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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4
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2answers
348 views

Age of the universe and the singularity at the Big Bang

Using the standard model of cosmology we calculate the Hubble time to obtain an estimate of the age of the universe. This model assumes a beginning of time in the past. But that point is a true ...
0
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1answer
33 views

Cosmology: collisionless vs collisional fluids?

I try to understand the difference between collisionless and collisional fluids in cosmology. My first question is the following. In the context of FLRW cosmology, we suppose that the Universe can ...
0
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2answers
158 views

Physics in the movie 'INTERSTELLAR'?

have a question , this movie is praised by the scientific accuracy however how the hell does relativity justify that the character can be thrown in black hole and survive ? also if the robot can not ...
1
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1answer
111 views

Why I cannot cross the Einstein-Rosen bridge?

I have been told that no observer can ever cross the wormhole present in the Kruskal-Szekeres coordinates, connecting region 1 and 4 in the Kruskal-Szekeres diagram, usually called Einstein-Rosen ...
1
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0answers
65 views

How does a rotating black hole look like? How would it be to descend into one?

This image from Wikipedia shows how a black hole would look like: A black circle that acts as a gravitational lens for light rays coming from behind. How would a rotating black hole look like? How ...
0
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0answers
40 views

How do you calculate perihelion precession in the general spherically symmetric space time?

I am trying to find the approximate solution of the differential equation obtained for the the motion of massive particle around Riessner-Nordstrom-AdS solution, equation and its solution are given in ...
0
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1answer
73 views

Free-falling from rest into a Kerr black hole

Is it impossible for a particle (with zero angular momentum) to free-fall from rest at infinity into the ergosphere of a Kerr black hole? It seems like it is very easy to show this is the case, but ...
-1
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1answer
41 views

Time dilation and biological changes

I have watched the movie Interstellar and like most of the people who watch it, I was intrigued by the effects of time travel on the astronauts. After reading some articles and watching some videos, I ...
0
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1answer
34 views

Does asymptotically AdS mean as $z \to 0$ or as $z \to \infty$ in Poincare metric of AdS?

The Poincare metric of AdS_3 is given by $ ds^2 = \frac{R^2}{z^2}(dz^2 - dx_0^2 + dx_1^2)$. Using the coordinate transformation $\rho = \log(z)$, we can write this as, $ds^2 = R^2 (d\rho^2 + e^{-2 ...
1
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1answer
54 views

Two spherically symmetric shells of matter collapsing into a black hole

Suppose I have a thin spherically symmetric shell of matter of (rest) mass $M$ that collapses to form a black hole, and later a second thin spherical shell of mass (rest) $M'$, concentric to the ...
1
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1answer
68 views

Equivalence principle for test fields

My question is very simple. We all know that, for a test particle(classical) in a gravitational field, the motion is only determined by the geodesic lines(let's forget about the initial conditions for ...
-1
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3answers
80 views

One-body General Relativity

Does it make sense to talk in General Relativity about only 1 body ? Can you have a universe in which there is only one body and that body is producing a gravitational field ? I'm asking this because ...
0
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2answers
104 views

Could time dilation bend the path of a photon? Does time dilation have a refractive index?

The main question I am getting at is, does time dilation have a refractive index? What I mean is, if I were to shoot a laser past a black hole, would the laser's path "bend" strictly from time ...
1
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0answers
34 views

How can a black hole have a charge? [duplicate]

Under current particle theory, the four fundamental forces use a force-carrying particle. The particle for electromagnetism is the photon. By definition a black hole is a mass from which light can ...
0
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1answer
32 views

If there are any discernible effects of travelling through curved space..?

If one is on a spaceship traveling through a 'very' curved section of space-time, are there experiments one could perform on the ship that would reveal measurable differences between the very curved ...
5
votes
2answers
122 views

What is the experimental evidence that suggests space-time is curved?

Sorry, if this is a stupid question. tl;dr: Skip to the last paragraph for the question. I know curved space-time is one way to express gravity and so far it seems to work well. I still need a lot ...
3
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1answer
124 views

How warped spacetime bends trajectories of light and moving objects?

I fail to see why the light follows something like the blue line and not the green line on the attached image. Figure 1 - light bends around warped spacetime Afaik. something similar happens ...
1
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0answers
25 views

The speed of light sets a lower limit to the rate at which a reference frame can pass through time. Is there anything that sets an upper limit? [duplicate]

Is there any "slowest" velocity that sets a cap on how fast a reference frame passes through time, or can you pass through time infinitely fast given a "slow" enough velocity?
0
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1answer
94 views

What is the smallest amount of neutrinos needed to create a black hole? [duplicate]

Is there some smallest amount of neutrinos needed to create a black hole? Note that this question is not at all the same as the question here If a 1kg mass was accelerated close to the speed of light ...
-5
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2answers
121 views

Both Special and General Relativity carry long term unresolved paradoxes. Should not they now be “inconsistencies”? [closed]

I thought when a theory carries paradoxes, and they go unresolved, eventually they get called inconsistencies and the theory is assumed wrong somewhere. GR doesn't work at distances, say between ...
1
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1answer
65 views

Will the Velocity of an object change if it moves fast,close to speed of light?

If an rocket moves with a speed of 0.5c. So, the speedometer in that rocket will show 0.5c. But there will be time dilation when someone sees it from the earth. Then it's Time dilation will be So, ...
0
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0answers
37 views

Penrose diagram for Schwarzschild metric

Can someone show me a procedure (I mean a complete series of mathematical passages) to derive the Penrose diagram for Schwarzschild metric? I don't want to do that passing through the Kruskal-Szekeres ...
0
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1answer
51 views

Non-pertubative renormalization and correctness of a theory

Even if I start to understand why perturbative renormalization is necessary, I'm not exactly sure why non perturbative renormalization is. After asking the question to several theorists, what I think ...
1
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1answer
50 views

How can gravitational energy cancel out the rest energy of mass in the universe [duplicate]

I've heard that some physicists think that the net energy of the universe is zero. For this to happen, I would assume that the negative gravitational energy of a body ought to cancel out its rest ...
0
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1answer
52 views

Converging light

Imagine that we emit a light pulse. As is the nature of light, it will expand. However, light is affected by gravitational fields and light has its own. Therefore, will the light converge given ...
2
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3answers
59 views

Why is the photon-sphere around a Kerr Black Hole spherical and not ellipsoid?

Kerr Black Holes have usually (excluding extrema $a=0$, $a=1$) due to their spinning activity an ellipsoidal ergosphere. So why does the photon-sphere does not have an ellipsoidal form? ...
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3answers
1k views

Is there a constant/baseline for how fast time passes?

Say we have an object completely unaffected by the effects of gravity/velocity. Is there a way to measure the passing of time for this object? Since time moves slightly slower for us on or near ...
1
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1answer
50 views

Dark energy and exotic states of space-time

So far as I know attempts to detect new particle that responsible for the nature of dark matter/energy are not successful. And there are reasonable explanation for this, like energy levels we can get ...
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0answers
18 views

What are maximally dissipative boundary conditions?

I ran into this term when reading about the initial boundary value problem in general relativity. They seem to be relevant when you need to impose boundary conditions on a timelike boundary, for ...
1
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1answer
57 views

What is the gravitational effect inside a electromagnetic shield due to an external electromagnetic field?

I am new in General Relativity. I know that electromagnetic field (or, the electromagnetic energy tensor, $T^{ik}=1/4\pi[1/4F_{mn}F^{mn}g^{ik}-F^i_lF^{lk}]$) can affect gravitation. Now if we take a ...
2
votes
1answer
109 views

Null geodesic equation

For a null geodesic curve $X^i$, $$0=g_{ij}V^iV^j.$$ When we derive the geodesic equation from E-L equations, will this affine parametrization cause it to blow up? How is it justified to use the ...
4
votes
2answers
102 views

Understanding the AdS/CFT Correspondence [duplicate]

I am beginning to learn about the AdS/CFT correspondence, but I can't find a comprehensive introduction that includes the relevant gravitational/string theory physics. What specific areas of general ...
3
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2answers
132 views

Understanding Mach's principle: What does it answer?

What is the question that Mach tried to address in his principle? I mean, we know how to detect the inertial and non-inertial frames (by Newton’s law). Once this is understood we also see that due to ...
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1answer
50 views

Singularities in the Reissner–Nordström metric

I am doing a presentation on black holes but I'm having trouble finding information on the Reissner–Nordström metric. From the metric ...
1
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3answers
124 views

In general relativity, how do we think of Newton's third law for gravity?

In GR everything become geometric, gravity becomes curvature in spacetime. How do we think of Newton's third law in the context of GR? What corresponds to action and what to reaction?
2
votes
1answer
30 views

Mass Distribution Inside Sphere with Relativity

(Shell Theorem) If a mass is spherically symmetrically distributed within a spherical region, an observer measuring the gravitational pull from that spherical region would not know how the mass is ...
3
votes
1answer
61 views

Is there an algorithm for N body simulations in General Relativity [duplicate]

I am new to general relativity but have a background in computer science. Why is it so hard to do n-body simulations in GR? For example, there could be a program which takes the properties (mass, ...
2
votes
4answers
119 views

Any tips on evaluating Riemann tensor?

I am calculating the Riemann tensor for the Schwarzschild solution. I've calculated all 9 non-vanishing Christoffel symbols already. Now I need to evaluate the Riemann tensor and I find no easy way to ...
0
votes
2answers
58 views

A couple of questions on the ADM formalism in general relativity

I've been reading up on the ADM formalism in general relativity and have been stuck on a couple of concepts. The first is to do with the foliation of spacetime into space-like hypersurfaces. I ...
0
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0answers
34 views

Derivative of time with respect to proper time

When wants to solve the Schwarzschild-Two-Body-Problem with the Runge-Kutta-Method, the second derivative of the time $t$ with respect to the proper time of the moving particle $\tau$ is needed. How ...
0
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0answers
17 views

Diversion of large Earth impactors

I ask"Can a beam of particles at relativistically high speeds be directed 'across the bow'of an object moving toward the Earth in order to use gravity to gradually divert it from its path?"I am ...
0
votes
1answer
36 views

Determinant of the curved space scalar wave operator

I am reading a paper titled 'Analogue Gravity' (http://www.livingreviews.org/lrr-2011-3 or http://arxiv.org/abs/gr-qc/0505065) In the paper (page 15/159) they say this: $$\det(\sqrt{-g} g^{\mu \nu}) ...
22
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2answers
2k views

Layman's explanation and understanding of Einstein's field equations

Most of us have heard of Einstein's amazing equations which describe the universe around us, yet only some of us understand what the equations are actually saying. What are these equations ...
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1answer
124 views

Age of the universe [closed]

Does the fact that the edge of our observable Universe contains information from the beginning of the Universe give us an ability to determine its age? The edge of our observable universe surely has ...
0
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0answers
41 views

Finding inverse tensor operator

For example I have such tensor operator: $$ O^{\mu \nu \alpha \beta} = (a^2+m^2)(\eta^{\mu\nu} \eta^{\alpha\beta} + \eta^{\mu\alpha} \eta^{\nu\beta}) + a^\mu a^\nu \eta^{\alpha\beta} + a^\mu ...
0
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0answers
23 views

References on the 3 body problem

Does anyone know good references for the general 3 body problem? I'm looking for both analytical and numerical approaches.
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1answer
145 views

Why a timelike geodesic maximizes path length?

I'm studying some GR and my book says that in Pseudo-Riemannian manifolds geodesics may even maximize the path locally. That's what happen to the timelike geodesics, for example. My first question: Is ...
0
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2answers
160 views

If you shine a light away from the center of a Schwarzchild black hole, will it stay still?

$$ A $$ Light is travelling away from the absolute center of the Schwarzchild black hole (i.e. none of that spinning/stretching field) at $\ C $, and so shouldn't $\ \Delta C$ need to be greater than ...
2
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0answers
37 views

Maximum Power transmitted using General Relativity waves - cf Schwinger limit

In Electromagnetism, QED says that the linearity of Maxwell's equations comes to an end when field strengths approach the Schwinger limit. Its about 10^18 V/m. What is the corresponding formula for ...
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0answers
73 views

Lagrangian, geodesics and relativity [closed]

My background is in maths, but I have been studying some basic physics with occasional input from a friend who is studying for a physics PhD. Due to my background, I am keen to visualize things ...