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 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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Why has the neutrino cosmic background a lower temperature than the cosmic background radiation?

Does the neutrino gas pervading the universe (cosmic neutrino background, CNB) always have the same temperature? Does it still have the temperature as the neutrino gas that emerged from the big bang? ...
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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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How can cosmologists distinguish between CMB variations caused by dark matter and those created by baryonic matter?

Charlie Wood, "How Ancient Light Reveals the Universe's Contents", Abstractions Blog, Quanta Magazine, January 28, 2020, https://www.quantamagazine.org/how-the-cosmic-microwave-background-...
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Temperature of Closed Universe in future

This is a question from "Introduction to Modern Cosmology" by Andrew Liddle: Suppose we live in a closed universe(k > 0), which will recollapse some time in the future. What will the ...
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Why do the TT, TE and EE power spectra in the CMB lead to different values for the Hubble constant?

Table 2 of Planck 2018 results Why are these three values different? In particular, why is the EE value so much closer to the local universe value, and have so much higher error?
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How is speed of Milky Way determined relative to CMB dipole?

I read that our galaxy the milky way is moving at approx 630km/s relative to CMB dipole, I think they applied Doppler shift to find this number but how do they do that? I know when universe is a hot ...
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How does the Planck satellite's detailed map of the CMB lead to a value of the Hubble constant, $H_0$?

Cosmologists have put great faith, it seems, on the cosmological model that led to a value (of 67) of the Hubble 'constant', after carefully peering at Planck's map of the cosmic microwave background.....
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Cosmic microwave background dipole anisotropy

I'm trying to wrap my head around dipole anisotropies of the Cosmic Microwave Background (CMB). I think my confusion is rooted in a misunderstanding of how multipole expansion is used in describing ...
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Is the commonly accepted Universe age of 13.8B years really accurate? [closed]

Hmm...challenging the error margin of a specific calculation result of a specific model based on confirmed inconsistencies is regarded as "opinion-based". Interesting. Just curious, is the ...
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What is the concordance model formulate for calculating the CMB temperature?

Folks, I am looking for the concordance model formula to calculate the temperature of the CMB for some time in the future. I have seen the formula T0=2.7(1+z) the Einstein version or Concordance model?...
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How do you relate the number densities of neutrinos and photons soon after the positron–electron annihilation?

I found this equation: $n_\nu = \frac{3}{4} \frac{g_\nu T_\nu^3}{g_\gamma T_\gamma^3} n_\gamma$ Where does it come from?
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Gravitational analogue for Cosmic Microwave Background?

Penzias and Wilson famously discovered the CMB as a signal that they failed to be able to account for after removing all other known radio-sources. It's apparently close to the same strength in all ...
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How to plot the CMB power spectrum?

It's possible to get the power spectrum of the CMB from the Lambda CDM model. But how do I get this plot? I'd like to mainpulate the parameters like it's possible in this "ancient" tool ...
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How is Hubble constant measured by the method of observing BAO?

How is Hubble constant measured by the method of observing BAO?By just reading some articles it seems to me a more complex method than the astronomic scale.Can this method be explained in few words to ...
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What equation precisely defines the epoch of recombination? [duplicate]

I understand that a very rough first estimate would be to assume this happens when the mean photon energy drops below the value required to photoionise hydrogen, namely when \begin{equation} \label{...
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Understanding the CMB power spectrum

We are able to expand the CMB temperature anisotropy map in terms of spherical harmonics. My current understanding is that each l (on the x-axis of the power spectrum below) corresponds to a unique ...
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How are the alpha vacua, the Bunch Davies vacuum and Adiabatic vacuum different in context of inflationary cosmology?

I do understand that the Bunch-Davies is the most standard vacuum to consider as an initial condition, but what if there are deviations from a de Sitter spacetime that do not generically reduce the ...
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Does the Cosmic Background Radiation (CMB) indicate that we may be any kind of privileged observer?

To first order, the Cosmic Background Radiation (CMB) looks the same in every direction. Apparently, however, at the level of parts per million, there are small distinctive variations in the ...
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What is the meaning of “current” CMB rest frame or the CMB rest frame at redshift $z$?

As I know that the definition of the CMB rest frame is the comoving frame of the plasma emitting CMB. And the anisotropy of CMB is due to the velocity difference between the earth frame and the CMB ...
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Does it make sense to measure the time from the Big Bang until the CMB was emitted?

It is very common to hear cosmologists talking about what happened some time after the Big Bang. Here is a good example of chronology: https://en.wikipedia.org/wiki/Chronology_of_the_universe The ...
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How long does it take for 1 mole $H_2$ at STP to diffuse to a density of one $H_2$ molecule per $m^3$ in interstellar space?

One can read here: The molar volume, or volume of one mole of gas, depends on pressure and temperature and is 22.4 liters - at 0 °C (273.15 K) and 1 atm (101325 Pa), or STP (Standard Temperature and ...
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Angular size of the largest region in causal contact at the moment of recombination

I want to calculate the angular size of the largest region in causal contact at the moment of recombination (z = 1100) to our universe, so we have: $H_0 = 68$ (km/s)/Mpc, $\Omega_{m,0} = 0.31$, $\...
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Red- / Blueshifting and relativistic length contraction at $0.8c$ - How would it look?

I am a CG artist working on a specific shoot, that I have no clear answer to how it would look. And I seek your help. :D The idea for the shoot is a flyby of two Interstellar Vessels named ITV Europa ...
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Considering the history of microwave Background radiation, was it ever in visible range? When will it fall to be able to heat water like in our oven?

Please do provide assurance of what formula you used and that you did the calculations for the answer. Thanks. My back of letter calculation says that CMBR was never in visible range since it became ...
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Is the Energy Associated with the Loss or Gain of Information Dependent on Temperature?

I believe it was Leo Szilard who derived a relationship between entropy and information: /S = k ln(2) where k is Boltzmann's constant and /S is the change in entropy of a bit of information. If each ...
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Why was the universe initially opaque after the Big Bang?

It is theorized that till about 380,000 years after the Big Bang, the universe was opaque. Why did the particles present before the formation of atoms make the universe opaque? Why did the universe ...
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How superhorizon power spectrum would have looked like if there was no inflation?

As it is well known, one of the main motivations for the idea of inflation is the explanation of superhorizon CMB correlations: we observe the existence of perturbations with sizes larger than the ...
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Can we produce the CMB power spectrum from a given model of inflation, theoretically? If yes, how?

To the best of my knowledge, the CMB power spectrum is obtained from a statistical analysis of the observed temperature anisotropies of the CMB sky. Is there a way of getting the power spectrum ...
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CMB Temperature Spectrum

I have read in many references (for instance: http://www.revistacubanadefisica.org/RCFextradata/OldFiles/2019/v36n2/RCF_v36n2_2019_147) that the peaks of the CMB Spectrum is related with the curvature ...
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Thermodynamics of Hawking radiation and cosmic microwave background

Black holes can emit Hawking radiation. The larger the mass of a black hole the lower the frequency of emitted radiation (aka the temperature of the object). Hawking radiation of a large enough black ...
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What does CMBR has to do with quantum fluctuations during rapid inflation?

I know the almost homogeneous of cosmic microwave background radiation is claimed to be caused by the rapid expansion of quantum fluctuations in the early universe, but what does density of photons ...
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Where can i get the step by step expression for CMB anisotropy?

I never able to wrap my head around alm term used in expression If you know the expression, kindly explain but also give textbook references. It would be helpful.
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How smooth does reheating (after inflation) need to be?

Let's estimate the size of perturbations in the very early (GUT scale or earlier) universe required for consistency with CMB. The CMB fractional temperature (and hence density) perturbations are of ...
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Does the Sachs-Wolfe effect depart from $1/3$ for large $k$?

In the Sachs-Wolfe effect (the one at last scattering, not the ISW), the standard result is $$ \frac{\Delta T}{T} = \left( 1 - \frac{2}{3} \right) \Delta \Phi = \frac{1}{3} \Delta \Phi . $$ To ...
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How isotropic is the universe?

In Wayne Hu's tutorials, as well as Wikipedia, I've seen the CMB quoted as being isotropic to 1 part in 100,000. I tried to get a reference for this, so I dug and found out that, after subtracting ...
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What is the energy spectrum of all photons in the observable universe?

Does anyone know what the energy spectrum for the entire universe looks like? In other words, what would the graph look like if you plotted the number of photons on the $y$-axis and frequency on the $...
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Pivot scale in cosmology and CMB

What is a pivot scale, pivot frequency in general, and particularly in the cosmology? I don't get the idea. Almost everywhere I found the same the same sentence "we take the standard value of a ...

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