How can a black hole work???

[xelasnave]

I have been reading about waves and particles and black holes.
Now we know a black hole has such powerful gravity that not even light can escape....

So how can the message of gravity escape the black hole...

irrespective of the message being conveyed by a particle interaction or by a "wave" the problem of inescapability seems to be there...

either a particle or a wave must escape the black hole to tell the Universe via its message of gravity that it is there...but the black holes power suggests nothing can leave ... and presumably neither can the messenger particles or waves...


Needless to say I see this as another reason why push gravity will work best... for in that Universe the gravity is external and has no problem with the event horizon ...

alex

[sjastro]

Originally Posted by xelasnave

I have been reading about waves and particles and black holes.
Now we know a black hole has such powerful gravity that not even light can escape....

So how can the message of gravity escape the black hole...

What's the message of gravity?

irrespective of the message being conveyed by a particle interaction or by a "wave" the problem of inescapability seems to be there...

either a particle or a wave must escape the black hole to tell the Universe via its message of gravity that it is there...but the black holes power suggests nothing can leave ... and presumably neither can the messenger particles or waves...

Why is this a problem? Is black paint a problem as well?

Needless to say I see this as another reason why push gravity will work best... for in that Universe the gravity is external and has no problem with the event horizon ...

How?

Regards

Steven

[Zuts]

Hi,

Since there is not yet a unified theory of everything take your pick on whether you want to talk about gravitons (quantum mechanics) or curved spacetime (general relativity).

When a sun becomes a black hole the event horizon is far below the original surface of the star. Gravity is not infinite at the event horizon and in fact at a distance from the singularity of the original surface the gravity would be as or a bit less than before. Gravity or spacetime around a mass is only dependant on the mass and the black hole has less mass than the original star because to form a black hole the original star blew up and lost a lot of mass.

The curvature of spacetime or gravity only becomes infinite if you get very close to the black hole singularity. This is because all the mass is concentrated at a point and you can get very close to it.

Before a star becomes a black hole there is a gravitational field which in GR is eqivalent to a particular curvature of spacetime. Once the black hole forms this curvature does not change. If you think it does then you need to say what force you think it is that somehow smooths out the original curvature of spacetime once a black hole forms.

Cheers
Paul

[xelasnave]

Thanks Steven for considering the proposition.

From my reading I formed the idea that the message of gravity must travell in some manner at least out and away from a black hole.

String theory speaks of messenger particles and duality speaks of waves and particels ...now whatever the way gravity is communicated I wondered, how, given the immence gravity of a black hole, such messengers, whatever they be, can escape to pass on their message.

Now I know that space time distorts in proximity to mass but finially I figure this quality, although a property of space time, must be communicated in some form of particle or wave..again how does that message escape I wondered... they speak of gravity waves in the context of disruption to space time originating from a super nova and although that is an out of the norm ripple the ripples ..or waves would seem to be present all the time... the super nova just excentuates the wave... and someone said recently attraction wave communicated via a wave...

So I specualte that notwithstanding general relativity and the relationship of space time and matter how could the physical communicator escape the black hole.

So although it is easy to say there is no problem I think there is ,,, simply because of the properties given to a black hole... nothing can escape and if light can not escape I think it must raise the question ..how then does the black hole communicate its message of gravity... or how does it bend space time.

No black paint is not a problem for me...

in fact black features largely in my wardrobe..

it is all black ..
everything I wear is black..
my camera bag is also black..

I do like my scopes white however.

I like black paint..it has solved problems for me rather than to create then...when applied to the inside of my scopes that actually eliminates problems..stay light can be minimised with some good flat black paint.

And so after considering the apparent difficulties a black hole would face in a Universe governed by the force of attraction I realised that no such difficulty would exist if the force of gravity manifested from an external pushiing force.. simply in the push case there is no message of gravity necessary to originate from the black hole … so which approach will stand the slash of the razor on that appraoch

Thanks for enjoying in the fun.

alex

[xelasnave]

Thanks Paul for your input..
Irrespective of where the surface of the black hole is I thought that the event hoizon was the point of no return...
Other than my confusion on that point I enjoyed the rest of you post
alex

[xelasnave]

I cant answer the question posed in your last sentence by the way... I will think about all you said

alex

[Dog Star (Phil)]

Sorry Alex, I can't answer your question, but I do have one of my own
Black holes are so dense mass-wise that nothing can escape them - not even light.
"Their existence can only be inferred from their gravitational effects on their surroundings and " the radiation emitted by material falling in to them.""
(Cambridge Dictionary of Astronomy)
So, if light cannot escape a black hole, how is it that radiation can be released?
Or does this release occur outside of or before the event horizon.
Everyone else probably knows the answer to this one but I have to admit that I don't

[xelasnave]

Hi Phil..

I dont know really as I have the same problem as everyone else.
Lets not forget that we comment upon something we do not have the advantage of seeing or observing directly.
We are looking for something we have maths to establish that it could exist and predictions that around these predictions we should witness certain things..gravity disruption and exotic rays generated from the rapid and horrific destruction of matter.

So such observations are believed to evidence a black hole. Its size is estimated from the gravitational influences in the region and the prescence of rays evidencing matter destruction.

Mr Hawking has worked out out it (radiation escape from within the black hole apparently) is possible from a mathmatical approach (such that nothing is offended) but such an approach does go against the concept I feel.

One would think that the only opportunity of escape for any matter or energy would be before it goes past the event horizon. but once in nothing comes out..except via Mr Hawkings math but I think there may be observation in support...but I can not recall anything specific... I read a lot and remember mostly only where I can find it if I need an authority... but that is my feeling.

AND so this property of a black hole must make getting a message out very difficult and presuming that some particle or wave interchange is required to communicate any of the forces I feel this raises a curiosity that maybe will throw light on the very nature of gravity itself.

In my view my question offers good reason why gravity is probably not a force that works via attraction but more in the nature of a pressure of space.

The good thing is until someone brings a black hole into the lab we can speculate upon it and perhaps figure out some new hypothisis.
Good wet weather material...but the Sun is out so that is it for me.

Thanks for your participation.

alex
alex

[sjastro]

Originally Posted by xelasnave

So although it is easy to say there is no problem I think there is ,,, simply because of the properties given to a black hole... nothing can escape and if light can not escape I think it must raise the question ..how then does the black hole communicate its message of gravity... or how does it bend space time.

alex

Here's the shocking news Alex.

Blacks holes aren't black outside the event horizon. An observer outside the horizon will never see an object (photon, rocket, astronaut) disappear into a black hole.

In most cases Newtonian physics is a good approximation for GR, but black holes is not one of them.

If a probe is released from rest and allowed to fall into a black hole, Newtonian physics will predict the probe will reach a maximum velocity at the event horizon before disappearing across the horizon. This is from the observer's frame of reference outside the event horizon. It's a common and incorrect way of visualizing the behaviour of particles near black holes.

GR predicts a totally different scenario. To the observer the probe will reach a maximum velocity at 3 times the radius of the event horizon. Assuming the probe is not destroyed by tidal forces, it will then slow down and come to a grinding halt at the event horizon.

This is tied in with gravitational redshift. An object at the event horizon is literally frozen in time. The information is still there as it hasn't crossed the horizon and never will.

From the probes frame of reference it will pass through the event horizon. What is beyond the event horizon is pure speculation. The mathematics of GR inside the event horizon is very strange and scientists have struggled to interpret the mathematics.

Regards

Steven

[g__day (Matthew)]

Here's another theory- starting with what is inside the event horizon.

Relativity fails to describe what happens within the event horizon of a black hole because spacetime breaks down as the equations describing its topology tend toward infinity.

The GR models used generally state there must be a naked singularity (think spacetime meets divide by zero maths) at the centre. A slight modification are gravstars - who replace this singularity with a rapidily rotating core that is saved from collapse (and divide by zero) by the angular momentum of matter and energy falling into the core. In other words centrifugal motion resists gravity to a large enough degree to prevent a naked singularity.

The next theory works by stating as matter and energy gets crushed its density in any given volume of spacetime raises. Once you are talking about the regions at or within the event horizon these are extremely high energy densities, that only rise towards the centre. Eventually you will climb above the energy thresholds that form what is called the hierarchy problem (10^14 GeV up to 10^19 GeV). Our understanding of physics is that the four fundamental forces seperated out at these energy levels, and may well re-combine from the four (e/m, nuclear strong, nuclear weak and gravity) back to one (quantum gravity). So there may well be transition phases within a black hole's event horizon related to the number of dominant forces in existence. So what you ask? Well the topology or curvatue of spacetime relates at least in part to the energy and matter within it and the force carriers - change the force carriers and you may well change the geometry. Put more simply - the rules describing the curvature of spacetime (general relativity) cover a four force model - not a one force one. A yet to be described quantum general relativity might give you a model to describe the in workings of a black hole. In this model the framework (spacetime) and its contents (matter, energy and force carriers) could be radically different and no singularity might ensue.

* * *

Next under GR near the event horizon space and time almost swap properties with each other. Matter and energy can be modelled by wave eqautions. Waves exist in a framework and the framework is getting servely curved by the model. But does time turn around? The only reason why time appears to run forward in a GR framework that I am aware of is that neutral kaons seem to violate CP (charge parity) invariance. For all other particles their past as much as their future describes there presence state. Stated another way preference towards a prefered future - that is inherited from that future under a wave probability framework leaks from the future back to the present to describe the present. So the inflormation flow should work forwards and backwards within spacetime and therefore have a carrier. All particles have a neutral tendency towards past or future - except it seems neutral kaons. These particles have a strong bias towards inheriting information from the future, not the past - so statistically there dominantly want to move forward in time - or at least resist moving backwards.

Isn't theoretical physics grand?

To your original question think spacetime as a framework - say a strechable plastic or rubber sheet, think energy and matter as an interconvertable substance within this sheet (e.g ice, liquid water or steam). Threat GR as describing the ice and liquid states of water and the sheet itself where quantum gravity might describe the plastic and the steam state of the environment. Perhaps gravity is closer tight to the shaping the interactions (streching or contracting of the sheet then the interactions of the substances within the sheet) - that's why it isn't contained within the event horizon.

[xelasnave]

Thats great...

So everyone agrees gravity must push

alex

[xelasnave]

Sorry I could not help myself.
I am as happy as just arrived in Sydney and no one is here to welcome me.. I like it that way.
AND just got away as "she" and "he" (the new driver I hope) stopped me as I was leaving..dam if I did not have to go to court on Tuesday I could have stayed... but not withstanding happy to have arrived save and more importantly alone
Thanks Matt and Steven for all that I will heat my pies recover etc and read it all again.

Just in case I was wrong about your general acceptance of the push thing

alex

[xelasnave]

Steven said.......

GR predicts a totally different scenario. To the observer the probe will reach a maximum velocity at 3 times the radius of the event horizon. Assuming the probe is not destroyed by tidal forces, it will then slow down and come to a grinding halt at the event horizon.

Alex's question.........
I presume the slow down is observational .... I have heard of this early in my black hole reading and assummed it was observational but reading the next bit ............anyways observational or does GR say it literally stops???

You then said.......

This is tied in with gravitational redshift. An object at the event horizon is literally frozen in time. The information is still there as it hasn't crossed the horizon and never will.

Is this not observational... the way I though it worked was the light leaving an object about to cross over (at a point which is not the issue) was held back by the gravity such that the "illusion" was that the object seemed to slow up...

If it is not observational and the information is litterally frozen in time will that not support my proposition that not even gravity can leave...

However if GR says it is more than observational that will indeed be curious and interesting.

If it is more than observational that will really spin my head...

alex

[xelasnave]

Well the more I think about all this the more I think about it.

Matt said...........

Perhaps gravity is closer tight to the shaping the interactions (streching or contracting of the sheet then the interactions of the substances within the sheet) - that's why it isn't contained within the event horizon.

Yes... GR describes the properties of the sheet and at least for me not how these properties physically manifest.
My difficulty is marrying the physics to what may really be going on..which sometimes seems different although exactly the same.
Thanks Matt I found all you wrote extremly interesting and I am sure others will find is so.
alex

[sjastro]

Originally Posted by xelasnave

Steven said.......

GR predicts a totally different scenario. To the observer the probe will reach a maximum velocity at 3 times the radius of the event horizon. Assuming the probe is not destroyed by tidal forces, it will then slow down and come to a grinding halt at the event horizon.

Alex's question.........
I presume the slow down is observational .... I have heard of this early in my black hole reading and assummed it was observational but reading the next bit ............anyways observational or does GR say it literally stops???

The effects are all relative to the observer of the probe. The frequency of an atomic clock on the probe at the event horizon is equal to zero. So yes time does in effect stop.

On a lesser scale we see the same effect on Earth. Atomic clocks run faster at higher altitudes.

You then said.......

This is tied in with gravitational redshift. An object at the event horizon is literally frozen in time. The information is still there as it hasn't crossed the horizon and never will.

Is this not observational... the way I though it worked was the light leaving an object about to cross over (at a point which is not the issue) was held back by the gravity such that the "illusion" was that the object seemed to slow up...

There is nothing illusional.

Gravitational redshift/blueshift has been experimentally verified. Atoms can absorb photons of a certain frequency. Suppose a test is set up to show absorbance with the source of the photons and the atoms separated by a horizontal distance X. Horizontally the source and atoms are at the same gravitational potential. If the test is repeated but the source and the atoms are separated by a vertical distance X instead, absorbance no longer occurs. This is because the source and atoms are at a different gravitational potential and the photons have shifted in frequency.

A change in frequency results in a change in time it takes the photon to reach it's destination. This is the mechanism for time slowing down in a higher gravitational potential.

If it is not observational and the information is litterally frozen in time will that not support my proposition that not even gravity can leave...

I have no idea what you're on about Alex. Gravitational potentials are time independant.

Regards

Steven

[xelasnave]

Steven said.......

I have no idea what you're on about Alex.

I guess I was grasping at the proposition that as the probe for the reasons stated was frozen so could the gravity message...
But dont worry Steven as I have moved past that point thanks to your excellent explaination above... you have given me more understanding in that reply than most... I think I am learning something.

Still something does not sit right for me with the time dialation thing but in your post I see how it can be arrived at... may not be new for you but new for me..and that is good... and again I thank you for your help.

alex

[Karls48 (Karl)]

“GR predicts a totally different scenario. To the observer the probe will reach a maximum velocity at 3 times the radius of the event horizon. Assuming the probe is not destroyed by tidal forces, it will then slow down and come to a grinding halt at the event horizon.

This is tied in with gravitational redshift. An object at the event horizon is literally frozen in time. The information is still there as it hasn't crossed the horizon and never will.”

There is a small problem with this theory. If by some extremely unlikely accident a miniature black hole is created in LHC, there is no problem. It will commence swallowing surrounding molecules and slowly grow large and large. But from observers point of view (being in different frame of reference) nothing will happen as the matter drawn to the black hole will stop at event horizon frozen in time.

[sjastro]

Originally Posted by Karls48

“GR predicts a totally different scenario. To the observer the probe will reach a maximum velocity at 3 times the radius of the event horizon. Assuming the probe is not destroyed by tidal forces, it will then slow down and come to a grinding halt at the event horizon.

This is tied in with gravitational redshift. An object at the event horizon is literally frozen in time. The information is still there as it hasn't crossed the horizon and never will.”

There is a small problem with this theory. If by some extremely unlikely accident a miniature black hole is created in LHC, there is no problem. It will commence swallowing surrounding molecules and slowly grow large and large. But from observers point of view (being in different frame of reference) nothing will happen as the matter drawn to the black hole will stop at event horizon frozen in time.

Mini black holes do not grow as they evaporate immediately.

Refer http://www.iceinspace.com.au/forum/s...503#post383503

So what exactly is the problem with the theory given that the scenario is a solution to Einstein's field equations?

Steven

[xelasnave]

Steven you said.

A change in frequency results in a change in time it takes the photon to reach it's destination.

Sorry I dont understand given the wonderful chat on light. Is a change in frequency the same as a change in wave length.. I am thinking that a cahnge in frequency must change the wave lenght.

Thank you
alex

[Zuts]

Originally Posted by Karls48

“If by some extremely unlikely accident a miniature black hole is created in LHC, there is no problem. It will commence swallowing surrounding molecules and slowly grow large and large. But from observers point of view (being in different frame of reference) nothing will happen as the matter drawn to the black hole will stop at event horizon frozen in time.

This seems very wrong to me and a bit like trying to argue that zeno's paradox is true. Frames of reference are seperate and I think you are getting caught up in the frame of reference of the wrong observer. From a photons point of view there is no time passage in it's 13 billion year journey across the visible universe. However this does not mean that it took no time to cross the universe. It depends on the frame of reference of the observer.

In any case I agree with stephen, the example is simply wrong as micro black holes evaporate in plank time scale.

Cheers
Paul