If no singularity, what’s inside a big black hole?

[Markus Hanke]

Dear person behind avatar Markus Hanke
Thank you for your attention.
I am pleased to see, my text was interesting for you.
But regrettably (probably my grammar was a bit too heavyish), there is some unnecessary misunderstanding here. I will try to use less grammar next time; but you, too, could you please next time consider reading a sentence from the beginning to the end (and if you don't get the point, then reading again and doing some thinktank work) ... before you try to make fun of it, OK?
Hint: compound sentences include often many parts and you should read all of these parts. You should not cut out 1 little piece and advertise this as the meaning of a compound sentence.

Dear mesinik, I must apologize if you felt offended by my post. Reading through it now, I must admit that it does read a bit like a personal attack on your post, poking fun at it. Please be assured however that I did not actually intend it to be that way; I was merely trying to illustrate that sitting just above an event horizon is just not a possible way to investigate the properties of a black hole. I suppose the style and language of the post got out of hand - entirely my fault.
So again, please accept my public apology. I genuinely did not mean it to come across like this.

 

[Bernie G]

“How can the gravitational acceleration at an event horizon be smaller than at the surface of a neutron star ?”

Because gravitational acceleration varies as the inverse of r squared. One of us is making a mistake. I was under the impression that distant super-massive black holes (10 billion solar masses) “disappeared” because the gravitational acceleration at the event horizon is so small (and the curvature so large) that infalling material doesn’t even radiate until it is well within the black hole. Hence I volunteer to sit on the ring and bravely stick my toes inside the event horizon of a trillion solar mass black hole, where the gravity (gulp) should be about as strong as in California.

To challange the staus quo even further, here in a nutshell is my minority viewpoint about the size of a star composed of relativistic material inside a black hole:

The gravitational energy could be as low as (4GM^2)/(5R) for a typical density profile, or possibly as high as (GM^2)/R (unlikely) if the star has a high density core. The total energy creating pressure would be (Mc^2)/3. Using the viral theorem (the energy creating pressure equals half the gravitational energy), a non-rotating star of relativistic material would have a radius as small as (1.2GM)/(c^2) or as large as (1.5GM)/(c^2), or between 60 - 75% of the Schwarzschild radius.

If this model is true, it could be verified someday by the observation of the merger of two approximately equal mass black holes: a massive ejection from the relativistic stars would occur.

 

[Markus Hanke]

“How can the gravitational acceleration at an event horizon be smaller than at the surface of a neutron star ?”

Because gravitational acceleration varies as the inverse of r squared. One of us is making a mistake. I was under the impression that distant super-massive black holes (10 billion solar masses) “disappeared” because the gravitational acceleration at the event horizon is so small (and the curvature so large) that infalling material doesn’t even radiate until it is well within the black hole. Hence I volunteer to sit on the ring and bravely stick my toes inside the event horizon of a trillion solar mass black hole, where the gravity (gulp) should be about as strong as in California.

To challange the staus quo even further, here in a nutshell is my minority viewpoint about the size of a star composed of relativistic material inside a black hole:

The gravitational energy could be as low as (4GM^2)/(5R) for a typical density profile, or possibly as high as (GM^2)/R (unlikely) if the star has a high density core. The total energy creating pressure would be (Mc^2)/3. Using the viral theorem (the energy creating pressure equals half the gravitational energy), a non-rotating star of relativistic material would have a radius as small as (1.2GM)/(c^2) or as large as (1.5GM)/(c^2), or between 60 - 75% of the Schwarzschild radius.

If this model is true, it could be verified someday by the observation of the merger of two approximately equal mass black holes: a massive ejection from the relativistic stars would occur.

I don't really get what you are saying; the event horizon is a boundary beyond which photons cannot escape the gravitational pull of the BH. Its radius is only dependent on the total mass of the BH. As neutrons stars are stable and do not collapse gravitationally, the gravitational acceleration at the event horizon for a BH of equal mass must be much stronger than at the surface of the neutron star ?! If it was the other way around all neutron stars would immediately collapse...

 

[Bernie G]

"the gravitational acceleration at the event horizon for a BH of equal mass must be much stronger than at the surface of the neutron star"

I should have been clearer and was referring to a typical neutron star of one or two solar masses.
What I said was: "if we consider a 10 million solar mass black hole, the gravitational acceleration at the event horizon would be about one millionth that at the surface of a neutron star."

 

[Markus Hanke]

Because gravitational acceleration varies as the inverse of r squared.

Wait a minute - you are using Newton's law for this. I don't think you can use the weak-field approximation of the field equations at the event horizon of a black hole; IMO the full general relativistic treatment is needed.

 

[Bernie G]

"Wait a minute - you are using Newton's law for this."

Thats correct. I think the Tolman–Oppenheimer–Volkoff equation is baloney and that the pressure of a relativistic star inside a BH is simply given by the relativistic pressure of (rho)(c^2)/3. I am using gravitational acceleration varying as 1/(r^2) and don't define the pressure between the surface of the star and the event horizon. I specify a non-rotating star to avoid the relativistic velocities caused by conservation of angular momentum which Einstein believed would prevent collapse, and besides think (rho)(c^2)/3 would provide a supporting mechanism much larger than angular momentum.

What formula for gravitational acceleration other than 1/(r^2) do you suggest? I'm open to it.

 

[Markus Hanke]

"Wait a minute - you are using Newton's law for this."

Thats correct. I think the Tolman–Oppenheimer–Volkoff equation is baloney and that the pressure of a relativistic star inside a BH is simply given by the relativistic pressure of (rho)(c^2)/3. I am using gravitational acceleration varying as 1/(r^2) and don't define the pressure between the surface of the star and the event horizon. I specify a non-rotating star to avoid the relativistic velocities caused by conservation of angular momentum which Einstein believed would prevent collapse, and besides think (rho)(c^2)/3 would provide a supporting mechanism much larger than angular momentum.

What formula for gravitational acceleration other than 1/(r^2) do you suggest? I'm open to it.

Well, for one thing there is no "relativistic star inside a BH"; beyond the event horizon there lies only the gravitational singularity, the exact form of which is as per yet unclear in the absence of a consistent theory of quantum gravity.
In the region of the event horizon itself relativistic effects are definitely significant, so to describe trajectories you will need to use one the solutions of the Einstein equations; since you are saying the black hole is static and has no charge, the Schwarzschild metric will probably be your metric of choice.
The TOV is not "baloney", but a direct consequence of above mentioned metric; saying that TOV is invalid amounts to saying that the Einstein equation, and hence GR, is wrong. That is a pretty strong statement, and will require equally strong evidence to support it.

Can I ask you please what it actually is you are trying to achieve ?

 

[Bernie G]

I’m maintaining that its logical that a large relativistic star exists inside a BH, and its OK if we differ on this. It will be settled someday by the observation of the merger of two approximately equal mass black holes. If each contains a large relativistic star, a huge ejection of the upper layers of the stars will occur.

Yes, in the region of the event horizon of a small black hole relativistic effects are significant. One would expect all the material in a collapsing star to go relativistic (quark matter + radiation). Most initial radiation would escape, and the remaining stuff would generate the almost unimaginable pressure of (rho)(c^2)/3.

Saying that TOV is invalid does not amount to saying that GR is invalid. The event horizon of a trillion solar mass black hole has a gravitational acceleration about that at the surface of the earth, but TOV predicts infinite pressure there. That doesn’t make sense.

I’m not analyzing charge or magnetic field effects of a black hole at this time, and think light cones are a good answer in the region between the event horion and the surface of the relativistic star.

You didn’t answer... what formula for gravitational acceleration other than 1/(r^2) should be used?

 

[Markus Hanke]

I’m maintaining that its logical that a large relativistic star exists inside a BH, and its OK if we differ on this. It will be settled someday by the observation of the merger of two approximately equal mass black holes. If each contains a large relativistic star, a huge ejection of the upper layers of the stars will occur.

Yes, in the region of the event horizon of a small black hole relativistic effects are significant. One would expect all the material in a collapsing star to go relativistic (quark matter + radiation). Most initial radiation would escape, and the remaining stuff would generate the almost unimaginable pressure of (rho)(c^2)/3.

Saying that TOV is invalid does not amount to saying that GR is invalid. The event horizon of a trillion solar mass black hole has a gravitational acceleration about that at the surface of the earth, but TOV predicts infinite pressure there. That doesn’t make sense.

I’m not analyzing charge or magnetic field effects of a black hole at this time, and think light cones are a good answer in the region between the event horion and the surface of the relativistic star.

You didn’t answer... what formula for gravitational acceleration other than 1/(r^2) should be used?

Ok, I think you are mixing things up a little. The TOV equation is the relativistic form of the usual hydrostatic equations describing a hydrostatic system in equilibrium; it has a different form than the Newtonian version because of relativistic effects being taken into account. This equation doesn't have anything to do with Black Holes, them being the end product of a gravitational collapse.
As for acceleration at the event horizon, unfortunately there is no simple, straightforward formula one can use. Assuming the black hole is stationary and has no charge, you can calculate the Schwarzschild geodesics, which describe the trajectories of a small mass moving in the vicinity of the black hole, like so :

http://en.wikipedia.org/wiki/Schwarzschild_geodesics

As you can see the maths involved in this are non-trivial, unlike in the Newtonian case.

 

[stevebd1]

what formula for gravitational acceleration other than 1/(r^2) should be used?

You might find the following web page of use also-

7.3 Falling Into and Hovering Near A Black Hole

Generally, for a static black hole, the following equations is used when calculating the proper local acceleration of a black hole-

$$a_g=-\frac{Gm}{r^2}\frac{1}{\sqrt{1-2M/r}}$$

where M=Gm/c²

 

[czes]

3. GRAVITATIONAL TIME DILATION NEAR BLACK HOLE

Gravitational time dilation is the effect of time passing at different rates in regions of different gravitational potential; the lower the gravitational potential (closer to the center of a massive object), the more slowly time passes. Albert Einstein originally predicted this effect in his theory of relativity and it has since been confirmed by tests of general relativity. Therefore the Black Hole can't be formed for an outer observer.

In quantum gravity time is created by a number of quantum events. Each event results with a Planck's time dilation (lp) and therefore we perceive a flow of the time. Time doesn't exist as an independent fundamental property or phenomenon.

We measure a distance and a time by a constant speed of light as a constant number of the quantum events which are passed by a photon N= R/lp.

A distance and time become contracted by the number of Planck's units when there is an additional non-local information from a real massive particle with its Compton wave length ly= h/mc . We calculate the interference of the information from the direction of the observer and from the direction of the massive particle as a vector sum in a triangle.

As we showed above N=M/m particles cause (M/m) [(lp /(ly/2) )] length contraction and proportional time dilation where ly is a Compton wave length information of the massive particle perpendicular to the information of the observer in vacuum.

Therefore time (tf) is a sum :

tf^2 (R/lp) = t0^2(R/lp) + tf^2 (M/m) [(lp /(ly/2) )]

t0^2(R/lp) = tf^2 {(R/lp) - (M/m) [(lp /(ly/2) )]}

where:

lp * lp – Planck length squared = hG/c^3

Compton wave length ly=h/mc

After substitution we receive a well known equation for gravitational time dilation:

t0^2= (1-2GM/Rc^2 )

http://en.wikipedia.org/wiki/Gravitational_time_dilation

 

[Bernie G]

Sorry for the long delay in responding.

“you can calculate the Schwarzschild geodesics, which describe the trajectories of a small mass moving in the vicinity of the black hole” Thats where you’ve got it wrong. Does orbiting particle analysis descibe the general motion of a particle in a star or black hole? Are all the particles in our sun orbiting? Of course not. General kinetic energy equations can be used to describe a specific case like an orbitting particle, but you can not use a specific case like an orbiting particle to describe the general kinetic solution. For example, see: http://math.ucr.edu/home/baez/virial.html To use orbital particle dynamics to describe reality in a star is simply incorrect.

Gas pressure or (rho)(c^2)/3 has no net velocity so relativistic equations are not needed. The TOV equation was not meant to apply to a BH, and it doesn’t even work that well for a neutron star. Saying that orbital particle dynamics is not the general support mechanism in a BH does not deny general relativity.

 

[czes]

In the Information Universe there aren't distances, motion, energy, time as the absolute values. The particle aren't orbiting. They do exchange the information from the space (vacuum) and the particle is moving toward the absorbed information.
In the gravitational field there is a gradient of the density of the information toward the emiting particles of the massive body and we observe the oscillations and acceleration toward the massive body.
The motion of a particle close to a star depends on the absorbed information and there are many different motions.

 

[Bernie G]

"The motion of a particle close to a star depends on the absorbed information and there are many different motions." I'm not evaluating particles close to the star or from the event horizon to the surface of the star; orbital mechanics are important there. I'm saying motion is random below the surface of a non-rotating star.

 

[Bernie G]

At a talk someone said they thought the pressure would be slightly higher than (rho)(c^2)/3 in a quark/radiation mixture ... maybe because the quark component can generate a pressure higher than (rho)(c^2)/3.

 

[czes]

"The motion of a particle close to a star depends on the absorbed information and there are many different motions." I'm not evaluating particles close to the star or from the event horizon to the surface of the star; orbital mechanics are important there. I'm saying motion is random below the surface of a non-rotating star.

According to Rueda, inertial mass is not intrinsic to a body at all. It is extrinsic, bestowed on a body from outside. Specifically, it arises from the interaction between the basic building blocks of matter and the great roiling ferment of virtual particles that make up the quantum vacuum .
http://www.calphysics.org/articles/gravity_arxiv.pdf
http://www.hologram1.glt.pl/

Therefore there isn't a random motion but the motion (oscillation) is due to absorbed information which is hidden in the superposition and contained in the vacuum.

 

[Bernie G]

Whatever theory you use for motion, when a non-rotating neutron star collapses it makes no sense to think that all particles start orbital motion, so using equations of orbital motion tell us little of what's going on in the collapsed star. Orbital motion does not determine the pressure in the collapsed star.

 

[czes]

Whatever theory you use for motion, when a non-rotating neutron star collapses it makes no sense to think that all particles start orbital motion, so using equations of orbital motion tell us little of what's going on in the collapsed star. Orbital motion does not determine the pressure in the collapsed star.

You are rigt. Therefore the most fundamental is an exchange of the information. The particle oscillates and moves because it absorbs and emits the information from and into an environment. If it absorbs more than emits it accelerates. It is Unruh-Davies effect.
http://en.wikipedia.org/wiki/Unruh_effect

The orbiting motion is an effect if the amount of the absorbed and emitted information is balanced but it isn't always as you see it inside a star. It is more complicated there because all particles are in motion and there is not a simple gradient of the density of the information. A particle is carrying many information and if it is in a relation with an another particle in the vicinity it overcomes the quantity of the information from the gravitational field of the distant particles. You observe the brownian motion then but it is always the exchange of the information as well.

 

[marcus]

In a certain sense this thread is kind of funny because very early on one of the top researchers in non-singular BH pointed out to us what is one of the most interesting recent answers to Jim's question ("what's inside") and nobody in the thread picked up on it!

The spires search, if anyone wants to see all the LQG black hole papers with date > 2004:
...

Tom, I decided there was too much old stuff in that search, given how much the field has changed in the past 3 years. So instead of setting the date at 2004, I changed to 2007:

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+GRAVITY%2C+LOOP+SPACE+AND+DK+BLACK+HOLE+AND+DATE+%3E2007&FORMAT=www&SEQUENCE=citecount%28d%29

Now it gives 45 papers and all have the date > 2007.

It may surprise readers to see which papers are the most-cited. The more highly cited ones are listed first.

It still may be a surprise! In that listing 3 of the top 10 are by Leonardo Modesto, and
if you take a larger sample it is 5 of the top 20. His are numbers 1, 3, 5, 11, 19 in citation ranking.
Recently Leonardo has co-authored about self-dual BH with Sabine Hossenfelder of NORDITA in Stockholm and with Bernard Carr of Queen Mary U. London. Modesto and Premont-Schwarz are at Perimeter.

And Leonardo showed up early on in the thread and pointed these papers out to us.

There are at least a couple of papers where
(in a particular model inspired by LQG) to find the answer :
1) arXiv:0905.3170
Self-dual Black Holes in LQG: Theory and Phenomenology
Leonardo Modesto, Isabeau Prémont-Schwarz
Journal-ref: Phys.Rev.D80:064041,2009;
2) arXiv:0811.2196
Space-Time Structure of Loop Quantum Black Hole
Leonardo Modesto Int.J.Theor.Phys.49:1649-1683,2010.

What brought my attention finally to Loop self-dual BH was not the high rate of citation (which I somehow had not registered) but seeing something similar going on in Asymptotic Safety gravity---papers by Cai and Easson where you also get very long lifetimes of primordial BH and can make a testable hypothesis that they constitute Dark Matter.

It's interesting that researchers coming from both directions find that (totally reversing Hawking) tiny BH have very long lives rather than very brief ones, and that both Loop and Safe gravity researchers propose DM to be clouds of tiny BH.

Both research lines converge on finding tiny BH to be very cold instead of very hot (as Hawking would have it.) Good stuff.

 

[phasl001]

So, to my understanding from what I have read (considering all possible theories), a Blackhole "appears" to be a super dense ball of compressed matter where gravity is beyond our comprehension and so strong that light/time cannot escape (Imagine: Our galaxy squeezed and compressed to a size as small as an atom). What is inside a black hole? Nothing, in theory, matter doesn't exist and its appropriate to say the laws of physics do not apply inside this phenomenon (and therefore doesn't exist?), but outside the event horizon it still holds the laws in tact. These are just my thoughts, as I am not a scientist of any sort, just an average Joe Schmoe interested and curious of the unknown.

 

[jimgraber]

Hi Marcus,
Thanks for the post. I will try to read some of those papers and post a slightly informed response in a week or two. I have noticed several papers that suggest black holes should have a discrete spectrum, rather than a continuous or thermal one. But this primarily applies to small black holes, not big ones. And it only indirectly tells you what is inside the black hole, big or small. But I will read some of these papers and see what I learn. Thanks again for the informative and helpful response. Jim Graber

 

[marcus]

Hi Jim, good thread! I did not see your post when I was typing this and meant it as a response to the guy just before:

So, to my understanding from what I have read (considering all possible theories), ...and curious of the unknown.

Here's how I read the question: If no singularity, what’s inside a big black hole?

He's asking what, in quantum gravity, takes the place of the classical GR singularity?
What actually is there where (in old classical GR) the "singularity" mistake used to be?

We assume the known laws of physics hold as usual inside the event horizon, except in one very tiny region in the center. A singularity is a place where a theory breaks down so it does not apply and we need an improved theory to describe what goes on. That is what QG is about.

So to get a handle on it the obvious thing to do is to read QG papers that deal with black holes. Particularly ones that get rid of the singularity, and hopefully are testable as well (that's hard but has to be done.)

Here's a good overview introductory paragraph from a 2009 paper. Google "hossenfelder non-singular collapse" and you get http://arxiv.org/abs/0912.1823
It gives a quantum gravity model for "non-singular black hole collapse and evaporation"
This is a model of stuff collapsing to form a black hole, but something else besides a singularity down in the heart of it, and it turns out that the model is testable to some extent by looking for certain kinds of radiation which BHs like this would make (if the model is right.)

Here's a short quote from the introduction that explains the motivation and philosophy behind the research:

From the perspective of quantum gravity, black holes are of interest because of the infinite curvature towards their center which signals a breakdown of General Relativity. It is an area where effects of quantum gravity are strong, and it is generally expected that these effects prevent the formation of the singularity. Since the black hole emits particles in the process of Hawking radiation [1], the horizon radius decreases. In the standard case it approaches the singularity until both, the singularity and the horizon, vanish in the endpoint of evaporation [2]. However, if the singularity does not exist, this scenario cannot be correct. Since the singularity plays a central role for the causal space-time diagram, its absence in the presence of quantum gravitational effects has consequences for the entire global structure [3], and the removal of the singularity is essential for resolving the black hole information loss problem [4]. To understand the dynamics of the gravitational and matter fields, it is then necessary to have a concrete model.

It is thus promising that it has been shown in a simplified version of loop quantum gravity, known as loop quantum cosmology (LQC) [5], a resolution of singularities, the big bang as well as the black hole singularity [6–8], can be achieved. The regular static black hole metric was recently derived in [9], and studied more closely in [10]...​

 

[czes]

If I understand physics, the problem of the singularity appears in General Relativity because of the continuous space-time.
In Quantum Gravity the problem disappears because the space (vacuum) is discrete.
Therefore the main problem is to find the structure of the space:
1. Continuous space and singularity.
2. Discrete space without singularity:
- 2.1. Physical polarized space changing polarization of the photon.
- 2.2. Non-material (holographic) Information Space conserving original photon.

 

[marcus]

- 2.2. Non-material ... Information Space conserving original photon.

I like the term "non-material information space"! You do not need the word "holographic", I think, because there are various ways to present the information.

For example, in Loop you do not even need a "holographic screen". A spin network represents information and is completely non-material.

 

[jimgraber]

The old orthodoxy: There’s a singularity in there.
The new orthodoxy: There’s no singularity, but there is a Planck scale wormhole, which acts almost like a singularity FAPP.
It’s interesting that ST and LQG come to almost exactly the same conclusion.
More later.

 

[czes]

I like the term "non-material information space"! You do not need the word "holographic", I think, because there are various ways to present the information.

For example, in Loop you do not even need a "holographic screen". A spin network represents information and is completely non-material.

Yes. Holographic is too specific. There was a time of the fascination.

 

[MTd2]

So, quantum gravity is becoming Sartre now?

 

[marcus]

So, quantum gravity is becoming Sartre now?

Geometry = information. Relational. I think some Greeks already knew this. Not what it "is" but how it responds to measurement.

What interests me especially:

The old orthodoxy: There’s a singularity in there.
The new orthodoxy: There’s no singularity, but there is a Planck scale wormhole, which acts almost like a singularity FAPP.
It’s interesting that ST and LQG come to almost exactly the same conclusion.
More later.

Hoping to see more about this.

 

[tom.stoer]

The old orthodoxy: There’s a singularity in there.
The new orthodoxy: There’s no singularity, but there is a Planck scale wormhole, which acts almost like a singularity FAPP.
It’s interesting that ST and LQG come to almost exactly the same conclusion.

not like a singularity, but like the smooth geometry far away from the "would-be-singularity" and outside the event horizon is the same.

 

[marcus]

... the smooth geometry far away from the "would-be-singularity" and outside the event horizon is the same.

Yes, that is what I understood Jim to mean when he said "which acts almost like a singularity FAPP."

FAPP is abbr. "for all practical purposes." so same geometry away from the wormhole or whatever--the would-be singularity as you say.

I think the interesting differences come when you consider small holes evaporating. Or not evaporating entirely. Or doing so more slowly than Hawking's picture allows.

Intuitively for large BH it seems to make no difference whether the singularity is resolved and replaced by something else, or not.

 

[tom.stoer]

FAPP is abbr. "for all practical purposes." so same geometry away from the wormhole or whatever--the would-be singularity as you say.

marcus, there's a big difference, even fapp!

The singularity is at the center whereas the geometry extends to infinity; this geometry is identical (!) for all objects of the same mass M, angular momentum J and charge Q, regardless if they are black holes, stars or planets.

 

[marcus]

The singularity is at the center whereas the geometry extends to infinity; this geometry is identical (!) for all objects of the same mass M, angular momentum J and charge Q, regardless if they are black holes, stars or planets.

That is what I believe, and that is what I understood Jim to be saying, the whatever-it-is at the center (that takes the place of the classical singularity) has the same mass and the same effect on the geometry, which of course extends from center out to infinity. Perhaps I misunderstood Jim's casual remark? AFAICS you and he are saying the same (obvious) thing. But this seems like a big fuss over nothing, let's move on.

 

[marcus]

BTW some nice news related to BHs! In a couple of hours Eugenio Bianchi will be giving a LQG talk over at the Physics building here at UC Berkeley!

The title is Black Hole Entropy and the Shape of the Horizon.

It's an hour talk preceded by tea, should be fun, and a chance to talk with other Berkeley people interested in quantum gravity.

Bianchi was formerly at Marseille in Rovelli's group, and is now at Perimeter Institute in Canada. He's just visiting here for a few days.

 

[jimgraber]

Sorry to be such a late slow poster, but it has been a busy week at home and work.

Also, I do not claim to be any kind of expert on either ST or LQG.

The LQG part, in particular, is based on a very preliminary scan of the Modesto et al recent work, which Marcus just pointed out. (I am sorry I missed this the first time around.)

Yes, one thing I meant was that any large (even stellar mass) black hole in the new theory looks almost exactly the same (both inside and outside the event horizon) as the classical Schwarzschild black hole. Or also a ST black hole for that matter. At any scale above a few tens of Planck lengths, space looks classical despite being actually composed of strings or loops.
This is different from the fuzzball model of Mathur where things get all fuzzy right inside the event horizon, or the much older model of Yilmaz which was respected and professional studied when it was first proposed, but is now both mostly forgotten and not much appreciated. The Yilmaz model predicts a 20 to 30 % variation from Schwarzschild at the event horizon for black holes of all sizes. (A variation this big would probably be detected by LISA, but probably not LIGO.)

The second thing I meant is that from a distance (macro scale) the geometrical part of the Modesto type LQG self dual black hole, a Planck scale wormhole with a twist, the geometrical view of the ST black hole consisting of many overlapping strings (or high winding number) and the geometrical view of the classical singularity or infinitely dense mass point, all look pretty much the same. (In particular, they all trap mass in a very small space, if you ignore the other side of the wormhole, and outside this nearly pointlike region, space(time) remains smooth and empty and very well approximated by Schwarzschild.) From a micro scale structure viewpoint these three quasi-singularities are very different and the Hawking-like radiation predictions are different as are the associated lifetimes and temperatures. I think that the ST predictions and the Hawking semi-quantum or semi-classical predictions agree, which is regarded as a good thing by the ST people. But I think I have seen several different nonthermal discrete spectrum predictions associated at least loosely with LQG. I will try to look these up when I have time.

In addition Modesto et al make the very interesting prediction of black holes with masses much smaller than the Planck mass. My first reaction is skepticism, but it seems to be a very direct consequence of their r goes to (1/r) duality. (I am skeptical not about the math, but about the existence of these objects.)

However, my main point is that all these fine points are hidden or unimportant at the macro level, and so the new BIG black holes look very much like the old BIG black holes, unlike the really small ones (Planck scale) which are very different. I am at least a little bit disappointed by this.

Thanks for the comments and further information.

 

[John232]

I don't think anything has been accepted among the scientific community of what really exist inside of a black hole. I have read pure energy a few times, in explanations of what happens when a black hole create a white hole (in old books), but white holes have not been found. I don't think they could be made of matter since the density of suppermassive black holes can be really low (close to 1). My hypothesis is that matter would have to be broken down into energy in order to maintain these low densities, and the concentrated energy itself would need to bend spacetime. I don't think it is too far fetched since energy itself is affected by spacetime curvature and has zero rest mass but it would be moveing, it is just that the amount is too small to be detected. That could be why we don't see white holes, the curvature created by energy itself wouldn't be enough to peirce through space to another location.