Questions tagged [cosmology]
The study of the large-scale structure, history, and future of the universe. Cosmology is about asking and answering questions about the "big picture" - the extent, origin, and fate of everything we know.
5,568
questions
9
votes
4
answers
652
views
Understanding expansion of the Universe as things flying apart
Say that we have a Universe uniformly filled just with matter (let's not bring dark energy into this). And say that we fill it with very light particles (so that the gravitational interaction between ...
- 6,142
2
votes
1
answer
473
views
Prove that the value of the cosmological constant equals the energy density of the vacuum
I know that Einstein introduced his cosmological constant assuming it as an independent parameter, something characteristic of the Universe, in itself, but the term of it in the field equations can be ...
CommunityBot
- 1
1
vote
1
answer
210
views
How do I interpret the unit of [1/dex]?
I am trying to reproduce the mass function graph from a paper. I have calculated the mass function $\frac{\rm{d}f}{\rm{d}\log M}$, where $f$ is the mass fraction with respect to the total mass in the ...
CommunityBot
- 1
10
votes
7
answers
5k
views
Why is FTL travel impossible if the universe expands FTL?
If the universe is expanding spacetime faster than light (FTL), is FTL travel no longer completely impossible?
Do not care about energy requirements or needing new tech, just if it is NOT physically ...
- 6,479
0
votes
1
answer
67
views
Why can we use Bose-Einstein statistics in this expression for number density
In a system with $N$ particles in some volume $V$ in contact with a reservoir of temperature $T$, we find that
$$\bar{n_i}=\frac{g_i}{e^{\frac{{\epsilon}_i -\mu}{kT}} \pm 1}$$
depending on whether the ...
- 91
2
votes
1
answer
96
views
What causes the 41k obliquity cycle?
The obliquity cycle refers to the oscillation of the Earth's axial tilt, which has a period of about $41,000$ years.
When the Moon is the main cause of the tilt, and it is receding linearly, how can ...
- 11.7k
0
votes
0
answers
51
views
The data file of the LISA Interferometer results
How to extract the data of the strain versus frequency plot of the Laser Interferometer Space Antenna (LISA): Figure (2) in this paper:
https://arxiv.org/abs/1702.00786
The paper doesn't contain any ...
- 207k
2
votes
0
answers
264
views
Singularities in Bianchi models in general relativity (physical science)
what are the conditions to check point type singularity in a bianchi type model?
bianchi type model are of Type I,II,III,IX,IV or u can say we use different Bianchi type models having some specific ...
- 207k
0
votes
0
answers
30
views
Magnetic monopole in CPT universe model
I've recently read this paper CPT universe, and a thought came into my mind.
Is it possible to discuss magnetic monopole based on this CPT universe model?
This paper points out that some mysterious ...
- 529
1
vote
2
answers
69
views
Can Bose-Einstein condensates and Fermionic condensates survive for long periods of time in space?
Imagine we have a cold region of the universe, almost devoid of matter and radiation. Or perhaps in a future universe where the CMB has "cooled" down to sufficiently low "temperatures&...
- 628
2
votes
1
answer
110
views
Saddle Shaped Universe
The universe, as described by FLRW metric, if $k = -1$ is clearly a 2 sheet 3-hyperboloid described by $x^2+y^2+z^2-w^2=-R^2$. So where does the more common saddle shaped picture of the open universe ...
- 73.8k
0
votes
1
answer
64
views
Beginning of a dark energy (cosmological constant) dominated universe
Consider a flat universe with only dark energy (cosmological constant)
In such universe, the Friedmann Equation can be written as:
$$H(t)^2 = \left(\frac{\dot a}{a}\right)^2 = \frac{8\pi G \...
- 9,072
3
votes
2
answers
144
views
How can we model the primordial Universe while the interior of a neutron star and comparable states of matter are still mostly unknown?
There is something I never quite understood about the physics of the primordial Universe. There are states of matter at high temperature/high pressure that are still, today, poorly understood. The ...
- 133k
0
votes
1
answer
42
views
Friedmann Equation and a contracting universe
Consider a universe with a nonzero curvature and matter.
One can write the Friedmann Equation in this universe as such:
$$\frac{H(t)^2}{H_0^2} = \frac{\Omega_0}{a^3}+\frac{1-\Omega_0}{a^2}$$
Where $H(...
- 207k
-4
votes
0
answers
46
views
Simple question about finite Universe [duplicate]
If, by Big Bang, Universe was created from initial singularity, with finite "speed" of expansion of matter, shouldnt it be finite as well?
- 207k