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)

0
votes
0answers
72 views

Topology of a black hole

How many dimensions are theorized for a black hole, in view of the fact that black holes are not observed directly.
1
vote
0answers
44 views

For gravitational wave from twin stars, how was the tidal effect counted?

As the primary indirect evidence, the work on calculating the rotational slow down earned the 1993 Nobel prize. However, I cannot find any where mention how the work deal with the tidal effect. Are ...
3
votes
1answer
284 views

Is dark energy around a black hole locally curved?

The repartition of dark energy in the vacuum is homogeneous all over the universe. The diagram below represents space with a black hole in the middle. The square is divided in small unit squares. If ...
0
votes
1answer
59 views

What are the differences between special and general relativity? [duplicate]

What are the differences between special relativity and general relativity? I am looking for a naive, non-mathematical explanation.
2
votes
1answer
606 views

Why does the Ricci tensor vanishes in Schwarzschild metric? [duplicate]

If the Schwarzschild metric is suppose to describe the behaviour of a spherical object in flat space, so the Schwarzschild is different from the flat metric because it describes curved space so why ...
0
votes
1answer
18 views

Replacing the flat part of ads metric with another flat metric.

In the poincare co-ordinate representation metric of the ads space has a flat part that corresponds to the minkowski metric. Can one show that this flat part can be replaced by other metric that ...
0
votes
0answers
79 views

If gravitational field has negative energy density, how does gravitational radiation carry positive energy?

The following question uses the analogy between EM (electromagnetism) and GM (gravitomagnetism). In order to force two like electric charges nearby, some work has to be done. This implies that the ...
4
votes
1answer
157 views

Is it, and if so, why, impossible to build perpetual motion machines (PMMs) in GR?

I am wondering about this. I have heard that in General Relativity (GR), the energy in a space-time may not be well-defined. If that is the case, then it would seem "conservation of energy" would not ...
0
votes
1answer
64 views

Wondering about Energy [duplicate]

Me and Energy I'm trying to move along with my study of non-advanced physics but not grasping what energy really is, is driving me nuts. Whenever i see anything about energy ( Kinetic, ...
0
votes
0answers
39 views

Available material on Giant Gravitons

I am looking for a pedagogical introduction to giant gravitons (if one exists!). I have basic string theory/SUSY knowledge but no introduction to AdS/CFT. (Do I need to do some reading on AdS/CFT ...
1
vote
0answers
120 views

Quadratic order perturbation terms in the expansion of Ricci tensor [closed]

I want to expand Einstein-Hilbert action for the metric $$ g_{\mu \nu} = \eta_{\mu \nu} + h_{\mu \nu} $$ up to quadratic order in $h_{\mu \nu}$. For this purpose I need to calculate the Ricci tensor ...
5
votes
2answers
369 views

Evidence for electrodynamics in curved spacetime

Field theories in curved spacetime is usually formulated by integrating their Lagrangian over the curved spacetime. For example, for electrodynamics, we have the action $$ S = \int d^4x \left( ...
1
vote
2answers
188 views

Is there an accepted axiomatic approach to general relativity?

I am reading Steven Weinberg's book Gravitation and Cosmology. He makes a big deal out of the equivalence principle and showed a bunch of deductions you can make based on it. This surprised me since ...
4
votes
1answer
118 views

Eddington-Finkelstein coordinates: Why $\ln(r-2m)$ instead of $\ln|r-2m|$?

If one considers the Schwarzschild metric $$ \text d s^2 = -V(r)\text d t^2 + \frac{1}{V(r)}\text d r^2 + r^2 \text d \Omega^2\;,\qquad V(r) = 1-\frac{2m}{r}\;, $$ and introduces the ...
0
votes
0answers
43 views

Klein Gordon equation in de-sitter spacetime with time dependent Hubble parameter

If i try to solve Klein-Gordon equation for a scalar field in de-sitter background, the usual method is to transform to conformal spacetime : $$ds^2 = -dt^2 + e^{Ht}\bf{dx}^2$$ $$=>ds^2 = ...
0
votes
0answers
58 views

Would an Alcubierre drive actually allow FTL travel? [duplicate]

If I do not phrase this question right, please forgive me in advance because I am a layman on the subject of physics, but a software engineer, nonetheless. I do understand many technical subjects. ...
0
votes
0answers
101 views

Propagator for massless spin 2 particle

In my quantum field theory class, we saw ad derived the propagator for both spin-0 and spin-1 particles, massless and massive. I am curious to know what the propagator looks like for a spin-2 ...
1
vote
1answer
136 views

Inertial and Non-inertial frames of reference

I'm really beginner in physics and I recently started to study the concept of frames of reference, inertial and non-inertial ones. In the end, I thought I had understood it: frames of reference ...
0
votes
1answer
72 views

Confusion about Weinberg's discussion of equivalence principle. Help understanding formula

I am reading Steven Weinberg's book Gravitation and Cosmology. On pages 67-68, he begins his discussion of the Principle of Equivalence of Gravitation and Indertia by saying the following: The ...
0
votes
2answers
64 views

Hermitian Metric and Geodesics

Why isn't general relativity developed with a Hermitian metric and a theory of complex valued paths and geodesics? The concept of arc length and geodesic suffers under a pseudo-Riemannian metric. My ...
2
votes
2answers
147 views

Recommendation on books with problems for general relativity?

I am reading Sean Carroll's book on GR and have read the first two chapters, which are on manifolds and differential geometry. However, there are only 12 problems for both chapters. In fact, there ...
0
votes
1answer
51 views

Invariance of the low energy effective string action

It is well known that the action of General Relativity $$S = \frac{1}{16\pi G}\int R\;\sqrt{-g} d^D X$$ is invariant under "diffeomorphisms". The low energy effective action for bosonic strings is ...
0
votes
0answers
22 views

Measuring speed of an object relative to what? [duplicate]

I understand that everything in the universe is moving through spacetime and the spacetime vector is equal for all the objects. So if If something is moving at speed of light, the mass of it is zero ...
0
votes
0answers
25 views

Will the center of mass of the whole system change when object swims on curved surface?

In the example given here, the object can move on the frictionless surface of the sphere by changing its shape periodically. So will the center of mass of the whole system change after the object ...
2
votes
0answers
135 views

Is Energy attracted to Energy?

Newton taught us that bodies with mass attract each other according to the universal law of gravitation (mass-mass attraction) and Einstein taught us that mass and energy are equivalent though his ...
2
votes
1answer
121 views

Doubt regarding stress-energy tensor definition

I'm having some trouble understanding the following definition of the stress energy tensor: $T^{\mu\nu}$ is the flux of four-momentum $p^{\mu}$ across a surface of constant $x^{\nu}$. Here's an ...
3
votes
3answers
285 views

It's established that universal energy is not constant. But is the net change positive or negative?

Dark energy is density is constant and that's something like 75% of the universe, so I am pretty sure that the net change must be positive. But photons redshift and so loose energy. I assume other ...
1
vote
0answers
68 views

What is static mass increase effect predicted by General relativity?

According to wikipedia, static mass increase is predicted by Einstein's General Relativity. In the book 'The Meaning of Relativity' by Einstein, inertia will increase when the object is near a ...
1
vote
0answers
33 views

Is energy-momentum of curvature a boundary/holographic density?

Since the beginnings of General Relativity, we have had this awkward, unholy separation of the universe in marble versus wood. divergence of the stress-energy momentum holds at all points of ...
1
vote
0answers
64 views

Does the curvature of spacetime by gravity affect homogeneity and isotropy of the space of the universe?

The FLRW metric starts with the assumption of homogeneity and isotropy of space.(Wikipedia) FLRW metrics of the universe have no or only very weak curvature - It is curved space. In contrast, ...
1
vote
2answers
117 views

Gravity: Is there curved space besides curved spacetime?

Wikipedia: Curved spaces play an essential role in General Relativity where gravity is often visualized as curved space. Is the Wikipedia article "curved space" talking about curved space or ...
0
votes
0answers
76 views

Penrose diagram (Reissner-Nordstrom metric)

I try to derive the Penrose diagram for the Reissner-Nordstrom metric $$ \text d s^2 = -\frac{(r-r_+)(r-r_-)}{r^2}\text d t^2 + \frac{r^2}{(r-r_+)(r-r_-)}\text d r^2 + r^2 \text d \Omega^2\;,\qquad ...
1
vote
0answers
33 views

Assigning an asymptotic power to the volume form?

I was reading about the covariant theory of asymptotic symmetries in this review: http://arxiv.org/abs/hep-th/0111246 I have a question about eq. (1.8), but before I ask I should describe what the ...
36
votes
5answers
7k views

Shine a beam of light horizontally, drop a stone from same height - would both hit the ground at the same time?

If a beam of light was shone horizontally, and simultaneously a stone was dropped from the same height, would they both hit the ground a the same time? Of course on Earth they would not, but let's ...
2
votes
1answer
184 views

Are the Jacobi equation and the geodesic deviation equation related?

On page 111 in his book Riemannian Geometry, Manfredo Do Carmo states what he calls the Jacobi equation \begin{equation} \frac{D^2J}{dt^2} + R(\gamma'(t),J(t))\gamma'(t) = 0 \end{equation} ...
1
vote
1answer
88 views

Stress-Energy Tensor Integral Identity [closed]

I'm attempting to work a problem in Schutz's A First Course in General Relativity, and I'm running into something curious with tensor indices. The problem states: Use the Identity ...
1
vote
1answer
85 views

White Hole Formation [duplicate]

How does a white hole form in nature if it were to exist? No knowledge of general relativity or advanced mathematics but doing a researching a physics project and need a basic explanation.
1
vote
2answers
239 views

What am I missing in this thought experiment about a black hole?

I've got a problem setting up a general relativity (GR) thought experiment. Thanks for your help! I'm the observer, in a lab that is falling through the event horizon of a black hole, observing a ...
0
votes
1answer
59 views

Definition of “nonlinear” in the context of perturbation of gravity

What exactly is the definition of a nonlinear perturbation when applied to a background spacetime metric? I have seen so called "linear perturbations" which look like $$ds^2 = -(1+2\Phi)dt^2 ...
3
votes
3answers
769 views

Are quantum mechanics and general relativity predictions of string theory, or were they built into the theory from the start?

Are quantum mechanics and general relativity predictions of string theory, or were they built into the theory from the start? If the former, why aren't tests of GR and QM considered simultaneous tests ...
2
votes
1answer
136 views

Spin connection and covariant derivative

How to prove explicitly (i.e., to don't postulate it) that by including Lorentz indices $a$ the covariant derivative $D_{\mu}$ looks like $$ D_{\mu}A^{\nu a} = \partial_{\mu}A^{\nu a} + ...
0
votes
1answer
83 views

Hawking radiation (black hole evaporation) [duplicate]

I understand that one of the simplified ways of looking at Hawking radiation is a pair of virtual particles close to the event horizon (but outside of it). The particle with negative energy falls into ...
1
vote
1answer
109 views

Question on Einstein's derivation of the equation of the geodesic line?

While reading one of the original paper on general relativity written by Albert Einstein, titled the foundations of general relativity, I came across the following passage in pages 167-168, or pages ...
0
votes
1answer
81 views

What does this Hodge dual symbol $\star_3$ mean?

We know that in this $$\star {f(...)}$$ the $\star$ represents the Hodge dual. But in this: $\star_3 f(...)$ what does specifically the $\star_3$ symbol mean?
1
vote
1answer
84 views

How much of General relativity follows from the invariance of $c$ and an escape velocity?

Just supposing Einstein hadn't come up with his idea of the equivalence principle, leaving him blind for a while. Would he still have been able to come up with General Relativity just using the ...
0
votes
1answer
47 views

Schwarzschild Solution Convention

In looking at the components of the Schwarzschild Metric, one finds $ g_{00} = (1 - \frac{r_s}{r})c^2 $. Wikipedia states that $r$ is measured as the circumference, divided by $2π$, of a sphere ...
0
votes
1answer
67 views

Can a free falling observer localize the event horizon by calculations?

I'm think that in general relativity we can always pass the one curve in one coordinate system for another coordinate system. My intuition say that the free falling observer locate the event horizon ...
10
votes
4answers
708 views

Can a metric in General Relativity, Supergravity, String Theory, etc., be asymmetric?

Why is it that all problems I encountered until now have metrics that when represented in a matrix form turn out to be symmetric? Aren't there asymmetric matrices representing some metrics?
0
votes
1answer
56 views

Duality and 1 forms

If a Killing vector is equal to: $$X= -\frac{1}{\sqrt{2}}\partial _t + \frac{\alpha}{\sqrt{2}}\partial_1.$$ But as far as I know is that the dual of a vector is a 1-form, so can I represent that ...
5
votes
3answers
600 views

Is it correct to say that falling object are standing still?

As I was browsing youtube I came across the BBC video "Brian Cox visits the world's biggest vacuum chamber - Human Universe: Episode 4 Preview - BBC Two" He drops a bowling ball and a feather in a ...