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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Why does gravitational collapse occur suddenly in a supernova progenitor?

I was reading the Wikipedia article on Supernovae, and it says that one of the reasons why a supernova occurs is due to sudden gravitational collapse when the core of the star has little fusable ...
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Geometric interpretation of Electromagnetism

For gravity, we have General Relativity, which is a geometric theory for gravitation. Is there a similar analog for Electromagnetism?
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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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Event Horizon violability?

Is the "event horizon" of a black hole potentially violable? Black holes are commonly described as being unidirectional (matter / energy goes in, but doesn't come out), but is the event horizon of a ...
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Does a ball resting on the ground have acceleration?

Does a ball resting on the Earth's ground have acceleration caused by gravity?
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Calculating Atmospheric Pressure on an Imaginary Planet

I am planning a series of science fiction novels that take place on an imaginary binary planet system. Both planets have a lower surface gravity than the Earth and one has slightly more mass than the ...
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Why water in the sink follow a curved path?

When you fill the sink with water and then allow the water to be drained, the water forms a vortex.. And then it starts to follow a curved path downwards by effects of gravity.. Why this phenomena ...
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Effects of space mining on Earth's orbit

I was reading a post about space mining, specially lunar mining. I was thinking about what would change in Earth's orbit if we start bringing tons of rocks to it? I mean, in a huge scale. So, would ...
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Surface gravity of Kerr black hole

I'm going through Kerr metric, and following the 'Relativist's toolkit' derivation of the surface gravity, I've come to a part that I don't understand. Firstly, the metric is given by ...
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Wavefunction collapse and gravity

If gravity can be thought of as both a wave (the gravitational wave, as predicted to exist by Albert Einstein and certain calculations) and a particle (the graviton), would it make sense to apply ...
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Why does Jupiter emit more energy than it receives?

I hear that Jupiter and Saturn emit more energy than they receive from the Sun. This excess energy is supposedly due to contraction. Is this accepted as fact (or is it controversial)? Does this ...
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Does the mass of a star change as it collapses into a black hole?

I know (I think!) that when a really big star collapses on itself it creates a black hole. My question: When a star collapses, is the mass equal to the mass of the star when it's not a black hole? Or ...
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Materials with different gravitomagnetic permeability?

If you start with general relativity, and assume small perturbations around a nearly flat metric, it is possible to obtain linearized equations of gravity that look a lot like Maxwell's equations, ...
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Duality between Euclidean time and finite temperature, QFT and quantum gravity, and AdS/CFT

The thoughts below have occurred to me, several years ago (since 200x), again and again, since I learn quantum field theory(QFT) and statistical mechanics, and later AdS/CFT. It is about the duality ...
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Why do 3d spheres and gravity tend to rotating discs on one plane?

Whether is it our solar system or a whole galaxy, there is usually a massive object (star or black hole) at the centre with gas and objects rotating around it. The gravitational effect of the ...
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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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Gravitation law paradox for very close objects?

We all know that gravitation force between two small (not heavenly) bodies is negligible. We give a reason that their mass is VERY small. But according to inverse square law, as $r\to 0$, then $F\to ...
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Why aren't all rocks in space orbiting bigger rocks?

Why do only big rocks (planets) have satellites, and not small ones? Why doesn't cosmic dust orbit rocks that are many times heavier than the dust grains? If dust is still too heavy then what about ...
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What prevents the accumulation of charge in a black hole?

What prevents a static black hole from accumulating more charge than its maximum? Is it just simple Coulomb repulsion? Is the answer the same for rotating black holes? Edit What I understand from ...
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If gravity is a bend in Space-time then what is magnetism?

Einstein postulated that gravity bends the geometry of space-time then what does magnetism do in to the geometry of space-time, or is there even a correlation between space-time geometry and ...
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Can a black hole be explained by newtonian gravity?

In the simple explanation that a black hole appears when a big star collapses under missing internal pressure and huge gravity, I can't see any need to invoke relativity. Is this correct?
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Speed of light in a gravitational field?

How do I solve the speed of light in gravitational field? Should I just add gravitational acceleration in speed of light? $$c'=c_0+g(r)t~?$$
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Gravitation is not force?

Einstein said that gravity can be looked at as curvature in space- time and not as a force that is acting between bodies. (Actually what Einstein said was that gravity was curvature in space-time and ...
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What is the radius of the event horizon?

I know that the Schwarzschild radius is given by $$r~=~\frac{2GM}{c^{2}}.\tag{1}$$ However, If we had the metric $$ds^2~=~−A(r,t)dt^2+\frac{dr^2}{B(r,t)}+r^2(dθ^2+\sin^2{θ}dϕ^2),\tag{2}$$ where ...
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How is light affected by gravity?

Light is clearly affected by gravity, just think about a black hole, but light supposedly has no mass and gravity only affects objects with mass. On the other hand, if light does have mass then ...
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Why is it hard to detect a black hole

I've read in some texts that we can't directly observe a black hole in space because not even light can escape from its gravity. Some of the indirect observational methods mentioned are, gravitational ...
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A change in the gravitational law

What would happen if the force of gravitation suddenly starts varying as $1$$/$$r^3$ instead of $1/r^2$ ? Would the symmetry of universe now seen be disrupted?
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What is the escape velocity of a Black Hole?

The escape velocity of Earth is $v=\sqrt{\frac {2GM}{R}}$, where $M$ is the mass of the Earth and $R$ it's radius (approximating it as a sphere), and is much less than light speed $c$. But I want to ...
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Vacuum and repulsive gravity

How can one show from General Relativity that gravity is attractive force, and under which conditions it becomes repulsive, also why positive energy vacuum drives repulsive gravity?
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What physical forces pull/press water upwards in vegetation?

Each spring enormous amounts of water rise up in trees and other vegetation. What causes this stream upwards? Edit: I was under the impression that capillary action is a key factor: the original ...
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Do objects with mass “suck in” spacetime?

I don't really understand the general theory of relativity (GTR) really deeply, but according to my understanding, the GTR say that gravitation is caused by the curvature of spacetime by objects with ...
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Why would Antimatter behave differently via Gravity?

Confinement of antihydrogen might help provide a future answer. http://arxiv.org/abs/1104.4982
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Why do helium filled balloons move away from the Earth?

From my understanding objects do not fall but are pulled to the earth from gravity. With this in mind, I can't understand why if helium filled balloons are not pulled by gravity then shouldn't they ...
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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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What is the likelihood of ever discovering the graviton?

How would one look for and confirm existence of a graviton? Someone was speaking to me about perhaps one day discovering the graviton, but to me it seems unlikely, although I'm young and essentially ...
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Does Super Mario physics work in reality? [duplicate]

This illustration summarizes my question: Please assume no air resistance (unless that makes a large difference). Here's what we concluded, but I could use both confirmation and also help with the ...
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why there is no accuracy of the measured value of $G$?

With the advancement of Modern Technology still there is no accuracy of the measured value of $G$ Gravitational Constant, why!?
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Does rotational energy have effect on gravity/metric?

Intuitively, if energy can be stored in rotational motion, it has to obey $E=mc^2$. Does rotation of typical stellar-sized objects - BHs, pulsars, binaries - have measurable effect on their overall ...
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Tidal force on far side

I have a question about tidal forces on the far side of a body experiencing gravitational attraction from another body. Let's assume we have two spherical bodies $A$ and $B$ whose centers are $D$ ...
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What does it mean for objects to follow the curvature of space?

In science documentaries that touch on general relativity, it is often said that gravitational pull isn't an actual a pull (as described by classical physics), but rather one body travelling in a ...
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Why can't airplanes just keep going up? [duplicate]

Possible Duplicate: Why do space crafts take off with rockets instead of just ascending like an aircraft until they reach space? Ignoring that the engines only work in air, so say its a ...
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Alternate layman's metaphors for illustrating curved space-time

The metaphor of a surface (typically a pool table or a trampoline) distorted by a massive object is commonly used as a metaphor for illustrating gravitationally induced space-time curvature. But as ...
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Why does dark matter form walls and filaments

Related: How are galaxy filaments formed? And do they have any analogues in stellar formation? But I want to come at this from a different angle. Like the user asking that other question, I was a bit ...
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Is Dyson Sphere a stable construction?

Suppose that a star is encompassed by a Dyson Sphere. Do we need a position control system for the Dyson Sphere to keep its origin always aligned with the center of the star? Will it stay aligned ...
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Is anti-gravity possible in theoretical physics?

Is anti-gravity possible in string theory? I have read some articles about scientists making assumptions about the existence of anti-gravity, but is it possible in string theory?
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Could the acceleration of universe expansion be caused by gravity itself?

Dark energy is suggested to be a repulsive force in the universe causing an accelerated expansion. If the amount of mass outside our observable universe is greater than inside (higher mass density), ...
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Quantum mechanical gravitational bound states

The quantum mechanics of Coloumb-force bound states of atomic nuclei and electrons lead to the extremely rich theory of molecules. In particular, I think the richness of the theory is related to the ...
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What exactly is the microgravity field in orbit?

The ISS and other objects in orbit still experience small acceleration outside from the perfect line of orbit (of the system CM). For instance, two objects in the ISS that are let to be at rest will ...
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Mass Needed to Clear an Orbital Neighborhood

In 2006 the IAU deemed that Pluto was no longer a planet because it fails to "clear" the neighborhood around its Kuiper Belt orbit. Presumably, this is because Pluto (1.305E22 kg) has insufficient ...
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Quantization of Gravitational Field: Quantization conditions

I'm begining to study Quantization of field with the second quantization formalism. I've studied phononic field, electromagnetic field in the vacuum and a generic relativistical scalar field. I ...