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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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Does Big Bang predict the size of the fluctuations in the CMB?

From this Ethan Siegel’s article The temperature fluctuations in the CMB are only 1-part-in-30,000, thousands of times smaller than a singular Big Bang predicts. Does big bang predict the size ...
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Relationship between power spectra, density perturbations and temperature?

I am trying to understand how density perturbations relate to temperature fluctuations in the CMB. I understand the physical effects involved, but my question is how is the density power spectrum ...
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Can we make a box isolated from Cosmic microwave background radiation?

If we make a square box with lead thick walls (1 meter thick or more), can me have a space inside this box 100% (or 95%) free of Cosmic microwave background radiation or it is something which we ...
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If decoupling means that photons no longer scatter how does neutral gas absorb CMB photons giving rise to the 21 cm signal?

Recombination is the time in the universe when free electrons and protons combined into neutral hydrogen. One of the most important features of this transition is that after recombination the photons "...
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Trying to reproduce curves with angle of CMB anisotropies as a function of distance and curvature parameter

I am looking for a way to get, by a simple numerical computation, the 3 curves on the following figure: For this, I don't know what considering as abcissa (comoving distance ?, i.e $$D_{comoving} = ...
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The surface of the last scattering and pictures of deep field

Maybe this question (in fact I have a few of them) is naive but nevertheless, let me try to ask it: it is concerning the furthest regions of our universe. Is the Hubble telescope capable to ...
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Are these arguments to inflationary predictions in this Fact-Checking page legitimate?

ISL(Anna Ijjas,Paul Steinhardt,Abraham Loeb) have put together a Fact-Checking page in response to the letter. https://physics.princeton.edu/~cosmo/sciam/index.html#facts In their letter, the ...
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How far back in cosmology is there observational evidence?

It seems "the first three minutes" are well established... back to the first second? 10 seconds? What about the "hadron epoch" going back to the first microsecond? Or before that? I know there are ...
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How do you explain cosmological red shifting in terms of gravitons?

We know that the photons from the big bang are continually being red shifted and losing more and more energy. In terms of the graviton view, how would you explain that? Where is the energy going? Are ...
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Cosmic Microwave Background Radiation [closed]

I'm going through the NRAO Essential Radio Astronomy course and on the section about Cosmic Microwave Background Radiation, it mentions that BB radiation is $T_0 = 2.725 \pm 0.002$ K equating to "...
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CMB Power Spectrum dependence on cosmological parameters?

I'm studying the CMB Power Spectrum in cosmology and after much research I did not find sources that treat the dependence of the CMB Power Spectrum on the spectral index $n_s$. So how do the peaks ...
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What does CMB polarization has to do with its temperature or temperature anisotropy?

Wikipedia says that "The cosmic microwave background is polarized at the level of a few microkelvin.". I have no idea what this means. What does temperature anisotropy have to do with polarization? ...
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Is last scattering surface synonymous to the size of the observable universe?

As far as I understand, the last scattering surface is that surface where the CMB photons last scattered. But isn't that same as the particle horizon or the size of the observable universe?
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How to distinguish between primordial versus kinematic anistropies of CMB

The CMB temperature anisotropy, at each order (monopole, dipole, quadrupole etc) in the multipole expansion, is contributed by two effects: (i) partly by the motion of the earth w.r.t the CMB-the ...
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How is Thomson scattering responsible for the CMB polarization?

Due to Thomson scatterings in the early Universe, the CMB is predicted to be polarized at the level of roughly $5\%$ of its temperature anisotropies. Physically, how did the Thomson scattering of ...
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Finding the CMB temperature anisotropies contributed at different orders due to a uniform boost

I've just started reading about the physics and features of Cosmic Microwave Background. I came across this pdg review titled Cosmic Microwave Background by D. Scott and G. F. Smoot says that At ...
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If CMB photons are in equilibrium why is there a temperature variation of the background?

The CMB has the blackbody radiation spectrum which implies that the CMB photons are in equilibrium. Blackbody distribution amounts to an equilibrium distribution. If there is equilibrium, the CMB must ...
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Meaning of $\langle…\rangle$ in the definition of a typical correlator in CMB physics

Let $\Theta(\hat{\textbf{n}})\equiv \frac{\delta T(\hat{\textbf{n}})}{\bar{T}}$ denote the measured CMB temperature fluctuations in a direction $\hat{\textbf{n}}$ in sky. The correlations between the ...
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Diffuse and background

What is the difference between diffuse emission and background? I understand that background supposed to be more general but I am not really understand what the difference between the two.
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Simplifying CMB correlation function with spherical harmonics

I originally asked this on the physics Stack Exchange site, but perhaps it could be more easily answered here. Given the definition of the correlation function for CMB temperature fluctuations as $$ ...
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Angular Diameter Distance to the last scattering surface

The definition of the angular diameter distance is the ratio of an object's physical transverse size to its angular size. However when I was reading my textbook, Astrophysics in a Nutshell by Dan Maoz ...
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Understanding the CMB background as a reference frame

We say the Earth is in relative motion with respect to the cosmic microwave background (CMB), causing anisotropies in the CMB spectrum. I have four very simple questions about this. How is it ...
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Can we use redshift measurements to determine absolute velocity?

Here's a thought experiment: suppose I'm in a large box in space without windows or sensors, and I fire a laser in 6 different directions and measure the redshift along each direction. Could that data ...
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Why did CMB decouple when neutral atoms formed?

Atoms can absorb and emit photons. But it is said that when the neutral atoms were first formed the photons got decoupled. If the atom-photon interaction is allowed how can we say that photons were ...
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Does the Cosmic Microwave Background falsify relativity of velocity?

In special relativity velocity is relative and there is no absolute rest frame . However the cosmic microwave background radiation does have a rest frame. Earth is moving with 328 km/s with respect to ...
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What is the product of a proton interacting with the CMB?

Assuming the CMB is at 2.7 K, if a proton interacts with it, what would be the particles resulting of this collision? I read that at the GZK cut-off (~$10^{21}$ eV), there is photo-pion production, ...
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Derivation of the Hubble constant from the cosmic microwave background

In the paper which presents the results of the Planck measurement (DOI: 10.1051/0004-6361/201321591) the Hubble constant is a derived parameter. How does this derivation work? Moreover, how does the ...
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Is the mean CBM frequency more red-shifted since discovered in the 1960's?

If the universe is uniformly expanding at rate x, is possible to measure that the CBM has increased its red-shift value over time? If the red-shift is a static value, is it possible that the ...
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CMB and entropy in the early universe

The Second Law of Thermodynamics states that the entropy of the Universe must increase. When we look a the Cosmic Microwave Background Radiation we see that the early Universe was in thermal ...
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What does temperature refer to in the vacuum of space? [duplicate]

If light was released ~.38MY after the big bang and the expansion of the universe has caused it to shift into the microwave region why is it referred to as being 2.7K? Temperature is the movement of ...
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Dark matter and standard model of cosmology: how does it enter into the equation? [duplicate]

I am a physics student and don't know very much about dark matter nor cosmology. But today I went to a talk in which the speaker showed us this image (or a very similar one): showing how the ...
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For how long CMB was being emitted?

Or equivalently, how long was the recombination period? Was it a fraction of a second? Millions of years?
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How much does the expansion of the universe affect the uniformity of the CMB?

The CMB is (I think) uniform to one part in one hundred thousand. Has the expansion of the universe been allowed for in calculating this number or is it ignored because it averages out or maybe ...
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Origin of electromagnetic radiation in the universe

I don't know if the total electromagnetic radiation in the universe is finite or not. But either way: what is the origin of the electromagnetic radiation in the universe? Can we say that all of it ...
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Temperature of the CMB

We say that the temperature of the Cosmic Microwave Background is about 2.73 K but this temperature is measured by the radiation that would have arrived on the earth millions of years after it was ...
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How much uncertainty has the relic graviton background?

In the paper https://www.osti.gov/biblio/6051438-relic-gravitational-waves-extended-inflation, it is mentioned that inflation predicts that a relic graviton background is about 0.9 K (cf. cosmic ...
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Abundance of energetic CMB photons produced due to Sunyaev-Zel'dovich effect

Is the number of energetic CMB Photons (produced due to Sunyaev-Zel'dovich effect) abundant in the whole universe now ? The Sunyaev–Zel'dovich effect is the distortion of the cosmic microwave ...
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Effect of local reference frame and rotation of Universe in CMBR anisotropy

In Kolb and Turner's Early Universe, (see here) it is mentioned that Variation in the CMBR temperature in different directions is expected due to several effects: the motion of our local reference ...
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If photon decoupling was a departure from equilibrium why does CMB exhibit a blackbody spectrum?

Decoupling of photons from the cosmic plasma or thermal bath is said to be a point of departure from thermal equilibrium. But we know that the cosmic microwave background (CMB), consisting of the ...
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Why can't B mode polarization noticed in CMB be result of acoustic waves instead of gravitational wave

I am trying to understand how B modes polarization identified in CMB has anything to do with gravitational waves. At the beginning universe was opaque there was all the possibility of sound wave ...
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The most perfect Blackbody measured [duplicate]

I hope this question is appropriate for physics stackexchange. In this interesting video, Robert Laughlin and David Gross are debating cosmic inflationary models. Gross makes the claim that the ...
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Formula of Planck Spectrum with right factors to get density of photons

I am interested in to study the CMB (Cosmological Microwave Background). From this link, the author defines the density of photon $n_\gamma$ (in ${\rm cm}^{-3}$) by : $$ n_\gamma = \frac{1}{\pi^2}\...
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How is temperature of space calculated?

wikipedia says: The CMB has a thermal black body spectrum at a temperature of (T=) 2.72548±0.00057 °K. The spectral radiance dEν/dν peaks at 160.23 GHz Could you explain how is T= 2.72 K ...
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Observation of Hawking radiation

Is it conceivable that Hawking radiation could be observed using e.g. gravitational waves or imprints in the CMB?
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CMBR isotropy after inflation

Inflation can explain why the Cosmic Microwave Background Radiation (CMBR) is so isotropic to a high degree despite that many regions of the universe were never in contact with each other. According ...
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What are red spots at 353 channel of Cosmic Background Radiation?

As shown on http://thecmb.org/ the 353 channel of Cosmic Background Radiation has red spots that are opposite to each other and NOT at right degrees angle to our galaxy plane (instead they are at ...
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How did the visible universe look 13.6B years ago from a planet in the Milky Way?

I have seen the other questions that ask if there is an edge to the universe, what it would look like near that edge, etc. But I have not seen a question posted that answers this question... As I ...
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Do hot spots in the CMB anisotropy map actually correspond to denser or less dense regions?

When looking at the map of the anisotropies of the CMB, do slightly hotter (red) spots correspond to denser or less dense regions at the time of decoupling? I am getting confused, because I have read ...
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How do we know that universe is flat?

Last measures by WMAP indicates that the universe is flat with a 0.04 margin of error. What does that exactly mean? Is it almost flat but with a soft curvature that could be negative or positive?
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CMB anisotropies without dark matter

One of the strongest hints of dark matter are the CMB anisotropies and the peaks. What should a non-dark matter theory do in order to reproduce that evidence? I mean, what is the feature that a pure ...