Uncovering the Mysteries of Black Holes

[danihel]

Hi,
I have to say that I'm not sufficiently educated in physics but I'm very interested in it so please excuse my silly questions.
First I'd like to ask what determines the quantity of space that the black hole occupies. Is it just the amount of matter that imploded during the super nova explosion or does the black hole grow bigger with everything that gets in it? If it grows bigger all the time doesn't it mean the matter doesn't completely disappear in the BH, nor it does appear again in other places?

Another question is: when the BH spews out energy it's because the heat and density along with magnetic field somehow overwhelms the gravitational pull of the BH? Does it spew out of the BH itself? does it spew out matter that's within the event horizon?

 

[DaveC426913]

Hi,
I have to say that I'm not sufficiently educated in physics but I'm very interested in it so please excuse my silly questions.
First I'd like to ask what determines the quantity of space that the black hole occupies. Is it just the amount of matter that imploded during the super nova explosion or does the black hole grow bigger with everything that gets in it? If it grows bigger all the time doesn't it mean the matter doesn't completely disappear in the BH, nor it does appear again in other places?

The black hole itself is theoretically zero volume - all the mass has been compressed to a point. But a BH is normally defined by its event horizon. This is nothing more than a radius. Anything less than this radius, including matter or energy can never escape.

This radius is entirely determined by the amount of mass in the black hole.

Another question is: when the BH spews out energy it's because the heat and density along with magnetic field somehow overwhelms the gravitational pull of the BH? Does it spew out of the BH itself? does it spew out matter that's within the event horizon?

A BH does not spew out energy. What happens is that infalling matter forms an accretion disc outside the EH. This disc radiates energy as it compresses.

 

[danihel]

Thank you very much for explanation, so if i understood well- every BH has this one infinitely small point of singularity but differs in the extent of gravitational deformation of space around it.
Does the event horizon grow with stuff falling into the hole?

 

[DaveC426913]

Thank you very much for explanation, so if i understood well- every BH has this one infinitely small point of singularity but differs in the extent of gravitational deformation of space around it.

Yes.

Does the event horizon grow with stuff falling into the hole?

Yes.

 

[Matterwave]

Black holes also radiate (theoretically) Hawking radiation. The simplest model for which is the creation of particle-anti-particle pairs near the Event horizon (allowed because of QM). One of the particles drop into the BH, the other particle escapes. This process steals energy from the black hole until the black hole completely evaporates. For a massive black hole, this would take a really really long time (something like a googol years for a supermassive black hole), but for theoretical micro-black holes, this process may evaporate the black hole within a matter of seconds.

 

[Prologue]

The black hole itself is theoretically zero volume - all the mass has been compressed to a point. ...

Why does the BH have to have zero volume? Why can't it just be a lump that is contained within its own event horizon? Is it because the highest counter-compression (that I know of) is neutron degeneracy pressure, and in order to be dense enough to be within it's own event horizon the pressure would be greater than this?

 

[Matterwave]

There are no known forces of nature which would prevent further gravitational collapse once the matter is squished within the Event horizon. We don't know if the matter really is concentrated at a point, we just don't know of any pressure or force that could "win" against gravity inside the EH.

 

[qraal]

Why does the BH have to have zero volume? Why can't it just be a lump that is contained within its own event horizon? Is it because the highest counter-compression (that I know of) is neutron degeneracy pressure, and in order to be dense enough to be within it's own event horizon the pressure would be greater than this?

Pressure is a measure of a system's internal energy - thus it adds to the gravity and so causes the necessary counter-pressure to increase. Confinement pressures from Pauli Exclusion and the like, mean the pressure-gravity feedback becomes positive and so runs away into a singularity. Thus the singularity is really where quantum and GR conspire to create the incomprehensible. A strong motivation to develop 'quantum gravity', but so far the proposed QGR theories have no clear front-runners we can confidently say describe/eliminate the singularity.

 

[qraal]

There are no known forces of nature which would prevent further gravitational collapse once the matter is squished within the Event horizon. We don't know if the matter really is concentrated at a point, we just don't know of any pressure or force that could "win" against gravity inside the EH.

Good point. We don't know, but what theory tells us is that the mass is infinitely compressed because of the pressure-gravity runaway feedback... which makes more than a few people wonder if the theory is wrong.

There's two ways of handling that. One involves quantum gravity effects which prevent the singularity and smear it out or cause a daughter Universe to explode as a new space-time. The other option is to propose that a new kind of space-time is either just above the event horizon or just within it, and some kind of repulsive gravity is at work producing a 'gravastar' or similar non-singular space-time. The event horizon becomes a real physical boundary between two very different space-time states in the second option. The race amongst theorists working with either option is to produce real observational tests to distinguish between the options and/or classical GR black-holes.

 

[Chronos]

I would quibble over the density of a black hole. It is theoretically a point in space, but Heisenberg suggests it must have a finite, albeit miniscule, volume.

 

[danihel]

Is the fact that everything that falls into the black hole adds to its gravitational pull consistent with the notion that it appears in some other universe or bigbang or some other place in the universe?

 

[DaveC426913]

Is the fact that everything that falls into the black hole adds to its gravitational pull consistent with the notion that it appears in some other universe or bigbang or some other place in the universe?

In fact, no it seems pretty inconsistent. Whatever it has undergone, as far as we can tell, the mass it still there, at the centre of the BH.

 

[danihel]

thanks a lot again for such a quick answer
I was just wondering because in some documentaries I heard various ideas about black holes maybe being worm holes to other universes and stuff like that

 

[Chronos]

A wormhole to another universe would drain energy from this universe. No observations to date suggest loss of energy from this universe. Were this so, we would observe black holes eating matter without increasing in mass. Black holes would be all appear to be about the same mass if this was the case.

 

[DaveC426913]

I was just wondering because in some documentaries I heard various ideas about black holes maybe being worm holes to other universes and stuff like that

TV is a notoriously bad place to pick up knowledge. You just can't fit all the necessary foundational material in a half-hour or one-hour show. And almost all science shows go for gimmicky or flashy speculative stuff rather than good science.


Go with books.

 

[qraal]

A wormhole to another universe would drain energy from this universe. No observations to date suggest loss of energy from this universe. Were this so, we would observe black holes eating matter without increasing in mass. Black holes would be all appear to be about the same mass if this was the case.

Oddly enough we wouldn't see a mass-loss. The external field is "frozen" at the value set by infalling matter. In fact wormholes would exhibit a similar mass change with respect to inflow and outflow through them. A net negative flow would cause a wormhole to become repulsive.

But I wasn't referring to regular wormholes. Some theories - Lee Smolin's for example - have black holes producing "baby universes" from their mass.

 

[wofsy]

couple of questions:

- Why can't a BH be something other than a point?

- Someone once said to me that as a BH forms an outside observer will see the clocks in the forming hole slow down continually towards zero. So it would thus take an infinite amount of time on the outside observer's clock for the hole to form. If this is true how can a BH ever be observed? Put another way, how can a BH exist unless it already existed at the creation of the Universe?

 

[Frame Dragger]

I would quibble over the density of a black hole. It is theoretically a point in space, but Heisenberg suggests it must have a finite, albeit miniscule, volume.

A good point which is supported by theoretical existence of ring singularities.

@wofsy: I think as long as people are talking about Black Holes and the possible sigularity at its center interchangeably, finer points should be abandonded for the basics.

A black hole is never a point, it's an entity including an event horizon past which GR says there will be a point of zero volume. A singularity doesn't have to be a point... it can be a point, or a string, or a loop... maybe. If they exist. You have to understand, while there is observation of BHs, nothing has ruled out the possibility of something just at or below the radius of a BH existing with or without an event horizon. The margin of error in astronomical observations leave room for argument, and no one has detected the emission of phonons or the like from lab-bound analogues. The question is as up in the air as DaveC426913 pointed out.

As for the red shift you're talking about, you're ignoring relativity. To an observer it may appear that infalling matter fades to unobservability at the event horizon (after a long redshift) assuming you could see through the radiation from the accretion disk (and maybe Hawking Radiation or other thermal-like process). To the subject B falling into the black hole, they can pass the event horizon without noticing anything until tidal forces, radiation, etc, tear them to bits. This requires a VERY large black hole, and a hardy observer, but you get the idea. The whole problem with black holes and the event horizon is that it marks a boundary condition on reality if the theory is formalist in GR.

This is why some people believe that a black hole is a series of events which eventually comes to a complete halt (not as in frozen, as in oblitered), and not an "object". The Singularity by definition never interacts with the universe, only the event horizon, and surrounding accretion disc. Gravitic effects are the result of within the radius of the event horizon. If GR is correct, then black holes represent a boundary condition on anything like Classical and Relative space-time. Whatever describes an object with a radius of or less than the event horizon requires physics other than GR or SQM in their current state, assuming they are open to description or observation... which is an iffy assumption. Some String Theorists and many other have ideas, but they are completely untested and theoretically also untestable. Fantastic and amazing ideas are born around the topic of black holes, but in terms of hard science they are still pretty damned enigmatic.

 

[Frame Dragger]

Oddly enough we wouldn't see a mass-loss. The external field is "frozen" at the value set by infalling matter. In fact wormholes would exhibit a similar mass change with respect to inflow and outflow through them. A net negative flow would cause a wormhole to become repulsive.

But I wasn't referring to regular wormholes. Some theories - Lee Smolin's for example - have black holes producing "baby universes" from their mass.

You're right and wrong. A TRAVERSABLE wormhole to another part of the same universe might not show mass loss, but one to another universe surely would. I'm not sure exactly what kind of wormhole you're talking about... and ERB? Something far more stable presumably... As for the idea that black holes spawn baby universes, I think that is just people enjoying the apparent similarity to the initial state of the universe and the mathematics of a gravitational singulariy. Most resptable "multiverse" theories involve a primordial vacuum, brane cosmology, etc... not our universe blowing inverted bubbles out of its own existence.

 

[Chronos]

The external observer will see the event horizon form, but, never the singularity.

 

[wofsy]

The external observer will see the event horizon form, but, never the singularity.

so how can a BH exist unless it existed at the creation?

 

[sylas]

so how can a BH exist unless it existed at the creation?

Just put enough mass together in one place; the collapse of a big star should do it. Not seeing past the horizon has nothing to do with whether it exists or not. Horizons are limits of visibility or influence; not limits of existence.

Cheers -- sylas

 

[wofsy]

Just put enough mass together in one place; the collapse of a big star should do it. Not seeing past the horizon has nothing to do with whether it exists or not. Horizons are limits of visibility or influence; not limits of existence.

Cheers -- sylas

but sylas - the outside observer will never see the clocks go to zero time - it will take infinitely long - so how can the singularity form?

 

[Dmitry67]

it will take infinitely long for the outside observer only
For freely falling observer it takes a short time

 

[Frame Dragger]

Just put enough mass together in one place; the collapse of a big star should do it. Not seeing past the horizon has nothing to do with whether it exists or not. Horizons are limits of visibility or influence; not limits of existence.

Cheers -- sylas

Remember wofsy, what the central tenants of GR mean. Along with Mass-Energy equivalence, the concept that there is no universally valid "clock" is central to this issue. Imagine GIANT body of gas collapsing to form a black hole, such as the ones that exist in Active Galaxies. You could be there for the formation of such a hole, pass the "point of no return" that is the Event Horizon and you would NOT NOTICE A THING.

To the person watching you from a distance, it would be a VERY different story. You would appear to become dimmer and dimmer... redder and redder... the closer you came to the event horizon. You wouldn't experience that however as the person falling inward until you began to experience tidal forces that turned you into subatomic spahgetti.

This is what "Relativity" is. Each entity, person, particle, space-like slice... etc... has its own unique "clock" that tells local time. No two clocks will agree. The event horizon of a black hole represents an end to the ability of GR to predict any further behaviour beyond speculation, or the concept of a literal singularity that truly exists. An event horizon is the boundary at which a photon's possible degrees of freedom ALL take it within the BH, and make escape impossible. As nothing is believed to be FTL, presumably all "information" is lost to observers (unless there is a Holographic Principle that works, some kind of Beckenstein-busting remnant, etc... who knows), but that means NOTHING to the person passing that horizon except that they are inevitably going to encounter the singularity. And be torn apart. You get the idea.

Again... anything COULD be crushed into a singularity if you compress it past its Schwarzschild Radius. In nature this happens to massive bodies (probably) undergoing collapse or accretion. A neutron star accretes matter and then collapses further, or a star or other gas cloud collapses under its own gravity beyond the force that even degeneracy pressures can overcome.

Remember, a white dwarf = Atoms stripped of their electrons in a soup of degenerate matter. A Neutron Star is one in which those electrons and protons can no longer overcome gravity and are forced to fuse. They become neutrons, so a neutron star is probably varying configurations and densities of degenerate neutron matter. In THEORY, you could have a quark star, or a gravstar and they might, or might not have an event horizon. In theory, it may be event horizons do not exist, and neither do singularities. A BH is a BH, not so much because of the singularity at its heart... which is still open to TONS of theoretical speculation... but the event horizon that separates anything within its radius from the universe outside.

 

[wofsy]

it will take infinitely long for the outside observer only
For freely falling observer it takes a short time

Ok but I am an outside observer say the center of of a distant galaxy. Why then do astronomy web sites say that there are Bh's in their center. that seems impossible.

 

[Frame Dragger]

Ok but I am an outside observer say the center of of a distant galaxy. Why then do astronomy web sites say that there are Bh's in their center. that seems impossible.

I don't mean this as an insult, but if you haven't understood the principle of what relativity means, you need to study this subject more. You're not at this point yet. People are trying to tell you as simply as possible: THE EVENT HORIZON IS LIKE ANY OTHER HORIZON. You can't see beyond the horizon on the ocean... right? Does that mean the ocean beyond the horizon doesn't exist? This is a different configuration and type of horizon, but the meaning is VERY SIMILAR.

 

[wofsy]

I don't mean this as an insult, but if you haven't understood the principle of what relativity means, you need to study this subject more. You're not at this point yet. People are trying to tell you as simply as possible: THE EVENT HORIZON IS LIKE ANY OTHER HORIZON. You can't see beyond the horizon on the ocean... right? Does that mean the ocean beyond the horizon doesn't exist? This is a different configuration and type of horizon, but the meaning is VERY SIMILAR.

i understand more than you think. think about my question.
the presence of an event horizon does not mean that there is a black hole.

 

[Frame Dragger]

i understand more than you think. think about my question.

*facepalm*. Look man... Relitivity = event horizon forms and everything beyond that is unknowable. Add mass to a black hole, and its radius increases. Allow it to radiate, and the radius shrinks. What you're describing is only paradoxical from the point of view of a particular observer. It's understanding that both are valid viewpoints forming only PART of a whole that is at the core of Relativity.

Your experience as the observer is precisely why a black hole would be BLACK. The event horizon would be a true black-body in theory, but detection would fail before that point. Send in 10,000 observers at intervals, and you'd either get their mass added to the black hole, or in another theory their information is sort of... smeared... across the Event Horizon. Either way, in principle the varying accounts of each observer would differ from an external observer, and each other.

GR says that space and time are an inseprable fabric, and that everyone at any distance will agree on the outcome of an event. They will percieve it slightly (or in extreme cases such as a black hole VERY) differently, but the event itself must be universally THE SAME... until the Event Horizon, which is the point past which all of those theories cease to make meaningful predictions!

EDIT: you added another statement... An event horizon doesn't mean there is a black hole, as I and others have said previously many times on this thread. However, anything beyond the event horizon doens't interact with the universe outside, so in essence a Black Hole as studied and understood is a gravtiational field bound by the region of the horizon beyond which there could be, "green slime and socks." :)

 

[DaveC426913]

Ok but I am an outside observer say the center of of a distant galaxy. Why then do astronomy web sites say that there are Bh's in their center. that seems impossible.

You're imagining this happening a bit too idealistically. It's not not like have a perfect view into the BH.

'The singularity forming taking infinite time' is really only in principle. What you really see is a fade-to-black, because, very rapidly, the number of photons reaching you drops to near zero. If, in principle, you could crank up the gain on those few photons, you'd see that each successive photon showed less and less change. Eventually, photons rising out of the BH would become few and far between - so few that you'd no longer have an image, you'd simply have discrete photons. Additionally, each photon would show very little change from the last. Ultimately, you'd get bored waiting for photons, especially since the information they brought with them would be horribly out-of-date.

Think about watching a video. At first, the video looks fine, with full pixel information and 30fps frame rate. But very rapidly the frame rate drops to 1fps and then 1 frame every ten seconds. Additionally, each frame begins rapidly dropping information, so that only a few pixels are being updated. You' quickly reach a point where there's only a frame change every minute, and that frame change only updates a couple of pixels. The movie you are trying to watch will take an infinite length of time to play out - not so much because it's slowing down, but because your view of it has virtually ground to a halt.

 

[wofsy]

*facepalm*. Look man... Relitivity = event horizon forms and everything beyond that is unknowable. Add mass to a black hole, and its radius increases. Allow it to radiate, and the radius shrinks. What you're describing is only paradoxical from the point of view of a particular observer. It's understanding that both are valid viewpoints forming only PART of a whole that is at the core of Relativity.

Your experience as the observer is precisely why a black hole would be BLACK. The event horizon would be a true black-body in theory, but detection would fail before that point. Send in 10,000 observers at intervals, and you'd either get their mass added to the black hole, or in another theory their information is sort of... smeared... across the Event Horizon. Either way, in principle the varying accounts of each observer would differ from an external observer, and each other.

GR says that space and time are an inseprable fabric, and that everyone at any distance will agree on the outcome of an event. They will percieve it slightly (or in extreme cases such as a black hole VERY) differently, but the event itself must be universally THE SAME... until the Event Horizon, which is the point past which all of those theories cease to make meaningful predictions!

EDIT: you added another statement... An event horizon doesn't mean there is a black hole, as I and others have said previously many times on this thread. However, anything beyond the event horizon doens't interact with the universe outside, so in essence a Black Hole as studied and understood is a gravtiational field bound by the region of the horizon beyond which there could be, "green slime and socks." :)

you are very poetical

 

[wofsy]

You're imagining this happening a bit too idealistically. It's not not like have a perfect view into the BH.

'The singularity forming taking infinite time' is really only in principle. What you really see is a fade-to-black, because, very rapidly, the number of photons reaching you drops to near zero. If, in principle, you could crank up the gain on those few photons, you'd see that each successive photon showed less and less change. Eventually, photons rising out of the BH would become few and far between - so few that you'd no longer have an image, you'd simply have discrete photons. Additionally, each photon would show very little change from the last. Ultimately, you'd get bored waiting for photons, especially since the information they brought with them would be horribly out-of-date.

In other words, there really aren't any new black holes that have formed in this incarnation of the Universe

 

[Frame Dragger]

you are very poetical

I'm a really *****y poet... I appreciate the irony/insult... and while I shouldn't laugh along with it, I am. Probably that isn't a good sign of my mental health. Ah well.

You are at the very least, extremely curious and persistant. Not bad qualtities at all.

 

[DaveC426913]

the presence of an event horizon does not mean that there is a black hole.

Yes it does, pretty much by definition.

You have a horizon out of which light cannot escape. You have mass inside. Regardless of what's actually happening inside, that's a black hole.

Now, the issue is whether you have a singularity. Well, you do. Same way.

When we project known physics (GR) into the space inside a BH, our understanding tells us there's no force that can withstand gravitational collapse. But: it doesn't matter what actually happens, what matters is that our current physics is unable to describe it. That is the definition of singularity.

 

[DaveC426913]

In other words, there really aren't any new black holes that have formed in this incarnation of the Universe

Why do you say this? This is nonsensical.

Are you trying to say that, because we don't observe it from our current coordinates, it does not exist?


By the same logic there are no stars outside our observable universe. If I flew in my spaceship 1 billion light years East (i.e. l change my coordinates), I would see an empty void at the end of the universe.

 

[Frame Dragger]

In other words, there really aren't any new black holes that have formed in this incarnation of the Universe

Large Gamma Ray Bursts would argue otherwise for one. Again, you could take a styrofoam cup, and with an ungodly amount of pressure it could be compressed beyond its Shwarzschild Radiius at which point Gravity would dominate all other forces... create an event horizon, and whatever the hell is really beyond such a horizon.

If DaveC went on, he could tell you that the photons would come arbitrarily slowly, and finally not at all. The point at which photons cease to return IS the Event Horizon. Measurements of bodies believed to be rapidly rotating black holes seem to support the notion of an event horizon, and Black Holes.

Take Stephen Hawking's analogy of time as a globe. At the north pole is the big bang, which expands in space-time either in an expanding cone or a sphere that reaches maximum size and returns to collapse at the opposite pole. In that scheme, you can imagine that if you cut the universe into time and space -like slices, different slices would also represent different physical states of the BH. However, as observers outisde the Event Horizon, what is inside can only ever be of academic interest, or of interest to an unimaginaby advanced society.

 

[Frame Dragger]

Yes it does, pretty much by definition.

You have a horizon out of which light cannot escape. You have mass inside. Regardless of what's actually happening inside, that's a black hole.

Now, the issue is whether you have a singularity. Well, you do. Same way.

When we project known physics (GR) into the space inside a BH, our understanding tells us there's no force that can withstand gravitational collapse. But: it doesn't matter what actually happens, what matters is that our current physics is unable to describe it. That is the definition of singularity.

I vote for "green slime and lost socks" myself. :lol:

 

[DaveC426913]

Again, you could take a styrofoam cup, and with an ungodly amount of pressure it could be compressed beyond its Shwarzschild Radiius at which point Gravity would dominate all other forces... create an event horizon, and whatever the hell is really beyond such a horizon.

It seems he's not questioning if the physics say a BH can form; in fact, he's not even refuting that they do exist. He's simply saying that, since BHs appear (to an outside observer) to take forever to form, that none have formed since the BB. He seems unable to get past this block.

I am eager to see him deduce that, since we cannot see them from Earth, stars beyond our observable universe never actually formed.

 

[Frame Dragger]

It seems he's not questioning if the physics say a BH can form; in fact, he's not even refuting that they do exist. He's simply saying that, since BHs appear (to an outside observer) to take forever to form, that none have formed since the BB. He seems unable to get past this block.

I am eager to see him deduce that, since we cannot see them from Earth, stars beyond our observable universe never actually formed.

Maybe he's a solopist? ;)

 

[Frame Dragger]

In other words, there really aren't any new black holes that have formed in this incarnation of the Universe

Hmmm... I was just re-reading this a few times to fully soak it all in. If the BHs take an infinite time to form according to your (wrong) view... then they wouldn't exist. New, or old in ANY universe with a history like ours. You also seem to be making a "big crunch/big bang" cycle of universal history, which seems to be unlikely given the observed cosmological constant. In essence, you're wrong in every possible and meaningful way you can be.

I'm not saying any of this to taunt or tease you. I'm trying to get through to you. You have a grasp on some interesting concepts, but only in piecemeal. You need to open your mind a bit and go back to the basics of General and Special Relativity. I think when you do, the answers to your questions about the formation and evolution (including the DEATH/evaporation) of a black hole.

This is one of those entities that emerged from the math FIRST, and then observations have shown bodies which lookk and behave a LOT like Black Holes. Something superdense and massive is out there, in the center of our galaxy, and many others... and other BHs are all over the place. However... just what that is, whether objects can be crushed out of existence (Hawking view) and then radiated through a quantum process thus breaking Unitarity is open to a lot of questions.

However, based on the rotation of some of these bodies and their mass, whatever is out there is VERY like a black hole, which is why it's so crucial to see how Event Horizons (sonic in this case) behave in the lab. Do they radiate phonons (photons for Grav)? Is information encoded in the event horizon, or is it lost? Is there some kind of superdense remnant that defies the Planck Scale and Beckenstein Bound? The answer is: This is what string theorists, loop quantum gravity fans, GR theorists, and everyone else wants to know.

The entire point of studying black holes is that they represent an extreme case where gravity overwhelms the other 3 forces (EM, Strong Nuclear, Weak Nuclear) and the "edges" of GR and SQM can be studied.

 

[Dmitry67]

wofsy, in GR you can not assume the 'global time'.
Even more, in highly curved spacetime there are many different ways to 'map' events to each other. Depending on the method, the answer can be positive or negative.
Don't assume that there is a global time flow in the Universe

 

[skeptic2]

From post #16 referring to matter draining from a black hole through a wormhole.

Oddly enough we wouldn't see a mass-loss. The external field is "frozen" at the value set by infalling matter. In fact wormholes would exhibit a similar mass change with respect to inflow and outflow through them. A net negative flow would cause a wormhole to become repulsive.

But I wasn't referring to regular wormholes. Some theories - Lee Smolin's for example - have black holes producing "baby universes" from their mass.

Graal, this is an interesting concept that I wish you would expand upon. Does the theory suggest that spacetime becomes plastic at the horizon and remains permanently deformed even in the absence of matter or that matter, as it passes through the horizon, leaves its gravitational and electrical fields behind?

 

[Frame Dragger]

From post #16 referring to matter draining from a black hole through a wormhole.



Graal, this is an interesting concept that I wish you would expand upon. Does the theory suggest that spacetime becomes plastic at the horizon and remains permanently deformed even in the absence of matter or that matter, as it passes through the horizon, leaves its gravitational and electrical fields behind?

Mass and Charge are added to a black hole when matter (or matter with charge) is added. In fact, Mass, Charge, and Angular Momentum are it for what you get from a Black Hole. That.. is the problem! lol

You could in theory cause a nonrotating uncharged BH to being to rotate, gain a charge, and increase its mass by dropping in charged matter with angular momentum.

 

[skeptic2]

Since it is generally accepted that a black hole is empty except for the singularity, one would suppose that mass, charge and angular momentum would be properties of the singularity. How can properties of the singularity influence anything outside the event horizon? The short answer is they can't. This is why I suspect the hypothesis suggests that these properties are frozen into spacetime at the horizon as matter passes through. I am looking for a more detailed explanation of the basis for that assumption.

 

[wofsy]

wofsy, in GR you can not assume the 'global time'.
Even more, in highly curved spacetime there are many different ways to 'map' events to each other. Depending on the method, the answer can be positive or negative.
Don't assume that there is a global time flow in the Universe

Thanks Dmitry I understand that there is no global time. I am just asking the question from our particular frame of reference..

 

[Frame Dragger]

Since it is generally accepted that a black hole is empty except for the singularity...

Really? This isn't in line with many theories, including those predicted by virtually all QM interpretations. I would be interested to know why you believe this.

As for these properties freezing at the event horizon, who knows? HR takes place at the EH, and is separated from the inside of the BH. If the Holographic Principle is correct, then the EH contains the otherwise 'lost' Information. That said, it doesn't imply that time stop at the EH, which would of course be Relative. Whether the EH is a boundary condition or just a point of no return, it's still a brick wall for physics and the beginning of either unified GR/QM, or pure metaphysics.

 

[wofsy]

Hmmm... I was just re-reading this a few times to fully soak it all in. If the BHs take an infinite time to form according to your (wrong) view... then they wouldn't exist. New, or old in ANY universe with a history like ours. You also seem to be making a "big crunch/big bang" cycle of universal history, which seems to be unlikely given the observed cosmological constant. In essence, you're wrong in every possible and meaningful way you can be.

I'm not saying any of this to taunt or tease you. I'm trying to get through to you. You have a grasp on some interesting concepts, but only in piecemeal. You need to open your mind a bit and go back to the basics of General and Special Relativity. I think when you do, the answers to your questions about the formation and evolution (including the DEATH/evaporation) of a black hole.

This is one of those entities that emerged from the math FIRST, and then observations have shown bodies which lookk and behave a LOT like Black Holes. Something superdense and massive is out there, in the center of our galaxy, and many others... and other BHs are all over the place. However... just what that is, whether objects can be crushed out of existence (Hawking view) and then radiated through a quantum process thus breaking Unitarity is open to a lot of questions.

However, based on the rotation of some of these bodies and their mass, whatever is out there is VERY like a black hole, which is why it's so crucial to see how Event Horizons (sonic in this case) behave in the lab. Do they radiate phonons (photons for Grav)? Is information encoded in the event horizon, or is it lost? Is there some kind of superdense remnant that defies the Planck Scale and Beckenstein Bound? The answer is: This is what string theorists, loop quantum gravity fans, GR theorists, and everyone else wants to know.

The entire point of studying black holes is that they represent an extreme case where gravity overwhelms the other 3 forces (EM, Strong Nuclear, Weak Nuclear) and the "edges" of GR and SQM can be studied.

thanks. this was helpful. although I still don't see the answer I will wait until I learn more about GR.

I was just just imagining an astronomer on Earth watching a star collapse and wondered when it would be that he saw the resulting black hole if the observed time in the star slow to zero in a infinite amount of his time. And if it isn't quite right to say that he could observe the hole he would still be able to predict that it would never form in finite time - thus never completely form.

The question is not whether there are black holes - but when in his frame of reference, did they form?

 

[George Jones]

Someone once said to me that as a BH forms an outside observer will see the clocks in the forming hole slow down continually towards zero. So it would thus take an infinite amount of time on the outside observer's clock for the hole to form.

For an observer who follows a particular worldline.

If this is true how can a BH ever be observed? Put another way, how can a BH exist unless it already existed at the creation of the Universe?

By following a different worldline, i.e., you could choose to cross the event horizon. You are free to choose to see or not to see the black hole region, just as in SR you are free to follow a wordline from which you can observe all of spacetime, or to follow a worldline for which parts of spacetime are always observationally inaccessible to you, even if you live to an infinite age.

Just put enough mass together in one place; the collapse of a big star should do it. Not seeing past the horizon has nothing to do with whether it exists or not. Horizons are limits of visibility or influence; not limits of existence.

And if the volume of space is large, the density of matter needed can be arbitrarily small, smaller even than the density of our atmosphere.

i understand more than you think. think about my question.
the presence of an event horizon does not mean that there is a black hole.

The definition of the black hole region of an asymptotically flat spacetime is the region of spacetime from which it is impossible to escape to future null infinity. An event horizon is the boundary of this region.

Within ten years, black holes should be "observed" as black disks with certain properties.

[edit]Back to my day job.[/edit]

 

[skeptic2]

Really? This isn't in line with many theories, including those predicted by virtually all QM interpretations. I would be interested to know why you believe this.

Please excuse my ignorance. What is the interior of the event horizon filled with?

As for these properties freezing at the event horizon, who knows? HR takes place at the EH, and is separated from the inside of the BH. If the Holographic Principle is correct, then the EH contains the otherwise 'lost' Information. That said, it doesn't imply that time stop at the EH, which would of course be Relative. Whether the EH is a boundary condition or just a point of no return, it's still a brick wall for physics and the beginning of either unified GR/QM, or pure metaphysics.

Are you saying that the encoded information at the horizon creates the gravitational, electrical and angular momentum properties felt outside the EH?