Questions tagged [space-expansion]
The expansion of the universe is a phenomenon wherein, at scales much larger than galaxies, the distance between objects grows over time. This phenomenon is often described as "expansion of space", although there is no difference between space expanding and objects moving apart.
1,996
questions
3
votes
1
answer
180
views
Will expanding space rupture an empty box floating in outer space
Under the theory that space itself is expanding, but the space inside of atoms and molecules doesn't expand because nuclear and electromagnetic bonding forces exceed the forces that expand space, ...
- 12.4k
2
votes
3
answers
132
views
Can a light signal from Earth reach a galaxy outside the Hubble Horizon?
Is this video on the FLRW metric (timestamp 29:00 minutes) mistaken in its claim that a light signal from Earth cannot catch up with a galaxy outside the Hubble horizon, due to the horizon receding at ...
- 27.5k
2
votes
1
answer
354
views
How does the redshift - distance graph show the rate of expansion of the universe at every moment in time?
By plotting the graph of redshift against the distance of the object from earth, we are able to obtain a best-fit curve showing the relationship of redshit against the distance. How does this ...
CommunityBot
- 1
1
vote
2
answers
48
views
Viable values for the $K$ parameter in the FLRW metric
The FLWR metric is sometimes given as $$c^2 d\tau^2 = c^2 dt^2 - \frac{a(t)^2}{(1-KX^2)} dX^2. $$
I am not interested in the tangential motion so I set $d \Omega = 0$ although it is of interest in ...
- 6,404
2
votes
1
answer
549
views
Dilaton field causes apparent universe expansion?
In string theory low-energy $n$-dimensional gravity is described by an action of the following form:
$$S^{(n)}=\frac{1}{2\kappa^{(n)}}\int d^nx\sqrt{-G}e^{-2\Phi}\Big(\mathcal{R}+4\partial_\mu\Phi\...
- 5,925
9
votes
4
answers
651
views
Understanding expansion of the Universe as things flying apart
Say that we have a Universe uniformly filled just with matter (let's not bring dark energy into this). And say that we fill it with very light particles (so that the gravitational interaction between ...
- 6,112
10
votes
7
answers
5k
views
Why is FTL travel impossible if the universe expands FTL?
If the universe is expanding spacetime faster than light (FTL), is FTL travel no longer completely impossible?
Do not care about energy requirements or needing new tech, just if it is NOT physically ...
- 6,404
0
votes
1
answer
42
views
Friedmann Equation and a contracting universe
Consider a universe with a nonzero curvature and matter.
One can write the Friedmann Equation in this universe as such:
$$\frac{H(t)^2}{H_0^2} = \frac{\Omega_0}{a^3}+\frac{1-\Omega_0}{a^2}$$
Where $H(...
- 207k
-4
votes
0
answers
46
views
Simple question about finite Universe [duplicate]
If, by Big Bang, Universe was created from initial singularity, with finite "speed" of expansion of matter, shouldnt it be finite as well?
- 207k
-1
votes
1
answer
173
views
Is the observable universe analogous to a white hole?
My instinct is no, but my lack of understanding with respects to white holes doesn't tell me why. My thinking is this: The universe is expanding and the further away from us the faster it is expanding....
-1
votes
1
answer
502
views
Dark energy and virtual particles
If space time is accelerating away from itself everywhere due to dark energy, could this acceleration be the cause of virtual particles, essentially Unruh radiation?
CommunityBot
- 1
2
votes
1
answer
69
views
Increasing the view of observable universe
I have read that the maximum observable universe is about 92 billion light years in diameter by measuring the microwave background waves emitted after some few million years ago from the big bang and ...
- 5,097
0
votes
2
answers
111
views
Is it true that $\dot{H}(t)\sim H(t)$, and if so, why?
In the context of working with the FRW metric in Cosmology, I'm trying to reproduce the results of a paper where an expansion of the metric in terms of perturbations is performed. The author gives a ...
- 12.4k
5
votes
3
answers
439
views
Changes to a Length of Physical Ruler Caused by Gravity vs Caused by Cosmological Expansion of Space
I read here (Feynmann Lectures, Lecture 42) that "Just as time scales change from place to place in a gravitational field, so do also the length scales. Rulers change lengths as you move around." (...
1
vote
2
answers
2k
views
Are galaxies moving away from each other at a constant speed?
Im trying to understand what Hubble's law
$$v = H_0 d$$
means. The thing is I keep getting two different explanations.
Galaxies are moving at a constant speed, the ones further away are so because ...
CommunityBot
- 1