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.

learn more… | top users | synonyms (1)

4
votes
3answers
293 views

What would be the implications for current theories if gravitational waves are not detected? [closed]

Let's assume that scientists trying to detect gravitational waves get a huge raise in funding, design even better experiments, and run them for decades, but just can't find any gravitational waves ...
1
vote
0answers
51 views

Analogy of curvature of space with sheet and ball [closed]

Many times people try to explain why mass curves the space with the ball on a sheet but in this analogy, I believe there is so many wrong corespondencies that it is actually a bad one. Implication ...
2
votes
2answers
67 views

Local Lorentz transformations

If $\gamma^m$ denotes a tangent space gamma matrix, and $\gamma^\mu$ denotes a curved space gamma matrix, then they are related by $$\gamma^\mu(x) = \gamma^m e_{m}^{\mu}(x)$$ where $e_{m}^{\mu}(x)$ ...
6
votes
3answers
482 views

“Warp-drive” thought experiment

Why wouldn't this "warp-drive" work? Assuming we can build a flywheel that can survive near light speed and have an onboard power storage or beamed energy that can spin it up to that speed and back ...
0
votes
1answer
60 views

Deriving the motion equation for a minimally-coupled scalar field in general relativity [closed]

From the following Lagrangian $$ L = \sqrt{-g} (R+\epsilon\partial^\mu\phi\partial_\mu\phi) $$ I'm getting the motion equation (for the field $g_{\mu\nu}$ and vaccum)as: $$ R_{\mu\nu} - ...
1
vote
0answers
24 views

Book recommendation for self study of General relativity [duplicate]

I am a second year Chemical Engineering student. However out of interest I wish to learn General theory of relativity. Can anyone please suggest some books for learning this subject?
1
vote
2answers
81 views

How does general relativity explain the impact force after radial inward fall toward Earth?

I understand that, in the context of the Schwarzschild spacetime (General Relativity), a radially inward falling observer follows a time-like geodesic with zero four-acceleration. There are no forces ...
2
votes
1answer
62 views

Universe Expansion - Could galaxies be moving away from each other due to photon bombardment?

We know galaxies are moving apart from each other due to the ability to look at the color shift of those galaxies. The fact that galaxies are moving apart seems to be most-widely attributed to the ...
0
votes
1answer
58 views

Why is spatial conformal infinity a point

One property of spatial infinity is that all spacelike geodesics end at it. Since spacelike geodesics can have different directions, I do not understand why spatial infinity is a point. It looks more ...
0
votes
1answer
80 views

How to get null tetrad by metric?

How to get null tetrads ${l^a,n^a,m^a,\overline{m}^a}$ for this metric? This on is from Ryder's book (Introduction to general relativity) page 268 $g^{\mu\nu}=\begin{pmatrix} 0 & \frac{1}{c} ...
7
votes
1answer
200 views

Homotopy proof of the lack of foliation of the Gödel metric

A common proof of the lack of foliation of the Gödel universe, apparently mostly copy pasted from Hawking and Ellis, goes thusly : A closed timelike curve must cross a spacelike hypersurface ...
6
votes
3answers
263 views

Why does the FLRW metric assume constant curvature?

So the FLRW metric takes the following form in reduced-circumference polar coordinates. $$\mathrm ds^2 = -c^2 \mathrm dt^2 + a^2(t) \left(\frac{\mathrm dr^2}{1 - k\, r^2} + r^2 (\mathrm ...
2
votes
0answers
28 views

How fast can an object spin? [duplicate]

Without any forces in space to stop it, assuming an object does not collide with anything or enters any kind of gravitational pull, how fast could the object spin. I mean the earth spins quite fast, ...
1
vote
0answers
68 views

Can the force of Gravity be used to travel faster than light? [closed]

This question is just an idle curiosity of mine, but after reading the Honor Harrington novels, I was intrigued by the concept of using gravity to surpass light speed. Any thoughts?
3
votes
2answers
150 views

Why is “gravitational” red-shift neglected in galaxy and galaxy cluster scales?

The red-shift of the light of a star in a galaxy or that of a galaxy in a cluster of galaxies is generally interpreted as how fast the star or the galaxy is moving, i.e. it is interpreted in a purely ...
2
votes
0answers
56 views

Full form of the Pauli-Fierz action

In Deser's paper on the fully interacting version of the Pauli Fierz theory, he does a rather simple method of treating the Pauli Fierz equation without going with infinite sums, just by treating the ...
0
votes
0answers
35 views

Local Translation of frame field- Geometric Picture

In order to phrase my question I review my geometrical picture of the first order formulation of gravity: Given some d-dimensional manifold $\mathcal{M}$ one constructs the Frame bundle $FM$, a ...
1
vote
1answer
109 views

Does $g_{\mu\mu}$ in an expression follow the Einstein summation convention?

Assume that I have the expression for a Christoffel symbol: $$ \Gamma^\mu_{\alpha \beta}=\frac{1}{2}g^{\mu \lambda}(\partial_\alpha g_{\beta \lambda}+\partial_\beta g_{\alpha \lambda} - ...
0
votes
0answers
33 views

Solving the Stress-energy-momentum tensor with metric

Let's say I want to find an expression for $T_{00}$ in Einstein field equations given a particular metric. I need to find first $g_{00}$, which is not complicated to find, and $R_{00}$ which is ...
1
vote
2answers
140 views

Einstein field equations and SEM tensor + Alcubierre

I wonder how I can find, using the Einstein field equations, the SEM tensor in a region of space with a function $k(x,y,x)$ that describes the curvature of space in that region at a moment (so it is ...
1
vote
0answers
20 views

Do clocks near the centre of the galaxy run slower than clocks at the edge? [duplicate]

Does an astronaut floating in space near the center of the galaxy, where the mass density is higher (let's ignore the dark matter halo for this example) have a clock that runs slower than an astronaut ...
1
vote
1answer
72 views

Einstein equivalence principle cannot entirely predict gravitational time dilation

The Einstein equivalence principle can be used to derive the gravitational redshift of photons, but it does so in an unusual way. The derivation is as follows. Consider an source of photons on the ...
1
vote
2answers
46 views

How to make gravitational lens visualizing program?

I'm not living in the English-using country, so please understand my bad grammar. I want to make a program which is visualize gravitational lens. I want program give me an image, with metric tensor ...
-1
votes
1answer
57 views

The gravitation field of a “Kerr-Newman electron”? [closed]

Let us imagine a universe with a single electron. Person A observes the electron (from outside this universe, assume it's possible) and it's gravitational field in a certain frame. Furthermore it is ...
0
votes
0answers
39 views

Calculating propagation time along the path of a photon

In this paper $\tau(t) := \int_{t}^{t_d}ds$ is defined as "the propagation time between the detection time, $t_d$, and $t$, as incrementally measured by a set of local observers along the light path". ...
0
votes
0answers
27 views

de Sitter reviews?

I'm very interested in learning more about de Sitter and anti-de Sitter spaces and their applications in GR and cosmology. Can anyone recommend favorite review articles -- or, more likely, a series ...
1
vote
1answer
71 views

Schwarzschild equation physical meaning

When you pass an event horizon of a black hole according to the Schwarzschild equation time and space swap the physical meaning. So you can no longer move away from a black hole, in similar way as you ...
1
vote
2answers
209 views

Why do we never account for the extra mass carried by a gravitationally excited object?

The mass of a bound system is the mass of its part minus the binding energy. For instance if you put an electron and a proton together to form a hydrogen atom you get a $13.6 \text{ eV}$ photon and ...
1
vote
0answers
32 views

Why Black Hole are black? [duplicate]

I found it difficult to understand what behind the story of black hole, I have did some research but have no sense what it meant. This question is really base on my curiosity, I want to learn and ...
0
votes
3answers
127 views

GR: Pseudo Riemannian or Riemannian?

Is General Relativityy described by Pseudo-Riemannian manifold or Riemannian manifold? I cannot understand the vast difference between the two manifolds. In books, General Relativity is looked as a ...
2
votes
0answers
99 views

Undergrad in QFT/GR looking to do string theory Ph.D [closed]

I am currently a third year undergrad in physics who is currently taking QFT and GR. I took these classes just out of pure interest in the subjects but I find that my mind is being blown almost every ...
1
vote
0answers
98 views

Constructing Killing tensors from Killing vectors

Background: After reading about Carter constant and symmetries in GR, I became interested in Killing tensors. I tried reading this paper by Alan Barnes, Brian Edgar and Raffaele Rani, discussing ...
0
votes
0answers
37 views

Is the curvature formed due to mass/volume of spactime convex or concave?

I am really confused about the curvature of space-time. Does it bends in a concave shape in presence of mass/volume as shown by the example of rubber sheet and ball or does it bends in a convex shape? ...
-6
votes
1answer
64 views

How can we see the alien, who are travelling in light speed? [closed]

If aliens has the technology to travel in speed of light ,How can we see them with our 'below the speed of light' technology?. Because when we see that(!),definitely it will not be in its place.Is ...
1
vote
1answer
55 views

Difference between Distance and Space

So I take particle A and place it in space, then I place particle B 1,000,000 light years away from particle A. I strike a line between the two, and measure that line as having a length of 1,000,000 ...
1
vote
2answers
218 views

Confusion about gravity

I understand the “rubber sheet” model of Relativistic gravity is just an illustration, and beyond the initial issues of mixing three dimensional objects with a two dimensional representation of 3D ...
0
votes
0answers
76 views

How general relativity shows that gravity decreases as we go inside the Earth [duplicate]

Why is it that gravity decreases as we go deeper inside Earth? Can anyone explain theoretically with reference to general relativity?
0
votes
1answer
91 views

Infinite distance in finite time

It is shown in a previous thread (AdS Space Boundary and Geodesics) that it's possible for null rays to travel to infinity and back in AdS space in finite coordinate time. That is to say, an observer ...
0
votes
0answers
16 views

Anti de Sitter Motion without matter

I've read that a non zero cosmological constant can lead to "motion without matter" in vacuum spacetimes such as AdS. Initially I didn't understand what the significance of this statement was since I ...
0
votes
1answer
91 views

Accelerated reference frame in Minkowski space vs pure gravitational field

I just finished reading Einstein's "Relativity: The special and the General Theory", and if I understand Einstein correctly, he says that an accelerated reference frame in Minkowski space (i.e., empty ...
1
vote
1answer
217 views

Derivation of one-form/vector equation in Carroll confusion

I don't understand the derivation of Equation 2.14$$\mathrm{d}f\left(\frac{d}{d\lambda}\right)=\frac{df}{d\lambda} \tag{2.14}$$ in Carroll's Lecture Notes on General Relativity ...
2
votes
2answers
453 views

Killing Vectors in Schwarzschild Metric

Given the Schwarzschild metric with $(-,+,+,+)$ signature, $$ds^2=-\left(1-\frac{2M}{r}\right)dt^2+\left(1-\frac{2M}{r}\right)^{-1}+r^2(d\theta^2+\sin^2\theta\,d\phi^2)$$ the lack of dependence of ...
4
votes
2answers
261 views

Typo or not in those GR notes?

Given $$ds^2=-A(r)dt^2+B(r)dr^2+2C(r)drdt+D(r)r^2(d\theta^2+\sin^2d\phi^2),\tag{23.1}$$ we want to eliminate that cross term $2C(r)drdt$ Upon change of variable such that. This can happen upon ...
1
vote
0answers
55 views

Covariant Derivative commutator on a Spinor [closed]

I am trying to prove 8.14 of Supergravity - Freedman. The equation that I am trying to show is $$\gamma^\mu \nabla_\mu \gamma^\nu \nabla_\nu \psi = (g^{\mu\nu}\nabla_\mu \nabla_\nu - ...
1
vote
1answer
69 views

Does a rigid box of gas cool over cosmological timescales?

According to standard cosmology theory the physical momentum $p$ of both massive and massless particles decay like: $$p \propto \frac{1}{a(t)}$$ where $a(t)$ is the scale factor as function of ...
-1
votes
1answer
86 views

Why are Electromagnetism, Strong & Weak Nuclear and Gravitational Forces different?

If they are different then why the only thing that we 'see' in them, and that identifies them, the so called 'force' as we call and see it, is same among them all.
1
vote
1answer
46 views

Accelerating Frame and Gravity

I have recently learned briefly that an accelerating frame is equivalent to a gravitational field in the equivalence principle. I'm sitting on a chair and I am experiencing the force of gravity and ...
2
votes
1answer
82 views

Killing vectors in General Relativity?

I'm looking to derive the surface area of the event horizon of a Schwarzschild black hole. I was just wondering if it were possible for someone to explain to me this: $$ ...
2
votes
2answers
99 views

Observer inside event horizon of an extremely large black hole [duplicate]

Imagine a very large black hole, with a mass equal to a large number of galaxies. Assume a space station is in orbit around the black hole some distance from the event horizon at a point A. An ...
0
votes
1answer
46 views

Gravitational Time Dilation and Schwarzschild Coordinates

So I'm trying to use this equation for the time dilation of an object, but I don't know how to get the distance that I have (in meters) to a radial coordinate in terms of schwarzschild coordinates. ...