All Questions
81
questions
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Does dark energy work on the principle of anti-gravity, i.e. repulsive gravity?
Our universe is made up of 95% dark energy+ dark matter (of which most is dark energy), and this dark energy is considered to be the main reason for the expansion of our universe. But, anything that ...
0
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0
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33
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Turnaround radius being increased in fast collapsing regions?
In the context of formation of large-scale structures, there would be a turnaround radius where expanding matter would detach from the Hubble flow and start to collapse (https://www.aanda.org/articles/...
- 2,462
1
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1
answer
30
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Questions about cosmic sheets/walls/filaments
I had a couple of questions about cosmic filaments in the context of the cosmic web structure formation:
In this thesis (https://www.imprs-hd.mpg.de/51939/thesis\_cpenzo.pdf), the author indicates in ...
- 2,462
0
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0
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32
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Can the integrated Sachs-Wolfe and the Rees-Sciama effects have any influence on matter?
CMB photons can be affected by the expansion of the universe through the linear integrated Sachs-Wolfe effect (ISW) 1 and the non-linear ISW effect or also called Rees-Sciama effect 1.
In particular, ...
- 2,462
1
vote
2
answers
163
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“Negative energy” definition of “gravitationally bound” in expanding cosmology
First off, I realize that there is already a number of questions relating to gravitational binding in cosmology:
Gravitationally bound systems in an expanding universe
Gravitationally bound systems ...
- 486
12
votes
1
answer
1k
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Is there a distance from a gravitational source where the influence of gravity and dark energy are balanced out?
While gravity is a force that attracts
objects with mass, dark energy (or, alternatively, the accelerated expansion of the universe) is not.
However, I have found numerous articles, forums, questions ...
- 2,462
0
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0
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33
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How does the gravitational potential change when using physical instead of comoving coordinates?
If we consider the universe as filled by a self-gravitating fluid, then there will exist an associated gravitational potential $\phi$ and the Poisson equation $\nabla^2=4\pi Ga^2\rho$ will hold, where ...
- 293
1
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1
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238
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Poisson equation in Cosmology at first order in perturbation theory
The book Cosmology by Daniel Baumann states that the Poisson equation for a universe where we consider the effects of both gravity and expansion, expressed in physical coordinates $\vec{r}=a\vec{x}$, ...
- 293
0
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0
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65
views
Hydrogen atom in void
We have a hydrogen atom, in a gravitationally bound system nothing interesting happens to it. Let's put it in an empty world where there are only an electron and a proton. Several forces act on it: ...
- 1
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votes
2
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44
views
Age of the universe due to expansion
"If gravity working on matter is the only force at work on large scales, then the attactive force of gravity will act to slow the expansion. In this case, the universe was expanding more rapidly ...
1
vote
1
answer
49
views
Do expanding mass shells gain energy?
I've found an article which says in section 2
an expanding gravitational system of given mass gains energy
Does an expanding gravitational system or an expanding shell of a given mass gain energy as ...
- 2,462
2
votes
2
answers
87
views
Why the megaastrophysical objects do not collapse due to their gravitational selfattraction?
At the largest scale in the universe exist formations called filaments which form something like a spider web along the whole universe. But they seem to be quite static. So my question is about the ...
- 2,255
2
votes
1
answer
71
views
Can empty space 'press' galaxies?
If gravity slows the effects of time, then empty space will see greater expansion than space inhabited by massive objects. So the space within a galaxy will be expanding more slowly than the space ...
1
vote
0
answers
95
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Black Holes, Gravity, and the Creation [duplicate]
As I suppose we all accept, the universe started as an unintuitive singularity—either, "Let there be light," or "The Big Bang". Something from nothing expanded and at luminal ...
- 111
3
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1
answer
151
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Is the Hubble constant actually constant? [closed]
For this question I completely understand the the constant is different over time, but just having one of those daydream thoughts and thought I'd ask. As a layman, I've been made to believe the ...
