All Questions
480
questions
1
vote
1
answer
96
views
When a curve is future (past) inextendible?
Future (past) endpoint: We say that $p\in M$ is a future (past) endpoint of a curve $\lambda$ if for every neighborhood $O$ of $p$ there exists a $t_0$ such that
$\lambda(t)\in O$ for all $t>t_0$ (...
- 27
2
votes
1
answer
69
views
Question on the spacetime outside Earth
The general metric for a slowly rotating body is $[1]$:
$$ds^{2} = -B(r)dt^{2}+A(r)dr^{2}+r^{2}[d\theta^{2}+sin^{2}\theta(d\phi-\Omega(r,\theta)dt)^{2}]\tag{1}$$
My question is:
Considering $\Omega = \...
- 3,085
0
votes
1
answer
132
views
Junction Conditions: In what cases is matching the extrinsic curvature at a boundary tantamount to matching metric derivatives at the boundary?
My understanding of the Israel junction conditions are as they are laid out in Poisson's "A Relativist's Toolkit", namely that if one wishes to join 2 different spacetimes across some ...
- 19
-3
votes
1
answer
99
views
Would time dilation increase the distance between objects? [closed]
Two objects are moving towards a gravity well. They are at $x$ distance from each other and moving at a fixed speed. The gravity well is massive enough for the objects to experience significant time ...
- 141
0
votes
1
answer
80
views
How to sync up different timelines and real events in general relativity? [closed]
Imagine this scenario:
Mike lives on a massive planet, so massive he experiences time going slowly.
Le petit prince lives on a small planet ( not much time dilation )
After millions of years (making ...
- 111
-2
votes
2
answers
75
views
Is it true that time dilation in a universe with no gravity could not be calculated without knowing how much mass is present in the universe?
Looking for a quick clarification on something. I am a layman and I have been trying to find out how much time dilation would exist if there was no gravity anywhere, and ignoring what seem to be ...
2
votes
0
answers
79
views
What is Dirac talking about here? [duplicate]
https://www.youtube.com/watch?v=xJzrU38pGWc&ab_channel=mehranshargh
"I might say that my recent work has been very much concerned with Einstein's general relativity and I believe that the ...
- 195
7
votes
5
answers
2k
views
Why do we say gravity curves space but the other forces don't?
I'm generally aware that there have been attempts to describe things like magnetism and the other forces geometrically, like with gravity, and that QFTs have essentially supplanted them. But it's also ...
- 450
0
votes
0
answers
81
views
Why fully does the curvature of Spacetime cause gravity? [duplicate]
I´m already quite familiar with concepts of spacetime curvature and have heard of the metaphor of two men walking north on the Earth appearing to gravitate towards one another as they approach the ...
- 55
5
votes
1
answer
547
views
Lagrange Points in General Relativity
In the Newtonian formulation of celestial mechanics it makes sense that a Lagrange point is a point where two gravitational forces of two bodies (and the centrifugal force of the rotating reference ...
- 648
-3
votes
5
answers
213
views
Can some regions of space (independent of size), be completely devoid of matter?
Before answering the question, keep in mind that I am a second year Biology student, with no experience in studying Physics and a very basic understanding of Mathematics. However, I have some ...
- 69
0
votes
2
answers
429
views
Why is gravity not a force? [duplicate]
Gravitation is the mutual attraction of masses, yet Einstein showed it is how spacetime is curved by mass and how mass moves in relation to this curvature. Why then do we still consider gravitation a &...
- 510
3
votes
2
answers
368
views
Confusion about near-identical terms: gravity, gravitation, gravitational force - are they all the same?
As my other questions also point out, I study this for fun. I am in no university yet.
as the title (hopefully summarizes), my question is this:
is these words(or terms,) the same?
gravity
...
- 398
0
votes
1
answer
112
views
Understanding consequences of spacetime relativity
If I understood right, time flows slower where there is more gravitational force (or to be more precise, as it was pointed out to me, where gravitational potential is lower), compared to where there ...
- 141
1
vote
0
answers
50
views
Which curve has the maximum proper length? [closed]
Below is a spacetime diagram in the rest frame of a lab on Earth (with a gravitational field). Which of the worldlines shown below has the greatest proper time?
My attempt: B, because $d\tau=\sqrt{1-...
- 131