How deep is down?

"Massive black holes do not "shrink"; they consume and grow."

According to Prof. Stephen Hawking ("A Brief History of Time", Chapter 7: "Black Holes Ain't So Black"), there is a mechanism which leads to Black Holes evaporating, as I outlined in my previous response. They take a very long time to disappear, but the rate accelerates as the Hole becomes smaller. Admittedly this book was published back in 1988, but my understanding is that this idea has become generally accepted. Perhaps avid0g knows better?

Geoffrey H. Grayer BSc PhD

That's why I used the qualifier "massive".

What black holes really are...

http://www.youtube.com/watch?v=AApmn2gVU20

"...... the event horizon is also still "ahead".......". An observer falling into a black hole has no means (e.g. some measurement) to tell whether he has passed the event horizon. But he can calculate whether that event has occurred, because it occurs at a specific finite point in time as per his clock, which he could calculate by knowing his initial conditions and the black hole's properties. So the event horizon won't still be "ahead" from his perspective. Just that nothing extraordinary will happen at the passing, and he'll probably wonder what all the fuss about that point in time was anyway.

An observer outside would observe this falling observer approach the event horizon (which to him is an observable, measurable phenomenon, namely the point beyond which he has no information from) slower and slower, never really reaching it.

The transformation between the two frames of reference is such that the event of crossing the horizon would occur at infinite time for the external observer but at finite time for the one falling in.

"An observer falling into a black hole has no means (e.g. some measurement) to tell whether he has passed the event horizon."

On the contrary, It is quite easy to tell when the event horizon is passed. If you were watching a clock out there, it would seem to slow down as it becomes red-shifted and smaller. The universe is distorting, compressing to the sides. There is a black ring ahead, getting wider, then surrounding you on all sides. The visible part of the universe is retreating ahead of the ring, concentrating farther and farther "up" or "out" As you pass the event horizon, the entire outside universe has shrunk to a point, infinitely red shifted and infinitely dim (black).

"An observer outside would observe this falling observer approach the event horizon (which to him is an observable, measurable phenomenon, namely the point beyond which he has no information from) slower and slower, never really reaching it."

This is a misconception. A clock on the falling object is slowing down, but the object itself is accelerating inward. At the event horizon it's apparent speed would be the speed of light, however, it cannot be observed because both emitted and reflected light is infinitely red shifted.

The journey is not over, because other in-falling matter is still visible all around. There is still a black hole event horizon further in/down from the perspective of the falling observer. Below that event horizon, light cannot escape. This is where the balance of the mass of the black hole is contained.

Yes, I did realize that the event horizon for the falling observer would lie forever ahead for him. But it is certainly true that a non-accelerating observer from outside would never see him reach the horizon. In the non-accelerated frame outside, the event of the falling observer "crossing" the horizon would occur at infinite time. I have made the calculation myself for a Schwarzschild black hole at least, but it was a couple of years ago when I'd taken the course, so I don't remember the details.

Here's an excerpt from Wikipedia, which I have enough confidence in to rely on for correctness: "Light emitted from beyond the horizon can never reach the observer, and any object that approaches the horizon from the observer's side appears to slow down and never quite pass through the horizon, with its image becoming more and more redshifted as time elapses. The traveling object, however, experiences no strange effects and does, in fact, pass through the horizon in a finite amount of proper time."

The reason why I think the falling observer "can't tell" is because, from his perspective, what he's passed is simply not the horizon. His horizon is receding further and further. Wikipedia says, "Observers who fall into the hole are moving with respect to the distant observer, and so perceive the horizon as being in a different location, seeming to recede in front of them so that they never contact it. Increasing tidal forces (and eventual impact with the hole's gravitational singularity) are the only locally noticeable effects."

So no qualitative change occurs in the physical phenomena he observes. However, he can know when he has passed the distant stationary observer's horizon. He can't tell from his physical observations, but he can from calculations. Beyond that point, he can still see the external observer and other objects outside, but he knows any attempted contact with them is futile.

According to General Relativity: the volume within the event horizon is Space-like, the surface of the event horizon is Light-like, and the Universe outside is (gradually) Time-like. Therefore, infalling matter seems to reach the speed of light at the event horizon.

This free falling matter is not being accelerated in the Relativistic sense, so reaching lightspeed is normal. It may help to imagine Space flowing into the black hole, carrying matter with it.

If an object never reaches the "bottom" of a black hole, and never collides with the first object drawn in, then how can the mass of the hole increase? The hole must really be caused by a string of objects, rather than a single point.If these strings are compressed into an infinitely small size,or separated on the atomic layer into atoms, and even smaller components,electrons,protons, quarks, etc.then this "black string" of matter must have an increasingliy sharp "point".Perhaps it is "sharp" enough to emit "strings", becoming a "white emitter" that generates the strings from which our universe is created.Matter has thus come full circle.

This would surely be symmetrical, as nature seems to be.

Comments?

My unpublished "onion skin" hypothesis/model of a black hole says that the mass of the original black hole doesn't increase (in external time), but as the accretion disk accumulates the total mass becomes large enough to generate a new event horizon outside of some of the accretion disk matter, creating a new, larger black hole around the original (an extra infinitesimally thin "skin" on the onion) .

Additionally, because infalling matter inside the black hole is becoming denser then if external physics still applied you would get additional event horizons forming inside the original, "trapping" matter in time stasis until there was not enough matter inside the innermost event horizon to create more event horizons. The core of the black hole would thus never become a singularity, with the bulk of the mass trapped in a thick shell of frozen time.

Three caveats:

1. No true black hole event horizons might ever quite form, as the slowing of time may mean the horizons will still be on the verge of forming an infinitude of universe lifetimes from now, so you'd only ever have virtual event horizons.
2. Quantum effects such as the uncertainty principle could allow matter to jump the barrier of frozen time. However as quantum effects are time-related they should have very little effect on matter in the frozen time shells in external time, and as quantum effects decrease dramatically with distance they should only have significant effect on micro black holes.
3. According to accepted scientific theory external physics doesn't have to apply inside an event horizon, so if an event horizon did manage to fully form then all bets are off as to what's inside.
   

If,as you postulate, the mass of the original black hole doesn't increase, how then do millions of solar mass black holes occur in the center of galaxies? The "mass" of a black hole is "seen" by its gravitational effects on space-time, and the gravitational effects on surrounding matter, such as other stars, and indeed the entire external galaxy.

Maybe it would be better worded as "the mass inside the original event horizon doesn't increase".

Even with the original wording, if you look towards the end of the paragraph you'll see "creating a new, larger black hole around the original", which allows for the formation of multi-million solar mass black holes.

As for the "mass" of the black hole being "seen", if gravitational effects travel at the speed of light then what is "seen" is merely the gravitational after-image of the mass just prior to formation of the event horizon, as the current gravitational effect is trapped behind the event horizon. This would mean that a black hole with a true classical event horizon could never evaporate, even if it lost all it's mass. Even wierder, that mass could evaporate out of the black hole then fall back down onto the black hole and increase the hole's size and apparent mass, albeit too slowly to account for large black holes.

Thanks for stimulating further development of my hypothesis.

An additional black hole event horizon forms outside of the first, and then another outside of that, and so on. These are composed of mass that never reaches the event horizon of the original black hole, plus the mass of the original black hole, which retains it's original mass and event horizon.

Thus the massive black hole is like an onion in that it actually consists of multiple layers of event horizons. In practice each layer is infinitesimally thin, so that the massive black hole consists of a small black hole surrounded by a thick layer of material stuck in the frozen time of the multitude of event horizons that have formed outside the original event horizon.

Since gravity, and thus the changes in spacetime that create event horizons apparently travels at the speed of light and is thus subject to the time freezing effects of the event horizons it is creating, things can get rather complex. Matter can infall past where the event horizon is going to form before the gravitational wave creating the event horizon can get there.

One interesting complication is that mass falling onto the far side of a black hole can only exert a gravitational influence around the black hole, and not through it, because the influence would take forever to pass through the event horizons. This means that the influence is weakened due to the greater distance around the black hole and the inverse square law, and may mean that normal calculations of a black hole's mass from it's gravitational effect may be underestimates.

"If an object never reaches the "bottom" of a black hole, and never collides with the first object drawn in, then how can the mass of the hole increase?"
The short answer is: Mass distorts space-time. The illusion is "force of gravity".

"The hole must really be caused by a string of objects, rather than a single point."
Exactly, all the matter that ever fell in is still falling further in.

"If these strings are compressed into an infinitely small size..."
There is no compression, instead, there is a "tidal force" that stretches and breaks objects apart as they fall further in. This is called "spaghetti-fication"

To call the process spaghetti-fication is incorrect.The objects could not cling together as a string.They would be stretched and ultimately broken into the smallest possible size, perhaps a Planck length.

Call this the Pixel Resolution of Reality, for want of a better term.They will not collide and reform strings or particles inside the singularity, but be emited into another dimension by the lensatic shape of the singularity, where they are projected onto (or into) our 4 dimensional universe to create the Holographic Reality in which we exist.

Our observations of our universe are limited by the observable size, both large and small, and we cannot hope to ever have the complete picture.

To parapharse an unknown author:" If the universe were simple enough for us to understand it, we would be too simple to understand it."

The mass density of a black hole is estimated by some researchers to be in the neighborhood of the mass density of an atomic nuclease. The gravitational field prevents light escaping, not falling in. Same for mass falling in. Many black holes exhibit rotational effects like a neutrino emission axis and periodic variability of their emissions. These effects clearly indicate, but do not prove that the mass in a black hole is discrete and highly centralized.

Any measurements of radiation are, by definition, external to the black hole. Perhaps these are properties of an accretion disk?

Since we are talking escape velocity, then there should be some point where light, and matter orbits the core of the black hole, like electrons around a nucleus.Perhaps our universe is a giant black hole,and the speed of light+ is required to exit it.

Somewhere in the center of a black hole, where mass is equal in all directions, there would be no gravity at all, being neutralized by equal gravity from all directions.

Since the size of a black hole is not defineable, this area can also be indefineable, perhaps another whole universe.

that is the same as being in the centre of theearth - no gravity - but a lot of pressure

"...there would be no gravity at all, being neutralized by equal gravity from all directions."
It is true that at the center of mass, there is no net force in any direction. However, this "micro-gravity" environment is found in any free falling orbital object.

"Somewhere in the center of a black hole..."
At the center of the black hole is the super-nova remnant of the original star that started it all: a neutron star.

"there should be some point where light, and matter orbits the core of the black hole, like electrons around a nucleus"

Cool hypothesis. Most massive black holes are presumed to be fed by a torroidal accretion ring. This would tend to feed the BH with a consistantly increasing angular momentum. A proposal for a toroidal core model has been published...

The event horizon is only related to the mass. A black hole is a theoretical object. Nobody really has any proof of their existence much less any experience with them, so you're on your own here. We don't know if they get larger with more mass or not.

...yeah, black holes are JUST theoretical objects, and we only theorize the conditions found therein....

....just like other theoretical smoke and mirrrors such as 'the center of a galaxy, pulsars, math and the big bang. No one has any experience traveling to those places either.

Why, maybe the sun is just theoretical.... maybe it is just a very high quality visual display....no one has any real upclose firsthand experience.

It is reassuring to me when common objects begin to slip into theoretical unreality to remember our communications and systems are all based on models and all models are incomplete and inherently flawed...(especially this one).

But that is just a theory...

Benbenben

p.s. How long is the redshift going to delay the messages sent from the first lucky chap who gets 'experience' with a black hole?
B

How long? Forever. The light received from the probe, including data transmissions, approaches infinite time dilation, red shift, and dimness at the event horizon.

It is not that the probe itself is inferred to slow down drastically, just the information climbing back out of the gravity well. This is the common misconception I mentioned earlier. The probe reaches an inward velocity of c at the event horizon.

Proof:

star movements in infrared images

Surely all the matter and light should be localised and stored within the blackhole or near the entrance, the immense gravitational pull must originate from some matter even if that matter is now occuping a very small space in space. My understanding is that gravitational forces only exist where matter is present? If the hole was infinite then the material will keep on traveling away from the entrance and take its gravitational pull with it.

If the compaction rate in the blackhole due to gravitation is so high, then is it reasonable to say that there is no space (volume with no matter) left free of material or energy and therefore there will be no space in the hole for a heavier object to fall through and settle. rather it will be compressed and added to a common density with no "room for movement" Not sure what to think, this always seemed a bit of a mystery to me.

Here is one for you. Whenever you see a black hole depicted, it is depicted as a vortex with a single wide mouth tapered down to a singularity. For those of you who don't get that, imagine a tornado with a nice wide cloud at the top and a compressed mobile home at the bottom. So, does this mean that you could approach a black hole from the rear or the side in relative safety? Or does a black hole actually have a 360 degree event horizon in all directions from the singularity? Should a black hole be called a black ball, empty space or for you science fiction lovers, a death star? Seems that the term hole defines the event horizon as a flat surface, which if this is true, then space is flat? But we all know that it isn't, right? Cannot wait to here the comments......I say we can sneak up on it....say from the back and snatch the singularity and encase it in a jar, of course then the jar would encompass all of space if everything we know is true? This of course is just "string" theory stamped flat, right? Wrong?

By the way, this discussion is getting "deep" couldn't resist the bad pun...

Maybe my naivete might help in thinking about this question. Great question by the way. Seriously. My plan is: answer the question "how deep is a black hole?" using purely my intuitive faculties and mind etc., post here, then come back and read what's posted and then...well...just maybe do some research, and add some books to my pile of books to read. :-) Let's say that if a black hole were a hole, then the question would be legit, but it's not actually a hole. Wells can be a certain length deep and that is what a hole is. However, black holes look like holes and are actually portals. So, they suck and squeeze and spit out on the other side. Their size is related to their power. So, the stronger the vortex, the larger both sides are. So, more informed folks may tell me whose footsteps I'm treading in with my intuitive conjecture, whether there's anything new or helpful in my guesses, and what I might read to go further. One thing, though, is that, with a question this "far away" essentially, is knowing current theories even relevant? I mean, how do we test what is factual? For example, how could someone disprove the following: 1) Black holes are big graphic images portrayed in a 3D movie theater we call our universe. It seems unending, because our universe is made to fold in on itself, so that it could be contained in the same space. You think you are somewhere new, but you are in the same place, changed slightly in accordance with patterns, thereby indicating newness, but actually not new 2) Black holes are big coffee grinders used to grind 18 dimensional being coffee. We are actually little specks inside of 18-dimensional coffee beans. Jose, our 18-dimensional coffee farmer has just switched to organic farming, which explains the natural farming movement on our planet (however, Jose is actually a genetic engineer who almost destroyed his entire species a decade ago by creating single-generation coffee bean bushes that he went on a wild mission to stop, and thankfully, he did, cuz otherwise, his existence and ours, would have simple stopped in a cosmic batting of an eye). 3) Black holes are holographic projections of our imaginations 4) Black holes are wells dug by advanced multi-dimensional aliens that suck out stuff from our dimension and bring it into theirs. Kind of like a 3-D fax machine. You're in Atlanta, and your mom is in Greece, well, just make her a cup of coffee and hand it through your computer screen. How's it going to get to your mom? Well, through one of these black holes, silly! ...my point is, how the heck can we "test" any of this?

You may be right,our universe itself may be a holographic projection.Check out this link:

http://www.newscientist.com/article/mg20126911.300-our-world-may-be-a-giant-hologram.html

There is no point in asking about what happens inside a Black Hole, because there is no way of finding that out from the outside. In fact, it has been mathematically proven that the only properties of a Black Hole one can measure are its mass and spin. Remembering that the event horizon is the radius at which light cannot escape, it is surely intuitive that this radius increases with increasing mass, which is indeed the case. Black holes only get smaller ('evaporate') if they loose mass. This occurs because one of a pair of virtual photons, formed as a result of the Heisenberg Uncertainty Principle, becomes a real particle (is 'put on the mass shell') by positive energy given out as a result of the other entering the Hole. All this is explained in the popular book, 'A Brief History of Time' by Prof. Stephen Hawking.

Geoffrey H. Grayer BSc PhD

Along the lines of uncertainty, the Shroedinger cat comes to mind.What if the cat is in a box with a very high speed camera.An observer removes the film and determines whether the cat is dead or alive (if alive, presume the cat is standing, and if dead presume it is lying down).Does the state of the cat become real at that point, or is it in a unstable state still, or is it's fate determined when the picture is taken, not when it is viewed?

Even Einstien was confused about reality.He said it "is an illusion, but a very convincing one."

Properties of mass, angular momentum, and also electric charge. The latter is assumed to auto-regulate around neutrality - but that is not yet confirmed by observation.

My theory: The larger the velocity the "longer" time gets. For instance while sky diving at terminal velocity, feels like an eternity. Whould time stand still inside a "black hole"? Due to the velocity?

Hi Guest,

If you want to know the answer to this and other `deep` `space` `matters` (Is'nt it cool how many pun's you can get in) check out a book called

Black Holes, Worm Holes and Time Machines by Jim Al-Khalili it explains all these questions and is easier to read than A Brief History of Time.

If you want to know what a Black Hole looks like, look into your bank account 3 weeks after Christmas!!

merlin