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.

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How does one expand gravity Lagrangians about an $AdS$ background?

I had previously asked this question. This is kind of a continuation of that. I recently found this expression which seems to be called the "Fierz-Pauli action" which is apparently the quadratic ...
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1answer
78 views

Virtual Gravitons?

In QED, the field strength dependence is expressed by a field of virtual photons of varying spatial density. I know that we describe gravity as a warp in space-time, but how can one warp space (and ...
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5answers
2k views

Is the graviton hypothetical?

Wikipedia lists the graviton as a hypothetical particle. I wonder whether graviton is indeed hypothetical or does its existence directly follow from modern physics? Does observation of gravitational ...
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1answer
280 views

If the sun stopped burning, would we ever know it?

I read somewhere that since gravity moves at the speed of light, if the sun were to leave its position we would "know" about it through the absence of light and its gravitational effects on our planet ...
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1answer
74 views

How is gravitational lensing possible? [duplicate]

How is it possible that a force that affects mass (gravity) can affect massless particles like photons?
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3answers
93 views

At an instant, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges?

Question: In principle, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges? (At a single instance in time?) Additional Notes: I am ...
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1answer
471 views

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 ...
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0answers
100 views

Position vs Time Function for a Falling Object Without Assumption of Constant Acceleration

If you have an asteroid for example and a planet, isolated from all other gravitational influence and initially at rest with respect to each other, how would you find a position vs time function for ...
0
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1answer
56 views

Effects of gravity on light [duplicate]

If gravity can bend light, why can't gravity slow light. At least momentarily? Wouldn't that give the illusion of the universe expansion speeding up?
0
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1answer
83 views

Does gravity act in the centre of the Earth? [duplicate]

If we we dig a hole from north pole to the south pole of the Earth and we throw a ball in this hole where would it stop? Will it come back on the surface or it will stop at the centre?
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1answer
65 views

Irrep decomposition of direct product of stress tensors

I have stress tensors direct product of the form $T^{ab}(x)T^{cd}(y)$. I want to write this in terms of a tensor $I^{abcd}$ in the form. $T^{ab}(x)T^{cd}(y)= I^{abcd}$. This is like decomposing the ...
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3answers
912 views

Does a black hole have any kind of mass?

Currently in my academics I am studying about the Gravitation. In the chapter I came across a term called the Escape Velocity (It's the velocity of any celestial body which is required by an object to ...
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1answer
88 views

Will we feel the gravity of a star 10 light years away for the next 10 years if, somehow, it vanishes today from its position? [duplicate]

I was watching a relativity video, and although I am not sure, I felt that it was trying to tell that the effect of gravitation of a body is instantaneous, in the sense that a sudden change in the ...
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42 views

About parametrizing quadratic fluctuations in the metric about $AdS_2 \times S^2$

I am referring to the contents of page 20-23 of the paper, http://arxiv.org/abs/1108.3842.pdf Equation 4.5 seems to suggest that one wants to restrict the metric fluctuations $h$ to a subset such ...
2
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1answer
322 views

Gravity, a weak force?

Why is gravity such a weak force? It becomes strong for particles only at the Planck scale, around $10^{19}$ $\text{GeV}$, much above the electroweak scale ($100$ $\text{GeV}$, the energy scale ...
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2answers
53 views

What is is a molecular/microscopic explanation for why a balloon rises in water?

If we consider a balloon full of air submerged in water then we all know that it will rise rapidly. I am having trouble understanding this at the level of individual molecules of air and water. What ...
2
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1answer
124 views

What is intrinsic gravitational entropy?

What is intrinsic gravitational entropy? Does it have to do with dark matter or coarse graining in the universe? Is it unique to general relativity, or there are predictions from quantum mechanics as ...
4
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84 views

How to calculate gravity path integrals about an AdS background?

Suppose I have some Lagrangian of some higher derivative gravity coupled to a may be matter fields. Now I want to fluctuate it to quadratic order about an AdS background and calculate the 1-loop ...
2
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1answer
103 views

How to calculate the Wald functional?

I want to calculate the Wald functional for arbitrary higher curvature Lagrangians - like getting equation 6.31 from 6.30 in this paper. A priori the above looks like an extremely complicated ...
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2answers
144 views

Principle of locality and forces

I have a silly confusion about the statement written in the link Einstein and Locality ''external influence on A has no direct influence on B; this is known as the Principle of Local Action.'' ...
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1answer
99 views

How exactly can we describe the normal force on a static person standing on earth's surface using general theory of relativity?

For planetary motion I can understand that the planets move along the geodesics e.g. the warped space-time geometry. Imagine that the moon gets suddenly stopped by some external force and comes to ...
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3answers
190 views

What will happen after escaping earth's gravitational field?

Suppose that I escaped the gravitational field of earth. Then: am I going to be pulled by Sun's gravity?
3
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1answer
130 views

Is the concept of space-time curvature a recursive one? [duplicate]

A way some people explain (or try to explain) how gravity works is using space-time curvature: an object with high mass distorts the surrounding space-time plane like a bowling ball distorts a sheet ...
42
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5answers
16k views

How exactly does gravity work?

The electromagnetic force and strong and weak forces require particles like photons and gluons. But in case of gravity there is no such particle found. Every mass bearing object creates a ...
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2answers
261 views

Speed of gravity

Consider two objects presented in the figure below. Objects have equal masses and are separated by a distance of 60 light seconds. Assume that we move left object by 3 light seconds to the left in ...
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2answers
343 views

Does gravity actually contract space-time?

In the Big Crunch Theory it says that gravity (curvature in space-time) will stop the universe's expansion and gravity will cause the universe to contract on itself. My question is if gravity is a ...
2
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2answers
100 views

Lagrangian point or dark matter?

We know that spiral galaxies spin in a way such that we have to assume that dark matter is responsible for the extra mass required to do so. My question is, can Lagrangian points (L1 and L2) be used ...
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1answer
99 views

Gravity proofs/can it be measured? [closed]

Is it possible to measure gravity other than cause and effect. Gravity is a principle which can only be measured by cause and effect. Ie since an object falls we assume there must be something pushing ...
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0answers
75 views

How come gravity is $\mathcal{N}=8$? Why is graviton spin 2 [duplicate]

I never understood why supergravity $\mathcal N=8$, nor why the spin of a graviton is 2. I've been reading around but I still don't have a back-of-the-envolope understanding.
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4answers
209 views

Could a photon travel faster than the speed of light in vacuum?

If the cosmic speed limit is the speed of light in vacuum, then what happens when a photon traveling through space meets gravity? Wouldn't gravity pull on the photon that's already traveling at max ...
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1answer
78 views

What happens to atoms in extremely strong electromagnetic fields?

I know that strong gravitational fields on the order of neutron stars (at the crust) atoms get compressed so tightly, the empty space between them is significantly reduced and it becomes denser. ...
3
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1answer
137 views

Could the Earth be ejected when the sun burns out?

My younger brother came home from school today and told us at the dinner table that when the sun burns out the Earth could be ejected from its orbit. Skeptical, I asked his source. He quoted his ...
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2answers
32 views

Are combined masses in space, such as galaxies, considered to be uniform bodies? *In addition, a related question about force

If we were to calculate the force that one galaxy exerted onto another, would we consider the individual masses within the galaxies, or the masses of the galaxies as a whole? Do the individual stars ...
0
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1answer
106 views

Consequences of inverse square law with vast distances (Gravity); (in addition, is light speed broken)? [duplicate]

As is well known, the gravitational force between two masses is dependent on the spatial distance between them. Therefore, even at vast distances, the masses exert equal and opposite forces on one ...
4
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2answers
188 views

What is the difference between gravitation and electromagnetism?

I am currently studying electrodynamics. And when looking at Maxwell's equations, I don't see any reason, why we cannot apply them to gravity. We know that charges generate a force field that ...
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2answers
69 views

Chemical effect on gravitation?

We know, that gravitation field of charged black hole is different than one of uncharged. I this true only for objects with singularity or is true for all objects? If true, then may we say, that ...
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3answers
214 views

Energy Required to Rip Spacetime

I have heard that the presence of an extremely strong gravitational field possesses the capacity to warp or tear spacetime and to potentially create a wormhole. Is any energy lost when spacetime is ...
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2answers
550 views

What is the shape of a rope hanging from two ends

If I hang a rope from two points that are at the same height above the ground, what is the mathematical function that describes the shape of the rope between the two points? Assuming the mass of the ...
2
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4answers
358 views

Where does the idea gravity=curvature of spacetime really come from?

I have been searching for quite a while but mostly found the answer: Einstein's genius. Quite unsatisfactory. I know and understand that the idea gravity=curvature of spacetime works. Furthermore I ...
6
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3answers
481 views

Can one assign an equivalence principle of some kind to the EM field?

Introduction: Consider the EM field. There was a time when the field was defined in a similar manner to that of the gravitational field. This changed when the view on gravitation evolved to this ...
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1answer
105 views

changes in horizontal velocity and the effect on time airborne (thus overcoming gravity)

I would like to know if a object is launched horizontally in the air at a lower speed and a higher speed, why does the higher speed keep it airborne longer. what are the forces and why does gravity ...
0
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2answers
126 views

What physical conditions would allow for this kind of perpetual seesaw

I'm working with a simulator(Box2D) and need to create these conditions. I have a perpetual seesaw with two objects on either side. I'd like for the following conditions to be met. The first ...
4
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1answer
60 views

Galaxy rotation curve and dark matter

I am reading "The Essential Cosmic Perspective" by Jeffrey O. Bennett, Megan O. Donahue, Nicholas Schneider, Mark Voit. In Chapter 14, it is stated that an evidence of the presence of dark matter in ...
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1answer
38 views

maintaining atmosperic pressure on mars

how would mankind be able to maintain an earth like atmospheric pressure on mars since mars only has 1/3rd the mass? I am not, nor have i ever attended college, but am very curious.
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2answers
168 views

Is there a mistake in this example in my mechanics textbook?

This is a worked example in my mechanics book: But I think this worked example is wrong. In the 6th line. shouldn't $X=4R$ as the expression for distance above the surface is $(X-R)$ and when the ...
6
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1answer
130 views

Is $4 \pi G$ the true most fundamental gravitational constant? [closed]

Newton's law of gravitation is: $$F = G m_1 m_2 \frac{1}{r^2}$$ It looks simple and natural. But that's only in 3 dimensions. Let's look what happens in $n$ dimensions: $$n=2 : F = 2 G m_1 m_2 ...
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4answers
333 views

What was the Law of Gravity better explained by?

In mechanics, our professor made the declaration that "all laws of physics" have been disproven. He mentioned several examples including the Law of Gravity, mentioning briefly that it is better ...
2
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0answers
30 views

Magnetic fields and forces, Gravitation fields and forces

Is a current carrying wire affected by the magnetic field that it produces? In other words, will a current carrying wire be acted on by a magnetic force produces by its own magnetic fields? Is a mass ...
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3answers
513 views

Does the conversion of crude oil to greenhouse gases have any measurable effect on earth's gravitational pull?

Oil underground is much denser than greenhouse gas in the atmosphere. Does the conversion in anyway effect the gravitational force from earth.
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2answers
60 views

How did gravity affect gas clump after the big bang

In the first episode of Cosmos. It was said that after the big bang, gravity worked to pull clumps of gas together and heating them. My question is what was exerting the gravitational pull to make ...