# Questions tagged [cosmic-microwave-background]

Questions about is the electromagnetic radiation remnant from the early stage of the universe, also known as "relic radiation".

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### Tolerances given for Galactic Directions in answer to 'How fast are we moving relative to the CMB?'

Question: Tolerances given for Galactic Directions, in answer to 'How fast are we moving relative to the CMB?' Where: $$ℓ = 264.021º ± 0.011º$$ $$𝑏 = 48.253º ± 0.005º$$ I can find these values on ...
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### Would it be possible to use existing radio-telescopes to do spot measurements of CMB?

With CMB peaking at roughly 158GHz would it be possible to create a more precise map of CMB just by sampling 'points' using existing Earth-based radio telescopes? I understand that large dish ...
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### CMB maps analysis (Planck, ESA, FITS)

I wanted to analyze Planck mission FITS files and was wondering about the parameters. So the map uses color coding for temperature-based anisotropies right? So the maximum angular resolution is ...
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### How is the Cosmic Microwave Background so big?

If the CMB is an image of the universe when it was 379,000 years old, how is it so large? Since the light is 13.8 billion years old, the image represents the surface of a sphere with a radius of 13.8 ...
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### given angular diameter distance turnaround, is it then that the background microwave radiation is now background because it was 'close' initially?

the idea of objects nearer the start of the visible universe appearing larger to us now because when their light started out they were nearer to us leads to the idea that the "largest" such &...
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### Which is brighter, starlight or the CMB?

Which do we receive more energy from, the CMB or starlight? (Not including the sun of course.)
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### How does the number of CMB photons vary with time?

When the CMB temperature is calculated does it take into account photons absorbed by gas clouds and dust over billions of years?
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### Cosmic background radiation - what frequency tells us?

I understand that cosmic microwave background radiation is remnant of the universe after 380,000y of the origin. To me, this radiation is still a wave which has a microwave frequency and I also ...
1 vote
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### Are there any hints in the CMB as to why the James Webb telescope is finding galaxies larger than expected in the early universe?

"James Webb telescope detects evidence of ancient ‘universe breaker’ galaxies | Astronomy | The Guardian" https://amp.theguardian.com/science/2023/feb/22/universe-breakers-james-webb-...
1 vote
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### Can the CMB Cold Spot be explained by dark matter redshifting photons?

One explanation for the Cold Spot in the cosmic microwave background (CMB) is that dark matter is redshifting CMB photons; see Fermilab's article "Scientists move a step closer to understanding ...
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### In CMB data analysis, when calculating the signal-to-noise ratio for a binned power spectrum, do we use the bin centers in the SNR calculation?

The signal-to-noise ratio for angular power spectrum signal $C_l$ under theoretical noise $N_l$, where $C_l$ and $N_l$ are functions of multipole $l$, is given as $$(S/N)^2= \sum (2l+1) (C_l/N_l)^2$$ ...
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### Why is it Cosmic microwave background not Cosmic gamma ray background [duplicate]

If the universe was at so much heat at the singularity point at big bang , Then the light of CMB must be gamma rays (high energy photons) but how did they transfer into microwaves?
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### Why does the CMB conform to black-body formula for 2.71 degrees, when it's the stretched emission at a far hotter temp?

Physicist Chad Orzel in "Einstein's Legacy" discusses Planck's Black-Body formula, stating that it fits perfectly to everything we see, from toasters to stars. Fine. Then he says it ...
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### Proportion of dark energy, dark matter, matter

According to the article "Dark Matter" https://en.wikipedia.org/wiki/Dark_matter the current Lambda-CDM model estimates the total mass-energy content of the universe consists of 68.2% dark ...
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### what does it mean to have momentum suppressed cross section

What does it mean to have momentum suppressed cross section and zero momentum transference in direct and indirect detection of dark matter
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### CMB dipole anisotropy maping to earth visualization

I do not see how this dipole anisotropy is due to the motion of the earth (and thus a doppler effect). Does anyone have a visualization of how this maps onto the earth and the motion of the earth such ...
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### Cosmic microwave background the same as the first visible light at 379,000 yrs after the Big Bang? How do these measure the age of the universe?

Was the CMB emitted at the same time as visible light at 379,000 yrs after the BB ? Was this a one time event ? If headed away from us, how does it measure the age of the universe?
1 vote
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### Since the Hubble Constant changes over time (it's a variable parameter), why can't the conflicting values of 67.4 and 73 both be right?

Are the conflicting values from the 'early universe' (Planck) method and the 'late universe' (Distance ladder) method actually compatible? Since during the latter period of the universe 'dark energy' ...
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### How did astronomers get rid of microwave radiation from stars and galaxies in picures of the CMB?

Images of the CMB show no sign of stars or galaxies. If they did, shouldn't the Milky Way be a bright band dividing the CMB into hemispheres? Black body radiation in a given wavelength/frequency range ...
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### What is a 'square' Kelvin degree? μ$K^2$? In terms of the cosmic microwave background's (CMB's) temperature fluctuations?

From what I have read and seen, the minute temperature fluctuations in the CMB are measured in microKelvin, or μK. However, many charts and graphs show μK2, or 'microKelvin-squared'. Do they simply ...
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### Where's the matter that created the CMB?

I know that the CMB was created at the recombination, when photons could finally travel freely. But each of those photons was deflected one last time before this happened. Where's the matter that ...
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### CMBR: Is the cold spot a hint at the edge of the universe?

Could the big cold spot in the CMBR map be a sign that almost all radiation from that direction has already passed us, and that be a sign that the end of the universe is closest to earth in that ...
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### Why do most astrophysicists believe the cosmic microwave background (CMB) provides the best evidence for dark matter? What, exactly, IS that evidence?

I frequently read that the cosmic microwave background contains the best overall evidence for the existence of dark matter, and conversely against alternative gravity theories like MOND. However, I ...
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### Explanation for Planck 2018 temperature fluctuations strongest peaks

As it can be seen from Plank 2018 Cosmic Microwave Background temperature fluctuations data- There are 3 sharp peaks at multipole expansions $\ell \approx 250, 550, 800$. Also as multipole expansion ...
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### Why is the CMB's redshift so high?

It is pretty well-established that the CMB was originally emitted around 380,000 years after the Big Bang, at a redshift of ~1100. The most distant known object is HD1, the light from which was ...
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### Will the upcoming experiment PICO measure kSZ temperature anisotropy? [closed]

I know for sure PICO will be measuring polarization anisotropies with high fidelity. In addition, the PICO science paper shows that it will make full-sky Compton-y maps but the plots are mostly ...
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### How are CMB frame redshifts of galaxies corrected for coherent flows?

Say, if I downloaded the CMB frame redshifts of some galaxies from NED database, then what is the procedure to correct it for coherent flows? I'm using the SNooPy(snpy) Python package to analyze some ...
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### Does the Cosmic microwave background (CMB) have an amplitude? Does it vary, like the 'temperature' (wavel./freq.) and the polarization?

Somehow, I have never read about this or thought about, until now... Does the number of photons from the CMB hitting us from all directions vary at all?
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### What is the 'TE correlation' in the CMB, or 'temperature-E-mode' correlation, aka 'temperature-polarization' correlation?

There are several places on the web that mention this, a couple in some technical detail, but I cannot wrap my head around what exactly it means...
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### Is luminosity distance related to both heliocentric redshift and CMB restframe redshift？

The luminosity distance $$d_l=(1+z)r(z)\ ,$$ where $r(z)$ is given by $$r(z)=cH^{-1}_0\int_{0}^{z}\frac{dz'}{E(z')}\ .$$ When I use the SNe dataset "Pantheon", I find there are two redshifts:...
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### What happened to the reemitted photons during recombination?

To my understanding, the Cosmic Microwave Background Radiation (CMBR) is light released during the recombination epoch where the formation of neutral hydrogen atoms allowed for a sudden drop in the ...
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### Back when the CMB was predominantly in the visible spectrum, would it have been visible to the naked eye?

The CMB is a near-perfect black-body spectrum, and assuming this has been true since the de-coupling, we should have been able to see the glow. In fact, at a certain point, it should have been almost ...
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### Why does the first measurements of the thermal Sunyaev-Zel’dovich effect from ALMA show a temperature decrease and not an increase at the cluster?

Seeing the phrase a fully functional Stewart Platform I Wikipediad it and that article shows the AMiBA a CMB interferometer mounted on a hexapod (shown below). Wikipedia's Sunyaev–Zeldovich effect; ...
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### Why was the Cosmic Microwave Background (CMB) released at a blackbody temperature of 3000K rather than 30,000K?

If the ionization (or reionization, or Recombination) energy of atomic hydrogen is 13.6 EV, which corresponds to a black body temperature of 30,000K, why did the CMB not begin to appear then? Why did ...
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### Why isn't the CMB blurred by the blackbodies emitted in the time after atoms first formed?

I am confused about why the light released from the moment when gas first formed was so dominant in comparison to the light released afterwards. Why isn't the CMB in interference with a series of ...
1 vote
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### How can scientists deduce the number of types of neutrinos, or 'effective number', from Planck satellite data?

Is it related to the way they deduce the Hubble constant from Planck data? Would more types of oscillating and mixing neutrinos mean faster or slower expansion of the universe? Would a fourth mass ...
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### Cosmology context plotting : Covariance matrix - Script to plot Omega_m vs Omega_Lambda diagram in Python

I have covariance matrices and Markov chains coming from the SCP (Supernova Cosmology Project) and I would like to plot all these data in the particular diagram Omega_Lambda vs Omega_m or w vs Omega_m....
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### Is the sound horizon 500 thousand light years or 500 million light years?

At 06:30 in the nice video Sound Waves from the Beginning of Time about the baryon acoustic oscillations (BAO), the speaker says the sound horizon is about $500$ ...
1 vote
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### Why does the 'Big Bang Nucleosynthesis' theory require that neutrinos, or at least sterile neutrinos, have a LARGE mass rather than a tiny one?

From Wikipedia, Sterile neutrino Particles that possess the quantum numbers of sterile neutrinos and masses great enough such that they do not interfere with the current theory of Big Bang ...
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### Explain as simply as possible how the Sunyaev-Zeldovich (SZ) effect is used to estimate the Hubble constant

The Sunyaev–Zeldovich effect (SZ effect) is useful in determining the Hubble constant because it is independent of the cosmic distance ladder. This effect occurs when CMB (cosmic microwave background) ...
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### Where does the energy of the decaying CMB go?

I would expect that energy of photons in the Cosmic ray Microwave Background gets less and less because their wavelengths are stretched due to the expansion of space. How can this be possible? Does it ...
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### Is it Possible to Calculate The Centre of Mass of the Visible Universe?

It is easy to deduce that we appear to be at the centre of the visible universe, assuming the visible universe is approximately isotropic and homogeneous in all its properties, including expansion ...
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### Is the universe macroscopically transparent to CMB? Is the fraction intercepted by stars and dust so tiny that it doesn't have a correction factor?

Background The question Why do some electromagnetic waves continue travelling while others disappear? is interesting, and in addition to the answer there I started to write: This is a supplementary ...
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### Understanding better the factors on $C_l$ in Angular power spectrum and Relation with Matter power spectrum

I am looking for an explanation on the angular power spectrum. I found this extract that is interesting but not fully understood for me (I will cite the step that I didn't understand) "what is ...
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### Are features in the CMB correlated with features in the SDSS map of the most distant galaxies?

This is a follow up to an earlier question to which @pela gave an excellent answer. Apparently the statistics of the length-scales of the CMB fluctuations are similar to those obtained from other ...
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### Is there any correlation between the Cosmic Microwave Background (CMB) and the distribution of distant galaxies?

The Cosmic Microwave Background (CMB) is remarkably isotropic but does exhibit a distinct dipolar Doppler shift and also much smaller but measurable fluctuations in intensity and polarization. ...
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### How can the CMB have a "monopole anisotropy"?

Wikipedia's Cosmic Microwave Background (CMBR) radiation monopole anisotropy (ℓ = 0) says When ℓ = 0, the ${\displaystyle Y(\theta ,\varphi )}{\displaystyle Y(\theta ,\varphi )}$ term reduced to 1, ...
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A very simple question: why should it be that the CMB power spectrum allows constraints to be placed on the combination of parameters $$\omega_c = \Omega_c h^2$$ $$\omega_b = \Omega_b h^2$$ as opposed ...