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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Are there any experimental bounds on the ratio of neutrinos to antineutrinos in the universe?
In the Standard Model, both baryon number and lepton number are conserved quantities (excluding the theoretical possibility of sphaleron processes which are exceeding rare, at least at non-"near in ...
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Time diffeomorphisms breaking in inflation
I am currently working on the topic of inflation.
It seems that at the stage of inflation, the universe can be described as a de Sitter space. In such a space, all spacetime diffeomorphisms are ...
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Equation of motion for cyclic model of the universe
I recently started to study the cyclic universe. I came across this article [1]. My question is about the action used for describing the cyclic model:
$$S = \int d^{4}x\sqrt{-g}(\frac{1}{16\pi G}R-\...
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Lagrangian for Perfect fluid Stress-Energy tensor
The wiki article on the Einstein-Hilbert action for General Relativity says that the stress-energy tensor $T_{\mu\nu}$ is related to the Lagrangian of matter, $\mathcal{L}_M$, by
$$T_{\mu\nu}=-2\frac{\...
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Is it a coincidence that Big Bang nucleosynthesis lasted about one free neutron half-life?
The free neutron half-life is about 10 minutes. Big Bang nucleosynthesis, which mostly involves protons and neutrons interacting, lasted about 20 minutes.
Question: Is it a coincidence that these ...
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The color of deep space background of an arbitrary universe
While writing my notes on cosmology in general relativity and the Olber's paradox, I was wondering about the color of the deep background of space. Our universe is mostly black because light didn't ...
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The emergence of space-time from entangled states
I recently read an article by Yasunori Nomura (https://arxiv.org/abs/1711.05263), in which he says that space-time is an emerging phenomenon. At the same time, space-time disappears when the ...
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How do inflationary models predict the generation of gravitational waves during the inflationary period?
Recent results from the BICEP2 experiment have produced a lot of talk about the primordial gravitational waves produced during the inflationary period.
I would like to have some explanation about how ...
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Why is the Ricci tensor diagonal for isotropic spacetime?
I'm reading Zee's Einstein Gravity in a Nutshell and while calculating the Ricci tensor for FRW spacetime he claims that because the spacelike slices of constant $t$ are rotationally invariant, the ...
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Does quark color contribute to "spin degeneracy" for QGP calculations?
Like the title say, does quark color matter in counting contributions in a early universe plasma (QGP), as when adding up the total plasma energy density, or is it just spin? The book I have (Pathria) ...
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Does the Standard Model plasma develop a spontaneous magnetisation at finite temperature?
Reference: arXiv:1204.3604v1 [hep-ph] Long-range magnetic fields in the ground state of the Standard Model plasma.
Alexey Boyarsky, Oleg Ruchayskiy, Mikhail Shaposhnikov.
The authors of this paper ...
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Implications of Unruh-inertia to theories of gravity
If it turns out to be true that the galaxy rotation curves can be explained away by Unruh modes that become greater than the Hubble scale at accelerations around $10^{-10} m/s^2$ as proposed in here, ...
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How many apparent horizons could the universe have?
I was reading a paper written by Nobel laureate George Smoot, Go with the Flow, Average Holographic Universe, which assumes the holographic principle as true and conjectures that our universe would be ...
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Is GR the only theory in physics which cares about absolute energy?
In my QFT course, they justify dropping the vacuum energy as 'physics only cares about relative energies except for GR in the stress-energy tensor'.
Is this strictly true?
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Trying to reproduce curves with angle of CMB anisotropies as a function of distance and curvature parameter
I am looking for a way to get, by a simple numerical computation, the 3 curves on the following figure:
For this, I don't know what considering as abcissa (comoving distance ?, i.e
$$D_{comoving} = ...
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