Questions tagged [cosmology]
Questions about the origin, history, evolution and fate of the Universe.
287
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Create an inhabited black hole
Hello I was watching one of Isaac Arthur's videos about the end of time and i just got a crazy idea
Is it theoretically possible to "create" a "solar system" that would look like a supermasive black ...
2
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0answers
65 views
Is the Big Bounce Theory valid? If so does that mean all this have happened before?
IF the universe is just an infinite loop of events from expanding to contracting does that mean all this has happened before? The initial conditions for the next big bang would (or rather could) be ...
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0answers
29 views
Absorption line in quasar spectrum
I have quasar spectrum which includes emission and absorption lines. I need to find absorption lines in between 2 wavelength. How can I do it with coding?
2
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0answers
48 views
+50
Force to fix $\sigma_{8}$ or $A_{s}$ for Forecasts
In the context of Forecasts with Fisher's formalism, I make vary cosmological parameters to compute the elements of the Fisher matrix.
First, I generate with CAMB code a linear power spectrum. Then, ...
0
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0answers
68 views
Could the Sun's planetary nebula be dangerous for the planets?
Since the Sun's mass isn't high enough it won't go supernova being a red giant but instead release a planetary nebula. So that seems to be kind of a substitute for a supernova. Would ejecting the ...
2
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1answer
94 views
Did Einstein supported Big Bang Theory cosmological model?
Einstein made many predictions, including gravitational waves and the possibility of black holes.
Relativity is taken into consideration for the Big Bang model, so did Einstein agree with it or did ...
3
votes
3answers
69 views
light emission of quasars
I'm studying Astrophysics and I have some video's from a past course. I'm currently studying the reionization of the universe. At the current point in the class, the instructor is talking about ...
1
vote
0answers
30 views
Nebula and its Colours [duplicate]
A Nebula boasts of Too Bright Awesome Colors that includes red, blue, green, orange, white, etc?
They're result of excitation of electrons.
Is there a clear explanation as in which Color is ...
4
votes
1answer
57 views
How is the Dating of Samples of Cosmic Objects Performed, Including Pre-Solar Dust?
In the new Space.com article 7 billion-year-old stardust is oldest material found on Earth I had read about some pre-solar grains dating back to 7 billion years. What techniques are used in ...
0
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1answer
35 views
Metal lines in Lyman-alpha forest
I need to find metal lines in the Lyman-alpha forest of quasar spectra, without the red side of lyman alpha emission line.
Can you guide me how to do this?
0
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1answer
66 views
Why is constant velocity drift not an accepted explanation of Hubble expansion?
Edward A Milne at the Oxford University proposed that what Hubble was
observing was simply a natural sorting of random galactic motions. If
a group of galaxies formed together moving at various ...
3
votes
2answers
72 views
Are there predictions of the distribution of matter at the end of time
Are there any theoretical predictions or "educated speculation" by cosmologists on how matter will be distributed at very, very distant times in the future?
For example, will matter be:
agglutinated ...
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0answers
11 views
Formula to Compute sigma8 for correction in non-linear regime
I try to explain my issue on this forum since it seems to be appropriate.
I need to apply a correction on $\sigma_{8}$ between linear and non-linear regime to keep it fixed (I make change the values ...
0
votes
1answer
39 views
What reference frame do age-of-the-universe calculations assume?
I'm thinking, in particular, about general relativity. When we speak, for example, of neutrino decoupling, what do we mean when we say this happened in the first second after the Big Bang? Do we mean ...
1
vote
0answers
118 views
Scale factor 0 for expanding universe
Does the FLRW model have a scale factor $0$ at the singularity, meaning that even infinite distances become $0$ there according to the mapping $x \mapsto a(t)x$, for $a(t)=0$?
I am asking this ...
3
votes
2answers
98 views
Why does the Supernova 2006cm give a very different value for the Hubble constant? Why doesn't it increase error bars for the Hubble constant?
The Supernova 2006cm has a redshift of 0.0153 which translates into a recession speed of 4600 km/s.
It has a distance modulus of 34.71 which translates into a luminosity distance of 87 Mpc.
This ...
1
vote
0answers
68 views
Aligning of 7 unidentified objects in the sky, what are they? What did I see? [duplicate]
So this morning (4th December 2019, 0518hrs) I was out turning my horses out in the fields and noticed a strange arrangement of what I perceive to be stars, only I’ve never seen it before and wondered ...
15
votes
1answer
284 views
A Sky Map of Gravity - what would it look like?
PREAMBLE
Sky Maps exist which show the distribution and intensity of electromagnetic radiation received on Earth at various wavelengths. An obvious form is a map of the stars (Star Chart).
Maps ...
2
votes
0answers
42 views
Redshift and Velocity relation
Let us say that we have a stellar object so its total velocity is defined as
\begin{equation} v_{tot} = v_{pec} + V_{rec} \end{equation}
Where
\begin{equation} V_{rec} = H_0r \end{equation}
...
5
votes
1answer
120 views
At what rate is the observable universe expanding?
The observable universe is $4.4 \times 10^{26} m $ in every direction. I told this to my daughter and then added, "And guess what? It's a little bigger today than it was yesterday."
"Wow!"
But by ...
0
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1answer
44 views
who use the GADGET-2 pack for simulation? can I do it with my PC? [closed]
I want to do hydrodynamic simulatin for universe at vary redshifts. How can I do it?
or how can I find an simulation of universe for use my work?
2
votes
2answers
83 views
Could different views of the universe simply be different points in time?
I'm not sure if this is the correct stackexchange site for this question.
I've been reading this article on Vice Motherboard There’s Growing Evidence That the Universe Is Connected by Giant ...
0
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1answer
571 views
Troop of moving stars through a straight line [duplicate]
Last night,I and my brother suddenly saw that some(50-60) dots of light( exactly like stars) were moving through a straight line(from NW to SE) above us with same velocity and towards exactly same ...
0
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0answers
17 views
Calculate rest flux density from emitted flux density derived from fits data of SDSS data tool
Say I have a spectrum of a galaxy at a redshift z, with flux density units of erg/s/cm^2/Angstrom. I'd like to convert flux density(in the same units) at z=0, i.e. at its rest it's rest emisison. How ...
12
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138 views
The recent results on Hubble constant measurements
In recent news there is this announcement
In the introduction they say:
Distance measurement discrepancy: a $4.4σ$ tension on the value of $H_0$
and I understand the discrepancy is with the ...
2
votes
1answer
82 views
Why do we expect Type Ia Supernovae to be brighter in a decelerating Universe than what has been observed?
This seminal review paper in the PNAS by Robert P. Kirshner (https://www.pnas.org/content/96/8/4224) says the following:
If the universe had been decelerating—–in the way it would if it contained ...
3
votes
1answer
94 views
Time dilation due to the expansion of the universe
This is not a homework question. I want some help in being able to clearly perceive the expansion of the universe and the consequences thereof.
We know that the universe is expanding in an ...
2
votes
1answer
62 views
Difference between 3D real space and 3D redshift space?
With regards to cosmological simulations (e.g., N-body dark matter only simulations), I've seen people talk about the positions of objects (halos, galaxies) in the simulation in terms of 3D real space ...
8
votes
1answer
152 views
How do we know so many details about Big Bang, but we do not know if Universe is finite/infinite?
I understand that this question may be too vague, but I am confused about the following:
On one hand we know a lot of "details" about Big Bang, like really precise details, evolution of universe, age ...
0
votes
1answer
126 views
Cosmological redshift - How do we know it's not caused by the observer's time dilation?
Instead of cosmological redshift being caused by the metric expansion of space, why couldn't cosmological redshift be caused by our perspective moving faster in time? Said another way, if the ...
2
votes
1answer
91 views
The energy density of DM (to be fluid,state parameter=-2)increases with time. Does it violate the concept of accelerating universe?
We know that dark energy with value of state parameter $\omega<-1$ is called phantom dark energy model. In this model if we assume dark energy to be a fluid with value of state parameter $\omega=-2$...
6
votes
3answers
223 views
Cosmological redshift vs doppler redshift
I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift.
He ...
2
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1answer
30 views
Redshift, velocity, distance
How are redshift, (recessional) velocity and distance of a galaxy related?
I understand what v=HD states. So I assume that Hubble measured a direct relation between the distance and recessional ...
1
vote
2answers
83 views
The size of Copernicus’ and Ptolemy’s corrections
I understand that both Copernicus and Ptolemy needed epicycles, but one might assume that a heliocentric system would need much smaller corrections to account for the non-circular motion of the ...
0
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1answer
93 views
Why does an open universe expand forever, while a closed one does not?
It makes sense to me that the universe would eventually stop expanding, as bodies of mass attract each other, and I understand that dark energy can counteract this attraction. However, I don't ...
4
votes
2answers
128 views
What is the effect of this expanding universe on the energy density of it?
We know that our universe is expanding i.e. volume of the universe is getting larger with time with total energy being conserved. My question is whether the energy density is getting smaller with ...
3
votes
1answer
56 views
What is assembly bias in context of cosmology?
I see the term "assembly bias" being used quite a bit in cosmology literature? I have not been able to find a good primer on what it means, and why it is important.
3
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40 views
Cosmology : Formula for the bias of galaxies
first I have posted originally on the physics stackexchange but I have not had answers about my question, so I try my luck on this specific forum (if forums leaders want to delete the original post on ...
4
votes
1answer
129 views
Observable universe equals its Schwarzschild radius (event horizon)?
The estimated age of the universe is 14 billion years.
The estimated Schwarzschild radius (event horizon) of the observable universe is 14 billion light-years.
What are the ramifications?
2
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3answers
252 views
Is the universe older than 13.7 Billion years?
I came to know that the cosmic horizon is the part of universe beyond which we cannot see. So if the light from 13.7 billion years ago is what we can observe, does that mean the universe is older than ...
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1answer
83 views
Does space being at right angles to time imply that the expansion or contraction of each occurs in a direction opposite the other's?
The Minkowski diagrams that are employed to illustrate Special Relativity depict changes in the motion of objects through the dimensions of space as occurring within a field (that's otherwise divided ...
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1answer
92 views
How Essential is the Vacuum Energy to Our Present Model of the Expanding Universe? [closed]
How essential to modern cosmology is the vacuum energy concept, and what would happen to our model of the expanding universe if it were proved to be non-existent?
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1answer
58 views
Discrepancy Between Results of Cosmological Observations & the Assertions of Quantum Mechanics [closed]
Quantum mechanics requires a vacuum energy 40 orders of magnitude higher than that indicated by cosmological observations. Which side is most likely to be right,& when the truth is finally ...
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0answers
48 views
How are constraints on dark energy improved the most?
Today we have various data available from independent probes to constrain dark energy, i.e. its equation of state $w$. These include Type 1a supernovae, BAO, CMB, large-scale galaxy surveys, etc. Are ...
0
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1answer
169 views
Where do Neutrinos Go if They Don't Interact?
It is said that neutrinos can travel for billons of years at almost the speed of light without interacting with anything. That being the case,what do they do - is it possible they could orbit the ...
4
votes
1answer
204 views
Has the Big Crunch been ruled out?
If the dark energy equation of state $\omega$ evolves with time, and becomes larger, this would result in decelerated expansion and eventually a Big Crunch. If $\omega$ decreases with time, becoming ...
2
votes
1answer
48 views
How is the expansion rate of the universe obtained from Baryon Acoustic Oscillations?
I understand that we can measure the sound horizon from the anisotropies in the CMB. Large galaxy surveys today can construct two-point correlation functions, which reveal peaks at distances equal to ...
0
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0answers
49 views
Expansion of space or constriction of length scales?
According to wikipedia,
"Technically, neither space nor objects in space move. Instead it is
the metric governing the size and geometry of spacetime itself that
changes in scale. Although ...
0
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0answers
53 views
How is “surface brightness dimming” derived from redshift in the NED extragalactic database
I have several questions regarding “Surface Brightness Dimming” in the “Quantities Derived from Redshift” section of the Nasa/ipac Extragalactic Database.
As an example, please use quasar IRAS F08279+...
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0answers
55 views
Understanding the statistical mechanics of Recombination Epoch (“Cosmology” Weinberg)
In Steven Weinberg's 'Cosmology' Chapter 2.3 (pg 113), he begins with a number density for some particle via the Maxwell-Boltzmann Formula:
While I have some familiarity with statistical mechanics, I ...
