All Questions
352
questions
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1
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126
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Time and causality at the beginning of the universe
I have been, quite a few times, been caught up in arguments on the internet, where my opponent posits causal events existed before the "singularity" at the "beginning" of the ...
- 1
0
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0
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24
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What was the volume of the universe a short time after the big bang? [duplicate]
I assume this question is somehow ill posed, but I do not know in which way.
I think it is not a difference here whether the universe expanded into space,
or space expanded itself.
Seen from the ...
- 3,901
0
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0
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41
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In general relativity, could our curved spacetime be embedded in a higher dimension flat spacetime (5D+1) of the compatible metric? [duplicate]
I took General Relativity at university, years ago and have a question that has recently occurred to me. This might be a dumb one, so I apologise if the answer is a well known negative.
Mathematically,...
- 1,087
2
votes
0
answers
68
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What would happen if universe wouldn’t accelerate faster than speed of light? [closed]
Its quite stunning to assume that not only space-time is expanding but also the rate of expansion is greather that speed of light.
But after the initial surprise, I ve been wondering if that fenomena ...
- 21
2
votes
3
answers
113
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Is my intuitive understanding of physical infinity correct?
Quite possibly I got the section wrong again but the question is about cosmology. When they talk about an infinite Universe, they do not mean that in such a Universe there are two objects, the ...
- 956
3
votes
3
answers
1k
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How can the universe possess rotational symmetry yet have no center?
From Noether's theorem we understand that conservation of angular momentum means that the laws of nature have rotational symmetry. From cosmology we understand that the universe has no center. But ...
- 159
1
vote
1
answer
463
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Einstein's Static Solution with $\Lambda =0$ to The Friedmann Equations?
Is it possible to show the universe is static (i.e., $a=a_*=\rm{const}$) without assuming $a=\rm{const}$ to begin with, and using a mix of $w=0$ and $w=-1$? Let $\Lambda=0$ in the Friedmann equations, ...
- 61
2
votes
1
answer
897
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Static solution to the Friedmann equation [duplicate]
I want to find the static solution for the Friedmann equation:
$$ \bigg(\frac{\dot{a}}{a}\bigg)^2=H_0^2\bigg(\Omega_m\bigg(\frac{a_0}{a}\bigg)^3+\Omega_v+\Omega_k\bigg(\frac{a_0}{a}\bigg)^2\bigg) $$
...
- 135
1
vote
2
answers
227
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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
0
answers
51
views
Can a cosmological constant model inhomogeneities?
Consider the following zero-order approximation to the universe:
Spacetime is perfectly homogeneous, and
The cosmological constant is exactly zero.
This doesn't quite work. Neither assumption is ...
0
votes
0
answers
74
views
Will time exist in heat of the universe? [duplicate]
Will there be any sense of time during the heat death of universe? Since there is no interesting events I think you cannot measure time.
- 123
29
votes
5
answers
5k
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What does the concept of an "infinite universe" actually mean?
When physicists talk about the universe being infinite, or wondering whether it is or not, what do these two options actually mean? I am not interested whether the universe is infinite or not, I am ...
- 406
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
81
views
Amount of matter in two infinite universes [closed]
I don't know exactly where to find any other information on this question so I thought I would ask here. If there were two infinitely large universes one where 20% of the space in the universe was ...
- 21
1
vote
0
answers
35
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While space itself expands, why does it seem to expand more between the stars than between me and my desk? [duplicate]
this is my first post in this community and I am not entirely sure if it is appropriate.
I am not an educated physicist, just an ethusiastic person trying to understand the universe.
So I apologise if ...
- 111