All Questions
36
questions
25
votes
9
answers
6k
views
Why are spherical shapes so common in the universe?
I have a simple question. Why are most objects in the observable universe spherical in shape? Why not conical, cubical, cuboidal for instance? I am furnishing a few points to justify this statement:
...
- 517
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
3
votes
0
answers
97
views
Coordinate Charts to Describe the Universe
This is a bit of a soft question. I'm currently taking a GR course. The professor has asserted that, because the universe has curvature, one needs to cover it by more than one smooth coordinate chart. ...
- 131
3
votes
3
answers
327
views
May the space be flat and infinite or curved and finite?
May the space be flat and infinite or curved and finite? Personally I cannot explain myself a infinite object and how eventually to describe it but on the other hand a curved and finite space should ...
- 2,255
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
1
vote
2
answers
121
views
Geometric features of a closed finite universe
I am a student, so the question may sound silly. If the 2-sphere is the surface of a ball, that is, it is embedded in a three-dimensional space, then the 3-sphere must also be the surface of a four-...
- 956
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
0
votes
1
answer
88
views
If the universe is closed, does that also mean time is closed?
Speaking just about space, we say that the universe is either open (topologically $E^3$) or closed (topologically $S^3$). But since a metric connection defines curvature on spacetime and not just ...
- 577
7
votes
1
answer
277
views
Does positive curvature imply a closed universe?
Topologically speaking, our universe is either open (topologically $E^3$) or closed (topologically $S^3$). Then with time we'd have another factor of $E^1$ and a metric connection would determine the ...
- 577
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