All Questions
13
questions
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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
2
votes
3
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458
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Can you explain this line from "A brief history of time"?
Newton realized that, according to his theory of gravity the stars should attract each other, so it seemed they could not remain essentially motionless. Would they not all fall together at some point? ...
- 39
0
votes
1
answer
101
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Dark Matter/Energy & Space-Time [closed]
After searching for quite a while for a minimalist approach to explaining Dark Matter as well as Dark Energy, unfortunately without much good, I decided I may as well help fill the explored paths, or ...
- 11
-1
votes
2
answers
116
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Version of Olber's Paradox for gravity [closed]
Olber's Paradox is a famous problem in cosmology.
In astrophysics and physical cosmology, Olbers' paradox, named after the German astronomer Heinrich Wilhelm Olbers (1758–1840), also known as the &...
- 107
4
votes
2
answers
205
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Why Newtonian mechanics works in cosmology? [closed]
Could anyone please provide an intuitive explanation of why Newtonian mechanics can be used to describe our universe at extremely large scales?
A typical explanation goes "since speeds and energy ...
- 2,921
2
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0
answers
27
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Is there an effect analogous to the slowing down of massive particles in Newtonian cosmology?
We know that massive particles slow down by $a^{-1}$ in the Robertson-Walker metric , where $a$ is the scaling factor.
If the particle velocity is non-relativistic, can we understand this slowing ...
1
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1
answer
113
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Accounting for expansion in $N$-Body gravitational simulations
I have an $N$-Body simulation for the evolution of the universe. It uses a hybrid Tree Particle-Mesh scheme to compute the forces. The tree code used Newtons law of gravity:
$$\textbf{F}_i = -G \sum_{...
- 13
2
votes
2
answers
97
views
Validity of Newtonian gravity inside the Hubble radius
When dealing with structure formation in Cosmology, it's often said that well inside the Hubble radius we can use Newtonian gravity and therefore the starting point to obtain equations for the ...
- 1,597
1
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1
answer
238
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Modification of Gravitational force's law and related problem
I'm facing a problem which states the following:
Suppose that it is discovered that Newton's law of gravitation is incorrect and that the force $F$ on test particle of mass $m$ due to a body of ...
- 3,705
1
vote
2
answers
388
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Confusion regarding the concepts and derivation of Hydrostatic Equilibrium for a star
First and foremost I am sorry for this; in order to make the questions clear I must first upload the lecture notes from my institution $^\zeta$ for the derivation of Hydrostatic Equilibrium:
$^\...
- 2,470
1
vote
1
answer
91
views
Newtonian derivation of perturbation in density
In Barbara Ryden's Introduction to Cosmology, chapter 12.3, she derives an equation describing the evolution of mass perturbations with time, for small perturbations $|\delta|\ll 1$. Before she starts ...
- 980
0
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0
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About the use of Newtonian Relations for the movement of stars in the Galaxy [duplicate]
From a General Relativity point of view Gravity is given as the result of spacetime curvature interacting with energy-mass density. To get to the Newtonian limit one needs to take
a) Non-relativistic ...
- 1,574
12
votes
1
answer
2k
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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