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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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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2 votes
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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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2 votes
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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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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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9 votes
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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 ...
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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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3 votes
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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 $500$ ...
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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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Why are CMB peak heights sensitive to the physical densities

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 ...
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Objects beyond 13.3 billion light-years away are (apparently) moving away from us at faster-than-light speeds? [duplicate]

That is, if you use the cosmic distance ladder method, and a value of about 73.5 for the Hubble constant.... But, if you plug in the Planck CMB value of about 67.5, you get a distance of about 14.5 ...
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How is the density parameter estimated via cosmic microwave background anisotropies?

In 2003 and again in 2018, the density parameter was estimated based on measurements of the cosmic microwave background anisotropies. Can someone please explain how that works? Why do the anisotropies ...
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Equilibrium Temperature for Extremely Cold Planets: Incorporating the CMB and Intrinsic Radiation

I want to check if I'm doing this right. I'm computing the equilibrium temperature for planets where the CMB and/or the planet's intrinsic radiation (as in weakly radiating jovians) matters. I start ...
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Understanding the angular peaks in the CMB power spectrum

I have read up quite a bit on the CMB power spectrum, but one feature evades my understanding. The first peak is often referred to as the "first compression peak", meaning that the plasma ...
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Can Gravitational astronomy look beyond the CMB?

In another question dealing with the earliest explored phenomenon in the Universe the observing limit of the CMB was mentioned. Prior to CMB the Universe was opaque to photons, I believe. I'm ...
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How did we determine the distance of the CMB?

The cosmological microwave background (CMB) is the oldest electromagnetic radiation in the universe. How do we know how far away the CMB is?
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How, exactly, does the precise measurement of the CMB's polarization modes and temperature fluctuations tell us the value of Hubble's 'constant'?

Amidst all the talk a year and change ago about the value of the Hubble parameter reached by the Planck satellite team, and how it's value differed from the value reached by the 'distance-ladder' team(...
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What are the pros and cons of angular cross-correlation in real space and harmonic space?

In observational cosmology people often measure and model cross-correlations between different tracer maps. There are generally two ways to measure cross-correlations: in real space (two-point ...
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5 votes
2 answers
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Confused about rubber sheet analogy!

How to resolve confusions on the rubber sheet analogy of the spacetime curvatures? I am a newbie to spacetime curvature. I have watched several youtube videos on Einsteins GR and spacetime curvature ...
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1 answer
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Why is the Cosmic Microwave Background at the same distance no matter the direction we look?

I've read from different sources that: The CMB is visible at a distance of 13.8 billion light years in all directions from Earth, leading scientists to determine that this is the true age of the ...
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Why is the peak value(s) of the spectral radiance of the CMB different if you calculate with freq. instead of wavelength?

On Wikipedia, the calculated value of the peak frequency of the cosmic microwave background is 160.23 GHz, but it says if you do the calculating with wavelengths, then convert to frequency, you get a ...
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What was the energy/wavelength/frequency of the CMB when first emitted/released?

Given the z redshift of 1089, and the temperature difference between then and now of about 1089, I tried scaling the ev, freq. and wavelength by 1089.... Is that right? I get a freq. of about 240 ...
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18 votes
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Why does the Fourier transform of this CMB image have a hole in it?

The BBC's Desert telescope takes aim at ageing our Universe contains the image below of the Cosmic Microwave Background from the Atacama Cosmology Telescope or ACT. It looks like this is plotted with ...
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Pivot scale in cosmology, CMB observatiion

What is a pivot scale, pivot frequency in general, and particularly in the cosmology? I don't get the idea. Almost everywhere I found the same the same sentence "we take the standard value of a ...
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Highest frequency that's been imaged by a radio telescope?

In this answer to Should we update definitions and remove the 100 GHz hard limits on radio astronomy related tags? I wrote the following partial answer: Yes, there are plenty of dishes that focus ...
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2 votes
1 answer
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How is Cosmic Microwave Background's temperature measured?

How do Cosmic Microwave Background missions/telescopes measure CMB temperatures? I understand that CMB has Planck's spectrum. So I was thinking one strategy could be to measure the spectral radiance ...
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7 votes
1 answer
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Cosmic Microwave Background Map

When a satellite takes measurements of the radiation from different patches of the sky to construct a map of the thermal radiation of the universe on the surface of a sphere, it would also contain ...
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Does the image of the cosmic microwave background radiation show us what the universe used to look like?

Is it possible to interpolate using the cosmic microwave background radiation and currently what we can see in the sky at night to predict what the night sky will look like in the future? I’m guessing ...
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6 votes
1 answer
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Why is the Cosmic Microwave Background evidence of for a hotter, denser early Universe?

In his book Gravitation and cosmology, Steven Weinberg says that CMB makes it "difficult to doubt that the universe has evolved from a hotter, denser early stage". In my understanding, the ...
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2 votes
1 answer
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Does The ISW Effect Predict Net Redshift Over Distance?

The Integrated Sachs–Wolfe (ISW) effect is concerned primarily with the study of the Cosmic Background Microwave Radiation (CMBR), but seems to demonstrate that photons passing through voids suffer a ...
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When do radio and tv signals become indistinguishable from background noise of the universe?

I understand the rate an EM signal broadcast uniformly from the Earth will decrease in its power is governed by the inverse square law. How far from Earth will radio and tv signals become ...
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7 votes
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Understanding The Fluctuations In The CMB Maps

If I'm understanding this correctly the fluctuations in CMB are a result of the "last scatter" of photons when electrons joined together with nuclei that before this formed plasma. CMB is among other ...
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How fast are we moving relative to the CMB?

The cosmic microwave background radiation should provide kind of a global reference frame, because you can determine your speed relative to it using the redshift. Is it known how fast we are moving ...
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Can the patterns in the CMB be detected by off-the-shelf antennas/sensors?

I recently wrote a paper (will attach soon if feasible) for an astronomy class that analyzed the usefulness of the Cosmic Microwave Background as a static reference for attitude determination. The ...
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