All Questions
Tagged with space-expansion event-horizon
32
questions
2
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3
answers
132
views
Can a light signal from Earth reach a galaxy outside the Hubble Horizon?
Is this video on the FLRW metric (timestamp 29:00 minutes) mistaken in its claim that a light signal from Earth cannot catch up with a galaxy outside the Hubble horizon, due to the horizon receding at ...
- 6,112
1
vote
1
answer
109
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Does the current size of the cosmological sound horizon play a relevant role in the universe?
I am doing some interactive plots about cosmological horizons and in my research I stumbled upon the sound horizon, the baryonic acoustic oscillations and how it had an impact on the formation of the ...
3
votes
0
answers
61
views
Hypothetically, could the interior of a black hole look exactly like the universe that surrounds us?
I do understand that we can't experimentally verify anything we imagine about the interior of a black hole.
If we were to apply what we know about the physics of the observable universe and assume ...
- 33
0
votes
1
answer
138
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When will the particle horizon reach its limit of 63 billion light years?
In the far future, the particle horizon will reach 63 Gly，so when will that time? Just like today's universe time is 13.82 Gyr and the particle horizon is 46.5 Gly, how many years will the particle ...
2
votes
1
answer
125
views
How to avoid the Cosmological Horizon problem in the Tethered Galaxies problem?
I found an interesting article by Edward Harrison [1] who proposed a way to harness energy from spacetime expansion by attaching a string to a receding cosmic object (like a galaxy). However, one ...
- 2,462
2
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2
answers
133
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If galaxies beyond the cosmological event horizon move faster than light is then that motion a combination of their KE and space expansion?
If galaxies beyond the cosmological event horizon move faster than light is then that motion a combination of their KE and space expansion? Their KE alone isn't enough for them to move faster than ...
- 2,255
2
votes
1
answer
82
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In an expanding universe, can two people communicating to each other about their cosmological horizons get around their horizon limit?
I want to pose a preamble question that I will answer first to build up to the main scenario. Then I will pose the main question. The main question concerns the special case of an expanding universe ...
- 8,640
1
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2
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136
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Is a photon emitted beyond the Earth cosmological event horizon towards Earth actually moving away from Earth?
Is a photon emitted beyond the Earth cosmological event horizon towards Earth actually moving away from Earth due to space expansion? Is that the reason why we can't see beyond the horizon?
- 2,255
1
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2
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310
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Opposite of event horizon - causality horizon or sphere?
Is there an opposite of event horizon - let's call it causality horizon or causality sphere - past which current objects in space can never be influenced from Earth because of the accelerating ...
- 1,928
0
votes
0
answers
57
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What is Observed by a Planet in a Region of Spacetime in a Theoretical Universe that has a Mass Density Gradient?
Planet M exists in a theoretical Universe that is like our Universe in every way except it can contain Large regions of Spacetime that have mass density gradients.
For a specific time, t, Planet M is ...
- 143
1
vote
1
answer
82
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Is the cosmic event horizon viewed from Andromeda different from the one viewed from Earth?
If the most distant galaxies we see in deep space are in proximity of our cosmic event horizon does it mean that if we were on Andromeda galaxy and looking in the same direction we would see objects ...
- 2,255
3
votes
1
answer
2k
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Interpretation of horizon in de Sitter
Given the de Sitter metric for spacetime
$$ds^2 = \left( 1 - \frac{\Lambda}{3}r^2\right) dt^2 - \frac{1}{\left( 1 - \frac{\Lambda}{3}r^2 \right)}dr^2 - r^2d\Omega^2 $$
we understand this is a solution ...
- 4,448
16
votes
2
answers
551
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Mathematical coincidence of the Schwarzschild radius of the Universe?
I read here that a black hole with a mass of the observable universe, $M=8.8\times10^{52}kg$, would have a Schwarzschild radius of $r_s=13.7$ billion lightyears.
I immediately noticed that at the ...
- 690
3
votes
1
answer
134
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What happens in the distant future of the universe?
In the standard cosmological model LCDM the universe approaches the asymtotic deSitter state in the distant future. Is it correct to say that all light-sources situated on the ultimate lightcone of a ...
- 928
2
votes
1
answer
157
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What is the evidence for the existence of a Hubble sphere beyond which galaxies recede faster than light
The title has been changed from the original title, because that is what I
meant, but I misused the terminology, and probably some physics, asking about
evidence for the existence of a horizon for the ...
- 3,798