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.
3
votes
2answers
497 views
Value of the Hubble constant over time
There is something I don't understand about the Hubble "constant" H, as it seems to clump two concepts together that I can't quite unify in my head. On the one side, we have
V = D * H
which means ...
1
vote
0answers
174 views
The structure of space-time
I came across this paper recently called The Small Scale Structure of Spacetime and the following idea occured to me:
To uninformed humans the universe appears Euclidean but we know from GR that on a ...
6
votes
4answers
259 views
Velocity Time Dilation
In Wikipedia article about time dilation, it says:
"Hafele and Keating, in 1971, flew caesium atomic clocks east and west around the Earth in commercial airliners...the moving clocks were expected ...
2
votes
1answer
212 views
Vanishing Ricci flow on a curved manifold
If I understand this right the Ricci flow on a compact manifold given by
$\partial g_{\mu \nu} = - 2R_{\mu \nu} + \frac{2}{n}\!R_{\alpha}^{\alpha} \,g_{\mu \nu}$
tends to expand negatively curved ...
1
vote
2answers
197 views
Is it necessary to embed a 4D surface in 5D space?
Lets consider the line element:
$$ds^2=dr^2+r^2[d\theta^2+\sin^2\theta d\phi^2]$$
There are three variables r,theta and phi.
If we use a surface constraint like r=constant the number of
independent ...
-1
votes
1answer
130 views
Law of conservation of energy at the space.? [closed]
Energy can neither be created nor be destroyed,
if energy disappear in one form it will reappear in another form without any loss.
so what will happen if FAN switched on in the space. ?
1.Electrical ...
1
vote
2answers
176 views
curvature tensor component capable of doing work on $T_{\mu \nu}$
I'm wondering what part of the curvature tensor is able to do work (and hence transfer energy) in matter. I'm wondering if this tensor: http://en.wikipedia.org/wiki/Stress-energy-momentum_pseudotensor ...
4
votes
1answer
448 views
Lagrangian for Relativistic Dust derivation questions
In most GR textbooks, one derives the stress energy tensor for relativistic dust:
$$
T_{\mu\nu} = \rho v_\mu v_\nu
$$
And then one puts this on the right hand side of the Einstein's equations. I ...
2
votes
1answer
128 views
Dark matter and mass-energy conservation
I have been thinking recently about dark matter, and it lead me to the following question.
Consider a hypothetical particle which, like the photon, is chargless and massless. However, unlike the ...
2
votes
2answers
1k views
What is the affine parameter for null geodesic?
For time-like geodesic, the affine parameter is the proper time $\tau$ or its linear transform, and the geodesic equation is
...
2
votes
2answers
287 views
Theoretical basis for black hole evaporation
What is the basis for black hole evaporation?
I understand that Hawking-radiation is emitted at the event horizon, a theoretical result originating in General Relativity and Quantum Field Theory, but ...
6
votes
4answers
657 views
Is there a fundamental reason why gravitational mass is the same as inertial mass?
The principle of equivalence - that, locally, you can't distinguish between a uniform gravitational field and a noninertial frame accelerating in the sense opposite to the gravitational field - is ...
-3
votes
2answers
230 views
Local Charts in General Relativity
We may consider a "local" region in curved spacetime (local in respect of the spatial and the temporal coordinates). A "local inertial frame" may be constructed by some transformation that produces ...
1
vote
1answer
116 views
Violation of Lorentz symmetry on cosmological distances
This question is about the domain of validity of Lorentz symmetry.
As far as I know, general relativity is a generalization of special relativity. Does that mean that Lorentz symmetry is violated on ...
1
vote
1answer
126 views
On BE and FD Statistics
Lets consider the Bose-Einstein and Fermi-Dirac statistics:
Bose-Einstein statistics:
$$\langle n_i\rangle = \frac{1}{\exp{[(\epsilon_i-\mu)/kT]} - 1}$$
Fermi-Dirac statistics:
$$\langle ...
2
votes
1answer
171 views
Laws of physics and general relativity
I'm reading that general relativity let's us describe physics from the point of view of both inertial and accelerated observers. What does that actually mean in terms of doing actual physics? For ...
1
vote
2answers
396 views
Is 4-velocity normalized to -1 even for non-geodesic timelike curves?
In Hartle's General Relativity book ("Gravity"), one of the problems (chapter 8 problem 6) is to prove that $g_{\mu\nu}u^\mu u^\nu$ is conserved along geodesics (really not hard to show), where ...
2
votes
0answers
113 views
Intuitively, what is the source term of the Einstein field equation? [duplicate]
My copy of Feynman's "Six Not-So-Easy Pieces" has an interesting introduction by Roger Penrose. In that introduction (copyright 1997 according to the copyright page), Penrose complains that Feynman's ...
2
votes
1answer
165 views
What determine whether the dynamical equations are tensor equations or vector equations?
Newton's 2nd law which is central to Newtonian dynamics, is a vector equation
$\sum\textbf{F}_{external}=m\textbf{a}$
Same with Maxwell's equations in the covariant form.
On the other hand, ...
4
votes
2answers
453 views
Critics of Mannheim's Conformal Gravity Theory?
I'm looking for more articles/reactions/critiques/support for Philip Mannheim's recent conformal gravity theory.
See here: http://arxiv.org/abs/1101.2186v1
Any ideas on where to start?
1
vote
1answer
150 views
Can a super-extremal charged black hole be made out of electrons only?
In a previous Question it was argued that it would be impossible to add enough charge to a black hole to make it pass the extremal black hole limit since adding charge would increase the mass of the ...
1
vote
1answer
613 views
Neutrino unaffected by gravity
Are neutrinos affected by gravity?
If not, could that be a plausible reason for a neutrino taking a shorter path than light, since light is affected by gravity?
3
votes
1answer
177 views
Could a ship equipped with Alcubierre drive theoretically escape from a black hole?
Also could it reach parts of the universe that are receding faster than the speed of light from us?
3
votes
2answers
239 views
Pressure Inside an Ideal Gas
A non-relativistic ideal gas exerts a pressure at the surface of its container
$p = \frac13 \rho \langle v^2 \rangle$
where $\rho$ is the mass density of the gas and $\langle v^2 \rangle$ is the ...
4
votes
1answer
303 views
How does an object falling into a plain Schwarschild black hole appear from near the black hole?
I know that when viewed from infinity (or from a very large distance from the black hole event horizon), an object that falls into the black hole will appear to slow down and will become more and more ...
5
votes
1answer
146 views
Gravitational lensing from an extended body Vs. a point mass
I am interested in gravitational lensing caused by a cluster of galaxies (say it has a diameter of 1 Mpc and mass of $10^{12}$ solar masses). How close must a light travel as it passes by to be ...
18
votes
5answers
658 views
Should a neutron fall faster than a proton?
If you drop a proton and a neutron in a gravitational field, they both fall, but the proton has a charge and accelerating charges radiate energy, so that leaves less kinetic energy for the proton and ...
1
vote
2answers
148 views
Understanding difficulty with proving strong cosmic censorship theorems
I want to get a grip about the technical problems related to proving Penrose conjecture
Intuitively, it seems it should not be too difficult; just start by classifying it in 0-dimensional (i.e: ...
2
votes
1answer
457 views
Schwarzschild black hole geometry in Novikov coordinates
As I am a layman in gravitation I would really appreciate any suggestions on how to approach and tackle the following problem:
Choose a time-symmetric 3-geometry for the initial geometry of ...
1
vote
2answers
252 views
Apple falls for which of these 2 reasons?
Needles to say I am a visitor here. I do not belong to the science world;)
But I have read both of these things before:
Apple falls to the ground because curved spacetime pushes it there (same ...
2
votes
1answer
201 views
Spacetime assumptions at OPERA
I would like to know what are the assumptions about the spacetime metric between the neutrinos emiter and detector, I mean, perhaps (just a stab in the dark) could be a mistake to asume the metric of ...
5
votes
2answers
215 views
Schwarzschild metric
Why, if the Schwarzschild metric is a vacuum solution ($T_{\mu\nu}=0$) , do textbooks state that $T=\rho c^{2}$ when approximating Poisson's Equation from the Einstein Field Equations?
Thank you.
3
votes
1answer
167 views
Is General Relativity applicable for all coordinate systems?
My understanding was that relativistic physics can be expressed in any inertial coordinate system, but not arbitrary systems. That is, no experiment can determine if we are "still" or "moving" at a ...
4
votes
2answers
202 views
Introduction to relativity books for an engineer [duplicate]
Possible Duplicate:
Getting started general relativity
I am an engineer who loves to read science fiction books especially when there's more science than fiction but usually I see that I ...
3
votes
1answer
236 views
Why is Dirac Lagrangian in Curved Spacetime Weyl Invariant?
Are there any references on the Weyl invariance of the Dirac Lagragian in general spacetime?
Thanks a lot!
15
votes
3answers
2k views
What is the physical meaning of the connection and the curvature tensor?
Regarding general relativity:
What is the physical meaning of the Christoffel symbol ($\Gamma^i_{\ jk}$)?
What are the (preferably physical) differences between the Riemann curvature tensor ($R^i_{\ ...
1
vote
0answers
119 views
Trying to understand the weak gravitational field metric (3)
I've worked through Carroll's explanation of the Newtonian limit as far as $h_{00}=-2\phi$ (page 106 - Lecture Notes on General Relativity). As he's previously stated that ...
5
votes
1answer
237 views
Trying to understand the weak gravitational field metric (1)
In Carroll's online Lecture Notes on General Relativity (p112) he says, "the weakness of the gravitational field allows us to decompose the metric into the Minkowski form plus a small perturbation"
...
2
votes
1answer
143 views
Trying to understand the weak gravitational field metric (2)
I'm still struggling with Carroll's discussion of the Newtonian Limit. I'm hoping no one will mind if I ask several questions here as they all relate to the same section (pages 105-106) of his ...
3
votes
2answers
296 views
Singularities and quantized space time
Discrete space time quanta would solve the problems of infinite densities for singularities in General Relativity and Quantum Gravity by imposing a non zero limit on the minimum radius of black holes. ...
1
vote
2answers
288 views
How long did inflation take to happen?
If inflation happened, it ended about 13.7 billion years ago. But how long was inflation going on before that? Was it just a short burst of time so that it's really okay to say that the age of the ...
1
vote
0answers
88 views
Knowledge needed to study and understand general and special relativity theory [duplicate]
Possible Duplicate:
What are the prerequisites to studying general relativity?
I'am 27 now and i have a burning desire to study math and physics from the ground up and I strongly prefer ...
4
votes
0answers
99 views
K3 gravitational instanton
Could you please recommend a sufficiently elementary introduction to K3 gravitational instanton in general relativity and the problem of finding its explicit form?
Under 'sufficiently elementary' I ...
4
votes
2answers
394 views
Positive Mass Theorem and Geodesic Deviation
This is a thought I had a while ago, and I was wondering if it was satisfactory as a physicist's proof of the positive mass theorem.
The positive mass theorem was proven by Schoen and Yau using ...
1
vote
1answer
125 views
General relativity at 0K
Relativistic gravity affects particle in motion, does it affect particle that are resting too? How? and if not could one say that the matter at 0K is not affected by gravity?
I'm not a physicist; is ...
2
votes
2answers
1k views
Ricci scalar for a diagonal metric tensor.
I was wondering if there is a general formula for calculating Ricci scalar for any diagonal n by n metric tensor?
4
votes
2answers
329 views
Can a black hole be formed by radiation?
I'm trying to find out if black holes could be created by focusing enough light into a small enough volume.
So far I have found (any or all may be incorrect):
Maxwell's equations are linear, ...
3
votes
2answers
429 views
What role does electrical charge play in black holes?
Not having studied General Relativity, I have sometimes been puzzled by references to the behaviour for "classic" black holes — as they are popularly portrayed — as being true for black ...
-1
votes
1answer
198 views
How to bend 3d space embededd in a 4d enviornment? [duplicate]
Possible Duplicate:
Calculating position in space assuming general relativity
I recently started to program a 4 dimensional visualization program.
I have the 4 dimension space perspectively ...
13
votes
5answers
689 views
Does GR provide a maximum electric field limit?
Does GR provide a limit to the maximum electric field?
I've gotten conflicting information regarding this, and am quite confused. I will try to quote exactly when possible so as not to confuse ...
