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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$f^{\prime}(R)=0$ in $f(R)$ gravity

Suppose in a certain $f(R)$ gravity theory, $f^{\prime}(R)=0$ for some finite value of $R$. (e.g. let $f(R)=R+\alpha R^2$ with $\alpha<0$. $f^{\prime}(R)=0$ at $R=-\frac{1}{2\alpha}$.) Also ...
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3answers
68 views

Space time curvature and gravity [duplicate]

Is Space time curvature responsible for gravity or Gravity responsible for the curvature in space-time.
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1answer
60 views

Distorting the space-time fabric

If point masses could be generated in a controlled manner distorting the fabric of space-time objects could be made to move in any direction relative to each other and not simply attract as is ...
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38 views

Gravity Theory Question [closed]

Three Questions: Is the Modern Five Dimension Theory of gravity an adaptation of Einstein's relativity theory? If so, can it allow us to accurately predict the movement, speed and direction of ...
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0answers
18 views

Why is graviton not found yet? [duplicate]

Why is graviton not found yet? Newton said gravity pulls us, Einstein said space is bent and it pushes us, hawking predicts the existence of graviton and 'hawking radiation'. How far are we from ...
3
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2answers
86 views

Gravothermal catastrophe: looking for simple explanation

I am beginning to try to understand the gravothermal catastrophe. I was hoping someone could provide an explanation to help me understand what the gravothermal catastrophe is and why it is important, ...
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2answers
85 views

Assuming there is no wind, do two raindrops of different sizes fall at the same speed?

Assuming there is no wind, do two raindrops of different sizes fall at the same speed? Simple enough question. Look forward to your answers.
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If matter and antimatter repel, how do we know other galaxies aren't made of antimatter? [duplicate]

Wikipedia's article on antimatter says this: There is considerable speculation as to why the observable universe is composed almost entirely of ordinary matter, as opposed to a more even mixture ...
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1answer
24 views

C60 Macro Ojects

What would happen if you could make a ball or hollowed geometric shaped say the size of a basketball made out of C60.. due to its superconductivity could it have exotic or anti- effects on gravity and ...
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45 views

Why does astronauts hair stick up, and not in other directions?

I understand that in microgravity it doesn't have to fall down, but why does it stick up, instead of each hair-strand going in a random direction?
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3answers
85 views

Why doesn't a swing make a full revolution on a swingset in a park? [closed]

I'm familiar with the concept of swinging of a swing in a park, but I'm confused why it doesn't it swing at a complete circle around the center bar?
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1answer
120 views

Why does the 'sticky bead argument' for (gravitational waves carrying energy) work?

Throughout much of the 20th century there was debate about whether Gravitational Waves were real, and whether or not they carrier energy and could be detected. It is often presented that Feynman's '...
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2answers
98 views

How Far Does Gravity Extend? [duplicate]

How far does gravity's influence extend? I've recently (re-)seen 'The Universe' season 1 where it's said that 'take these two dice, place them perfectly still in empty space 1 inch apart and within ...
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39 views

What´s the physical foundation of the assumption that the curvature of spacetime can be quantised? [duplicate]

At the moment different paths (by percentual very few people in the world) are taken to arrive (that is, if an arrival exists) at a theory that can quantise the curvature of spacetime. Considering the ...
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17 views

What might be the nature of gravitational force produced by the antimatters? [duplicate]

The proton and the electron is replaced by the anti-proton and the positron respectively from the conventional hydrogen atom in anti-hydrogen atom.
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1answer
106 views

Proportionality Constant in Einstein Field Equations

The Einstein Field Equations: $$G_{ab}~=~8\pi T_{ab}.$$ I am familiar with how to obtain the $8\pi$ proportionality factor through correspondence with Newtonian gravity, but am wondering if this ...
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45 views

Gravity's effects on time

So, in the movie Interstellar they say that one year by the black hole is about 35 years back on Earth (excuse any lack of accuracy in the numbers, I haven't seen the movie in over a year). Now, the ...
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56 views

Gravity modeled by warping of spacetime or by field field theory?

I've recently read "Fields of Color" by Rodney Brooks who states that there are currently two ways of understanding the phenomenon of gravity. One involves a warping of 4D spacetime a la Einstein, ...
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26 views

can superconductors and other meisner materials be used as magnetic shielding in space to protect diamagnetic artificial gravity of 45 teslas?

I have seen people referring to Geim's floating frog that a human in 45 Tesla's would be held to the ground from diamagnetism above them. A very real but crude artificial gravity using powerful ...
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1answer
27 views

How would be effect gravitational field of an accelerated object?

We have a mass in space and it is accelerating until 0.7C (which gives it nearly 50% mass equivalence in momentum.) I'd like to hope to understand the changes in gravitational fields after ...
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36 views

Does energy produce a gravitational force [duplicate]

$E=mc^2$. From this, I would assume that any form of energy (not just rest-mass energy, but kinetic energy as well) would produce a gravitational force. Am I being too naive in my application of ...
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1answer
62 views

Why Do planets Rotate while Sun As a massive Body Don't [closed]

We all are Very much familiar with the rotation Of Planets about their Own Axis But Someday i thought That if Planets Like Earth , Mars , Jupiter ets.. Rotate why not Sun Rotate around its Own Axis ??
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34 views

How would a BEC respond to the gravitional force of a small mass so sensitively?

Recently I watched a BBC programme on anti-gravity, most of which was wishful thinking by NASA and BAe Systems 20 years ago. At the end of the program through, they did show what appeared to be a ...
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2answers
96 views

Difference between gravity and standing on a platform accelerating upwards at 9.81 m/s^2

So, according to Einstein's theory of general relativity, gravity is not a force instead it is a consequence of objects with mass deforming spacetime, right? And so, according to him, there is no ...
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24 views

Action and equation of motion for codim-2 “cosmic” brane in Einstein gravity, in 3d

Consider the following action, $$ S = S_{EH} + S_{B} = -\frac{1}{8\pi G_N}\int d^3 X \sqrt{G}R + T \int dy \sqrt{g} , $$ where, $G_{\mu \nu}$ is the bulk metric, and $g$ is the induced metric on the ...
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What would the effects of the GW150914 gravity wave burst be on observers much closer that 1.3B LY? [duplicate]

The effects of the GW150914 gravity wave burst were barely observable with state of the art instruments, i.e. LIGO. What would the effects of GW150914 gravity wave burst be on observers much closer ...
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43 views

How Can LIGO or Any Such Gravitational Wave Detector Detect Displacement Which Are Billionth of Times Smaller Than Mirror Tolerances

I am very excited about GW150914, the maiden direct detection of gravitational waves. Since i am naive about experimental nitty-gritties, allow me to pose a naive question: After all the interference ...
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2answers
101 views

Are gravitational force and gravitational time dilation proportional?

Particles in gravitational fields are subject to gravitational time dilation. The closer a particle is near a gravitational source, the slower is running its clock. I would like to know more about the ...
14
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1answer
248 views

What happened to the black hole firewall theory?

What happened to the black hole firewall theory? Back in 2012, some physicists apparently came up with strong evidence that one of three things must be wrong for black holes to work the way we thought ...
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2answers
98 views

Gravity and spacetime bending [duplicate]

Something that puzzles me if gravity is just bending of space time near a mass then what is gravitational force? If say two massive bodies were perfectly at rest relative to each other they would ...
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1answer
55 views

Could particle wave duality be caused by gravity? [closed]

We know that light (and other particles) displays particle wave duality, or the ability to be a particle and a wave at the same time. After that it becomes confusing. We also know that gravity is a ...
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29 views

Can Earth be converted into a black hole? If so, how? [duplicate]

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—including particles and electromagnetic radiation such as light—can escape from inside it. The theory of ...
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109 views

Do gravitational waves travelling through a medium produce sound?

Say Alice decided to orbit dangerously close to a couple of black holes circling each other. She is in a heavily enclosed astronaut suit, as is Bob, who is floating much further away. Assuming Alice ...
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52 views

The energy of dual boundary field in AdS/CFT

In AdS/CFT, when the spacetime is a planar AdS black hole with dimension ($d+1$), the corresponding energy of boundary field theory is proportional to the black hole mass parameter. For example when $...
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1answer
79 views

If we could perfectly control gravitational waves, could we play music with them? [closed]

Sound is just a kinetic wave propagating through a medium, right? In that case, if we had the ability to make gravitational waves exactly as we want them, could we play music to an observer some ...
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51 views

Do black holes really exist, theoretically?

Do black holes really exist? Casting aside all the experimental proof, how do we arrive at the idea of a black hole theoretically using any metric (say Robertson-Walker) other than the Schwarzchild ...
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19 views

Is the fabric of space time a real thing? [duplicate]

With ny limited intelligence I think Einstein said that the gravity is caused by a curvature in spacetime.But unless there is an actual feelable fabric(or someting similar) how is a curvature caused ...
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72 views

What is the explicit form of $\tau^{\alpha\beta}$ in the linearized Einstein field equations $\Box h^{\alpha\beta}=-16\pi\tau^{\alpha\beta}$?

If we let $h^{\alpha\beta}=\eta^{\alpha\beta}-g^{\alpha\beta}\sqrt{|det(g)|}$ then, according to wikipedia, the Einstein Field Equations become $$\Box h^{\alpha\beta}=-16\pi\tau^{\alpha\beta},$$ where ...
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18 views

Gibbons-Hawking-York boundary term expanded at second order in the fluctuation

Does anyone know a general form for the Gibbons-Hawking-York boundary term expanded at quadratic order in the fluctuation of the metric? Assume to define the fluctuation of the metric $g_{\mu \nu}$ ...
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1answer
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Minimum gravity required to suck light? [closed]

I was studying about gravitational forces of black holes when I came to a thought of what is the minimum gravity required to capture light in vacuum?BY capturing I mean the inability of light to ...
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1answer
124 views

Final Velocity of an object on Parabolic Curve

I decided to participate in a school challenge involving launching a marble off a curved ramp from a given height and determining the distance the marble will travel. I can no longer participate, ...
3
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1answer
75 views

Entropy and gravity

Entropy, at an intuitive level, is often described as a general level of disorder within a system. For example, I have a gas in a container divided in two areas by a divider, the gas all on one side. ...
3
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2answers
156 views

Is curvature space-time has impact on the object geometry

When we have e.g. metallic cube of dimensions 1x1x1m and we put it on the space without gravitational force the cube has equal 1x1x1m and we can use Euclidean geometry. But when this cube move on ...
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1answer
74 views

S-duality of Einstein-Maxwell-Dilaton theory

Consider theory with action $$S = \int d^D x \sqrt{-g} (R - \frac{1}{2} \partial_\mu \phi \partial^\mu \phi - \frac{1}{2k!} e^{a \phi} F^2 _{[k]} ) $$ where $\phi$ is dilaton and $F_{[k]}$ is ...
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29 views

Why doesn't electricity and magnetism distort space as well? [duplicate]

I think Kaluza/Klein was partly worked on to find additional dimensions to account for electric and magnetic fields. I am confused why the gravity field gets the privileged spot of distorting space-...
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2answers
246 views

What would have been the story of the Universe if there was no mechanism to produce massive fundamental baryonic particles? [duplicate]

Thanks for those of you who took their time answering my problem but it seems that there is a misunderstanding between us. Most answers are based on the assumption of Electroweak symmetry breaking ...
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Charged gravity: what magnitudes, if any, would be consistent with observations so far? [duplicate]

(Disclaimer: the following might fit better on Worldbuilding - on the one hand, I'm not looking to write a story, but on the other, I don't know enough physics to know whether this is a trivial "no, ...
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29 views

How does gravity really work [duplicate]

Am only 12 years old and I'm constantly wondering and trying understand how gravity really works. On YouTube everyone always talks about objects wrapping space time around themselves and uses the ...
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64 views

What is the metric at the center of a star? [duplicate]

If there is only one star in the universe then is the metric at the center of the star flat?
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1answer
257 views

Projectile time of ascent not equal to the time of descent?

Why is the time of ascent less than the time of descent in a projectile motion. I understand that while going up the air resistance and gravity act downwards and while coming down gravity is ...