All Questions
47
questions
1
vote
0
answers
60
views
Is the universe closed or flat?
Apparently there is a tension in the measuring of the curvature of the universe (https://arxiv.org/abs/2307.07475) as apparently in 2018 the Planck collaboration got a series of results consistent ...
- 2,472
2
votes
1
answer
135
views
How do you relate $\Omega_{k}$, the curvature term in the FLRW metric, to the radius of curvature?
I have assumed, for reasons a bit too detailed to go into here, that if $\Omega_{k}$, the curvature term in the FLRW metric, is equal to 1, then the radius of curvature is equal to 13.8 billion light ...
- 371
3
votes
0
answers
84
views
Why are departures from flat spacetime geometry small on scales smaller than the Hubble radius?
In Chapter 5 of Baumann's cosmology book where he discusses structure formation starting from Newtonian perturbation theory, Baumann mentions at the beginning that
Newtonian gravity is a good ...
- 394
2
votes
1
answer
3k
views
Ricci scalar curvature in FLRW flat universe
I have a simple question about the relation between the Ricci scalar curvature and the $k$ constant in the Friedmann–Lemaître–Robertson–Walker solution. Assuming $k=0$, such that the space can be ...
- 308
1
vote
1
answer
117
views
Universe flatness
On: https://en.wikipedia.org/wiki/Shape_of_the_universe
It is written:
"The exact shape is still a matter of debate in physical cosmology, but experimental data from various independent sources (...
- 97
8
votes
4
answers
3k
views
Confusion about the shape of the universe
From what I understood, a Universe with a positive curvature should behave like a sphere, and light will eventually reach the point where it started. Similarly to a ball, when an ant starts to walk on ...
user311398
1
vote
0
answers
98
views
Where is the warped throat in Klebanov-Strassler geometry?
In string theory, it is common to work in the Klebanov-Strassler geometry to find AdS and dS vacua. Applications are that anti-branes can be placed at the tip of this deformed/warped conifold to ...
- 119
2
votes
1
answer
221
views
Can we have positively curved space within negatively curved spacetime?
Thinking about the universe as a whole. One could imagine that the three spatial dimensions each have the same, say positive, curvature, making space spherical, while time is negatively curved, making ...
- 371
1
vote
2
answers
274
views
Does a positive curvature necessarily indicate the finiteness of the universe?
Imagine the following situation: more and more accurate measurements of the average density of the Universe reveal that it is greater than the critical one, which corresponds to the model of a closed ...
- 956
1
vote
1
answer
59
views
Curvature sign-changing Friedman models
Isotropy and homogeneity of space leads to the spacetime metric of the form
$$
ds^2=-dt^2+d\sigma_k^2,
$$
where $d\sigma_k^2$ is the metric on one of the standard manifolds (the 3-sphere, Euclidean 3-...
- 421
5
votes
4
answers
1k
views
Connection between spatial, temporal, and spacetime curvature?
There is an innumerable quantity of questions and answers on this site about spatial, spacetime, and temporal curvature. None of these answer my question.
Unfortunately, many use the terms in ...
- 29k
0
votes
2
answers
60
views
Does the increasing rate of expansion of the universe have any implication on or alter the curvature of the universe?
I'm not really knowledgeable on physics but was curious about this and couldn't find any good answers related to it.
- 3
2
votes
2
answers
124
views
Measuring the Hubble constant in a curved universe
In an article from the University of Chicago, July 17, 2020, it is stated that
"Judging cosmic distances from Earth is hard. So instead, scientists measure the angle in the sky between two ...
- 24.8k
0
votes
1
answer
135
views
Curved spacetime and geodesics
Is it right to take in account that the Universe might be similar to the Earth regarding curvature so when we look at two galaxies equidistant to Earth but at a right angle observed from Earth their ...
- 467
1
vote
2
answers
490
views
Curvature of spacetime in Friedman cosmological models
Short version of my question is as follows: What is curvature of spacetime (rather than space) in Friedman cosmological models?
Now the long version, including evolution of my thoughts and background ...
- 2,173