Gravity is an attractive force that affects and is effected by all mass and - in general relativity - energy, pressure and stress. Prefer newtonian-gravity or general-relativity if sensible.

learn more… | top users | synonyms

0
votes
2answers
156 views

Why does gravity affect time?

So Special Relativity states that for all non-accelerating objects of matter the laws of physics are the same. I'm confused on why this law of physic applies to objects in acceleration and gravity ...
1
vote
2answers
94 views

Why is sometimes more difficult to lift a baby?

I have a small cousin and she enjoys when I pick her up, which I can do pretty easily. Sometimes though she decides she wants to make my life difficult, and when she decides so, she tells me she is ...
0
votes
0answers
31 views

Singular isothermal density distribution

Does anyone know where the Singular isothermal density distribution $$ \rho(r)=\frac{\sigma_{V}^{2}}{2\pi\,G\,r^{2}} $$ or how it was derived. Are there any good references on how this equation was ...
2
votes
2answers
229 views

Has the speed of gravity been measured experimentally? How? [duplicate]

In Newtonian physics, changes in gravity propagate instantly. In general and special relativity, gravity propagates at the speed of light, $c$. From reading answers to questions about gravity on this ...
2
votes
1answer
199 views

What causes gravity in M-Theory?

New and updated, because people were misunderstanding what I meant! General relativity describes gravity as the result of....(very roughly) spacetime curvature Newtonian gravity describes gravity as ...
1
vote
1answer
89 views

How relativity affects projectile motion?

If, for example, I'm in a train traveling on earth at $.99c$, and I drop a ball from a $1~\text{m}$ height inside that train how long would it take to hit the ground from the ball's frame of ...
3
votes
1answer
47 views

What does gravitational mass mean if (weak) equivalence principle invalid? [closed]

As equivalence principle states Mass and weight are locally in identical ratio for all bodies. --Newton This implies that the gravitational mass does only depends on its inertial mass. Suppose ...
0
votes
2answers
88 views

Infinite Accelatation

Before I ask my question, let me just say, I know very little about particle physics and general relativity, so I may ask a obvious question or a question that makes little or no sense. Now, what ...
0
votes
2answers
553 views

2D space-time curvature [closed]

Actually, why is the space-time curvature considered 2D plane. As 2-D dimensional space-time curve is used to explain why moon revolves around the earth stating because the massive objects wraps the ...
2
votes
0answers
56 views

Generalized gravitational entropy and entanglement entropy

What are the differences (if any) between Generalized gravitational entropy (Lewkowycz-Maldacena) and holographic entanglement entropy (Ryu-Takayanagi)? More specifically, I was wondering following ...
0
votes
0answers
47 views

If a spaceship accelerates enough can it overcome spaghettification?

If a spaceship accelerates at the right amount would that counteract the spaghettification caused by falling into a black hole?
0
votes
1answer
75 views

Do black holes have a puff pastry point?

If a person falls into a certain sized black hole they accelerate very fast, which increases the g forces on them. These g forces flatten the person out into a pancake. As the person falls further ...
73
votes
6answers
15k views

Am I attracting Pluto?

My question is simple: as the title says, am I exerting a force over for example Pluto, although it is a very small force, it is there, right? Or maybe let's go further: Am I exerting a gravity force ...
1
vote
2answers
77 views

Stand on a black hole

Is there an theoretical possibility that an black hole rotates so fast that the acceleration pushing you out of the black hole is nearly equal to the gravity?
1
vote
1answer
143 views

Does acceleration of time explain gravity (rather than the other way round)? [closed]

I have a question about interpreting (explaining, even) the general theory of relativity. A common interpretation of GR, as I understand it, is to imagine two-dimensional space represented by ...
-2
votes
2answers
88 views

Save a falling person by nullifying their mass or reversing gravity [closed]

Let's say you have the superpowers to manipulate matter, mass and gravity. Imagine a person falls off a plane, flying few kilometers above the air, and they are about to get splattered onto the hard ...
0
votes
3answers
109 views

Can Gravitational force between two bodies always produce motion?

Imagine there are two bodies of mass 1 Kg each separated by some distance.Then by Newton's formula of calculating gravitational force we can see that the gravitational force between them is very ...
0
votes
1answer
137 views

What would be gravity in one spatial dimension? [duplicate]

First of all, I should say that I understand if this is put on hold for being unclear... but I'll try my best to make it as clear as it can get. For all the time I spent learning Newtonian Gravity ...
3
votes
3answers
314 views

Why Can a Skydiver Hit the Ground and Be Killed? [duplicate]

This is a follow on question from Physics SE Question "Can a Skydiver Land On a Large Slide and Survive?". User Steeven gives this answer here. User Dargscisyhp asks: What is it exactly that ...
54
votes
6answers
6k views

Can a Skydiver Land On a Large Slide and Survive?

Please forgive my lack of artistic ability, but here's my question: Consider that a skydiver, without using his parachute, were to fall exactly parallel to a giant curved slide that starts at ...
4
votes
2answers
186 views

Gravity in 2d space and inverse linear law

In our three-dimensional universe, gravity obeys the inverse square law. In a four-dimensional universe, gravity would be expected to obey the inverse cube law et cetera. In a two-dimensional ...
1
vote
0answers
57 views

Gravity dual of N free scalars in 2D

I have a very basic (and might be very naive) question. What should be the dual gravity description of $N$ (with $N>>1$) free scalars in two dimensions? I was wondering whether it would be ...
0
votes
0answers
23 views

How does space-time behaves between opposite gravitational pulls? [duplicate]

this is my first question in physics.stackexchange. I'll try to be more specific. I have a very basic understanding that time flows (is there a better word?) differently depending on the gravity ...
2
votes
0answers
24 views

Inertial frames and Sagnac interferometers

Let's posit: I am in orbit around a large body, like a planet, and I am close enough to be tidally locked to the large body. Am I in an inertial frame? Even without looking at the stars, couldn't ...
4
votes
2answers
122 views

Could you view yourself in high gravity situations?

I'm trying to understand what effects gravity can have on light. First of all, I don't understand how gravity can even affect it, since it doesn't have mass, right? That is probably a separate ...
3
votes
0answers
51 views

If it takes infinitely long for someone to fall in a black hole, wouldn't it evaporate first? [duplicate]

Let's say I decide to jump into a large black hole. A distant observer never sees me enter the black hole, but he does see the black hole evaporate. According to this reasoning, I would then keep ...
2
votes
1answer
47 views

Mass eigenstates and occupied physical volume?

I recently read about atom lasers and it made me wonder about something I recalled from my limited experience with quantum (two undergraduate and two graduate level classes). I recall that some ...
0
votes
0answers
43 views

Problems of General Relativity on small and large scales [duplicate]

As far as I know, the most important problem of GR on large scales is the cosmological constant problem which in some manner can be thought of as a dark energy problem (please correct me if I am ...
0
votes
1answer
116 views

What is the conformal mode of a metric?

I have a problem in terminology. This article talks about the conformal mode of a physical metric. I know what a conformal transformation is. But what is the conformal mode of a metric?
1
vote
1answer
54 views

Interpretation of black hole area

I'm studying properties of Kerr spacetimes and a lot of fuss is made about area of BH. It is defined to be integral of area element on event horizon $r=r_+$, $t=const.$ where $r_+$ is radial ...
1
vote
4answers
209 views

How do gravitational waves work without internal tension?

One implication of general relativity is the concept of gravitational waves or gravitational radiation, ripples in spacetime thought to travel at speeds close to the speed of light. As far as I have ...
0
votes
0answers
61 views

Can you use the force of gravity (ie. surface of Earth = 9.8m/s^2) to calculate gravitational time dilation?

I am having trouble tying the Schwarzschild radius to gravitational force as I believe it is not fixed when considering different masses. I am getting results that show a different time dilation for ...
0
votes
0answers
24 views

Gravitational boson violating relativity [duplicate]

Currently doing a introductory degree level physics course, they were talking about how changes in gravity/gravitational field cause changes so quickly that if you assigned it the "graviton" said ...
0
votes
1answer
72 views

Is it possible to directly test whether of not the vacuum gravitates?

According to GR, all sources of stress-energy (e.g. everything on the $T_{\mu\nu}$ side of the EFE) should gravitate (e.g. affect the curvature/$G_{\mu\nu}$ side of the EFE). We observe the expansion ...
1
vote
1answer
33 views

Planetary Gravity and its effects [duplicate]

I live in Tunisia, exactly in Gafsa .. and there's a weird effect is happening, i really tried to ask people but no one had a clue, also i have seen that in other places on the internet. If you put a ...
-2
votes
1answer
69 views

Quantum Gravity [closed]

By the Pauli exclusion principle fermions cannot occupy the same space, cannot have identical quantum numbers. The bosons however can. We also know that the universe, and in particular the various ...
0
votes
1answer
138 views

Asymmetry of relativistically treated EM force between atoms

There are two neutral atoms set separated at a long distance $R$ and let's consider them phenomenologically through Bohr model. Let's also assume that the nuclei (charged $+q$) of the atoms are fixed ...
1
vote
2answers
45 views

How can contact binaries persist?

This answer discusses contact binaries, which I did not even know existed. I can understand how they could exist for a short time (maybe) as gravitational waves carry off energy that causes the stars' ...
2
votes
3answers
92 views

Einstein's principle of equivalence; Standing on earth vs sitting in accelerated car

When I am seated in a car that is accelerating in a particular direction I could, for example, throw a ball and it would appear to be flying the opposite way. With the windows covered etc. An ...
-1
votes
4answers
113 views

What exactly produces gravitational force? It just can't emerge out of no where depending on mass, distance etc

I tried getting the answer from the internet but it says that it is still a mystery.
1
vote
0answers
79 views

Any textbook about non-renormalizability of gravity?

I have learned general relativity in a graduate-level. My knowledge about QFT is very rudimentary. But, I need to learn about non-renormalizability of gravity. I have these questions. Is there any ...
0
votes
0answers
79 views

Vibrating water container problem

I am struggling with visualising and understanding the phrasing of this question - cross posted from Math stack exchange since this forum is more appropriate: "A water-filled container is ...
5
votes
1answer
185 views

Crying in microgravity

So I looked around the net and found that you really cant "cry" as we do on earth in space floating around, because the tears would just stay near your eyes, because the pull of gravity is not strong ...
3
votes
4answers
254 views

Is a black hole's mass uniformly distributed?

If you were to fly around a black hole, would the gravitational pull be uniform and centered on the singularity, regardless of your relative location? If yes, how can this be consistent with models ...
0
votes
1answer
104 views

What force causes massive objects to bend space? [duplicate]

The visualization of gravity as shown by this video is pretty good at explaining how massive objects bend space, and such bending causes objects around it to fall towards it (a.k.a: gravity). ...
3
votes
2answers
147 views

Square root of a matrix appears in massive gravity. How to solve $\sqrt{A+B}$ perturbatively

$A=\text{diag}\{\lambda_1,...,\lambda_n\}$, where $\lambda_i$ can be any number and not necessarily a small number, $\lambda_i>0$, $B$ is a positive definite symmetric matrix, and ...
0
votes
0answers
29 views

Scalar gravity coupled to matter

I am reading Ortin's Gravity and Strings and trying to understand the generalisation of Newtonian Gravity to a relativistic field theory. On page 47 (link above) he motivates the study of the Poisson ...
4
votes
4answers
259 views

How can I add dark matter to my $N$-body simulation?

I've written a simple non-scientific N-body simulation for fun: http://magwo.github.io/fullofstars/ I expected to create something looking like spinning galaxies (there are two invisible very heavy ...
0
votes
0answers
37 views

Calculating initial velocity to achieve orbital motion using verlet integration

I'm attempting to build a simple computer programme which models bodies orbiting other bodies. I've implemented a Verlet integrator (https://en.wikipedia.org/wiki/Verlet_integration) and I can ...
32
votes
8answers
10k views

Why does a free-falling body experience no force despite accelerating?

Note: For the purposes of my question, when I refer to free fall assume it takes place in a vacuum. From my (admittedly weak) understanding of the equivalence principle, falling in a gravitational ...