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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15
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2answers
933 views

Is spacetime flat inside a spherical shell?

In a perfectly symmetrical spherical hollow shell, there is a null net gravitational force according to Newton, since in his theory the force is exactly inversely proportional to the square of the ...
2
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1answer
111 views
6
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1answer
63 views

Post-Minkowskian expansion of some quantities in Post-Newtonian theory

I'm studying Post-Newtonian theory on the book "Gravity" by Poisson and Will and I found a few formulas that I can't obtain by myself. I'm pretty sure it must be quite simple, but can't find the right ...
3
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1answer
116 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 ...
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0answers
60 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
45 views

Proof of Schwarzschild metric construction (O'neill chap 13)

I am struggling with a few steps of the proof in O'neill book $\textit{Semi-Riemannian Geometry, with applications to Relativity}$ on the construction of Schwarzschild's metric (chap13, Lemma1). Is ...
2
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3answers
91 views

Milky Way galaxy central black hole and time contraction of life story

We know that life is almost 4 billion years old on Earth. We also know that time contracts as we approach the event horizon of the massive black hole at the center of the Milky Way galaxy. Now the ...
0
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1answer
32 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 ...
4
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2answers
335 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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2answers
132 views

why do x Schwarzschild radii equal time dilation effects of speed of light going y times faster than an object^2?

let me walk you through the math. First you start with the gravitational time dilation formula where: $$ T_1=T\sqrt{1-\frac{2GM}{rc^2}} $$ and rather than entering $r$ for the radius we replace $r$ ...
0
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2answers
142 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 ...
2
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2answers
256 views

Visualizing GR spacetime distortion in 1+1D spacetime instead of 2D space

Usually spacetime distortion due to mass in GR is visualized as a rubber sheet distorted under some massive object, like this: source or as shown in this link. But what has always bothered me is ...
0
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0answers
34 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
95 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 ...
6
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1answer
332 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 ...
0
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1answer
29 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 ...
8
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1answer
103 views

Role of the canonical ensemble and electric charge in AdS/CFT

If we consider a charged black hole in AdS spacetime, we can either do thermodynamics in the grand canonical or the canonical ensemble. In the former, we fix the electrostatic potential ...
1
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3answers
119 views

How strong must gravity be to stretch time?

I'm not sure if this is true or not but I heard that gravity has the ability to stretch time, and I was wandering if this is true. If so, how intense/powerful does the gravitational force have to be ...
0
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0answers
44 views

What level of mathematics would I need to understand the physics of a black hole? [duplicate]

I recently went to go see the movie Interstellar and was awed by the visualizations of the wormhole and the black hole Gargantua. I read that noted physicist Kip Thorne was a consulting producer on ...
0
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1answer
91 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 ...
6
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1answer
146 views

Non-trivial scalar quantity

Is there any scalar quantity made of only the Christoffel symbols, determinant of a metric and tensors, not derivatives? In other words, can we construct a scalar quantity which cannot be written in ...
0
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1answer
63 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
52 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
297 views

Questions about MTW's “thousand” tests of the Einstein principle

In Misner, Thorne, Wheeler (henceforth written as "MTW"), "Gravitation", Box 16.4, there's an experimental setup construction (or method) presented by which "Each geodesic clock is constructed and ...
-2
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1answer
34 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 ...
1
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1answer
66 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 ...
0
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2answers
96 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 ...
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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 ...
-8
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1answer
100 views

humans travelling at the speed of light [closed]

Could it be possible for us humans to travel at or faster than c, if we introduced magnets to cancel out inertia as we travelled at this speed on our bodies? Based on light particles and atomic ...
1
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0answers
32 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 ...
18
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4answers
1k views

Detection of the Electric Charge of a Black Hole

By the "No Hair Theorem", three quantities "define" a black hole; Mass, Angular Momentum, and Charge. The first is easy enough to determine, look at the radius of the event horizon and you can use the ...
0
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1answer
30 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 ...
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
107 views

What is the covariant basis around a Schwarzschild black hole?

First of all, I'm not interested in time for this question. So lets consider a 3-manifold whose metric is the spatial part of the Schwarzschild metric, so it has the event horizon and the singularity ...
-5
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2answers
120 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 ...
3
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1answer
312 views

Gravity's Rainbow

What is it? I've seen it in context of a few research papers such as Absence of black holes at LHC due to gravity's rainbow and Thermodynamics of black holes in gravity’s rainbow formalisms My best ...
1
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1answer
62 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, ...
1
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1answer
112 views

$U(1)$ 5-dimensional Kaluza-Klein topological defects

Five-dimensional Kaluza-Klein theory is well-known to predict that the electromagnetic field can be described as a curled additional dimension over four-dimensional spacetime. That is, you only need ...
1
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3answers
111 views

How can we define a frame of reference in general relativity?

I have started reading general relativity. (A First Course in General Relativity, Bernard Schutz). I am finding very hard to understand a frame of reference. When I was reading special relativity ...
1
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1answer
74 views

using tetrads to glue local currents into global currents

According to John Baez it is possible to take a locally conserved tensor $\nabla_\mu\: T^{\mu\nu}(x)=0\ \ \ \ \ \mbox{(locally)}$ and convert it to a globally conserved tensor by "patching" ...
1
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1answer
45 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 ...
2
votes
3answers
51 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? ...
9
votes
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 ...
0
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0answers
32 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
43 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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5answers
156 views

A ball in the gravity potential field of a black hole — seems a paradox

As illustrated in the following diagram (A, B, C, D are 4 specified space points, and C is close to a black hole), a small ball at distance of a black hole is stationary (suppose now it's mass is m0) ...
1
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1answer
46 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 ...
3
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2answers
79 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 ...
2
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2answers
617 views

Time Reversal in a Black Hole

I had a lively discussion with a person about black holes recently, and was making the point about gravitational acceleration in GR being paralleled by speed in SR. One thing that I know people talk ...
0
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0answers
13 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 ...