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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What is the effect of gravitational waves on time? [duplicate]

I always struggle with the time concept when it comes to general relativity. In the recent discovery the gravitational waves have been detected by the "displacement" of the mirrors and the difference ...
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1answer
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How much force is required to produce a noticeable gravitational wave?

By noticeable, I do not mean noticeable from half way across the galaxy to our observatories, but noticeable as in, if there were an object with enough mass and energy within say, the distance of our ...
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Will the photon wavelength fluctuate in the presence of a gravitational wave?

The microwave background is due to the expansion of the Universe where the wavelengths of radiations are stretched by spacetime. As in the LIGO experiment, in the presence of gravitational wave, ...
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1answer
57 views

Why are Gravitational Waves so small?

I'm sure you've all seen the diagrams and/or 3D visualizations of gravity; the ball sitting on a piece of fabric which makes it sink down. They've also started using it in the videos that explain ...
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1answer
68 views

Does the existence (now proved) of gravitational waves imply the existence of Gravitons?

I studied the theoretical part about the Gravitational waves in General Relativity (linearization of gravity and small perturbations of the metric and so on). But I was wondering about: since ...
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In what shape do gravitational waves radiate?

The recent detection of gravitational waves made me wonder how the amplitude of the waves fell off with distance. My first naive thought was that it was probably by the cube of the distance. ...
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Still unknown stuff about gravity/spacetime?

I'm doing a research on gravity, but i often get stuck because i just forget what do i want to know about it in the first place. So, my question is: What do we not know about gravity and what about ...
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The existence of gravity waves has just been demonstrated by direct observation, 2016 [duplicate]

How does the apparent confirmation of gravity waves effect String Theory today
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What is the proof of gravity being curvature of spacetime?

According to general relativity gravity is an illusion caused by curvature of space-time, rather than real force. As I understand there is overwhelming experimental evidence to support general ...
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How did LIGO detect the source location of the black holes mentioned to be the cause of today's announcement?

Today LIGO announced discovery of Gravitational waves. What method was used to determine the source location of the waves?
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31 views

Does gravitational time dilation have a direction?

I understand that higher the gravitational potential, "slower" time runs. So a clock on international space station will run "faster" than a clock at sea level. However does it matter where the ...
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4answers
68 views

Graviton and photon

I understand that photon is the carrier of a change in the EM field. Is the graviton a carrier of the gravitational field itself or a carrier of a change in the gravitational field?
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2answers
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How strong were the gravitational waves that LIGO detected at the source?

Congrats to the LIGO team on the announcement of their discovery of gravity waves! The articles I've read say that the distortion we see here is much smaller than a proton. What about at the source? ...
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How were gravitational waves discovered?

It was announced today that gravitational waves were discovered. The article gives the following explanation of the experiment: When a gravitational wave passes LIGO, the tunnels deform ...
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5answers
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People went down two different length slides end up at the bottom at the same time

Discussion I am having: If there are two slides that are at the same height. One slide is 100m long and the other slide is 200m long. The endpoint and start point are the same displacement. In a ...
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1answer
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Meaning of $R=0$, $R_{ab}=0$. $R_{abcd}=0$.

First let me state some definition The Einstein tensor is given by \begin{align} G_{\mu\nu} = R_{\mu\nu} - \frac{1}{2} g_{\mu\nu} R \end{align} and note that \begin{align} G^{\mu}_{\phantom{\mu} ...
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Why do you believe in [on hold]

Is it possible that gravity doesn't exist?
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1answer
43 views

Integrating the geodesic equation to obtain Newtonian energy of test particle

I am studying General Relativity, and have come across a question that I am finding rather intractable: In Newtonian Theory, the energy equation for a test particle in orbit around a point mass ...
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2answers
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Does gravity have two directions?

Imagine a particle that interacts strongly with gravity, but not with any of the other forces, and does not interact with normal matter (this may be analogous to the description of dark matter, I'm ...
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6answers
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If gravity is additive, then how does it cancel itself out?

I understand that gravity, as far as we know, is always attractive. Also, it has additive qualities - i.e. the size and strength of the field are proportional to the quantities of mass. This seems to ...
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identity : $ \epsilon_{abcd} R^{cd}_{\phantom{cd}mn} = \epsilon_{mncd} R^{cd}_{\phantom{cd}ab}$ in vacuum

starting from \begin{align} \epsilon_{\rho\lambda\xi \kappa} R^{\xi \kappa}_{\phantom{ab} \sigma\tau} + \epsilon_{\rho\sigma \xi \kappa} R^{\xi \kappa}_{\phantom{ab} \tau \lambda} + \epsilon_{\rho ...
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In the process of Bel-robisons tensor: identity for $R_{amnk} R_{b}^{\phantom{b}mnk} = \frac{1}{4} g_{ab} R_{dmnk} R^{dmnk}$

Recently, i an starting to study some subject related with Bel-Robinson tensor. In the process of computing its some basic properties i noticed i need to prove following identity which holds on ...
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2answers
49 views

gravitational force and irreversibility

If we place a ball at a certain height it falls and the process is irreversible. Is there any entropy change associated with the falling of ball? If so why?
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39 views

Calculating Gravity: Small scale vs Large scale

In some calculations I've ran, I've noticed that when the gravitational forces between individual particles are calculated and when the gravitational force between bodies are calculated there tend to ...
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2answers
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Why do stellar boundaries exist?

What theorems or insights are available to decide wether a star with some given interdependence between its density, pressure and temperature distributions ought to have a boundary at a finite ...
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0answers
20 views

Liquid jet in the absence of gravity [on hold]

On earth, we have liquid jets which are falling and accelerating under influence of gravity ( this cause their radius to decrease ) My question is about liquids in the absence of gravity. Can we make ...
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1answer
51 views

Why is it difficult for 2 black holes to merge?

Apparently as part of the merger of galaxies, sometimes the central supermassive black holes of colliding galaxies get really close, however once they come to a distance of about <1 parsec, it ...
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What would be the research advances if we discover the gravitational waves? [on hold]

As researchers of LIGO (USA) and VIRGO (France/Italy) say that they have discovered gravitational waves thanks to black hole collision today, what would be, apart of the important confirmation of ...
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2answers
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Weight of mass falling through liquid

If I place a container of fluid on a scale and drop a non-buoyant mass into the fluid, will the scale read less as long as the mass is in motion downward as compared to when the mass is at rest on ...
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Work by Gravity using Tensors [closed]

Now I'm familiar with the various methods for deriving work done by gravity, but I noticed a few things about the situation, and wanted to see if I could properly apply a tensor treatment to the ...
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Freely falling body applied some external force [closed]

A body of mass $10kg$ is thrown upwards with initial velocity = $10m/s$. Then it moves up and falls back down at the same point, after which an external force of $10N$ is applied in the upward ...
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1answer
53 views

Would the Moon be able to take water from Earth?

I know that if you add mass to the moon, it would get closer to the Earth. We all know that the moon causes the tides because it's gravity pulls the water. So, my question is: If the moon gained more ...
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34 views

Could a satelite be pulled away by gravity while the object it was orbiting keeps unaffected in its own orbit?

I'm asking this, since I try to educate my self a bit in the field of astrophysics. From my point of knowledge the by title given scenario could occur. But I haven't yet read anything that sounded ...
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1answer
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Virtual particles, gravity, and dark matter? [closed]

In Hawking's radiation, virtual particles respond to intense gravitational tidal forces with pairs being ripped apart. One crosses the event horizon and the other escapes. On the other hand, in ...
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How do stars from far away affect Earth?

I know that we obviously get light (or we wouldn't be able to see them), but are there any other ways that they affect Earth and maybe just our solar system in general?
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Gravity, Acceleration, Time Dilation and the Equivalence Principle

Three clocks are started at exactly the same time on Earth. The first and second clocks are taken into the vacuum of space. The first clock accelerates until it reaches 100,000m/s, then stays at this ...
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At what temperature can water escape from the earth?

After a period of million years the water level of the earth increased. But I'm wondering whether the amound of water is always has been the same since that time. Imagine the atmosphere is about ...
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1answer
22 views

Eddy current induce emf

Q1Suppose there is a wire having AC current so as ac current is alternating it creates back emf wether that back emf produces current ?? If yes then that current is same as eddy current or not?? ...
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Gases Expanding Vacuum

Why do gasses expand in space rather than attract forming a liquid? Do some gasses attract when they are colder?
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1answer
43 views

Precision of the Gravitational Constant [closed]

I went to a theological talk where the speaker, while answering a question on intelligent design, claimed that, if $G$ was different by one part in $10^{120}$,then the universe would either collapse ...
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33 views

Can 1km diameter ball of water preserve it's integrity before hitting the ground falling from 10km altitude?

I still argue with my friend over some big ball of water (1km in diameter) that is being instantly created 10km over the surface of the earth in perfect sphere form. I stated, that as it hit the Earth ...
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1answer
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Is the polarization of light changed by gravity?

The Gravitational_redshift shows, that the wavelength of light gets altered in a gravitational field. But what about polarization of light? I imagine that e.g. by tidal forces circular polarized light ...
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1answer
81 views

How much force would it take for you stop the Moon from crashing into the earth once it has started to fall?

In my previous question, I asked how much force it would take to destabilize the Moon's orbit enough for the moon to start falling into the Earth and collide. Assume this has already happened. Now, ...
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Centripetal force at the pole is different from the equator

why is the centripetal acceleration in the poles and equator if different? I know that it's related to Equatorial budge. But what I don't get it is that the centripetal force is zero at the poles. ...
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51 views

What happens when one uses a blender in zero gravity?

I was recently told by a friend that using a blender type apparatus in a zero gravity environment will act like a centrifuge instead mixing properly. Is this the case? Furthermore, can anyone provide ...
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1answer
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Will the energy of gravitational collision be the same?

If you put two small stationary spherical objects (say 1 meter wide weighting 1kg) 1 light year across and let them collide after some time. Will the energy of collision be the same as if you put ...
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1answer
86 views

Could there exist (and if not: why?) non-elementary particles composed of gravitons?

I read about glueballs, which should be particles made purely out of gluons. This is a quite theoretical thing but its existence has at least been theorized. Now, I don't know so much about ...
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1answer
28 views

Does matter stacks up as it approaches Black hole?

When something approaches Black hole it'll experience time dilation with respect to a frame away from the black hole. So to an observer away from the hole the object would seem to slow down until ...
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1answer
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Why is the gravitational constant.. constant? [duplicate]

Many scientists have now come to the conclusion that a big bang might not explain the 'start' of the universe and are coming up with alternatives. Could it be that gravity is dependent on the ...
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2answers
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Super massive Black Hole and photon reduction [closed]

This is a picture of 2 galaxies taken from The Hubble. The arrow shows a smaller galaxy's black hole starving of the usual stars because of the binary rotation about the bigger galaxy that is pulling ...