All Questions
254
questions
34
votes
6
answers
5k
views
Could gravity be an emergent property of nature?
Sorry if this question is naive. It is just a curiosity that I have.
Are there theoretical or experimental reasons why gravity should not be an emergent property of nature?
Assume a standard model ...
- 13.5k
22
votes
5
answers
28k
views
Stephen Hawking says universe can create itself from nothing, but how exactly?
Stephen Hawking says in his latest book The Grand Design that,
Because there is a law such as gravity, the universe can and will create itself from nothing.
Is it not circular logic? I mean, how ...
- 329
17
votes
3
answers
4k
views
Is dark matter repulsive to dark matter? Why?
I think I saw in a video that if dark matter wasn't repulsive to dark matter, it would have formed dense massive objects or even black holes which we should have detected.
So, could dark matter be ...
- 1,077
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
14
votes
2
answers
874
views
Has Verlinde's theory made significant advance recently?
In 2010-2011, Verlinde's theory for explaining gravity as emergent from thermodynamics started to get known in the physics community.
It was (and seemingly still is) lacking evidence, and faced ...
- 4,256
12
votes
1
answer
1k
views
Is there a distance from a gravitational source where the influence of gravity and dark energy are balanced out?
While gravity is a force that attracts
objects with mass, dark energy (or, alternatively, the accelerated expansion of the universe) is not.
However, I have found numerous articles, forums, questions ...
- 2,462
12
votes
1
answer
2k
views
Gravitationally bound systems in an expanding universe
This isn't yet a complete question; rather, I'm looking for a qual-level question and answer describing a gravitationally bound system in an expanding universe. Since it's qual level, this needs a ...
- 3,888
11
votes
3
answers
2k
views
What would the wavelength of the Cosmic Background Gravitational Wave radiation be?
Considering electromagnetic CMB can only see light as old as 380,000 years after the Big Bang, whilst theoretically those being gravitational should be formed from the beginning, what would their ...
- 441
11
votes
2
answers
513
views
Why is nonzero net charge density incompatible with the cosmological principle?
In an answer to a question about the overall charge-neutrality of the universe, benrg writes,
A nonzero net charge density is incompatible with the cosmological
principle. Unlike the gravitational ...
rob♦
- 91.5k
11
votes
1
answer
582
views
Gravity with more than one metric tensor
As weird as it sounds, yes, there are gravity theories with more than one metric tensor. This is called bimetric gravity.
My question to those who have encountered bimetric gravity before:
a) ...
user106422
10
votes
2
answers
1k
views
Dark Matter vs Modified Gravity
Why do cosmologists and astrophysicists assume that the reason for the higher velocities of outer stars in galaxies is due to matter at all? The name dark matter seems misleading. Couldn't gravity ...
- 168
10
votes
4
answers
2k
views
Is the "Great Attractor" an indicator of the "Multiverse"?
I have heard a bit about the Great Attractor (the gravitational anomaly that seems to be "sweeping" our universe in one direction). Someone (and forgive me, I do not recall the specifics) has ...
- 7,704
9
votes
1
answer
608
views
Is it possible to determine whether distant galaxies are gravitationally bound
In a previous question, one issue was related to the potential energy
of cosmic structures. This raised in particular the question of
whether these structures are gravitationally bound.
If you ...
- 3,798
9
votes
5
answers
1k
views
Could the acceleration of universe expansion be caused by gravity itself?
Dark energy is suggested to be a repulsive force in the universe causing an accelerated expansion. If the amount of mass outside our observable universe is greater than inside (higher mass density), ...
- 91
9
votes
3
answers
1k
views
Why does dark matter form walls and filaments
Related: How are galaxy filaments formed? And do they have any analogues in stellar formation?
But I want to come at this from a different angle. Like the user asking that other question, I was a bit ...
- 18.5k