Galaxy filaments are "amongst the largest known cosmic structures in the Universe. They [...] form the boundaries between large voids in the Universe."
As their name suggests, filaments are essentially 1-dimensional objects (significantly longer and wider than thick, and significantly longer than wide), but how can such objects be the (very) boundaries of 3-dimensional voids?
In the same Wikipedia article, "supercluster complexes", "great walls", and "great attractors" are proposed as synonyms for "filaments" which suggest other dimensions ($d$):
- unspecified for "complexes"
- $d=2$ for "walls"
- fractal ($1 < d < 2$ or $2 < d < 3$) for "attractors"
What is/can be said about the dimension of these cosmic objects?