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Results tagged with cosmology
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user 34155
Questions about the origin, history, evolution and fate of the Universe.
1
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0
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What is the 'TE correlation' in the CMB, or 'temperature-E-mode' correlation, aka 'temperatu...
There are several places on the web that mention this, a couple in some technical detail, but I cannot wrap my head around what exactly it means...
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1
vote
1
answer
113
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Why is the FLRW universe (general relativity solution(s)) sometimes called the 'FRW universe'?
Why is the letter L for Georges LeMaîtres often, or even usually, left out?
Does he, or does he not, deserve some credit for this cosmological solution to Einstein's general relativity?
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5
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1
answer
151
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How, exactly, does the precise measurement of the CMB's polarization modes and temperature f...
Amidst all the talk a year and change ago about the value of the Hubble parameter reached by the Planck satellite team, and how it's value differed from the value reached by the 'distance-ladder' team …
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0
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1
answer
87
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Are the most distant known objects in the universe more than 14 billion light years away? [duplicate]
When I hear about the most distant objects in the universe, such as the recently discovered galaxy GN-z11, their distances are usually stated to be a little under 14 billion light years away....
But, …
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7
votes
1
answer
877
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If an object 1 billion light years away emits light, does it take more than 1 billion years ...
From page 7 of the recent (September 26, 2020) edition of Science News Magazine:
Detected May 21, 2019, the gravitational waves came from a source about 17 billion light-years from Earth, making this …
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1
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0
answers
108
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Why do most astrophysicists believe the cosmic microwave background (CMB) provides the best ...
I frequently read that the cosmic microwave background contains the best overall evidence for the existence of dark matter, and conversely against alternative gravity theories like MOND.
However, I ca …
- 5,585
2
votes
1
answer
888
views
What is the 'scale factor' equation for a dark-matter dominated universe?
This family of solutions labelled by ${\displaystyle w}$ is extremely important for cosmology. E.g. …
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3
votes
1
answer
114
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Does the Cosmic microwave background (CMB) have an amplitude? Does it vary, like the 'temper...
Somehow, I have never read about this or thought about, until now...
Does the number of photons from the CMB hitting us from all directions vary at all?
- 5,585
21
votes
1
answer
3k
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Why doesn't dark matter clump strongly in the center of galaxies, since it doesn't feel eith...
Dark matter is described as being spread not only throughout a galaxy, but also around it in a halo of some sort that extends far beyond the visible parts of the galaxy...
In fact, dark matter haloes …
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0
votes
1
answer
1k
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How do you calculate comoving distance and light's travel distance? According to the formula...
According to Wikipedia, Distance measures (cosmology),
Comoving distance:
$${\displaystyle d_{C}(z)=d_{H}\int _{0}^{z}{\frac {dz'}{E(z')}}}$$
Light-travel distance:
$${\displaystyle d_{T}(z)=d_{H}\int … From 'Distance measures (cosmology)' on Wikipedia:
Is there an example on the web somewhere of these two things, comoving and travel distance, being calculated? That might help.... …
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3
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1
answer
104
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What does lowercase 'beta' mean in this graph of radio-emitting galaxies?
Correlation between the mass of the galaxies (X-axis) and the difference of their radio emissions at different radio frequencies (Y-axis). Each symbol represents an individual galaxy. The image of a …
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8
votes
1
answer
2k
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Why was the Cosmic Microwave Background (CMB) released at a blackbody temperature of 3000K r...
The redshift is known quite precisely from the theory, since a hot big bang model (the standard model of cosmology) predicts the point at which the plasma de-ionized to form neutral hydrogen. … (Screenshot)
The redshift is known quite precisely from the theory, since a hot big
bang model (the standard model of cosmology) predicts the point at
which the plasma de-ionized to form neutral hydrogen …
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1
vote
2
answers
390
views
What is a 'square' Kelvin degree? μ$K^2$? In terms of the cosmic microwave background's (CMB...
From what I have read and seen, the minute temperature fluctuations in the CMB are measured in microKelvin, or μK.
However, many charts and graphs show μK2, or 'microKelvin-squared'.
Do they simply me …
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7
votes
1
answer
149
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What exactly is a 'gravastar'? How is it different from a 'regular' black hole?
The Wikipedia article on gravastar says that it has a 'regular' black hole metric (Schwarzschild, I presume?) on the outside, but a de Sitter metric on the inside....
What exactly does that mean?
Don' …
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1
vote
1
answer
115
views
Shouldn't the estimate of the universe's age be higher, not lower, after the attractive stre...
From 'Fundamentals: Ten Keys to Reality', by Frank Wilczek :
"Running the movie of cosmic history backward in our minds, we found the galaxies all coming together to meet at a definite time. When did …
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