A theory that describes how matter produces and responds to 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.

learn more… | top users | synonyms (1)

1
vote
2answers
91 views

Cosmological constant doubts

I have read about cosmological constant given by einstein in universe in nutshell as well as in general and special relativity. But still I am not able to understand the aim to use it or to introduce ...
1
vote
1answer
40 views

Can weakness of gravity explore new dimensions

Since gravitational force is weakest force out of the four fundamental fources at the microscopic level. Is it possible that gravitational force is strong in a particular direction at a new ...
3
votes
0answers
51 views

Why is the Ricci tensor diagonal for isotropic spacetime?

I'm reading Zee's Einstein Gravity in a Nutshell and while calculating the Ricci tensor for FRW spacetime he claims that because the spacelike slices of constant $t$ are rotationally invariant, the ...
0
votes
2answers
39 views

Would an Object Near a Pre-Blackhole Star Experience the Same Gravity as Post-Blackhole?

My question was inspired by this question, which got me thinking. According to Newton's Law of Gravitation, $$F = G\frac{m_1m_2}{r^2},$$ the gravity of an object is inversely proportional to the ...
0
votes
0answers
33 views

How to derive the schwarzchild metric?

I'm having trouble differentiating the following when making a change of co-ordinates to determine the Schwarzchild metric. $$r'^{2}=r^{2}C(r)$$ Then taking the total derivative of both sides, the ...
0
votes
1answer
55 views

The Spin Connection

Why do we need to introduce the spin connection coefficients $\omega_{\mu \space \space b}^{\space \space a} $ in General Relativity? To me, they just look (mathematically) like the Christoffel ...
3
votes
0answers
40 views

Rigid rectangle in Schwarzschild

Say I build a perfect rectangle. Side lengths $l_1$ and $l_2$ and perfect right angles. I am on earth and the metric is given by the Schwarzschild metric. Setting $dt=0$ leads to the spatial ...
-1
votes
1answer
35 views

How to calculate the gravity level at the boundaries of a black hole? [on hold]

Imagine that a body is attracted to a black hole and it has a mass $M$, if the body is moving with $v=.99c$, will its speed and mass affect the gravity relation between the body and the black hole? or ...
0
votes
1answer
67 views

Metric for infinite straight cosmic string

A string theory question on my general relativity problem set: Metric is given as $$\mathrm{d}s^2 = -A(r)\mathrm{d}t^2 + B(r)\mathrm{d}r^2 + r^2 \mathrm{d}\theta^2.$$ a) Solve the vacuum equations ...
4
votes
2answers
96 views

What is the notion of a spatial angle in general relativity?

Is there a notion of spatial angles in general relativity? Example: The world line of a photon is given by $x^{\mu}(\lambda)$. Suppose it flies into my lab where I have a mirror. I align the mirror ...
4
votes
0answers
52 views

The difference between The Dilaton and The Radion?

I have read this question on the Dilaton, but I am a little confused with the distinction between the Dilaton and the Radion. I definitely have the feeling that these two scalar fields are different ...
14
votes
2answers
1k views

Wouldn't angular momentum of a binary star system decrease?

Consider a binary star system, as these stars go around one another they would emit gravitational waves. Since, the graviton is a spin 2 particle. Wouldn't the angular momentum of the stars decrease? ...
-1
votes
0answers
44 views

Non-commuting vector multiplication in GR

If the tensors of GR were composed of non-commuting vector multiplications, this would at least in spirit bring GR closer to QM. Has this approach been attempted?
4
votes
2answers
353 views

Why gravity is a spin-2 field? How can I read the spin from Einstein-Hilbert action?

I have often heard that the gravitational field has spin $2$. How can I read the spin of the field from the Einstein-Hilbert action $$S=\int \! \mathrm{d}^4x \,\sqrt{|g|} \, \mathcal{R} \, \, \, ?$$
0
votes
0answers
15 views

Instabilities in the CDMT

Could anyone explain or refer to references on why the CDMT f(R) gravity model suffers from Instabilities any why the sign of ${\mu}^{4}$ matters.
0
votes
0answers
29 views

Can you discern the cause of a time shift? [closed]

Einstein points out that it is impossible ( with out knowing you are on a rocket) to tell whether you are experiencing gravity due to a different position in a gravitational field, or if you are in a ...
0
votes
1answer
47 views

How to calculate spatial distance in space-time?

Pinning two test particles at two different points in space, how can I calculate their spatial distance, when the geometry is given by the Schwarzschild metric? Let's say particle 1 is pinned at ...
1
vote
2answers
73 views

Stress-energy-momentum tensor

In Wald's General Relativity, he writes on pg 61 For an observer with 4-velocity $v^a$, the component $T_{ab}v^a v^b$ is interpreted as the energy density, i.e. the mass-energy per unit volume, as ...
0
votes
0answers
42 views

Does non-matter energy curve spacetime? [duplicate]

I know that matter (mass) curves spacetime, but do other forms of energy do the same? I.e. is matter the only form of energy that curves spacetime?
0
votes
1answer
69 views

Quantum entanglement [closed]

I've been reading articles about Quantum mechanics (for a sci-fi project of mine) - especially Quantum entanglement. The measurements of physical properties of the entangled particles are correlated, ...
0
votes
1answer
26 views

Calculating Hubble Radius using relativistic effects

I am trying to calculate the Hubble Radius, or the distance from which an object will recede from an observer at the speed of light. I initially tried using $v=H_0d$ which gives $d=1.424\times10^{26}$ ...
0
votes
1answer
48 views

Covariant derivative of a vanishing tensor component [closed]

Is the covariant derivative of a vanishing tensor component necessarily zero?
-2
votes
4answers
90 views

A question about moving and time dilation

I was thinking that if you are in empty space with another person (with no other objects around), and from a distance you see that the other person is approaching you a constant speed, you wouldn't ...
0
votes
0answers
44 views

What is the theory behind Anti Gravity field? [closed]

Can any one explain what is the theory behind anti gravity fields? Tell me a way to simulate that effect!
0
votes
1answer
73 views

Geodesic devation on a two sphere

So the geodesic deviation equation gives the relative acceleration between two geodesics in motion. But given a pair of geodesic (let's say on the two sphere) that start at the equator, separated by ...
0
votes
1answer
47 views

velocity in inertial and nontial frames

I got confused about the difference between the last term of both pictures. In the first one, we have w x r, but in the second we have w x r underlined. Does anyone have a better explanation? They ...
1
vote
0answers
45 views

Riemann curvature tensor in first order perturbation theory as a Lie derivative of Riemann curvature tensor in zero order

I am having a difficulty solving my homework so I was hoping I could get some help, so here it is. It is about gravitational waves and first order gravitational perturbation theory, I have to prove ...
0
votes
1answer
32 views

Does the universal expansion affect the gravitational constant?

If the universe was not expanding, would gravity be stronger? since the expansion happens everywhere and can overcome gravity at long distances? If not, then are there any changes that would happen to ...
1
vote
0answers
45 views

Can a magnet or a magnetic field push gravity? [closed]

I have been asking around at my school and at the high school and at EWU but no one can answer this question: can a magnet or a magnetic field push gravity?
2
votes
4answers
145 views

Can we think of gravity as space itself moving?

So if you move through space with a constant acceleration you experience longer time dilation than when you're at rest, but you also experience the same time dilation when you're under the effect of ...
1
vote
0answers
41 views

SPEED of LIGHT as photons reach black holes [duplicate]

As photons reach a black hole and begin fall in - is their speed increased as they go down (like a vacuum cleaner does to dust).
1
vote
0answers
37 views

General covariance and global Poincaré algebras

Reading an article (page 7) I read this: Just as ordinary general covariance may be regarded as the local gauge symmetry corresponding to the global Poincare algebra and local gauge invariance ...
3
votes
1answer
55 views

Field equations in extended EH-GHY action. Is Schwarzschild a solution?

When taking the EH action, $$S_{EH} = \frac{1}{16\pi G}\int_M d^4x \sqrt{-g}R$$ and making a small variation in the metric while ignoring boundary terms, we obtain $$\delta S_{EH} = \frac{1}{16\pi ...
1
vote
1answer
74 views

Is the Hilbert-Felber model of repulsive gravity correct?

This theory states that at relative velocities exceeding 3^-0.5 c, gravitational repulsion ensues. The relevant papers are on arXiv by Franklin Felber. Here's one of them ...
1
vote
1answer
41 views

Poincaré symmetry and linearized gravity

When working with linearized gravity, is Poincaré symetry assumed to be the symmetry of space-time?
0
votes
3answers
61 views

Speed of light originating from a star with gravitational pull close to black-hole strength?

Imagine you have a star which is on the brink of turning into a black hole. Lets say it is infinitely close to become a black hole, but not there yet. Since there is no event horizon, but a great ...
3
votes
2answers
117 views

Hilbert action's invariance under general coordinate changes

In an article, when considering invariance of the Hilbert action under a general coordinate change this formula appears for how the metric changes ...
3
votes
3answers
107 views

Local Lorentz invariance or local Poincaré invariance?

Fast question. I know that the group of all the isometries in Minkowski's space-time is the Poincaré group that is just Lorentz's group (rotations and boosts) and translations in space-time. Now, ...
2
votes
1answer
55 views

Null Geodesics in Einstein Universe

I am currently taking a course in General Relativity, and I've hit a bit of a roadblock with a homework assignment. We are given the metric for Einstein's universe to be (forgive me, this is meant to ...
0
votes
4answers
335 views

At which point of the universe $R_{\mu \nu}=0$ if there is a source of gravitation (point mass)

Schwarschild found his solution to Einstein's field equations for vacuum ($T_{\mu \nu}=0$) by placing a point-mass in the center of origin. Since the Ricci tensor $R_{\mu \nu}$ and the Einstein ...
1
vote
1answer
82 views

The source of gravitation in a spacetime without matter

In a discussion concerning: Physical meaning of non-trivial solutions of vacuum Einstein's field equations there were a number of answers claiming that the flatness of the Ricci space (Rµv=0) ...
0
votes
1answer
35 views

Would gravity on the surface of a planet which is being consumed by a black hole change?

Assuming that the black hole starts grow in the exact center of the planet and that the general structure of the planet does not degrade as it is eaten from the inside, would the gravity on the ...
1
vote
0answers
58 views

What if UV behaviour of gravity was perturbative?

I understand that the UV behaviour of gravity ought to be dominated by black hole production and that graviton-graviton scattering ought to blow up above the Planck scale. Suppose, however, that ...
1
vote
0answers
41 views

Are there 'special' cases for when special relativity can be applied for accelerating bodies?

I have the following theoretical situation: A space station modeled as a ring in free space is rotating about its centre point at a high speed. I am trying to work out where time flows slower. From ...
12
votes
7answers
685 views

Is it foolish to distinguish between covariant and contravariant vectors?

A vector space is a set whose elements satisfy certain axioms. Now there are physical entities that satisfy these properties, which may not be arrows. A co-ordinate transformation is linear map from a ...
0
votes
1answer
58 views

How does a black hole slow time? [duplicate]

I've been reading about black holes, and I keep coming across the fact that time runs slower near a them. My questions are: Does this mean that if you left Earth at age 30 and spent 30 years near the ...
2
votes
0answers
56 views

What transformation is the metric of general relativity invariant under?

My limited understanding of metrics comes from Cartan. From there, I understand that a metric is something invariant under certain transformations, e.g. Lorentz in special relativity. But with the ...
1
vote
1answer
54 views

Where is Strong Equivalence Principle stronger than Weak Equivalence Principle

In my note, the two equivalence principles are stated as follows Weak Equivalence Principle: Gravitational and inertial masses are equal. Strong Equivalence Principle: There is no observable ...
1
vote
2answers
48 views

Direction of future time cone inside Schwarzschild horizon

Following is the picture copied from enter link description here, illustrating the future time cone inside the Schwarzschild horizon. My question is, on the left side of $r=2M$, why must the time ...
1
vote
0answers
26 views

Metric to describe an expanding spacetime from coordinates reflecting the perspective of a local observer

The FLRW metric describes the metric expansion of spacetime from the perspective of comoving coordinates. Given the way this metric is usually formulated, comoving distances stay constant, and the ...