All Questions
Tagged with terminology cosmology
31
questions
1
vote
1
answer
95
views
Why do people say that the $\Lambda$-CDM model has six independent parameters?
The Wikipedia article on the $\Lambda$-CDM model says that the model has six "independent parameters". It also says that the model has several "fixed" parameters and several "...
- 48.4k
0
votes
1
answer
66
views
Name of metric used by Friedmann
In his original paper, Friedmann used the following dynamic and symmetrical metric:
$$\mathrm{d}s^2=a(t)^2\left(\mathrm{d}\chi^2+\sin (\chi)^2\left(\mathrm{d}\theta^2+\sin (\theta)^2 \mathrm{d}\phi^2\...
- 181
2
votes
5
answers
506
views
What is the branch of physics that asks the question 'what was before the Big Bang'?
What is the branch of physics that asks the question 'what was before the Big Bang', assuming the Big Bang is truly what happened at the beginning of the universe? If there could be a better model ...
- 421
1
vote
2
answers
214
views
Origin of the term “physical density parameter” for $\omega_i = \Omega_i h^2$
When measuring cosmological density parameters, the parameters that are actually determined are the combinations $\Omega_i h^2$, sometimes defined as $\omega_i = \Omega_i h^2$, rather than the “plain” ...
- 486
5
votes
1
answer
1k
views
de Sitter space vs de Sitter universe
I have heard of the term de Sitter space.
From this post user G. Smith writes,
De Sitter spacetime is curved; specifically, it has the same positive scalar curvature at every point.
Likewise, when I ...
- 8,650
1
vote
0
answers
202
views
What do freeze out and freeze in mean in the context of cosmology?
I have read that when the interaction rate is much greater than the Hubble expansion rate a species is in thermal equilibrium the hot plasma, when the interaction rate fall below the Hubble expansion ...
0
votes
1
answer
126
views
What is glass-like in cosmology?
This is from Galaxy Formation and Evolution by Hou-Jun Mo, and this chapter is about numerical simulations of the initial conditions.
The cosmological N-body integrator is then used to follow their ...
29
votes
5
answers
5k
views
What does the concept of an "infinite universe" actually mean?
When physicists talk about the universe being infinite, or wondering whether it is or not, what do these two options actually mean? I am not interested whether the universe is infinite or not, I am ...
- 406
1
vote
0
answers
88
views
Why is Cauchy horizon named after Cauchy?
I think the title says it all; I have done a lot of Googling, but I could not find the answer.
Since (I assume) the concept was discovered after Cauchy's death, I speculate that there is a connection ...
- 11
0
votes
1
answer
577
views
Physical meaning of the space-space components $T^{ij}$ of the stress-energy tensor $T^{\mu\nu}$
The time-time component $T^{00}$ and the time-space components $T^{0i}$ of the energy-momentum tensor $T^{\mu\nu}$ are respectively called the Hamiltonian (energy) density and the momentum density. ...
- 11.7k
1
vote
2
answers
294
views
Nature of motion between comoving observers; What is the common time that they agree on? [closed]
This is a set of follow-up questions regarding this post. The following four queries are very closely related and needed to asked at the same place.
Question 1 Is it really possible to regard the ...
- 26.8k
1
vote
1
answer
187
views
How to understand the Planck data?
I want to analyze the Planck data to get relevant Cosmological parameters from it. But I don't know how can I go about this.
Can anyone guide me? Online sites/Research papers would be nice.
I know ...
- 624
4
votes
1
answer
700
views
What is Cosmic Downsizing?
I've had a quick look at a few lecture pdfs and papers as supplementals to my own given lecture notes, but I can't seem to get a proper explanation for what cosmic downsizing is.
The closest ...
- 147
4
votes
1
answer
976
views
What's the meaning of canonical and phantom scalar field?
I read in some paper about non-minimal derivative coupling that $\varepsilon = +1$ correspond to canonical scalar field, while $\varepsilon = -1$ corresponds to phantom scalar field. $\varepsilon$ is ...
- 41
2
votes
1
answer
87
views
The condition for cosmic acceleration
I'm currently writing a review paper on the accelerated expansion of the universe (focussing on scalar field models like quintessence) and was wondering if there is a specific name for the ...
- 215