All Questions
10
questions
4
votes
2
answers
205
views
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
votes
1
answer
143
views
Rigorous derivation of non-relativistic limit in cosmology?
The standard way to derive the non-relativistic limit and its corrections in general relativity is to formally expand Einstein equation in powers of $1/c$ around a background space-time. The non-...
- 21
2
votes
2
answers
466
views
Why isn't general relativity equivalent to Newtonian gravity?
I know this question may seem a bit laughable, but the way the equations for general relativity are formed is through Poisons equation:
$$\nabla^2\phi=4 \pi G \rho$$
Which are formed using Newton's ...
- 775
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
vote
1
answer
238
views
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
0
answers
62
views
How do we measure the masses of far away galaxies?
One piece of evidence that is supposed to show that dark matter exists is the rotation curve diagram. Apparently Fritz Zwicky used the Viral Theorem to make a prediction which does not fit with the ...
- 839
1
vote
1
answer
66
views
Use of general Relativity to analyse cosmological perturbations in a non-expanding background
The theory of cosmological perturbations can be developed in the context of the Newtonian gravitational theory in a non-expanding background. This is all well and good.
However, density fluctuations ...
- 3,203
0
votes
0
answers
24
views
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
4
votes
1
answer
296
views
Why is Newtonian cosmology correct for curved space?
The Newtonian model of an expanding Universe gives Friedmann's equation exactly for non-zero spatial curvature $k$ (see http://hyperphysics.phy-astr.gsu.edu/hbase/astro/expuni.html). Instead of using ...
- 5,925
1
vote
1
answer
111
views
Newtonian approximation in cosmology
In Peeble's "Large scale structure of the Universe"
the Newtonian approximation in cosmology is examined by looking at a transformation that makes the metric locally Minkowski. On pg 38 it is stated ...
- 2,094