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 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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Will we ever stop receiving CMB photons on earth? [duplicate]

If there is a lamp $1$ meter away from me which is switched on at time $t_1$ and switched off at $t_2$, I'll start receiving the light at time $t_1+\frac{1}{c}$ and stop receiving it at $t_2+\frac{1}{...
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Primordial perturbations, scale invariance and fundamental length

In cosmology, the initial perturbations to the metric can be described as $$\mathrm ds^2=-\mathrm dt^2+a(t)^2e^{2\zeta(\mathbf x)}\mathrm d^2x,\qquad(1)$$ where $\zeta(\mathbf x)$ is a gaussian random ...
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Sachs-Wolfe Effect on power spectrum

From my understanding, there are two main types of Sachs-Wolfe effect: 1)Non-intergrated Sachs-Wolfe effect happens when the photon escapes from a potential well/peak at the last scattering, therefore ...
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Transformation of the frequency of a photon after an infinitesimal coordinate transformation

I am having trouble understanding a calculation done by V. Mukhanov in his book "Physical Foundations of Cosmology". In the beginning of the chapter 9, the following arguments are stated: ...
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What is the maximum wavelength of the CMB? The minimum?

What are the longest and shortest wavelengths of the cosmic microwave background? Since it is 'black-body' radiation, does this correspond to max. and min. temperatures?
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Silk damping in CMB power spectrum

Can someone explain Silk-damping in a conceptual way? I understand that it is the effect causing the power spectrum to decrease in amplitude at smaller angular sizes because the effect is apparently ...
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Does the cosmic microwave background (CMB) put a upper bound on Universe radius and size?

We know the universe is filled with a near uniform radiation at a equilibrium temperature(T) of approximately 2.725K. It's a remnant of the Big Bang. My reasoning to propose this question is, we can ...
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Does the frame in which the CMB is isotropic violate the Copernican Principle?

The Copernican Principle states that Earth is not at a special place in the Universe, and by extension, that there are no "special places" in the Universe (per homogeneity of the universe, ...
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How many cosmic strings are there in the Universe?

While researching cosmic strings, one often encounters terminology ranging from "scaling solutions" to "correlation lengths". As a newcomer, one of the first questions I have had is "how many cosmic ...
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What does it mean to say the CMBR has a “temperature”? [duplicate]

We say the cosmic microwave background radiation “has a temperature” of 2.7K. Does this mean it has a temperature in the way we say the air around a warm lightbulb has a temperature of 120° or in the ...
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How is the Redshift of Recombination Calculated?

In all the text, they do a hand waving exercise where they say the re-ionizing temperature of Hydrogen in the plasma is 3,000K, the current temperature of space is 2.75K, so you divide 3000/2.75 and ...
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Should the CNB be comoving with the CMB? [duplicate]

The neutrino decoupling and the photon decoupling happened after the big bang, though at different times. The CMB is very detectable, and although there is no universal reference frame, the CMB is ...
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Analysis with CMB Data

I have read about Cosmic Microwave Background Radiation from Weinberg's Cosmology Book. I'm looking forward for specific resources to analyse real time CMB Data recorded by Physicists. Any papers, ...
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How is it possible that photons can exist for 13 billion years? [closed]

Implicit in the evidence of the Big Bang is the fact photons have travelled for a period of time that is greater than 13,000,000,000 years. What special circumstance exists that would exempt photons ...
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Cosmic microwave background polarization and detecting primordial gravitational waves

I have a few questions about primordial gravitation waves What are primordial gravitational waves? Wikipedia says that they are observed in the cosmic microwave background (CMB), but gravitational ...
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CMB variance as percentage - does that make any sense?

Reading a popular science book that is pretty accurate and in depth, but stumbled upon this line (translated): The variation, that the CMB pattern reveals amounts to less than one hundredth of a ...
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How uniform is CMB?

I gather that elaborate cosmological theory which predicted CMB and a lot of detail about universe evolution before recombination was available even before we were able to even detect CMB. CMB is the ...
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Since the CMB is the oldest thing we can see, how do we know for sure what happened before the CMB?

I keep wondering about how can we be so sure about what happened before the CMB, given that it is the oldest thing we can actually see. It seems like we are very confident about what really happened ...
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What part of static noise in FM radio and analog TV is due to CMB?

When you switch analog FM radio or analog TV channel to non-existing station (in-between channels),- then you hear/watch just plain static noise. Question what I am interested is- what part exactly of ...
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Are CMB polarisation measurements affected by cosmic variance?

I was reading Wayne Hu's CMB polarisation notes (https://arxiv.org/pdf/astro-ph/9706147.pdf) and at the bottom of page 14 he says; For $z_{ri}∼5–20$ the difference in the power spectrum is confined ...
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Did Penzias and Wilson really made a *picture* of the CMB, as stated on the web, or is it completely wrong?

Did Penzias and Wilson really made a picture (graphical picture of skyp map using a computer) of the CMB, as stated on the web, or is it completely wrong ? Indeed, If I consider what they say here : ...
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Is the decoupling matter/radiation in the universe evolution due to the electron/nuclei recombination or to the *density* decrease or to *both*

Is the matter/radiation decoupling in the evolution of universe due to -the electron/nuclei recombination (because temperature decreases), so that photon-matter cross-section reduces since there is ...
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Radiation Density Parameter Today

I would like to insert in my thesis the value of the radiation density parameter today with its appropriate error and I was checking the latest Planck results here. I am a bit confused since I thought ...
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How does the baryon asymmetry control temperature fluctuations of CMB?

The temperature fluctuations of the Cosmic Microwave Background (CMB) have a sensitive dependence on the quantity of baryon asymmetry of the universe. In fact, analysis of CMB fluctuations is one of ...
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Is it feasible to simulate CMB scattering surface in a lab?

The CMB last scattering occurred at ~3000K, z=1100. Is it possible to simulate these conditions under lab conditions to help verify the CMB last scattering hypothesis ?
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How is Universe expansion measured with CMB

There are plenty of articles about measuring the universe with standard candles, parallax, certain types of stars, etc. CMB measurements are usually introduced into the article to bring attention to ...
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Is the light coming from the CMB redshift?

I know that using the standard cosmological model you can get a relation of the temperature and redshift $$T=T_{0}(1+z)$$ and using that formula with $T_{cmb}=3000 K$ and $T_{0}=2.7 K$ you conclude ...
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What is the Relation between the Cosmic Microwave Background and the Hubble Sphere?

I've learnt that The cosmic microwave background (CMB) is the light emitted just after the Big Bang and which is reaching us now after being hugely red shifted by our expanding universe. Now Hubble ...
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Big Bang most outer edges [closed]

If we can experience or see the beginning of the universe - i.e. see the Big Bang through devices - then can we perceive or see the most forward edges of the big bang racing outward?
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Why is the GZK cutoff at such high energies?

Why is theGZK cutoff at such high energies? The threshold energy for Compton scattering is 0.511 MeV. But the inverse Compton scattering has a very high energy threshold. For example in ...
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How long will last the CBMR?

I am confused about the duration of the cosmic background microwave radiation.Will it eventually be replaced by same radiation from discrete directions?
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Density of radiation at CMB

I was trying to find the radiation density at the CMB time. For two different methods, the first one is using the Planck Law and the data for the actual measured temperature $T_{0}=2.7255° K$. $$ \...
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Why is CMB an evidence of hotter and denser early Universe?

In his book Gravitation and Cosmology, Steven Weinberg says that the Cosmic Microwave Background (CMB) makes it "difficult to doubt that the universe has evolved from a hotter denser early stage". In ...

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