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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Spacetime geometry around two black holes

For space-time geometry we all know images like he one below. But if I were to take a neutron star and put it right next to but not touching a black hole what effect would that have on the geometry of ...
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1answer
63 views

Could synchrotron radiation be produced by a gravitational field instead of a magnetic field?

I know that synchrotron radiation is produced when a charged particle is accelerated radially by a magnetic field, but I was wondering if synchrotron radiation could also be produced by an uncharged ...
2
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2answers
172 views

If photons have no (rest) mass, why would black holes attract light? [duplicate]

I was told that photons have no (rest) mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is ...
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1answer
63 views

Higgs boson and gravity [closed]

I was reading earlier about how Higgs boson (aka The God Particle) is responsible for giving mass certain properties. Among these properties is gravity. What I'm wondering is, by studying Higgs boson, ...
3
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2answers
84 views

Gravity and its energy

Where does gravity get its energy from? So, I'm taking a high school environmental science class and we just started a unit on energy. We were talking about different types of energy and one was ...
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3answers
1k views

Event Horizon of Supermassive Black Holes

I'm going to ask/explain this as best I can; I'm sure I have some fundamentals wrong here. Spaghettification is a phenomenon which occurs only in stellar-mass black holes owing to the immense gravity ...
3
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2answers
81 views

Is gravity a force? [duplicate]

If gravity just emerges from the curvature of spacetime, is it actually a force? Why is it one of the 4 fundamental forces of nature?
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2answers
125 views

How do we know that gravity is a fundamental force, rather than an emergent one?

How do we know that gravity is a fundamental force, rather than an emergent one? Also, what are the smallest masses and length scales for which we have measured it?
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3answers
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What would happen if you open a bottle of fizzy drink in a weightless environment?

On Earth, pouring a fizzy drink into a glass or opening a bottle, you see the gas start to condense out into bubbles which rise upwards. You can't pour a Coke into a glass on the ISS but you could (I ...
2
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1answer
82 views

Virtual Photon transmission speed of a Static Electric Field?

In the case of a non-accelerating point charge "A" of stable velocity, its static field is treated as though it is instantaneously present at a distance, i.e. a second point charge "B" will react to ...
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64 views

What is the source of water and waves on the water planet in the movie Interstellar?

We will ignore some of the more obvious issues with the movie and assume all other things are consistent to have fun with some of these questions. Simple [hopefully] Pre-questions: 1) If the water ...
2
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1answer
146 views

If space warps distort moving objects' trajectories, does it mean that static objects are immune to gravity? [closed]

If gravity is just space distortion, which affects trajectories of moving objects, then a static object (not moving, thus no trajectory) will not suffer any type of accelerating force from gravity? ...
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1answer
92 views

Can the Alcubierre Drive be explained by Gravitoelectromagnetism? [closed]

Even though there is no experimental evidence, that the Alcubierre drive works. The Einstein field equations permit this solution. For Gravitoelectromagnetism there are hints and ongoing efforts to ...
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0answers
50 views

Length contraction due to gravity [closed]

The proper length in Schwarzchild metric can be expressed as $d\sigma^2=\left(1-\frac{2GM}{r}\right)^{-1}dr^2+r^2d\theta^2-\left(1-\frac{2GM}{r}\right)dt^2$ (we set $\phi=0$) So in order to get the ...
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1answer
359 views

Does a ball resting on the ground have acceleration?

Does a ball resting on the Earth's ground have acceleration caused by gravity?
0
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1answer
51 views

Gravitation between a homogeneous ring and a mass [closed]

I got a problem with describing the gravitational attraction between a homogeneous ring and a point mass. Let $m$ be the point mass as showed in the picture, lying a $x$-distance away on the ...
1
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2answers
96 views

Can other fundamental forces bend spacetime?

I was wondering what makes gravity so special that it bends spacetime? and if it is part of the four-fundamental forces, why or why cant the other forces bend the time space continuum?
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2answers
67 views

How could gravity affect the expansion of the universe?

I've read several books which talk about gravity slowing down, halting, or reversing the expansion of the universe. The expansion is often compared to a stretching of space at every point, so that the ...
3
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1answer
249 views

The original thorium reactor?

With lunar thorium being common, and heavier than iron or nickel, does earth's core have the the occasional nuclear reaction?
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2answers
153 views

Could a really tall tube suck garbage in to space?

When I was around 10 years old, I had this idea that was supposed to solve our waste problems; I imagined having tubes miles high that would stretch in to space. Every tube would have a door at the ...
4
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2answers
230 views

Visualizing gravity in 3D

We've all seen the depiction of gravity bending space downwards, and so attracting objects into the dent it creates, cf. e.g. this and this Phys.SE posts. That's intuitive and makes a lot of sense, ...
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3answers
320 views

What is gravity and what causes objects to act against it?

So I understand the concept of gravity, in that it's not actually a force, but more of a displacement in the spacetime grid. An object with a big enough mass will bend the spacetime, causing smaller ...
6
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0answers
113 views

Monopole Gravitational waves exist?

GR says that monopole gravitational radiation does not exist. I understand the reasons for this. However there is this effect (which seems to me to have the hallmarks of a wave). Paper at arXiv: ...
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2answers
289 views

When objects fall along geodesic paths of curved space-time, why is there no force acting on them?

On cseligman.com, it is written that So, we see things falling with an acceleration which we call the acceleration of gravity,and thinking that we live in a straight line , uniformly moving or ...
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2answers
70 views

Is gravity a centripetal force?

In curved space-time, there are curved paths. Since curved paths in our experience require some centripetal force to create them, isn't then gravity a centripetal force?
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1answer
49 views

Gravitational… confinement?

This is a followup to Ergil's question "Weak isospin confinement?". According to the Wikipedia article on color confinement: The current theory is that confinement is due to the ...
4
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1answer
78 views

Work performed by a stationary object in a gravitational field “on Earth”

I was thinking about this problem: How much work is required to hold an object stationary in a gravitational field? or: How much energy is required to keep an object stationary in a ...
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1answer
82 views

Why does the motion of the planet around a star cause a centrifugal force?

Please consider the differences in Newtonian physics and general relativity. Newtonian physics In Newtonian physics it makes sense that objects placed on a planets surface facing away from the ...
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3answers
66 views

Does uniform distribution of background matter affect the dynamics of a gravitational system?

Situation 1: A test particle of mass m moves around a big mass M in a Keplerian orbit. The orbital period is easily found, given certain initial conditions. Situation 2: The same system of two bodies ...
3
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1answer
61 views

Electromagnetic radiation bending on Earth

Most articles say that a radiowave is able to propagate itself beyond the horizon because it is reflected off by the ionosphere (and the Earth itself). But do radio waves also get bent according to ...
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0answers
30 views

Antimatter traveling back in time and gravity [duplicate]

I've been reading on the construct of considering antimatter as matter traveling backward in time, which seems like an useful tool. There seems to be some discussion around this concept, if ...
2
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2answers
96 views

How would gravitons couple to the Stress-Energy tensor?

How would gravitons couple to the Stress-Energy tensor $T^{\mu\nu}$? How did physicists arrive at this result? I've read that it follows from the analysis of irreducible representations of the ...
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1answer
46 views

Does light or waves have any kind of mass? [duplicate]

Just like the previous question, Even I have been studying Hawking's A Brief History Of Time and even I was thinking of Einstein's General Relativity. But I was unable to accept his view of GRAVITY. ...
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1answer
159 views

How can magic be explained with Physics? [closed]

Assuming that, hypothetically, and for this example only, "magic" means things like magical powers. In movies, games, etc. we witness magic; however, it's never explained how it works with regards ...
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1answer
100 views

Questioning Einstein's view on gravity [duplicate]

Oke, so my mind is blown by Einsteins view on gravity, at least as far as I understand the basics and principles he based his views on. One of the first things that struck me was that most of his ...
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1answer
58 views

How do you find the tension in the real world? (Given a rope in a pulley system)

I'm well aware of the formula to calculate tension, however, given a real world situation where you have a closed pulley system. How do you measure the force (i.e., tension) required to pull on the ...
4
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3answers
133 views

Is gravitational Chern-Simons action “topological” or not?

Here are the 2+1D gravitational Chern-Simons action of the connection $\Gamma$ or spin-connection: $$ S=\int\Gamma\wedge\mathrm{d}\Gamma + \frac{2}{3}\Gamma\wedge\Gamma\wedge\Gamma \tag{a} $$ $$ ...
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2answers
138 views

If an airplane is flying sideways, is it in free fall?

If a plane turns 90 degrees such that it is flying sideways, is it accelerating towards the earth at the usual 9.8 m/s^2? My guess is that the plane must be in free fall because I don't see what ...
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1answer
90 views

How possible is it that the Large Hadron Collider (LHC) on its second try, could disrupt the gravity of Earth?

How possible is it that the Large Hadron Collider, on its second try, could disrupt the gravity of Earth?
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1answer
186 views

Why is the gravitational force $10^{38}$ times smaller than the strong nuclear force?

Also, why is the weak interaction force $10^7$ times smaller than the strong nuclear force?
4
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1answer
179 views

What would happen if a negative mass crossed the event horizon of a black hole?

If negative mass really existed and somehow a very fast traveling negative mass object reached near the black hole's event horizon. What would happen when it crosses the event horizon? According to ...
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0answers
26 views

Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth? [duplicate]

Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth? According to a detailed analysis by Dave Typinski, Marvin the Martian’s Illudium Q-36 ...
0
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2answers
88 views

Why is the potential energy for a body raised up by a height negative?

I tried deriving the potential energy of a body when raised at a height $h$ above the earths surface, using the formula: $$PE = -W_\text{conservative}$$ where $W_\text{conservative}$ is the work ...
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1answer
89 views

How can gravity truly be infinite?

From my knowledge, gravity is infinite and extends throughout all of space. It diminishes as distance increases but is still present everywhere. So given enough time, no matter where something is in ...
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0answers
123 views

Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth?

According to a detailed analysis by Dave Typinski, Marvin the Martian’s Illudium Q-36 Explosive Space Modulator will require $1.711 \cdot 10^{32}~\text{J}$ to shatter the Earth into a gravitationally ...
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2answers
223 views

Where did the energy released due to gravitational binding energy of the Earth go?

The gravitational binding energy of the Earth is $2×10^{32} J $, so the same amount of energy must have been released during the Earth's history. According to this and this, the current internal ...
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0answers
23 views

How would gravitons be detected? [duplicate]

How would gravitons be detected indirectly or directly, in space or on earth? And what experiments are going on to find gravitons?
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2answers
135 views

How much pressure does the earth's central atom experience?

If mass is distributed evenly about it: "central atom", then it should be weightless right? If reasonably so, does it still experience the pressure? I would like to calculate, but I'm not so ...
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1answer
66 views

Where does gravity originate?

Does it emanate strictly from energy dense regions of space? What does that mean? Is it possible to, say, arrange clumps of matter in such a way as to create a virtual gravity well in space where ...
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2answers
231 views

Can very large objects have a gravitational moment?

I was reading this answer about center of gravity vs. center of mass and it stated: Consider the Sears Tower. Its CG is about 1 millimeter below its CM. The reason why is because the base of the ...