My understanding is that observations supports that universe has a large scale structure consisting of large voids with lower density and filaments with higher density. How are the filaments affected by the expansion of the universe? My best guess is that the voids expand and the filaments stretch.

This page forbes.com/startswithabang/cosmic-superclusters  has a pretty good pop-sci explanation. Filaments stretching and dissolving can also be found for example here: medium.com/starts-with-a-bang.

My reason for asking is that I’m somewhat confused by other descriptions where filaments consists of gravitationally bound matter, for instance wikipedia.org/Galaxy_filament. To me “gravitationally bound” and “dissolving” sounds like a contradiction which probably means I have misunderstood something.

 

 

An example of the structure; results of a digital simulation showing the large-scale distribution of matter, with filaments and knots:

Université de Genève. (2015, December 2). The cosmic web: Seeing what makes up the universe. ScienceDaily. Retrieved April 13, 2019 from www.sciencedaily.com/releases/2015/12/151202132934.htm

46 minutes ago, Ghideon said:

My understanding is that observations supports that universe has a large scale structure consisting of large voids with lower density and filaments with higher density. How are the filaments affected by the expansion of the universe? My best guess is that the voids expand and the filaments stretch.

This page forbes.com/startswithabang/cosmic-superclusters  has a pretty good pop-sci explanation. Filaments stretching and dissolving can also be found for example here: medium.com/starts-with-a-bang.

My reason for asking is that I’m somewhat confused by other descriptions where filaments consists of gravitationally bound matter, for instance wikipedia.org/Galaxy_filament. To me “gravitationally bound” and “dissolving” sounds like a contradiction which probably means I have misunderstood something.

 

 

An example of the structure; results of a digital simulation showing the large-scale distribution of matter, with filaments and knots:

Université de Genève. (2015, December 2). The cosmic web: Seeing what makes up the universe. ScienceDaily. Retrieved April 13, 2019 from www.sciencedaily.com/releases/2015/12/151202132934.htm

A description in your Forbes link under one of the illustrations sums it up in my view..."Over time, gravitational interactions will turn a mostly uniform, equal-density Universe into one with large concentrations of matter and huge voids separating them". 

Also as per your Wiki link, DM plays an important part best described here...."In the standard model of the evolution of the universe, galactic filaments form along and follow web-like strings of dark matter.[4] It is thought that this dark matter dictates the structure of the Universe on the grandest of scales. Dark matter gravitationally attracts baryonic matter, and it is this "normal" matter that astronomers see forming long, thin walls of super-galactic clusters."

53 minutes ago, Ghideon said:

My understanding is that observations supports that universe has a large scale structure consisting of large voids with lower density and filaments with higher density. How are the filaments affected by the expansion of the universe? My best guess is that the voids expand and the filaments stretch.

This page forbes.com/startswithabang/cosmic-superclusters  has a pretty good pop-sci explanation. Filaments stretching and dissolving can also be found for example here: medium.com/starts-with-a-bang.

My reason for asking is that I’m somewhat confused by other descriptions where filaments consists of gravitationally bound matter, for instance wikipedia.org/Galaxy_filament. To me “gravitationally bound” and “dissolving” sounds like a contradiction which probably means I have misunderstood something.

 

 

An example of the structure; results of a digital simulation showing the large-scale distribution of matter, with filaments and knots:

Université de Genève. (2015, December 2). The cosmic web: Seeing what makes up the universe. ScienceDaily. Retrieved April 13, 2019 from www.sciencedaily.com/releases/2015/12/151202132934.htm

This simulation of the early universe expansion might give a clue: Formation of the large-scale structure in the Universe: filaments

Thanks for your answers @StringJunky and @beecee. I’ll have to study the topic some more, and I’ll likely post additional questions later. 

I think I found my issue in @StringJunky's reference, co-moving coordinates!

Short explanation, I'll try posting a better followup if I understand more details later. 
Evolution of structures in a 43 million parsecs (or 140 million light years) box, taken from a simulation. Showing two frames; early universe and present epoch:

 

From the above two frames it looks to me like the density on large scales is the same. The same amount of matter in a 140 million light years box in two different configurations. What I have missed is that such models and simulations can use different coordinate systems, the side of the box is not necessarily 140 million light years in proper distance. From the reference: On large scales seen here, gravity cannot compete with the dark energy-driven acceleration and the growth of structures ceases. As the contraction of large-scale structures is halted they expand with the universe and appear "frozen" in our co-moving system of coordinates.