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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What kind of fundamental interaction is gravitation?

Einstein showed that gravitation is not a force but a effect caused by curvature of space time. Then why does theories of quantum gravity treats gravitation as one of fundamental force?
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30 views

Is gravitation a fundamental interaction between mass and spacetime? [on hold]

Please explain in detail about the nature of gravitation as a fundamental interaction.
0
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1answer
18 views

Wormhole Construction & ~ “Jump Conditions”

Throughout the literature Wormholes are typically constructed by "Minkowski" or "Schwarzschild Surgery" (see e.g. Visser, Lorentzian Wormholes...), i.e. under quite simple and/or highly symmetric ...
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0answers
28 views

Why is the frame dragging effect trillions times as strong around a spinning superconducter?

It´s a bit of a forgotten experiment, but why measured Tajmar and his team a frame dragging effect in the surrounding space of a spinning niobium superconductor, that was even measurable in the lab? ...
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0answers
24 views

Applying AdS-CFT to traversable wormholes? [on hold]

ER=EPR recently brought up the connection between non-traversable wormholes and entanglements. What about traversable wormholes? Can we apply AdS/CFT to traversable wormholes?
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0answers
29 views

Conservation of Komar Mass

The definition of Komar Mass in GR is associated with one asymptotically flat end. However, a hypersurface may contain more than one end, such as the spacelike Einstein Rosen bridge in Kruskal ...
3
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2answers
79 views

Can bending spacetime produce electromagnetic fields?

Let's say that we can somehow bent spacetime, can this produce electromagnetic fields? or EMF can only be emitted from charged particles of matter?
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0answers
14 views

Is the distortion of spacetime caused by frame dragging continuously changing, or fixed?

Consider a very heavy star and let´s take a look at the distorted spacetime accompanying the star. Does the spacetime gets increasingly wind up, or is it stationary? If it´s not stationary, then we ...
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1answer
19 views

Stress-Energy Content

I think that the Einstein Field Equation relates the pseudo metric to the the distribution of matter-energy as represented by the stress-energy tensor. Are the stress entries in the stress-energy ...
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0answers
32 views

Black Holes and dimensions [on hold]

In a mental experiment, I was pondering the paradox of the event horizon of a black hole and the use of multiple dimensions. I have seen the question before. If gravity increases infinitely as you ...
3
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0answers
32 views

Is there high ring-down frequencies in LIGO's recent discovery?

This question is from Physics overflow: question in physicsoverflow. I am reading LIGO's new discovery of gravitational waves by black hole merger. During the merger, two phases are not hard to ...
2
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0answers
52 views

(Causal) Set notation round brackets vs square brackets? [on hold]

In many (quite old) papers & books I have been reading recently in the causal theory of general relativity (e.g. On the structure of causal spaces, Kronheimer & Penrose, 1967) I find sets ...
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0answers
37 views

How does an observer at the center of a black hole collapse explains the singularity? [on hold]

Suppose an observer at the center of a cloud of mass. Imagine that the cloud collapses with the observer at the center and forming a crust with an almost empty core and forms a black hole. So, from ...
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1answer
62 views

Can there exist an observer able to observe a collapse of a star into a black hole?

We know that an observer at infinity cannot see a star forming into a black hole as the matter will take progressively longer and longer time to compress (from this observer's point of view). Is ...
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0answers
17 views

Newman-Janis algorithm (Schwarzschild to Kerr metric) [on hold]

my question is how to find the null tetrad for the Schwarzschild metric in Eddington-Finkelstein coordinate? pic 1: I only get the last two values but not able to find the first two tetrad values ...
3
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2answers
106 views

Is this video's notion of general relativity correct? [duplicate]

In this video it explains the path of the apple in the general relativity version of gravity as being a straight line on a curved surface. Is this valid? Edit: this isn't a duplicate of the supposed ...
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2answers
43 views
+50

Two Robertson-Walker observers, at what time will a light signal be received?

Here is a question I have that is inspired by this question here. The spacetime metric of a radiation-filled, spatially flat ($k = 0$) Robertson-Walker universe is given by$$ds^2 = - dT^2 + T[dx^2 + ...
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1answer
53 views

Cosmic Rest Frame

Cosmic Rest Frame is defined in the paper "Adventures in Friedmann cosmology :A detailed expansion of cosmological Friedmann equations" by R Nemiroff and B Patla as the frame at a point where average ...
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0answers
30 views

How does Einstein's curved space time produce acceleration in a free falling object? [duplicate]

I never really thought much about all of this before so I'm definitely a newbie. Please excuse my ignorance. If I understand what I have read so far: if spacetime is curved time would click by at a ...
2
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1answer
43 views

An example of a theory that respects the Weak Equivalence Principle but violates the Einstein Equivalence Principle

The Weak Equivalence Principle has any one of the following forms: the inertial mass is equal to the gravitational mass there exists a preferred class of trajectories through spacetime, known as ...
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1answer
115 views

Torsion-free, symmetric connection and non-coordinate basis

The torsion tensor is defined as (Hawking p.34) \begin{equation} \mathbf{T}(\mathbf{X},\mathbf{Y}) = \nabla_{\mathbf{X}}\mathbf{Y} - \nabla_{\mathbf{Y}}\mathbf{X} - [\mathbf{X},\mathbf{Y}]. ...
1
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1answer
42 views

About periodicity of coordinates given a metric

If I am given a metric how do I decide which coordinate is periodic? Eg. can I look at metric in plane polar coordinates and tell that θ direction is periodic. Also How do I calculate the period of ...
0
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1answer
52 views

Questions about null geodesic [closed]

Show for the null geodesic in 3D flat spacetime using polar coordinates so the line element is $ds^2=-dt^2+dr^2+r^2d\phi^2$. Do light rays move on straight lines? My question is that I only learned ...
2
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1answer
41 views

Energy conservation around a black hole

In the Schwarzschild black hole, the Killing vector "time translation" $k^a$, so that the following quantity is conserved along a geodesic: $$E = -g_{ab}k^au^b = (1 - ...
4
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1answer
61 views

Indicating that indices are equal in Einstein notation

tl;dr: I have an expression like this: (dramatization) $$ R_{\mu\nu} = \begin{pmatrix} B^{00}C_{00} & 0 & 0 & 0 \\ 0 & B^{11}C_{10} & 0 & 0 \\ 0 & 0 & B^{22}C_{20} ...
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0answers
32 views

Difference in time for clock in attic vs clock in cellar [closed]

This question is regarding relativity: Two clocks are stationed in a house, one in the cellar and one it the attic. Which one of the following statements is true? A : The clocks tick at the ...
3
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1answer
47 views

Difference between Fermi and Riemann normal coordinates

What is the difference between Fermi normal coordinates and Riemann normal coordinates? Which one of them is related to the vanishing of the Christoffel symbols?
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2answers
78 views

What is more fundamental: Geometry and Topology or physical matter? [closed]

Since, there is always an interplay between gravity and the fabric of spacetime. I wonder which is more fundamental: Geometry and Topology or physical matter?
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0answers
23 views

Does a black hole ever fully form to an outside observer? [duplicate]

According to general relativity, I had understood that time appears to slow down when looking into high gravitational fields from afar, so that as a black hole forms, the light from a collapsing star ...
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0answers
23 views

Relative motion in particle measurements

I was thinking about measurement of particles at almost-zero energies/temperatures and the movement associated with it. Compared to an observer next to the particle who sees the particle moving at ...
0
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0answers
44 views

Interpretation of black-hole infalling and apparent geometry of the event horizons

Consider a citizen of the cosmos crosses the event horizons of a black hole. For sake of discussion let's suppose is a Kerr black hole, so that his fate is not sealed the moment he crosses. Does at ...
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0answers
13 views

What is the difference in subjective time experienced by an orbiting and stationary observer? [closed]

Two observers start in rockets 1000kms above Earth's north pole. Observer 1 remains stationary relative to Earth, burning fuel to hover in place. Observer 2 is in a circular polar orbit. Both ...
3
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1answer
61 views

What happens if I slowly lower a dangling object into a black hole?

I could've sworn I've seen this question before, but I couldn't find it. Suppose I have an object on the end of a really long string. I can slowly lower it near the event horizon of a black hole, ...
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0answers
32 views

Doubts about Chern-Simons state as a solution of the Hamiltonian constraint in quantum gravity

I've been doing some work with both Baez's Knots, gauge fields and gravity (1) and Gambini, Pullin's Loops, knots, gauge Theories and quantum gravity (2), lately. I have basically two problems: I ...
0
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0answers
15 views

Can the density of a black hole be altered (if at all) by absorption? [closed]

If a black hole is an object of sufficient density that it distorts spacetime, when a black hole absorbs mass, does the dense material that constitutes the black hole become less dense if the absorbed ...
2
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2answers
79 views

Using $\sqrt{-g}$ in integrals of proper volume

I am a little confused over integration using proper volume element. When do we use $\sqrt{-g}$ in calculations? For example, in many calculations involving stars, say when using TOV equation, this ...
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0answers
35 views

Interpreting meaning of coordinates given a metric

I was working problem 3.6 in Carroll's GR textbook and was given the following metric, which is a good approximation to the metric outside the surface of the Earth. $ds^2=-(1+2 \Phi(r))dt^2 + ...
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0answers
36 views

The derivation of the Mass-Energy(including mechanical energy) equivalence principle [duplicate]

(Not duplication! I couldn't find the answer for the general case, instead of the special case that I've already seen in Youtube I hyperlinked.) I will fully satisfy with not only a mathematically ...
1
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0answers
23 views

The mass-energy equivalence is a principle which can not be derived from anything? [duplicate]

Not duplication) I couldn't find the answer for the general case, instead of the special case that I already seen in Youtube I hyperlinked. I will fully satisfy with not only a mathematically ...
1
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1answer
82 views

Simulation of relativistic probe passing through an external solar system

I recently read about the Breakthrough Initiative to launch "StarShot", a nano-probe that is designed to travel to Alpha Centauri at $0.2c$. One of the challenges to be solved involves the precise ...
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2answers
49 views

Does the constancy of the speed of light in vacuum hold for any observer in GR as well?

From SR, we know that the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source. But in GR, does it still hold for all observers? I mean the constancy ...
0
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2answers
126 views

Why would a modern smartphone not work if the theory of general relativity hadn't been discoverd? [on hold]

My teacher told me that todays smartphones wouldn't work if the theory of relativity hadn't been discovered, but he didn't explained why.
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1answer
27 views

How are the frequency and wavelength of electromagnetic waves affected within an event horizon?

I apologize if this has been asked previously or if my thinking is way off base, but I am inexperienced with relativity (and this is my first question on the site). I am wondering; as one (not ...
9
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4answers
160 views

How do we know the Schwarzschild solution contains an object of mass $M$?

The Schwarzschild metric is $$ds^2 = - \left( 1 - \frac{2GM}{r} \right) dt^2 + \left(1-\frac{2GM}{r}\right)^{-1} dr^2 + r^2 d\Omega^2.$$ In Carroll's GR book, it is claimed that $M$ is the mass of the ...
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1answer
60 views

Gravitational wave equations worked out

Is there a website where gravitational wave equations are worked out numerically? I would like to experiment with mass configurations but can't find examples.
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0answers
25 views

Non equilibrium black hole radiating away energy and angular momentum, with total energy and angular momentum conserved

The question refers to whether mass (i.e., energy) and angular momentum can be considered to have been carried away by the gravitational radiation in the hole settling down. And whether those entities ...
6
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2answers
181 views

What manifold is spacetime?

In General Relativity, spacetime is a $4$-dimensional manifold with one Lorentzian metric tensor defined on it. In the Special Relativity case what manifold is spacetime is quite clear: it is ...
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0answers
28 views

What are the effects of relativity on the universe itself? [closed]

I'm obviously not anything like an expert on the subject, but it occurs to me that the relativity of objects or lack thereof would affect the environment around it. Time moves fastest when there is ...
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0answers
29 views

Geodesic tangent vector in a Riemannian 4-space

I am doing a question in Lewis Ryder's introduction to General relativity. I am very close to the answer but not quite there. The question is: A Riemannian 4-space has metric $$ds^2 = ...
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1answer
62 views

On the proof of the existence of geodesics coordinates

From "Introducing Einstein’s Relativity" by Ray D’Inverno page 77-78 In my calculation, the process is $$\frac{\partial{x^{'a}}}{\partial{x^d}}=\frac{\partial{x^{a}}}{\partial{x^d}}+\frac{1}{2} ...