Questions tagged [general-relativity]
A theory that describes how matter interacts dynamically with the geometry of space and time. It was first published by Einstein in 1915 and is currently used to study the structure and evolution of the universe, as well as having practical applications like GPS.
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Are the optical medium of 10.1007/BF00758153 and the Lorentz Ether of 10.1007/s00006-011-0303-7 the same thing? [closed]
On the gravitational field acting as an optical medium
A Generalization of the Lorentz Ether to Gravity with General-Relativistic Limit
The first paper seems to be facing a question: whether there ...
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Do the Komar/ADM mass equations also hold in 2+1D?
All definitions I have come across for the ADM mass require asymptotic flatness, which always is defined for 4 dimensional spacetimes. I was wondering if these formulae in 3+1D hold in 2+1D aswell?
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Doppler Effect and the concept of relative velocity in GR
While reading Sean Carroll's book on General Relativity, I understood that the concept of velocity is ill-defined over large distances in arbitrarily curved manifolds, like the one used to describe ...
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How to determine if gravity is roughly linear?
The Einstein field equations are famously nonlinear, which is one of the properties that makes them difficult to solve. I know (or at least I believe) that a linear system's behavior is roughly ...
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Weyl variation of a generic action
In this paper https://arxiv.org/abs/hep-th/9906127 (see eq. 15)
The following identity appears
$$ \delta_{W} \int d^d x \sqrt{-\gamma} \tilde{\mathcal{L}}^{(n)} = \int d^d x \sqrt{-\gamma} \sigma\left(...
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Does (covariant) divergence-freeness of the stress-energy tensor ${T^{\mu\nu}}_{;\nu}=0$ follow from the Bianchi identity?
I'm working through Chap. $30$ of Dirac's "GTR" where he develops the "comprehensive action principle". He makes a very slick and mathematically elegant argument to show that the ...
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Prerequisites to learn/work on double copy theory and amplitude methods for gravity
I am a PhD student in classical gravity; specifically in BH perturbation and GW.
I am interested in learning about the double copy and the use of scattering amplitudes in understanding GW physics. I ...
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Cyclic Universe Problems
In Penroses's hypothesis, at the end of each iteration the universe undergoes a conformal transformation, meaning distances are rescaled. If I am right, it implies that a planet from the previous ...
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Homogeneous and Isotropic But not Maximally Symmetric Space
Is this statement correct: "In a homogeneous and Isotropic space the sectional curvature is constant, while in a maximally symmetric space the Riemann Curvature Tensor is covariantly constant in ...
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Electric field under gravity
For a spherically symmetric mass m of radius r and charge q, how does the electric field vary with distance d from the center where d > r.
Does it still vary as $\dfrac{1}{r^2}$ or is there a ...
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Understanding expansion of the Universe as things flying apart
Say that we have a Universe uniformly filled just with matter (let's not bring dark energy into this). And say that we fill it with very light particles (so that the gravitational interaction between ...
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On the index orderings for Christoffel symbols [duplicate]
Update: The difference with this question is that it is a much narrower question than the much broader referenced question, and no answer was ever provided to this narrow question either here or on ...
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Constant curvature on a sphere?
$ds^2 = \frac{1}{1- r^2}dr^2 + r^2d\theta^2$ denotes a 2d spherical surface and it should have a constant curvature. The Riemann curvature tensor components are linear in their all 3 inputs. Since the ...
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WKB Approximation of the Quasinormal Mode Spectrum of the Poschl-Teller (PT) Potential
In Black Hole Spectroscopy, it is well known that the Pöschl-Teller (PT) potential behaves approximately, or similarly to the more complicated Regge-Wheeler (RW) Potential.
The WKB Approximation has ...
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A few doubts regarding the geometry and representations of spacetime diagrams [closed]
I had a couple questions regarding the geometry of space-time diagrams, and I believe that this specific example in Hartle's book will help me understand.
However, I am unable to wrap my head around ...
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