All Questions
11
questions
-1
votes
3
answers
419
views
How "accurately" does the CMB tell the age of the universe?
Just to clarify, I am not asking about clock accuracy per se at all. The reason I am asking this question stems from the fact that on this site, most questions about the age of the universe answer ...
- 29k
2
votes
6
answers
983
views
Can there be a theoretical synchronised ‘now’ moment at all points across the universe?
Einstein’s relativity rejects the notion of a universal ‘now’ moment. It underlines how the concept of ‘now’ is compromised due to time passing at differing rates in differing frames of reference, ...
- 719
1
vote
1
answer
326
views
Is the center of the universe at absolute rest? [duplicate]
A twelve year old relative of mine asked me: If after there is a center of the universe (maybe the center is the point where the bigbang happened), could it be at absolute rest? Because everything is ...
- 111
1
vote
1
answer
199
views
Which time is there in the FRW metric?
The FRW metric is given by $$ds^2=dt^2-a^2(t)\Big[\frac{dr^2}{1-kr^2}+r^2(d\theta)^2+(r\sin\theta)^2(d\phi)^2\Big].$$ There is a time $t$ sitting in this metric. In which frame is this time measured?
- 26.8k
1
vote
0
answers
38
views
What does it mean by "the age or our universe"? [duplicate]
I am always puzzled by the notion "the age of our universe" because, correct me if I am mistaken, the universe is the entirety of the spacetime. So how can we measure how much time has the entire ...
- 11
3
votes
1
answer
527
views
Is any reference frame truly inertial?
I'm aware of the potential duplicate question here. However, that question centres on the Newtonian argument of there being a force, and hence acceleration. However, my issue is with the expansion of ...
- 1,788
2
votes
1
answer
179
views
At a center of Gödel's universe
A few quick questions clarifying a picture about Gödel's universe, they bug me badly!
Taken from here.
So Gödel's universe is made out of dust particles. All of them have angular velocity.
Do this ...
- 529
7
votes
1
answer
903
views
Doesn't dating the universe violate the concept of spacetime's inseparability?
It would seem that measuring an age of the universe from the big bang requires separating spacetime into a 3D coordinate system and a time track. I fail to understand why it is appropriate to take ...
- 121
2
votes
3
answers
2k
views
Why doesn't a global frame of reference exist for GR?
I only have at best a layperson's familiarity with GR, so forgive me if I am asking a basic question, but I have heard that in GR, we cannot have a global frame of reference, that is a frame of ...
- 41
0
votes
2
answers
157
views
Can I see stars in my light-cone that you can never see?
The light cone of our galaxy is a lot different to the light-cone of a galaxy 5 bly away. Our Hubble volumes are much different. Everyone is born in/at a different space/time.
Can I see stars in my ...
- 2,421
4
votes
2
answers
355
views
Since the universe is expanding, does anything ever occupy the same point in space?
Let's say we can observe expansion in a supercluster.
We define origin of our frame of reference at the center of the supercluster.
We observe an object/atom at point A at time T. The object is ...
- 151