All Questions
480
questions
1
vote
0
answers
50
views
Does gravity accelerate you towards the geodesic of light between you and the mass?
If there's a planet far away, you will accelerate straight towards it due to gravity. If you place a Schwarzschild black hole right in the middle between you and the planet (the distance between the ...
- 171
8
votes
5
answers
1k
views
Do you always experience the gravitational influence of other mass as you see them in your frame?
You see a galaxy far away. That galaxy is attracting you with a certain amount of gravity. I'm wondering if the gravity influence of the galaxy on you, as measured by you, always ends up being what ...
- 171
-3
votes
3
answers
76
views
Does Matter Cause Curvature or Vice-Versa [closed]
From the way explanations about gravity-acceleration-curvature equivalence are usually phrased here or elsewhere, it would appear many or most think that matter causes space-time curvature.
I cannot ...
- 115
1
vote
0
answers
48
views
How can you use gravity while trying to model gravity? [duplicate]
So consider the usual pop-science spacetime model, a bowling ball on a trampoline. Apparently, the ball should sink into the trampoline, causing a dip in the fabric which causes nearby objects to fall ...
- 141
1
vote
1
answer
104
views
Does dark matter have mass?
When trying to understand what dark matter is, it is helpful to know that some properties of it can already be derived from various observations, such as, it only interacting via gravity and no other ...
- 413
-7
votes
1
answer
138
views
So just because gravity "merely" bends space and isn't "really" a force at a distance - isn't it still a thing at a distance? [closed]
As a preamble, just for clarity as far as I can remember (I was awfully drunk) I have a degree in physics, math and comp sci: my point is "here's a probably stupid question at the level of person ...
- 994
19
votes
6
answers
8k
views
If gravity is not a force, what makes massive objects spheroid?
For most of my life, the explanation given for why celestial bodies like stars, planets, etc. are round is due to gravitational force. Simply put, if an object has enough mass, it will, in turn, have ...
- 413
1
vote
1
answer
89
views
How does gravity act and propagate in a 2+1D universe?—Newtonian versus general relativity
In a hypothetical 2+1D universe:
if we apply the Newtonian concept of gravity, we might expect that the gravitational force between two mass points with a distance of $r$ would diminish linearly with ...
- 618
-1
votes
1
answer
83
views
Apparent paradox in general relativity wrt relative gravity, spacetime curvature and time dilation [closed]
Imagine Alice is near a massive black hole and Bob is on the Earth.
Obviously their gravitational fields are different for each other. In other words, their spacetime is flat for themselves but curved ...
- 27
2
votes
2
answers
111
views
Why does the warping of spacetime make objects move closer together?
I understand why the warping of spacetime affects moving objects, but why would it affect stationary ones if it even does? Would two completely stationary objects not move closer together because they ...
1
vote
2
answers
117
views
Curvature of space from approaching gravity sources affecting observations of expansion
Since gravity curves space, I wonder how the locally increasing density of matter and energy due to the current galactic mergers with the Milky Way affects our perception of the universe.
Basically, ...
0
votes
1
answer
59
views
Are gravitons suggested as the cause of matter curving space?
My understand is that GR says that mass curves space but it does not say why or how this occurs. Is the idea of gravitons that they are the entities that actually affect space?
- 2,238
0
votes
1
answer
85
views
How does light get affected by gravity? [duplicate]
If photons don't have mass, how come gravity can bend light? Because if photons have no weight, wouldn't they not be affected by the fabric of spacetime?
-2
votes
2
answers
115
views
What is the current most widely-accepted explanation of gravity? [closed]
What do physicists typically say gives gravity the ability to act on a pair of objects?
I am not asking for a description of gravity as a scalar field, but rather what the current accepted theory is ...
0
votes
1
answer
85
views
How time creates gravity? According to time curve [duplicate]
How time dilation creates gravity? I'm assuming gravity is not a force(Einstein's words)
0
votes
0
answers
73
views
Are there any ways to conceptualize the relationship between gravity and space-time other than curvatures?
This might sound like a random question, but it came to me while I was trying to conceptualize the size of the universe and started thinking of entire galaxies resembling grands of sand floating ...
0
votes
2
answers
77
views
Gravitational field of the star changes the paths of light rays, how is this observed during eclipse?
The gravitational field of the star changes the paths of light rays in space-time from what they would have been had the star not been present. I understand that the light cones are bend slightly ...
- 103
1
vote
1
answer
97
views
Limit of gravity
Is there any limit to the bending of spacetime due to gravity?
I have been reading about wormholes and how they bend spacetime and connect two systems. But if there is no limit to gravity, we can ...
-2
votes
2
answers
71
views
Shouldn't there be a gravitational field without any mass in our 3d space? [closed]
Imagine there is a Neutron star Displaced a small distance from our accessible 3d slice in the direction transverse to that 3d slice. It will bend the space around it. It will also bend the space of ...
2
votes
7
answers
1k
views
I can't wrap my head around the idea of matter interacting with spacetime. How is the interaction taking place? [closed]
I have tried Googling this for a long time. I have read many forums on this. But still, it doesn't make sense.
General relativity says that space-time is bent/changes when a massive object is there. ...
0
votes
0
answers
49
views
How the equivalence principle leads to the idea of curved spacetime? [duplicate]
In wikipedia https://en.wikipedia.org/wiki/Equivalence_principle, there are three forms of equivalence principle ( equivalence of gravitational and inertial mass ) :
Weak version (Galilean) :
The ...
- 323
5
votes
2
answers
312
views
The limit of GR with infinite speed of light $c$
Just answer what you can. I don't mean the zero curvature flat space time version. I know that the Einstein Field equations use $c$ as a constant, but what would the universe be like if gravity was ...
- 83
1
vote
1
answer
67
views
Is pp-wave spacetime strongly causal?
Is pp-wave spacetime, strongly casual?
If not, where is it on the causal ladder?
- 1,268
0
votes
0
answers
53
views
Question on gravity and spacetime curvature [duplicate]
In General Theory of Relativity, it is explained that the fabric of reality i.e. spacetime bends around objects with mass, and that curvature causes other objects to come close to/ fall towards the ...
1
vote
1
answer
44
views
A question on the causal hierarchy/ladder and the existence of CTC
What does the existence of CTC imply for the Causal Structure of the spacetime?
Can a strongly causal spacetime have any CTC[without fluctuating the metric]?
Is there any such example?
Can someone ...
- 1,268
2
votes
1
answer
101
views
About the nature of gravity
Let's consider a corner of spacetime far enough of any other mass so that the spacetime would be nearly flat in this neighborhood, a kind of mass desert.
Let's consider a mass in the center of this ...
- 723
4
votes
6
answers
1k
views
How does general relativity theory explain gravitational pull? [duplicate]
I watched some videos on YouTube that explain why gravity is not a force,
according to general relativity theory.
I can wrap my head around the idea that spacetime can be curved due to a massive mass,
...
- 141
2
votes
1
answer
143
views
Question on Tolman-Oppenheimer-Volkoff (TOV) equation for time-dependent spacetimes [closed]
Is there a way to conceive a TOV equation, and therefore the stability analysis for a metric like:
$$ ds^2 = -dt^2 + a^2(t,r)\big(dr^2 + r^2d\Omega ^2\big)~?\tag{1}$$
- 3,085
1
vote
0
answers
49
views
Initial-value problem for gravitational waves
Gravitational waves have been very much in the news recently and I would like to understand them better. I know vaguely that they cause transverse changes to the geometry of matter as they pass by. ...
- 593
2
votes
2
answers
387
views
Is there a relation between spacetime curvature and radiation?
To my understanding, the curvature of spacetime is determined by the stress-energy tensor.
I was wondering if we could calculate some of those components using radiation.
Is it possible that objects ...
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
0
votes
0
answers
45
views
When gravity is not a force but an effect of mass bending the curvature of space, why? [duplicate]
When gravity is not a force but an effect of mass bending the curvature of space, why do masses bend the curvature of the space in the first place?
The reasoning as it is demonstrated now seems ...
0
votes
1
answer
92
views
Are photons affected by "temporal gravity?"
Since objects follow geodesics in spacetime, that is the locally shortest path, it would seem to me that unless objects move, they do not trace any path at all. In other words, if I'm stationary on ...
- 47
-2
votes
3
answers
301
views
Why doesn't the curvature of spacetime around Earth cancel the Sun's curvature?
If the Sun and Earth both act on the same medium, which is spacetime, then why the Earth curvature of spacetime around itself does not isolate it from the Sun's curvature? If it does not, and the Sun ...
user348262
17
votes
2
answers
5k
views
Space falling faster than light after it falls inside the event horizon of a black hole?
Typing my question directly so people know what I am asking, afterwards providing background and context.
Q: What does it mean when space is falling, faster than light?
(I am specifically wondering ...
- 398
1
vote
0
answers
146
views
Equivalence Principle: Uniform to Non-uniform gravitational fields
2Einstein in his 1916 GR paper describes the equivalence principle and makes a case for general relativity i.e a person in a non-inertial frame is equivalent to a person in a uniform gravitational ...
- 141