clipka <nomail@nomail> wrote:
> Then again, I could turn my speculation indeed into an objection: As of now, no
> singularity (i.e. a condition where a formula gives "infinity" as an answer)
> predicted by any scientific theory has ever been observed in true life.

  Lack of evidence is not evidence of the contrary. Just because a
singularity has not been observed and measured doesn't necessarily mean
that singularities cannot exist.

  There are basically two choices:

1) Assume that GR equations are correct in all situations, including
   the extreme ones. There's little evidence to show that this wouldn't
   be so. One consequence of this is accepting singularities, at least
   until better evidence shows up.

2) Object to the notion of a singularity to be possible. This implies that
   GR equations do *not* work in all possible situations, and that they
   start to deviate in extreme conditions. However, no concrete evidence
   of this exists, nor widely accepted alternative theories.

  It may well be that singularities can not exist in this Universe, and
that something else is happening with collapsing stars (stars do collapse
due to gravity, which is something basically nobody doubts). However, as
long as viable theories or, better yet, evidence of alternatives are not
presented, science in general has to take choice #1.

  As far as I understand it, science is not about the Truth. The Truth may
be impossible to achieve. Science is about the best we know so far. About
getting as close to the truth as we can, by observing and measuring.

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> If his clock slows to zero on the outside

  "On the outside" means "from the point of view of an external observer".
In other words, someone far away from the influence of the black hole,
looking at the falling clock.

  The observer who falls into the black hole *with* the clock will
perceive it normally. (Well, relatively speaking. Let's forget for
a moment the space-warping.)

> and he never crosses the event 
> horizon, then the next tick of the clock is infinitely far in the future of 
> the universe, yes?

  From the outside perspective.

>  So he never experiences crossing the EH

  The observer who is falling into the black hole does experience the
crossing.

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> Rotating highly charged black holes that don't have the same Schwartzchild 
> equations. (The Schwartzchild equations only work for non-rotating 
> non-charged black holes, methinks.) If you spin the black hole fast enough, 
> the equator doesn't have an EH, or the pole doesn't, or something. (I've 
> heard speculation that the equations must therefore be wrong.)

  If I remember correctly, for a rotating black hole the singularity
will have a torus shape (with a minor radius of zero). The faster it
rotates, the larger the torus. I might remember this wrongly, though.

  Likewise the event horizon elongates, and if it rotates fast enough,
might even get some kind of torus shape itself as well, or something
like that.

-- 
                                                          - Warp

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Warp wrote:
> clipka <nomail@nomail> wrote:
>> Then again, I could turn my speculation indeed into an objection: As of now, no
>> singularity (i.e. a condition where a formula gives "infinity" as an answer)
>> predicted by any scientific theory has ever been observed in true life.
> 
>   Lack of evidence is not evidence of the contrary. 

If course it is.  It's not *proof*, but it's certainly evidence.

Do you go to the doctor to check if you have the flu, even if you have no 
symptoms? No, because lack of evidence is evidence to the contrary. :-)

> 1) Assume that GR equations are correct in all situations, including
>    the extreme ones. There's little evidence to show that this wouldn't
>    be so. One consequence of this is accepting singularities, at least
>    until better evidence shows up.

That would assume that QM is broken, and there's little evidence to show 
*that* would be so. :-)

> 2) Object to the notion of a singularity to be possible. This implies that
>    GR equations do *not* work in all possible situations, and that they
>    start to deviate in extreme conditions. However, no concrete evidence
>    of this exists,

Except fermions.

I don't think anyone on p.o-t knows whether GR or QM is wrong for sure.

But it has been fun talking about it, because I think I understand better 
what the problem is.

> long as viable theories

... which is where we came into the thread. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   "Ouch ouch ouch!"
   "What's wrong? Noodles too hot?"
   "No, I have Chopstick Tunnel Syndrome."

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Warp wrote:
>   The observer who is falling into the black hole does experience the
> crossing.

OK. Maybe I'm just incapable of understanding this. :-)  But yes, I get a 
glimmering of what you're saying. That whole lack of simultaneity.

But if he's still emitting photons when the black hole evaporates, it would 
seem to be rather paradoxical even for GR.

If he never crosses the EH as seen from outside, and the black hole is (say) 
only one stellar mass, then the outside observer will see the hole evaporate 
(thus eliminating the EH) before the spaceship actually crosses the EH.

It would seem the occupant would think he *did* cross the EH, while those 
outside would have a constant view of the occupant outside the EH.

Plus, the occupant *can* look out and conceivably see what the universe 
looks like even after he's past the event horizon, which would imply the 
universe hasn't ended for *him*?

(Modulo the space ship being bigger than the black hole physically, if it 
is, and that "constant view" would be very intermittent, and I may be 
misremembering how big a hole needs to be to be stable. Ignore that bit for 
now. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   "Ouch ouch ouch!"
   "What's wrong? Noodles too hot?"
   "No, I have Chopstick Tunnel Syndrome."

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Darren New <dne### [at] sanrrcom> wrote:
> But if he's still emitting photons when the black hole evaporates, it would 
> seem to be rather paradoxical even for GR.

  GR doesn't predict black hole evaporation. It's those quantum mechanists
messing around.

> If he never crosses the EH as seen from outside, and the black hole is (say) 
> only one stellar mass, then the outside observer will see the hole evaporate 
> (thus eliminating the EH) before the spaceship actually crosses the EH.

  Thinking about it, this is probably what would happen:

  If we assume the mass of the black hole would decrease, then the EH would
recess. The photons which were emitted extremely close to the EH will get
a speedup when the EH recesses. Basically the "point of entry" will stop
being *at* the EH and becomes being *above* it. Thus all the photons will
reach the external observer in finite time. The external observer will
end up actually "seeing" the falling object cross the EH.

  After all, how would the external observer actually see the black hole
getting smaller?

> Plus, the occupant *can* look out and conceivably see what the universe 
> looks like even after he's past the event horizon, which would imply the 
> universe hasn't ended for *him*?

  I don't think that's possible. When he is exactly at the EH, the entire
EH engulfs the entire view on all sides. He doesn't see anything else
than the EH. What he "sees" inside... I don't know.

-- 
                                                          - Warp

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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> But if he's still emitting photons when the black hole evaporates, it would 
>> seem to be rather paradoxical even for GR.
> 
>   GR doesn't predict black hole evaporation. It's those quantum mechanists
> messing around.

Good point. :-)

> reach the external observer in finite time. The external observer will
> end up actually "seeing" the falling object cross the EH.

Hmmm... Yes, that's possible.

>   I don't think that's possible. When he is exactly at the EH, the entire
> EH engulfs the entire view on all sides.

Even straight up?   And again, QM comes in there, as there might be 
uncertainty in the sense of what is it that's "straight up"?

I don't know either. By now, I'm entirely in BS mode. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   "Ouch ouch ouch!"
   "What's wrong? Noodles too hot?"
   "No, I have Chopstick Tunnel Syndrome."

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Darren New <dne### [at] sanrrcom> wrote:
> >   I don't think that's possible. When he is exactly at the EH, the entire
> > EH engulfs the entire view on all sides.

> Even straight up?

  Perhaps you see an infinitely small, very blue-shifted point.

>   And again, QM comes in there, as there might be 
> uncertainty in the sense of what is it that's "straight up"?

  The opposite direction of where gravity is pulling you. :)

-- 
                                                          - Warp

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Warp escreveu:
> Darren New <dne### [at] sanrrcom> wrote:
>> Plus, the occupant *can* look out and conceivably see what the universe 
>> looks like even after he's past the event horizon, which would imply the 
>> universe hasn't ended for *him*?
> 
>   I don't think that's possible. When he is exactly at the EH, the entire
> EH engulfs the entire view on all sides. He doesn't see anything else
> than the EH. What he "sees" inside... I don't know.

I think I'm finally understanding what Darren means.

If time slows down nearing a massive graviational field and an external 
observer sees the voyager freezing as he aproaches the EH, but still for 
him time would be the same as always, except perhaps he would see the 
external observer and the rest of the universe behind going by extremely 
faster as ages go by until eventually getting out of view once passing 
the EH.

The question Darren seems to pose is:  does it get an eternity for the 
voyager to get through the EH?  I believe not, even in the so called 
supermassive blackholes supposedly in the center of galaxies.  Spacetime 
dilatates near the EH, but don't become infinite (except in the 
singularity).  So, if we think otherwise we come to the turtle and 
Achilleus tale.

It's also interesting that a blackhole is as obscure as the future and 
the objects farther away we can get a glimpse of are from a bright 
distant past that gets away from us under heavy acceleration...

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nemesis wrote:
> The question Darren seems to pose is:  does it get an eternity for the 
> voyager to get through the EH?  

Something like that. Complicated by the question "who is asking?" :-)

Another interesting thought I saw somewhere:

The cosmological horizon is not unlike an event horizon - things moving 
towards it are going faster and faster relative to us, and hence are slowing 
down time-wise[1].  Perhaps the background microwave radiation is really 
just all the galaxies that used to be close red-shifted waaaaay down as they 
pile up near the border of the observable universe.



[1] Do they really slow down (for us) if their speed is caused by new space 
being created?  I have no idea, but from what I know of it, I think the 
answer is "yes".

-- 
   Darren New, San Diego CA, USA (PST)
   "Ouch ouch ouch!"
   "What's wrong? Noodles too hot?"
   "No, I have Chopstick Tunnel Syndrome."

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