Black Hole Question

[xelasnave]

General Relativity does not use force to explain gravity ..it is a geometric property of space and applies to both mass and energy. I suspect the photon is affected because it is energy.
I think gravitons are posited via quantum mechanics not General Relativity.
GR is the best model for gravity and QM has yet to offer a
better model

[speach (Simon)]

Originally Posted by PeterEde

If a photon has no mass why would gravity affect it?

It does, look and gravitational lensing

[Solitarian]

Originally Posted by PeterEde

I'm all for them. Make for great movies

... and the best pinball machine

[sjastro]

A few issues raised here......

Firstly gravitons have never been observed in nature.
This is compounded by quantum gravity theory that predicts gravitons, but is a mathematical train wreck unable to predict the interactions between gravitational fields without giving absurd results.

If gravitons do exist, they are created when gravitational fields interact with each other. Since a BH's gravitational field extends beyond it's event horizon, gravitons would be created outside the horizon. So there is no issue with gravitons having to escape the horizon.

Secondly as Alex alluded to gravity is not a real force in GR but a fictitious force which is dependant on the observer's frame of reference.
All particles including photons move along geodesic paths in a gravitational field. This explains why the trajectories of photons appears to be bent in a gravitational field.

Furthermore all geodesic paths converge and disappear at the BH singularity.
Space and time appear to end at the singularity.

A photon or any other particle reaching the singularity is literally kaput if our understanding of BHs is correct.

Steven

[xelasnave]

Well put Steven.
What happens when something goes kaput.
Say a hydrogen atom. Can you describe what happens to the structure of the atom and it's components under such energy.

[sjastro]

Originally Posted by xelasnave

Well put Steven.
What happens when something goes kaput.
Say a hydrogen atom. Can you describe what happens to the structure of the atom and it's components under such energy.

Alex,

The atom moves on a world line which is the space-time version of the atom moving along a trajectory in space.

From a mathematical perspective the world line ends at the singularity which for all intents and purposes means the atom ceases to exist.

From a physics perspective this cannot be right as the hydrogen atom or its constituent energy becomes part of the BH mass and doesn't "disappear".
It highlights the problem of GR at small scales and the singularity is an artefact of the theory which disappears when QM is applied.

While we can't speculate what happens at the singularity we can make an educated(?) guess what happens as the hydrogen atom approaches the singularity. We know the tidal forces acting on matter increase as one gets closer to the singularity and at progressively smaller scales.

At a certain distance from the singularity the tidal forces are strong enough to separate the electron from the proton in the hydrogen atom.
At smaller distances the tidal forces become so great the quarks themselves that form the proton begin to separate.
Now however we are in the murky world of quantum chromodynamics which states the force between quarks doesn't diminish as their distance increases. So whether free quarks are produced or not is anyone's guess.

There are experts at GR such as Kip Thorne who speculate worm holes, port holes to other Universes etc but these are non mainstream ideas.

Steven

[xelasnave]

That was excellent,
Thanks Steven

[rustigsmed (Russell)]

ok originally I thought the singularity was a tiny ball of infinitely heavy matter, and now I know that's not the case.

how do black holes grow in size (circumference) and gravitational pull? if the matter that goes 'into' a black hole effectively becomes massless energy (I hope I've got that right), you would think (well some may) that there is therefore no reason for the black hole to change from its original size which was dependent upon its original host star's size?

[sjastro]

Originally Posted by rustigsmed

ok originally I thought the singularity was a tiny ball of infinitely heavy matter, and now I know that's not the case.

how do black holes grow in size (circumference) and gravitational pull? if the matter that goes 'into' a black hole effectively becomes massless energy (I hope I've got that right), you would think (well some may) that there is therefore no reason for the black hole to change from its original size which was dependent upon its original host star's size?

It's E=mc^2 at work.
BHs even gain mass when massless photons pass over the even horizon.

The conversion of energy into mass has been demonstrated by the production of positron/electron pairs from high energy photons.

Regards

Steven

[rustigsmed (Russell)]

Originally Posted by sjastro

It's E=mc^2 at work.
BHs even gain mass when massless photons pass over the even horizon.

The conversion of energy into mass has been demonstrated by the production of positron/electron pairs from high energy photons.

Regards

Steven

thanks steven, i'm still a bit confused i understand that energy can be converted into mass and vice versa. in BH am i right in saying that all mass is converted to energy? so that would mean energy would have to have an affect on gravity in 'energy form' (as opposed from mass)?

cheers

russ

[sjastro]

Originally Posted by rustigsmed

thanks steven, i'm still a bit confused i understand that energy can be converted into mass and vice versa. in BH am i right in saying that all mass is converted to energy? so that would mean energy would have to have an affect on gravity in 'energy form' (as opposed from mass)?

cheers

russ

Russ,

Since our knowledge of what happens inside the event horizon is limited we can only speculate on whether all mass is converted into energy.
We know in the case of x ray binary stars where one of the companions is a BH, a large percentage of in-falling mass is converted into energy before it passes through the horizon.

One of the fundamental differences between Newton's theory of gravity and GR is the role of energy.
Suppose you have a planet under the gravitational influence of a binary star. In Newton's theory the total gravitational force between the planet and binary star is simply the sum of the gravitational forces between each component star and planet.
In GR the total gravitational force is the sum of the gravitational force of each component star and planet plus the gravitational binding energy between the stars.
The gravitational binding energy is the amount of energy required to separate the binary star.

So in GR energy does contribute to gravity.

Regards

Steven

[rustigsmed (Russell)]

Originally Posted by sjastro

Russ,

Since our knowledge of what happens inside the event horizon is limited we can only speculate on whether all mass is converted into energy.
We know in the case of x ray binary stars where one of the companions is a BH, a large percentage of in-falling mass is converted into energy before it passes through the horizon.

One of the fundamental differences between Newton's theory of gravity and GR is the role of energy.
Suppose you have a planet under the gravitational influence of a binary star. In Newton's theory the total gravitational force between the planet and binary star is simply the sum of the gravitational forces between each component star and planet.
In GR the total gravitational force is the sum of the gravitational force of each component star and planet plus the gravitational binding energy between the stars.
The gravitational binding energy is the amount of energy required to separate the binary star.

So in GR energy does contribute to gravity.

Regards

Steven

Ok that helps a lot now thanks Steven.