All Questions
18
questions
6
votes
4
answers
2k
views
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.
...
- 181
0
votes
0
answers
33
views
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?
- 476
0
votes
0
answers
26
views
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 ...
2
votes
1
answer
319
views
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
1
vote
0
answers
35
views
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?
- 2,255
3
votes
1
answer
619
views
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 ...
- 51
18
votes
2
answers
4k
views
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
5
votes
3
answers
585
views
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
1
vote
1
answer
82
views
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
votes
1
answer
282
views
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 ...
- 63
1
vote
1
answer
114
views
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?
- 1,815
0
votes
1
answer
793
views
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 ...
- 19
2
votes
1
answer
281
views
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 ...
- 252
1
vote
1
answer
116
views
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
1
vote
1
answer
67
views
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 ...
- 11