All Questions
252
questions
1
vote
1
answer
71
views
Age of universe vs Hubble time in Milne universe
Consider an empty universe where energy density $\varepsilon = 0$, thus the Friedmann Equation can be reduced into:
$\dot a^2= -\frac{kc^2}{R_O^2}$
$k$ is the curvature of space, $R_0$ is the radius ...
- 411
7
votes
3
answers
5k
views
If we consider the spacetime of the universe to be four-dimensional, does the Big Bang lie in its center?
Apologies for the (hopefully now somewhat less) clickbait-y title. Now, of course, I know that the Big Bang did not happen at any point connected to a single point in our current $3$-dimensional ...
- 1,897
2
votes
1
answer
123
views
Could the universe have a form of a $T^3$-torus?
Cosmological measurements suggest that we live in a flat universe. However, what might be less clear is its topology. So could the flat universe have the form of a $T^3$-torus, i.e. the torus whose ...
- 9,778
1
vote
1
answer
80
views
Cosmic web shape
Does anybody know why the cosmic web is shaped like a web? I feel like it would be more likely that it is more like a galaxy with a supermassive black hole in the center, if that were true, what would ...
0
votes
0
answers
100
views
Movement of galaxies vs expansion of space
I can readily accept the theory that the universe is expanding as a mathematical model to explain the fact that all galaxies are moving away from each other, but I have difficulty understanding ...
- 1
1
vote
0
answers
60
views
Is the universe closed or flat?
Apparently there is a tension in the measuring of the curvature of the universe (https://arxiv.org/abs/2307.07475) as apparently in 2018 the Planck collaboration got a series of results consistent ...
- 2,462
3
votes
4
answers
3k
views
Is the universe really a closed physical system? [closed]
It is assumed in most physics discussions that the universe is a closed physical system. But is it really? I am defining the universe as the entirety of everything physical, not merely the observable ...
- 1,252
-4
votes
1
answer
78
views
The background of the universe [closed]
Mass(-energy-momentum) curves space(-time).
However - what is space-time?
Is it (the background) necessarily flat(without something in it) ?
If there were an empty universe - is there still spacetime ...
- 63
2
votes
5
answers
1k
views
Why is it that the further a galaxy is, the greater is its recessional velocity?
The exam question is:
Explain how red-shift provides evidence for the Big Bang theory.
One of the points in the answer is:
the further away the galaxy is, the greater is their recessional speed
...
- 21
2
votes
0
answers
58
views
Space expansion or generation [duplicate]
When physicists assert that space is expanding, does this imply the creation of new space? If so, why do they use the term "expansion" instead of "generation"?
- 31
0
votes
1
answer
191
views
Are black holes the edge of our universe?
Are black holes the actual edge of the universe? Because spacetime is another dimension, I would assume the universe doesn’t have perceived corners or edges. At least humans cannot perceive it.
The ...
- 11
1
vote
2
answers
106
views
In spacetime time is a coordinate. Does it mean there is a single objective timeline for the Universe?
If every event can be defined with x, y, z, t coordinates - does it mean all events with the same t are composing the whole Universe at the moment t?
0
votes
0
answers
26
views
What is the expansion of space of one megaparsec in one year?
suppose we know Hubble's constant. In a hypothetical scenario an astronomer finds and confirms Hubble's law for a galaxy 1 mega parsec away.
Next year, how much distance will the hypothetical ...
1
vote
1
answer
67
views
Does the universe have an infinite volume? [duplicate]
The implications of a spatially infinite universe is profound, but so are the implications of a finite universe. What we know about this issue?
- 11
0
votes
1
answer
122
views
Cosmological principle: can there be a center of the universe "outside" the universe?
I've been watching youtube videos about the cosmological principle. I understand that the expansion of the universe is not concentric (around a specific point in space). The balloon example helped me ...
- 3