All Questions
20
questions
0
votes
0
answers
98
views
How can we use CMB to measure the value of the cosmological constant?
Another mystery facing cosmologists is the accelerating expansion of the universe. In 1929, astronomer Edwin Hubble showed that the universe was expanding, but for this expansion to be justified, ...
11
votes
3
answers
3k
views
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 ...
- 111
0
votes
2
answers
194
views
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 ...
- 2,255
2
votes
1
answer
486
views
What is the mean free path (MFP) of a Cosmic microwave background radiation (CMBR) photon?
If the IGM (inter-galactic medium) had a massive particle (proton) every cubic metre, or a carbon grain every cubic kilometre, what would be the MFP of a CMBR photon? The coherence length of the ...
- 304
3
votes
1
answer
107
views
Gravitational wavelength shift of microwave background radiation
I can't find this precise question answered. It is basically a two part question.
Would the microwave background radiation, as well as light travelling to us from stars in an expanding universe ...
- 533
18
votes
3
answers
2k
views
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 ...
- 2,403
4
votes
1
answer
114
views
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 $...
- 555
2
votes
1
answer
268
views
How/why did the Thomson scattering by early plasma of the CMB create a particular polarization?
I understand how Thomson scattering polarizes EM radiation, but why/how did particles of the early universe create a particular polarization pattern of the CMB? (E-mode polarization)....
I mean, the ...
- 4,509
4
votes
1
answer
178
views
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 ...
- 7,592
15
votes
1
answer
4k
views
Why can’t you see at the start of the Big Bang?
I’m quite confused with regards to photon emission throughout the creation of the universe.
From what I’ve heard, there was no light (of any frequency) in the universe until 300,000 years after the ...
- 2,356
0
votes
1
answer
1k
views
What is the present day photon density, $\rho_{\gamma, 0}$?
I'm attempting to perform the integration that will yield the sound horizon at recombination:
$$
c_s^2 = \frac{c^2}{3}\left[\frac{3}{4}\frac{\rho_{b,0}(1+z)^3}{\rho_{\gamma,0}(1+z)^4}
+ 1\right]^{-1}...
user32023
18
votes
2
answers
4k
views
Did the big bang create an infinite number of photons?
We will always be able to see the cosmic microwave background (CMB) at about [the age of the universe] light years away.
Always.
Does that mean that infinite photons were created at that time? If ...
- 781
1
vote
1
answer
106
views
CMB - Excess Energy? [duplicate]
Today in physics we were looking at how the energy of a photon is the product of Planck's constant and the frequency of the photon, therefore the lower the frequency, the lower the energy of the ...
7
votes
0
answers
323
views
Trying to reproduce curves with angle of CMB anisotropies as a function of distance and curvature parameter
I am looking for a way to get, by a simple numerical computation, the 3 curves on the following figure:
For this, I don't know what considering as abcissa (comoving distance ?, i.e
$$D_{comoving} = ...
user87745
0
votes
2
answers
395
views
Origin of electromagnetic radiation in the universe
I don't know if the total electromagnetic radiation in the universe is finite or not.
But either way: what is the origin of the electromagnetic radiation in the universe? Can we say that all of it ...
- 156