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

[Bernie G]

"It is not even true that gravity becomes strong at the horizon. The larger the black hole the smaller the surface gravity is. Close to a sufficiently large black hole the surface gravity is very small, the observer feels nothing special, not even when he crosses the horizon."

I think you said it right. At the event horizon of the largest black holes the gravity and curvature is probably small enough that in-falling material doesn't radiate.

 

[genneth]

You have to transform the result accordingly

I know... but that transform is non-trivial! E.g. the part of the world line of the infalling observer which is inside the horizon is not even in the spacetime of the asymptotic observer, so the transform must have some singularities; my question is whether they are physical. Searching for literature on this gives remarkably thin results (i.e. none). I really would like to know the answer, but I don't think anyone has it --- I would be happy to be shown otherwise.

 

[Bernie G]

BTW, maybe its not appropriate here, but I went to a talk a few days ago where the Nasa speaker said there may be far distant black holes with up to 10^12 solar masses. If true, that's about the equivalent of 1000 Milky Ways. Wow.

 

[tom.stoer]

E.g. the part of the world line of the infalling observer which is inside the horizon is not even in the spacetime of the asymptotic observer ...

I was only talking about the evaporation time compared to the time it takes for the infalling observer to cross the horizon; not to hit the singularity.

You only need a rough estimate.

The black hole evaporation time for a black hole of one solar mass (calculated based on Hawking radiation - which is definately incorrect as soon as the hole becomes smaller and has Planck size) is approx. 10⁶⁷ years. Now think about an observer not located at infinity but e.g. at the Earth orbit. The result is approx. the same (the gravity of the sun at the Earth orbit is small, therefore time dilation due to the gravitational field is very small). And now think about this observer falling into the black hole. It will definity take less than 10⁶⁷ years ...

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

 

[IttyBittyBit]

tom.stoer, I think what genneth is getting at is that near the event horizon, gravitational time dilation increases without bound.

http://en.wikipedia.org/wiki/Gravitational_time_dilation#Outside_a_non-rotating_sphere

No matter how long it took for the black hole to evaporate, there is some finite distance from the event horizon where you would experience this time to be very short.

Think about it this way. As you fall into the event horizon, the Hawking radiation from the black hole is blue-shifted to such a high energy that it appears that the black hole is evaporating very quickly.

The statement 'you would not notice anything while falling into a large black hole' is not technically true. I would hardly call being blasted by intense gamma radiation, increasing in energy to infinity, 'not noticing anything'.

Of course, this is just a re-stating of the trans-Planckian problem. Which indicates the difficulty current physics has with event horizons. There are proposed solutions of course, fuzzball being one of them. At the end of the day you need some form of quantum gravity to explain event horizons adequately.

 

[tom.stoer]

tom.stoer, I think what genneth is getting at is that near the event horizon, gravitational time dilation increases without bound.

...

No matter how long it took for the black hole to evaporate, there is some finite distance from the event horizon where you would experience this time to be very short.

That's true for a stationary observer but not for the infalling one. For him it takes finite proper time to cross the event horizon.

As you fall into the event horizon, the Hawking radiation from the black hole is blue-shifted to such a high energy that it appears that the black hole is evaporating very quickly.

This is wrong! (the blue shift is correct but the effect is tiny)

Of course, this is just a re-stating of the trans-Planckian problem. Which indicates the difficulty current physics has with event horizons.

There is no problem with event horizons in general relativity. They are well-understood and well-behaved.

There are proposed solutions of course, fuzzball being one of them. At the end of the day you need some form of quantum gravity to explain event horizons adequately.

All these proposals are attempts to resolve the singularity-issue. But there is no horizon-issue. They all agree that near the horizon of large black holes GR is still the correct low-energy limit.

Have you ever made a single calculation in general relativity by yourself?

 

[genneth]

That's true for a stationary observer but not for the infalling one. For him it takes finite proper time to cross the event horizon.

Finite proper time if the horizon is eternal --- but the point is that it isn't.

Consider the following statements, and tell me where the logic goes off the rails:

1. An asymptotic observer never sees an infalling observer cross the event/dynamical horizon.
2. The horizon evaporates in a finite time.
3. The asymptotic observer will see the infalling observer still there after the horizon evaporates.
4. Therefore from the asymptotic observer's point of view, she doesn't cross the horizon either, and will live to see it completely evaporate.

This calculation can indeed be pushed all the way until the semi-classical approximation breaks down, and I think it's correct. I think this paper by Krauss (http://arxiv.org/abs/gr-qc/0609024 or Phys.Rev.D76:024005,2007) says the same thing, though I'm not sure I entirely agree with the details (event horizon vs. dynamical horizon, and therefore the interpretation).

(Btw, I am in no way invested in the original genesis of this problem --- I just think this scenario is worth thinking about as a thought experiment and might be informative on matters in general, not necessarily including the issue of what replaces a singularity...)

 

[phinds]

Only thing that occurs to me is that is would appear this argument requires the the two observers see the same event as though it were happening at the same time for both of them. I'm not sure I've said that right, but my point is that it seems to merge the two reference frames in a way that is not correct.

 

[tom.stoer]

Finite proper time if the horizon is eternal --- but the point is that it isn't.

Consider the following statements, and tell me where the logic goes off the rails:

1. An asymptotic observer never sees an infalling observer cross the event/dynamical horizon.
2. The horizon evaporates in a finite time.
3. The asymptotic observer will see the infalling observer still there after the horizon evaporates.
4. Therefore from the asymptotic observer's point of view, she doesn't cross the horizon either, and will live to see it completely evaporate.

The first flaw is that the asymptotic observer sees the infalling one approaching the horizon and standing still only if the horizon does not change. But as soon as you let the black hole evaporate the horizon will shrink and the infalling observer will no longer be frozen at the horizon.

The general flaw is that you mix two scenarios, namely arguments for a static spacetime with arguments for a dynamic spacetime with an evaporating BH.

The third flaw is that you don't calculate (or believe) what the infalling observer will actually see. The free-fall time is much smaller than the evaporation time.

 

[suprised]

All these proposals are attempts to resolve the singularity-issue. But there is no horizon-issue. They all agree that near the horizon of large black holes GR is still the correct low-energy limit.

This is not correct. Practically all important discussions and confusions turn around the horizon, and almost not at all around the singularity. The point seems to be that despite the horizon is weakly curved, quantum effects are strong and emphatically quantum gravity effects must play a crucial role there. The fuzzballs were invoked to implement the required macroscopic non-locality within string theory and this is definitely a horizon issue. Indeed in certain circumstances, quantum gravity effects are very relevant in the IR, while many approaches too naively just concentrate on the UV. The whole last week of our quantum gravity workshop was, in fact, devoted to precisely this issue.

 

[tom.stoer]

OK, maybe there is a "horizon-issue", but only in the sense that there is an underlying microscopic structure to classical spacetime.

Or do you think that classical GR (to which I refer when I am talking about free fall, proper time etc.) will no longer be valid outside the horizon for large black holes? Of course we expect that the evaporation will change, but we do not expect any "quantum effects" for classical motian, do we?

 

[IttyBittyBit]

3. The asymptotic observer will see the infalling observer still there after the horizon evaporates.
4. Therefore from the asymptotic observer's point of view, she doesn't cross the horizon either, and will live to see it completely evaporate.

Actually, no. That is only true if the infalling astronaut is very far from the horizon. If the infalling astronaut is near the horizon, the asymptotic observer will see them go in, but only at the very last moment where the black hole vanishes in a blast of Hawking Radiation. Therefore, from the asymptotic point of view, the infalling astronaut never spends any time 'inside' the event horizon. This is explained in this page: http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html

This is wrong! (the blue shift is correct but the effect is tiny)

It seems you are right about this and I am wrong. I was thinking about a Schwarzschild reference frame. In such a reference frame you would see infinite blue-shift right before `going in'. However, a directly infalling observer would not see infinite blue-shift. Sorry for talking out of my a%$.

However, even though the blue-shift would not be infinite, it would still happen. It still remains that a theory of quantum gravity is needed before a definitive answer can be given. This paper talks about this subject at length: http://arxiv.org/abs/0806.0628

Have you ever made a single calculation in general relativity by yourself?

I've made many. If you know more about something than others, it is not appropriate to be rude about it.

 

[tom.stoer]

However, even though the blue-shift would not be infinite, it would still happen. It still remains that a theory of quantum gravity is needed before a definitive answer can be given. This paper talks about this subject at length: http://arxiv.org/abs/0806.0628

Thanks for the link.

I've made many. If you know more about something than others, it is not appropriate to be rude about it.

Sorry about that!

 

[Haelfix]

OK, maybe there is a "horizon-issue", but only in the sense that there is an underlying microscopic structure to classical spacetime.
Or do you think that classical GR (to which I refer when I am talking about free fall, proper time etc.) will no longer be valid outside the horizon for large black holes?

Hmm. The problem isn't in the details of the dynamics but rather that the horizon analysis leads to the seemingly inescapable clash between two cherished physical principles, namely unitarity and locality whereby only one of the two can remain true in our universe.

Details about the small corrections due to quantum gravity cannot change this conclusion, which is why the information loss paradox is one of the greatest unresolved problems in theoretical physics. It isn't some mere detail of quantum gravity to be determined by future generations but rather the type of clash (like the UV catastrophe) that signals a theoretical underpinning must be altered (which qg must thereafter explain in detail microscopically)

So in a sense the answer is yes, the classical theory most likely is incomplete (even macroscopically), or rather it appears necessary for there to be a complementarity between descriptions and/or a dual holographic formulation that rescues us from what would otherwise be an absurdity.

 

[suprised]

Details about the small corrections due to quantum gravity cannot change this conclusion, which is why the information loss paradox is one of the greatest unresolved problems in theoretical physics.

This is absolutely correct; see eg the arguments of Mathur (eg recent papers/reviews) why "small" quantum gravity effects cannot help, rather they need to be of order one near the horizon. How this actually works in detail is a highly controversial issue, the fuzzball proposal ist just one attempt, though quite explicit and at least for me, quite convincing.

At any rate, issues of singularity resolution at the center appear to be a red herring to this problem, it is not the relevant question to ask.

 

[atyy]

So how big roughly would the macroscopic effects be at the horizon? If say a 70 kg person fell through the event horizon of a large black hole, would he notice anything like a fuzzball?

 

[suprised]

So how big roughly would the macroscopic effects be at the horizon? If say a 70 kg person fell through the event horizon of a large black hole, would he notice anything like a fuzzball?

I guess, though this seems controversial, that the infalling observer experiences a coherent superposition of fuzzball states to the effect that he notices nothing particular at the horizon. I understand, though, that he infalling observer problem seems to be the weakest point in this proposal.

 

[MTd2]

I know... but that transform is non-trivial! E.g. the part of the world line of the infalling observer which is inside the horizon is not even in the spacetime of the asymptotic observer, so the transform must have some singularities; my question is whether they are physical. Searching for literature on this gives remarkably thin results (i.e. none). I really would like to know the answer, but I don't think anyone has it --- I would be happy to be shown otherwise.

This is why I don't believe in black holes. To make hawking radiation compatible to an asymptotic observer, an infalling observer would receive an infinitely strong blast of radiation when crossing the horizon. This is why I think the fuzzball is better than the LQG solution, at least how it is interpreted. The infinite blast should be actually the leaking gas of hot sphere made by whatever entity a fundamental theory of quantum gravity regards as fundamental.

EDIT.: Just noticed what suprised said above. So, what I mean is a killer fuzball.

 

[Bernie G]

A lot of smart people decades ago questioned if black holes existed, and if they did exist doubted they were a point singularity. But black holes have now been confirmed by observation in our galaxy with a high degree of certainty. I think this talk about what happens at the horizon is too complicated; its different for smaller or bigger black holes anyway. The interesting issue is what's inside the event horizon and if it can be confirmed by observation.

 

[MTd2]

I do not doubt that the objects seen are BH, classically. For all practical purposes we are at an infinite distance from all of them.

 

[suprised]

The interesting issue is what's inside the event horizon and if it can be confirmed by observation.

That's going to be the hard part... ;-)

 

[Bernie G]

"The interesting issue is what's inside the event horizon and if it can be confirmed by observation."

Not necessarily. Observing gamma ray bursts from other galaxies, which might be clearly identified as neutron star-BH mergers, might become routine in the future. Small BH-BH mergers will be rarer, perhaps only once a year. If two small black holes merge, and IF the internal object is 75% of the Schwarzschild radius, perhaps one solar mass will be ejected. Very observable.

 

[Bernie G]

The above post should have read: "Not necessarily that hard to observe."

 

[suprised]

The above post should have read: "Not necessarily that hard to observe."

Well you talked about _inside_ the event horizon... that's per def unobservable!

 

[Bernie G]

"Well you talked about _inside_ the event horizon... that's per def unobservable!"

Not when 2 small black holes merge. At the merger location the effect of gravity is canceled out.

 

[Constantin]

What cannot be observed does not exist.
For any observer outside the event horizon, there's nothing inside a black hole. The infalling matter remains frozen near the event horizon.

Discussions about the interior of black holes, observers inside a black hole, or observers falling into a black hole and passing through the event horizon, are just pleasant mind games.

 

[Bernie G]

"For any observer outside the event horizon, there's nothing inside a black hole. Discussions about the interior of black holes ... are just pleasant mind games."

Not so. If black holes merge, the gravity situation at the merger location changes dramatically. Are you saying small black holes don't merge?

 

[suprised]

I don't think that anything concrete is known about what happens quantum mechanically if 2 holes merge. It is not even known what precisely happens if two particles collide with sufficient energy as to form a black hole. As said, non-perturbative quantum gravity is relevant there, and AFIAK so far no existing formalis is able to capture that and eg compute the S-matrix.

And computing such an S-Matrix (say of formation and subsequent evaporation of a bh) is certainly not a mind game but of highest conceptional importance. Because eg violation of unitarity would, by virtual black hole loops, trickle down to low energies.

 

[Constantin]

I'm sure black holes do merge, but I don't think any information from inside the event horizon can escape during the merger, nor during any other event.

The explanations given by PAllen in his posts in this thread are quite interesting:
https://www.physicsforums.com/showthread.php?t=526367

They shed light on the behavior of the event horizon during a merger.

 

[Bernie G]

Yes. About BH mergers that thread says: "Thus whatever the details are at the point of collision are, they will quickly be shrouded behind the horizon." Yes. But if something exists inside a BH with 75% of the Schwarzschild radius, there will be a lot of stuff escaping during "quickly", perhaps roughly one solar mass of ejected radiation (for 2 merging 8 solar mass black holes). Thats quite an ejection.

 

[atyy]

I guess, though this seems controversial, that the infalling observer experiences a coherent superposition of fuzzball states to the effect that he notices nothing particular at the horizon. I understand, though, that he infalling observer problem seems to be the weakest point in this proposal.

I guess in the fuzzball proposal, the microscopic state is that there is actually no event horizon?

And the event horizon somehow appears by coarse graining to a macroscopic outside observer?

I'd also be interested in knowing whether http://arxiv.org/abs/1008.3439" 's ideas are consistent with fuzzball ideas.

 

[tom.stoer]

I guess in the fuzzball proposal, the microscopic state is that there is actually no event horizon?

What do you mean by that?

What is so special about event horizons? Classically black hole event horizons are nothing else but lightlike, closed, non-expanding 2-surfaces. The reason why a classical observer feels nothing special when crossing the horizon is simply due to the fact that the difference between an arbitrary lightlike surface and an event horizon cannot be defined locally. There are infinitly many lightlike surfaces the observer can cross. What's special about the horizon is that its closed and non-expanding. But the infalling observer can't detect that b/c it's a global property.

Does such a classical geometry emerge from fuzzballs?

 

[suprised]

I guess in the fuzzball proposal, the microscopic state is that there is actually no event horizon?

Right - the fuzzball microstates do not have horizons.

Incidentally, the fuzzball states really "require" the full compactified 10-dim (or corresponding non-geometric notion) string degrees of freedom. We knew that from state counting before, what is new here is the actual explicit construction of those microstates. And one really needs precisely all of those in order for this mechanism to work. This is a remark to those who believe that this problem can be solved from within pure gravity...

And the event horizon somehow appears by coarse graining to a macroscopic outside observer?

This is what is claimed.

I'd also be interested in knowing whether http://arxiv.org/abs/1008.3439" 's ideas are consistent with fuzzball ideas.

No idea...

 

[Physics Monkey]

I'm curious about the relationship, if there is one, between fuzzballs and black hole complementarity. I have favored the idea of complementarity for some time, but was never able to understand very completely how it relates to fuzzballs.

On a related note and in the spirit of complementarity, I have always found the nice slices used e.g. in Mathur's discussion to be rather disturbing since they include regions behind the horizon. This seems manifestly wrong to me.

 

[Bernie G]

Correction: Previously I said there may be some BHs with 10^12 solar masses. This is roughly 10X the mass of the Milky Way, not 1000X.

 

[tom.stoer]

This is a remark to those who believe that this problem can be solved from within pure gravity...

There is a proposal for black holes in LQG which defines horizons in terms of spin networks, i.e. with pure gravity ...

 

[suprised]

There is a proposal for black holes in LQG which defines horizons in terms of spin networks, i.e. with pure gravity ...

And how do they get the necessary states? Quite a few people doubt that it could ever work.

 

[tom.stoer]

They count spin network states forming the classical horizon area. The result reprocudes the Bekenstein-Hawking-entropy plus corrections. I bet marcus has a list of publications.

 

[suprised]

They count spin network states forming the classical horizon area. The result reprocudes the Bekenstein-Hawking-entropy plus corrections. I bet marcus has a list of publications.

AFAIK up to an arbitrary factor, which means that the result is meaningless?

 

[tom.stoer]

AFAIK up to an arbitrary factor, which means that the result is meaningless?

What is the proton mass according to string theory? Up to how many arbitrary factors?

So let's continue seriously? or polemically?

 

[Haelfix]

The difficult thing is not so much calculating the correct area scaling law (although that was difficult enough), but rather giving a precise microscopic story about what the two local observers see, and how details of their measurements must be somehow entangled and noncommuting.

Since this is very much about details of semiclassical states, afaik this is way beyond LQG's current technology and it is not even addressed yet.

In fact, the exact details is not even known in string theory or AdS/CFT, and the fuzzball proposal is the only one that even tries to address this incredibly difficult problem head on.

 

[suprised]

What is the proton mass according to string theory? Up to how many arbitrary factors?

So let's continue seriously? or polemically?

You start here polemics. Indeed has been shown since long that in string theory the factor comes out right, to every detail. And what contributes are states that do go beyond "pure gravity", ie., have, in a sense, an extra-dimensional origin. In LQG, as far as I know, the result is proportional to an abitrary constant, the Immirzi parameter. This ambiguity (in front of a log!) thus does not allow to decide whether the number of states contributing is correct or not. So this is meaningless for settling this question in LQG.

This string computation is undisputable. What is disputable, and is disputed, is whether Mathur et al's explicit construction of the microstates, which goes much beyond just counting the states, is correct or not. While it looks convincing, there has been criticism, like for example whether the nice slice argument is physically well-defined etc.

As said we have been running a workshop on Quantum Gravity right now, which discusses this kind of questions. Tomorrow is LQG day and we will see what the LQG persons have to tell.

 

[atyy]

As said we have been running a workshop on Quantum Gravity right now, which discusses this kind of questions. Tomorrow is LQG day and we will see what the LQG persons have to tell.

http://www.physics.ntua.gr/corfu2011/st.html ?

 

[qsa]

http://arxiv.org/PS_cache/gr-qc/pdf/9404/9404036v2.pdf


Wavefunction of a Black Hole and the
Dynamical Origin of Entropy

 

[tom.stoer]

You start here polemics.

Sorry about that, but you started this kind of reasoning.

Indeed has been shown since long that in string theory the factor comes out right, to every detail.

For extremal black holes with maximal SUSY, no Schwarzschild and no Kerr, right?

This ambiguity thus does not allow to decide whether the number of states contributing is correct or not. So this is meaningless for settling this question in LQG.

We know that all theories including quantum gravity (including string theory) are work in progress. So of course there are open questions. Everybody in the LQG community would agree that the Imirzi parameter os one of them.

All what I wanted to say is that there seems to be a very detailed description based on microscopic degrees of freedom which can be applied to "classical black holes". The Immirzi parameter has to be fixed, then the prediction is unambiguous. I do not see a problem to have one parameter in a theory w/o being able to derive it theoretically. You can't do that in other theories, either (QCD coupling constant / scale, GSW coupling / Fermi constant, ...)

As said we have been running a workshop on Quantum Gravity right now, which discusses this kind of questions. Tomorrow is LQG day and we will see what the LQG persons have to tell.

fine

 

[suprised]

Sorry about that, but you started this kind of reasoning.

not aware of...

For extremal black holes with maximal SUSY, no Schwarzschild and no Kerr, right?

Sure, that's the way non-perturbatively exact statements can be made without directly solving the theory.

We know that all theories including quantum gravity (including string theory) are work in progress. So of course there are open questions. Everybody in the LQG community would agree that the Imirzi parameter os one of them.

All what I wanted to say is that there seems to be a very detailed description based on microscopic degrees of freedom which can be applied to "classical black holes". The Immirzi parameter has to be fixed, then the prediction is unambiguous. I do not see a problem to have one parameter in a theory w/o being able to derive it theoretically. You can't do that in other theories, either (QCD coupling constant / scale, GSW coupling / Fermi constant, ...)

Maybe I didnt make the significance clear enough. This is not only just some parameter like the QCD coupling that needs to be fixed. This would indeed be a triviality and no reason to muck around. Rather, because it multiplies the entropy, it directly affects how you count the number of states of the theory. Since this parameter is arbitrary, AFIAK, it is impossible to tell whether the states provided by LQG are "enough" such as to account for the microstates of black holes. Tuning the parameter to the "right" value won't continuosuly change the number of states until it matches the correct count. Rather it should be seen as a prefactor multiplying an unknown state count.

Thus, this result does not shed light on the question whether LQG provides, or not, the correct degrees of freedom of QG. This in contrast to strings, where the state count (in toy model examples of black holes) comes out right on the nose, including subleading quantum corrections.

These facts are known to anybody working in the field, and this was also confirmed by today's discussions.

 

[phinds]

if matter and anti-matter annihilate,only the expansion of time can keep them apart.thus a singularity at the center of a black hole i suggest consists of anti-matter 13.7 billion years in the past(back to the big bang)and matter 13.7 billion years into the future.the matter in the surrounding galaxy is being sucked into the future this is my understanding of space time.

Welcome to the forum.

I don't know what your purpose is here but this kind of "personal opinion" doesn't fly well with the moderators, especially when it looks like nonsense. If you are asking a question (and I don't see one in the above post), I would suggest that it be "why is my understanding of space-time so totally at odds with accepted physics".

 

[tom.stoer]

... Rather, because it multiplies the entropy, it directly affects how you count the number of states of the theory. Since this parameter is arbitrary, ... it is impossible to tell whether the states provided by LQG are "enough" such as to account for the microstates of black holes. Tuning the parameter to the "right" value won't continuosuly change the number of states until it matches the correct count. Rather it should be seen as a prefactor multiplying an unknown state count.

...

These facts are known to anybody working in the field, and this was also confirmed by today's discussions.

I never understoof the Immirzi parameter as a multiplicative parameter for the number of states (for a given area) but always as a multiplicative constant for the (classical) area given a predefined state count. So there are two issues: is the counting correct? what's the value of the Immirzi parameter?

What was the result of the discussion with the LQG colleagues you mentioned.

 

[tom.stoer]

So there are two issues: is the counting correct? what's the value of the Immirzi parameter?

What was the result of the discussion with the LQG colleagues you mentioned.

I checked some papers (especially Sahlman, Agullo, Barbero) and I think they agree on the state counting. So this issue goes away.

I still have to look for recent results regarding the Immirzi parameter (which does not affect the entropy for a given spin network, but 'only' the area related to a given spin network; so as I said, the value must be fixed, but it does not affect the counting itself, only its relation to the 'classical area').

The picture within LQG is remarkable simple:
- the horizon is characterized by the 'isolated horizon condition'
- the state count is defined by spin network punctures of the horizon
- the microscopic degrees of freedom are spin networks (plus induced surface degrees of freedom)
- the calculation is known for realistic Schwarzschild black holes
- afaik the Kerr solution has not been studied so far
- afaik neither a dynamical collaps nor evaporation has been studied so far
- entropy is related to microstates but not yet to temperature

 

[suprised]

Well, we have had various discussions and the general consensus seems that this formula is inconclusive, with regard to the question whether the right number of states is counted. In fact the "right" value of the Immirzi parameter depends on the particular LQG model, and thus is non-universal. And for spin foam models, which seem to have replaced LQG, there are AFAIK few, if any, relevant entropy calculations, and the Immirzi parameter does not appear. So the general feeling seems that while there are encouraging signs, something still is wrong or at least not understood.

The whole issue seems always to boil down to the following two possibilities: either gravity can be made sense of out of itself (by regularizing/discretizing it, UV self-completing it, etc), or it needs to be embedded into a "larger" theory which UV-completes it. But this is getting off-topic.