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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Can a magnet or a magnetic field push gravity? [closed]

I have been asking around at my school and at the high school and at EWU but no one can answer this question: can a magnet or a magnetic field push gravity?
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4answers
175 views

Can we think of gravity as space itself moving?

So if you move through space with a constant acceleration you experience longer time dilation than when you're at rest, but you also experience the same time dilation when you're under the effect of ...
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How do we decode the image formed by a gravitational lens?

Using our own sun as a gravitational lens, we can scrutinise planetary surfaces in distant solar systems with a good deal of accuracy: ...
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5answers
409 views

Can entropy of Universe be constant?

If I understand entropy correctly, then for example two objects orbiting a centre of mass have lower entropy than when said objects eventually crash into each other and form a new one. So let's say ...
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1answer
98 views

Is the Hilbert-Felber model of repulsive gravity correct?

This theory states that at relative velocities exceeding 3^-0.5 c, gravitational repulsion ensues. The relevant papers are on arXiv by Franklin Felber. Here's one of them ...
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3answers
111 views

Speed of light originating from a star with gravitational pull close to black-hole strength?

Imagine you have a star which is on the brink of turning into a black hole. Lets say it is infinitely close to become a black hole, but not there yet. Since there is no event horizon, but a great ...
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2answers
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Gravity of very distant objects

As far as I know stars emit a finite number of photons in all directions in a given period of time and as an observer goes further away he experiences less and less photons to the point where the ...
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1answer
223 views

How stupid is this theory of gravity? [closed]

As will be evident, I am not a physicist. I've always been interested in physics but my education tapered out with general relativity and basic quantum mechanics, years ago. Several years ago a sort ...
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1answer
61 views

Speed of liquid being blocked at end of pipe

How fast would water go if at the end of of a 1 inch diameter pipe was closed by a valve? The system is as follows: 5 meter high source of water that feeds a 1 in pipe. The pipe goes straight down ...
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40 views

Fluidic gravity, TOE, what's your oppinion on this research? [closed]

It's interesting because we don't normally consider the "vaccuum of space" as a fluid, but it's becoming more apparent that it's an ocean of subatomic stuff. Here's a link to a book: Unified Fluid ...
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1answer
52 views

Two coffee beans in a cup of water + vibrations = gravity?

If you float two coffee beans in a cup of water that is being vibrated by your subwoofer (go to a sin wave generator online), the two beans will either be attracted to the sides of the cup or if ...
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1answer
52 views

Could there be massive gravitons and in our spacetime? [closed]

My question is: Could there in principle be sub-groups of gravitons (if they existed) that has mass (and in our spacetime dimensions) such as those affected by electric or by strong force or other ...
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4answers
403 views

At which point of the universe $R_{\mu \nu}=0$ if there is a source of gravitation (point mass)

Schwarschild found his solution to Einstein's field equations for vacuum ($T_{\mu \nu}=0$) by placing a point-mass in the center of origin. Since the Ricci tensor $R_{\mu \nu}$ and the Einstein ...
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3answers
632 views

What happens to gravity after matter-antimatter annihilation?

Both matter and antimatter have mass and thus gravity, but since energy from annihilation has no mass what happens to the force of gravity that was previously present? What about conservation of ...
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1answer
102 views

The source of gravitation in a spacetime without matter

In a discussion concerning: Physical meaning of non-trivial solutions of vacuum Einstein's field equations there were a number of answers claiming that the flatness of the Ricci space (Rµv=0) ...
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0answers
71 views

What if UV behaviour of gravity was perturbative?

I understand that the UV behaviour of gravity ought to be dominated by black hole production and that graviton-graviton scattering ought to blow up above the Planck scale. Suppose, however, that ...
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1answer
289 views

Can a gravitational field be diluted or shielded? [duplicate]

An electromagnetic field can be diluted in a volume by using a dielectric. The polarization of the dielectric material results in the field decreasing in magnitude. Can a gravitational field be ...
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1answer
56 views

Collected Gravitational Field

I wasn't sure what to call this, I'm not a physicist. I basically have a collection of massive bodies. I to calculate the gravitational field of all those objects collected; how to do this? The ...
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36 views

Mario Livio's book on symmetry and the relationship between gravity and acceleration

In his book: The Equation That Couldn't be Solved Mario Livio explains the equivalence principle in laymen's terms. I took the statement on page 209: The force of gravity and the force resulting from ...
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1answer
133 views

Gravity and antimatter

If we put earth like planet made up of antimatter (same mass of earth, same diameter etc..) with same distance from moon as current distance between earth and moon then center of gravity of moon and ...
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1answer
110 views

Any simple reason why spin 2 polarization tensor should be symmetric in $\mu\nu$?

Perhaps this is obvious to the not so tired one, but is there any reason why the five spin 2 polarization tensors $\epsilon_{\mu\nu}^{a}, a=1,\dots,5$ should be symmetric in $\mu\nu$? While I'm at ...
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1answer
30 views

Mass exchange between stars

I'm curious, are there specific conditions for a transfer of mass between two stars as they pass near each other? Its for my final project in computing, I'm writing a gravity simulation and thought ...
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2answers
314 views

How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)?

I'm looking to calculate parameters around launching, say, a model rocket STRAIGHT to the moon. This does not mean through orbital insertion into a stable ~17,000 MPH relative to earth's surface and ...
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0answers
36 views

Gravity propagation speed [duplicate]

Related to: The speed of gravity? In the related question and in many other questions here, it seems as if the propagation speed of the gravitational interaction is $c$. To my understanding, the only ...
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55 views

Degrees of freedom in physical equations

Say we have the field equation: \begin{equation} f^{\prime}(R)R+3\square f^{\prime}(R)-2f(R)={\kappa}^{2}T, \end{equation} why is the non-vanishing of the second term means that there is an extra ...
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2answers
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A small object on the opposite side of the earth's orbit with 0 velocity,“in line” with the core - would it collide with the earth?

If a small object (say mass 1 kg), at the opposite side of the earth's orbit (six months away), was placed in the same orbital position as the earth's core, at zero velocity in all directions, would ...
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69 views

Einstein frame vs. Matter frame

What is the difference between Einstein frame and Matter frame in General Relativity? -A brief comment on each could be useful too. These two frames were used in this manuscript ...
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1answer
212 views

Minimal vs. Non-minimal coupling

What is the difference between Minimal vs. Non-minimal coupling in General Relativity? A brief introduction to Minimal Coupling in General Relativity could be useful too.
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1answer
96 views

What's the reason behind Earth's gravity? [closed]

How can Earth attract any object irrespective of what it is made?
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1answer
103 views

Does gravity act instantaneously? [duplicate]

some one states that the earth would travel in it path for 8 min if the sun vanished. The equations of gravity show the Moon would crash into the Earth and the Earth would head for Mars the instant ...
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0answers
56 views

Topology of spacetime in 2+1 dimension

In the book Quantum Gravity in 2+1 dimension by S. Carlip, in the second chapter (section 2.1), he comments that a compact 3-manifold with a flat time orientable Lorentzian metric and a purely ...
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2answers
92 views

Force acting on center of mass

Pictured above is a biker (traveling in a curve) whose center of mass has two forces acting on it. These two forces - a horizontal centrifugal force F(centripetal)* and a vertical gravitational ...
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2answers
102 views

What happens to gravity in the middle of the earth? [duplicate]

So I was curious about, what if we make a tunnel from one side of the earth, to the other side of the earth? Gravity is ofcourse always negative, which makes you "fall" and not "float". If we take ...
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1answer
21 views

Inhomogeneties in gravitational acceleration at the surface of the Earth.

I am looking for data sets which clock the time and precise location of free falling bodies in a vacuum. I have been told that the acceleration of gravity is not absolutely 100% uniform, and I would ...
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1answer
173 views

Why would a pendulum experiment give $g > 9.8\ \mathrm{m/s^2}$?

I am taking an introductory lab course in which we've done an experiment on the physical pendulum. We've seen that for small oscillations, the period is ...
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3answers
148 views

Questions about spacetime curvature and gravity

These are some further important queries regarding the question here Why would spacetime curvature cause gravity? Q1. Explain the statement “Everything in spacetime moves at the speed of light”. Is ...
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4answers
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Why would spacetime curvature cause gravity?

It is fine to say that for an object flying past a massive object, the spacetime is curved by the massive object, and so the object flying past follows the curved path of the geodesic, so it "appears" ...
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1answer
703 views

Why quantising gravity necessarily give us gravitons?

Gravitons are supposed to be the quanta of gravitational field My question is, if we do not know how to quantize gravity yet, how do we know that quantizing it in principle should give us gravitons, ...
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entropy relation between ads$_2$ black hole and near extremal ads RN black brane

It seems that the entropy for AdS$_2$ black hole is independent of the temperature $s=s_0$. While for near extremal AdS RN black brane, $s=s_0+ s(T/\mu)$. Should not these two entropies be the same ...
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1answer
78 views

Object that causes spacetime to expand?

Is there any thing that will cause spacetime to expand, so that particles are pushed away from them rather than pulled towards it. I know things such as black holes and planets causes dips and curve ...
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1answer
147 views

General relativity, gravity and spacetime curvature [duplicate]

There is a very fundamental flaw in the common explanation given of the space-time curvature due to massive objects. It is said that a massive object curves space time just like a bowling ball on a ...
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1answer
49 views

Smaller mass in gravity well?

When sitting in a gravity well, as we do on earth, does our effective mass become smaller than our rest mass due to having negative potential energy? Correspondingly, does a free falling mass (from ...
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0answers
30 views

How to measure power used to sustain something in a (gravitational) field? [duplicate]

I've read this question and answers, but neither of the posts does seem to address my concerns. The problem is as follows: Assuming a device that keeps something in a gravitational field on a ...
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2answers
140 views

Speed of gravity in cosmological codes and ephemeris generation

There are few questions in Phys.SE concerning the speed of gravity, and the answers are traditionally that the speed of gravity equals to the speed of light. But in that case I have three more ...
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3answers
178 views

In what situations do water levels not reach equilibrium?

I have been taught that water levels will always equal out. However, now I find that sumps and some other setups allow for water not to become equal. What other arrangements allow for the water levels ...
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1answer
100 views

The nature of the gravity force: Is it attractive or repulsive between positive and negative mass? [duplicate]

If negative mass is rotating around fixed positive mass, then what will be the nature of force and how?
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1answer
164 views

Does gravity have any effect on sound waves? [duplicate]

If gravity at a place increases or decreases, does it affect the sound wave propagating through that place. If for certain place gravity increases on earth will there be change in direction or ...
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4answers
85 views

about the rotation of the earth and gravity, when all continents were merged

A long time ago, I read that the gravity force isn't the same if you are near the Andes Mountains or if you are at Paris. So today I asked to myself if when all continents were one, if the difference ...
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1answer
27 views

Shock Absorber - Bus - Not Uniform

Imagine a empty bus/lorry travelling at high speed over the "speed brake", why is that only rear seat is heaved relatively high compared to the fron seat?
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How much time would take to lift a person to 0.1m above floor of elevator? [closed]

How much time would take to lift a person to height $h$ above floor of elevator if the elevator goes down with acceleration $a$, where: $$h=0.1 \; \text{m}$$ $$ a=13 \; \text{m}/\text{s}^2 $$ How to ...