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 does apparent brightness (or stellar magnitude) change with distance in an expanding universe

Cosmological redshift causes wavelengths of a distant object to stretch by a factor $1/(1-Hr/c)$ where H is the Hubble constant, r is distance, and c is the speed of light. Consequently the received ...
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How does conservation of energy relate to cosmic microwave background radiation?

I've seen posters on a number of forums, including this one, telling us that conservation of energy doesn't apply to cosmic microwave background radiation. This is of some concern because, for ...
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Inverse of equation with Legendre polynomials [closed]

I have to find the inverse of the equation of the multipole moment of a field \begin{equation} \Theta_l(k)=\int_{-1}^1 \frac{d\mu}{2}\mathcal{P}_l(\mu)\Theta(k,\mu), \end{equation} where $\mathcal{P}...
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If we have a cosmic microwave background should't we also have a cosmic radio wave background?

I'm a layman in physics, but here is what I understand: What we see in the sky with naked eyes is a map of electromagnetic waves in the frequency visible to the human vision. But that kind of ...
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Why are power spectrum plots $l^2 P(l)$ instead of just $P(l)$?

Why is it typically plotted $l^2 P(l)$, or $l(l+1) P(l)$, vs $l$ instead of just $P(l)$ in power spectrum plots? For example, we can see it in this plot found in Introduction to Gravitational Lensing ...
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How can we still see the CMB? [duplicate]

May seem stupid but i cant wrap my head around it. if a star explodes we eventually see it when the light gets here. but once its got here we see the event and the star is now gone, we cant see it ...
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Correlation functions in cosmology

I'm reading an article about Non-Gaussianity of Large-Scale Cosmic Microwave Background (link) and the authors write that the n-point correlation function of $e^{\varphi(x)}$ where $\varphi(x)$ is a ...
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How can the Cosmic Neutrino Background (CνB) have a temperature? How can any neutrino have a 'temperature'?

The word temperature usually refers to the average velocity of massive particles, correct? And the Cosmic Microwave Background (CMB) has a 'temperature' based on the temperature of a 'black body' that ...
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Why do we say the universe is isotropic when we are clearly moving w.r.t the CMB?

Modern cosmology is built on the Friedmann equations, which in turn rely on isotropy — the idea that the universe looks the same in every direction — as a fundamental assumption. However, there's a ...
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How did neutrinos eliminated from dark matter? [duplicate]

I am reading "Dark Matter and Dark Energy" by Brian Clegg. In Chapter 3 it's discussing about cosmic microwave background radiation and the elliptical shape of early universe obtained from ...
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Does the gravitational constant $G$ impact the density parameter $\Omega$?

As far as I'm aware, for baryonic matter the estimated mass density is: $$\Omega_{\rm m} = 0.044 \pm 0.004$$ If in some other universe $G$ was say $22$ times what it is in ours, is there a linear ...
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Implications of the axis of evil in Big Bang theory and cosmological inflation?

According the the axis of evil feature of the CMB map verified twice by space missions our home location is on this center axis of the CMB map! Making our home location sort of the center of the ...
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Calculation of age of Universe

The age of the Universe is about 13.8 billion years, measured by light emitted from the time it emerged from opaqueness. But how was the time from the "beginning" to 380,000 years (era of ...
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Approximation of Spherical Bessel function [closed]

I am currently studying the CMB power spectrum from a numerical approach (easier than the analytical approach). In a Mathematica notebook that I am following, they work with spherical Bessel functions ...
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If CMB came from the big bang, how come we got to where we are before the CMB arrived? [duplicate]

I have read that the cosmic background radiation was formed 380,000 years after the big bang, when stuff changed from being opaque to light, because of free electrons, to becoming transparent. However,...
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Cosmic ray GZK limit calculation: subtleties with four-vectors

I'm considering an ultra-relativistic cosmic proton colliding with a CMB photon, creating a neutral pion, as depicted by this equation: $$\tag{1} p + \gamma \rightarrow p + \pi. $$ This process is ...
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Matter-antimatter annihilation and CMBR [duplicate]

Does this intensity of microwave background radiation correspond to the huge amount of gamma photons that could be released during the theoretical annihilation of matter and antimatter at the time of ...
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Wouldn't Miller's planet be fried by blueshifted radiation?

In Interstellar, wouldn't Miller's planet be fried by blueshifted radiation? The 61,000x time dilation multiplier would make even cosmic background radiation photons into extreme UV photons. I was ...
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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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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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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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