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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Wouldn't the cosmic background radiation (CMB) produce drag and thus create a preferential inertial frame?

Because the CMB is everywhere and is isotropic, if an object would have a certain velocity, it could have a pressure differential produced by the CMB which would produce drag till it would stop with ...
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Does photon-photon scattering influence classical vacuum E&M dynamics?

At a purely classical level, Maxwell's equations are completely linear, and associated with a linear coupling to a conserved current in the electrodynamical Lagrangian. When this Lagrangian is ...
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How can recombination lead to photon decoupling if scattering can still occur with neutral particles?

During the recombination era, two things happened: Electrons and protons bonded to form neutral hydrogen atoms. As a result of #1, Compton scattering is no longer efficient enough to keep photons and ...
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If the universe expands uniformly in all directions, wouldn't that make the basis for an universal and absolute "now" and reference frame? [duplicate]

Let's consider a universe with constant expansion for simplicity's sake. In such a universe, the Hubble Parameter drops to half its value after double the time. If it happens to be 70 km/s/Mpc today, ...
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Cosmic rest frame breaking Lorentz invariance

Is it surprising given that the existence of a preferred frame in the universe (from the cosmic microwave background), the cosmic rest frame, that there are no preferred observers? (Lorentz invariance ...
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Will a clock that is isolated and stationary with respect to the CMB report the highest possible value for the age of the universe?

We have a very special clock that has existed since the dawn of time. Its purpose is to measure the age of the universe. It is always very far from any massive body or gravitational field and it is ...
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Do we see the fluctuations of the CMBR slowed down by a factor of 1100?

Do we see the fluctuations of the CMBR slowed down by a factor of 1100? If redshift streches the signal like a spring it should last longer in our eyes and by a factor of 1100 so every change in the '...
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What does it mean for fluctuations to be constant over a range of physical scales

I'm self taught when it comes to physics/math, so apologies if this is a naive question. While reading Barbara Ryden's Into to Cosmology Ch8 on CMB (Section 8.5), she says that for physical scales ...
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Is CMB slowing down all moving objects in the universe?

1/ Object moving relative to the CMB frame of reference will see the CMB blue shifted where it is heading and red shifted where it came from. Correct? 2/ The blue photons ahead should have more ...
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On which speed the relic microwave background radiation becomes dangerous for the people on space ship?

If we travel with speed close to the speed of light, the light waves becomes shorter and their energy increases (because we flight through much more light for the same time). So, even background ...
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Why the CMBR redshift is so higher than the redshift of the most distant therefore oldest galaxies in the universe?

Why the CMBR redshift is so higher than the redshift of the most distant therefore oldest galaxies in the universe? We know that cosmological redshift rises with distance from the object but at ...
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Question: Is our Universe finite? [duplicate]

Is it at all possible to compare our three-dimensional space with the two-dimensional surface of an expanding ball where recombination-induced radiation from the point at the top of the ball travels ...
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1 answer
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Is the blackbody curve of the cosmic microvave background maintained as the Universe expands?

The cosmic microwave background is observed to have a blackbody spectrum. What happens to it as the Universe expands and is a blackbody curve maintained with the expansion? I know that the spectrum ...
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How can a photon emitted when the universe was just a few lightyears in diameter, travel for billions of years without bumping into something?

Admitted: I find it already surprising that a photon can travel for billions of years without bumping into something in a universe that has the size of current observable universe but there I guess ...
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How can we extrapolate gravitational waves in the early universe from CMBR?

I know it has to do with polarization of CMBR, but not sure how gravitational wave polarized early light.
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Planck's law and CMBR

Rereading statistical mechanics notes, I was recently struck by a fact that seemed very surprising to me. In the notes I am reading, one derives Planck's formula for the energy distribution of photons ...
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How is the Sound Horizon at Recombination calculated?

The Angular Scale (in a flat universe) is defined as:$$\theta_*=\frac{r_s(z_*)}{D_A(z_*)}$$Where $\theta_*$ is the angular scale, $r_s$ is the Sound Horizon (distance sound can travel until ...
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Plasma effects on CMB

I have been studying plasma physics and how photons acquire a longitudinal polarization when propagating through a plasma. However, I have not found any information about how this affects CMB photons ...
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Why is the CMB's frame not rotating?

I have read this question: The existence of a CMB frame asserts that there exists a global frame in which the universe is (approximately) space-translationally and rotationally invariant (though not ...
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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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2 votes
1 answer
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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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2 votes
1 answer
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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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3 answers
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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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4 votes
1 answer
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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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-1 votes
1 answer
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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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4 answers
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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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1 vote
1 answer
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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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-1 votes
1 answer
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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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10 votes
3 answers
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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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3 votes
1 answer
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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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4 votes
1 answer
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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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