogeshd it self has given his/her idea, you are allowed to discuss and give your own reference to the question.

 

[phinds]

Dryogeshd it self has given his/her idea, you are allowed to discuss and give your own reference to the question.

Not when your idea is unsupportable personal speculation. Read the forum rules

 

[ryanuser]

Is the question by itself supportable?
Are all theories SUPPORTABLE?

 

[phinds]

Is the question by itself supportable?
Are all theories SUPPORTABLE?

The original question was just that ... a QUESTION. The OP did not make unsupportable personal speculation, he asked a question. You made a statement.

 

[ryanuser]

Comment on the statement

 

[phinds]

Comment on the statement

The statement is unsupportable personal speculation, as I have already said.

 

[Drakkith]

I was thinking that dark matter even isn't matter, its a force because apparently it might be interacting with gravity and gravity is a force.

Forces act upon particles, so no, dark matter itself is not a force. Realize that there are no forces that act upon other forces. None of the 4 fundamental forces of nature interact with each other in any way. They act solely upon the particles themselves.

 

[ryanuser]

So how about gravity, that's not a particle, is it? Its the curvature of space-time which acts on particles and other matters.

 

[phinds]

So how about gravity, that's not a particle, is it? Its the curvature of space-time which acts on particles and other matters.

Yes, dark matter is known to interact gravitationally both with normal matter and with itself. What does that have to do with your statement that

I was thinking that dark matter even isn't matter

If it isn't matter how does it interact gravitationally? You seem to be really confused about this. There are numerous articles available about dark matter. Why don't you study up on it a bit?

 

[Drakkith]

So how about gravity, that's not a particle, is it? Its the curvature of space-time which acts on particles and other matters.

No, gravity is not a particle.

 

[Chalnoth]

Forces act upon particles, so no, dark matter itself is not a force. Realize that there are no forces that act upon other forces. None of the 4 fundamental forces of nature interact with each other in any way. They act solely upon the particles themselves.

Well, that's not quite true. The strong nuclear force acts on itself (in a sense: gluons carry strong force charges). This is why the strong nuclear force is a short-range force. Obviously a similar thing can't really be happening with dark matter for its impact to stretch across millions of light years.

But regardless, the idea that somehow dark matter might be a modification of gravity, or something else that acts sort of like gravity, is very hard to support these days. Ryanuser, I recommend checking out this blog post that posts one rather striking piece of evidence for dark matter:
http://www.preposterousuniverse.com/blog/2006/08/21/dark-matter-exists/

 

[Simon Bridge]

So how about gravity, that's not a particle, is it? Its the curvature of space-time which acts on particles and other matters.

... so you are thinking that either 1. there is something else out there that puts an additional curvature to space-time, or 2. that gravity just does not behave the way we think over long distances?

Both those would still be pretty much the same as "dark matter" though.
At least with thinking of the stuff as "matter" we don't have to suppose a, hitherto undiscovered, fifth force that otherwise acts exactly like gravity from mass we cannot see.

The idea that gravity is just different at long ranges has already been thought of and looked into...

But regardless, the idea that somehow dark matter might be a modification of gravity, or something else that acts sort of like gravity, is very hard to support these days.

+1 :)

Most of the suggestions in this thread have amounted to: "Hey, isn't dark matter actually something we already know about?" - insert specific personal favorite "stuff we already know about".

The answer is that, with the current state of knowledge, the closest thing we already know about that deals with the phenomena we need to explain is "matter". The "dark" part of the name is an attempt to label how it seems to be different from the regular matter we know about.

Don't get me wrong - these ideas are constantly being tested.
The mainstream models are the way they are for a reason.
Part of what PF exists for is to help people understand this.

 

[dryogeshd]

Hi all, Thank you so much for participating, Essentially, what I understand till now is that, dark matter is thought to be clumped in some places causing gravitational lensing, are these gravitational lenses located precisely around galaxies/black holes? or are they also distributed in the intergalactic space as well? If they are in the same positions as the galaxies, then it is probable that unaccounted for mass is within the matter that we measure in these galaxies... That implies we are missing a rather important particle/s that is contributing to the mass on the universe.

 

[PAllen]

Hi all, Thank you so much for participating, Essentially, what I understand till now is that, dark matter is thought to be clumped in some places causing gravitational lensing, are these gravitational lenses located precisely around galaxies/black holes? or are they also distributed in the intergalactic space as well? If they are in the same positions as the galaxies, then it is probable that unaccounted for mass is within the matter that we measure in these galaxies... That implies we are missing a rather important particle/s that is contributing to the mass on the universe.

I thought someone already linked to the bullet cluster. Here, you had two galaxies that collided, and the result is that the dark matter is displaced from both galaxies (as located by gravitational lensing). In the normal state of a galaxy, the COM for visible matter matches the gravitational COM sensitive to all matter (including dark matter).

In the present day universe, there is believed to be little dark matter between galaxies.

 

[Chalnoth]

Hi all, Thank you so much for participating, Essentially, what I understand till now is that, dark matter is thought to be clumped in some places causing gravitational lensing, are these gravitational lenses located precisely around galaxies/black holes? or are they also distributed in the intergalactic space as well? If they are in the same positions as the galaxies, then it is probable that unaccounted for mass is within the matter that we measure in these galaxies... That implies we are missing a rather important particle/s that is contributing to the mass on the universe.

There is a relationship with normal matter, but it isn't perfect. Read the blog post I linked above, as it highlights a case where the normal matter was separated from the dark matter due to a collision.

 

[kye]

Is the collision separation phenomenon 100% proof of dark matter? if so, why is that some scientists still doubt their existence.. even astrophysicists... and they even have data that suggest it is opposite to dark matter predictions. see:

http://www.sciencedaily.com/releases/2009/05/090505061949.htm

any familiar with what they are talking about?

 

[Simon Bridge]

The satellite galaxies are well studied objects.
That report was from 2009 ... how about something more recent?

The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via gamma rays.
$\qquad$ http://arxiv.org/abs/1310.0828 (Oct. 2013)​

More accessible:

“When the problem was first pointed out, there was some concern that it meant that our understanding of dark matter or cosmology itself might be flawed,” Bullock says. “Today we have come to understand that there are a lot of reasons why dwarf galaxy formation might be inefficient.
$\qquad$ Scientific American, Oct 2013.
$\qquad$ http://www.scientificamerican.com/article.cfm?id=milky-way-satellite-dwarf-galaxies​

As for why some scientists, yea even unto the astrophysicists, disagree with standard models ... that's because it's their job.
A model stands not on the amount of evidence in it's favor but on the cleverness of the failed efforts to refute it.

 

[kye]

The satellite galaxies are well studied objects.
That report was from 2009 ... how about something more recent?

The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via gamma rays.
$\qquad$ http://arxiv.org/abs/1310.0828 (Oct. 2013)​

More accessible: Scientific American, Oct 2013.
http://www.scientificamerican.com/article.cfm?id=milky-way-satellite-dwarf-galaxies

As for why some scientists, yea even unto the astrophysicists, disagree with standard models ... that's because it's their job.
A model stands not on the amount of evidence in it's favor but on the cleverness of the failed efforts to refute it.

Here's more recent the suggest MOND is more appropriate.. so how does it still support dark matter?

http://www.sciencedaily.com/releases/2011/02/110223092406.htm

 

[Simon Bridge]

I didn't say it supported Dark Matter - it doesn't have to! It is not fatal to dark matter models.
A model stands not on the amount of evidence in support but on the cleverness of the failed efforts to refute it.

Anyway - that Science Daily link:
http://www.sciencedaily.com/releases/2011/02/110223092406.htm
... is from Feb 2011.

Here's another one from Science Daily:
http://www.sciencedaily.com/releases/2011/09/110928131758.htm
... from Sept 2011.

Attempts to produce MoND models for cosmological scale structures seems to be problematical.
http://arxiv.org/abs/1309.6094 (Sept 2013)
(TLDR: Models suggest MoND may require different kinds of gravity from different objects)

You should realize that, at any time, there are a lot of models around that could work just as well.
How should we choose between them? What determines which model becomes mainstream and which are the serious contenders and so on? When you consider these questions, you'll be on the track to the answers to your questions.

The main thing blocking MoND from general acceptance, I suspect, is that it is sort-of begging the question as well as running foul of Occam's razor. That doesn't mean it's wrong ... just that there is still work to be done.

Anyway: when you read these sorts of news reports, have a go finding the actual papers the reports are based on, then see if anyone has done a followup (i.e. find out who is citing the paper).

 

[kye]

For the bullet clusters dark matter thing mapped by gravitational lensing (which I have been thinking for quite a few weeks as it's a strong support of dark matter) that is also shared in message #21, are their arxiv (or etc) papers that illustration how it can occur without using the concepts of dark matter? can anyone share the papers, thanks.

 

[Simon Bridge]

Discussion from the MoND guy.
http://www.astro.umd.edu/~ssm/mond/moti_bullet.html
We have known for some fifteen years now that MOND does not fully explain away the mass discrepancy in galaxy clusters. (See e.g. the 1999 paper by Sanders: http://xxx.lanl.gov/abs/astro-ph/9807023, but there have been quite a few others discussing this before and after, starting from 1988). Even after correcting with MOND you still need in the cluster some yet undetected matter in roughly the same amount as that of the visible matter. Call it dark matter if you wish, but we think it is simply some standard matter in some form that has not been detected.

 

[Chalnoth]

Is the collision separation phenomenon 100% proof of dark matter? if so, why is that some scientists still doubt their existence.. even astrophysicists... and they even have data that suggest it is opposite to dark matter predictions. see:

http://www.sciencedaily.com/releases/2009/05/090505061949.htm

any familiar with what they are talking about?

There's no such thing as 100% proof. But it is compelling evidence that makes MOND-type theories hard to support. The CMB is even more compelling evidence, but that's a little bit more difficult to wrap your head around as to precisely why.

Here's more recent the suggest MOND is more appropriate.. so how does it still support dark matter?

http://www.sciencedaily.com/releases/2011/02/110223092406.htm

The claim here still requires a form of dark matter to fit the data. In this case, they use an undetected heavy species of neutrino in the fit (we know the three neutrinos we know about can't have that much mass). So they have a much more complicated model than just having dark matter: they've got both dark matter and modified gravity. Occam's Razor suggests that this is rather unlikely.