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 can I calculate the variation on CMB Temperature because the expansion?

I don´t know if i am doing it correctly. I have a problem, in which is known the $T_{CMB}$, the temperature that was measured by COBE, with a value of $2,725(2) K$, and ask which temperature would ...
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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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Time evolution of radiation (black body) spectrum in expanding universe

I was looking at Peebles' paper on recombination (https://ui.adsabs.harvard.edu/abs/1968ApJ...153....1P/abstract) and I don't understand one of the key equations he uses in his derivation of the ...
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Does anyone recognize this function for the Hubble value as a function of density?

I'm trying to reverse engineer a C++ package I found for computing the power spectrum of CMB (EasyCMB). There's a formula that appears to be calculating the Hubble value at a given scale factor, a, ...
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Can cosmological parameters be quoted more precisely at other epochs?

Inspired by Value of density parameters in CMB time it seems to me that when cosmological parameters are quoted (e.g. from the CMB or type Ia supernovae), they are almost exclusively quoted in terms ...
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Value of density parameters in CMB time

I was looking for the value of the density parameters ($\Omega_{i}$) in cosmology at the time of decoupling (CMB Time). I know that the Planck Colaboration aproximatelly gives $\Omega_{m}=0.315$, $\...
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The distance sound waves could have traveled in the time before recombination

I was reading this page and find a concept that I dind't know, I was searching for the specific value of $r_{s}$ (The distance sound waves could have traveled in the time before recombination) and $\...
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Flat inflationary spectrum

As far as I know, any successful model of inflation must predict an almost flat spectrum of primordial perturbations ($n_s$ close to one). However, according to some reviews: http://pdg.lbl.gov/2019/...
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What caused quadrupole anisotropy at the time of recombination?

The polarization of CMB requires a quadrupole anisotropy of the incident radiation field acting on the plasma. How did such a special pattern (i.e. hot and cold in two orthogonal directions) generate ...
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How to assign a temperature and a time to cosmic events in the universe?

Sorry if this question to too silly for the experts here. But how do cosmologists assign a temperature and a time to each important cosmic event in the history of evolution of the universe such as ...
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Lorentz invariance of the CMBR [duplicate]

From the Wikipedia entry on the CMBR dipole anisotropy (emphasis mine), From the CMB data it is seen that the earth appears to be moving at 368±2 km/s relative to the reference frame of the CMB (...
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Can we look further than the CMB?

As I understood it, the map of the cosmic microwave background (CMB) corresponds to the time when photons decoupled from matter, making the universe transparent. In this sense, we might expect the CMB ...
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How far can we look into space?

Ho distant can we look into space by using a telescope? With "telescope" I mean here any device able to detect photons of any wavelength. In terms of distance, is it correct to sat that observing the ...
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Understanding the recombination and decoupling periods in the early universe

I have a couple of questions about the recombination and photon decoupling. The problem is I have 2 references that give different time scales for these two periods. For recombination: In Roos, it'...
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Why wasn't CMB radiation absorbed long ago, since when it was emitted the universe was much smaller?

When CMB radiation was emitted, the universe was only 350,000 years old or so, and so why wasn't it absorbed at that time? The universe is postulated to have been expanding at that point but I think ...
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How long until we can no longer see the CMB? [duplicate]

With every day passing, we see photons from the CMB that have been travelling farther / for longer than the photons we saw yesterday. I assume that due to the expansion of the universe, there is a ...
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How is cosmic microwave background radiation experimentally detected?

Can it be detected from the earth with a single dipole antenna or a series of such antenna forming an interferometer (with an electric circuit to filter out the noise due to radio stations and ...
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How do we determine the $H_0$ from standard rulers and standard candles

I am doing a research project about hubble tension. Even if I have some ideas about how we messure the $H_0$ by using the standard candles, i dont have much knowledge about it. I suppose we are ...
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Why is the Planck/WMAP estimate of the age of the universe preferred?

A recent physorg article is titled "The measurements of the expansion of the universe don't add up". The article says The current analysis of the variable brightness of cepheids with space ...
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Would other parts of the universe have a different rest frame for their own Cosmic Background Radiation?

The CMB, once the Doppler shift from the Earth's motion is subtracted, is fairly uniform, which seems to imply that all the matter that emitted it moved at more or less the same velocity when it did. ...
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How much photon energy has already been destroyed?

We get taught in school that energy can neither be created, nor destroyed. The law of energy conservation is confirmed by many processes. It is an incredibly accurate assumption for every-day life. ...
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Density fluctuations of the present Universe with Large scale structures

Disclaimer The question below is based on a vague knowledge, and hence, statements can be potentially wrong or misleading. An important quantity in Cosmology is the density fluctuation of matter ...
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Order of Magnitude of Cosmic Microwave Background Anisotropies

How does the statement about the anisotropies being of the order of $\frac{\Delta T}{T} \approx 10^-5$ which is often made in the literature (see, e.g. Description of CMB Anisotropies by Scott and ...
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How to justifiy that $\rho_{\text{rad}} \approx \rho_{\text{mat}}$ at recombination time?

In standard cosmology, the recombination time is estimated to be $t_{\text{rec}} \approx 380~000~\mathrm{years}$ after the Big Bang, when matter and electromagnetic radiation becomes decoupled. It's ...

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