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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What are the applications of hyperbolic $3$-manifold theory to cosmology?
I am a pure mathematician specialized in hyperbolic $3$-manifold topology. That has been an incredibly active field of research in the past few decades due to the seminal work of Thurston, as many of ...
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Does any spacetime admit a global foliation in spacelike hypersurfaces?
In the comments of this question the following new questions came up: in general relativity, local coordinates can be found around any point, that single out a time coordinate and a three dimensional ...
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Spatial dimension of galaxy filaments
Galaxy filaments are "amongst the largest known cosmic structures in the Universe. They [...] form the boundaries between large voids in the Universe."
As their name suggests, filaments are ...
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At what expansion rate (H) would virtual particles be ripped apart into real particles, and what might be the density (temperature) of such an event?
Is it even possible for a virtual particle-antiparticle pair to be torn apart by cosmological expansion? Virtual particle-antiparticle pairs are ripped apart near black hole event horizons, creating ...
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Is gravitational particle production due to symmetry breaking?
A well-known fact about QFTs in curved spacetimes is that there is a phenomenon of particle production in expanding universes, these being described by the line element $$ds^2=-dt^2+b^2(t)d\vec x^2.$$
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Is the amount of dark matter per galaxy the same as you look back through time (further away from earth)?
In the hope that it may inform us about the development/evolution (if any) of dark matter over time, are there any differences (eg. in structure or concentration) in the dark matter at large radial ...
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Breakdown of quantum mechanical observables in cosmology
In several different contexts, I've heard the claim that quantum gravity in an accelerating universe messes with our ability to define precise quantum observables.* One version of the argument goes ...
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What is the best way to describe a classical field in quantum field theory (coherent state)?
In quantum field theory, we have the following expansion on a scalar field (I follow the convention of Schwarz's book)
$$\phi(\vec{x},t)=\int d^3 p \frac{a_p exp(-ip_\mu x^\mu)+a_p^{\dagger}exp(ip_\mu ...
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Does dark energy violate causality?
Assume a perfect fluid with $p = w \rho$, approximately flat space-time and the existence of a hidrostatic equilibrium solution $\rho_0$ for $\rho$. With the definition of the speed of sound $c_s^2 = \...
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What kind of matter's energy density scales as the inverse of the scale factor
We know that radiation energy density scales as $a^{-4}$ with EoS parameter ($w=\frac{1}{3}$), matter as $a^{-3}$ with ($w=0$), curvature as $a^{-2}$ with ($w=-\frac{1}{3}$).
Then which kind of matter ...
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What is the current status or resolution of Greisen–Zatsepin–Kuzmin (GZK) cosmic-ray paradox?
The Greisen–Zatsepin–Kuzmin limit (GZK limit) is a theoretical upper limit on the energy of cosmic ray protons traveling from other galaxies through the intergalactic medium to our galaxy.
A number of ...
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Understanding the CMB power spectrum
We are able to expand the CMB temperature anisotropy map in terms of spherical harmonics.
My current understanding is that each l (on the x-axis of the power spectrum below) corresponds to a unique ...
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Understanding Verlinde: How to get from emergent gravity to MOND
Verlinde ( https://arxiv.org/abs/1611.02269 ) tries to deduce MOND from emergent gravity. Can you help?
Emergent or entropic gravity goes back to Jacobson. He starts with
the entropy-area connection $...
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Can one quantify the total luminosity of the cosmological horizon?
If I integrate all the power (radiation, matter particles, neutrinos) radiated from the cosmological horizon into the universe, what number do I get?
Is it true that the integral power/luminosity is ...
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What is the entropy of the cosmological horizon?
The Bekenstein-Hawking entropy for a black hole horizon is
$S_{BH}=\frac{c^3 A}{4Gℏ}$.
Is there a similar expression for the cosmological horizon?
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