Questions tagged [cosmology]
The study of the large-scale structure, history, and future of the universe. Cosmology is about asking and answering questions about the "big picture" - the extent, origin, and fate of everything we know.
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If dark matter is axion particles, how did such light particles slow down?
One candidate for dark matter is axions and there is tentative experimental evidence for their existence.
Axions are very light, most models weigh them in at tiny fractions of an eV. It seems like ...
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Does the fact that we are able to see CMBR implies that universe expanded faster than light?
Supposedly, the universe underwent rapid expansion immediately after the big bang, surpassing the speed of light. If we can detect remnants from that era, does this suggest they moved faster than ...
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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 ...
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Change of variables from FRW metric to Newtonian gauge
My question arises from a physics paper, where they state that if we take the FRW metric as follows, where $t_c$ and $\vec{x}$ are the FRW comoving coordinates:
$$ds^2=-dt_c^2+a^2(t_c)d\vec{x}_c^2$$
...
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Can the observable mass within the observable universe be estimated without using $G$?
The estimation of the baryonic mass of the observable universe can be done through its density parameter and the critical density, which depends on the gravitational constant $G$.
Is there a way to ...
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Friedmann fluid equation in the non-relativistic case
The Friedmann fluid equation I am referring to is:
$$ a\frac{d\rho}{da} = -3(\rho+P) .$$
In the non-relativistic (low temperature) case for an ideal gas universe (representing matter), I know that the ...
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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 ...
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How can baryonic CP violation contribute to the explanation of the large matter-antimatter asymmetry in our universe?
I have been doing baryonic CPV experimental search in the past few years. However, I never really get a good clue on this fundamental question.
The thing is that CPV has only been found in the meson ...
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Could a universe be expanding if its physics were scale invariant?
Imagine a universe where every field is massless and has scale-invariance. Would the expansion/contraction of the universe still be happening there? would it be detectable? Would it affect the ...
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What is the total mass-energy of baryonic matter?
From what I understand, conservation of energy does not apply to the total energy of the Universe, because it constantly expands and the new, created space has a constant non-zero energy of its own. ...
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If space has a positive curvature, is the expansion of the universe caused by time, not "dark energy"? [closed]
Ok, I will assume that space has a positive curvature, where space is the "surface" of this sphere, and time is the radius from the center, so the universe is a 4D hypersphere. Under these ...
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Feynman rule from dynamical Chern-Simons
Consider the following action that
\begin{equation}
S = \int d^4x\sqrt{-g}\left(-\frac{1}{2}(\partial\phi)^2 + V(\phi) + \frac{2R}{\kappa^2}
- \frac{\phi}{4f}{}^*RR\right)
\end{equation}
where
\...
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Can glueballs and bosons survive indefinetely in space (forming structures)?
I have been recently interested in looking for possible structures (ranging from clumped structures like "stars" to diffuse clouds of gas or halos) made from standard model-particles other ...
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GZK Limit in the Far Future and interaction with Vacuum energy?
The GZK limit stops high energy protons from propagating long distances because of the interaction with the CMB. But as the universe ages the CMB will become more red shifted. Will this mean the the ...
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Matter density estimates in the 1980s
Liddle (2015, p.67) writes: "From the crude estimates that a typical galaxy weighs about $10^{11}M\odot$ and that galaxies are typically about a megaparsec apart, we know that the Universe cannot ...