<p>I asked one of the authors of a paper about the expansion of voids and filaments in the cosmic web whether voids expand faster when dark energy started to dominate in the universe. But I am confused about what he said, as it seems contradictory...</p>
<p>This is what he said:</p>
<blockquote>
<p>The Universe is expanding faster (exponentially actually) when dark-energy dominated. Voids are expanding due to this effect, so their evolution is not dynamical per se, but rather a consequence of the frame of the Universe stretching out. As a consequence, voids don’t percolate faster with dark energy compared to during the matter-dominated era (the first half of the history of the Universe). The main effect of DE is to dilute structures, and thus, to change which structures are dense enough to overcome the expansion of the Universe and collapse under their own gravity.</p>
</blockquote>
<p>Also, in his paper, <em><a href="https://arxiv.org/abs/2309.08659" rel="nofollow noreferrer">Evolution of cosmic filaments in the MTNG simulation</a></em>, they say:</p>
<blockquote>
<p>Powering the increased expansion of voids at late times, DE (Dark Energy) can also act on the merging and disconnection of cosmic filaments</p>
</blockquote>
<p>So, on the one hand the co-author says that the universe is expanding faster due to dark energy and that voids expand due to this effect on spacetime, but on the other hand he also says that voids don't percolate faster due to this compared to when the universe matter-dominated era. Isn't this a contradictory statement? Do voids expand faster or not due to dark energy?</p>

CC BY-SA 4.0
2024-08-21T13:29:24.860Z
I think the first quote is saying: voids expand faster when dark energy dominates, but they don't *percolate* faster, because the rest of the universe is also expanding faster, so the voids aren't expanding *at the expense* of denser areas, and thus can't link up (which I think is what "percolate" means in this context).
Peter Erwin
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2024-08-21T13:43:58.377Z
@PeterErwin but if voids can't link up, how can filaments around them merge with each other as the paper says?
vengaq
CC BY-SA 4.0
2024-08-22T21:41:41.453Z
Voids have no matter.  They care not about the matter-dominated era.
eshaya
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2024-08-22T22:07:43.810Z
@eshaya but if voids expand faster due to dark energy, shouldn't it be obvious that they would expand faster in a universe with a cosmological constant than in one without one?
vengaq
CC BY-SA 4.0
2024-08-22T23:00:55.367Z
Voids have matter, including galaxies. They’re just less dense.
Peter Erwin
CC BY-SA 4.0
2024-08-23T15:21:04.063Z
I voted to close this because there is no coherent question here.
eshaya
CC BY-SA 4.0
2024-08-26T03:40:13.970Z
@eshaya I think the core question is a good one, even if it could be expressed more succinctly. Voids grow because of 2 different processes: (a) the contraction of matter into filaments & walls, and (b) the expansion of space itself. If voids "percolate" as part of this condensation of matter creating the Universe's foamy large-scale structure, then was this process most pronounced during the matter-dominated era? Or is the *relative* expansion of voids greater now under DE domination? I'm voting to keep the question open.
Chappo Hasn't Forgotten
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2024-08-26T18:12:42.567Z
When DE dominates, everything not collapsed expands at the same rate, ($\dot{r}/r$), determined by Lambda.  The shape of the matter distribution is therefore frozen as it expands.  How do you deal with percolation though?  The entire universe becomes a void, so is that a lot of void percolation? But, in expanding coordinates nothing changes, so is that no percolation?
eshaya
<astrophysics><cosmology><universe><expansion><space-time>
Do voids expand faster at dark energy domination era or not?
vengaq
# Do voids expand faster at dark energy domination era or not?

(Asked by: username_0 on 2024-08-21)

I asked one of the authors of a paper about the expansion of voids and filaments in the cosmic web whether voids expand faster when dark energy started to dominate in the universe. But I am confused about what he said, as it seems contradictory...

This is what he said:

> The Universe is expanding faster (exponentially actually) when dark-energy dominated. Voids are expanding due to this effect, so their evolution is not dynamical per se, but rather a consequence of the frame of the Universe stretching out. As a consequence, voids don’t percolate faster with dark energy compared to during the matter-dominated era (the first half of the history of the Universe). The main effect of DE is to dilute structures, and thus, to change which structures are dense enough to overcome the expansion of the Universe and collapse under their own gravity.

Also, in his paper, *[Evolution of cosmic filaments in the MTNG simulation](https://arxiv.org/abs/2309.08659)*, they say:

> Powering the increased expansion of voids at late times, DE (Dark Energy) can also act on the merging and disconnection of cosmic filaments

So, on the one hand the co-author says that the universe is expanding faster due to dark energy and that voids expand due to this effect on spacetime, but on the other hand he also says that voids don't percolate faster due to this compared to when the universe matter-dominated era. Isn't this a contradictory statement? Do voids expand faster or not due to dark energy?

**Tags:** astrophysics, cosmology, universe, expansion, space-time
> **Comments:**
> **username_1**: I think the first quote is saying: voids expand faster when dark energy dominates, but they don't *percolate* faster, because the rest of the universe is also expanding faster, so the voids aren't expanding *at the expense* of denser areas, and thus can't link up (which I think is what "percolate" means in this context).  
> **username_0**: @PeterErwin but if voids can't link up, how can filaments around them merge with each other as the paper says?  
> **username_2**: Voids have no matter.  They care not about the matter-dominated era.  
> **username_0**: @eshaya but if voids expand faster due to dark energy, shouldn't it be obvious that they would expand faster in a universe with a cosmological constant than in one without one?  
> **username_1**: Voids have matter, including galaxies. They’re just less dense.  
> **username_2**: I voted to close this because there is no coherent question here.  
> **username_3**: @eshaya I think the core question is a good one, even if it could be expressed more succinctly. Voids grow because of 2 different processes: (a) the contraction of matter into filaments & walls, and (b) the expansion of space itself. If voids "percolate" as part of this condensation of matter creating the Universe's foamy large-scale structure, then was this process most pronounced during the matter-dominated era? Or is the *relative* expansion of voids greater now under DE domination? I'm voting to keep the question open.  
> **username_2**: When DE dominates, everything not collapsed expands at the same rate, ($\dot{r}/r$), determined by Lambda.  The shape of the matter distribution is therefore frozen as it expands.  How do you deal with percolation though?  The entire universe becomes a void, so is that a lot of void percolation? But, in expanding coordinates nothing changes, so is that no percolation?  

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## 0 answers

