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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Path of light and gravitational waves

Now that gravitational waves are detected, the way they are detected was using laser beams and they were out of phase when the return from the same trip distance. Does this means it is based on ...
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1answer
19 views

How would a galaxy “bathing in radiation” behave?

For the sake of understanding mass and radiation interaction, I hope somebody could explain how this hypothetical situation would look. A spiral galaxy is subjected to such high levels of cosmic ...
3
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1answer
37 views

Do the photons emitted along with the gravitational waves take more time to reach earth than the ones emitted after them?

I'm puzzled because the gravitational waves do warp the spacetime locally. They do it continuously as they propagate. So the photons travelling in tandem with these waves must be constantly following ...
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1answer
30 views

General Relativity, Curvature, and extra dimensions

Setup of idea I had somewhat of a thought question regarding general relativity. Consider a simple situation of a sphere and arrow. You hold the arrow and walk from the equator to the north pole. ...
4
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49 views

G4v Gravity Wave vs General Relativity vs LIGO Observation

CalTech emeritus professor Carver Mead produced an alternative prediction, to General Relativity, for gravitation wave observation which he published last year in anticipation of LIGO observations. ...
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34 views

LIGO event - energies involved?

So, we have two Black Holes merging shortly after LIGO turns on after the upgrade. Some questions: a) How lucky was it to see this event? What are the expected rate of occurrence? b) Was this event ...
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7 views

Bondi mass aspect

I'm looking for a good reference that defines the Bondi mass aspect and his relations to Bondi and ADM mass. Googling a bit I've not founded any satisfactory exposition of the subject. A short ...
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20 views

In GR what is a “source-frame mass”?

In the recent LIGO paper, they refer to the masses in some models as: "... a nearly equal mass black-hole binary system of source-frame masses $36^{+5}_{−4} M_{\odot}$ and $29^{+4}_{−4} M_{\odot}$ ...
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42 views

Is it accurate to say that nothing can travel faster than c in a GR context, where more space can be created?

Years ago, my brother and I had an argument where I was trying to convince him that nothing could travel faster than the speed of light. I was pursuing this in the context of Special Relativity. My ...
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17 views

Can we always effectively describe a timelike worldline (non-geodesic) in one spacetime as a geodesic in some other spacetime?

Can we always effectively describe a timelike worldline (non-geodesic) in one spacetime as a geodesic in some other spacetime with a different metric? Is this implied by the equivalence principle ...
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81 views

What are the implications of today's direct detection of gravitational waves?

Here is the announcement from today's Physical Review Letters by Abbott et al.:"On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory ...
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34 views

What would it look like if the earth were suddenly put on the anti-node of a gravitational standing wave with a huge amplitude?

What would it look like if the earth were suddenly put on the anti-node of a gravitational standing wave with a huge amplitude? Can gravitational standing waves even exist? Say if there were two ...
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1answer
76 views

What is the proof of gravity being curvature of spacetime?

According to general relativity gravity is an illusion caused by curvature of space-time, rather than real force. As I understand there is overwhelming experimental evidence to support general ...
5
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1answer
150 views

How is it that distortions in space can be measured as distances? [duplicate]

Imagine yourself and anything you're able to perceive to be drawn onto a rubber band. Any means of determining distances would be affected by the stretching/contracting of the rubber band. The ...
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45 views

Gravitational waves now detectated [duplicate]

Based on the information released so far, have we learned anything new from the detection of gravitational waves at LIGO?
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2answers
88 views

At which point are gravitational waves generated when two black holes merge?

I was reading today's announcement of the gravitational waves and was wondering about this situation where there are two orbiting black holes. Did the wave come from the final merging or was it from ...
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101 views

Einstein's original papers predicting gravitational waves?

I came across the original handwritten papers in which Einstein predicted gravitational waves: and since LIGO announced they've detected a signal confirming the predictions I was wondering if ...
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2answers
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How strong were the gravitational waves that LIGO detected at the source?

Congrats to the LIGO team on the announcement of their discovery of gravity waves! The articles I've read say that the distortion we see here is much smaller than a proton. What about at the source? ...
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2answers
108 views

What will be the role of gravitational waves in future physics? [on hold]

What does this discovery mean for us? Can it lead to a better understanding of the cosmos?
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6answers
5k views

Why is the detection of gravitational waves so significant?

Since there is to be an announcement by LIGO about this today (11 Feb. 2016), I was wondering why the detection of gravitational waves was so significant? I know it is another confirmation of ...
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1answer
54 views

Meaning of $R=0$, $R_{ab}=0$. $R_{abcd}=0$.

First let me state some definition The Einstein tensor is given by \begin{align} G_{\mu\nu} = R_{\mu\nu} - \frac{1}{2} g_{\mu\nu} R \end{align} and note that \begin{align} G^{\mu}_{\phantom{\mu} ...
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2answers
113 views

A classical explanation of why there is a speed limit in the universe [on hold]

The question is - is there any flaw in this explanation, or it is the right explanation in general language? Let me break the explanation into two parts - (1) Why there is a certain speed of ...
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0answers
16 views

event horizon vs apparent horizon ramifications

If the event horizon doesn’t exist in the 2-dimension or 3-dimension time-space - and it doesn’t exist if it can’t be measured or observed - then an apparent horizon would be necessary to reconstruct ...
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52 views

Extrinsic Curvature of Surface of Codimension > 1 [migrated]

We can define the extrinsic curvature of a codimension-one surface as $$K_{ab} = q_a^{\phantom{a}c} q_b^{\phantom{b}d} \nabla_c n_d,$$ where $n^d$ is the normal vector to the hypersurface and ...
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1answer
30 views

Looking out from a collapsing star

From the perspective of the surface of a collapsing star, if you were riding it in as it formed a black hole, what would you observe looking out into the rest of the universe? As you approached the ...
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1answer
42 views

How do I derive geodesic equation using variational principle? [duplicate]

I am trying to derive the geodesic equation using variational principle. My Lagrangian is $$ L = \sqrt{g_{jk}(x(t)) \frac{dx^j}{dt} \frac{dx^k}{dt}}$$ Using the Euler-Lagrange equation, I have got ...
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1answer
46 views

Integrating the geodesic equation to obtain Newtonian energy of test particle

I am studying General Relativity, and have come across a question that I am finding rather intractable: In Newtonian Theory, the energy equation for a test particle in orbit around a point mass ...
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2answers
636 views

Evidence for quantum gravity from gravitational waves

The rumor spreads that physicists will make their big gravitational wave announcement this thursday. I am far from being an experimentalist, but I want to know if there is any chance that the ...
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Are objects like $a^{\mu \nu} a_{\mu \nu} b^{\mu \nu}$ consistent with Einstein summation?

I'm familiar with Einstein' summation notation and I understand objects like $a^{\mu \nu} a_{\mu \nu}$ just fine. But I'm wondering why I've never come across objects like this: $a^{\mu \nu} a_{\mu ...
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6answers
151 views

If gravity is additive, then how does it cancel itself out?

I understand that gravity, as far as we know, is always attractive. Also, it has additive qualities - i.e. the size and strength of the field are proportional to the quantities of mass. This seems to ...
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3answers
57 views

Twins paradox question [duplicate]

In the twins paradox, the twin that travels away from earth comes back to find that his (her) twin has aged much more due to relativity's effect on time. Why can't we posit that it is not the one twin ...
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34 views

What is conformal symmetry physically?

I'm reading a paper by t'Hooft http://arxiv.org/abs/1410.6675. There is an argument in the paper that I could not understand: "Now that system, described by Maxwell’s equations, does have conformal ...
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1answer
33 views

In the orthonormal tetrad method, what is the relation between basis one forms and commutation coefficients?

If $\omega_i$ are dual basis one forms corresponding to an orthonormal tetrad basis $e_i$, and given that the commutation coefficients $C_{ij}^k$ are defined by \begin{equation} [e_i,e_j]=C_{ij}^k ...
2
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56 views

What would be the research advances if we discover the gravitational waves? [on hold]

As researchers of LIGO (USA) and VIRGO (France/Italy) say that they have discovered gravitational waves thanks to black hole collision today, what would be, apart of the important confirmation of ...
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0answers
80 views

What is a good PhD Thesis Topic in General Relativity? [on hold]

For many reasons I am very uncertain whether I should agree to a particular topic for my PhD thesis. The thesis topic would be about "gravitational lensing". There are two main concerns: i) My ...
4
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2answers
356 views

How does one actually use the Einstein field equations?

I'm experimenting with the Einstein field equations (EFE) and I'm wondering how to actually use them. It seems to me that the simplest are those evolving a vacuum, which imply that the ...
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0answers
54 views

Undergraduate Physics Senior Research Topic (Theory/Mathematical Physics Based) [on hold]

This is most likely a question for those who have experience/knowledge of theoretical/mathematical physics at the graduate level and can provide recommendations following my criteria. Here is some ...
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1answer
105 views

How can space and time occur spontaneously? [on hold]

In the book: "A universe from nothing" by the theoretical physicist Lawrence Krauss he mentions that space and time can occur spontaneously. Unfortunately he does not explain how. So my question is, ...
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56 views

Shapes in a black hole

A question around an answer of Timaeus What happens to a particle in the exact center of a Kerr black hole?-answer Outside both is a normal type region of spacetime. In between the two the $r$ ...
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1answer
81 views

Quantum teleportation + time dilation = time travel? [closed]

Thought of this a while back and thought it was pretty funny, not sure if there's been similar ideas discussed elsewhere. I can think of at least 2 reasons this won't work: 1) As far as I know, ...
5
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1answer
93 views

Non-Euclidean mechanics; is it useful?

Special relativity has the following single-particle Lagrangian: $$S = \int_{t_0}^{t_f}\sqrt {\langle \mathrm d\vec{s},\mathrm d\vec{s}\rangle}.$$ Clearly it is based on Euclidean norms; it is in ...
2
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0answers
50 views

Where other frame observer will put new stick [closed]

my question is with relativity, if we draw two circle of same radii and fill the perimeter with stick (very small so it cover whole perimeter) now if we rotate a stick with veey high speed ...
3
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A problem with ADM mass in the derivation of 1st law of black hole thermodynamics

The definition of ADM mass is $M=\frac{1}{16\pi}\lim_{r\rightarrow\infty}\int(\frac{\partial h_{\mu\nu}}{\partial x^\mu}-\frac{\partial h_{\mu\mu}}{\partial x^\nu})N^\nu dA$ according to Wald. ...
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0answers
85 views

Gravitational waves: novel or confirmatory? [duplicate]

If the rumors are true and gravitational waves have been detected, would we learn any new fundamental physics from them? Or is this simply an important confirmation of a prediction of general ...
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58 views

A possible proof that time traveling to the past with the aid of a wormhole is impossible?

Suppose a wormhole connects two part of the place where I live. I find myself in a spaceship attached to one side of the hole, and my wife on the other side, so we can see and talk to each other. Now ...
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1answer
37 views

Gravity, Acceleration, Time Dilation and the Equivalence Principle

Three clocks are started at exactly the same time on Earth. The first and second clocks are taken into the vacuum of space. The first clock accelerates until it reaches 100,000m/s, then stays at this ...
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Components of dual vectors

(This is a close retelling of Wald, problem 2.4b. Not for homework; just curiosity and an increasingly alarming suspicion that I've never actually understood anything.) Let $Y_1 ... Y_n$ be a ...
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2answers
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Is there a doppler effect on the images of stars around rotating black holes?

I'm an illustrator working on a project involving rotating black holes like those discussed in "Gravitational Lensing by Spinning Black Holes in Astrophysics, and in the Movie Interstellar" by James, ...
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1answer
46 views

Divergence of inverse of metric tensor

I know that the Levi-civita connection preserves the metric tensor. Is the divergence of the inverse of metric tensor zero, too?! I'm not so familiar with the divergence of the second ranked tensor. ...
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1answer
55 views

Evaporating black hole Penrose diagram

The context for this is the diagram from From where (in space-time) does Hawking radiation originate? - the more I think of it, the less it makes any sense ) This particular question is about ...