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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How do you know what kind of space(time) you have when solving the Einstein Field Equations?

I'm experimenting with the EFE, and I ''invented'' a metric; a diagonal non-zero metric, and I discovered that the Riemann tensors are equal to zero which implies the Einstein tensor $G_{mn}$ equals ...
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1answer
30 views

Is there energy density arising from expansion velocity?

I'm taking a first course in cosmology, and I'm having a conflict of intuitions when it comes to the relative motion of objects arising from the growth of the scale factor. Intuition 1: The growth of ...
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0answers
40 views

What is the current status of Penrose Conformal Cyclic Cosmology?

A brief summary from wikipedia Penrose's basic construction is to connect a countable sequence of open Friedmann–Lemaître–Robertson–Walker metric (FLRW) spacetimes, each representing a big ...
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2answers
46 views

Light wave with gravitational component [closed]

It may sound a little naive but... Is it possible for a light wave to have a gravitational wave component?
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0answers
40 views

Photon Gas Stress-Energy Tensor

In standard texts it is typically discussed how one can obtain the stress energy tensor of a perfect fluid, in both coordinate-dependent and coordinate independent forms: \begin{equation} ...
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1answer
55 views

Electromagnetic four-potential for Kerr-Newman solution

Any textbook or paper on the Kerr-Newman metric I found contains the solution for the electromagnetic tensor $ F^{\mu}_{\phantom{\mu} \nu}$. Can you provide a (reliable) reference for the solution ...
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1answer
47 views

Using the Metric in Book Gravitation (MTW)

Here is the whole Box 2.2, at Page 55 The dot behind the second $-p^2$ seems to be a "planck mass" (sarcasm, flea egg) or just the book's style to use Dot behind the equations. So the Equation is ...
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1answer
64 views

How does the gravitational field behave inside a star?

The interior gravitational field of a star with constant density is given by ...
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2answers
88 views

Could there be a “massive gravity” theory?

If we talk about a "quantum theory" of General Relativity, we know that the particle that mediates the gravitational force would be the so called Graviton, a massless particle with spin $2$. I ...
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1answer
92 views

Should Anti de Sitter Universe collapse exponentially? (n0)

The de Sitter Universe is described by the Friedmann equation with $k=0$, $\rho=0$ and a positive cosmological constant $\Lambda$: $$\Big(\frac{\dot{a}}{a}\Big)^2=\frac{\Lambda c^2}{3}$$ The ...
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1answer
84 views

How do you calculate time dilation when neither frame is inertial?

I'm reading Hartle, Gravity and read bout the Twin Paradox. I understand why there isn't really a contradiction, one frame is inertial, the other isn't. However, I'd like to know how to calculate time ...
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3answers
135 views

Newton's gravity vs Einstein's gravity

Hello so if i were to simplify the difference between gravity as seen from Newton and gravity as seen from Einstein, could i say that Einstein's gravity is just adding the fact that gravity does not ...
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0answers
63 views

Black Holes and the Multiverse [closed]

Are there any peer-reviewed theories which explore the idea that black holes in our universe may spawn other universes - or that our universe came from a black-hole-like event in another universe? ...
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1answer
72 views

Interior material and spacetime of a black hole described from outside

This question is mostly about general relativity. Answers regarding the quantum physics behind it are also appreciated, but first I would prefer solutions from a relativistic viewpoint. If you ...
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1answer
62 views

Derivation of the Cartan Field equation

Please help me understand how, in this introduction to spacetime and fields, the Einstein Cartan equation: $$C^k_{\hspace{2mm} [ji]}-\delta_{[i}^{k}C^l_{\hspace{2mm} ...
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1answer
150 views

What's the hooke's law in general relativity?

Now I'm trying to derive the hooke's law in general relativity,but I have many difficulties with it. First,I try to search google/google scholar.But I found nothing about the hooke's law in general ...
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48 views

About the non-locality of gravitational energy 2

Gravitational energy is non-local which is essentially because of the equivalence principle. The equivalence principle says that you can always transform your frame so that you feel like in a ...
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1answer
30 views

Effects of time dilation in our Galaxy [duplicate]

Hi I am a bit of a science noob but anyway I'm writing a little Sci-fi story and I just want to know if there is a substantial difference in perceived time passed at point A and point B if Point A is ...
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1answer
60 views

LIGO detection: What do we know about the black hole system?

I would to know how much we can infer from the LIGO detection on the black hole system. I understand that at least the following can be verified: Spins Inclination Initial masses Final masses ...
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4answers
933 views

Coordinates vs. Geometries: How can we know two coordinate systems describe the same geometry?

Specifically, I'm asking this because I'm taking a class on General Relativity, and in Hartle's book Gravity, in Ch. 12, after having spent some time using Schwarzschild coordinates, we are introduced ...
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0answers
68 views

Are there any conditions under which the Christoffel symbols can be treated as a damping term in a harmonic oscillator?

(Mathjax did not seem to be working as I composed this question. Hopefully it will kick into action once I post.) Note I am a novice at tensor notation. I am working with the following Lagrangian ...
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2answers
1k views

Why there is no dipole gravitational wave?

I have read that "thanks to conservation of momentum" there is no dipole gravitational radiation. I am confused about this, since I cannot see the difference with e.m. radiation. Is this due to the ...
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0answers
74 views

Non-locality of gravitational energy

Gravitational energy is non-local which is essentially because of the equivalence principle. The equivalence principle says that you can always transform your frame so that you feel like in a ...
5
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2answers
120 views

Kerr Metric from rotated Schwarzschild?

Say we have got a system in GR that is described by the Schwazschild metric. Then we perform a coordinate transform that gives the metric in a rotating system. Why is the transformed metric not the ...
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1answer
29 views

Time dilation in a sphere of gas of constant density

If you have a sphere of gas of constant density, would something in the center of this gas experience time dilation relative to someone in empty space (not just someone outside the gas, but someone in ...
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3answers
325 views

Can an observer know what is the source of gravity?

There's an observer in a closed room without windows under an influence of gravity force. Can he determine what is the source of gravity - whether it's a spinning motion, acceleration or huge mass ...
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1answer
55 views

What is the affection of stress tensor of spacetime by the energy/mass density moment of a photon? [closed]

First of all what kind of moment exhibits the photon under its propagation to spacetime continium -quadrupole,dipole or monopole! Please, explain me- why. Do Give some arguements! When it propagetes ...
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0answers
86 views

Aren't black holes required to exist forever in our frame of reference?

I know that for an observer far away, nothing ever crosses a black hole horizon (due to time dilation), while in the frame of reference of a falling observer the horizon is nothing special on its way ...
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0answers
61 views

My question is about big bang theory [closed]

Oh srry my english is weak i am only 11 years old but i love physics my question was accourding to maxwell and enistien nothing can go faster than light and if we give an object enough energy to move ...
3
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0answers
78 views

Effective potential for Kerr incorrect?

I am self-learning GR. Background I have been following Christopher Hirata's lecture notes on Kerr geodesics. In Equation 38, the effective potential $V(r)$ is given by: ...
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1answer
53 views

Problem on parallel transport [closed]

I've been trying to go through an example for parallel transport but I cannot quite follow the solution. A surface (paraboloid) is given by the parametric equation $r(ρ, φ)$ = $ρ \cos(φ)\hat{i}$ + $ρ ...
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1answer
58 views

Does time and time dilation exist in a black hole?

Since being near stronger gravitational fields causes time dilation, can this be generalized to the region beyond the event horizon? i.e , is it meaningful to say that someone outside the black hole ...
7
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0answers
125 views

Do photons generate gravitational waves since they affect with their energy the stress tensor?

The gravitational waves are fact. They are produced in a way predicted 100 years before by Einstein. Anything with energy affecting stress tensor of space time produces them. What does it happen with ...
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1answer
95 views

Clock on constantly accelerating object approaches Gudermannian limit?

If an object is moving away from X with a constant acceleration of a, its velocity at time t (relative to X and accounting for relativity) is given by: ...
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86 views

On the nature of forces in general relativity

*** EDIT: I understand that it's not wise to fixate on Schroedinger words, however their meaning still remains obscure to me. Besides this my question on the possibility to abandon the concept of ...
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1answer
114 views

What are gravitational waves relative to? [closed]

I have been having trouble picturing what kind of waves say Sun and Earth would make. Looking from top perspective Sun is in the middle and denting space while Earth is moving which is also denting ...
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1answer
93 views

Two places having same gravitational acceleration - Do they also have same curvature of space time?

If there are two places (possibly on/above two different planets) having same gravitational acceleration (g), would it imply that the two places have same extent of space time curvature and will have ...
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1answer
44 views

Is there a parametrization for the shape of space?

I was thinking about how the space is curved. And how do we know that the shape of space arround a singularity is something like that: So I was trying to make a similar parametrization of this kind ...
3
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1answer
91 views

Is there a path to go from GR, to Gravitational Waves, to Gravitational Particles (Gravitons), to Quantum Gravity?

The articles on the subject often say : a part of the mass of the 2 celestial bodies became energy for gravitational waves after merging : E(gravity waves) = (M1 + M2 - M_merged).c^2 Intuitively I ...
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1answer
55 views

Is the correspondence between our universe and cellular automata in the presence of time travel just co-incidence? [closed]

I've written a paper discussing a modification to the game of life. Essentially, the traditional game is modified so that a cell is alive if there are 5 or 6 alive neighbours in total across the ...
2
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1answer
69 views

Dirac equation from a vierbein operator?

Klein-Gordon equation can be derived straightforwardly by getting the mass-energy relation from special relativity in tensorial form, $$\eta^{\mu\nu}p_{\mu}p_{\nu} = m^2c^2$$ and promoting the ...
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1answer
113 views

About the LIGO result and Abhas Mitra [closed]

Well I read this article https://en.wikipedia.org/wiki/Abhas_Mitra and he has claimed that "The so-called massive Black Hole Candidates (BHCs) must be quasi-black holes rather than exact black holes" ...
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2answers
87 views

Is Time Dilation in GR Simply a Consequence of Curved Space?

My understanding of time dilation in General Relativity is that it is the consequence of particles traveling at the speed of causality following longer, curved paths. Since it takes longer for two ...
2
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3answers
117 views

Gravitational wave detection and electromagnetic counterpart

Background Referring to this article on Fermi EM signal, 0.4 s after the gravitational wave detection by LIGO, FERMI detected an electromagnetic signal (poorly localized) with a false alarm ...
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0answers
59 views

Einstein's relativity of simultaneity train/embankment thought experiment

Einstein's thought experiment I'm referring to is this one: http://www.bartleby.com/173/9.html briefly: train/embankment experiment is where lightning strikes at either ends of the running train ...
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42 views

Can nonconserved energy in GR be thought of as going into gravitational field energy?

One of the most striking features of GR is that energy is not conserved. Carroll's GR text has an interesting statement about this: Clearly, in an expanding universe... the background is changing ...
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1answer
71 views

Is it possible to travel faster than the speed of light under extreme warping of spacetime?

The event horizon of a black-hole is defined as the point at which light itself cannot escape, supposedly due to a black-hole's immense gravity and effect on spacetime. However, would this not require ...
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4answers
99 views

Theoretical Possibility of “Opposite” Gravitational Mass? [duplicate]

This is an unusual idea that I have been entertaining for some time, and I can't find anything about it online. However, it is so simple that someone must have conceived it before. First, I will ...
3
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2answers
113 views

Finding geodesics: Lagrangian vs Hamiltonian

I have a question referring to how to compute geodesics of a given spacetime (say, Kerr). I know that the direct way is via the geodesic equation ...
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0answers
22 views

Gravitational Ripples [duplicate]

Recently the observance of Gravitational Ripples was reported using the LIGO detector. LIGO consists of two arms perpendicular to each other through which a split laser beam is passed and then ...