Questions tagged [gravity]
Gravity is an attractive force that affects and is affected by all mass and - in general relativity - energy, pressure, and stress. Prefer newtonian-gravity or general-relativity if sensible.
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Consistency of a khronon EFT with a scalar medium metric 𝑑 𝑠 2 = − 𝜌 2 𝑑 𝑡 2 + 𝜌 − 2 𝑑 𝑥 2 ds 2 =−ρ 2 dt 2 +ρ −2 dx 2 [closed]
I am studying a theoretical model where gravity emerges from a scalar “clock-rate” field
ρ=(−X)−1/2,X=gμν∂μϕ∂νϕ,
with the metric written in unitary gauge as; ρ=(−X)−1/2,X=gμν∂μϕ∂νϕ,
The scalar ...
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If gravity propagates at the speed of light, why doesn’t Earth orbit where the Sun was 8 minutes ago? [duplicate]
General Relativity says changes in the gravitational field propagate at the speed of light. Since sunlight takes about 8 minutes to reach Earth, any change in the Sun should also take 8 minutes to ...
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Question about backreaction in Jackiw-Teitelboim (JT) gravity
It is said that asymptotically AdS$_2$ space is different from its higher-dimensional counterparts because it suffers from backreaction; any small amount of matter added to the spacetime destroys the ...
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Building a theory for gravity by copying Electrodynamics
I am aware that the Hilbert-Einstein lagrangian density reproduces correctly Einstein's field equations. However, I also know most (Yang-Mills) gauge theories are built by "copying" the ...
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Time-averaged energy flux of a wave?
In the context of linearized General Relativity, if a monochromatic, plane-fronted gravitational wave in the transverse-traceless (TT) gauge is described by the metric perturbation:
$
h_{ij}^{\mathrm{...
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Can toroidal neutron stars theoretically exist?
Someone has proven that hydrostatic equilibrium of toroidal planets is possible and stable against small perturbations. However, these calculations are based on Newtonian gravity which is valid only ...
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Perturbative Expansion in the Vielbein Formalism
Most of perturbation theory in GR is done by perturbing the metric, i.e. writing $g = g_B + \alpha h$, where $\alpha$ is our expansion parameter and $h$ is our perturbation, and then developing either ...
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Objective collapses, stochasticity, conservation of energy and signalling
While reading about general objective collapse theories (not being bound to a specific models) I came across the following:
Any nonlinear and deterministic modification to Schrodinger equation ...
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Renormalizing Newton's gravitational constant $G$
Renormalization is a key part of QFT, and to its core, it involves admitting that magnitudes which we experience as constant in everyday life (i.e: the charge of the electron, its mass, etc.) depend ...
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Can Clebsch potentials provide a finite, quasilocal measure of rotation in singular spacetimes?
In Kerr spacetime, the Komar angular momentum uses the Killing field $\partial_\phi$ and curvature, which diverge at the singularity. Using Clebsch potentials $\beta = \phi + \beta_0(r,\theta)$, $\...
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In Spacetime curvature, how do masses creating the curvature interact?
In a spacetime curvature, how do two masses creating gravity wells interact with each other? For instance, I can visualize a rolling marble, which is a small mass compared to two large masses creating ...
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Gravitational Time Dilation and perception of time? [duplicate]
How does time dilate near a massive gravitational object in wrist watch time and human aging time?
If I synced my wrist watch with someone on a space station, left the space station in orbit with the ...
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WHY ARE WE NOT PULLED BY THE GRAVITY OF THE SUN [closed]
WHY ARE WE NOT PULLED BY THE GRAVITATIONAL FIELD OF THE SUN IF
IT IS STRONG ENOUGH TO KEEP PLANETS IN PLACE OR IF IT IS STRONGER THAN THE GRAVITATIONAL FILED OF
THE EARTH?
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Elementary conceptual doubt in classical newtonian mechanics about force, mass and acceleration [closed]
The quantity that we can measure as corresponding to that which we exert on a body or object is proportional to velocity, where the constant of proportionality is taken to be the inertial mass.
At ...
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Kerr infinite redshift surface: length of meridian less than equator
In Kerr spacetime geometry, consider a surface defined by $t = t_0$ (a constant) and the infinite redshift surface $r = r_{S\pm}$. (Not the event horizon)
Kerr geometry:
$$
d{s}^2 = -d{t}^2 + \frac{\...
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