Tagged Questions

60 views

How does gravity's space time distortion access energy to induce freefall? [on hold]

An observer, standing on top of a building, has a gravity switch (use your imagination) which allows him to turn gravity on and off. He turns the switch off, then releases a pool ball over the edge ...
74 views

Gravity of the accelerated particle in General relativity?

Suppose heavy particle or body ("billiard ball") is accelerated with very thin and very rigid (not absolutely rigid) rod of infinitesimal (not zero) mass ("cue stick") Acceleration is constant in ...
62 views

How to prove the energy of gravity in general relativity is non-local?

Every textbook in general relativity containing the energy of gravity all says that the energy of gravity is non-local and every energy-momemtum density received is pseudo-tensor, but "having not ...
46 views

Recommendation on ADM mass and Bondi mass

I want to learn some advanced topics in GR, such as ADM 4-momentum and Bondi 4-momentum. However nearly no textbooks on GR contain this area, such as Wald, MTW, Hawking, Carroll and Zee's. Can anyone ...
135 views

How do objects even move due to gravity?

I am an newbie general relativistic learner and I learnt that gravity is bending of space-time and since objects move in straight-lines but since its curved they follow curved movement through space ...
47 views

Graviton polarization in higher dimensions

It's not difficult to see that the graviton in $D$ spacetime dimensions has $(D-3)D/2$ polarizations. In $D=4$ there are two $\epsilon^{\pm}_{\mu\nu}$. What I find curious is that in $D=4$ I can ...
47 views

Is the spacetime generated by isolated system always asymptotically flat?

I read a saying in wiki of asymptotically flat spacetime http://en.wikipedia.org/wiki/Asymptotically_flat_spacetime "In general relativity, an asymptotically flat vacuum solution models the exterior ...
89 views

Why does time slow down the closer you are to a mass?

When ever i look this up all I get is sites saying how its because general relativity says "-" why does it do it though? it is because there is more motion near gravity than further away? Or is it ...
52 views

Gravity in spacetime

Can the effect of gravity in spacetime be thought of as if nearby particles have a tendency to "align" their four velocity direction? I.e. "to point in the same direction".
84 views

Invariant interval and gravity

Gravity is inversely proportional to the distance between objects. Do we use Euclidean distance or the invariant interval for that distance? Using the invariant interval makes everything a bit more ...
347 views

Speed of light in general relativity

My question has a few parts concerning the speed of light in general relativity. Firstly, time changes in response to gravity and speed. Therefore, as gravity effects time in an area of space, should ...
111 views

How does the gravity well change as space expands? [duplicate]

How does the gravity well change as space expands? If we assume that the Earth's gravitational field curves flat space to create a gravity well then how does the gravity well change as space expands ...
109 views

How exactly and WHY does matter affect space-time? [closed]

According to general relativity, inertial mass and gravitational mass are the same, and all accelerated reference frames (such as a uniformly rotating reference frame with its proper time dilation) ...
161 views

What makes General Relativity conformal variant?

I have a question regarding the well known fact that General Relativity is not a conformal invariant theory or to put it in other words about the fact that it is conformal variant: What are the ...
56 views

Tidal forces in free fall

Would a body free falling in a gravitational field which has a gradient large enough that it would affect the free falling body 'feel' the effect of the tidal forces on it. I'm curious because would ...
97 views

Speed of light versus pull of gravity - Is $c$ really the limit? [duplicate]

The understanding I have is that the speed of light is considered to be the highest attainable speed in physics. Of course there are theories of tachyons but since those haven't been proven we'll ...
51 views

Is Gravity related to velocity? [closed]

Is the missing link of what creates gravity, the velocity that an object rotates or moves through space ? Can a small object with little mass which rotates or moves in enormous speed create a strong ...
142 views

Energy of gravitation

EDIT: As some confusion has appeared, I want to make another clear question. If gravitational energy is meaningless in general relativity (since it is the geometry), how can one come up with the ...
91 views

How can gravity affect light?

I understand that a black hole bends the fabric of space time to a point that no object can escape. I understand that light travels in a straight line along spacetime unless distorted by gravity. If ...
37 views

Spin of anti-particles

Pretty simple question (I think), probably stemming from my lack of formal background in physics. I've been reading questions like this one related to attraction with respect to spin (a term I'm not ...
26 views

Is gravitational acceleration less affected by relativistic mass increase? [duplicate]

Acceleration due to mechanical force will lessen due to relativistic mass increase as kinetic energy becomes significant near c. But if acceleration is gravitational, the gain in relativistic mass ...
82 views

Why point mass leaves it's own gravitational well? [closed]

I suppose that point mass has its own gravitational well. Why this point mass is still attracted by other gravitational waves. I expect that this point mass is surrounded by "gravitational hills". Why ...
194 views

Space-time curvature creates gravity or is it (could it be) vice-versa too?

Mass (Energy) creates space-time curvature and thus it forms the reason for gravity. Can it be vice-versa too? Like, mass created gravitational field, gravitational field created space-time curvature? ...
117 views

Frame dragging — is there a “non-tiny” example?

Now. As I understand it, in fact, the earth (10^25 kg) creates a very small, very tiny, frame dragging effect. Indeed, we have measured this using satellite experiments. So, the Earth (10^25 kg) ...
64 views

Gravitational atraction of fast object [duplicate]

Let's imagine a asteroid that travels with 0.99999999999999999c. (I know it's impossible). Anyway... Relativistic mass of such object would be almost equal to earth's stationary mass. Now let's ...
85 views

Is inertia actually a property of the force rather than the mass?

I ask this because it occurred to me that the inertial property of mass only actually arises in the context of forces (such as the EM force) as a resistance to their accelerating effect. Inertia plays ...
71 views

Do alternate theories for Dark Matter (like MOND) explain it's effect on gravitational lensing?

For a long time, I was sceptical about the evidence for dark matter. To me, it seemed like a pretty big leap to make when we have no idea whether or not our current models of gravity should apply ...
498 views

Light and Gravity - bending of light around a massive body [duplicate]

Well, as I have read, a massive body can cause light to bend around itself due to its gravitational attraction. What I don't understand is how, as the Newtonian formula for the force of gravitational ...
186 views

Black hole thermodynamics in a time dependent metric

For a time dependent space time metric, to get the thermodynamics, does the standard procedure of Wick rotating the time, and then calculating the free energy, work ?
141 views

How does gravity slow light without an equal and opposite action? [closed]

This is regarding the gravity well sort of explanation. People claim that gravity doesn't slow light by saying it curves the road by which it travels but if space is indeed without properties and ...
35 views

Are particles with gravitomagnetic charge possible or excluded? [duplicate]

Are particles with a sole gravitomagnetic charge (gravitomagnetic monopoles) possible? Does the theory exclude this possibility? Were there attempts to find such particles, similar to the search for ...
131 views

Why does angular momentum shorten the Schwarzschild Radius of a black hole?

Angular momentum causes the event horizon of a black hole to recede. At maximum angular momentum, $J=GM^2/c$, the Schwarzschild radius is half of what it would be if the black hole wasn't spinning. ...
73 views

Is general covariance a symmetry?

Is general covariance a symmetry? If it is ,what is its symmetry group and corresponding generator?
449 views

Slowing of time under gravity

I am not calling this gravitational time dilation because that is a relativistic effect due to the equivalence principle. Now imagine two light clocks (a clock that ticks due to light) are placed ...
3k views

Is gravity just electromagnetic attraction?

Recently, I was pondering over the thought that is most of the elementary particles have intrinsic magnetism, then can gravity be just a weaker form of electromagnetic attraction? But decided the ...
230 views

General Relativity posits that matter curves spacetime, such that geodesics point towards the object in question, hence, gravity. Now, how does matter do this? What is spacetime "made of", anyway, ...
15 views

Why the position of apparent horizon depend on choice of Sigma t of foliation?

Whether a 2d surface is a trapped surface is independent of choice of Sigma t of foliation. Why its outer boundary (apparent horizon) depends on choice of Sigma t of foliation?
58 views

Does geodesics from solving full field equations are same as path from energy-momentum tensor?

As we know, if we had an energy-momentum tensor in all space-time we could obtain the metric tensor by solving field equations. Also i think if we had an energy-momentum tensor then we have ...
364 views

754 views

Does a black hole have any kind of mass?

Currently in my academics I am studying about the Gravitation. In the chapter I came across a term called the Escape Velocity (It's the velocity of any celestial body which is required by an object to ...
71 views

Will we feel the gravity of a star 10 light years away for the next 10 years if, somehow, it vanishes today from its position? [duplicate]

I was watching a relativity video, and although I am not sure, I felt that it was trying to tell that the effect of gravitation of a body is instantaneous, in the sense that a sudden change in the ...
57 views

What is intrinsic gravitational entropy?

What is intrinsic gravitational entropy? Does it have to do with dark matter or coarse graining in the universe? Is it unique to general relativity, or there are predictions from quantum mechanics as ...
95 views

Principle of locality and forces

I have a silly confusion about the statement written in the link Einstein and Locality ''external influence on A has no direct influence on B; this is known as the Principle of Local Action.'' ...
55 views

How exactly can we describe the normal force on a static person standing on earth's surface using general theory of relativity?

For planetary motion I can understand that the planets move along the geodesics e.g. the warped space-time geometry. Imagine that the moon gets suddenly stopped by some external force and comes to ...
122 views

What will happen after escaping earth's gravitational field?

Suppose that I escaped the gravitational field of earth. Then: am I going to be pulled by Sun's gravity?
90 views

Is the concept of space-time curvature a recursive one? [duplicate]

A way some people explain (or try to explain) how gravity works is using space-time curvature: an object with high mass distorts the surrounding space-time plane like a bowling ball distorts a sheet ...
145 views

Does gravity actually contract space-time?

In the Big Crunch Theory it says that gravity (curvature in space-time) will stop the universe's expansion and gravity will cause the universe to contract on itself. My question is if gravity is a ...