Can there be black holes in a universe of finite age?

[Rolando]

you might want to read this paper as it's directly related to this discussion and what you've been trying to describe.

 

http://arxiv.org/abs/gr-qc/0609024

 

Thanks for this link to a paper by Vachaspati, Stojkovic and Krauss (2007).

 

I see that I would have them on my side in the present discussion.

In their Introduction they say: “The process of black hole formation is generally discussed from the viewpoint of an infalling observer. However, in all physical settings it is the viewpoint of the asymptotic observer that is relevant.”

 

This is exactly my point, and several of you attempt to push me into the infalling observer position – which I refuse for the reason these authors express in the second clause.

 

Further below, they say: “A crucial aspect of our analysis is that we address the question of black hole formation and evaporation as seen by an asymptotic observer. Initially, when the domain wall is large, the spacetime is described by the Schwarzschild metric, just as for a static star. From here on, the wall and the metric are evolved forward in time, always using the Schwarzschild time coordinate.”

 

Now I understand that the Gullstrand-Painlevé metric, as suggested by Strange, would also be fully adequate.

 

 

You are interpreting this too harshly.

 

All coordinate systems are valid, even if they seem to be contradictory. There is of course no real contradiction here, just a poor use of one coordinate system to insist that all observers will absolutely agree on a duration.

 

Although my conclusions seem to be harsh, I maintain their validity for classical black holes.

 

Observers will not agree on a duration, but they should agree on the presence/absence of an impassable boundary.

Edited January 26, 2015 by Rolando

[Robittybob1]

 

..... Observers will not agree on a duration, but they should agree on the presence/absence of an impassable boundary.

Why is the boundary impassable?

[Strange]

Why is the boundary impassable?

 

It isn't. From the outside you would pass without even noticing. From the inside you can only get further way.

 

As I say, I think this is most easily understood in Gullstrand-Painlevé coordinates: http://jila.colorado.edu/~ajsh/insidebh/waterfall.html

[Mordred]

 

Thanks for this link to a paper by Vachaspati, Stojkovic and Krauss (2007).

 

I see that I would have them on my side in the present discussion

 

Observers will not agree on a duration, but they should agree on the presence/absence of an impassable boundary.

Your welcome, I posted that paper to assist you in this debate, so you have a reference to discuss. It will help keep the discussion on track.

 

You will also note I posted the second paper in a counter argument to the first paper. In the second paper the EH can be crossed by particles by a removal of the coordinate singularity due to the Schwartzchild metric. Adopting the "tortoise coordinates", is one method, the coordinates Strange mentioned being another.

 

 

A key thing to realize, GR has come a long way since Einstein and Schwartzchild. Minkowskii metrics for example has limitations. There have been numerous later metrics developed to overcome aspects of the older metrics,

 

The Mathius Blau book in my signature points out numerous shortcomings in the older metrics and shows the solutions with later developed coordinate systems.

 

 

The first paper, recognizes the coordinate singularity, it points out the possibility, of particles not crossing the EH. However it doesn't conclusively state it is the case.

 

The black hole wars is full of similar arguments lol

 

 

Oh in regard to Hawking radiation converting infalling matter outside the EH,mentioned in the first paper.

 

That process can't occur, the author of the first paper probably didn't realize Hawking radiation only occurs if the universe blackbody temperature is lower than the BHs blackbody temperature.

Just a side note

[Rolando]

Oh in regard to Hawking radiation converting infalling matter outside the EH,mentioned in the first paper.

 

That process can't occur, the author of the first paper probably didn't realize Hawking radiation only occurs if the universe blackbody temperature is lower than the BHs blackbody temperature.

Just a side note

 

This is off-topic, but it stroke me as even more evident than you made it appear. As seen from within a gravitational well that is close to being a black hole, the temperature of the CMBR is, of course, much higher than the 2.7 K we see.

Why is the boundary impassable?

 

I actually thought of something like "impassable in or to the view of an observer".

 

From the outside you would pass without even noticing.

 

This is what I had put into question because it cannot happen in e.g. Schwarzschild coordinates. I think that all the matter must remain in a thin shell outside the event horizon. This would make it impossible for anything to pass through, and this cannot reasonably depend on the choice of coordinates.

Edited January 26, 2015 by Rolando

[Mordred]

Unfortunately the choice of coordinates do make a difference.

 

The Schwartzchild metric is a static solution. Inside the EH it is anything but static.

 

Here read this page

http://en.m.wikipedia.org/wiki/Schwarzschild_coordinates

 

 

"Schwarzschild chart, a kind of polar spherical coordinate chart on a static and spherically symmetric spacetime"

 

please note the killing vector section

Edited January 27, 2015 by Mordred

[ajb]

Observers will not agree on a duration, but they should agree on the presence/absence of an impassable boundary.

If a black hole is present then an in falling and an external observer can agree on this. We can observe black holes and we have good candidates for them. You don't need to see anything cross the horizon to know there is a black hole, and as an external observer you will not see anything cross the horizon.

[imatfaal]

This is what I had put into question because it cannot happen in e.g. Schwarzschild coordinates. I think that all the matter must remain in a thin shell outside the event horizon. This would make it impossible for anything to pass through, and this cannot reasonably depend on the choice of coordinates.

 

I think this sums up our differences. I view the situation as follows: If I can show that an event happens in one properly calculated frame of reference then the event has HAPPENED and what other frames of reference can OBSERVE is not definitive (but very interesting). You seem to view the situation as follows: If You in some frame of reference can show that You can NEVER OBSERVE something happening then this event CANNOT HAVE HAPPENED in any frame.

 

To re-word - I think events MUST be frame independent and observer independent. From your argument You seem to claim that the observation or failure of same can affect an event. For your guidance - it is a basic tenet of relativity that events happen in a set order but that the timing and visibility of these events is very flexible; which I think supports my thinking.

...

The Schwartzchild metric is a static solution. Inside the EH it is anything but static.

 

Couldn't we also say that as Schild is a vacuum solution to the Einstein equations for R>r_s and thus specifically does not apply internally

[Mordred]

That is also accurate

[Rolando]

We can observe black holes and we have good candidates for them. You don't need to see anything cross the horizon to know there is a black hole, and as an external observer you will not see anything cross the horizon.

 

In order to be sure that we see a classical black hole, it would be necessary to have free sight down to the event horizon (not across it), and I claim that this is impossible if the universe is finite in age. The objects that have been observed and called black holes could all equally well be something like gravastars, in which nothing ever can cross the event horizon.

 

 

You seem to view the situation as follows: If You in some frame of reference can show that You can NEVER OBSERVE something happening then this event CANNOT HAVE HAPPENED in any frame.

 

To re-word - I think events MUST be frame independent and observer independent. From your argument You seem to claim that the observation or failure of same can affect an event.

...

Couldn't we also say that as Schild is a vacuum solution to the Einstein equations for R>r_s and thus specifically does not apply internally

 

Real events must be observer independent, but I think that certain frames of reference cover all of real spacetime and nothing else, while others transcend reality – they describe imaginary regions (and imaginary events) in addition to reality. Schwarzschild coordinates (for R>r_s) belong to the first set. In my view, there can be no real but just imaginary events within the region where R<r_s, and crossing the r_s boundary is also an imaginary event.

Edited January 27, 2015 by Rolando

[Strange]

Real events must be observer independent, but I think that certain frames of reference cover all of real spacetime and nothing else, while others transcend reality – they describe imaginary regions (and possibly events) in addition to reality. Schwarzschild coordinates (for R>r_s) belong to the first set. In my view, there can be no real but just imaginary events within the region where R<r_s.

 

And again, you are cherry picking one observer as more valid than the other, and one coordinate system as more valid than another (even though they are mathematically equivalent). This is not very logical.

[Rolando]

 

And again, you are cherry picking one observer as more valid than the other, and one coordinate system as more valid than another (even though they are mathematically equivalent). This is not very logical.

 

If you wish so, you can say that I am cherry picking reality. A coordinate system that does not extend to R<r_s is not mathematically equivalent to a system that does.

[ajb]

In order to be sure that we see a classical black hole, it would be necessary to have free sight down to the event horizon (not across it), and I claim that this is impossible if the universe is finite in age. The objects that have been observed and called black holes could all equally well be something like gravastars, in which nothing ever can cross the event horizon.

Maybe, however as general relativity as it stands has been a good model of macroscopic gravity we should take the possibility of black holes in nature quite seriously. I have no understanding of these gravastars, and I have no idea how the gravity community view them.

[Strange]

 

If you wish so, you can say that I am cherry picking reality. A coordinate system that does not extend to R<r_s is not mathematically equivalent to a system that does.

 

You are, by preferring the distant observers view as more "real" than the infalling observer.

 

 

The solution was proposed independently by Paul Painlevé in 1921 ^[1] and Allvar Gullstrand^[2] in 1922. It was not recognized until 1933 in Lemaître's paper ^[3] that these solutions were simply coordinate transformations of the usual Schwarzschild solution.

http://en.wikipedia.org/wiki/Gullstrand%E2%80%93Painlev%C3%A9_coordinates

[Rolando]

You are [cherry picking reality?], by preferring the distant observers view as more "real" than the infalling observer.

 

In the view of any observer who is not falling into the particular black hole in question, an infalling observer will reach the event horizon only in the infinite future. If this is true, infalling observers cannot either pass through the event horizon in their own view. They will approach the event horizon in a short time and be smashed there.

 

Unless nature is self-contradictory, the standard teaching, which says that the event horizon will not be noticed by an infalling observer, cannot be true. (At present I am not able to put my finger on exactly where the error in the standard teaching is.)

[Strange]

(At present I am not able to put my finger on exactly where the error in the standard teaching is.)

 

The error appears to be in your understanding of it.

[Rolando]

According to my understanding, infalling observers will not either see any further than the event horizon unitil they reach it. This does not suggest that they will be able to pass across it.

Edited January 30, 2015 by Rolando

[Strange]

According to my understanding, infalling observers will not either see any further than the event horizon unitil they reach it.

 

As I say, the problem seems to be with your understanding.

[imatfaal]

The Standard Teaching - to an extent - is Misner Thorne and Wheeler "Gravitation" ; and I can quote to you from my old copy

 

" Of course, proper time is the relevant quantity for the explorer's heart-beat and health. No co-ordinate system has the power to prevent him reaching r=2m."

 

Page 821 - Chapter 31.2 NonSingularity of the Gravitational Radius

 

AND

 

"Since the spacetime geometry will well behaved at the gravitational radius, the singular behaviour there of the Schwarzschild metric components g_tt = -(1-2M/r) and g_rr = (1-2M/r)^-1 must be fue to a pathology there of the Schwarzschild coordinates t,r, \theta \phi. "

 

Page 823 Chapter 31.3 Behavior of the Schwarzschild Coordinates at r=2M

There is also Taylor and Wheeler's Exploring Black Holes

 

"Does the raindrop cross the event horizon or not? To answer that question we need to track the descent with its directly-measured wristwatch time, not the global t-coordinate. ...

 

It shows that the raindrop's r-coordinate decreases as its wristwatch time advances, so the raindrop passes inward through the event horizon."

 

Chapter 6 Page 6.10 Diving

[Rolando]

"Since the spacetime geometry will well behaved at the gravitational radius, the singular behaviour there of the Schwarzschild metric components g_tt = -(1-2M/r) and g_rr = (1-2M/r)^-1 must be fue to a pathology there of the Schwarzschild coordinates t,r, \theta \phi. "

 

The fact that spacetime geometry is well behaved at the gravitational radius does not mean that there cannot be a hard surface there, which would prevent an object from falling any further. So, I think that the pathology does not reside in the coordinate systems but in the neglect of the presence of a hard surface. The Schwarzschild metric suggests such a surface to be present into future eternity.

 

By the way, "Schwarzschild" means 'black shield'.

Edited January 31, 2015 by Rolando

[MigL]

A 'hard surface which would prevent an object falling any further' ?

That could be an assumption made by a faraway observer, but in the frame of the infalling observer, what could possibly keep this 'hard surface' suspended ?

It would need to be moving outward faster than the speed of light.

[Robittybob1]

A 'hard surface which would prevent an object falling any further' ?

That could be an assumption made by a faraway observer, but in the frame of the infalling observer, what could possibly keep this 'hard surface' suspended ?

It would need to be moving outward faster than the speed of light.

If it had a surface at all, wouldn't it be more like the shell of a ping pong ball? Or even solid like a neutron star but forever incrementing in size?

[Strange]

If it had a surface at all, wouldn't it be more like the shell of a ping pong ball? Or even solid like a neutron star but forever incrementing in size?

 

More like a hollow unicorn turd. And about as realistic.

[Robittybob1]

 

More like a hollow unicorn turd. And about as realistic.

Or even troll-like crap toasted. Fair dinkum!

[jeffellis]

I think so. Don't some stars when they collapse create black holes?