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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Do light waves precisely follow null geodesic paths in General Relativity?

In special relativity one may show that a plane wave solution of Maxwell's equations (in a vacuum), of the form $A^a=C^a\mathrm{e}^{\mathrm{i}\psi}$ has the following properties: The normal ...
1
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1answer
82 views

How did inflation lead to the expansion of space?

Big bang Theory gives a scientific explanation of the evolution of the Universe, where the scientific picture of it starts with Universe(space) uniformly filled with matter and energy, already ...
0
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2answers
72 views

For a giving metric in GR, how do we learn which observer the metric refer to?

For example, I have been told the Schwarzschild observer is far away from blackhole and events,(namely, I think, the observer is static at infinity of the coordinate.) And the second example,the ...
8
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1answer
356 views

Simple quadrupole field not yet in Lorenz gauge?

I'm having trouble reproducing some of the results regarding gravitational waves in the Wald's General Relativity. In section 4.4 of gravitational radiation, eq.4.4.49 shows the far-field generated ...
6
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1answer
112 views

A question about gravity [duplicate]

Some time ago I encouraged by 11 year old son to watch Cosmos: A Spacetime Odyssey with Neil DeGrasse Tyson, and subsequently Cosmos: A personal Voyage with Carl Sagan, as well as other astronomy ...
3
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1answer
50 views

How does time look relatively in a gravity well? [duplicate]

Relativistically, when two frames, say A & B are moving apart inertially, then the clock of B will look slow compared to that of A; and the same holds for the clock of A from B. What does the ...
4
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0answers
61 views

How does Lorentz Contraction apply to the edge of a spinning disk and is Pi still constant?

This may seem like a dumb question, as I'm not really a physicist, but here it goes. So, π (3.14...) is the number of diameter distances required to equal the circumference of a 2D disk. Relativity ...
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3answers
89 views

Relativity: A modification on Sea Tower experiment

I first read about it on A Brief History of Time(Stephen Hawking). In 1962, a relativity experiment was executed: identical (classical) watches put on a water tower, one is on very high, other one is ...
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0answers
28 views

Guesses from a Rindler observer

Suppose an observer travels through Minkowski space $M=\mathbb{R}^4=\left\{x_0,x_1,x_2,x_3\right\}$ on a uniformly accelerated path: \begin{equation} \begin{cases} x_0= R \sinh(\frac{\tau}{R}) \\ x_1= ...
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1answer
130 views

Is this picture of relativity correct? [closed]

Can forces be said to exist in a real sense in general relativity?
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2answers
119 views

Coordinate Singularity in Metric

Suppose I have some metric $$ds^2=g(t)dt^2+\frac{1}{r}dr^2$$ which has a singularity at $r=0$. However, if I make the coordinate transformation $u=\frac{1}{r}$, then I get: $$ds^2=g(t)dt^2+r^3 ...
0
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1answer
61 views

Launching of artificial satellites [closed]

Whose theory is used today during launching of artificial satellites, Newton's or Einstein's or any other? Which theory is better in launching of artificial satellites and other orbiting bodies, ...
3
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1answer
181 views

Unbounded perturbed geometry due to analiticity

I have an interesting mystery for you, loosely inspired on work related with this question. I have a certain Ansatz for a gravitational wave perturbation of the metric $h_{\mu \nu}$ that is nonzero ...
0
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1answer
55 views

Possible inconsistency of mixed index tensor notation

I am posting this here, because in my experience, this sort of thing exists in physics-related works only. Given a local frame $\{e_{(i)}\}$ on some $n$-dimensional manifold $M$, and given a local ...
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0answers
54 views

Is the equivalence principle Machian?

There is a lot of discussion on the subject of Mach's principle, and whether it has any place in the theory of relativity. But it seems to me that one could argue that Mach's principle is at the heart ...
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0answers
47 views

Understanding Vaidya metric and pure radiation stress-energy tensor

I am following Vaidya metric and how it is related to pure radiation from Wikipedia. But when it reaches the line where stress-energy tensor is equated to product of two four-vectors, I cannot follow ...
0
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0answers
52 views

Transforming to the Transverse-Traceless gauge

I have a certain Ansatz for a gravitational wave perturbation of the metric $h_{\mu \nu}$ that is nonzero in a compact set of background flat Minkowski spacetime But the Ansatz field does not satisfy ...
1
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2answers
123 views

Classical physics in curved space

I'm trying to learn General Relativity. As a stepping-stone between classic (Newtonian) physics and complete relativity, imagine a universe where space is curved, but time is perfectly flat. Also, the ...
0
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2answers
48 views

Travel by Earth rotation [closed]

why we can't go outside the atmosphere and travel with earth rotation .. and can we travel in the opposite direction of atmosphere by the same speed of atmosphere it’s moving at about 1,000 miles an ...
0
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1answer
50 views

spin representations and polynomials

I'm reading Group Theory and General Relativity by Moshe Carmeli and his discussion of spin representations of SU(2) and the isomorphism to the space of homogenous polynomials is confusing me. I'll ...
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4answers
119 views

What does “the fabric of space and time” actually mean? [closed]

I've heard the term "the fabric of space and time" in both physics and science fiction, and although I know it has something to do with general relativity, I don't understand what, specifically, ...
0
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0answers
35 views

Spherically Symmetric Metric in Nordstrom gravity

Nordstrom's theory of gravity postulates that the metric is of the form $g_{\mu \nu} = \phi ^2 (x) \eta_{\mu \nu}.$ The field equations, in vacuum are of the form $R=0$, where $R$ is the Ricci ...
0
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1answer
37 views

Perfect fluid and EM tensor in rest frame

I see that we use perfect fluid which is characterized by a energy density and isotropic pressure for general forms of matter. When guessing the values of energy momentum tensor indices we can use ...
3
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1answer
79 views

Is it possible to tell which way a Universe is spinning?

Imagine a Universe spinning on the x-axis. So there is a centripetal directed away from the x-axis. According to General Relativity this is entirely equivalent to a non-spinning Universe with a ...
0
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1answer
42 views

How to obtain the four-velocity of a fluid from the metric?

Let's say I'm working with a metric tensor for some spacetime with components $g_{\alpha \beta}$ relative to some coordinates $(\tau, x, y, z)$. Is there a general way of obtaining the four-velocity ...
4
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2answers
78 views

Mountains and their local effects on Earth's gravity

I was once a truck driver and can feel the inertia and kinetic energy on heavy loads while traveling. While climbing mountains in the Rockies I noticed gravity was different on the side of the ...
0
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1answer
69 views

Looking for a reference for $\gamma_a e^{a}_{\mu} D^\mu \gamma_b e^{b}_{\nu} D^\nu =D^\mu D_\mu - \tfrac{1}{4}R$

I am having trouble finding references for the following identities: Dirac Operator: $$ \gamma_a e^{a}_{\mu} D^\mu \gamma_b e^{b}_{\nu} D^\nu =D^\mu D_\mu - \tfrac{1}{4}R \tag{1} $$ QED Operator: $$ ...
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3answers
116 views

What happens 'inside' the event horizon of a black hole, in particular to photon speed

This is a follow-up question to two answers given here and here, where the speed in different coordinate systems is discussed when approaching the Schwarzschild radius. To cite, derived directly from ...
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0answers
26 views

Definition of vacuum and occupation number in expanding Universe

Suppose for simplicity we have theory of free quantum scalar field in expanding Universe (metric plays the role of background field) $g_{\mu \nu} = \text{diag}(1, -a^2,-a^2,-a^2)$, where $a(t) \sim ...
0
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1answer
41 views

Leading order approximation of Proper Radial Distance in General Relativity

Context: I'm currently going through this article (http://arxiv.org/pdf/0704.2667v1.pdf). In the 3rd page last paragraph the variable corresponding to the proper distance $y = ...
3
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0answers
56 views

Would quantum fluctuations cause problems for scalar-field inflation?

Wheeler once said that spacetime would be highly curved at very small scales because of the uncertainty principle for energy-momentum. In which case the spacetime becomes very bumpy and not smooth ...
0
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1answer
53 views

Time dilation at the Innermost Stable Circular Orbit

According to general relativity the time dilation is given by following formular: $d \tau = \sqrt{g_{\mu \nu} \dot{x^{\mu}} \dot{x^{\nu}}}$ If I'm interestet in the time dilation at the ISCO I set ...
0
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1answer
64 views

Gravity: Why Do things fall to Earth? [duplicate]

If gravity is in reality spacetime geometry why when I drop an object on the surface of the Earth does it fall to the ground? Does spacetime push it?
0
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1answer
55 views

Exact meaning of radial coordinate of the Schwarzschild metric

In this answer as well as on Wikipedia the radial coordinate of the Schwarzschild metric is described as follows: ...the r co-ordinate is the value you get by dividing the circumference of the ...
0
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0answers
56 views

Is there something similar to Gauss's Law For Gravity in General Relativity?

In Newtonian Physics there is an equation that for the Gravitational Flux of an object known as Gauss's Law For Gravity. Gauss's Law for Gravity describes the number of Gravitational Field Lines ...
0
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2answers
81 views

Age of universe?

Well relativity teaches us that time interval between two events is a frame dependent quantity, then how can we say that our universe is 13.8 billion years old? Should it not depend on who is asking ...
5
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0answers
77 views

I don't see that general relativity is really needed for GPS to work correctly [duplicate]

From what I understand, GPS localization is based on the difference in the reception time from the time of emission of a signal from different GPS satellites whose positions are known. For this we ...
2
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4answers
236 views

Confusion about the concept of cosmological horizon

This question was inspired by this one By definition we cannot see any event happening beyond the cosmological horizon. Let us assume that the expansion rate of the universe is such that the radius ...
9
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5answers
939 views

How does “curved space” explain gravitational attraction? [duplicate]

They say that gravity is technically not a real force and that it's caused by objects traveling a straight path through curved space, and that space becomes curved by mass, giving the illusion of a ...
1
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2answers
105 views

Should dark matter play an important role in designing a quantum theory of gravity?

Since dark matter "accounts" for most of the matter of the universe, and its effect are inferred from the gravitational effects, should it play an important role in designing an unified theory between ...
0
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0answers
26 views

String spreading?

What is 'string spreading' (in the context of string theory)? Does it have implications for the observability of post-classical effective field theory of gravity terms near macroscopic black hole ...
4
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4answers
192 views

Relation of General Relativity to Dark Matter and Dark Energy

I was reading an elementary book on dark matter (in fact, a historical perspective) and there were mentioned how the scientific community react to the idea of dark matter proposed as a solution to ...
2
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1answer
55 views

What does Kaluza-Klein theory say about the attraction/repulsion of opposite/same charges?

Since Kaluza-Klein theory is made out of general relativity - a gravitational theory in 4 dimensions which is only attractive, then how does it takes into account the attraction/repulsion of ...
1
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4answers
136 views

Which tensor describes curvature in 4D spacetime?

I heard these two statements which don't work together (in my mind): In 4D spacetime the curvature is encoded within the Riemann tensor. He holds all the information about curvature in spacetime. ...
-2
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4answers
222 views

Why is “dark matter” theory accepted? Why wasn't general relativity rejected?

Dark matter was made up to account for unexplained effects such as gravitational lensing, the speed of expansion of the universe, or the rate of rotation of certain galaxies. However, as Feynman ...
1
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1answer
138 views

Null geodesic equations

If one is constrained to the $xt$ plane, one can define the intersection with that plane of the null hypersurfaces originating at some point $P$ as $$ g_{tt} \frac{d P^t}{d \lambda}\frac{d P^t}{d ...
0
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0answers
31 views

Can gravity affect light speed? [duplicate]

Can gravity affect light speed, for example slow it down ?
0
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0answers
48 views

Questions arising from the presentation of “Schild's ladder” in “Gravitation” (Misner, Thorne, Wheeler)

MTW, p. 248, presents a description of "Schild's ladder" construction which I quote here extensively enough for referencing some subsequent questions. A. Transport any sufficiently short stretch ...
0
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0answers
38 views

How is speed of light constant if it bends? [duplicate]

Gravitational lensing causes light to be bent.If light changes direction how can it be travelling with constant speed?Where am I wrong.Thanks for any help.
2
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1answer
98 views

Spacetime curvature effect on chemistry

Do current chemistry / astrophysics / stellar chemistry calculations include the effects of the curvature of spacetime on chemical reactions? For example, the heat transfer from a point closer to the ...