All Questions
Tagged with cosmology estimation
42
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Is there an estimate for how many monopoles would be produced in the very early universe?
The question really hits it with this one. I haven't really found some good numbers other than the whole “It'd be so many (per Hubble vol) to recollapse the universe”. I don't know if that comes of as ...
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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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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 ...
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What was the size of the observable universe at the matter-dominated era and its mass density?
For instance, at the scale factor $a=0.5$ and matter dominated era, what was the size of the observable universe and matter density?
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What is the expansion of space of one megaparsec in one year?
suppose we know Hubble's constant. In a hypothetical scenario an astronomer finds and confirms Hubble's law for a galaxy 1 mega parsec away.
Next year, how much distance will the hypothetical ...
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Why are departures from flat spacetime geometry small on scales smaller than the Hubble radius?
In Chapter 5 of Baumann's cosmology book where he discusses structure formation starting from Newtonian perturbation theory, Baumann mentions at the beginning that
Newtonian gravity is a good ...
- 394
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If all the black holes in the Universe were combined into one supermassive black hole, what would its diameter be?
I am curious to know if anyone has ever sat down and calculated what the diameter of a black hole would be, in kilometers, if it were to contain all the mass of all the black holes that are currently ...
- 478
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Size of the universe 13 billion years ago
When wee look at the sky in opposite directions, we can see early galaxies that were formed about 13 billion years ago. At that time, the distance between two such galaxies at the opposite ends of the ...
- 466
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Could gravitational waves be cosmologicaly 'redshifted'? [duplicate]
Is it posible that gravitational waves detected here on Earth could be cosmologicaly 'redshifted'? So, at emission they had higher frequency then after reaching Earth?
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2
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Is CMB slowing down all moving objects in the universe?
1/
Object moving relative to the CMB frame of reference will see the CMB blue shifted where it is heading and red shifted where it came from.
Correct?
2/
The blue photons ahead should have more ...
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answer
619
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How fast is the edge of the observable universe expanding from the Earth?
If the universe is expanding at 73 kilometers per second per megaparsec, what is the fastest expansion speed that we can observe from Earth? I'm assuming that's the edge of the observable universe ...
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Calculating the size of the universe
I read the numerous threads here for example:
Lower limit of the size of the Universe? (WMAP)
Determining the size of the universe to calculate its age
Size of the universe
But I would like to try a ...
- 1,721
18
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2
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4k
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How long ago was the Universe small enough for interstellar travel?
Currently, even the nearest stars are lightyears away, and impossible to reach in our lifetimes. If space is always expanding, and was once infinitely smaller, then at what point in the past was space ...
- 719
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1
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210
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Demonstration: Integral (discrete summing) of $C_\ell$ has a better variance than one single $C_\ell$
I am working in a cosmological context where I use the $C_{\ell}$ quantities coming from Legendre transformation.
I am faced to a issue to prove the gain that we get by computing the variance of an ...
user87745
5
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3
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585
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If a CMB photon traveled for 13.7 billion years to reach me, how far away was the source of that CMB photon when it first emitted it?
If a CMB photon traveled for 13.7 billion years (- 374,000 years) to reach me.
How far away was the source of that CMB photon when it first emitted it?
My attempt to solve this question was to use the ...
- 365
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1
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609
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How close can we calculate back in time to the instant of the big bang? (until, presumably we need a theory of quantum gravity?)
I've heard a few times in my 5+ decades that we can only calculate the "state of the universe" (loosely speaking, I don't know any math close to that high) back to very close, but not right ...
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Is the cosmic event horizon viewed from Andromeda different from the one viewed from Earth?
If the most distant galaxies we see in deep space are in proximity of our cosmic event horizon does it mean that if we were on Andromeda galaxy and looking in the same direction we would see objects ...
- 2,255
6
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1
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282
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How long would it take to get to the Hyperion proto-supercluster?
Right now, we set a ship carrying no humans going to the Hyperion supercluster (redshift is $z=2.45$, so around $11$ billion light years from Earth) at a velocity of $c/2$ ($c$ being the speed of ...
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If Hubble parameter varies with time how much it differs for low distances (present) and deep space (past)? [duplicate]
If deep space is shown as it was in the past how can we calculate this time lagging regarding the Hubble parameter which is a variable of time?
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What is the largest gravitationally bound structure in the universe?
I understand the galaxy superclusters are not bound due to dark energy. I wonder what matter scale will remain gravitationally bound - galaxy clusters, galaxies, stars - if anything at all, as dark ...
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Cosmology / Interpretation between credibility/confidence_level with bayesian/frequentist approaches
I try to understand the following article :
testing general relativity from curvature and energy contents at cosmological scale
I don't understand the title of figure 1 :
where it is indicated ...
user87745
2
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1
answer
281
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What is the expected size of primordial black holes?
I often see it implied that primordial black holes tend to be small compared to stellar masses;
Since primordial black holes did not form from stellar gravitational collapse, their masses can be ...
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Very Basic Hubble Constant Question
In an article titled "Gravitational Waves Could Solve Hubble Constant Conundrum"
Data from the cosmic microwave background suggests the universe is currently expanding at a rate of about 41.6 miles (...
- 2,706
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Is the mean CBM frequency more red-shifted since discovered in the 1960's?
If the universe is uniformly expanding at rate x, is possible to measure that the CBM has increased its red-shift value over time? If the red-shift is a static value, is it possible that the ...
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If I sliced the universe in half, would the slice go through a star?
This question is based on a discussion with a 10-year old. So if it is not clear how to interpret certain details, imagine how a 10-year old would interpret them.
This 10-year old does not know about ...
user78574
6
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1
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171
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At any given point in the universe, are there a huge number of photons crossing paths?
If you're standing in a dark night-time place on the Earth and look up at the sky, you see stars. (About 6000, if you're in a sufficiently dark place). You're seeing photons that have passed though ...
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How to derive number of nucleons in Universe?
I understand that there are roughly $N=10^{79}$ nucleons in the visible Universe. This number comes from adding up the nucleons of $100$ billion stars in $100$ billion galaxies in the visible Universe ...
- 5,925
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2
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181
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When must an alien civilization send off a signal that can reach us today?
Given the rate of expansion of the universe and the speed with which galaxies separate: Can a rough estimate be given, at which time T (in its proper time) a civilization that lives on a planet which ...
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Density of baryons
I wanted to recalculate the number of atoms in the universe according to What paper can I cite for the estimated number of atoms in the observable universe to be lower than $10^{82}$? .
But in the ...
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What paper can I cite for the estimated number of atoms in the observable universe to be lower than $10^{82}$?
The title contains the whole question. I am a logician in theoretical computer science and want to use the estimated number of atoms in the observable universe to show what a ridiculous amount of ...