All Questions
Tagged with universe general-relativity
11 questions
4
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0
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74
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What does it exactly mean for spacetime to have no global symmetries?
Are there spacetimes or metrics with no global symmetries? Spacetimes/metrics with no global Poincaré, Lorentz, diffeomorphism, CPT, translational and gauge invariances?
And if there are, what does it ...
- 1,333
3
votes
1
answer
107
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Scalar field displacement from the minimum of the potential gives rise to particles/dark matter, why?
The paper Lyman-alpha Constraints on Ultralight Scalar Dark Matter by Kobayashi et al. says, at the beginning of Section 3.1:
A light scalar field stays frozen at its initial field value in the early ...
2
votes
1
answer
79
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FLWR and curvature
The FLWR metric or model I believe results from Einstein's equations of general relativity if it is assumed the universe is 1. homogeneous and 2. able to expand (or contract). Solutions can have ...
- 245
1
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0
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74
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Why is rotational motion absolute, is the universe spinning? [duplicate]
When considering any object, one can say its translational movement is relative, depending on the point of view or reference frame adopted. If it moves at 1/4c relative to some observer, one might say ...
user16500
4
votes
2
answers
359
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What is the effect of this expanding universe on the energy density of it?
We know that our universe is expanding i.e. volume of the universe is getting larger with time with total energy being conserved. My question is whether the energy density is getting smaller with ...
user28809
1
vote
1
answer
93
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Looking at the Expanding Universe through the lens of relativity [closed]
The basis and most observable metric for how the universe is understood to be expanding at an accelerating rate is the red shift in observable light. I am assuming it has been thought about or maybe ...
- 11
8
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2
answers
2k
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Is the age of the universe relative to an observer's location in that universe?
According to Wiki the age of the universe is 13 billion years old, and I was taught that background radiation made the universe uniform in all directions.
Doesn't this define a sphere of space in the ...
- 947
4
votes
1
answer
1k
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Latest cosmological parameters
I'm looking for the latest values (with uncertainties) of the four main cosmological density parameters $\Omega_i$ :
\begin{align}\tag{1}
\Omega_{\text{mat}} &={} ?,
&\Omega_{\text{rad}} &=...
- 273
8
votes
2
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439
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Is the diameter of the observable universe a relative quantity?
The diameter of my observable universe is 90 billion ly measured in proper distance. But isn't lenght a relative quantity in the theory of Relativity? Could an observer moving at a different velocity ...
- 559
8
votes
1
answer
324
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What it would look like to observe people with a different time flows?
As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks.
So Imagine two different ...
- 183
31
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2
answers
6k
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Age of the universe and time dilation
Given our knowledge and the standard cosmological model, we estimate that the age of the universe is about 13.7 billion years old.
How much sense does it make to talk about the age of the universe as ...
- 635