The Naked Scientists

The Naked Scientists Forum

Author Topic: Is there dark matter in Earth's atmosphere?  (Read 9239 times)

Offline Victoria Cooper

  • First timers
  • *
  • Posts: 1
    • View Profile
Is there dark matter in Earth's atmosphere?
« on: 12/07/2010 10:30:02 »
Victoria Cooper  asked the Naked Scientists:
   
My son Patrick who is 8 years old wants to know:

Is there dark matter in our (earth's) atmosphere?  If not, why doesn't dark matter invade our atmosphere?

I'll keep listening to hear the answer.  Thanks

Victoria C.
Vermont, USA

What do you think?
« Last Edit: 12/07/2010 10:30:02 by _system »


 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #1 on: 12/07/2010 10:36:58 »
Nobody knows. I think it is likely that it is but it is believed that because it does not interact with ordinary matter it will be very thinly distributed and really passing through the atmosphere (and the earth) because of the earth and our sun's local velocity within the galaxy. Although it is thought that there is a lot of DM in our galaxy it is believed to be more evenly distributed and not even concentrated in the galactic disc but in a roughly spherical shape extended beyond the edge of the visible milky way galaxy. The likely density will therefore be very small. People are trying to detect it though, so more understanding will emerge in the years ahead.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Is there dark matter in Earth's atmosphere?
« Reply #2 on: 13/07/2010 00:00:29 »
As graham says most types of dark matter particles are unaffected by matter other than its gravitational field so approaching the earth they will accelerate in the gravitational field pass right through the earth unaffected and decelerate slightly as they leave.
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #3 on: 13/07/2010 04:02:27 »
There are particles called neutrinos which are probably a component of dark matter.  They are very tiny (and very light) particles that very weakly interact with matter.   Almost all of them heading towards the earth just pass through it without hitting anything.  From Wikipedia: "Most neutrinos passing through the Earth emanate from the Sun, and more than 50 trillion solar neutrinos pass through the human body every second."  They're dark because it's incredibly difficult to see them (they tend to just pass through detectors without being noticed), but occasionally we can see one, so we know they exist.
 

Offline flr

  • Sr. Member
  • ****
  • Posts: 302
  • Thanked: 2 times
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #4 on: 07/08/2010 19:03:38 »
See:
http://www.universetoday.com/15266/dark-matter-is-denser-in-the-solar-system/

I am citing from above link:
"
Over the history of the Solar System, Xu and Siegel calculate that 1.07 X 10^20 kg of dark matter have been captured, or about 0.0018% the mass of the Earth. To get a handle on this number, the mass of Ceres – the largest object in the asteroid belt between Mars and Jupiter – is about 9 times this amount.
"

I read somewhere that the density of dark matter around Earth may be about 0.39GeV / cm^3 , or equivalent in mass: 0.39 protons_masses / cm ^3

Quote
If not, why doesn't dark matter invade our atmosphere?

Actually we are kind of 'invaded' by dark matter and the density of dark matter around Earth is larger than overall dark matter density over the entire galaxy and much much larger than the overall density of universe. Yet, its density around Earth is small because it interacts with ordinary matter only via the [weak] gravity force. I am skeptic however that dark matter really exists because it would have too special properties and too restricted way to interact with regular matter.
« Last Edit: 07/08/2010 19:13:42 by flr »
 

Offline Farsight

  • Sr. Member
  • ****
  • Posts: 396
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #5 on: 08/08/2010 14:16:21 »
Victoria: IMHO the answer is kind of a yes and a no. People feel there's a lot more dark matter around than ordinary matter, as per the "dark matter pie":

 

However they've been having a lot of trouble detecting particles of dark matter, and there's a subtle explanation for this that's gaining some interest. Think about space. It's dark, and it has its innate vacuum energy. This energy has a mass equivalence, so in a way space itself is "dark matter". Take away every last atom of our atmosphere and what you're left with is space. You can wave your hand through it and it's like there's nothing there, but space isn't nothing. That mass-equivalence means that inhomogeneous space can behave gravitationally just like matter. It would be better to call it a dark mass-equivalence, but dark matter isn't too far of a stretch. On this basis, you could say that our atmosphere has invaded the dark matter! 
 

Offline Absalom

  • First timers
  • *
  • Posts: 5
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #6 on: 10/08/2010 03:47:46 »
I'm not sure I know enough to understand properly what all is meant here, so please feel free to tell me if there is too much that I'm not getting, but something in the comment by Farsight struck me strangely. Is it commonly accepted that space has an "innate vacuum energy," and that that vacuum energy "has a mass equivalence"?  Does this mean we assume a force maintaining the vacuum and an attendant stuff that is where everything isn't? It starts to sound a lot like the aether.
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #7 on: 10/08/2010 06:32:51 »
Well, there is little debate that a vacuum energy exists in some sense.  The vacuum needs to have a minimum energy level (you may have heard it called the zero-point energy of the vacuum) in order for much of quantum mechanics to make sense and work.  This has been tested experimentally in terms, and it appears to be true on the small scale. 

But when you scale up that energy to the size of the universe and ask how it would interact gravitationally, quantum mechanics predicts 10^120 times more energy than appears to be there!  This is a part of the problem of dark energy. 

So I would say that it is commonly accepted that the vacuum has energy, and this has been confirmed on the small scale.  I think it's a it dubious to say that we're positive of how this vacuum energy interacts gravitationally, since just plugging it into our equations for gravity gives an answer that seems to be wrong...
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #8 on: 10/08/2010 07:11:48 »
I think there might also be a little confusion about how dark matter and dark energy differ.  Gravity is a result of the stress-energy tensor, which contains terms for both energy and mass.  Depending on your reference frame, energy can appear as mass and mass as energy.

I'm not an expert in the field, but from what I understand, dark matter is pretty normal stuff--it's just matter/energy that doesn't interact electromagnetically so we can't see it with telescopes.  It attracts other mass, though and we detect it by seeing that there's stronger gravity somewhere than we can account for with the matter that's emitting electromagnetic radiation.

Dark energy is the term used to describe whatever is making the universe accelerate in its expansion.  It's also assumed to be a gravitational effect, but it's a repulsive effect.  There are various ways to account for this--one way is a vacuum energy.  Since it's a part of the fabric of space-time itself, it turns out that it can interact gravitationally in a repulsive manner.  But again, as I said above, getting the vacuum energy we've actually measured to agree with the "dark energy" that's accounting for the expansion is an unsolved problem.

Certainly in the case of dark energy, the vacuum energy doesn't behave like mass sitting in space and attracting other mass to it.  I don't know if there are proposed models where vacuum energy does somehow behave like dark matter. 
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #9 on: 10/08/2010 09:56:16 »
It is very unfortunate that "dark energy" is named this way. It is not thought to be directly related to "dark matter" in any way, but the use of the word "dark" in both cases causes no end of confusion. It would be better to refer to "dark energy" as "vacuum energy" and remove the word "dark" altogether.
 

Offline acsinuk

  • Sr. Member
  • ****
  • Posts: 235
  • Thanked: 1 times
    • View Profile
    • electricmagnofluxuniverse.blogspot.com
Is there dark matter in Earth's atmosphere?
« Reply #10 on: 20/08/2010 13:56:24 »
I agree Graham.  Dark matter is I believe the invisible matter that we know is there as observation show a star wobble or blink. Beyond that there is dark gases and ions in the vacuum of space. 
But dark energy should be renamed "the force pushing the universe apart" which may well be an electric force with no mass in it whatsoever.
 We haven't lost 70% of the universe really; or have we?
CliveS
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #11 on: 20/08/2010 15:54:31 »
But without the term "dark", people woudn't be so fascinated, is it?  ;)
 

Offline acsinuk

  • Sr. Member
  • ****
  • Posts: 235
  • Thanked: 1 times
    • View Profile
    • electricmagnofluxuniverse.blogspot.com
Is there dark matter in Earth's atmosphere?
« Reply #12 on: 23/08/2010 16:41:37 »
The real problem lightarrow is that the standard gravitional model from wikipedia considers that there is no electric fields in space as the positive charges cancel out the negatives in all matter.
We used to think that the solar system was the same until the solar wind was discovered.
If there are any gas molecules in the space between the sun and earth they will be ionized only if a voltage is applied.  The solar wind is full of protons or H+ ions not hydrogen molecules. If the sun earth connection voltage collapses then the H+ ions will pair with a free electron and a gas molecule will just float around in the vacuum.
There are, I am sure, be electric fields in outer space also which may  have the effect of being a force that pushes the universe apart
CliveS 
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11978
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #13 on: 09/09/2010 10:18:08 »
JP how do they think when they expect virtual particles to interfere with gravity? Isn't those outside Plancscale? And if it is so, they should be outside our arrow of time too, it seems to me? And if they do influence? How do they do it? 

Is that some statistical probability reasoning? That even if they 'individually' are outside Planck time there still will be enough of them spontaneously fluctuating in and out of SpaceTime so that they can create a probability of gravitational influence? And if so, why can't it be the estimate of those fluctuations that is wrong?
 

Offline DoryT

  • Jr. Member
  • **
  • Posts: 13
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #14 on: 09/09/2010 12:54:14 »
Victoria: IMHO the answer is kind of a yes and a no. People feel there's a lot more dark matter around than ordinary matter, as per the "dark matter pie":

 


I'm suddenly in the mood for burnt pie...
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
Is there dark matter in Earth's atmosphere?
« Reply #15 on: 09/09/2010 13:18:37 »
I'm suddenly in the mood for burnt pie...

You're having a Homer Simpson moment too, eh?
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #16 on: 09/09/2010 15:05:33 »
JP how do they think when they expect virtual particles to interfere with gravity? Isn't those outside Plancscale? And if it is so, they should be outside our arrow of time too, it seems to me? And if they do influence? How do they do it? 

I'm not sure I follow you exactly.  I don't know if virtual particles interfere with gravity, but the zero-point energy is certainly a real physical energy.  I'm don't think you have to think about virtual particles in order to consider it.  As I understand it, simply thinking of the vacuum as a field requires that it has a minimum energy, regardless of what that energy is doing.  That value disagrees with what we see, though, so there's something funny going on...
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11978
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is there dark matter in Earth's atmosphere?
« Reply #17 on: 09/09/2010 22:05:30 »
It's just that from my point of view, vacuum energy and virtual particles seems very near each other, just as the idea of virtual photons being 'transporters' of energy in transformations. Probably because I miss those finer nuances of the math behind it:) They all seem to discuss something going on, on a quantum level, and as far I understand, 'everywhere', inside matter, in space, and if one stretch it a little even our 'normal photons' can be seen as a form of the exact same type, only time drawing the borders for how to define it, like using Rindler observers to get virtual photons to become measurable, as real as any photons we see 'normally' as I understand it?

In what way are vacuum energy thought not to be a offspring of photons?
 

The Naked Scientists Forum

Is there dark matter in Earth's atmosphere?
« Reply #17 on: 09/09/2010 22:05:30 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums