2
votes
How much energy one would get by tethering an imaginary rope to a galaxy and let it unwind until reaching the Hubble horizon?
A simple argument in a de Sitter background gives an extracted energy of $mc^2$.
The usual static coordinates for de Sitter space are
$$ds^2 = \left(1-\frac{r^2}{R^2}\right)dt^2 - \left(1-\frac{r^2}{R^...
- 19.2k
1
vote
Accepted
Why the megaastrophysical objects do not collapse due to their gravitational selfattraction?
We live in a specific time and gather cosmological observations which we model with the mathematical theories proven successful up to now. These theories predict and explain stable gravitational ...
- 224k
1
vote
Accepted
On the implementation of the spherical collapse model in cosmology
Let's replace $a$ in your expressions by $r$, so that we can discuss the global expansion factor $a$ separately. So we have
$$
r=A(1-\cos\theta),
\\
t=B(\theta-\sin\theta).
$$
Under the approximation ...
- 86
1
vote
When will the particle horizon reach its limit of 63 billion light years?
The maximum particle horizon size is approached asymptotically over an infinite span of time.
There is no particular time at which the light from distant objects stops reaching us. Rather, the ...
- 19.2k
1
vote
How can you determine distances to obejcts further away than 13.72 billion light years?
It doesn't make sense to treat the light travel time times $c$ as a distance when the light travel time is large, because of spacetime curvature.
In a comment you implied that you want to know the ...
- 19.2k
1
vote
Varying energy density of photons?
For self-consistency, we need the energy to come from somewhere. For astrophysical sources, it of course comes from matter. In that case you can assume that there is some energy exchange rate $\Gamma$ ...
- 86
1
vote
Energy from spacetime expansion?
General relativity, in an arbitrary spacetime, has local conservation of energy but not global conservation of energy. On practical scales, spacetime can be modeled as asymptotically flat. In an ...
- 11
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