All Questions
Tagged with space-expansion general-relativity
407
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Viable values for the $K$ parameter in the FLRW metric
The FLWR metric is sometimes given as $$c^2 d\tau^2 = c^2 dt^2 - \frac{a(t)^2}{(1-KX^2)} dX^2. $$
I am not interested in the tangential motion so I set $d \Omega = 0$ although it is of interest in ...
- 6,112
2
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3
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132
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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
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Understanding expansion of the Universe as things flying apart
Say that we have a Universe uniformly filled just with matter (let's not bring dark energy into this). And say that we fill it with very light particles (so that the gravitational interaction between ...
1
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2
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Please help me with this paradox [closed]
Physicists believe that some galaxies are moving away from us at faster than the speed of light. A galaxy that is moving away from us at faster than the speed of light would be moving backwards in ...
- 53
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2
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109
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How do we account for the 'one way' drag of moving space?
As I understand it, the rotating space outside a Kerr black hole drags radially falling particles into circular motion. Similarly the river model posits that the inward flow of space ensures particles ...
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Could Space and Time Be Decoupled Pre- Big Bang?
The traditional view holds that both space and time emerged together from the Big Bang. However, I'm curious about the possibility that time could be eternal, with no beginning, while space began to ...
- 489
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How to find the relation between flow-parameters and number of e-folds?
In models of single field inflation the Friedmann equation reads
$$ H(t)^2 = \frac{8\pi G}{3} \big(V(\varphi) + \frac{\dot{\varphi}^2}{2}\big) \tag{1}\label{eq1}. $$
In the slow-roll approximation one ...
- 126
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Are comoving distances time-independent?
A comoving reference frame expands along with the universe, factoring out the effect of the Hubble expansion. Suppose a galaxy has a redshift $z = 1$ and its comoving distance DM is $11 \,\mathrm{Gly} ...
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Does the Schwarszchild solution require the cosmological constant to stop it from expanding?
When Einstein developed his field equations for general relativity, he attempted to apply them to the entire universe. He found the universe had to expand, which at the time was believed not to be the ...
- 131
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A problem on cosmic inflation
I analyze inflation in this following scenario: Suppose that at some very early epoch, $t_1 ≤ t ≤ t_2$ (where $t_1 ≪ t_2 ≪ t_r$ and $t_r$ is the time at the recombination epoch), the universe resides ...
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Why is it mysterious that space is apparently expanding at different rates everywhere? [closed]
New-ish measurements from Hubble + Webb say that the Universe is expanding at different rates everywhere: https://www.livescience.com/space/cosmology/james-webb-telescope-confirms-there-is-something-...
- 115
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Can the integrated Sachs-Wolfe and the Rees-Sciama effects have any influence on matter?
CMB photons can be affected by the expansion of the universe through the linear integrated Sachs-Wolfe effect (ISW) 1 and the non-linear ISW effect or also called Rees-Sciama effect 1.
In particular, ...
- 2,462
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1
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63
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Difference between general formula for cosmological comoving distance compared to Carroll's one
I came across two different formulas for the transverse comoving distance in cosmology from GR based on Friedmann's solution in the FLRW metric for an expanding space homogenoeus and isotropic:
a) .....
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3
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252
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How does the "York time" measure the expansion of space; why is it equal to the divergence of the comoving observer's four velocity for warp drive?
The mysterious York time, θ is important in warp drive topic. It is plotted on the famous diagrams and is considered the measure of the mechanism that "drives" the warp drive bubble at ...
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2
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108
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Would continuously increasing curvature of space explain seeming expansion of the universe? [closed]
Could expanding universe phenomenon be explained by slowly but continuously increasing curvature of space around masses like galaxies and galaxy clusters? In other words, I am curious whether the ...
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