All Questions
23
questions
2
votes
1
answer
123
views
Could the universe have a form of a $T^3$-torus?
Cosmological measurements suggest that we live in a flat universe. However, what might be less clear is its topology. So could the flat universe have the form of a $T^3$-torus, i.e. the torus whose ...
- 9,778
1
vote
1
answer
67
views
Does the universe have an infinite volume? [duplicate]
The implications of a spatially infinite universe is profound, but so are the implications of a finite universe. What we know about this issue?
- 11
4
votes
3
answers
2k
views
Will a light come back within finite years?
In this answer Javier said
Imagine the universe was the inside of a ball. We're 3D now, so no one is hiding any dimensions. This ball has a border, except it's not really a border. You should think ...
- 405
2
votes
0
answers
85
views
Could the universe be a 4-ball?
I recently thought of the idea that the universe could be an infinite 4-ball. The Big Bang would be its centre, and time would be outward from its centre (one layer would be one point in time). I ...
user334229
-1
votes
2
answers
169
views
Can space only be infinite? [closed]
I have read before that if you could just go fast enough, as a thought experiment, and you move in a straight line, in any direction, that you eventually might reach the spot from which you started. I ...
- 11
1
vote
2
answers
227
views
Cosmology - Confusion About Visualising the Universe as the Surface of a 3-Sphere
Consider the FRW metric for the Universe in the form found in many standard cosmology textbooks:
$$ds^2 = -dt^2 + a(t)^2\left(\frac{dr^2}{1-Kr^2}+r^2(d\theta^2 + \sin^2\theta d\phi^2)\right)$$
I am ...
- 201
0
votes
3
answers
436
views
Explain why the universe could be compact
Regarding the topology of the universe, it could be compact like a sphere or open like a Euclidean space, but since the universe started from a single point, doesn't that mean that the shape of the ...
user279762
2
votes
1
answer
369
views
Does visible universe have shape of a 3-sphere?
Here's my logic:
If you look out in the visible universe you see further back in time. Look enough back and you get to the big bang singularity.
This means whichever way you look in the visible ...
user84158
1
vote
1
answer
226
views
Positive local spatial curvature of the universe implies that the universe is compact (i.e. finite)?
I quote from the Wikipedia page about the shape of the universe:
If the spatial geometry [of the universe] is spherical, i.e., possess positive curvature, the topology is compact.
I'm trying to ...
- 3,369
2
votes
0
answers
41
views
What is the shape of the universe? [duplicate]
If it's flat then how a volume can be flat?
And I've read that it's actually not flat .....it's a "Poincaré dodecahedral space".
Any suggestions for books posts or articles are highly appreciated.
- 31
0
votes
0
answers
195
views
Can the shape of our Universe be a Mobius strip? [duplicate]
The Friedmann Equations describe three possibilities for the shape of our using General Relativity, I read in a book that the shape of our Universe is a 3-sphere such that in any direction if you ...
- 1,368
1
vote
1
answer
175
views
Self-intersecting universe
General relativity says space-time is a $4$-dimensional manifold which may have non-zero global curvature. Now if we take a random curve or surface or $n$-fold, it may fail to be a manifold because it ...
- 111
1
vote
2
answers
279
views
What is outside the boundaries of our universe (Future horizon) [duplicate]
I m having difficulty understanding what is after the "Future Horizon" as defined per wikipedia
https://en.wikipedia.org/wiki/List_of_cosmological_horizons#Future_horizon
I read the similar "If the ...
- 119
-1
votes
2
answers
208
views
Shape of the observable universe or Cosmic Horizon
My question is about the shape of the observable universe or Cosmic Horizon.
In literature it is described as having a radius, constant.
But in an accelerating expanding universe this seems ...
- 63
18
votes
4
answers
3k
views
If the Universe is Flat, has Finite Mass/Energy, and is Simply Connected, Then there MUST be an Edge, Mustn't there?
Assumptions:
The universe is flat (currently supported)
The universe is simply connected (the edges aren't glued together as in a torus)
The universe contains finite mass and energy
Conclusion:
...
- 199