All Questions
18
questions
1
vote
0
answers
44
views
Expansion of the universe and superluminal speeds - an analogy
To illustrate, let's imagine the whole universe having a coordinate grid. Essentially a great big mesh grid of interlocking meter sticks.
Now... Einstein's theory of relativity tells us that nothing ...
- 41
1
vote
0
answers
60
views
Why is the age of the universe $=D/v$, despite that $v$ is not constant with time?
I am watching a series of lectures by the Noble prize laureate Brian Schmidt and Paul Francis and in this episode (at 4:20) they make the simple assumption that a galaxy receding from us due to the ...
- 157
0
votes
1
answer
175
views
FLRW metric, universe expansion, and the energy-momentum relationship
This is a follow-up to a previous question of mine.
I am getting myself confused by some basic things in cosmology, so I hope whoever reading this is patient.
The Euclidean FLRW metric is given by
$$ ...
- 8,640
1
vote
2
answers
142
views
Why is special relativity not enough to explain the seemingly accelerating expansion of the universe?
I have only recently studied Special Relativity, and have yet to learn anything regarding General Relativity, so I may be asking this due to a lack of knowledge - please educate me.
I just read about ...
- 297
2
votes
0
answers
48
views
Does expansion of space over time assume a particular space/time dichotomy?
Regarding the expansion of the Universe, Wikipedia states:
The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe ...
- 222
1
vote
3
answers
59
views
Indirectly breaking the speed of light through inflationary phase
How do you define velocity? Rate of change of "space" between two objects-and that will give relative velocity between them. Now in inflationary phase the universe expanded faster than light ...
- 483
1
vote
0
answers
52
views
What implications does special relativity have on the accelerating expansion of the universe? [duplicate]
Under special relativity we have the Lorentz factor:
$$
\gamma = \sqrt{\frac{1}{1-\frac{v^2}{c^2}}}
$$
Which essentially mathematically describes how the relative speeds between objects can never ...
- 261
7
votes
1
answer
2k
views
Is the observable universe equivalent to 'our' light cone?
All the objects we can observe (stars, galaxies, ...) must be in our past light cone, since otherwise we couldn't see them. Presumably there are more objects located outside of our observable universe ...
- 1,438
1
vote
1
answer
104
views
Is all matter within the observable universe?
The observable universe is everything within the range of the distance light can travel since the beginning of the universe. Since relativity states that matter cannot travel faster than light in any ...
- 11
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?
0
votes
2
answers
214
views
Time dilation and length contraction for light and how this is interpreted where space is expanding faster than the speed of light
First off I am an engineer and not a scientist. Consequently my course work emphasized classical mechanics and I was never formally introduced to topics like relativity and quantum mechanics in ...
- 1
1
vote
0
answers
70
views
As space-time expands between two stars, what happens to the gravitational potential energy seemingly lost as U~1/r => ZERO.?
As the space-time between two stars grows (the accelerating expansion of the universe) the gravitational potential energy between two stars is reduced as 1/r -> ZERO (r is the distance between stars).
...
4
votes
1
answer
313
views
Hubble's constant measured by observer approaching light speed
I recently read about expansion of the universe and I can't figure out if Hubble's law (and other models of expansion of the universe) is compatible with the theory of relativity.
My question is: In ...
- 149
0
votes
3
answers
152
views
Observing a point 13.82b ly away, 1b years ago
I understand that we can observe far away galaxies to get an idea how the universe looked like in the past.
Assuming the universe is 13.82b years old, would it be correct to say that if we looked at ...
- 153
1
vote
1
answer
86
views
Are the edges of a galaxy moving inwards?
Space is expanding, but as I understand it, galaxies are not since gravity keeps them together.
If you think of space becoming bigger, your galaxies just become further apart. But taking the size of ...
- 129