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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Robertson-Walker metric and cosmic homogeneity
The Robertson-Walker metric is of the form
$$\tag{1} ds^2 = dt^2 - a(t)^2 \Big(\frac{dr^2}{1 - kr^2} + r^2 d\theta^2 + r^2 \sin^2\theta \, d\phi^2 \Big).$$
My question is related to the $a^2(t)$ ...
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Quantum fluctuations producing CMB fluctuations also cause inflation to be eternal?
It is believed that quantum fluctuations in the inflaton field caused inflation to end at different times in different places, which led to CMB fluctuations (1 part in 100,000).
Eternal inflation ...
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Energy conservation in cosmological phase transitions
Let us consider a cosmic phase transition, in which fermions $\psi_f$ condense and the vacuum expectation value $|\langle \bar{\psi}_f \psi_f\rangle |$ of the resulting fermion-bilinear field gives ...
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How are the dark matter (DM) thermalization rates derived in singlet DM model?
This well-cited paper talks about a minimal renormalizable extension to the Standard Model (SM) to incorporate particle dark matter (DM) into it by adding a real scalar field $S$ which (unlike the ...
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Entropy and the curvature of the Universe
Foreword
What I know (and please correct me if I'm stating malarkey):
The entropy of the Universe (its description) is contained in Weyl tensor. Einstein's field equations don't directly relate the ...
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Cosmological constant phase transition?
I recently watched at a talk by Cumrum Vafa in which he stated that the cosmological constant allows us to define a time-scale $T_\Lambda=1/\sqrt{E_\Lambda}$. The time scale of this time is about 10¹¹ ...
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Why is a theory of quantum gravity expected to solve the BigBang singularity problem?
This a follow-up question related to this. A successful theory of Quantum gravity is expected to solve the BigBang singularity problem.
Why (and how) is the quantization of gravity supposed to solve ...
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How is matter density derived from CMB?
As the question says. I am looking for a technical but brief overview of how $\Omega_m$ can be derived from the CMB data to high accuracy for example as in the Planck papers.
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Are there any non-stationary asymptotically flat and geodesic complete solutions to the vacuum Einsteins's field equations
I read the book The global nonlinear stability of the minkowski space by Christodoulou, D., and Klainerman, S.
In the Chapter I, Page 10 it says:
“However, it remains questionable whether there ...
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Is Poplawski's "Cosmology with torsion" a "variable speed of light" cosmology?
In his 2010 paper "Cosmology with torsion", Poplawski mentions that, in the hypothesized formation of a new temporally-local universe within a black hole, its "expansion is not visible for observers ...
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Distribution of wavelengths of monochromatic light sources in expanding FLRW universe
I'm looking for the distribution of all wavelengths (or frequencies) of light that a stationary observer would receive at his location (at $r = 0$ and time $t_0$), from light sources emitting a single ...
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LFRW Universe - equivalence principle and Hubble flow
After a suitable change of coordinates, the metric for the (flat) FLRW universe becomes
$$
ds^2 = (1 + 2 \Phi(\vec{x},t))dt^2 - (1-2\Psi(\vec{x},t))d\vec{x}^2,
$$
where
$$
\Phi(\vec{x},t) = -\frac{1}...
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Why do some stars actually produce "Gamma ray bursts"?
I looked it up but I haven't found any explanation as to why some stars produce them, I understand that collapsing and merging stars produce them, but my question is why is the energy concentrated in ...
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How to understand particle decoupling in the early universe?
We often say that when the rate of some interactions, say the beta decay and electron capture, are slower that the rate of universe's expansion, then the corresponding particles, say neutrinos, ...
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Avoiding Pseudo-tensors when addressing global conservation of energy in GR
Discussions about global conservation of energy in GR often invoke the use of the stress-energy-momentum pseudo-tensor to offer up a sort of generalization of the concept of energy defined in a way ...
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