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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Are the principles of space-time homogeneity and Isotropy independent of one another?

Einstein in deriving the Lorentz transformations, used the principles of space-time homogeneity and Isotropy. Does space-time isotropy follow from space-time homogeneity or are they completely ...
6
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1answer
78 views

does the background spacetime of a black hole affects its thermodynamic properties?

The question is this: will the thermodynamic properties of a black hole (Hawking radiation spectra and temperature, entropy, area, etc.) depend if the black hole sits in a DeSitter or an Anti-DeSitter ...
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2answers
615 views

Does a charged or rotating black hole change the genus of spacetime?

For a Reissner–Nordström or Kerr black hole there is an analytic continuation through the event horizon and back out. Assuming this is physically meaningful (various site members hereabouts think ...
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3answers
417 views

Could metric expansion create holes, or cavities in the fabric of spacetime?

Is it possible for metric expansion to create holes, or cavities in the fabric of spacetime? According to the Schwarzschild metric, the metric expansion of space around a black hole goes to infinity ...
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2answers
421 views

Space-time geometry and metric

I am confused in one question in general relativity, why we can always express a space-time geometry only by metric. It means a metric, which is just about distance in tangent space, can tell us all ...
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2answers
317 views

Is this closed time-like curve in a Godel universe a “circle”?

Would the observer moving along the circle in this Godel space-time diagram feel fictitious forces as though he is accelerating along a circular path or would he simply arrive at an earlier point in ...
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0answers
79 views

Why don't black holes have magnetic hair? [duplicate]

Possible Duplicate: What happens to an embedded magnetic field when a black hole is formed from rotating charged dust? It is well stablished that the only hair a black hole can have is: ...
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1answer
396 views

How does a warp field interferometer work?

Assume I have a solid grasp of undergraduate physics. From what I've read the warp field interferometer is supposed to be a sort of Michelson interferometer, except instead of adjusting the ...
8
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1answer
251 views

Would warp bubbles emit gravitational Cerenkov radiation in general relativity?

Inspired by the gravtiomagnetic analogy, I would expect that just as a charged tachyon would emit normal (electromagetic) Cerenkov radiation, any mass-carrying warp drive would emit gravitational ...
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2answers
1k views

What happens to orbits at small radii in general relativity?

I know that (most) elliptic orbits precess due to the math of general relativity, like this: source: http://en.wikipedia.org/wiki/Two-body_problem_in_general_relativity I also know that something ...
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4answers
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To which extent is general relativity a gauge theory?

In quantum mechanics, we know that a change of frame -- a gauge transform -- leaves the probability of an outcome measurement invariant (well, the square modulus of the wave-function, i.e. the ...
4
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1answer
222 views

What's the deal with the gyroscope?

In this article ("The problem with physics", Tony Rothman, ABC science) the author says in the 5$^\textrm{th}$ paragraph: For example, one needs only first-semester equations to describe ...
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1answer
167 views

Why is energy-momentum 4-vector so much easier to explore/observe than spacetime 4-vector

I have read that spacetime 4-vector is quite difficult to observe/explore and that energy-momentum 4-vector is much more appropriate for CERN etc. Why is that? Could anyone give me a brief ...
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1answer
618 views

Can a deformable object “swim” in curved space-time? [duplicate]

Possible Duplicate: Swimming in Spacetime - apparent conserved quantity violation It is well known that a deformable object can perform a finite rotation in space by performing deformations ...
8
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1answer
284 views

Materials with different gravitomagnetic permeability?

If you start with general relativity, and assume small perturbations around a nearly flat metric, it is possible to obtain linearized equations of gravity that look a lot like Maxwell's equations, ...
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1answer
118 views

GR limit with massless particles and strong fields

What the mechanics arises if to take limit of general relativity with massless particles interacting with strong fields? Suppose there a system of attracting particles that have zero rest mass. What ...
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2answers
346 views

Does General Relativity encompass Special Relativity?

Can all of the predictions made in Special Relativity (SR) also be made in General Relativity (GR)?
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4answers
1k views

What is background independence and how important is it?

What is background independence and how important is it? In order to be a theory of everything, will the final string-theory/m-theory have to be background independent? Does the current lack of ...
8
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2answers
531 views

Wavefunction collapse and gravity

If gravity can be thought of as both a wave (the gravitational wave, as predicted to exist by Albert Einstein and certain calculations) and a particle (the graviton), would it make sense to apply ...
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2answers
1k views

Do black holes have infinite areas and volumes?

How to calculate the area / volume of a black hole? Is there a corresponding mathematical function such as rotating $1/x$ around the $x$-axis or likewise to find the volume?
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3answers
672 views

Action for a point particle in a curved spacetime

Is this action for a point particle in a curved spacetime correct? $$\mathcal S =-Mc \int ds = -Mc \int_{\xi_0}^{\xi_1}\sqrt{g_{\mu\nu}(x)\frac{dx^\mu(\xi)}{d\xi} \frac{dx^\nu(\xi)}{d\xi}} \ \ d\xi$$
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0answers
187 views

Can Parallel Transport always move a Vector Parallel to Itself?

Consider two tiny plane(flat) surfaces A and B meeting at a straight line L.We have a preassigned vector on A at some point P on it.Is it always possible to have a vector parallel to the first one ...
7
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1answer
141 views

Kerr solution for finite collapse time

The Kerr black hole solutions gives an analytic continuation that is asymptotically flat. Some people have argued that this is another universe, but others state that the analytic continuation ...
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1answer
249 views

observable quantities are gauge invariant?

I have a simply question, that is whether spatial velocity is gauge invariant. It is seems that under a infinitesimal coordinate transformation the velocity is just transform as other vectors, and it ...
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0answers
75 views

transition between extremal and nonextremal black hole states

Extremal black holes are at zero temperature, hence they do not radiate. my question is twofold: 1) is extremality of micro black holes a stable property? electric charge is quickly emitted from ...
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1answer
568 views

On Parallel Transport

Let's consider the issue of parallel transport in relation to the figure on the following Wikipedia link: http://en.wikipedia.org/wiki/Parallel_transport With reference to the Figure on the link: ...
6
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1answer
376 views

Alcubierre warp bubble effect on gravity and space

I read the question Faster-than-light communication using Alcubierre warp drive metric around a single qubit?, and these questions came to mind: What kind of impact would an Alcubierre warp bubble ...
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270 views

Cosmology questions from a novice

These ideas/questions probably represent a lack of understanding on my part, but here they are: 1) Cosmologists talk about the increasing speed of expansion of the universe and talk of dark energy as ...
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2answers
491 views

What is the consequence of “infinite” gravitational force?

Introduction I am a mathematically minded individual. I do not intuitively comprehend physics, and as a sophomore in high school who has only taken Intro to Physics in his freshman year, I may very ...
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2answers
777 views

is there a way to split a black hole?

Classically, black holes can merge, becoming a single black hole with an horizon area greater than the sum of both merged components. Is it thermodynamically / statistically possible to split a black ...
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3answers
809 views

Mechanism for the gravitational field generated by photons

This question follows from a schooling I received in this thread. I figured that photons do not interact with gravity, except when they've spontaneously converted into a particle-antiparticle pair. ...
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2answers
622 views

Newton's third law and General relativity

Is Newton's third law valid at the General Relativity? Newton's second law, the force exerted by body 2 on body 1 is: $$F_{12}$$ The force exerted by body 1 on body 2 is: $$F_{21}$$ According to ...
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3answers
875 views

How do the Einstein's differential equation of the curvature of spacetime come out of Einstein's field equation?

The classical theory of spacetime geometry that we call gravity consists of the Einstein equation, which relates the curvature of spacetime to the distribution of matter and energy in spacetime. ...
3
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1answer
143 views

An issue about the compactness and the existence of CTCs

There is a well known fact that a compact spacetime necessarily contains a closed timelike curve (CTC). Proof can be found in several books on GR (e.g. Hawking, Ellis, Proposition 6.4.2), and in ...
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1answer
919 views

Potential Energy in General Relativity

I often hear about how general relativity is very complicated because of all forms of energy are considered, including gravitation's own gravitational binding energy. I have two questions: In ...
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2answers
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Can we have a black hole without a singularity?

Assuming we have a sufficiently small and massive object such that it's escape velocity is greater than the speed of light, isn't this a black hole? It has an event horizon that light cannot escape, ...
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5answers
951 views

General relativity and the microscopic/macroscopic distinction

Here is Wikipedia's diagram of the stress-energy tensor in general relativity: I notice that all of its elements are what would be termed "macroscopic" quantities in thermodynamics. That is, in ...
4
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1answer
1k views

How do Einstein's field equations come out of string theory?

The classical theory of spacetime geometry that we call gravity is described at its core by the Einstein field equations, which relate the curvature of spacetime to the distribution of matter and ...
17
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1answer
2k views

Is String Theory formulated in flat or curved spacetime?

String Theory is formulated in 10 or 11 (or 26?) dimensions where it is assumed that all of the space dimensions except for 3 (large) space dimensions and 1 time dimension are a compact manifold with ...
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0answers
63 views

What is (or where can I discover) the Burke Potential?

I have very much enjoyed William L. Burke's Applied Differential Geometry. Reading around on the web it seems that he discovered something which is called the (retarded) Burke Potential, but I have ...
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2answers
366 views

Are the intersections of past and future light cones spacelike?

Given a timelike reference worldline (not necessarily geodesic), we can define light-cone coordinates $\tau^+$ and $\tau^-$ so that the 3-D hypersurfaces of constant $\tau^+$ are past light cones of ...
3
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1answer
619 views

Problem with convergent geodesics at 2D sphere

There is a chapter on general relativity in the book Spacetime Physics Introduction To Special Relativity by Taylor and Wheeler, which qualitatively explains how attractive gravitational force can be ...
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1answer
194 views

Information faster-than-light and GR vs. QM

What is meant by the statement that information cannot travel faster than light? If I write down something on a paper, isn't there according to QM a non-zero probability that an identical paper can ...
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1answer
253 views

Way to escape from a black hole

I’ve had a question on WHY a traveler couldn’t “escape” from a black hole under specific conditions (I have an image I'd like to send to clarify, but the website won't let me)> The key is for the ...
16
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0answers
511 views

Positivity of Total Gravitational Energy in GR

I read the following statement in the introduction to an article: Over the last 30 years, one of the greatest achievements in classical general relativity has certainly been the proof of the ...
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1answer
375 views

Where did Karl Schwarzschild derived his solution?

Does anyone know more about circumstances of Karl Schwarzschild at the Russian front in 1915 where he allegedly derived his famous solution of the Einstein equations (describing a black hole)? Sources ...
4
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3answers
678 views

Vacuum energy and perpetual motion

The part of the Einstein equations of general relativity referred to vacuum energy, introduce a repulsive term in gravity. This means that as the space become bigger and bigger, vacuum part become ...
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4answers
178 views

How do black holes accrete mass?

Thanks to time dilation, a distant observer watching a man fall in to a black hole will only see him asymptotically approach the event horizon. So how do black holes ever get bigger?
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1answer
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Tiling hexagons on a sphere surface

In attemopt to understand basic principles of non-Euclidean geometry and its relation to physical space, I am reading General Relativity by Ben Crowell. On page 149 there is a discussion of hexagons ...
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2answers
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Another faster-than-light question

Imagine we have something very heavy (i.e supermassive black hole) and some object that we can throw with 0.999999 speed of light (i.e proton). We are throwing our particle in the direction of hole. ...