What Happens Inside a Black Hole's Event Horizon?

[ClamShell]

Don't know where I picked it up, but something
indicated to me that inside R_eh = 2GM/c^2 lies
a black hole whose R_bh = GM/c^2. And that at
R_bh lies the energy singularity. And that at R_eh
there is not an energy singularity, but only an end
to communication with the world outside. I know
that outside observers cannot detect what is inside
the event horizon sphere, but that should not stop
the mathematics from predicting what is going on
in there. Especially since authors(wiki) say that
nothing in particular is experienced by an observer
passing through the event horizon. The "mathematical
breakdown" seems only to be a "communications
breakdown" in other words. Mathematics predicts
stuff we cannot see...like the "dark properties"...
What's the problem here? Is quantum mechanics
going on in there?

 

[JaredJames]

Not entirely sure what you mean here, but the event horizon is the boundary within which nothing can escape from the black holes gravity, including light. Which is why it appears black.
There wouldn't be anything special in the event horizon, it is just the boundary for the above mentioned limit.
Anything within the gravity of a black hole gets pulled into it unless you can provide enough energy to escape, however, once past the event horizon you would need an infinite amount of energy to get away.

(This all ignores the fact you wouldn't survive the immense gravitational forces long enough to get to that point.)

A bit simplistic, but I believe it covers it.

I'm not sure what these 'dark properties' you refer to are. Dark Matter? Dark Energy?

 

[Chronos]

The event horizon marks the point where observational evidence, as we know it, ends. It can only be probed using math. As history has taught us time and again, math without observational evidence is unreliable.

 

[JaredJames]

Unreliable it may be, but then if it shows nothing can escape it, what is there to 'observe'? Just black, as we see (or don't on the backdrop of space). You'd have to go in, but then you'd never be able to tell anyone what you observe. Bit of a pickle you'd find yourself in (assuming you survive).

I guess we'll never know...

 

[nismaratwork]

The event horizon marks the point where observational evidence, as we know it, ends. It can only be probed using math. As history has taught us time and again, math without observational evidence is unreliable.

...Especially when the math in question breaks down at that specific point. Let's be honest, at this point John Earman's hypothesis is as good as any: "lost socks and green slime."

JarednJames: We may never know, but if there is a way to explore the Planck scale someday, and an effective theory of quantum gravity or something else emerges "never" may just mean "never within the foreseeable future".

 

[ClamShell]

The event horizon marks the point where observational evidence, as we know it, ends. It can only be probed using math. As history has taught us time and again, math without observational evidence is unreliable.

Yes, when I "probe" the event horizon with Newton's equation for orbital
velocity:

V = square root[GM/R] and plug in R = 2.95 Kilometers and M = our sun,
I get 212000 km/s, not 300000 km/s as I expected. I'm not telling you
my values for G and M because I am now thinking that I've got them
wrong...do you get 300000 km/s for the orbital velocity near the event
horizon? Does Newton's equation need more terms when relativity
is accounted for?

 

[JaredJames]

JarednJames: We may never know, but if there is a way to explore the Planck scale someday, and an effective theory of quantum gravity or something else emerges "never" may just mean "never within the foreseeable future".

Never for me means up to the point I expire. After that, can't say I'll be that bothered if they do or don't get to explore it. Everyone does keep calling me a pessimist so saying 'never' sounds about right from that point of view.

 

[JaredJames]

Yes, when I "probe" the event horizon with Newton's equation for orbital
velocity:

V = square root[GM/R] and plug in R = 2.95 Kilometers and M = our sun,
I get 212000 km/s, not 300000 km/s as I expected. I'm not telling you
my values for G and M because I am now thinking that I've got them
wrong...do you get 300000 km/s for the orbital velocity near the event
horizon? Does Newton's equation need more terms when relativity
is accounted for?

I didn't think our sun was big enough to become a black hole, I thought it had to be quite a bit larger, which would increase your mass figure somewhat. (According to another site, it's around 10 times the mass of the sun). By factoring this in, it would add a 0 to your required orbital velocity increasing it by a factor of 10.)

Also, why orbital velocity? Surely you mean escape velocity? You could calculate the gravity using:

F = ( G M1 M2 ) / r^2 and that gives you the acceleration due to gravity. From that you can work out the orbital velocity. (I don't do this stuff much so I'm not the best person here).

 

[Oldfart]

Unreliable it may be, but then if it shows nothing can escape it, what is there to 'observe'? Just black, as we see (or don't on the backdrop of space). You'd have to go in, but then you'd never be able to tell anyone what you observe. Bit of a pickle you'd find yourself in (assuming you survive).

I guess we'll never know...

Well, don't get discouraged...

Just build a very durable black hole probe, which trails a very long antenna which transmits in a clever way via Hawking radiation or something like that for the few milliseconds while the probe is inside and the antenna is still outside of the event horizon.

An interesting question for bar room conversation is: What sensors to put on the probe?? A camera? is there anything to see in there, like another universe or something? What would you look for?

OF

 

[ClamShell]

I didn't think our sun was big enough to become a black hole, I thought it had to be quite a bit larger, which would increase your mass figure somewhat.

Also, why orbital velocity? Surely you mean escape velocity? You could calculate the gravity using:

F = ( G M1 M2 ) / r^2 and that gives you the acceleration due to gravity. From that you can work out the orbital velocity. (I don't do this stuff much so I'm not the best person here).

Anyone desire to point me to a wiki or such?...this is not a homework
problem...so fear not. I don't know how to get to orbital velocity from
force.

 

[JaredJames]

I've just checked and your equation for orbital velocity is correct.

As I pointed out though, a typical black hole (apparantely) is about 10x the mass of our sun. If you factor this into your calculation, it increases the orbital velocity to 2,120,000 km/s (well over c).

 

[ClamShell]

I've just checked and your equation for orbital velocity is correct.

As I pointed out though, a typical black hole (apparantely) is about 10x the mass of our sun. If you factor this into your calculation, it increases the orbital velocity to 2,120,000 km/s (well over c).

And R_eh becomes 29.5 km...it's still 212000 km/s, or did I add insult to
injury again. Hate it when the answer is not what I get.

 

[nismaratwork]

Never for me means up to the point I expire. After that, can't say I'll be that bothered if they do or don't get to explore it. Everyone does keep calling me a pessimist so saying 'never' sounds about right from that point of view.

Well, I don't believe in an afterlife so I'm not inclined to characterize your view as pessimistic, just realistic; I doubt we'll have these answers within our lifetimes, so yeah... never works. It's a novel use of the word, but I understand your position.

 

[ClamShell]

Well, I don't believe in an afterlife so I'm not inclined to characterize your view as pessimistic, just realistic; I doubt we'll have these answers within our lifetimes, so yeah... never works. It's a novel use of the word, but I understand your position.

The answer I want is 299792 km/s...the answer you want is DEATH AND TAXES.

 

[Chalnoth]

...Especially when the math in question breaks down at that specific point.

Er, the math doesn't break down at that specific point. The Schwarzschild metric breaks down, but that's just because of the particular coordinate system used. There are other coordinate systems for describing the same black hole that have no unusual behavior at all at the horizon.

The math doesn't break down until you get to the singularity at the center, but I strongly suspect that General Relativity gives the wrong answer before that.

 

[ClamShell]

Also, why orbital velocity? Surely you mean escape velocity? You could calculate the gravity using:

F = ( G M1 M2 ) / r^2 and that gives you the acceleration due to gravity. From that you can work out the orbital velocity. (I don't do this stuff much so I'm not the best person here).

This is the post I give 5 stars because it got me thnking about
escape velocity and its relation to orbital velocity. Yup, it applies
here...Newton found that V_escape = sqrt(2) times V_orbital.
Same thing seems to hold classically as well as relativistically. So,
when V_escape becomes c, V_orbital = c/sqrt(2) = 212000 km/s.
Hats off to jarednjames for finding a way to make me think.

 

[ClamShell]

Anyway, the hypothetical probes don't have any wiki's.
so put them low on the list of things to be ruled-out. After
reading wiki's on black holes, worm holes, and white
holes, the scenario I put on the top of the list to rule
out is the freefall into a non-rotating BH experiment.
I think it makes sense that, for the entire experience,
the subject would be weighess and unharmed. The subject
would of course enter the event horizon going very fast
but nonetheless weightless. But suddenly, a star filled sky
would appear where none was an instant before. IE, from
BH horizon, through the wormhole, to the WH horizon in an
instant (with no possibility of return). The wiki's don't seem
to rule this out. If no human wanted to volunteer for this
experiment, a huge and powerful radio transmitter would
suffice. The experiment would continue by searching the
heavens for the WH by searching for the radio source that
was introduced into the BH earlier. If the radio source could
not be found, it was either worm holed too far away, or got
ground to dust. If the radio source was eventually found, its
WH would be nearby and it would get written up in journals.

 

[Chalnoth]

I think it makes sense that, for the entire experience,
the subject would be weighess and unharmed.

No, according to GR this isn't what happens. Basically, as a macroscopic object falls inward, the gravitational force difference between the bits closer to the black hole and the bits further away gets greater and greater. As the object draws towards the singularity, this difference gets so great that the object basically gets drawn into a long thin strand. I've heard it referred to as "spaghettification".

For smaller black holes, this process occurs outside the event horizon. For more massive ones, objects pass through the event horizon more or less unharmed (though they apparently encounter an infinite blast of radiation as they pass the horizon), and don't spaghettify until they get closer to the singularity.

 

[ClamShell]

No, according to GR this isn't what happens. Basically, as a macroscopic object falls inward, the gravitational force difference between the bits closer to the black hole and the bits further away gets greater and greater. As the object draws towards the singularity, this difference gets so great that the object basically gets drawn into a long thin strand. I've heard it referred to as "spaghettification".

For smaller black holes, this process occurs outside the event horizon. For more massive ones, objects pass through the event horizon more or less unharmed (though they apparently encounter an infinite blast of radiation as they pass the horizon), and don't spaghettify until they get closer to the singularity.

Where is the wormhole and WH in your theory? May we limit our discussions
to situations where we assume wormholes and WHs exist...instead of that
pesky singularity?

 

[Dmitry67]

(though they apparently encounter an infinite blast of radiation as they pass the horizon)

Blue sheet?
This is applicable only to rotating BH, and it happens when thje probe crosses the second horizon.

 

[Calimero]

Where is the wormhole and WH in your theory? May we limit our discussions
to situations where we assume wormholes and WHs exist...instead of that
pesky singularity?

It is not Chalnoth's theory, it is science. Anyway, you don't need to send radio transmitter to black hole to rule out your experiment. Stuff falls into the black holes all the time, but we don't see it popping around the universe.

 

[ClamShell]

Blue sheet?
This is applicable only to rotating BH, an it happens when thje probe crosses the second horizon.

Of what second horizon do you speak? If mine, do you
agree that the first is just a loss of communications and the
second is nearer the center? I'd really prefer that the
mathematical description be replaced with the BH, wormhole,
WH concept...it fits better with my opinion of order. Imagine
that there are two basic types of galaxy; the dying BH centered
galaxy and the growing WH centered galaxy.

 

[Chalnoth]

Blue sheet?
This is applicable only to rotating BH, and it happens when thje probe crosses the second horizon.

Perhaps. I thought it happens in a non-rotating black hole as well, due to Hawking radiation at the horizon and the divergence of time dilation at horizon crossing.

 

[Dmitry67]

Perhaps. I thought it happens in a non-rotating black hole as well, due to Hawking radiation at the horizon and the divergence of time dilation at horizon crossing.

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 howering observer, so true, observer howering near the horizon would see the Universe accelerated and blue-shifted. However, falling observer would see the Universe red-shifted (surprise!)

 

[ClamShell]

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 howering observer, so true, observer howering near the horizon would see the Universe accelerated and blue-shifted. However, falling observer would see the Universe red-shifted (surprise!)

Can other sources support these position and radiation conclusions?
Redshifted universe is seen by an observer free-falling? Come on now,
I want some peer references...it all looks good for the BH,wormH,WH model.

 

[Chalnoth]

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.

That makes sense. I guess I misremembered.

 

[JaredJames]

And R_eh becomes 29.5 km...it's still 212000 km/s, or did I add insult to
injury again. Hate it when the answer is not what I get.

OK, I agree with your figure for the event horizon and if you were to try to maintain an orbital velocity at that point, you would indeed require 212000km/s (which is related to c correctly via Vescape = root(2) * Vorbital).

 

[Chalnoth]

OK, I agree with your figure for the event horizon and if you were to try to maintain an orbital velocity at that point, you would indeed require 212000km/s (which is related to c correctly via Vescape = root(2) * Vorbital).

Actually, that's not the case. There is no orbit just above the event horizon. The smallest possible orbits are unstable, and some distance from the event horizon. I forget the exact numbers, but I seem to remember that photons orbit a non-rotating black hole at ~4/3 the Schwarzschild radius or somewhere thereabouts. Obviously matter would have to be further out.

 

[JaredJames]

Actually, that's not the case. There is no orbit just above the event horizon. The smallest possible orbits are unstable, and some distance from the event horizon. I forget the exact numbers, but I seem to remember that photons orbit a non-rotating black hole at ~4/3 the Schwarzschild radius or somewhere thereabouts. Obviously matter would have to be further out.

Of course, naturally you couldn't get anywhere near the event horizon. The gravitational forces present would limit our approach to far outside the event horizon.

 

[nismaratwork]

Er, the math doesn't break down at that specific point. The Schwarzschild metric breaks down, but that's just because of the particular coordinate system used. There are other coordinate systems for describing the same black hole that have no unusual behavior at all at the horizon.

The math doesn't break down until you get to the singularity at the center, but I strongly suspect that General Relativity gives the wrong answer before that.

Let me be more precise: the math holds, but the theories fail to make meaningful predictions... better?

 

[Chalnoth]

Let me be more precise: the math holds, but the theories fail to make meaningful predictions... better?

Well, the theories definitely make meaningful predictions. Most people just don't trust them.

 

[nismaratwork]

Well, the theories definitely make meaningful predictions. Most people just don't trust them.

I'm one of those people, and for a prediction to be meaningful it has to be testable. I think we may be arguing semantics here...

 

[ClamShell]

Actually, that's not the case. There is no orbit just above the event horizon. The smallest possible orbits are unstable, and some distance from the event horizon. I forget the exact numbers, but I seem to remember that photons orbit a non-rotating black hole at ~4/3 the Schwarzschild radius or somewhere thereabouts. Obviously matter would have to be further out.

Why is that? Are you in fact referring to the unstable orbits that
slow(and stop) BH spin? I like the unstable orbits better than the
stable orbits if we are still referring to non-rotating BH's. Unstable
orbits carry away the energy that is spinning a BH...another reason
for non-rotating BH's to become more common. That stable orbits
for matter are further out than the photon sphere is not clear to me.

 

[Chalnoth]

I'm one of those people, and for a prediction to be meaningful it has to be testable. I think we may be arguing semantics here...

Well, yes, there is definitely a semantic issue here.

What I would suggest, first, is that it does not automatically follow that extending a theory outside of observable limits will necessarily be unreliable. We could, in principle, show that certain aspects of the theory outside of our observable limits, for instance, can be directly tied to things within our observable limits, making it very strange for things to vary just beyond. For a very simple case, we do not expect the assumption of homogeneity to break down close to the edge of our observable universe, but extend for quite some distance beyond it, because it would be difficult to conceive of a theory that broke that symmetry in some significant way that is also completely unobserved within the visible region. We can't expect the assumption of homogeneity to extend forever, but we can expect it to extend for some significant distance beyond the observable universe.

But there are independent reasons to not trust General Relativity immediately inside the event horizon. Here I pose three different points:
1. Hawking Radiation ensures that black holes always exist for a finite amount of time for an external observer.
2. An external observer will never see anything actually pass the event horizon of a black hole (the proper time coordinate of an infalling observer past the horizon is identified with times beyond positive infinity for an external observer). This may indicate that for a real infalling observer, the black hole will evaporate before the infalling observer ever enters the horizon (caveat: this is an unsolved problem in GR. We know of some special cases where this does not hold. For instance, an evaporating black hole that extends infinitely into the past certainly does have some infalling observers reaching the singularity. But we don't know, at present, what this means for real, astrophysical black holes.)
3. We know that information is conserved in the formation and destruction of a black hole, indicating that the information about what falls into a black hole is somehow encoded in the Hawking radiation that comes from the horizon.

These three points, to me, seem to indicate that something very strange is going on at the event horizon of a black hole that we just do not understand, and quantum gravity is likely to have quite a lot to say to the behavior of a black hole right at the event horizon. I do not think this behavior is in principle unknowable. Just that at present our knowledge is insufficient to be even reasonably confident of any inferences we might make about it, as we can be reasonably confident that the assumption of homogeneity extends some distance beyond our visible universe.

 

[nismaratwork]

Well, yes, there is definitely a semantic issue here.

What I would suggest, first, is that it does not automatically follow that extending a theory outside of observable limits will necessarily be unreliable. We could, in principle, show that certain aspects of the theory outside of our observable limits, for instance, can be directly tied to things within our observable limits, making it very strange for things to vary just beyond. For a very simple case, we do not expect the assumption of homogeneity to break down close to the edge of our observable universe, but extend for quite some distance beyond it, because it would be difficult to conceive of a theory that broke that symmetry in some significant way that is also completely unobserved within the visible region. We can't expect the assumption of homogeneity to extend forever, but we can expect it to extend for some significant distance beyond the observable universe.

But there are independent reasons to not trust General Relativity immediately inside the event horizon. Here I pose three different points:
1. Hawking Radiation ensures that black holes always exist for a finite amount of time for an external observer.
2. An external observer will never see anything actually pass the event horizon of a black hole (the proper time coordinate of an infalling observer past the horizon is identified with times beyond positive infinity for an external observer). This may indicate that for a real infalling observer, the black hole will evaporate before the infalling observer ever enters the horizon (caveat: this is an unsolved problem in GR. We know of some special cases where this does not hold. For instance, an evaporating black hole that extends infinitely into the past certainly does have some infalling observers reaching the singularity. But we don't know, at present, what this means for real, astrophysical black holes.)
3. We know that information is conserved in the formation and destruction of a black hole, indicating that the information about what falls into a black hole is somehow encoded in the Hawking radiation that comes from the horizon.

These three points, to me, seem to indicate that something very strange is going on at the event horizon of a black hole that we just do not understand, and quantum gravity is likely to have quite a lot to say to the behavior of a black hole right at the event horizon. I do not think this behavior is in principle unknowable. Just that at present our knowledge is insufficient to be even reasonably confident of any inferences we might make about it, as we can be reasonably confident that the assumption of homogeneity extends some distance beyond our visible universe.

OK, this I can agree with.