Linked Questions

10 votes
4 answers
8k views

Is there a limitation on Gauss' law? [duplicate]

Recently I had a question to find the electric field at a distance $R$ from the origin, where the space is filled with charge of density $\rho$. I did this by assuming a Gaussian surface of radius $R$....
avz2611's user avatar
  • 327
18 votes
3 answers
1k views

Infinite grid of planets with Newtonian gravity

Assuming only Newtonian gravity, suppose that the universe consists of an infinite number of uniform planets, uniformly distributed in a two-dimensional grid infinite in both directions and not moving ...
Joe Kearney's user avatar
9 votes
5 answers
2k views

What makes the stars that are farther from the nucleus of the galaxy go faster than those in the middle?

It has no sense that stars that have a bigger radius and apparently less angular speed($\omega$) goes faster than the ones near the center.
moreno94's user avatar
  • 103
8 votes
3 answers
1k views

Physical origin of the inflaton field?

I have two particular questions regarding the inflationary scenario. They are: What is the physical origin of the inflaton field? Why has the potential of the inflation field its particular form?
Hamurabi's user avatar
  • 1,323
4 votes
1 answer
1k views

Fulvio Melia's linear cosmology

I would be interested in what people think of Fulvio Melia's argument for a linearly expanding Universe. I realize that the experimental evidence seems to be pointing to an accelerating Universe but ...
John Eastmond's user avatar
4 votes
3 answers
441 views

Finite or ∞ set of masses & ∃ gravity center?

Any finite & non empty set of masses has a computable center of gravity: $\vec{OG} = \frac{\sum_i m_i \vec{OM}_i}{\sum_i m_i}$ . Does the contrapositive permits to conclude that a mass system ...
dan's user avatar
  • 723
9 votes
3 answers
752 views

Did really everything begin with a state with very low entropy?

As emphasized by Penrose many years ago, cosmology can only make sense if the world started in a state of exceptionally low entropy. The low entropy starting point is the ultimate reason that the ...
Newman's user avatar
  • 2,576
6 votes
2 answers
1k views

Questions about the Jeans length

I have a couple of questions about the Jeans length. Suppose the universe has a homogeneous energy density, except there's a spherical region that is overdense. I understand that if the region is ...
Samantha's user avatar
  • 163
3 votes
2 answers
1k views

How come that an Infinite universe will collapse under gravity?

In this PSE post the issue is about the stability of an infinite universe under Newtonian gravity. Here I'will drop the Newtonian constraint because we know of the finite speed of interactions and I ...
Helder Velez's user avatar
  • 2,657
3 votes
2 answers
136 views

Galaxies Center

It is believed (to my understanding) that at the center of all large galaxies are super massive black holes. Why is it then when you see photos of galaxies that the center is extremely bright if a ...
L84's user avatar
  • 205
4 votes
1 answer
79 views

What would happen if we had a crystal structure but only gravitational interactions?

The idea is simple. Let's say we arrange similar bodies (call them planets, ions, anything) in an infinite crystal structure, but the only possible interactions are gravitational interactions. A ...
UriAceves's user avatar
  • 165
2 votes
2 answers
113 views

Question about gravity felt at various radii within a massive sphere

Imagine there's a sphere of radius $R$ which has constant density $\rho$ and you can stand anywhere inside of the sphere. Wherever you stand within the sphere, you'll only feel gravity coming from the ...
user26866's user avatar
  • 3,492