B Why can't we see dark matter in the solar system?

If the distribution of elements in the universe is also the distribution of elements in the solar system for regular matter, and being dark matter so overwhelmingly prevalent in the universe, why can't we see it overwhelmingly in the solar system?
 

Bandersnatch

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Because it doesn't clump.
 
Because it doesn't clump.
Thanks for the answer Bandersnatch.

Why not clumping would matter? Shouldn't gravity only be enough to keep it together?
 

Bandersnatch

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Imagine a galaxy made up of the regular baryonic matter that is not clumping. That is, not able to interact electromagnetically to shed energy and form local overdensities. The galaxy would still have the same mass, but all the matter would be spread across the entire volume of space comprising the galaxy. And there's a whole lot of space to fill. So rather than have massive clouds, stars, and planets coalescing in particular locations, with strong gravitational signatures, you could at best detect but a few particles streaming by at any given place.
 
Imagine a galaxy made up of the regular baryonic matter that is not clumping. That is, not able to interact electromagnetically to shed energy and form local overdensities. The galaxy would still have the same mass, but all the matter would be spread across the entire volume of space comprising the galaxy. And there's a whole lot of space to fill. So rather than have massive clouds, stars, and planets coalescing in particular locations, with strong gravitational signatures, you could at best detect but a few particles streaming by at any given place.
Awesome explanation. Thanks!
 
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If the distribution of elements in the universe is also the distribution of elements in the solar system for regular matter, and being dark matter so overwhelmingly prevalent in the universe, why can't we see it overwhelmingly in the solar system?
First, the distribution of matter in the universe is NOT the same as the distribution in the solar system. For reasons I'm not sure are even understood, there is much less dark matter in the solar system than you would expect from the normal ratio of baronic matter to dark matter. The best estimate of the amount of dark matter in the solar system is that it has a total mass equivalent to a small asteroid, but it is spread out over the entire solar system. Even if it were baronic matter it would be too little to detect.
 

Bandersnatch

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For reasons I'm not sure are even understood, there is much less dark matter in the solar system than you would expect from the normal ratio of baronic matter to dark matter.
The reason is because DM doesn't clump. I think that's pretty well understood.
 
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The reason is because DM doesn't clump. I think that's pretty well understood.
Yeah, that's reasonable. The solar system is, on average, much more dense than the density of the Milky Way galaxy. DM is spread out evenly whereas solar systems are clumps within the galaxy.
 
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I don't understand the relevance of the questions. Please elaborate.
You wrote that
you could at best detect but a few particles streaming by at any given place.
and I need to know why do you think that DM particles are behaving like this. What experimental/theoretical evidence suggests that DM particles are "streaming by"?

In the conversation I mentioned you offered a link about the possibility that DM particles behave like a gas. As far as I remember it was a promising idea. So, why "few [DM] particles streaming by" instead of "myriad of tiny DM particles 'hovering' around"?

And what makes you think that DM particles are (directly) detectable, that they have enough energy (per unit) to be detected?
 

Bandersnatch

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What experimental/theoretical evidence suggests that DM particles are "streaming by"?
The most widely assumed model for DM is weakly interacting particles (i.e. collisionless gas), affected solely by gravity. As such, each particle follows Keplerian trajectories in gravitational fields. I.e. they're 'streaming by' on the basis of theoretical predictions of their assumed properties.

In the conversation I mentioned you offered a link about the possibility that DM particles behave like a gas. As far as I remember it was a promising idea. So, why "few [DM] particles streaming by" instead of "myriad of tiny DM particles 'hovering' around"?
DM without qualifiers should refer to DM as used in the concordance (LCDM) model - because that's what's implicit in the question in the OP. This type of DM is collisionless.
This is not to say that this model is the correct one, or the only one possible. Or, for that matter, that even the existence of DM is a given.
But when somebody asks general questions about DM (or e.g. universal expansion), they'll get answers about the most favoured model and not some of the even more speculative outliers.
The answers in this thread should not be taken as authoritative proclamations declaring what DM certainly is or isn't, but rather, descriptions of how it is typically modelled.

And what makes you think that DM particles are (directly) detectable, that they have enough energy (per unit) to be detected?
Am I thinking that? They might not be. This has no bearing on the fact that, for a collisionless DM with required densities, the flux on the scale of the solar system must be tiny.
 

Wes Tausend

Gold Member
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We can't see dark matter because it is clear like glass. To every electromagnetic frequency apparently. That is why it only has a lensing effect. They should have called it Clear Matter instead of Dark Matter. I'm mostly kidding. :smile:

Wes
 
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We can't see dark matter because it is clear like glass.
No, that is a very poor analogy. "Clear like glass" implies a macro-sized object. The consensus is that DM is particles and it is not a meaningful statement to say a particle is "clear like glass".
 
We are not built that way by evolution, and this is because dark matter was not affecting us during this whole time of 4 billion yrs.
 
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We are not built that way by evolution, and this is because dark matter was not affecting us during this whole time of 4 billion yrs.
Your point is sort of valid but totally irrelevant. You are ignoring the fundamental fact that DM interacts only by gravity, so there is no "built that way" that would allow us to detect it with nothing but human senses.
 
Oh I meant only by senses, sorry for not being clear. Well i agree on that it could be possible with machinery in future. And thanks for the reply.
 
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There's yet another possible 'gotcha', compounded by our ignorance of what 'Dark Matter' actually is/does.

gross simplification:
Our solar system is currently within a thinner 'Local Bubble' blown in interstellar medium by the shock-front of at least one supernova, possibly three or more. Plus legacy stuff from older...

Also within this bubble, there's clouds of 'Local Fluff', possibly where stuff riding such shock fronts has collided and merged into 'dust bunnies'...
gs/

IMHO, it's currently 'catch-22'.
Until we know much more about 'Dark Matter', we don't know if there is any near here.
Perhaps those multiple supernova shock-waves have swept our neighbourhood clear of the stuff...
D'uh, where's serendipity when you need it ??

Whimsy:
Funny thing...
There's a curious correlation between our solar system entering 'Local Bubble' and human intelligence developing exponentially.
Such correlation, of course, does not imply causation, but I may yet spin an off-beat SciFi tale from it...
w/
 
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Our solar system is currently within a thinner 'Local Bubble' blown in interstellar medium by the shock-front of at least one supernova, possibly three or more.
Since such a shock wave would only affect normal matter, I fail to see what it has to do with the distribution of DM. Am I missing something?
 
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The mass-movement of so much 'normal matter' plus, perhaps, the intense neutrino flux, may carry some or most 'Dark Matter' along.

Sadly, currently impossible to prove or disprove such fun speculation...
;-(
 
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Fair point.
As 'Insufficient Data' to offer any plausible hypothesis concerning such, I'll leave it there...
 

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