All Questions
16
questions
0
votes
1
answer
128
views
Do we really know the universal gravitational constant?
We've all heard $$F_g=\frac{gm_1m_2}{r^2}.$$ However, since I took physics, we've discovered "dark energy," which if I have any concept of the current thinking is caused by space being ...
4
votes
2
answers
199
views
Is Hubbles law due to Gravity?
Hubble's law states that Distance is proportional to Velocity. A ScienceDirect article states that Classical Hubble expansion is characterized by a proportional increase in the rate of expansion ...
user348071
1
vote
1
answer
47
views
Based on structure formation and the lifetime of the universe why is there an upper bound on the cosmological constant?
I understand that significantly greater values than the cosmological constant would result in difficulty for the formation of large gravitationally bound structures within the lifetime of the universe....
- 51
1
vote
0
answers
228
views
Is there a valid solution to Einstein's equations for this cosmological model?
The cosmological model below has been developed in order to explain the flatness problem.
At first it's from Newtonian considerations, then a solution of the Friedman equations is looked for
$$\left(\...
- 13.7k
7
votes
1
answer
511
views
Does zero point energy really contribute to the cosmological constant?
The zero point energy is usually supposed to contribute to the cosmological constant. And the mismatch between the small cosmological constant compared with the huge zero point energy is deemed as one ...
- 4,452
2
votes
1
answer
281
views
How does universe expand when cosmological constant is zero?
From what I learned, Einstein believed in a static universe but from his general relativity equations universe must collapse under gravity. Hence Einstein adjusted this gravity with cosmological ...
- 126
2
votes
2
answers
421
views
Can gravity slow down the expansion of the universe?
If dark energy drives a repulsive force between galaxy clusters, proportional to their distance which makes space expand, which creates space between them, and gravity between the clusters has the ...
- 281
3
votes
1
answer
796
views
What exactly is the cosmological constant? [duplicate]
I know that the cosmological constant was developed as an addition to the Einstein Field Equation as an anti-gravity force: $$R_{\mu \nu} - \frac{1}{2} R g_{\mu \nu} + \Lambda g_{\mu \nu} = \frac{8 \...
- 2,162
5
votes
2
answers
301
views
Is the cosmological constant problem real? [duplicate]
The cosmological constant problem assumes that the cosmological constant (determined experimentally) can be identified with the vacuum energy density. Theroretical arguments from quantum gravity ...
- 191
4
votes
1
answer
94
views
Cosmological constant phase transition?
I recently watched at a talk by Cumrum Vafa in which he stated that the cosmological constant allows us to define a time-scale $T_\Lambda=1/\sqrt{E_\Lambda}$. The time scale of this time is about 10¹¹ ...
- 6,611
1
vote
1
answer
426
views
Does the cosmological constant represent anti-gravity? [duplicate]
Does the cosmological constant represent anti-gravity?
According to the current Lambda-CDM cosmological model, there must be a fair amount of the dark energy in the universe responsible for the ...
- 12.7k
1
vote
1
answer
1k
views
Anti de Sitter and FLRW metrics
Perhaps this is a naive question, but I have been reading about conformal invariance and conformally related metrics and I would like to know if someone can clarify me some concepts on this.
Anti de ...
15
votes
1
answer
907
views
The cosmological constant as a Lagrange multiplier?
The cosmological constant $\Lambda$ can be introduced into the gravitational action like this :
\begin{equation}
S = \frac{1}{2 \kappa} \int_{\Omega} (R - 2 \Lambda) \sqrt{-g} \; d^4 x + \text{matter ...
- 7,592
3
votes
1
answer
243
views
Is it possible to directly test whether or not the vacuum gravitates?
According to GR, all sources of stress-energy (e.g. everything on the $T_{\mu\nu}$ side of the EFE) should gravitate (e.g. affect the curvature/$G_{\mu\nu}$ side of the EFE). We observe the expansion ...
- 1,677
2
votes
3
answers
339
views
Does general relativity entail singularities if there's a positive cosmological constant?
I've heard that Hawking and Penrose proved that general relativity entails singularities. But it says in the abstract of what seems to be the paper in which they proved it (The Singularities of ...
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