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Davis and Lineweaver correctly point out some persistent mistakes in others' descriptions of FLRW cosmology, but they make errors of their own. One of those is the idea that there is superluminal expansion in cosmology and that this has something to do with "expansion of space itself". Recession speeds larger than $c$ appear even in the $ρ=p=Λ=0,\, ...


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With your edited question, I think perhaps your misunderstanding is different than what I thought first, so here's another answer. I leave the first answer in the bottom. Redshifts vs. recession velocities First, although it's not uncommon to quote measured redshifts in terms of recession velocities — and even more so in the past — it's a bad idea. If our ...


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I have to correct my answer written here before. The Reissner-Nordström metric has the shape (see https://de.wikipedia.org/wiki/Reissner-Nordstr%C3%B6m-Metrik): \begin{equation} \mathrm{d}s^2 = -\left(1-\frac{2GM}{c^2 r} + \frac{Q^{2} K G}{ c^4 r^2}\right)c^2 \mathrm{d}t^2 +\left(1-\frac{2GM}{c^2 r} + \frac{Q^{2} K G}{ c^4 r^2}\right)^{-1} \mathrm{d}r^2 + r^...


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The suggested value of the Lambda Hubble Time surprised me. It is by far much higher than I had expected. As I see the Lambda-CDM, there are two processes: starting with 100 % CDM, ending with 100 % Lambda. And together they should all the time sum up to 100 % With 100% CDM, H(now) would be 1/(20.7 Gyr), with 100% Lambda Hubble Time H(now) would thus be 1/(...


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Most of this answer is based on First-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Implications For Inflation. As I am not an expert in this area, I am more transcribing the computation rather than interpreting it. The tensor/scalar ratio is given by: $$r \equiv \frac{\Delta^{2}_{h}(k_{0})}{\Delta^{2}_{\mathcal{R}}(k_{0})}$$ Where the ...


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This is an answer that I am writing up based on comments by ProfRob and Mike G. The meaning of 'beta' in these plots is the slope of the line. The figure itself is from Radio spectral properties of star-forming galaxies in the MIGHTEE-COSMOS field and their impact on the far-infrared-radio correlation (arXiv link). From the caption of the figure in the ...


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The two values are the peculiar velocity of the local group relative to the Cosmic microwave background The Local Group — the galaxy group that includes our own Milky Way galaxy — appears to be moving at 627±22 km/s [390±14 mps ] in the direction of galactic longitude ℓ = 276°±3°, b = 30°±3° Or the peculiar velocity of the solar system relative to the CMB: ...


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The spacetime geometry of the universe is determined by the total energy density, which includes contributions from matter (including dark matter), dark energy, radiation and curvature (if non-zero). In the present-day universe the sum of these, dominated by matter and dark energy, adds up to something that is consistent with the critical density and the ...


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The CMB is produced as the ionisation fraction of hydrogen falls from a high value to a very small value. Contrary to what is written in the Quora answer you may have been misled by, this happens at a temperature of about 3000 K. The value given by 13.6 eV/$k_B$ (remember to multiply by the electric charge to put the energy in SI units) is not even "...


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In simple Newtonian gravity, uniform mass density does not give rise to any gravitational field (avoiding arguments as to whether the universe is finite or infinite or expanding or stationary). So, within a universe of constant mass density, any mass concentrations give rise to negative (converging) fields and likewise mass voids give rise to positive (...


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It would be rather difficult to make negative mass consistent with the rest of physics and not have a bunch of weird stuff happen. According to general relativity, mass causes a curvature in spacetime, and objects follow that curvature. So whatever effect negative mass has on spacetime, and thus on positive mass objects, would also be the effect it has on ...


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