Questions tagged [gravity]

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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Does convection occur in microgravity due to pressure gradient?

Context: On Earth, with gravity, when heating a fluid, the particles gain thermal energy and decrease in density, and a difference in density throughout the fluid causes thermal energy transfered by ...
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AdS-CFT correspondance from 1D to 4D

From what I understand the AdS-CFT correspondence states that the bulk dynamics of a $n$-dimensional gravitational theory are encoded in the degrees of freedom of its dual CFT in the $(n-1)$ ...
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How to find the fine structure constant? [closed]

Is given in the scalar field below the lagrangin. How to find the finite structure constant?
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Boussinesq Approximation Term in Momentum Equation

According to the Boussinesq equation: $\rho = \rho_o ( 1 - \beta_t ( t – t_o) - \beta_c ( c – c_o ) ) $ So, $\rho \cdot g$ should be equal to : $\rho g = g \rho_o ( 1 - \beta_t ( t – t_o) - \...
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Mutual gravitational acceleration (or deflection) of light beams as a function of the angle between them

Given Einstein's famous equivalence between energy and mass, $E=mc^2$, a light beam with power, $P$, has an energy per unit length of $P/c$ and an equivalent mass per unit length of $P/c^3$. A short ...
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Bad explanation by Poincare [closed]

I am writing about poincares objection to Lesage theory, which is well known. Poincare says the energy present would he huge therefore it's impossible. It's all lost in internal collisions. It's like ...
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What is space? Does it curve around itself? [closed]

Update for focus: Learning about spacetime curvature and general relativity years back, i've come to a question that still no one has answered me. Does space curves in itself? when we say "space ...
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Is gravity a direct result of Lorentz Contraction?

I am not a physicist. Curious to know if Gravity is a direct result or manifestation of the Lorentz Contraction between particles within a denser field of matter? Curious to know if anyone has tried ...
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How is the gravitoelectromagnetism approximation of GR valid if it seems to yield unstable solutions?

In the gravitoelectromagnetism approximation of GR, we have equations analogous to Maxwell's equations with some sign changes. As pointed out in another post of mine, this leads to unstable run-away ...
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Schwarzschild-deSitter horizon singularity

The Schwarzschild-deSitter spacetime in Euclidean signature is given by: $$ ds_{E}^{2}=\left(1-\frac{2M}{r}-\frac{H^{2}r^{2}}{3}\right)d\tau^{2}+\frac{dr^{2}}{\left(1-\frac{2M}{r}-\frac{H^{2}r^{2}}{3}\...
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Is the mass of two vertically stacked blocks greater than when they're placed side by side?

At the end of this video on mass-energy equivalence, it's states that two blocks stacked vertically have more mass than when placed side by side because they have more gravitational potential energy. ...
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Where does gravity come from?

First, in my childhood, I learned that gravity is a force. Later, I learned that gravity is a property of spacetime. If gravity is a property of spacetime, then why is it one of the fundamental forces....
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Why are globular clusters always denser in the core?

Stars falling towards the core speed up--thus, the amount of time they spend in any given volume goes down. Stars out near the edge move more slowly, thus their residence times in outer volumes should ...
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Help in understanding how general relativity describes space-time near black hole poles that emit astrophysical jets

I am aware that General relativity does not explicitly deal with 'expanding' or growing and due to that reason 'cosmologically pressurised' aether (proposed by the 'Theory of a river flow' but that ...
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Based on structure formation and the lifetime of the universe why is there an upper bound on the cosmological constant?

I understand that significantly greater values than the cosmological constant would result in difficulty for the formation of large gravitationally bound structures within the lifetime of the universe....
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In general relativity, assuming a spherical uniform mass distribution, what is the total energy value of the gravitational field inside the sphere?

In Newtonian mechanics, assuming a spherical uniform mass distribution, the total gravitational potential energy (gravitational self-energy) inside the sphere is $$U_{gs}=-\frac35\frac{GM^2}R.$$ In ...
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Does the curvature of spacetime resulting from the mass of an object imply acceleration [closed]

I recently saw a video about general relativity, to help improve my understanding of the curvature of spacetime and gravitational acceleration. From the video, I have made the following conclusions: ...
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Metric tensor relations

I need to check some simple tensor relations for continuing my calculations. Please write me if you think anyone is incorrect. P.S.: I know this is very simple question, but i need to be assured about ...
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Lense-Thirring effect around rotating black holes

The Lense-Thirring angular velocity of a particle around a rotating black hole in the weak-field limit is given by the formula $$\omega=\frac{2J}{r^3}$$ where J is the angular momentum of the black ...
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Energy-momentum relation for Dirac spinor in curved spacetime

Consider the Dirac equation in curved spacetime \begin{equation} (i\gamma^\mu\nabla_\mu+m)\psi=0 \end{equation} where $\gamma^\mu=e^\mu_a\gamma^a$ is the curved spacetime Gamma matrices, and the ...
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How does Schwarzschild spacetime bend a free falling rigid body?

How does Schwarzschild space-time bend a free falling rigid body? Will it be stretched or squeezed? How much it will be modified? Can we find an effect of Lorentz contraction? When will the assumption ...
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Do there already exists solutions to quantum gravity which are mathematically consistent and consistent with PRESENT observations? [closed]

This question is inspired by a recent video by Sabine Hossenfelder on the topic of black hole information loss. At about 8:23 the makes the claim that "...there are many possible solutions to the ...
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If contact forces are repulsive then how are we able to pull stuff? [closed]

I searched a lot on internet(especially physics stackexchange) about the nature of contact forces. I came to know through most of them that it is repulsive in nature which surely means that your hand ...
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Will 'free' photons exert gravitational force [duplicate]

From my general understanding, it is widely accepted that light will bend around a massive object, as it will experience gravity, is predicted by GR, and was experimentally verified. Also, the energy ...
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Is it possible to distinguish the intensity and the frequency of the graviton?

The wave equation of the graviton was assumed to be similar to that of the EM waves, which a "frequency" parameter could be identified by comparison. However, in EM, there was intensity as ...
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Under PPN Formalism, would the gravity of a mass double as its velocity approaches $c$?

I'm looking at the answer Michael gave to my question. Does this imply that under parameterized post-Newtonian formalism, under the $β1$ factor for kinetic energy, the gravity of a mass doubles as it ...
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Angular momentum of gravitational wave

I am thinking about what is spin and angular momentum of gravitational beams. I came up with the answer that spin is intrinsic to a wave and is related to its source. But I can not start thinking of ...
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Interpretation of Angular Momentum flux from stress energy tensor in Black hole superradiance

While studying the superradiance of a scalar field in Kerr geometry, we show that the energy and angular momentum of the Kerr black hole are extracted by the superradiant modes. I understand the ...
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Calculate Projectile impact with a moving Target [closed]

I'm trying to solve the classic shoot moving object issue in 3D Space, but with acceleration and gravity added to it. I already tried several ways approaching the correct calculation, yet I face the ...
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Understanding the derivation of the Newtonian limit of GR

I'm having difficulty understanding some of this derivation. The relevant information, as I understand it is: We've let the lorentzian metric be a perturbation of the minkowski metric: $$g_{\mu\nu} = \...
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How is gravitational time dilation different from the time dilation from Special Reativity? [duplicate]

In Special Relativity, acceleration i.e. a changing velocity 4-vector results in time dilation, that is asymmetric aging of observers. In General Relativity, the 4-vector does not change along a ...
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Has it been experimentally proven that energy causes gravity?

I know that under general relativity energy and mass are equivalent under $E=mc^2$. But has it been experimentally proven that energy alone causes gravity, for example, does a nuclear reaction ...
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Why is gravity not a physical property?

I was just curiously looking at the Wikipedia page for physical properties https://en.wikipedia.org/wiki/Physical_property and noticed that gravity is not there. Why is that?
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Inertial properties of negative masses

Pondering Casimir effect and negative mass and Gravitational binding energy as alternative to dark matter? I start to think that each form of negative energy has negative gravitational mass. The list ...
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When calculating the internal energy of a falling mass, why do Physicists use the unit of time local to the mass?

Physicists calculate the internal energy of a mass that's falling towards the ground based on the local unit of time that changes as the mass falls to the ground. They conclude that it remains the ...
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Would our orbit really remain the same if the sun were a black hole of equal mass?

There seems to be an idea floating around that the sun could be replaced by anything of equal mass with no consequence to our orbit. It seems to me that if the mass of the sun were confined to a ...
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Single gravitational plane wave or their interference can carry spin angular momentum?

I would be grateful if anybody could tell me if I had one gravitational wave in the form of a plane wave, it still would carry spin angular momentum? We know that gravitational waves are mostly the ...
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"Correct" gauge for Chern-Simons terms in 5d?

Consider 5d Einstein-Maxwell-Chern-Simons gravity with action $$S=\frac{1}{16\pi G}\int d^5x\sqrt{-g}\left[R-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}-\frac{1}{12\sqrt{3}}\frac{\epsilon^{\mu\nu\rho\sigma\lambda}...
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Is time dilation due to relative velocity equivalent in principle to time dilation due to relative gravitational strength?

Is time dilation due to relative velocity and relative gravitational strength equivalent? That is, similar to Einstein's thought experiment where an observer in an enclosed capsule with no windows ...
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Is there a way to know if you accelerate in empty space or in a uniform gravitational field?

If I'm in a room that accelerates through empty space uniformly I won't measure tidal forces. The situation is the same as standing on an infinite massive plane. So I could think, while looking ...
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Why does gravity seem to have two natures (force or warping of space and time)?

In classical mechanics, gravity is regarded as a force but in general relativity it's a warping of space and time in presence of mass. Are these two definitions the same? Or is this a duality nature ...
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Is Bertrand's Theorem Consistent with GR?

Bertrand's Theorem - Please observe the gif of orbits with different exponents in the denominator. (I couldn't get the image upload feature to work for this) Note, the orbit with a 1.9 exponent ...
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What explains the descrepancy between Asaph Hall's equation for Mercury's precession and GR?

In regard to What is the weight equation through general relativity?, the answer is: $$F=ma=\frac{GMm}{r^2}\frac{1}{\sqrt{1-\frac{2GM}{c^2r}}}.$$ This source provides a different equation: $$f \approx ...
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Why gravitational constant not considered while measuring gravitational charge?

I was reading about inertial mass and gravitational mass equivalence from this post Answer to https://www.quora.com/Why-is-gravitational-mass-equal-to-inertial-mass/answer/Leo-C-Stein?ch=15&oid=...
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How do you integrate by parts when you have a triple integral?

I'm studying how particles of equal mass behave in a spherical cluster held intact by gravity. I will assume that the mass density $\rho(R)$ of the cluster is a function of the magnitude of the ...
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How deep is a gravity well of a supermassive black hole? [closed]

Just for the sake of curiosity I am trying to understand how far we should stay away from the black hole to avoid influence of its gravity on us. In the first iteration I know about the 2nd and the ...
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Newtonian gravity as curvature of space

Since Newtonian gravity is also indistinguishable from acceleration, it should be possible to formulate it as a curvature in space, right? For example, if a body changes velocities purely under the ...
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The work done by an external agent and gravitational force of a planet on an object of much smaller mass

The work done on an object by an external agent in bringing it closer to a planet is given by mΔV. So, when the object is brought closer to a planet, the work done by the external agent is negative. ...
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Does a uniform circular disk make a perfect gravitational lens?

I'm surprised at this. I'm expecting to be corrected, but these are my back-of-the-envelope workings ... Starting out with a cylindrical lens oriented along the line of sight. Assuming the cylinder ...
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Free Fall time in General Relativity

Suppose you are working with the Schwarzschild metric in GR. $$ -c^2 \mathrm d \tau ^2 = -c^2 \left (1 - \frac{2 G M}{c^2 r} \right) \mathrm d t^2 + \left (1 - \frac{2 G M}{c^2 r} \right)^{-1} \...
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