All Questions
Tagged with cosmology special-relativity
127
questions
3
votes
3
answers
209
views
One-Way Speed of Light and the Big Bang
Variations on this question have been asked a few times (e.g. here, here, and a few YouTube videos here and here). The claim seems to be that because we can only measure the round-trip speed of light, ...
- 6,112
2
votes
2
answers
700
views
Does the Cosmic Microwave Background falsify relativity of velocity?
In special relativity velocity is relative and there is no absolute rest frame . However the cosmic microwave background radiation does have a rest frame. Earth is moving with 328 km/s with respect to ...
- 25.3k
0
votes
1
answer
615
views
Four-Vector For Number Flux of Particles
Imagine a four-velocity $U^\mu(x)$ defined all over spacetime. Define the number-flux four-vector as
$$N^\mu = nU^\mu$$
where $n$ is the number density of a collection of particles in their rest frame....
CommunityBot
- 1
-3
votes
1
answer
185
views
Somewhat silly special relativity and cosmology thought experiment [closed]
Edit: I have already tried to delete this several times. I have already posted that I would delete this if I could and it was deleted. I have three very legitimate masters degrees in physics and more ...
-1
votes
1
answer
79
views
Is the equation of state of the cosmological vacuum $P=-(1/3)\rho$?
I understand that the equation of state of the vacuum is assumed to be $P = -\rho$ due to the Lorentz invariance of its stress-energy tensor. But this argument assumes flat spacetime. We know at ...
- 1,143
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
2
answers
99
views
Why does the light intensity of stars distribute almost uniformly across the night sky, if earth is not special?
According to special relativity, the direction of light should change when a reference frame is moving at near-light speed. There was a question on stack exchange about this topic before: Light in ...
- 48.4k
-6
votes
1
answer
97
views
What exists in the world according to the special relativity? [closed]
Before I learned about special relativity, I thought that only one 3-dimensional state of the world exists. Then, like in game of chess, in one "turn" previous state is destroyed - and the ...
- 26.4k
4
votes
6
answers
789
views
Why are distant galaxies not actually tiny bits of matter?
Distant galaxies are said to be moving away from the Milky Way (and us) at speeds approaching the speed of light. Since Special Relativity tells us that any object moving away from us at a velocity of ...
- 2,908
0
votes
2
answers
130
views
The twin paradox in a Finite Dark energy less universe
Let's imagine we have a universe that is finite and curves back on iself. So if you go far enough in one direction you end up back where you started. (e.g. 3-Sphere/3-torus) Then lets imagine that it ...
- 21.4k
1
vote
0
answers
45
views
Does strongly gravitating object travel along geodesic of a background field？ [closed]
That test particles travel along the geodesic is assumed in the context of GR. But does it apply to strongly gravitating object, such as black hole in an expanding universe, binary neutron star, etc.? ...
- 619
-6
votes
1
answer
113
views
Are cosmological Black Holes superluminal FTL phenomena? [closed]
What does it mean, "gravity is so strong that not even light can escape from a BH..."?
This can physically interpreted IMHO that beyond the event horizon of the BH, light is phase ...
-5
votes
1
answer
117
views
Is it important to understand the concept of a universal 'now'? [closed]
Is it important to understand the concept of a universal 'now', to explain that time is a local phenomenon, and the rate of time varies throughout the universe, always dependent on the local ...
- 26.4k
1
vote
0
answers
43
views
Could inhomogeneties and/or topological defects break the fundamental symmetries of the universe?
I have heard that some types of inhomogeneties and topological defects (like cosmic strings) in cosmology have been proposed to be able to break fundamental symmetries of nature such as the Poincaré, ...
- 2,462
4
votes
1
answer
765
views
Relativistic Doppler Effect: Intensity change
My physics prof. mentioned briefly, that in the framework of the relativistic Doppler effect, not only the frequency (alternatively, the wavelengh) changes when objects move with respect to each other ...
CommunityBot
- 1