Okay, let's try to reformulate. What is the average density of dark matter in places we know there is dark matter? Then, assuming here were dark matter with that density in earth, how much that would be?
I am just trying trying to get my head around how sparse the dark matter actually is, wherever it actually exists. Would we have one kilogram of dark matter to observe?
Damn. Should have googled in the first place. Here is an estimate of dark matter density in solar system:
But even then, there's no reason to assume that there is any in that space. For example, imagine that all the dark matter was in a disk around the solar system, way out farther than the asteroid belt. If you could see through it, you would never know. Or maybe it rings galaxies. Or maybe it hangs out in clumps between galaxies. Or... It literally could be anything because we can only measure it on the scale of mind boggingly massive structures.
I believe it’s generally believed that dark matter clumps near galaxies because it interacts through gravity. So would it be reasonable to say that it should clump together near massive objects in the solar system?
DM usually forms a halo as it orbits the center of mass of whatever it orbits (galaxy, globular cluster), and because it doesn't interact otherwise, it cannot slow down, cannot shed momentum, so it is likely mostly not a disk, but a big sphere, and probably a shell around galaxies.
That sounds a little like an additional dimension or alternative something truly “out there”. Ie maybe gravity’s force relies on some process that reverses at the macro scale.
I mean, If there were appreciable amounts of it (i.e. not on the scale of kilograms in or around the earth), so that it could have a measurable impact on planet orbits, we could gain information on its distribution within (or interaction with) the solar system. That's why this density estimate is interesting - it sort of determines what the smallest scale is at which we'd have a chance of observing interactions/structure with dark matter.
I am just trying trying to get my head around how sparse the dark matter actually is, wherever it actually exists. Would we have one kilogram of dark matter to observe?
Damn. Should have googled in the first place. Here is an estimate of dark matter density in solar system:
http://cdms.berkeley.edu/Education/DMpages/FAQ/question36.ht...
6x10^-28 kg/cm3
Volume of earth is around 10^27 cm3 so that makes the dark matter mass within earth around 600 grams. Admittably that is a bit difficult to measure...