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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Proving that the CMBR remains thermal after a Lorentz boost

Suppose $S$ is a frame in which the CMBR is thermal and isotropic. I'm taking this to mean it follows the Planck Blackbody distribution $$n(\omega)=\frac{1}{\pi^2 c^3}\frac{\omega^2}{e^{\beta\hbar\...
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Spectrum of the background radiation on earth

Suppose we consider an object of temperature $T_o$, whereas the air temperature is $T_a$. The object will exchange heat with its environment via a range of processes: Radiating and absorbing heat ...
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Where did the CMB come from? What is due to the matter/antimatter annihilation? Or perhaps the radiation released when the electrons decoupled?

Where did the CMB originate from? I get that at the beginning of the universe, by the Big Bang theory temperatures and pressures were too high for matter to exist, and even if it did, it would just ...
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Do more distant galaxies move faster with respect to the cosmic background radiation rest frame?

Aparently our galaxy is moving approximately 1/500th lightspeed with respect to cosmic background radiation. While this is certainly fast, it stands to reason that it could had been a lot faster, so ...
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Is cosmic background radiation consistent with the Cosmological Principle? [duplicate]

Is the observation of cosmic background radiation really consistent with the cosmological principle? It implies that there is a "special" rest frame of motion with respect to the big bang. ...
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What is the motion of the Earth compared with cosmic background radiation? [duplicate]

Does cosmic background radiation have a frame of reference where it is symmetrical in all directions? If so, what is the motion of this planet, solar system, or galaxy with respect to this?
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If the sky is full of microwave radiations then why don't we see it?

So basically we know that the sky is full of microwave radiations but why can't we see it if so ?
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Surface of Last Scattering Spacelike or Timelike from us

As far I understand, the whole universe, at a redshift of 1100, became transparent to light, and the phenomenon occurred throughout the whole universe. It is in our past, not in our left or right ...
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Which inflation models does BICEP3 rule out?

Polarization data from BICEP3 combined with BICEP2 and Keck in a recent analysis is reported to rule out several simpler categories of inflation models. Which are these? e.g. single-inflaton models?
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How can I understand these averages? (CMB context)

I am currently reading Prof. Mukhanov's book on "Foundations of Cosmology". In chapter 9 he is very briefly explaining free streaming and all of a sudden averages labeled with a direction ...
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Is it possible that the the Big Bang is still taking Place? [closed]

My question is the same mechanism by which particles formed at the big bang still active here and now? To clarify the lambda CDM model fir instance say the observable universe was very dense at the ...
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Why does $10^{-31}$K change the orbits of the stars, but 2.7K does not?

Many people discussing the rotation curves of the stars in galaxies explain that the rotation curves are influenced by a cosmological acceleration of about $1.2 \cdot 10^{-10}\,\rm m/s^2$, and that ...
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Detection of Variation of CMB Radiation with Time and Space

According to the standard model of cosmology, the CMBR temperature increased as $T(z)=2.7(1+z)$ at higher redshift. Has there been any study to actually probe the variation of the CMBR with redshift, ...
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Resource on CMB Spectrum

I want a good article that will help me generate the CMBR spectrum from first principles of basic cosmological perturbation theory. In other words, I want to start with the cosmological perturbation ...
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Temporal Variation of Cosmic Microwave Background Radiation

For some time now I am wondering how fast the Cosmic Microwave Background (CMB) Radiation varies with time, in particular, how fast the primary CMB anisotropies are varying. These anisotropies were ...
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Why is Cosmic Microwave Background Radiation thermal? [duplicate]

Cosmic Microwave Background (CMB) Radiation is known to be thermal to very good approximation. This means that when it was created, this radiation has already been thermal. This is because the ...
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Speed of photons in Cosmic Microwave Background Radiation relative to the earth (or solar system)

At https://living-universe.com/questions-and-answers/absolute-motion-of-photons-in-the-2-7cbr/, we are told that the Cosmic Microwave Background Radiation (CMBR) is propagating relative to the earth (...
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Did we really determine a positive curvature of the Universe in 2019?

This arXiv paper says: The recent Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in CMB power spectra compared to that predicted in the standard $\lambda$CDM ...
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Why does CMB radiation propagate towards us?

There is something with CMB radiation that does not sit well with me... It seems very counterintuitive that we are able to see it. If CMB radiation formed at the early phases of the universe, would it ...
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Is there a fundamental time limit to how long a superposition of two states can maintain coherence?

If a system composed of two states is coherently split, for example, into a coherent superposition of two momentum states or two hyperfine levels of the ground state. Is there a fundamental time limit ...
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Redshift of the Cosmic Microwave Background: increasing or decreasing?

$$\dot z\equiv\frac{\mathrm d z}{\mathrm d t_{\text{obs}}}(t_0)=(1+z)H_0-H(z)$$ The picture and equation above are quoted from Liske et al. (2008). According to the equation, the redshift of the ...
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Given current densities of dark energy, dark matter and normal matter in universe currently, calculate ratio of density of dark matter at CMB to now? [closed]

I stumbled upon this question while preparing for the astronomy Olympiad. It is question #17 in this pdf. Given that dark energy is vacuum energy, and that the densities of dark energy, dark matter ...
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If atom ionization energy increases, how will the Cosmic Microwave Background (CMB) radiation temperature change today?

I know that the Cosmic Microwave Background (CMB) radiation is the leftover radiation of the photon emitted by the last cosmic-scale combination of electrons and ions to neutral atoms in the history ...
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Confidence in COBE, WMAP, and PLANCK measurements of the CMB?

I'm heavily unfamiliar with error analysis in astrophysics and have been curious about how confident we are about the measurements of the CMB by the respective satellite missions COBE, WMAP, and then ...
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What would the wavelength of the Cosmic Background Gravitational Wave radiation be?

Considering electromagnetic CMB can only see light as old as 380,000 years after the Big Bang, whilst theoretically those being gravitational should be formed from the beginning, what would their ...
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The distance to last scattering surface incerease?

The cosmic background radiation was released 38 million years after the Big Bang and is observed as the last scanning surface. How does the distance to the last scattering surface differ when the ...
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Why do hot and cold spots in CMB maps have an average angular size of 1°?

CMB all-sky maps issued by the PLANCK and WMAP satellites show that CMB hot and cold spots have a physical average angular diameter of about 1°. Why is this size statistically preferred, and what is ...
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Correspondence between average size of spots in CMB map and location of first peak in CMB spectrum

The size of an average hot or cold spot in the CMB all-sky map is about 1° in diameter. Can you explain why this scale also corresponds approximately to the location of the first peak in the CMB ...
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Thinking on a 2D plane, Is the "point" of the big bang still active?

From what I understand, the light from CMB that we can observe is the result of the last scattering from the big bang which happened 380,000 years prior to the pattern we can see. Referencing: While ...
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Definition of the sound horizon

I have been looking at the sound horizon $r_s$ as used for CMB and BAO analysis. In the literature this is defined as $$ r_s(z,\mathbf{x}) = \int_0^z \frac{c_s dz^\prime}{H(z',\mathbf{x})} \quad (1), $...
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Is the CMB still red shifting?

If the CMB is red shifted from what used to be infrared and visible light, now shifted to microwave wavelengths, will there be a time where it red shifts so much that it becomes the cosmic radio ...
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How does the Cosmic Background Microwave work?

I sort of understand it but I am not sure if my understanding is correct. So what I understand of the CMB is: When the universe was created it was very hot, too hot for matter to form. When matter ...
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What is the mean free path (MFP) of a Cosmic microwave background radiation (CMBR) photon?

If the IGM (inter-galactic medium) had a massive particle (proton) every cubic metre, or a carbon grain every cubic kilometre, what would be the MFP of a CMBR photon? The coherence length of the ...
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Status of photon velocity in perturbative calculation of QED in curved spacetime

In the paper by Drummond et. al. by doing perturbative calculation of photon propagator in a curved spacetime they found that in certain directions in a given spacetime quantum correction suggests the ...
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Connection between BAO & CMB power spectrum

During the entire pre-recombination phase, the plasma is the site of acoustic oscillations. These have left their mark both in the CMB power spectrum and in the matter power spectrum. The first peak ...
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Gravitational wavelength shift of microwave background radiation

I can't find this precise question answered. It is basically a two part question. Would the microwave background radiation, as well as light travelling to us from stars in an expanding universe ...
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How to perform experiments near absolute zero temperature when the background temperature of the universe is 2.7 K?

The cosmic microwave background (CMB) radiation as a remnant from an early stage of the universe (Big Bang) is filled all space and has a thermal black body spectrum at a temperature of $2.72548±0....
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Has anyone considered a gradual change in Gravitational Potential across the universe as a cause for cosmic red shift?

Since the formation of fundamental particles at the beginning of the universe (roughly the time of the CMB emission, and after the inflationary epoch of Big Bang theory), the gravity wave front of all ...
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Looking for the experimental spherical harmonics coefficients of the CMB

Using Mathematica, I would like to plot the Cosmic Microwave Background has a spherical harmonics decomposition. As experimental data, I need to know the values of the $a_{l,m}$ coefficients in the ...
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Will the cosmic microwave background radiation eventually not be microwaves?

I was reading through this answer about the cosmic microwave background radiation, which implied that we receive it as microwaves because it's been shifted to that wavelength by the expanding universe....
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How does the scale factor depend on temperature? [duplicate]

So, I'm studying cosmology and my professor often uses the result $a=\frac{T}{T_0}$, but he never derived this relation and he just treates it as something intuitive... I think I can see how this ...
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Why would a gravity wave signature in CMB favour inflationary cosmology?

I was reminded recently of the BICEP2 experiment which seeks to discover B mode signature in the CMB, indicating early-universe gravitational waves. I noticed that when there was, briefly, a flurry of ...
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Since the microwave background radiation came into being before stars, shouldn't all existing stars (given sufficient equipment) be visible?

It's commonly said that, due the rapid expansion of the universe, it is possible that there are objects (such as stars) that could be beyond our field of vision, given the finite speed of light. ...
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Why isn't there a high spike visible in the CMBR, due to a massive recombining of electrons and protons

This answer made me wonder about something. The CMBR has its origin in the beginning of the universe. The gas of electrons, protons, etc. was in thermal equilibrium. When the electrons and protons ...
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Is the amplitude of the Cosmic Microwave Background (CMB) correctly predicted or just its spectral shape?

I see this beautiful graph of the CMB in Wikipedia Apparently the measured data-points match the theoretical curve for black body radiation very exactly and the discrepancies and error-bars are simply ...
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If I live on a planet that is heavy enough, would the CMB get blue shifted to be in the visible spectrum?

If I live on a planet that is heavy enough, would the CMB get blue shifted enough in the atmosphere of this heavy planet, due to gravitational blue-shifting, that the CMB would be in the visible ...
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References on Cosmic Inflation and CMB fluctuations [without QFT]

I'm making my final seminar for a Cosmology class I am taking as an undergraduate, and I'm going to talk about how quantum fluctuatuions during the inflation period are a reason for the anisotropic ...
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Intuitive explaination for the influence of different mass-energy components on the CMB

So I'm going to be giving a talk to a local astronomy club, and I want to be able to give them an intuitive understanding of why the CMB tells us about both the geometry of the universe and the matter ...
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Are there equal amounts of energy on each half of the Cosmic Microwave Background image?

And what about if we quartered the image, took it to eights etc.
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If a CMB photon traveled for 13.7 billion years to reach me, how far away was the source of that CMB photon when it first emitted it?

If a CMB photon traveled for 13.7 billion years (- 374,000 years) to reach me. How far away was the source of that CMB photon when it first emitted it? My attempt to solve this question was to use the ...

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