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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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How is pressure calculated in the early universe?

I'm trying to calculate the sound horizon from the start of time to decoupling. To do this I need to know the speed of sound and how it changes as the universe grows. The speed of sound in a fluid ...
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What is the best book for learning how to model the CMB Power Spectrum?

I would like to understand the science behind the CMB Power Spectrum. How the harmonics are calculated (distance to surface of last scattering, sound horizon), how the amplitudes are predicted (...
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Where did the energy from the CMBR go? [duplicate]

Basically the title. The wavelength of light from the CMBR has expanded as the universe expanded and so it has lost energy since it is inversely proportional to the wavelength. Where did this energy ...
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Does the pattern of CMB anisotropies change over cosmic time?

Currently, the Universe is about 14 billion years old, and we now see a certain pattern of anisotropies in the cosmic microwave background (CMB). If we wait another 14 billion years, and repeat the ...
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What objections are there to “The New Tired Light Theory correctly predicts the redshift of the CorBor galaxy cluster” [closed]

The publication on Academia.edu claims: Taking the ‘K line’ of ionised calcium (from Galaxy A2065 in the Corona Borealis (CorBor))... the spectra of this galaxy the New Tired Light Theory was used ...
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Energy conservation in the Universe [duplicate]

When the Universe expand CMB photons lose energy because each photon has its wavelength getting augmented. This represent a loss of energy for each photon in the Universe as the Universe expand. Where ...
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Is dark energy just a cooling effect of CMB?

(1) Cosmic microwave background cooled down from about 3000K billions of years ago to a couple of Kelvin nowadays. (2) Adiabatic expansion causes gas (of photons in this case) to cool. (3) Dark energy ...
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CMB homogeneity: Inflation vs. common initial conditions?

As I understand it, inflation was proposed to provide a mechanism by which now-causally disconnected regions of the universe could have once been in causal contact, and thus explain correlations in ...
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How are the tensor-scalar ratio and tensor spectral tilt in the CMB measured for massless and massive power spectrums?

When testing the tensor-scalar ratio and the tensor spectral tilt using CMB data, does it matter whether the power spectrum is massive or not? i.e. is the tensor-scalar ratio $r_{total}$ just $$r_{...
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Did the big bang create an infinite number of photons?

We will always be able to see the cosmic microwave background (CMB) at about [the age of the universe] light years away. Always. Does that mean that infinite photons were created at that time? If ...
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Why does the first peak of the temperature power spectrum of CMB imply a flat Universe?

According to Wikipedia, the first peak of the temperature power spectrum of CMB determines the curvature of the Universe. And this answer by @pela says that the first peak is consistent with a flat ...
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What is the current value for the temperature at which Recombination took place?

I'm looking for the most recent, most accepted value for the temperature at which the photon first decoupled from the atoms during the Epoch of Recombination? That is, what was the temperature of the ...
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What is the future of the CMBR?

Galaxies farther away than let's say z=2 are beyond our reach. If we today receive a message from such a galaxy, our response message will never reach back to them. So goes the current knowledge. This ...
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Quantum fluctuations producing CMB fluctuations also cause inflation to be eternal?

It is believed that quantum fluctuations in the inflaton field caused inflation to end at different times in different places, which led to CMB fluctuations (1 part in 100,000). Eternal inflation ...
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What does the gravitational potential of the Milky Way do to the CMB?

We sit in a gravitational potential, so there should be a blue shift on the CMB light from the potential of the Milky Way. Is this blue shift dependent on direction? Is it being subtracted from the ...
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what are possible explanations for the larger scale anomaly in Planck satellite's data?

In the Planck satellite's image of the Cosmic Microwave Background (CMB), there have been anomalies, the most important of which is a deficit in the signal at large angular scales on the sky, which is ...
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How to Interpret WMAP's statement they have “nailed down the curvature of space to within 0.4% of ”flat“ Euclidean””

I find myself slightly frustrated when I'm reading a NASA page and they claim they have “nailed down the curvature of space to within 0.4% of "flat" Euclidean” 0.4% of what? Mathematically this ...
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CMB details of wavelength, amplitude and frequency

Hi could someone help me with a small project with the CMB signal. I need the details of wavelength, amplitude and frequency of the cosmic microwave background. Thank you from Marc.
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Nature of peaks in the CMB power spectrum and the underlying physical processes giving rise to them

The power spectrum is the Fourier transform of the two-point correlation function of a noise $X(t)$ where $t$ is time. It gives us the frequency content of a noise or in other words, tells how much ...
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Results of WMAP mission

The NASA WMAP mission mapped the cosmic microwave background (CMB), the the residual high temp photons from the condensed space 380000 years after big bang that expanded into the much high volume we ...
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Probability that a photon has suffered its last scattering

An important consideration in the post-recombination epoch is the issue of the optical depth $\tau$ of the Universe due to Compton scattering. This is a dimensionless quantity such that $exp(−\tau)$ ...
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Why can we see the cosmic microwave background radiation?

This radiation (CMBR) is said to have its origin at the surface of last scattering that exposed itself when the big bang universe had expanded for less than a million years. In order to see radiation ...
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CMB free containment area for proposed experiments

Could someone please help me? I would like to have a method whereby I can do experiments I have in mind involving a purpose built container of dimensions of at least a foot cubed or it can be larger ...
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How the map of cosmic microwave background is being made?

I wonder Where are we in this picture? How this picture is being made? does this have a similarity with world map, if so, we know world map is depicting a 2 dimensional space, how the map of CMB ...
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CMB - Excess Energy? [duplicate]

Today in physics we were looking at how the energy of a photon is the product of Planck's constant and the frequency of the photon, therefore the lower the frequency, the lower the energy of the ...
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How do we know the age of Cosmic microwave background? [duplicate]

How do scientists know the age of the CMB? And how does it correlate to the age of universe?
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Why is the cosmological “Axis of evil” surprising?

I know this is probably a silly question but i'm not sure I understand why it is special that radiation is cooler on one side of our solar system than the other. It seems like it would indicate that ...
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Big Crunch vs Big Rip vs Heat Death vs Conformal Cyclic Cosmology… What's the Most Common View? [closed]

I just saw that Penrose recently published a paper on Conformal Cyclic Cosmology and it made me wonder, what exactly is the consensus view these days? I first heard of Penrose in connection with Orch-...
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What happens when cosmic background microwaves enter a bound system?

Gamma radiation after spending eons in expanding space have now “stretched “ into microwaves. What happens when these waves enter a bound system like a galaxy or galaxy cluster. Expanding space ...
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Does Big Bang predict the size of the fluctuations in the CMB? [duplicate]

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? [closed]

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 ...