All Questions
Tagged with electromagnetic-radiation cosmology
55
questions
6
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4
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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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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
0
votes
0
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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/...
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1
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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
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1
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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
0
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2
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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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130
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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
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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?
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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 ...
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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 ...
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18
votes
3
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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
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0
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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 ...
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1
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1
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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).
...
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4
votes
1
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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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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
answer
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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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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
15
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1
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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
2
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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
answers
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 ...
0
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1
answer
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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:
$$
c_s^2 = \frac{c^2}{3}\left[\frac{3}{4}\frac{\rho_{b,0}(1+z)^3}{\rho_{\gamma,0}(1+z)^4}
+ 1\right]^{-1}...
user32023
18
votes
2
answers
4k
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Did the big bang create an infinite number of photons?
We will always be able to see the cosmic microwave background (CMB) at about [the age of the universe] light years away.
Always.
Does that mean that infinite photons were created at that time? If ...
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1
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1
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106
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CMB - Excess Energy? [duplicate]
Today in physics we were looking at how the energy of a photon is the product of Planck's constant and the frequency of the photon, therefore the lower the frequency, the lower the energy of the ...
7
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0
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323
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Trying to reproduce curves with angle of CMB anisotropies as a function of distance and curvature parameter
I am looking for a way to get, by a simple numerical computation, the 3 curves on the following figure:
For this, I don't know what considering as abcissa (comoving distance ?, i.e
$$D_{comoving} = ...
user87745
53
votes
4
answers
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Red shifted to what?
I searched and found a lot of questions and answers about red shift here but none with the answer to mine. (sorry if it is there somewhere and I did not find it.)
Everyone is saying the light from ...
- 611
0
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2
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395
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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 ...
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-2
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1
answer
213
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Tired light question
How do we arrive at the conclusion that redshifted light from cosmological sources has 'lost' energy during its transit from source to us? If in fact no actual measurement of the energy of the ...
- 49
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4
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598
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Which one is more fundamental in nature: matter or radiation?
I am following a geometric perspective on abelian gauge theory as done in the lecture notes by Timo Weigand, chapter 6, pp 165-167, here:
http://www.thphys.uni-heidelberg.de/~weigand/QFT1-13-14/...
user56963
5
votes
3
answers
207
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Is the total amount of light today the same as it was 13.8 billion years ago?
Is the total amount of light today the same as it was 13.8 billion years ago? Is it fair to assume that the total background photon flux (ignoring local deviations) given by
$\ cm^{-2}s^{−1}sr^{−1}$ ...
- 69
0
votes
2
answers
139
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Is it possible for the momentum of star light to cause the accelerating expansion of the Universe?
So photons have momentum right? And stars are constantly expelling light on all directions, which eventually hits any object on its way and transfers a small amount of momentum. So wouldn't this ...
-1
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3
answers
671
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Is light dark energy?
I was wondering if it was possible for light itself to be dark energy, might sound silly but it's been breaking my brain for months and I can't find any reason why not. If light can interact with ...
3
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1
answer
457
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Can the wave length of a photon be stretched out caused by expansion of spacetime? [closed]
Strictly speaking perhaps it is not right to say that a photon is a wave so its wave length can't be stretched out; a photon is actually just a point. So is its wave property only a relativistic ...
- 3,348
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1
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99
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Does light orbit the universe? [closed]
Or rather, does mass-less particles orbit the matter in the universe due to the infinite range of gravity? And if yes, in what shape are they orbiting? A ring as on Saturn? Maybe a whirlpool due to ...
- 121
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1
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147
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How do we filter out radiation from galaxies from the cosmic background radiation?
When a whole sky view is done to get a picture of the cosmic background radiation the radiation from our Galaxy is filtered out, and we are left with a picture which show radiation coming, more or ...
- 1,141
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2
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594
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Finding the cosmological redshift of a galaxy in the expanding Universe
Firstly, I understand what the Doppler effect is when it comes to sound or light waves.
From everything that I've read, we are told that the universe is constantly expanding since the all the ...
- 323
6
votes
1
answer
348
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How does the Cosmic Microwave Background give us information about the Big Bang?
I was reading about CMB after this new breakthrough last week and I could not figure this out. The CMB did not exist before the epoch of Last Scattering. They were just photons which were formed at ...
user42733
9
votes
4
answers
2k
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Do photons make the universe expand?
I have a problem understanding the ideas behind a basic assumption of cosmology. The Friedmann equations follow from Newtonian mechanics and conservation of Energy-momentum $(E_{kin}+E_{pot}=E_{tot})$ ...
- 10.1k
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2
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Do photons and cosmic rays radiate energy through gravitational waves? If not, why not?
Due to the mass-energy equivalence, both matter and EM radiation bend spacetime, and both are capable of forming singularities (black hole, white hole/kugelblitz). In light of this, why do photons ...
user40753
3
votes
2
answers
436
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Do electromagnetic fields gravitate?
It's well known that electromagnetic fields contains energy but do they gravitate?
When we talk about the composition of the universe it's now accepted that the 74% is dark energy, the 22% is dark ...
- 905
3
votes
3
answers
620
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How much of the universes mass is bound up in photons traveling between stars?
I was watching a Scott Manley video on youtube and he mentioned that the Sun was loosing 4 million tons of mass a second as it converts to energy.
With a few trillion trillion stars also converting ...
- 133