Can Black Holes Really Die and What Are Their Secrets?

[Chalnoth]

This is one version of the "bounce" model (Hawking, among others, I believe, calls it the "baby universe" model), but it's not the only possible one, correct?

There are other bounce models, certainly. But those models do not occur inside a black hole. Inside a black hole, it is impossible to do anything at all that impacts the world outside the horizon. To do so would be to violate General Relativity at such a fundamental level that it is highly unlikely to accurately describe reality. I also doubt it would be able to fit with current observations of black holes.

 

[PeterDonis]

There are other bounce models, certainly. But those models do not occur inside a black hole.

If there is no actual event horizon (as there is not in the second bounce model I described in my previous post), then there is no actual black hole. There is only an apparent horizon and an apparent black hole. There is also no actual singularity; there is just a region of spacetime inside an apparent horizon where the density of matter and energy gets very high for a while before the bounce spreads it out again.

There are plenty of physicists in the field who think that is how the black hole information paradox gets resolved: there's never an actual event horizon or an actual singularity, so there can be a global unitary quantum state everywhere. Again, as far as I can tell, that is the kind of model described in the article Monsterboy linked to.

current observations of black holes.

Current observations can only tell us about the presence, or highly likely presence, of apparent horizons--surfaces where, locally, radially outgoing light no longer moves outward. Observation alone cannot tell you whether there is an actual event horizon present; you have to know the entire future of the spacetime. If quantum gravity effects can significantly change your prediction of the entire future of the spacetime (which they most likely can), then you would need to have a well-tested theory of quantum gravity in order to know which of the apparent horizons you observe are actually event horizons (more precisely, which ones are closely associated with event horizons). We are obviously not in that position today.

 

[Chalnoth]

If there is no actual event horizon (as there is not in the second bounce model I described in my previous post), then there is no actual black hole. There is only an apparent horizon and an apparent black hole. There is also no actual singularity; there is just a region of spacetime inside an apparent horizon where the density of matter and energy gets very high for a while before the bounce spreads it out again.

There are plenty of physicists in the field who think that is how the black hole information paradox gets resolved: there's never an actual event horizon or an actual singularity, so there can be a global unitary quantum state everywhere. Again, as far as I can tell, that is the kind of model described in the article Monsterboy linked to.

These cosmological bounce models have nothing to do with astrophysical black holes. They have completely different dynamics, as they generally have a (fairly) uniform FRW-style universe collapsing in the pre-bounce phase. Such a universe doesn't have a black hole event horizon even in General Relativity, before any quantum considerations are taken.

Current observations can only tell us about the presence, or highly likely presence, of apparent horizons--surfaces where, locally, radially outgoing light no longer moves outward. Observation alone cannot tell you whether there is an actual event horizon present; you have to know the entire future of the spacetime. If quantum gravity effects can significantly change your prediction of the entire future of the spacetime (which they most likely can), then you would need to have a well-tested theory of quantum gravity in order to know which of the apparent horizons you observe are actually event horizons (more precisely, which ones are closely associated with event horizons). We are obviously not in that position today.

Quantum gravity isn't likely to change our idea of the horizon except to explain in more detail how the Hawking radiation is emitted.

 

[PeterDonis]

These cosmological bounce models have nothing to do with astrophysical black holes.

Cosmological bounce models don't, no. But the article Monsterboy linked to wasn't talking about a cosmological bounce model. The features of loop quantum gravity that are key to cosmological bounce models also allow other kinds of bounce models. Here's the paper by Rovelli et al. that the article was referring to; it's specifically about a bounce model for a black hole-like spacetime:

http://arxiv.org/abs/1407.0989

Quantum gravity isn't likely to change our idea of the horizon

It isn't likely to change our idea of the apparent horizon, no. But once again, the event horizon is a very different thing from the apparent horizon. The apparent horizon is local, so quantum gravity can only affect it if it affects local physics; and for a large enough black hole, curvature at the horizon is small enough that classical GR should be valid locally.

But the event horizon is global, so quantum gravity can affect it if it affects the global geometry of the spacetime. It can potentially do that if the curvature anywhere becomes large enough for the classical GR approximation to break down; and we know for sure that that happens in black hole models. So the question of whether quantum gravity effects are enough to make a spacetime not contain event horizons is an open question, even if we are pretty sure that quantum gravity effects can't stop apparent horizons from forming.

 

[Monsterboy]

http://www.iflscience.com/space/supermassive-black-hole-discovered-early-universe
Is this an example of a primordial black hole?

 

[Haelfix]

Here's the paper by Rovelli et al. that the article was referring to; it's specifically about a bounce model for a black hole-like spacetime:

http://arxiv.org/abs/1407.0989

It isn't likely to change our idea of the apparent horizon, no. But once again, the event horizon is a very different thing from the apparent horizon..

Rovellis Planck star proposal is a radical proposal that violates all sorts of laws of physics, including in particular GR, even at very long distance scales. The bounce event destroys the smooth horizon that GR predicts.

The problem doesn't really go away if you imagine that it is an apparent horizon either. Right now, in this room where I am typing, you have a very large amount of apparent horizons that form from the intersection of two outgoing light cones. It's only if you trace out the global history of the universe that you can determine if those rays loop around and stay trapped. So the question is, how does LOCAL unitary physics determine whether it is dealing with those fake apparent horizons, or the real thing? It is as if one must appeal to some sort of nonlocal mechanism to determine how things proceed.

Of course every solution of the black hole information problem involves some sort of really crazy proposals, so things are relative

 

[Quds Akbar]

1. Black holes are points of infinite density in spacetime (singularities), they are formed of collapsed stars
3. Black holes do die eventually: http://arxiv.org/pdf/1401.5761.pdf
4. They are points of zero volume, the circle is the event horizon
5.No, according to relativity, the more energy you gain the more mass you gain, so, theoretically, it would take infinite energy.
6. No

Those are the ones I am aware of, I am not sure of number two.

 

[mfb]

5.No, according to relativity, the more energy you gain the more mass you gain, so, theoretically, it would take infinite energy.

Not in the way "mass" is used in physics.

 

[Drakkith]

1. Black holes are points of infinite density in spacetime (singularities), they are formed of collapsed stars
3. Black holes do die eventually: http://arxiv.org/pdf/1401.5761.pdf
4. They are points of zero volume, the circle is the event horizon
5.No, according to relativity, the more energy you gain the more mass you gain, so, theoretically, it would take infinite energy.
6. No

1. A black hole is not a point of infinite density. That's the singularity.
4. Black holes have a non-zero volume.
5. You do not gain mass as your velocity increases.

 

[Chronos]

Relativistic mass has gone the way of the dinosaur, but, with prejudice ...

 

[Quds Akbar]

1. A black hole is not a point of infinite density. That's the singularity.
4. Black holes have a non-zero volume.
5. You do not gain mass as your velocity increases.

A black hole is formed by a singularity, the singularity is a point of infinite space time curvature, at the center of a black hole is a singularity, so if you are close enough you would approach the center you would be approaching the singularity. There is no black hole with no singularity. Also, black holes do have non-zero volumes yes, but isn't a black hole essentially a space time singularity? I also never said velocity, our mass increases with the more energy you posses, at 10% the speed of light, your mass will only be 0.5% more, at 90% the speed of light it would be more than twice the original mass.
"The energy which an object has due to its motion will add to its mass" - Stephen Hawking, A Brief History of Time

 

[Drakkith]

A black hole is formed by a singularity

No, it is not. A black hole is formed by the matter of a collapsing star.

There is no black hole with no singularity

From here: http://en.wikipedia.org/wiki/Black_hole#Singularity

The appearance of singularities in general relativity is commonly perceived as signaling the breakdown of the theory.[63] This breakdown, however, is expected; it occurs in a situation where quantum effects should describe these actions, due to the extremely high density and therefore particle interactions. To date, it has not been possible to combine quantum and gravitational effects into a single theory, although there exist attempts to formulate such a theory of quantum gravity. It is generally expected that such a theory will not feature any singularities.

As you can see, it is expected that singularities do not really exist, that they are an artifact of an incomplete theory.

Also, black holes do have non-zero volumes yes, but isn't a black hole essentially a space time singularity?

Nope.

I also never said velocity, our mass increases with the more energy you posses, at 10% the speed of light, your mass will only be 0.5% more, at 90% the speed of light it would be more than twice the original mass.

Yes, you're talking about velocity, and no, our mass does not increase, despite what Stephen Hawking says. This is because Hawking is using 'Relativistic Mass' which is not, as far as I know, standard terminology. Mass is usually used to describe what is known as 'Rest Mass' or 'Invariant Mass'. Consider that an observer moving at 0.9c relative to the Earth does not experience twice the gravity in their own frame of reference, as would be the case if their rest mass increased.

 

[Monsterboy]

Cores of very massive stars collapse when iron starts forming right ? In the discovery channel they said the core can collapse just seconds after the iron starts forming , if the core collapses so fast how did the Iron get out of the core and become available to us ?

 

[Monsterboy]

How do you answer to a lay person when he/she asks a question like this ..." If nothing can escape a black hole, not even light , how does hawking radiation escape from the black hole and eventually kill it ?".

 

[Drakkith]

Cores of very massive stars collapse when iron starts forming right ? In the discovery channel they said the core can collapse just seconds after the iron starts forming , if the core collapses so fast how did the Iron get out of the core and become available to us ?

Iron is produced both in the core of massive stars as well as in supernovas themselves.

https://en.wikipedia.org/wiki/Nucleosynthesis

Supernova nucleosynthesis within exploding stars by fusing carbon and oxygen is responsible for the abundances of elements between magnesium (atomic number 12) and nickel (atomic number 28).[1] Supernova nucleosynthesis is also thought to be responsible for the creation of rarer elements heavier than iron and nickel, in the last few seconds of a type II supernova event. The synthesis of these heavier elements absorbs energy (endothermic) as they are created, from the energy produced during the supernova explosion. Some of those elements are created from the absorption of multiple neutrons (the R process) in the period of a few seconds during the explosion. The elements formed in supernovas include the heaviest elements known, such as the long-lived elements uranium and thorium.

 

[Drakkith]

How do you answer to a lay person when he/she asks a question like this ..." If nothing can escape a black hole, not even light , how does hawking radiation escape from the black hole and eventually kill it ?".

Hawking radiation is created and emitted from outside the event horizon, so it isn't captured by the black hole.

 

[Monsterboy]

Hawking radiation is created and emitted from outside the event horizon, so it isn't captured by the black hole.

If that's the case how come the black hole loses it mass and evaporates away ?

 

[Drakkith]

If that's the case how come the black hole loses it mass and evaporates away ?

That's beyond my ability to explain. Have you read the wiki article?

 

[mfb]

Physics cannot answer "how"-questions on a fundamental level. You can calculate it with quantum field theory, but I don't think some pages of calculation are a proper answer of "how".

 

[rootone]

If that's the case how come the black hole loses it mass and evaporates away ?

In simple terms without going into virtual particles and etc...
The Hawking radiation is emitted from very slightly outside of the event horizon and is thus is able to escape.
Since mass and energy are equivalent, the lost energy is equivalent to lost mass.

 

[Monsterboy]

In simple terms without going into virtual particles and etc...
The Hawking radiation is emitted from very slightly outside of the event horizon and is thus is able to escape.
Since mass and energy are equivalent, the lost energy is equivalent to lost mass.

Drakkith said the same thing, the mass of a black hole is the mass and/or energy that has entered the singularity or atleast entered the event horizon right ? So, for it to lose mass something will have come out of the event horizon and/or the singularity that is impossible right ? That goes against the definition of event horizon right ? Without using virtual particles and negative energy things etc (which I don't really understand), it's not possible to explain right ? like mfb said physics doesn't answer "how" questions on a fundamental level or maybe its more appropriate to say that our current understanding of physics cannot answer some "how" questions.

 

[rootone]

It took somebody of the calibre of Stephen Hawkins to deduce from quantum math how it is that these virtual particle (pairs) could pop into existence and some of them end up becoming real particles emitted as radiation.
It took quite a while for him to convince others at his own level that this is likely.
Without the complicated math, and I am no math genius anyway, the key point to grasp is that the particles are not particles which have traveled from inside of the horizon to outside.
They literally just appear outside the horizon 'from nowhere', pairs of them having equal and opposite properties.
Yes, quantum mechanics is weird like that.

 

[PeterDonis]

the mass of a black hole is the mass and/or energy that has entered the singularity or atleast entered the event horizon right ?

Not quite. To an observer 'hovering" anywhere outside the horizon, the "mass" of the hole is whatever mass is at a smaller radial coordinate than he is. So if matter falls into the hole, you, as an observer "hovering" outside the horizon, will measure the hole's mass to be larger as soon as the falling matter passes you.

for it to lose mass something will have come out of the event horizon and/or the singularity

No. See below.

Without using virtual particles and negative energy things etc (which I don't really understand), it's not possible to explain right ?

Not really, but the quantum explanation of Hawking radiation does violate key assumptions of the theorem (due to Hawking, btw) that says a classical black hole can't lose mass and a classical event horizon can't decrease in area. That theorem requires that certain conditions called "energy conditions" are assumed to hold. The quantum fields that produce Hawking radiation violate the energy conditions, so the theorem no longer applies and it is possible for Hawking radiation to cause a black hole to lose mass and its event horizon to decrease in area. This is a quantum effect and it doesn't involve anything classical "coming out" of the horizon.

Violating the energy conditions does not require "virtual particles and negative energy things" (those are just interpretations of the quantum physics involved, and other interpretations are possible), but it does create some counterintuitive possibilities--though no more counterintuitive, IMO, than anything else in QM.

 

[mfb]

like mfb said physics doesn't answer "how" questions on a fundamental level or maybe its more appropriate to say that our current understanding of physics cannot answer some "how" questions.

It is not just a limit of our current understanding, it is a fundamental limit. You can replace theories by theories that are more fundamental, unify more effects, require fewer free parameters and so on, but they will always stay theories.

 

[Monsterboy]

It is not just a limit of our current understanding, it is a fundamental limit. You can replace theories by theories that are more fundamental, unify more effects, require fewer free parameters and so on, but they will always stay theories.

Is that because we have not been able to test these theories with a real black hole ? If we manage to create micro black holes in LHC then will those fundamental "how" questions be answered ?

 

[Chronos]

Even if [a very big if] the LHC could produce a micro black hole, it is believed they would instantaneously evaporate. Any testing would be like trying to play ping pong in a hurricane

 

[mfb]

Is that because we have not able to test these theories with a real black hole ? If we manage to create micro black holes in LHC then will those fundamental "how" questions be answered ?

It is a general limit of physics everywhere. You cannot describe "how" things are attracted by Earth on a fundamental level, for example. You can say "spacetime curvature!" but then the follow-up question is "how does mass bend spacetime?" and you are back to the same type of question.