All Questions
54
questions
2
votes
2
answers
149
views
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. ...
- 7,514
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 ...
2
votes
1
answer
82
views
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
views
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
views
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
views
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 ...
1
vote
2
answers
136
views
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
3
votes
2
answers
130
views
Faster-than-light gravitational waves and faster-than-light expansion in the inflation
I have no introduction to the inflationary epoch. I know, however, that during this time space-time expanded with a speed faster than the speed of light. If gravitational waves are perturbations of ...
- 585
2
votes
1
answer
169
views
How can a photon emitted when the universe was just a few lightyears in diameter, travel for billions of years without bumping into something?
Admitted: I find it already surprising that a photon can travel for billions of years without bumping into something in a universe that has the size of current observable universe but there I guess ...
- 289
1
vote
3
answers
473
views
Are we seen or not by an observer from a galaxy farther away than the age of our solar system?
I looked at this question. There's one answer that alludes to what I'm asking, but I don't find it satisfactory, because to me the following is still a paradox:
The most distant galaxies we have ever ...
15
votes
4
answers
2k
views
Can light reach far away galaxies in an expanding universe?
I've read that, since the universe is expanding at an increasing rate, light that leaves our galaxy now will never reach far away galaxies. That even though a galaxy is moving away from us slower than ...
- 267
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
3
votes
2
answers
260
views
Why speed of light in vacuum remains constant over space and time?
Imagine a Pulse of light traveling through space at $c$, coming towards an observer on Earth, while at the same time, Space-time fabric (metric) is continuously changing (expanding), then why is the ...
- 149
3
votes
1
answer
118
views
Can gravity weaken due the inflation of the universe?
As I understood the gravitational force is exchanged between particles at the speed of light. If there is an increment of distance between astronomical objects is it true to think that the ...
- 2,255
6
votes
1
answer
282
views
How long would it take to get to the Hyperion proto-supercluster?
Right now, we set a ship carrying no humans going to the Hyperion supercluster (redshift is $z=2.45$, so around $11$ billion light years from Earth) at a velocity of $c/2$ ($c$ being the speed of ...
- 63