I How is dark matter thought to have formed a network scaffolding?

Summary
How is dark matter, responding to gravity, thought to have formed filaments and walls--the scaffolding for the large scale structure of the universe--rather than random clumps?
The summary pretty much says it all: How is dark matter, responding to gravity, thought to have formed filaments and walls--the scaffolding for the large scale structure of the universe--rather than random clumps? I can understand how scattered matter might not coalesce while exchanging photons (and receiving momentum away from other, reflective, matter), and that dark matter, by not interacting with light after the Big Bang, might be able to form a scaffolding with sufficient mass to have matter be attracted to it, despite the photon bath. But why filaments and walls, rather than randomly, though perhaps fairly regularly, arranged clumps?
 

kimbyd

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It's the natural result of gravitational collapse from gaussian primordial perturbations. Here's an example of one simulation which demonstrates this visually:
 

kimbyd

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Actually, this simulation is better for the purposes of this thread:
 
Thanks. Beautiful simulations--especially the 2nd one. In both simulations, however, it seems filamentous structures arise almost immediately. Is this because they've been placed into the models? In other words, the initial distribution of dark matter (or matter) seems decidedly non-uniform. (I don't understand what you mean by "primordial perturbations," unless you mean perturbations away from perfect homogeneity, and maybe even away from random clumpiness.)
 

kimbyd

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Thanks. Beautiful simulations--especially the 2nd one. In both simulations, however, it seems filamentous structures arise almost immediately. Is this because they've been placed into the models? In other words, the initial distribution of dark matter (or matter) seems decidedly non-uniform. (I don't understand what you mean by "primordial perturbations," unless you mean perturbations away from perfect homogeneity, and maybe even away from random clumpiness.)
Nope! They just use uncorrelated Gaussian random perturbations as the initial state. At least, they're uncorrelated at the start. Later on they become correlated due to gravitational interactions. That's what gives rise to the filamentary structure.
 
Can anyone explain this to me in gravitational, mechanistic terms? It's inevitable that, with a random initial distribution, there will be some units of mass closer to one another than others, and that those initially close units will coalesce in a linear arrangement (if only 2 units participate). But why is it that neighboring (dark) matter is subsequently pulled into filamentous alignments, along the axes of the 2-unit coalescences (for lack of a better term), rather than from all directions? Is it due to momentum from multi-unit approaches "pulling" the coalescences apart, like taffy, in a necessarily linear way (along the line of the net momentum of approach)? I don't recall seeing this sort of thing in the simulations.
 
I must take that last comment back. The first simulation (but not at all the 2nd) does indeed show such motions within the coalescences, and a lengthening effect of momentum--especially at the very end.
 
They just use uncorrelated Gaussian random perturbations as the initial state. ... Later on they become correlated due to gravitational interactions. That's what gives rise to the filamentary structure.
Is my understanding of exactly how those filaments arise reasonable/correct in your view? (See previous two responses--though subsequent to your quoted comments.)
 
Still it is hard to imagine how these huge voids and walls formed. The software could have been written with a bias towards making these structures form. Could the voids and walls have been caused by catastrophic explosions of massive stars early in structure formation? (My suggestion is probably nonsense.)
 

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