> Fascinatingly, it is known that the interaction of the dark matter with the Earth is so weak that there would be no "clumping" of it around the Earth at all!
Would I be right in thinking that also puts severe limits on how much it interacts with itself? Because my intuition would be, if you loose normal matter into a gravity well, it will clump, even if it doesn't interact with the source of the gravity.
> Because my intuition would be, if you loose normal matter into a gravity well, it will clump, even if it doesn't interact with the source of the gravity. Am I inferring correctly?
Now I have a little of Newton for you: look at our Solar system: you see the planets, and even more interesting, all the small asteroids circling around the Sun? Can you answer why don't they all fall to the Sun, but move in the orbits?
The way the gravitation works was not "intuitive" before Newton, 300 years ago, and now it's obviously still so for many non-professional readers.
What's actually happening, according to the dark matter model, and the dark matter actually more easily fits much more of our cosmological observations than anything else, is that there is a lot of dark matter but it is simply much more "spread" around the volume of the galaxies. And just like all the visible stuff of the whole galaxy doesn't fall to the galaxy center (like the planets don't fall to the Sun!), the dark matter remains "around" the galaxies, where more of dark matter is "outside" (as in "in the outer regions of it") than in the "inside" of the galaxy (and in the case of the "Bullet Cluster", that I've mentioned in some other comment, dark matter is obviously lagging all the movement of non-dark matter! (1)). That dark matter that is in the inside of the galaxies actually initially "clumped" somewhat, but that "somewhat" is, according to our estimates, significantly below what we are able to measure, when we're interested in the gravitational effect on the Solar system.
Sweet of you to bring me Newton. Always a welcome gift.
But I think you misunderstand where my question is pitched.
The solar system is rather clumped, you see. A little Aristotle for you. :)
In all seriousness, the more dark matter is around, the less it can have mutual interactions, before it would clump, surely? Assuming such forces exist, there is a nonzero probability that two particles of dark matter will approach close enough that non-gravity forces will be significant, And they will no longer act under an ideal Newtonian gravity. Dust clouds coalesce into suns, given time. Can dark matter have its own dark-only version of the electromagnetic force? Or is that ruled out by the lack of clumping? Or is there just too little of it to make a conclusion on that? My question was entirely consistent with ol' Issac.
We think we're quite sure in our observations, so that helps, but to be able to claim how the simple laws can exactly produce what we see, we have to do a lot of work. Just like what Newton figured out was not provable before without all the computations:
Would I be right in thinking that also puts severe limits on how much it interacts with itself? Because my intuition would be, if you loose normal matter into a gravity well, it will clump, even if it doesn't interact with the source of the gravity.
Am I inferring correctly?