Black holes and causality

[irR4tiOn4L]

Originally Posted by hlokk

..So, the 'gravity' from an external observer would never appear to cross the event horizon. Consider some large mass moving into the black hole. It distorts the fabric of spacetime, now as it passes the event horizon, it cant update the field, so the field sticks around...

Hlokk, you describe what we OBSERVE happens (or expect to observe) but thats mistaking what we see happen with what does happen when you say that because it never appears to cross the event horizon from our perspective that somehow that should justify it's 'gravitational distortion' not dissapearing. Thats what im trying to tackle - although it appears never to 'make it' to the black hole this is just an 'optical illusion' - im not really interested in what APPEARS to happen due to these optical illusions, but what actually DOES happen. Infalling matter either DOES, or DOES NOT actually dissapear from OUR SIDE of the event horizon once it reaches it. Now if it actually NEVER DISSAPEARS from our side, then this is a significant point in itself - but if it DOES, then WHY SHOULD THE DISTORTION BE LEFT BEHIND?

The theory i was making there relied on this premise - as soon as more matter falls past the event horizon, the contribution of that mass will IMMEDIATELY ENLARGE THE EVENT HORIZON - such that the VERY LAST POSITION of the mass before it crossed is actually now covered by the event horizon - and no 'information' on what USED to be there (ie the infalling mass) can now escape to 'update' the universe that it is NO LONGER there. This 'trapping' will include the matter's gravity distortion.

The reverse also works - as soon as matter escapes the black hole, the loss of mass will immediately shrink the event horizon, which will FREE UP an area previously under the event horizon to be updated (from the point of view of an observer outside the event horizon) - since this area will include some 'fossil matter' and its 'fossil fields' (gravitational distortions that used to be there when the matter fell in) those 'fossil's will now be updated and dissipate - and the black hole will appear to 'lose' mass and gravitational effect.

In this way a black hole, though no information on mass or gravity can escape it's event horizon, will nevertheless appear to grow and shrink with the addition or loss of matter, via the 'capture' and 'loss' of 'fossil fields' as the expanding event horizon encompasses them before the universe outside the event horizon can be updated on the fact that they are no longer located there - but are now heading toward the singularity.

I do hope that made more sense than the last post.

As a final point - your version - that merely because to an outside observer the light from infalling matter appears to redshift and fade, but never show the object dissapearing, that this alone is proof that the 'gravitational distortion' should be left behind - actually makes a lot of sense, since a distortion travelling no faster than light should mirror the behaviour of light - and appear never to dissapear. However, just like the object eventually 'fades' because its simply old light finally reaching us, and no new light can possibly hit its location, so if gravitational distortions can be measured in the negative - ie that there IS NOT a distortion present - then the last position of the matter and its distortion, if we assume the event horizon does not expand, will actually REMAIN IN THE 'UPDATEABLE' AREA - the area where, if light originated (or information on the existence or lack thereof of a gravitational field) it would actually eventually reach us, the external observer - thus this area could not possibly sustain the illusion of a 'fossil field' - only an area inside the event horizon, which cannot be verified for or against a gravitational field, could sustain such a fossil field.

It is absolutely imperative we remember what is ACTUALLY happening to infalling matter and light hitting infalling matter is different and subject to an optical illusion - if fossil fields existed for the same reason we never OBSERVE infalling matter pass the event horizon, then we would expect an analogous situation - such as superheated plasma emitting light as it falls in - to keep emitting as it hit the event horizon, instead of 'fading out' - otherwise why should a 'fossil field' also not dissipate in this way?

[hlokk]

Relativity states that there is no preferred reference frame. For example, if we have two clocks, one on earth, and one near the speed of light, the time each one experiences will be different. The space-clock will run slow relative to the earth-clock, and the earth-clock will run fast relative to the space-clock. Neither is the 'correct' reference frame. It is perfectly fine for the spaceship to consider itself stationary, and earth is the thing thats moving. It might help to envision two spaceships (as we tend to think of our usual reference frame as fixed). If your in a spaceship, and one zooms by, did it zoom by you, or did you zoom by it? Which is correct? It depends what reference frame you want to consider.

As far as I understand it, these reference frames are not optical illusions per se. Whether matter crosses the event horizon depends on what reference frame you are in. Its not quite that it goes in, but 'appears not to'. (well, whether it is or not is determined why which reference system you pick, rather than there being a universal answer)

So, for an external observer, if light is never observed to cross the event horizon, then gravity would do the same. I.e. if I chuck a torch in, it will keep shining (but get redshifted and dimmer due to fixed size photons). Similarily, the gravity of it will stay there too (though the distortion isnt subject to redshift, though the gravitons may, but afaik the gravitions are like ripples rather than the surface itself).
http://cosmology.berkeley.edu/Education/BHfaq.html#q4
also: http://www.astronomycafe.net/qadir/q2592.html
(keep in mind, the redshift would occur relatively quickly before the object disappeared, perhaps fraction of seconds to hours or so, rather than eons)

Consider a building, with some sign like "free buffet" on it. People are happy (lots of gravity) as they walk to it. As they go inside though, they dont see any buffet, but cant complain as no information can escaped (they're locked in). So they cant tell people not to be so excited, so the joy of people entering is still there. Ok, its a crap example, and the people inside the building would keep going, but the point was they cant communicate outwards once they pass the threshold so they couldnt change anything outside.


You're expanding event horizon explanation is a little confusing to me. Larger black holes have a larger event horizon, yes, but I dont see how an expanding event horizon would increase the gravitational field of the black hole? The size of the event horizon does not dictate the mass of the black hole, or the gravitational field, but rather the other way around.

Originally Posted by irR4tiOn4L

It is absolutely imperative we remember what is ACTUALLY happening to infalling matter and light hitting infalling matter is different and subject to an optical illusion - if fossil fields existed for the same reason we never OBSERVE infalling matter pass the event horizon, then we would expect an analogous situation - such as superheated plasma emitting light as it falls in - to keep emitting as it hit the event horizon, instead of 'fading out' - otherwise why should a 'fossil field' also not dissipate in this way?

What is ACTUALLY happening depends on your reference frame. I dont quite understand your plasma example. If we have a light source, any light source, the reason it gets dimmer is because the light redshifts and the 'packets' of light get more spread out (less photons per second if you will, or a finite number of photons tending to zero, such that the rate changes).
I'm not sure how the light source being plasma affects things. Plasma still emits a finite number of photons (though it might last a litle longer than the low powered torch). Perhaps you are getting a little confused with plasma forming in accretion disks? (the gas bumping into each other heats up as it orbits, getting hotter as it gets closer (eventually emmitting x-rays). If we had this gas, it would get hotter and hotter (from its reference frame), and black body radiate higher energy photons/higher frequency EMR. At some point that would be redshifted back as the plasma got closer the event horizon. Eventually it would redshift and get dimmer.

also, a bunch of Q&A on black holes (as well as the other link)
http://www.astronomycafe.net/qadir/abholes.html


edit2: To shorten: Because of time dilation effects, to the outside observer (i.e. us), the original star, the additional matter, etc, never enter the event horizon. It appears as if they are stuck just outside it, both optically and gravitationally (though, keep in mind, optically at least they get redshifted and dimmer)


edit3: on the original question:
http://www.astronomycafe.net/qadir/q1498.html
and put very succintly: http://www.astronomycafe.net/qadir/q2770.html

Originally Posted by astronomycafe

Why can gravity be 'seen' from a black hole but not light?

Because as seen from a distant observer, all of the mass of the black hole perpetually hangs just outside its event horizon, and from there its gravitational field can reach infinity. Light, however, gets badly redshifted rendering it optically invisible, hence black.

(largified for those skimming the thread for answers, not to ram a point )

[Zylatis]

Light, however, gets badly redshifted rendering it optically invisible, hence black.

Wha thats a load of shit. well sort of. It doesnt emit any light (apart from hawking radiation which is very little) because the path the light takes is curved by the mass and ends up back on the 'surface' of the black hole. it is correct however that the mass is detectable outside the event horizon and as such its gravitational effects are not bound inside it.

[hlokk]

Did you read a few more of the links Zylatis? Black holes dont emit light, true. The redshift bit refers to the observation of infalling light. An object emitting light (such as the forming star) will have its light redshifted until it goes black (due to stretched wavelengths and less photons per second). If you were to watch a black hole form from a star, it would get dimmer and redder of the course of a couple of hours until it redshifted to oblivion. Which is why a forming blackhole turns black. Of course, if something was trying to emit light inside it wouldnt get out (consider that the 'ongoing light level' which is black).

[irR4tiOn4L]

Originally Posted by hlokk

Did you read a few more of the links Zylatis? Black holes dont emit light, true. The redshift bit refers to the observation of infalling light. An object emitting light (such as the forming star) will have its light redshifted until it goes black (due to stretched wavelengths and less photons per second). If you were to watch a black hole form from a star, it would get dimmer and redder of the course of a couple of hours until it redshifted to oblivion. Which is why a forming blackhole turns black. Of course, if something was trying to emit light inside it wouldnt get out (consider that the 'ongoing light level' which is black).

Over here (http://www.physicsforums.com/archive...p/t-75122.html) i found a good summary of what I think your saying

"..(Q) Assuming the speed of gravity is c, does an objects gravitational field have to slow down as light it emits slows down? i.e. as an extreme example, if an object is falling towards a black hole, any light it emits takes longer and longer to reach an observer as it nears the event horizon, so it's gravitational field should take longer and longer [presumably equally as long] to reach the observer as well. Yes, this is basically addressed in this section (http://math.ucr.edu/home/baez/physic...k_gravity.html) of the Usenet Physics FAQ (http://math.ucr.edu/home/baez/physics/index.html): How does the gravity get out of the black hole?

(A) Purely in terms of general relativity, there is no problem here. The gravity doesn't have to get out of the black hole. General relativity is a local theory, which means that the field at a certain point in spacetime is determined entirely by things going on at places that can communicate with it at speeds less than or equal to c. If a star collapses into a black hole, the gravitational field outside the black hole may be calculated entirely from the properties of the star and its external gravitational field before it becomes a black hole. Just as the light registering late stages in my fall takes longer and longer to get out to you at a large distance, the gravitational consequences of events late in the star's collapse take longer and longer to ripple out to the world at large. In this sense the black hole is a kind of "frozen star": the gravitational field is a fossil field. The same is true of the electromagnetic field that a black hole may possess. This is the classical answer, they go on to explain that in terms of virtual photons, or "virtual gravitons" if such things exist, the explanation for the black hole's electromagnetic/gravitational field would be a little different.

(Q) If that is true, can a blackhole's gravitational pull ever increase? Would it be possible to have the object's (delayed) gravitional field exist near the event horizon, and have the blackhole's gravity increase?

(A) A BH's gravity does increase as more mass falls into it, so I'd guess that something along the lines of your second suggestion would be the explanation.

One additional complication is that although gravitational waves travel at the speed of light, gravitational waves are only produced by changes in acceleration, in general relativity the gravitational field acts like it can "extrapolate" the motion of objects which are accelerating at a constant rate. So, for example, the earth is pulled towards Jupiter's current position (in the frame where both are orbiting at approximately constant speed), not the position it was a few minutes ago. Similarly, electromagnetic fields can "extrapolate" the motion of charges which are moving at constant velocity. See this post (http://www.physicsforums.com/showthr...5934post435934) along with some of the subsequent posts by pervect for more details."


So i think that's the idea of 'fossil fields'. However Hlokk, as ive said before - if this is the case, how could a Black Hole's observed gravitational pull ever DECREASE? (such as from hawking radiation taking away from its mass) No such possibility is mentioned anywhere ive seen - its like asking new light emitted from an object to erase old light that is still en-route. Its just not possible, and in fact, this 'new matter' would actually add to the observed mass, not take it away.

[hlokk]

Reference frames. The matter DOES NOT enter the black hole from the reference of an external observer. The matter DOES enter the black hole from its own reference frame. Both of these are equally valid.

Take two spaceships in space, with no matter or light to orientate them. The spaceships pass each other. Which is moving? It is just as true to say that spaceship A is stationary and B is moving, as it is to say that B is stationary and A is moving. Now, it seems contradictory to say that spaceship A is both moving and stationary at the same time, but there is no contradiction, because the two statements are from different reference frames.

And lastly, only light is subject to the redshifting, not the gravitational distortion of spacetime. Gravitons may be subject to doppler effects though.

What might be confusing is that you are thinking of gravitons are analogous to photons. Think of an electric field, it doesnt need electrons whizzing around in outer space, it can exist in a vacuum, then affect charged particles. Same with a gravitational field.




edit: My post now seems a little tangential after you edited your post above. I'll address the point you raised:

So i think that's the idea of 'fossil fields'. However Hlokk, as ive said before - if this is the case, how could a Black Hole's observed gravitational pull ever DECREASE? (such as from hawking radiation taking away from its mass) No such possibility is mentioned anywhere ive seen - its like asking new light emitted from an object to erase old light that is still en-route. Its just not possible, and in fact, this 'new matter' would actually add to the observed mass, not take it away.

The black hole evaporates via Hawking radiation. Relativity is suffient to explain the formation, properties and appearance, but under relativity black holes do not evaporate. However, quantum effects cause energy to be removed from the black hole, decreasing its mass. Theres links out there that should explain it a lot better (the linked sites in the above sites for example).
As far as I understand it, virtual particles form, with one postive, one negative, then rejoin. If you're at the right location, then one particle may be just above the radius to be sucked in, and the other just below. If the negative one is sucked in, then a particle with mass leaves (it was never in the black hole though), and the negative one was sucked in (decreasing energy/mass of the black hole). As the black hole is getting some 'negative energy' and some 'positive energy' is leaving, then the effect is the same as if a particle had left the black hole. Its a very small amount of energy, so black holes take a very long time to evaporate.

[irR4tiOn4L]

Originally Posted by hlokk

Reference frames. The matter DOES NOT enter the black hole from the reference of an external observer. The matter DOES enter the black hole from its own reference frame. Both of these are equally valid.

Take two spaceships in space, with no matter or light to orientate them. The spaceships pass each other. Which is moving? It is just as true to say that spaceship A is stationary and B is moving, as it is to say that B is stationary and A is moving. Now, it seems contradictory to say that spaceship A is both moving and stationary at the same time, but there is no contradiction, because the two statements are from different reference frames.

And lastly, only light is subject to the redshifting, not the gravitational distortion of spacetime. Gravitons may be subject to doppler effects though.

What might be confusing is that you are thinking of gravitons are analogous to photons. Think of an electric field, it doesnt need electrons whizzing around in outer space, it can exist in a vacuum, then affect charged particles. Same with a gravitational field.




edit: My post now seems a little tangential after you edited your post above. I'll address the point you raised:

The black hole evaporates via Hawking radiation. Relativity is suffient to explain the formation, properties and appearance, but under relativity black holes do not evaporate. However, quantum effects cause energy to be removed from the black hole, decreasing its mass. Theres links out there that should explain it a lot better (the linked sites in the above sites for example).
As far as I understand it, virtual particles form, with one postive, one negative, then rejoin. If you're at the right location, then one particle may be just above the radius to be sucked in, and the other just below. If the negative one is sucked in, then a particle with mass leaves (it was never in the black hole though), and the negative one was sucked in (decreasing energy/mass of the black hole). As the black hole is getting some 'negative energy' and some 'positive energy' is leaving, then the effect is the same as if a particle had left the black hole. Its a very small amount of energy, so black holes take a very long time to evaporate.

Hlokk, the only point id make is that i dont agree the matter is 'stationary' from the frame of the observer - I do not think relativity requires matter to act or be as its appearance through light shows it to be. In fact, it would be flat out incorrect for the observer to claim that the matter is ACTUALLY located where it appears to be located - in the same way it would be to assert the position of a star whose light is subject to gravitational lensing before it reaches us. Thus i dont think it would be incorrect to say that, although the object never APPEARS to cross the event horizon, even from the point of view of the observer we should expect that it has crossed, and based on our modelling and redshift, even when it has crossed - even though no information is reaching us to tell us this.

Your right, your post seems a little tangential after my edit - but that edit was necessary, because i had realized that the 'fossil field' mechanic - that as the object crosses the horizon, the progress of its 'trace' light and gravity out past the black hole would be closer and closer to zero, and that this could sustain 'waves' of trace light and gravity whose spacing would be progressively larger but would persist to near infinity - actually made a lot of sense.

Now there is clearly a dichotomy here between some of the quantum mechanical explanations and the relativistic explanation - and as i said, the relativistic explanation cannot have the black hole losing mass - but as long as we accept that gravitons do not travel faster than light (some QM theories insist they do) then its not too different in practise to relativity, except hawking radiation. The 'negative mass' particle being the one that needs to be captured for hawking radiation is actually an important point and explains a fair bit. Doesnt this mean that even virtual particles with no mass are subject to gravity? because my brother insisted otherwise.

I think im getting a much clearer picture of how this might actually work - but im not still not quite satisfied that gravity MUST be subject to gravity - with another theory, it could just as easily escape a black hole regardless and thered be little way to tell which is correct untill we tested them.

[hlokk]

For what happens to the mass, you are considering the masses reference frame. There are no preferred reference frames, so there is no reason why this is the 'true' reference frame.

If two spaceships pass each other, which was moving? To say spaceship B was, then you are using the reference frame of spaceship A (this would equate to matter never entering the black hole). However, we could consider B stationary, and therefore spaceship A moved past B (this would equate to mass entering the black hole). Both are correct, it depends on your chosen reference frame. There is no universal truth to it.

In terms of the black hole, and infalling matter not reaching the event horizon being an illusion. For this statement to be true, you must be asserting that the mass is the preferred reference system, and relative to that reference system then the outside observer is seeing an illusion. This is correct. However, it is equally valid to say, that the mass never enters the event horizon, and the mass experiencing that it does is the optical illusion.

Whether we call it an illusion or not doesnt matter too much (its just a label). For all intents and purposes, the mass has not crossed the event horizon. Every measurement we make from an outside reference frame will show that it hasnt entered. Therefore, if we measure gravity, light, other EMR, electric fields, anything, they will all show that the mass never entered. Because all measurements would show that it never entered (because to a stationary external observer it never did), the properties outside the event horizon would be as if it didnt enter.

Gravity is distorted spacetime remember. Gravity is not subject to gravity, gravity IS gravity.

[tompee]

My eyes have rolled around in my head trying to read this thread, and I won't pretend I have the theoretical foundation to understand most of what is being said (I didn't do any science subjects for my HSC, for starters!), but I have a very basic question.

FIRSTLY, to make sure I have this clear - the apparent paradox discussed in this thread is that information manages to escape a black hole (otherwise how do we know it's there, what its gravitational pull is etc), but information is not meant to be able to travel faster than light, and light can't escape a black hole, so how does information escape?

My two, lay-man, type thoughts on this are:

1) Unless information has a stricter definition than what I am envisaging, it can travel faster than light. Or rather, "NOT-information" (in a logical sense, and from which we can derive information) can travel faster than light. If it could not, we wouldn't have even been able to measure the speed of light itself, because we wouldn't have been able to check our light sources destination "before" it got there... if that makes sense?
What I mean is, if you put a light source one "light minute" away and triggered it, if you checked for light in 30 seconds, it will not have reached you, so would already have information about speed of light coming from the source, you would know how fast it ISN'T.

Could a lot of what we know about black holes be derived from what ISN'T coming out?
Could gravity itself (whatever it is... I know it's something to do with a warp in spacetime caused by matter) somehow be influenced by what is NOT?

2) We assume that for something to get out of a black hole, it must be go FASTER than light, but speed isn't the only property of "stuff" trying to escape a gravitational field, is it? Yes it is, doh! Next thing I'll be saying a glass full of water falls faster than an empty one :-)

[ShadowGeoff]

Originally Posted by tompee

My eyes have rolled around in my head trying to read this thread, and I won't pretend I have the theoretical foundation to understand most of what is being said (I didn't do any science subjects for my HSC, for starters!), but I have a very basic question.

FIRSTLY, to make sure I have this clear - the apparent paradox discussed in this thread is that information manages to escape a black hole (otherwise how do we know it's there, what its gravitational pull is etc), but information is not meant to be able to travel faster than light, and light can't escape a black hole, so how does information escape?

My two, lay-man, type thoughts on this are:

1) Unless information has a stricter definition than what I am envisaging, it can travel faster than light. Or rather, "NOT-information" (in a logical sense, and from which we can derive information) can travel faster than light. If it could not, we wouldn't have even been able to measure the speed of light itself, because we wouldn't have been able to check our light sources destination "before" it got there... if that makes sense?
What I mean is, if you put a light source one "light minute" away and triggered it, if you checked for light in 30 seconds, it will not have reached you, so would already have information about speed of light coming from the source, you would know how fast it ISN'T.

Could a lot of what we know about black holes be derived from what ISN'T coming out?
Could gravity itself (whatever it is... I know it's something to do with a warp in spacetime caused by matter) somehow be influenced by what is NOT?

2) We assume that for something to get out of a black hole, it must be go FASTER than light, but speed isn't the only property of "stuff" trying to escape a gravitational field, is it? Yes it is, doh! Next thing I'll be saying a glass full of water falls faster than an empty one :-)

Triangulation. You have three points, A, B and C all equally distant from one another. A beam of light is sent from A to B. The observer at C can derive the speed of light from the time it took for the light to get from A to B from his point of reference. There is also a delay in the light getting from A to C and from B to C but it is the same in both cases and so is not relevent to the maths.

[irR4tiOn4L]

Originally Posted by tompee

My eyes have rolled around in my head trying to read this thread, and I won't pretend I have the theoretical foundation to understand most of what is being said (I didn't do any science subjects for my HSC, for starters!), but I have a very basic question.

FIRSTLY, to make sure I have this clear - the apparent paradox discussed in this thread is that information manages to escape a black hole (otherwise how do we know it's there, what its gravitational pull is etc), but information is not meant to be able to travel faster than light, and light can't escape a black hole, so how does information escape?

My two, lay-man, type thoughts on this are:

1) Unless information has a stricter definition than what I am envisaging, it can travel faster than light. Or rather, "NOT-information" (in a logical sense, and from which we can derive information) can travel faster than light. If it could not, we wouldn't have even been able to measure the speed of light itself, because we wouldn't have been able to check our light sources destination "before" it got there... if that makes sense?
What I mean is, if you put a light source one "light minute" away and triggered it, if you checked for light in 30 seconds, it will not have reached you, so would already have information about speed of light coming from the source, you would know how fast it ISN'T.

Could a lot of what we know about black holes be derived from what ISN'T coming out?
Could gravity itself (whatever it is... I know it's something to do with a warp in spacetime caused by matter) somehow be influenced by what is NOT?

2) We assume that for something to get out of a black hole, it must be go FASTER than light, but speed isn't the only property of "stuff" trying to escape a gravitational field, is it? Yes it is, doh! Next thing I'll be saying a glass full of water falls faster than an empty one :-)

I was at the same point as you when i got here - basically though, 'information' here means any sort of signs that an object is there - either through some sort of particles, light or 'gravity' of the object. Now obviously if it isnt there, then that 'lack' of information signals it 'isnt' there - the problem is - if nothing is coming out of a black hole it should appear to us to have no gravitational pull - it does however, so why? Note that it would still look like a big black hole in space - so we could tell it was there by those 'inferences' from what it is NOT that you mentioned, but basically, we are asking why something that should not be signalling gravity at all (and should thus appear that it 'isnt' there) actually signals a lot.

Now under relativity, all of these things actually ARE sucked into a black hole - and cant escape it. This is so even with the 'gravity' of an object because a black hole is a 'distortion' or 'pit' in 'space-time' that is actually getting DEEPER at the speed of light! - so imagine that you have a pit in a trampoline that has broken the laws of physics and is getting deeper at a constant rate - if you make a new 'distortion' in that pit, it would have to travel UP and OUT of the pit before it could affect anything else - but if it moves no faster UP than the pit is going DOWN - then it stays still, and never makes it out.

This applies to almost all 'things' capable of communicating something's position - gravity, particles, light etc. All are limited to the speed of light, and cannot escape the pit-that-goes-down-faster-than-light (black hole).


Now the problem in this thread is how come a black hole, to us outside, has gravity, and appears to get heavier when it sucks stuff in? If gravity cant escape the black hole, how can it attract other objects?

Well the answer is interesting, but quite simple - there is a point near the black hole where anything traveling at light speed away from it will JUST stay on the spot - neither escaping nor falling in. This is the 'event horizon' - because past this point no information can reach us about an object and so no object ever appears, TO US, to pass this point (it actually does pass it).

As an object falling into the black hole approaches this 'horizon', it is constantly releasing 'light' and 'gravity' 'waves' toward us - but as it gets closer and closer, these travel slower and slower, and take longer and longer to get to us - in fact, it could be millions, billions, who knows how many years before the VERY LAST WAVE of 'information' (light, gravity etc) that the object released just before it crossed the event horizon ACTUALLY makes it to us.

The funny effect of this is that although the object isnt really 'there', we are still getting 'trace' light and gravity from it for a long time - and this trace 'gravity' is what we are actually observing as the gravity of the black hole! If lots of matter fell in, there will be lots of this 'trace' gravity and thus a very strong gravitational field around the black hole. This is what is known as a 'fossil field'.

An interesting side effect of all this is that a black hole should thus never appear to LOSE gravity - it can only appear to get heavier!

Now the same roughly holds true, depending on which version you are told, in quantum mechanics - but a really strange phenomena calling 'hawking radiation' actually escapes from near the black hole AND causes it to appear to get smaller! This is on a small scale though. Otherwise, no other information or matter can escape the black hole.


Its a very strange topic and seems to be on the edge of relativity and quantum mechanics - even Einstein acknowledged that something must be missing from relativity when he couldnt predict both the velocity and position of particles in experiments - so this area is still developing.

[Luke212]

Originally Posted by irR4tiOn4L

.

tnx this was very clear.