All Questions
Tagged with electromagnetic-radiation cosmology
55
questions
6
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4
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2k
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Accelerating Expansion of Universe - Why Not Caused by Radiation?
As I understand it, dark matter and dark energy are used as an 'explanation' for how universe expansion is accelerating; because without it gravity would be expected to cause a long term shrinking.
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- 181
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votes
1
answer
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What fraction of the universe's energy is contained in photons?
From each point in the universe, the light of billions of stars, galaxies, supernovae etc. can be detected. So there seems to be a lot of energy/momentum "in flight".
Is it possible to ...
- 347
0
votes
1
answer
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Mass density of radiation in Friedmann equation?
$$\frac{{\ddot a}}{a} = - \frac{{4\pi G}}{3}(\rho + 3P) + \frac{\Lambda }{3}$$
In the case of matter, pressure $P=0$,
In the case of radiation, pressure $P=(1/3)ρ$,
In the case of cosmological ...
- 117
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0
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98
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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, ...
3
votes
1
answer
69
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Frequency shift of photon using magnetic field
According to GR, it is possible to redshift the frequency of a photon using a magnetic field as demonstrated by the Gerstenshtein Effect:
https://web.archive.org/web/20210225134450/http://jetp.ac.ru/...
- 183
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0
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Radiation from a moving charge particle in expanding universe?
Moving charged particles generally emmit energy in form of radiation.
Assume a charged particle that is situated in a zone that can join the Hubble flow and therefore starts moving away from us.
As it ...
- 2,462
11
votes
3
answers
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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 ...
- 111
-1
votes
1
answer
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Redshift Due to Expanding Space (not increasing distance) [closed]
Please NOTE: "For example, a question that proposes a new concept or paradigm, but asks for evaluation of that concept within the framework of current (mainstream) physics is OK."
And: "...
- 23
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votes
2
answers
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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 ...
- 2,255
1
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1
answer
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If cosmological redshift causes wavelength elongation does it mean the whole emitted signal is elongated?
If cosmological redshift causes wavelength elongation does it mean the whole emitted signal is elongated? Let say we have ten waves on the see hitting the shore.... If we somehow elongate every single ...
- 2,255
1
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3
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116
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How does light fill the entire universe? [duplicate]
Light is a particle and a particle is discrete. So say light is emitted from a star 7 billion years far, how is it possible that this light particle emitting from a star fills every point in the ...
- 283
1
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3
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Can cosmological redshift only decrease photons' energy by increments (that correspond to Planck's constant)?
I have read this question:
The equations that govern quantum mechanics predict that the angular momentum (that is, spinning or orbiting) in a system can't take on any value, but instead come in lumps....
- 29k
1
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0
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19
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Universe expansion and energy conservation principle [duplicate]
If photons lose energy due to expanding of the universe where the lost energy is stored? Does the energy conversation principle is violated?
- 119
2
votes
1
answer
486
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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
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3
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Are the constituents of the known universe matter (including antimatter) and electromagnetic radiation?
Is it correct to say that the constituents of the known universe are matter (including antimatter) and electromagnetic radiation, leaving aside the comparatively hypothetical ‘dark’ entities? This is ...
- 135
3
votes
1
answer
107
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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
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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 ...
- 2,403
0
votes
0
answers
36
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Changes to an EM-wave that is propagating in an inflating space
I am trying to get an easier picture of what happens to an em-wave considering space expansion. My question is: If a star in a non-inflating space emits light recorded at a certain distance of the ...
- 1,815
4
votes
1
answer
228
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How much energy is in the Universe as photons? [duplicate]
The mass of Universe in kilograms is about 10 power 53.
But how much energy exists in the Universe in form of photons?
And if they would all be converted into mass, how much mass that would make?
Dark ...
- 233
1
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1
answer
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Why are there fewer lines on the absorption spectrum than on the emission spectrum for some gases?
I don't know if this is right, but I think that it is because:
when the gas is heated, the electrons get 'excited' and move up to an energy level (lets say an electron moves up 4 energy levels).
...
- 220
4
votes
1
answer
114
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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 $...
- 555
2
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1
answer
268
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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
0
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0
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169
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Infinite universe and the impossibility of monochromatic light and infinite plane waves
I recently asked a question relating to this excerpt from the textbook Optics, fifth edition, by Hecht:
Mathematically, the plane wave extends out to infinity in all its directions, and, of course, ...
- 889
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votes
1
answer
47
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What does a universe look like where light cannot lose energy and is emitted all the time? [closed]
In a universe where light cannot lose energy, and is emitted all the time, what is the result?
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4
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1
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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 ...
- 7,592
14
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1
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4k
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What percentage of the mass/energy of the universe is in the form of electromagnetic waves? [duplicate]
Is there any theoretical framework or model that would lead to a prediction, either precise or approximate, about how much or what proportion of the universe's total mass is in the form of photons, or ...
- 533
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0
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70
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Matters Including Resolution of Olbers' Paradox
Is there evidence for galaxies receding from us faster than the speed of light? If so,that might help resolve Olbers' paradox, though other factors must also be taken into consideration. Could such a ...
- 1,710
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votes
1
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4k
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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
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2
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244
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What happens when the wavelength of light becomes as large as the observable universe? [closed]
Say the wavelength of a photon became so large that it approached the size of the observational universe. Does something unexpected happen?
-2
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2
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278
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Could photons decay into Dark Matter? [closed]
So, we can "see" 13.7 billion (intentionally not including expansion) light years in all directions and we "see" a red shift.
What if, the reason we can't observe photons beyond this limit is that ...
