What's inside the event horizon


by ClamShell
Tags: black hole, event horizon, singularity
ClamShell
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#55
Sep24-10, 11:29 PM
P: 221
Quote Quote by nismaratwork View Post
Nothing that crosses the event horizon IS matter anymore, at best you're talking about radiation. Remember, a neutron star, or even a hypothetical quark star isn't dense enough to have an event horizon; by the time you reach that you've already gone beyond the limits of degenerate matter. MASS yes, but what is that in the context of an unobservable region?
There are some pretty smart posters on this thread; if we let your post
cook for awhile, you should get a decent answer.
ClamShell
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#56
Sep24-10, 11:52 PM
P: 221
Quote Quote by nismaratwork View Post
Nothing that crosses the event horizon IS matter anymore, at best you're talking about radiation. Remember, a neutron star, or even a hypothetical quark star isn't dense enough to have an event horizon; by the time you reach that you've already gone beyond the limits of degenerate matter. MASS yes, but what is that in the context of an unobservable region?
Dense mass without a horizon seems to be like a brick wall to falling matter.
Dense mass with a horizon seems to be like a curtained stage with the brick
wall there or not there or both or neither. IE, if we linger long enough just
above the horizon, by the time we finally cross the horizon, the brick wall
will have evaporated.
nismaratwork
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#57
Sep25-10, 12:33 AM
P: 2,281
Quote Quote by ClamShell View Post
Dense mass without a horizon seems to be like a brick wall to falling matter.
Dense mass with a horizon seems to be like a curtained stage with the brick
wall there or not there or both or neither. IE, if we linger long enough just
above the horizon, by the time we finally cross the horizon, the brick wall
will have evaporated.
There's no wall, especially since you have to remember that everything falling into a black hole is ripped apart by gravitational tidal forces, and blasted by radiation. The EH has no physical existence, it's just the ever-changing (as long as there is infalling matter or HR) demarcation of the point of no return. Degenerate matter is dense, yes, but even that would be "sphagettified" as it fell into a BH. In a very real sense, anything on OUR side of the EH can never be observed by us to cross the EH, so there is the theoretical notion of a wall. Keep in mind that the infalling mass will not experience any such barrier, and crosses the EH without any resistance. I believe that your understanding of Einstein's view of gravity and spacetime is incomplete, and to grasp just what a black hole is, you need to understand that first.

Quote Quote by skeptic2 View Post
I understand that when matter reaches the singularity it may no longer be matter but it's no longer traveling either. Between the EV and the singularity, how fast can massive particles travel and why? Is there some prohibition against exceeding c in that region?
I truly have no idea... certainly as Chalnoth has said earlier until you hit the singularity you can work out numbers with GR equations, but there is in my view, plenty of reason not to trust them. I don't think velocity and the notion of individual particles applies beyond the EH, but who knows? Truly, we just can't know anything about what happens past the EH; there is only theory that ceases to be meaningful at the most critical point (the singularity). I think that a theory of quantum-gravity should eliminate the singularity, and then you might have some reasonable predictions, but we're just not there yet.
ClamShell
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#58
Sep25-10, 01:14 AM
P: 221
Quote Quote by nismaratwork View Post
There's no wall, especially since you have to remember that everything falling into a black hole is ripped apart by gravitational tidal forces, and blasted by radiation. The EH has no physical existence, it's just the ever-changing (as long as there is infalling matter or HR) demarcation of the point of no return. Degenerate matter is dense, yes, but even that would be "sphagettified" as it fell into a BH. In a very real sense, anything on OUR side of the EH can never be observed by us to cross the EH, so there is the theoretical notion of a wall. Keep in mind that the infalling mass will not experience any such barrier, and crosses the EH without any resistance. I believe that your understanding of Einstein's view of gravity and spacetime is incomplete, and to grasp just what a black hole is, you need to understand that first.
I would be the first to admit that my understanding of everything is incomplete.
Only fools are so confident as to think they know it all, and there are no fools
here. Not even Einstein would claim to have a complete knowledge of gravity.
I suspect you mean that my knowledge of Einstein is incomplete...yours is?

It is accepted by previous posters, that distant observers will never see a
a test mass cross the horizon. I take this to mean that when it does finally
happen(relative to the test mass), the stage and its contents will have evaporated.
Supposedly by Hawking radiation. And that a distant observer does not have a
long enough duration to observe this. But the test mass(by its own clock)
would experience nothing in particular because (after infinity by distant
observers clocks), the BH will have evaporated. A no show.
George Jones
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#59
Sep25-10, 01:44 AM
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Quote Quote by nismaratwork View Post
Nothing that crosses the event horizon IS matter anymore, at best you're talking about radiation.
This isn't true. If a star collapses and forms a black hole, then matter falling towards the star, but above the star, will remain matter far inside the event horizon. Matter that falls into a black hole at the centre of a galaxy won't spaghettified until far inside the event horizon.
Quote Quote by skeptic2 View Post
I understand that when matter reaches the singularity it may no longer be matter but it's no longer traveling either. Between the EV and the singularity, how fast can massive particles travel and why? Is there some prohibition against exceeding c in that region?
The speed of light is the local speed limit everywhere, even inside black holes.
Quote Quote by nismaratwork View Post
There's no wall, especially since you have to remember that everything falling into a black hole is ripped apart by gravitational tidal forces, and blasted by radiation.
According to the book Quantum Fields in Curved Space by Birrell and Davies, pages 268-269,
These consideration resolve an apparent paradox concerning the Hawking effect. The proper time for a freely-falling observer to reach the event horizon is finite, yet the free-fall time as measured at infinity is infinite. Ignoring back-reaction, the black hole will emit an infinite amount of radiation during the time that the falling observer is seen, from a distance to reach the event horizon. Hence it would appear that, in the falling frame, the observer should encounter an infinite amount of radiation in a finite time, and so be destroyed. On the other hand, the event horizon is a global construct, and has no local significance, so it is absurd to0 conclude that it acts as physical barrier to the falling observer.

The paradox is resolved when a careful distinction is made between particle number and energy density. When the observer approaches the horizon, the notion of a well-defined particle number loses its meaning at the wavelengths of interest in the Hawking radiation; the observer is 'inside' the particles. We need not, therefore, worry about the observer encountering an infinite number of particles. On the other hand, energy does have a local significance. In this case, however, although the Hawking flux does diverge as the horizon is approached, so does the static vacuum polarization, and the latter is negative. The falling observer cannot distinguish operationally between the energy flux due to oncoming Hawking radiation and that due to the fact that he is sweeping through the cloud of vacuum polarization. The net result is to cancel the divergence on the event horizon, and yield a finite result, ...
This finite amount of radiation is negligible for observers freely falling into a black hole.
Quote Quote by ClamShell View Post
It is accepted by previous posters, that distant observers will never see a
a test mass cross the horizon. I take this to mean that when it does finally
happen(relative to the test mass), the stage and its contents will have evaporated.
Supposedly by Hawking radiation. And that a distant observer does not have a
long enough duration to observe this. But the test mass(by its own clock)
would experience nothing in particular because (after infinity by distant
observers clocks), the BH will have evaporated. A no show.
Consider two observers, observer A that falls across the the event horizon and observer B that hovers at a finite "distance" above the event horizon, and two types of (uncharged) spherical black holes, a classical black hole that doesn't emit Hawking radiation and a semi-classical black hole that does.

For the classical black hole case, B "sees" A on the event horizon at infinite future time, and B never sees the singularity.

For the semi-classical black hole case, at some *finite* time B simultaneously "sees": A on the event horizon; the singularity. In other words, the singularity becomes naked, and A winks out of existence at some finite time in the future for B.

In both cases, A crosses the event horizon, remains inside the event horizon, and hits the singularity. In both cases, B, does not see (even at infinite future time) A inside the event horizon, as this view is blocked by the singularity.

These conclusions can be deduced from Penrose diagrams, FIGURE 5.17 and FIGURE 9.3 in Carroll's text, and Fig. 12.2 and Fig, 14.4 in Wald's text, or

http://www.google.ca/imgres?imgurl=h...ed=0CBwQ9QEwAA.
ClamShell
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#60
Sep25-10, 05:13 AM
P: 221
Quote Quote by George Jones View Post
Consider two observers, observer A that falls across the the event horizon and observer B that hovers at a finite "distance" above the event horizon, and two types of (uncharged) spherical black holes, a classical black hole that doesn't emit Hawking radiation and a semi-classical black hole that does.

For the classical black hole case, B "sees" A on the event horizon at infinite future time, and B never sees the singularity.

For the semi-classical black hole case, at some *finite* time B simultaneously "sees": A on the event horizon; the singularity. In other words, the singularity becomes naked, and A winks out of existence at some finite time in the future for B.

In both cases, A crosses the event horizon, remains inside the event horizon, and hits the singularity. In both cases, B, does not see (even at infinite future time) A inside the event horizon, as this view is blocked by the singularity.
I guess this holds even when B is a distant(but finite) observer. Is it because
A, in the Hawking radiation case, "pairs-up" with A' (a wave), that A can wink
out when A' escapes the grip of the blackhole(becomes Hawking radiation) and
heads for infinity as A drops through the event horizon? Does A' come from
additional infalling matter or does A' come from the blackhole? IE, does the
black hole in both cases, last forever? Do modern blackholes "evaporate"?
skeptic2
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#61
Sep25-10, 06:31 AM
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Quote Quote by George Jones View Post
The speed of light is the local speed limit everywhere, even inside black holes.
Thank you George. I understand why c is the limit outside of black holes but not why those reasons must also apply inside them.
nismaratwork
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#62
Sep25-10, 07:22 AM
P: 2,281
Quote Quote by George Jones View Post
This isn't true. If a star collapses and forms a black hole, then matter falling towards the star, but above the star, will remain matter far inside the event horizon. Matter that falls into a black hole at the centre of a galaxy won't spaghettified until far inside the event horizon.
Yes, I realize that, but for the sake of this thread I didn't think that getting into the distinction between stellar mass and AGNs was such a good idea.


Quote Quote by George Jones View Post
According to the book Quantum Fields in Curved Space by Birrell and Davies, pages 268-269,


This finite amount of radiation is negligible for observers freely falling into a black hole.


Consider two observers, observer A that falls across the the event horizon and observer B that hovers at a finite "distance" above the event horizon, and two types of (uncharged) spherical black holes, a classical black hole that doesn't emit Hawking radiation and a semi-classical black hole that does.
Well there shouldn't be ANY HR emitted if there's anyone around to fall into a black hole (background temps and all). I was thinking again, of a stellar mass black hole with an active accretion disk, not radiation emitted from the BH itself. Specifically a Kerr BH with a rapid rotation and a fairly robust ergoregion, probably with a companion star and constant infalling matter. Again, I didn't see the need to enter into those complexities when the basics seemed to be at issue. Thanks for the clarification however.
JaredJames
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#63
Sep25-10, 08:28 AM
P: 3,390
http://en.wikipedia.org/wiki/Wormhole

So here's the wiki page on wormholes.

Now, it describes two wormholes, one which may possibly be present by a black holes:
"The first type of wormhole solution discovered was the Schwarzschild wormhole which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that this type of wormhole would collapse too quickly for anything to cross from one end to the other."
But these cannot be traversed as it explains and as such, I don't understand how particles as the article puts it are able to 'cross between the two universes'.
Wormholes which could actually be crossed, known as traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them (many physicists such as Stephen Hawking[1], Kip Thorne[2], and others[3][4][5] believe that the Casimir effect is evidence that negative energy densities are possible in nature). Physicists have also not found any natural process which would be predicted to form a wormhole naturally in the context of general relativity, although the quantum foam hypothesis is sometimes used to suggest that tiny wormholes might appear and disappear spontaneously at the Planck scale.
This uses negative energy, enough said.

Now, you keep pointing us to the wikis and to read them, and I have done. I have also done some digging and following links provided in the wikipedia article (the articles I believe you are reading) I found this (http://casa.colorado.edu/~ajsh/schww.html):
Do Schwarzschild wormholes really exist?
Schwarzschild wormholes certainly exist as exact solutions of Einstein's equations.
However:
# When a realistic star collapses to a black hole, it does not produce a wormhole;
# The complete Schwarzschild geometry includes a white hole, which violates the second law of thermodynamics;
# Even if a Schwarzschild wormhole were somehow formed, it would be unstable and fly apart.
As the type of wormhole you are referring to is the above Schwarzschild wormhole, everything I have read so far is very clear in what it is saying regarding their existence - they only exist under the 'perfect' conditions of the equations. "when a realistic star collapses to form a black hole, it does not produce a wormhole.". So unless you can cite sources which show these wormholes can exist when a star collapses, this is overly speculative and against PF guidelines. It is pointless us discussing this if it just isn't possible and so far, nothing has shown it is.
ClamShell
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#64
Sep25-10, 08:58 AM
P: 221
Quote Quote by Dmitry67 View Post
Free falling observer does not observe the same Hawking radiation as observer located far from BH because for the falling observer event horizon is in different place. So the amount of hawking radiation he receives is very small. both position of the apparent Horizon and Hawking radiation are observer-dependent.

Time dilation is infinite only for the hovering observer, so true, observer hovering near the horizon would see the Universe accelerated and blue-shifted. However, falling observer would see the Universe red-shifted (surprise!)
I misunderstood this post first time through. Now I'm thinking Dmitry
has a clever way of minimizing the HR by allowing the HR evaporation
to reduce the BH mass and thereby reduce the horizon so the infalling
test mass has an even harder time getting to the horizon and minimizing
the HR for the free-falling test mass. Wait, is this a bit too circular?
Nevermind, whatever makes the HR non-lethal is OK by me.
ClamShell
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#65
Sep25-10, 09:56 AM
P: 221
Quote Quote by jarednjames View Post
http://en.wikipedia.org/wiki/Wormhole

So here's the wiki page on wormholes.

Now, it describes two wormholes, one which may possibly be present by a black holes:


But these cannot be traversed as it explains and as such, I don't understand how particles as the article puts it are able to 'cross between the two universes'.


This uses negative energy, enough said.

Now, you keep pointing us to the wikis and to read them, and I have done. I have also done some digging and following links provided in the wikipedia article (the articles I believe you are reading) I found this (http://casa.colorado.edu/~ajsh/schww.html):


As the type of wormhole you are referring to is the above Schwarzschild wormhole, everything I have read so far is very clear in what it is saying regarding their existence - they only exist under the 'perfect' conditions of the equations. "when a realistic star collapses to form a black hole, it does not produce a wormhole.". So unless you can cite sources which show these wormholes can exist when a star collapses, this is overly speculative and against PF guidelines. It is pointless us discussing this if it just isn't possible and so far, nothing has shown it is.
Yes, good work...wormholes are in the peer literature, so we can discuss
them. The GR model (guess it's not quantum mechanical) has them doing
such-and-such in GR metrics. QM is bound to be a better framework, but
pretty speculative...lets never mention them again...and lets never mention
quantum gravity either...and the strong force, what's that all about? Don't
mention it. And fringe physics and all the nuts in the basement doing it.
And alpha...who cares if it's changing. etc., etc. Can you add to the list
any more forbidden topics? I don't even like wormholes...I am much more
interested in a BH evaporating before matter can ever fall into it. Are
you going to forbid this too? Seriously, if a concept is only on somebody's
personal webpage, I rather not have it jammed down my throat either.
JaredJames
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#66
Sep25-10, 10:07 AM
P: 3,390
What are you talking about ClamShell? Seriously, I don't want to sound nasty here, but I find your posts to be full of metaphors and riddles and make little sense.

I have nothing against the concept of a wormhole, but so far everything I have read says they cannot be created when a star collapses into a black hole. So discussing it, unless I'm otherwise informed, is pointless.

You don't even like wormholes? A few posts back you were explaining how they were the potential answer to conditions inside the event horizon (something regarding entropy I believe and you not liking the idea of Hawking Radiation).

Stick to the black hole evaporation from now and and let's forget wormholes were ever brought into this particular topic of "What's inside the event horizon?".
ClamShell
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#67
Sep25-10, 10:46 AM
P: 221
Quote Quote by jarednjames View Post
...let's forget wormholes were ever brought into this particular topic of "What's inside the event horizon?".
Agreed, but I might forget every now and then.
And let's not mention Schroedinger's Cat either;
half the time when I open the box it's stiff as a
board. What is it that you said about metaphores
and riddles?

Consider this...a way to transport yourself into an infinitely
distant future, is to hover over the event horizon until the
BH finishes evaporating. Imagine all the cool stuff that would
just be lying around, free for the taking. And it should only
take a couple of minutes.

Somebody just hit on my *Wormholes?* thread...and my
dyslexia started acting up...need to take a Tum; or is it
dyspepsia...doesn't matter.
JaredJames
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#68
Sep25-10, 11:03 AM
P: 3,390
Quote Quote by ClamShell View Post
Consider this...a way to transport yourself into an infinitely
distant future, is to hover over the event horizon until the
BH finishes evaporating. Imagine all the cool stuff that would
just be lying around, free for the taking. And it should only
take a couple of minutes.
I believe this is the plot of the Andromeda TV show. A ship gets stuck in the event horizon of a black hole and experiences 300 years of time dilation.

Again, in reality, the gravity that causes the time dilation would cause your immediate destruction.
Chalnoth
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#69
Sep25-10, 11:58 AM
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Quote Quote by jarednjames View Post
I believe this is the plot of the Andromeda TV show. A ship gets stuck in the event horizon of a black hole and experiences 300 years of time dilation.

Again, in reality, the gravity that causes the time dilation would cause your immediate destruction.
Well, the idea here is that the ship was able to hover just above the event horizon (it is powered, after all). So it's not completely nuts (except for the fact that the power requirements would be astronomical). The real problem is that that degree of time dilation doesn't occur until you're just outside the event horizon, which means the ship itself was too large for it to work that way.

For an astrophysical black hole, I don't think the tidal forces outside the event horizon would have been enough to destroy the ship.
ClamShell
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#70
Sep25-10, 12:04 PM
P: 221
Quote Quote by jarednjames View Post
I believe this is the plot of the Andromeda TV show. A ship gets stuck in the event horizon of a black hole and experiences 300 years of time dilation.

Again, in reality, the gravity that causes the time dilation would cause your immediate destruction.
Remember, weightless, free-falling into a non-rotating BH, with Hawking
radiation of very low intensity inside the rocket ship. Infinity is much bigger
than 300; they must have only been stuck for a picosecond. This destruction
you speak of is only wishful thinking; plenty of sources disagree with
this. Anyway, what's immediate mean when you are approaching the
horizon? The important thing is what Alice(A) sees, not what Bob(B)
sees. Bob sees Alice wink out, that doesn't mean that Alice has past.
IE, Alice's past does not include the evaporation of the BH. And it's
the Carl Sagan movie 'Contact', not the kids show 'Andromeda'.
Calimero
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#71
Sep25-10, 12:05 PM
P: 256
For an astrophysical black hole, I don't think the tidal forces outside the event horizon would have been enough to destroy the ship.
But acceleration against gravity would be tremendous, and pretty unpleasant for anybody on board.
Chalnoth
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#72
Sep25-10, 12:06 PM
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Quote Quote by ClamShell View Post
Remember, weightless, free-falling into a non-rotating BH, with Hawking
radiation of very low intensity inside the rocket ship. Infinity is much bigger
than 300; they must have only been stuck for a picosecond. This destruction
you speak of is only wishful thinking; plenty of sources disagree with
this. Anyway, what's immediate mean when you are approaching the
horizon? The important thing is what Alice(A) sees, not what Bob(B)
sees. Bob sees Alice wink out, that doesn't mean that Alice has past.
IE, Alice's past does not include the evaporation of the BH. And it's
the Carl Sagan movie 'Contact', not the kids show 'Andromeda'.
If the ship were actually in the event horizon, the electromagnetic force would no longer be able to keep the ship's atoms together, so it would actually have been pulled apart. The only thing that rescues this scenario is the idea that it would have been just above the event horizon, not within it. But even then, as I mentioned earlier, it doesn't work numerically because the ship was just too big.


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