All Questions
254
questions
1
vote
1
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125
views
What if gravitation was the only force? [closed]
This is a follow up of Interactions within constituents of dark matter .
I wonder about dark matter, and, naturally, compare it with our observable world.
If gravitation would be the only force acting ...
- 1,028
3
votes
0
answers
126
views
Is Brans-Dicke theory really ruled out by solar system tests?
Brans-Dicke theory with small values of parameter $w$ are said to be ruled out by solar system general relativity tests like the Shapiro time delay test and the deflection of starlight by the sun.
But ...
- 5,925
0
votes
1
answer
112
views
Sean Carroll, can I skip to chapter 8 after chapter 4? [closed]
For anyone who has studied the book 'An Introduction to General Relativity Spacetime and Geometry' by Sean Carroll, can I study chapters 1 to 4 (which do differential geometry & field equations it ...
- 35
0
votes
0
answers
37
views
Is there a formula for gravitational time dilation at the cosmological scale?
There is a standard formula for gravitational time dilation used in eg the operation of the global positioning system. It is based on the integration of g(h) where g is a function relating ...
- 371
1
vote
2
answers
163
views
“Negative energy” definition of “gravitationally bound” in expanding cosmology
First off, I realize that there is already a number of questions relating to gravitational binding in cosmology:
Gravitationally bound systems in an expanding universe
Gravitationally bound systems ...
- 486
1
vote
0
answers
44
views
Effects of dark energy in the kinetic energy of a body?
If I launch a ball into the sky it would reach a distance after which it would return into the ground transforming the potential energy into kinetic energy as it hits the ground
This is similar to ...
- 2,462
0
votes
1
answer
134
views
Theoretically, is it feasible for the dark matter density to be constant and homogeneous, as dark energy is, and the two to be related?
I know that currently dark matter and dark energy are separate things, not related and one not deriving from the other. But if both are included in a generalized gravitation theory, the picture can ...
- 1
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
1
vote
1
answer
97
views
Dark energy contributing to, or modifying, mass estimates?
I have found some papers (like this one: https://www.aanda.org/articles/aa/full_html/2009/45/aa12762-09/aa12762-09.html) which say that dark energy increases the potential energy in a system of a ...
- 2,462
1
vote
0
answers
51
views
Zel'dovich pancake derivation
I am looking for a derivation of the Zel'dovich pancake. Does anyone have a reference to the derivation or a link to the original paper?
Y. Zel'dovich, Gravitational instability: An Approximate theory ...
-7
votes
1
answer
100
views
Contradiction of propagation speed of gravitational waves with non-locality of gravity?
Although LIGO at 2016 verified the speed of a traverse gravitational wave being the speed of light in a vacuum $c$ there is also the fact that gravity is a non-local phenomenon, meaning that it is not ...
- 4,170
1
vote
1
answer
121
views
Dark matter, MOND or flattened gravitational fields? [closed]
Could there not be a third variant to explain why e.g. long-distance multistar systems rotate faster than Newton's law of gravity suggests?
In addition to the Dark matter hypothesis and MOND then, ...
- 521
1
vote
2
answers
189
views
What is the gravitational field intensity of a uniformly distributed mass content in Newtonian gravity?
In an infinite universe composed of single point masses which can be simplified as a uniformly distributed mass density, what is the equation for the gravitational field intensity in Newtonian gravity?...
- 476
0
votes
0
answers
33
views
How does the gravitational potential change when using physical instead of comoving coordinates?
If we consider the universe as filled by a self-gravitating fluid, then there will exist an associated gravitational potential $\phi$ and the Poisson equation $\nabla^2=4\pi Ga^2\rho$ will hold, where ...
- 293
1
vote
1
answer
239
views
Poisson equation in Cosmology at first order in perturbation theory
The book Cosmology by Daniel Baumann states that the Poisson equation for a universe where we consider the effects of both gravity and expansion, expressed in physical coordinates $\vec{r}=a\vec{x}$, ...
- 293