All Questions
7
questions
3
votes
2
answers
149
views
Does spacetime bending contradict the universe following euclidean geometry?
According to experiments the universe is believed to be flat, meaning that it would follow euclidean geometry. However, is that compatible with the fact that spacetime bends due to gravity? Does ...
- 31
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
6
votes
3
answers
783
views
How do we know that the space metric is expanding as opposed to objects moving relative to one another?
So we observe that the Universe is expanding. We observe galaxies moving away from us and the speed/red-shift is greater for galaxies that are further away.
How do we know that this observation is ...
- 163
1
vote
1
answer
63
views
The description of a universe with one or two objects
I understand that in general relativity, we describe the universe by the relationship between objects "in it". I quote "in it" because in this model, there is no background where the objects exist.
...
- 1,171
2
votes
3
answers
303
views
Understanding expansion of the universe
I'm having problems to understand "graphically" what is the expansion of the universe.
Does it mean that if now we have two points A and B separated by 1 meter, in a future those points will be ...
- 241
1
vote
2
answers
540
views
Trouble understanding spacetime and invariant interval
First, how is the invariant interval useful? How can it help us understand things around us in the universe?
Second, I know that they changed time into space or better say SPACETIME in order to ...
- 736
22
votes
3
answers
9k
views
What is meant when it is said that the universe is homogeneous and isotropic?
It is sometimes said that the universe is homogeneous and isotropic. What is meant by each of these descriptions? Are they mutually exclusive, or does one require the other? And what implications rise ...
- 3,439