Register to reply

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

by jimgraber
Tags: black, hole, inside, singularity, what’s
Share this thread:
Markus Hanke
#145
Jan17-12, 09:43 AM
P: 89
Quote Quote by Bernie G View Post
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
#146
Jan17-12, 10:17 AM
P: 136
"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
#147
Jan18-12, 06:30 AM
P: 89
Quote Quote by Bernie G View Post
"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
#148
Jan19-12, 09:24 AM
P: 136
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
#149
Jan19-12, 01:44 PM
P: 89
Quote Quote by Bernie G View Post
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
#150
Jan21-12, 02:21 AM
P: 608
Quote Quote by Bernie G View Post
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-

[tex]a_g=-\frac{Gm}{r^2}\frac{1}{\sqrt{1-2M/r}}[/tex]

where M=Gm/c2
czes
#151
Jan27-12, 06:35 AM
P: 216
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/Gravita..._time_dilation
Bernie G
#152
Feb5-12, 01:42 PM
P: 136
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
#153
Feb7-12, 04:06 AM
P: 216
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
#154
Feb7-12, 04:46 AM
P: 136
"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
#155
Feb7-12, 11:31 AM
P: 136
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
#156
Feb8-12, 03:10 AM
P: 216
Quote Quote by Bernie G View Post
"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
#157
Feb8-12, 05:49 AM
P: 136
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 whats going on in the collapsed star. Orbital motion does not determine the pressure in the collapsed star.
czes
#158
Feb8-12, 07:24 AM
P: 216
Quote Quote by Bernie G View Post
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 whats 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
#159
Feb20-12, 01:31 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 23,099
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!
Quote Quote by marcus View Post
The spires search, if anyone wants to see all the LQG black hole papers with date > 2004:
...
Quote Quote by marcus View Post
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/...tecount%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.

Quote Quote by lmodesto View Post
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
#160
Feb20-12, 02:24 PM
P: 4
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 blackhole? 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
#161
Feb20-12, 04:58 PM
PF Gold
P: 171
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
#162
Feb20-12, 05:07 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 23,099
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:
Quote Quote by phasl001 View Post
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]...


Register to reply

Related Discussions
What's inside a black hole? Special & General Relativity 26
Black hole inside a larger black hole. Cosmology 33
Singularity of a black hole Special & General Relativity 0
Singularity of a black hole Astronomy & Astrophysics 1
Discernment , duality and perception ,singularity (not black hole) General Discussion 4