All Questions
Tagged with cosmology cosmic-microwave-background
441
questions
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40
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Spatial Curvature of Universe at recombination vs now
From my understanding, we use the CMB data to measure the spatial curvature of the universe today. Why is it the value for today if the CMB data reflects the universe at recombination (380K years ...
- 25
1
vote
3
answers
86
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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 ...
- 21
2
votes
0
answers
48
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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 ...
- 21
1
vote
1
answer
75
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Are there any observations from the beginning of the universe until the CMB?
The question that concerns my mind is that in the time period before the cosmic microwave background, did humans have any observations or not? I mean, are all the materials mentioned in physics about ...
- 21
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26
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Question about the "axis of evil"in cosmology and the Doppler effect due to the solar system's motion
The cosmic microwave background (CMB) can be described by its anisotropies in a direction $\hat{n}$ in the celestial sphere
$$
\delta T(\hat{n})=\frac{ T(\hat{n})-\bar{T}}{\bar{T}}
$$
where $\bar{T}$ ...
- 4,827
1
vote
1
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65
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Why do Baryonic acoustic oscillations imply peaks in the probability distribution of the position of galaxies?
I have been trying to understand baryonic acoustic oscillations (BAO) and there are some parts of the process I don't understand.
We start with a hot plasma of baryons and photons. There's also dark ...
- 4,827
11
votes
2
answers
1k
views
Redshift of the CMB
Has the $z\sim 1100$ redshift of the CMB been actually measured by comparing the fingerprint (absorption spectrum) of the CMB with the theoretical radiation pattern of a $2.725\,\mathrm{K}$ blackbody, ...
- 121
2
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44
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How to extract the "matter fluctuation amplitude" from the CMB power spectrum?
How do you convert the value listed in Planck 2018 results. VI. Cosmological parameters, $A_s = 2.101\times10^{-9}$ to the value of the matter fluctuation amplitude $\sigma_8=0.8111$? I tried ...
- 21
3
votes
2
answers
153
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Does neglecting dark matter solve the Hubble tension?
If the total mass of the universe is smaller than estimated by neglecting the gravitational pull of dark matter, the estimated expansion rate should be greater.
Does this consideration in the CMB ...
- 476
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27
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Why is the temperature of electron-proton recombination obtained from Saha equation so small?
I read a blog about the temperature of the Universe at recombination phase.
The ionization potential of a hydrogen atom is $13.6\, eV$, throw it into the thermal energy equation $E=\frac{3}{2}kT$, ...
- 13
2
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51
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Voids blueshifting CMB photons (in certain cases)?
I have some questions about this interesting work (https://iopscience.iop.org/article/10.1086/517603/pdf) where the authors analysed the effects of voids in the CMB radiation (particularly through the ...
- 2,462
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13
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CMB anisotropies due to moving clusters/voids?
Apparently, there is an effect where a moving overdensity/underdensity (or an object, e.g. a galaxy, moving in an overdensity/underdensity) that is going through an evolution of its gravitational ...
- 2,462
13
votes
5
answers
4k
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Why is the horizon problem a problem?
I am curious about physics and astrophysics in particular, although I have no academic basis.
Usually, I find it easy to understand the concepts and explanations, but I have particular difficulty in ...
- 233
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votes
1
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73
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Do we have to consider decoupled particles in the computation of $g_{*}(T)$?
I am studying the thermal history of the universe and I encountered the definition of effective degrees of freedom $g_{*}(T)$ defined as
$$g_{*}(T)=\sum_{Bosons}g_{B}(\frac{T_{B}}{T})^{4}+\frac{7}{8}\...
- 475
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2
answers
39
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Can we measure temperature in an isothermal Universe?
It is envisaged that ,in the future ,Universe can end in a big freeze, where there will be no energy gradient. It is also theorised that Universe was isothermal(with some irregularities I guess) in ...
