All Questions
29
questions
8
votes
2
answers
429
views
Are the mass, diameter and age of the Universe frame dependent?
Mass of the observable Universe is known to be $1.50×10^{53}$ kg. Age is approximately known to be 13.7 billion years.The observable Universe is a sphere with diameter of roughly $8.8\times10^{26}$ m.
...
0
votes
0
answers
45
views
Clocks at different redshift: does calculating luminosity distance shift the frame of reference?
Luminosity is energy per time.
When we calculate a luminosity distance, using angular diameter distance times $(1+z)^2$, I think we are correcting the energy (from redshifted photons) by $(1+z)$ and ...
- 821
6
votes
1
answer
1k
views
How is the expansion of space distinguishable from objects moving away?
Suppose you are standing 5 feet (1.5 m) away from me. Then I move 10 feet (3.0 m) further away. Now you are at 15 feet (4.5 m) distance from me.
You say I moved. I say no; the space between us has ...
user371657
2
votes
0
answers
57
views
If the universe expands uniformly in all directions, wouldn't that make the basis for an universal and absolute "now" and reference frame? [duplicate]
Let's consider a universe with constant expansion for simplicity's sake. In such a universe, the Hubble Parameter drops to half its value after double the time. If it happens to be 70 km/s/Mpc today, ...
- 139
17
votes
7
answers
3k
views
Is there any "Cosmological Principle"?
The term "Cosmological Principle" is widely invoked in cosmology discussions. I
think the basic idea here is that one might guess that the Milky Way is not at a special location in the ...
- 59.6k
0
votes
0
answers
32
views
Do more distant galaxies move faster with respect to the cosmic background radiation rest frame?
Aparently our galaxy is moving approximately 1/500th lightspeed with respect to cosmic background radiation. While this is certainly fast, it stands to reason that it could had been a lot faster, so ...
- 804
2
votes
1
answer
112
views
Is cosmic background radiation consistent with the Cosmological Principle? [duplicate]
Is the observation of cosmic background radiation really consistent with the cosmological principle? It implies that there is a "special" rest frame of motion with respect to the big bang. ...
- 804
0
votes
1
answer
86
views
Is there a "central" cosmological inertial frame?
I know there are no preferred inertial frames from the perspactive of special relativity, and I assume the same is true from the perspective of General Relativity. However, if the same is ...
- 24.8k
5
votes
2
answers
309
views
In what frame of reference is time measured, just after the big bang?
We often read about the expansion of the universe in the first seconds, or milliseconds after the big bang. What frame of reference is used for these estimates of time? If the entire universe was ...
- 4,783
3
votes
0
answers
50
views
Would other parts of the universe have a different rest frame for their own Cosmic Background Radiation?
The CMB, once the Doppler shift from the Earth's motion is subtracted, is fairly uniform, which seems to imply that all the matter that emitted it moved at more or less the same velocity when it did. ...
- 749
0
votes
5
answers
261
views
Does the Universe itself move to any direction on top of expansion?
So the universe expands right, but does this expansion move to any direction in hyperspace as an expanding cluster of matter somewhere?
It's like if you would explode a bucket of paint under the. ...
1
vote
1
answer
173
views
Cosmic scale factor $a(t)$ in a general frame of reference
In considering an FLRW type universe, the scale factor $a$ is generally indicated as being strictly a function of time $a(t)$. Isn't this only true for a comoving frame?
In some other reference ...
- 2,847
0
votes
2
answers
151
views
Space expansion and speed of light
I recently saw a video on gravitational waves that says that expansion of space can only be measured due to changes in speed of light as everything else that could have been used to measure the ...
- 126
0
votes
1
answer
42
views
Inertial mass increase of the farthest receding galaxies
If the farthest galaxies that we can see are receding at near the speed of light, shouldn't this increase their inertial mass as well relative to our galaxy?
-1
votes
2
answers
109
views
How is energy conserved?
From what I’ve heard, there is no absolute grid you can put on the universe, and therefore you can only ever talk about relative motion.
I’ve also heard that energy is conserved and constant no ...
- 293