Questions tagged [cosmic-microwave-background]
The cosmic microwave background (CMB) is the electromagnetic radiation in the microwave band which can be observed throughout the whole universe, not connected to any astronomical object. Its spectrum follows a very precise black-body radiation with a temperature of about 2.7 K.
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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 ...
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Multipole moment in the power spectra of the CMB
Why is the multipole moment l in the power spectra of the CMB corresponds to the radius (instead of diameter) of the sound wave horizon of the baryon-photon fluid?
It seems to me that it should be the ...
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Is there a Dark Matter Paradox?
According to this preprint, The Importance of Being Symmetric: Flat Rotation Curves from Exact Axisymmetric Static Vacuum Spacetimes, spiral galaxies possess flat rotation curves without assuming Dark ...
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What do we mean when we say the CMB has a temperature and how do we measure it?
I have read this:
An object without any internal degrees of freedom, like a single photon, can't really have a temperature. But an ensemble of photons can have a temperature. If you put an ensemble ...
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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 ...
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Is cosmic background radiation the same photons bouncing around?
Or are "new" photons from perhaps later stages of the expansion encountered?
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Is this tuning fork forever?
Imagine a tuning fork struck in the Boötes Void. At first, the phonons convert to friction \ heat and radiate off into blackbody photons. This happens for a long time, and then at some point, we reach ...
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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 ...
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Could the increasing anisotropy of the universe lead to an additional blueshift?
I'm contemplating the possible sources of a wavelength-shift within our universe:
The CMB had a lot more energy when it was produced (around 3000 K). Due to the expansion of the universe, it has been ...
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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 ...
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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 $\bar{T}$ ...
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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 ...
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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, ...
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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 ...
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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 ...
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