[carterac]

How do these filaments stay stable and not collape under their own gravity due to instabilities? Or, if there is 0 net force causing them to collapse, why doesn't the dark matter drift apart naturally and become less dense and more diffuse over time? Either way, filaments of high density don't seem to be a natural stable state. Can someone explain this?

[archgoon]

Well, the particles also have no way to radiate away energy, so the dark matter particles just whisk around each other under the gravitational force.

You can check out something like this on your computer

http://http.developer.nvidia.com/GPUGems3/gpugems3_ch31.html

To see what pure 1/r^2 interactions look like. You can download the simulations from here:

http://developer.nvidia.com/cuda/cuda-toolkit-40

[InclinedPlane]

The dark matter halos don't experience friction, and are incapable of emitting heat radiation to cool off and condense.

If you take a bunch of marbles and put them in a big bowl they will roll around for a while but eventually end up in the bottom of the bowl because they keep running into each other. But if you put in special marbles that just pass through each other and don't experience friction then you'll end up with marbles rolling around the bowl everywhere for ever, which is the way dark matter works.