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Speed of light in black hole.


Minato
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So, I have heard laws of space doesn't work inside the black hole so,

1) Can one move faster then light in black hole?

2) If it can't then what happens to the gravitational pull of black hole?

3) Follow up for last question if you can't break the speed limit of light in black hole then gravity also can't leave black hole as it also moves at speed of light. That means black hole should not have pull out side of event horizon that means matter should not be able to pulled in to black hole.

4) If it can then how is the physics different there?

5) Also if it can move faster then speed of light then it should be able to break past the escape velocity of black hole.

so, please explain this.

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The speed of light will not increase near a black hole or any other gravitational field, it is the space itself that is bending. Light will just follow said bending.

 

Lets wait for a more detailed explanation :) . The Speed of light is at least locally invariant.

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So, I have heard laws of space doesn't work inside the black hole so,

1) Can one move faster then light in black hole?

2) If it can't then what happens to the gravitational pull of black hole?

3) Follow up for last question if you can't break the speed limit of light in black hole then gravity also can't leave black hole as it also moves at speed of light. That means black hole should not have pull out side of event horizon that means matter should not be able to pulled in to black hole.

4) If it can then how is the physics different there?

5) Also if it can move faster then speed of light then it should be able to break past the escape velocity of black hole.

so, please explain this.

 

1) Physics within the event horizon is pretty much guesswork - time and space are no longer as we normally understand them; normal physics might not apply but we don't know what will.

2) The influence of gravity is not changed by its own influence. FYG the gravitational waves from the event detected by LIGO, and the changes of the gravitational field / strength propagated outwards at speed of light.

3) see 2

4) within the black hole we do not know how physics is different - but we would not expect the gravitational attraction of the black hole to be changed by the fact that it is a black hole

5) gravity does not have an escape velocity. gravity is the curvature of space-time, so is a black hole; you cannot divorce gravity from a black hole and treat it like EMR

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So, I have heard laws of space doesn't work inside the black hole so,

 

 

I don't know where you read that. We have no way of actually knowing what happens inside a black hole, but we can apply our current theories to the inside and say what we expect to happen.

 

1) Can one move faster then light in black hole?

 

The definition of the speed of light becomes complicated when you start considering gravity. But, as far as I am aware, even inside a black hole the speed of light is still a (local) speed limit. And all observers will measure the speed of light to be the same.

 

2) If it can't then what happens to the gravitational pull of black hole?

 

Not sure what this means. The gravity of a black hole is determined by its mass, in the same way as any other massive object. Again, things get complicated inside the event horizon as the radial space dimension gets swapped with the time dimension.

 

3) Follow up for last question if you can't break the speed limit of light in black hole then gravity also can't leave black hole as it also moves at speed of light. That means black hole should not have pull out side of event horizon that means matter should not be able to pulled in to black hole.

 

Changes in gravity travel at the speed of light. The gravity around a black hole is static and not dependent on the speed of light.

 

5) Also if it can move faster then speed of light then it should be able to break past the escape velocity of black hole.

so, please explain this.

 

 

I am going to quote imatfaal's reply from another thread as he put it so well:

 

The thing about escape velocity is true - but to an extent coincidental. The black hole forms because space time is so warped by the gravity that the geometry does not allow any outward passages from within the event horizon. Remember that on a normal object the escape velocity is the speed that you need to be going to escape with no further effort - ie you will coast to infinity without ever being pulled back. On a normal object you could (given a very long ramp*) just walk up the gravity well ( it would just take a very long time) at a much slower speed than escape velocity. Inside the event horizon of a black hole no amount of effort can lift you away from the centre - because all directions lead to the centre; it is a geometrical trap - all roads lead to the same place and that is further in.

 

 

*Four thousand metres vertical distance is a very respectable day of cycling up hills - at this rate of vertical ascent it would take 50 days to reach low earth orbit

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So, I have heard laws of space doesn't work inside the black hole so,

1) Can one move faster then light in black hole?

2) If it can't then what happens to the gravitational pull of black hole?

3) Follow up for last question if you can't break the speed limit of light in black hole then gravity also can't leave black hole as it also moves at speed of light. That means black hole should not have pull out side of event horizon that means matter should not be able to pulled in to black hole.

4) If it can then how is the physics different there?

5) Also if it can move faster then speed of light then it should be able to break past the escape velocity of black hole.

so, please explain this.

What I do know for certain is that once inside the EH of any BH, all paths lead to the singularity and doom.

Also photons/light always move at "c".

On the FTL aspect, I came across a model of a BH a while ago called the waterfall or river model.

here it is.......

 

https://arxiv.org/abs/gr-qc/0411060

Andrew J. S. Hamilton, Jason P. Lisle (JILA, U. Colorado)

Abstract:

"This paper presents an under-appreciated way to conceptualize stationary black holes, which we call the river model. The river model is mathematically sound, yet simple enough that the basic picture can be understood by non-experts. %that can by understood by non-experts. In the river model, space itself flows like a river through a flat background, while objects move through the river according to the rules of special relativity. In a spherical black hole, the river of space falls into the black hole at the Newtonian escape velocity, hitting the speed of light at the horizon. Inside the horizon, the river flows inward faster than light, carrying everything with it. We show that the river model works also for rotating (Kerr-Newman) black holes, though with a surprising twist. As in the spherical case, the river of space can be regarded as moving through a flat background. However, the river does not spiral inward, as one might have anticipated, but rather falls inward with no azimuthal swirl at all. Instead, the river has at each point not only a velocity but also a rotation, or twist. That is, the river has a Lorentz structure, characterized by six numbers (velocity and rotation), not just three (velocity). As an object moves through the river, it changes its velocity and rotation in response to tidal changes in the velocity and twist of the river along its path. An explicit expression is given for the river field, a six-component bivector field that encodes the velocity and twist of the river at each point, and that encapsulates all the properties of a stationary rotating black hole".

 

 

 

Here is Professor Hamilton's web page where he discusses it further......

http://jila.colorado.edu/~ajsh/insidebh/waterfall.html

Personally I like the model and its ability to explain simply. What do others think?
Edited by beecee
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I've found the river model handy to help the laymen better understand relativity. I've posted it a few times over the years.

 

Though one has to be aware it is its own coordinate system.

Edited by Mordred
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