All Questions
Tagged with speed-of-light cosmology
88
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, ...
- 106
2
votes
2
answers
149
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Cosmic expansion and the speed of light
The light from the galaxy GN-z11 took 13.4 billion years to arrive, but its distance from the earth is 32 billion lightyears. This is commonly explained as a result of cosmological expansion, i.e. ...
- 7,504
0
votes
1
answer
59
views
Visualizing the Hubble Sphere
I have viewed the definitions of the Hubble Sphere and related cosmological concepts, as well as various explanations, yet Im still struggling to comprehend a full visualisation of this, which I would ...
3
votes
1
answer
130
views
Confusion regarding recessional velocity and Lorentz transformation
Consider that you are receding at a velocity faster than the cosmic speed limit (say, $2c$ with respect to $A$) due to the expansion of our universe. According to me, $A$ is moving at $2c$ and thus ...
user355398
2
votes
1
answer
46
views
How to include the effect of cosmological expansion in the close to speed of light calculations of a relativistic rocket?
I calculated time ago as undergraduated and post it at my blog the calculations for traveling through the Universe in a (special) relativist way. At what level and how should we include the effect of ...
- 6,611
1
vote
1
answer
132
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How to rule out that the speed of light was different in the past?
The constancy of the speed of light is a fundamental principle in modern physics, and it is supported by a wide range of current experimental evidence.
There is no evidence to suggest that the speed ...
- 489
1
vote
1
answer
211
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The Ricci scalar in FRW, where am I getting wrong?
I'm trying to derive Ricci scalar with FRW metric, but additional $c^2$ makes me confused.
The book by D. Baumann says
\begin{align}
R &= g^{\mu\nu}R_{\mu\nu} \\
&= -R_{00}+\frac{1}{a^2}R_{...
- 169
1
vote
1
answer
172
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Twin paradox with black hole (based on Interstellar) [closed]
I'm an Undergrad student working on a summer project. I'm learning about Differential Geometry, Schwarzschild's Solution, General and Special Relativity. I want to include the twin paradox as well. In ...
- 11
1
vote
4
answers
326
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Do objects outside the Hubble sphere violate special relativity?
According to special relativity, objects can move with speed at most c.
However, objects outside the Hubble sphere recede from us faster than the speed of light.
How can these be reconciled?
- 1,440
2
votes
1
answer
82
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In an expanding universe, can two people communicating to each other about their cosmological horizons get around their horizon limit?
I want to pose a preamble question that I will answer first to build up to the main scenario. Then I will pose the main question. The main question concerns the special case of an expanding universe ...
- 8,640
4
votes
3
answers
759
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Constant speed of light violates accelerating expansion of universe?
My question regards the following:
One of the most fundamental principles of Einstein's GR is that all free bodies move through spacetime with constant velocity $c=1$.
However, in 1998 Hubble showed ...
- 201
1
vote
3
answers
136
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Measuring the Hubble Constant
Attempts to measure the expansion of the universe have come in various forms. The recent Cosmology Crisis (https://www.space.com/why-is-there-a-cosmology-crisis) has me pondering the expansion rate ...
- 11
-3
votes
1
answer
91
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What is the “conspiratorial anisotropy” if we would see no star redshifts in one direction of the sky? [closed]
Suppose we see no redshift of stars in one direction only (or better, in directions on a small patch around it). And suppose in that direction (on a patch of sky around it) we see a lot more stars ...
0
votes
1
answer
80
views
Thought experiment with the speed of light
Every time we look at a star we are looking to the past. That's because the light of that star needed to travel long distances at the speed of light. When the light reaches our sight maybe the star no ...
- 103
1
vote
2
answers
136
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Is a photon emitted beyond the Earth cosmological event horizon towards Earth actually moving away from Earth?
Is a photon emitted beyond the Earth cosmological event horizon towards Earth actually moving away from Earth due to space expansion? Is that the reason why we can't see beyond the horizon?
- 2,255