All Questions
Tagged with newtonian-gravity general-relativity
47
questions
34
votes
4
answers
8k
views
How can we recover the Newtonian gravitational potential from the metric of general relativity?
The Newtonian description of gravity can be formulated in terms of a potential function $\phi$ whose partial derivatives give the acceleration:
$$\frac{d^2\vec{x}}{dt^2}=\vec{g}=-\vec{\nabla}\phi(x)=\...
- 1,406
10
votes
2
answers
2k
views
Bending of light - photon's inertia instead of mass
Using classical mechanics, the formula for gravitational attraction is
$$F = G\frac{m_1m_2}{r^2}.$$
This formula does not work for photons, and we need to use Einstein's theory of gravity to ...
- 1,582
9
votes
2
answers
2k
views
Gravity in 2+1D spacetime and inverse linear law
In our 3+1D universe, gravity obeys the inverse square law. In a 4+1D universe, gravity would be expected to obey the inverse cube law et cetera.
In a 2+1D universe, one would similarly expect gravity ...
- 281
13
votes
4
answers
7k
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Can a black hole be explained by Newtonian gravity?
In the simple explanation that a black hole appears when a big star
collapses under missing internal pressure and huge gravity, I can't see
any need to invoke relativity. Is this correct?
- 1,436
10
votes
4
answers
14k
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Similarity between the Coulomb force and Newton's gravitational force
Coulomb force and gravitational force has the same governing equation. So they should be same in nature. A moving electric charge creates magnetic field, so a moving mass should create some force ...
- 1,975
20
votes
7
answers
7k
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Is Newton's Law of Gravity consistent with General Relativity?
By 'Newton's Law of Gravity', I am referring to
The magnitude of the force of gravity is proportional to the product of the mass of the two objects and inversely proportional to their distance ...
- 6,000
12
votes
1
answer
589
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Newton's law of gravitation in de Sitter space
Given two masses $M$ and $m$ (with $M\gg m$) in a de Sitter background with cosmological constant $\Lambda>0$ and positive spatial curvature ($k=+1$). What is the corresponding (semiclassical "...
user56224
8
votes
2
answers
3k
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How general relativity gets to an inverse-square law [duplicate]
I understand that a general interpretation of the $1/r^2$ interactions is that virtual particles are exchanged, and to conserve their flux through spheres of different radii, one must assume the ...
- 4,256
13
votes
1
answer
3k
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Gravitational Constant in Newtonian Gravity vs. General Relativity
From my understanding, the gravitational constant $G$ is a proportionality constant used by Newton in his law of universal gravitation (which was based around Kepler's Laws), namely in the equation $F ...
- 359
7
votes
2
answers
2k
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Is Earth's orbit around the Sun affected by the ~8 minutes light delay?
Gravitational change occurs at the speed of light. As a consequence, we experience on Earth the gravitational attraction of the Sun based on its position relative to us ~8 minutes ago. How does this ...
- 1,719
4
votes
1
answer
2k
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How does Newton's 2nd law correspond to GR in the weak field limit?
I can only perform the demonstration from the much simpler $E = mc^2$.
Take as given the Einstein field equation:
$G_{\mu\nu} = 8 \pi \, T_{\mu\nu}$
... can it be proved that Newton's formulation ...
user756
0
votes
3
answers
3k
views
What is gravity and what causes objects to act against it?
So I understand the concept of gravity, in that it's not actually a force, but more of a displacement in the spacetime grid. An object with a big enough mass will bend the spacetime, causing smaller ...
user68428
23
votes
4
answers
3k
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Is it possible that antimatter has positive inertial mass but negative gravitational mass? [duplicate]
Newtonian mechanics seems to allow for both positive and negative gravitational mass as long as the inertial mass is always positive. The situation is analogous to electrostatics but with the ...
- 2,403
13
votes
2
answers
48k
views
Newtonian gravity vs. general relativity: exactly how wrong is Newton?
Is there a simple function I can use to describe the difference between simple Newtonian dynamics and the actual observed motion? Or maybe some ratios for common examples of, say, the motion of stars ...
- 679
6
votes
1
answer
415
views
Why is general relativity in (2+1) dimensions different from cylindrical systems in (3+1) dimensional GR?
The gravitational potential $\Phi$ of an infinite rod in newtonian gravity is $\Phi \sim \ln(r)$. This is the same as the gravitational potential of a point charge in two-dimensional Newtonian gravity ...
- 9,910