Why are galaxy filaments the shape they are?

[tgoolsby2]

http://en.wikipedia.org/wiki/Galaxy_filament

I would think that if space were to be uniformly filled with matter, then over time the large scale structure of the galaxies would look more like round shaped clouds of galaxy clusters, but galaxy filaments look like there is something in the voids between the filaments which is pushing the galaxies away from that point, causing them gather in regions between these repulsive regions. That's what it looks like is happening, but unless space is expanding more quickly in some areas than others, I don't think these repulsive regions actually exist. Is my intuition of gravity on this large scale just wrong, and this shape is a natural outcome of gravity on these large scales?

[StupendousMan]

Your intuition is wrong, but so is just about everyone else's. After all, we don't have much experience with self-gravitating objects in our daily lives.

Suppose a cloud is slightly elongated. The material in the middle will feel a stronger gravitational force inward than the material near the ends. That means that the material in the middle will contract more -- causing the cloud to become MORE elongated. Then the material in the middle will feel an even stronger gravitational force .... and so on.

[noncryptic]

One force involved in causing those shapes is gravity, as StupendousMan points out.

At the scale of galaxy superclusters there's also an opposite force at work which at that scale is stronger than gravity: expansion.

I visualize it like this: Imagine a flat piece of dough with a blob of sirup on it, then stretch the dough: you get a filament of sirup on the dough. The stretching dough represents expansion, the 'self-stickiness' of the sirup represents gravity.

[astromark]

It would seem that direct observation has proven that

a repulsive force that is expanding the space that is not gravity bound is at work and eccelorating still.

That your conclusions of gravity is not backed by observation., but still interesting..

Do we know by what force of action is expanding the Universe... NO.