Darren New <dne### [at] sanrrcom> wrote:
> > That's a misconception here: Time for photons has not come to a standstill in
> > their *own* frame of reference,
>
> How do you know? They're moving at c, where relativity divides by zero. :-)

Okay, you got me here: Time for a photon doesn't exist anyway :)


> > "The true diameters of the Sun and Earth are 4.1 km and 4.4 mm GREATER,
> > respectively, than one would expect from applying Euclidean geometry (C = pi d)
> > to the observed surface of these bodies"
>
> Diameters are greater than they should be, circumference is shorter than it
> should be. Yes?

Hm, yes, I guess that is what it's saying.


> >>> Given that spacetime is notoriously distorted at the EH, this makes *no*
> >>> statement whatsoever about its radial distance from the singularity. It could
> >>> be - ta-ding! - zero after all...
> >> More like infinity, methinks.
> >
> > (*scratches head*)
> > Doesn't make sense to me: We get closer to the black hole's center, and when we
> > have reached the EH this distance becomes *infinite*?
>
> Yes. for the same reason that the diameter of the earth is *greater* than it
> should be given its circumference.

Don't believe. Although I must confess that the above reasoning indicates that
it's something different than zero, and actually greater than the "expected" EH
radius.

Darn, so much for world domination...

BTW, I had a look at those other metrices; I particularly like the Lemaitre
metric: I have no idea what the coordinates might stand for, but the concept of
a coordinate system that defines "here" as where I'll stay if I continue free
fall feels rather "natural"... if there is such a thing when dealing with black
holes.

So looks like Warp's right after all: The poor victim will cross the EH, after
all. Will take more than eternity as seen from an outside observer, but *after*
that "outside eternity" he'll make it.

Duh. Achilleus and the turtle, once again. (As it happens, the
Eddington-Finkelstein metric even has a component called "tortoise coordinate"
:))

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"nemesis" <nam### [at] gmailcom> wrote:
> "clipka" <nomail@nomail> wrote:
> > Warp <war### [at] tagpovrayorg> wrote:
> > > > >   So if he isn't inside the EH, that means that actually *nothing* can
> > > > > ever cross the EH, which means that nothing goes inside a BH, and thus
> > > > > nothing is "lost" there.
> > >
> > > > That's basically what I think it says, yes.
> > >
> > >   Well, I think you are wrong.
> >
> > Reminds me of that Monty Python sketch:
> >
> > "This is not argument, this is just plain contradiction"
> > "No, it isn't"
> > "Yes, it is!"
> > "No, it isn't"
> > "..."
>
> No, it doesn't! :D

Careful, or I'll teach you some "being hit on the head" lessons ;P

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clipka wrote:
>>> Doesn't make sense to me: We get closer to the black hole's center, and when we
>>> have reached the EH this distance becomes *infinite*?

>> Yes. for the same reason that the diameter of the earth is *greater* than it
>> should be given its circumference.
> 
> Don't believe. 

Watch. Lay a ruler across the width of a black hole, thru the middle. How 
long does the ruler have to be?

That's what warped spacetime *is* - when euclidean measurements don't work. 
When the angles of a triangle add up to more than 180 degrees, you have a 
mass inside the triangle.

 > Although I must confess that the above reasoning indicates that
> it's something different than zero, and actually greater than the "expected" EH
> radius.

I think you're confusing circumference and radius and diameter.

> Eddington-Finkelstein metric even has a component called "tortoise coordinate"

Is that Achillese tortoise or A-Tuin tortoise? :-)

-- 
   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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clipka <nomail@nomail> wrote:
> Warp <war### [at] tagpovrayorg> wrote:
> > > >   So if he isn't inside the EH, that means that actually *nothing* can
> > > > ever cross the EH, which means that nothing goes inside a BH, and thus
> > > > nothing is "lost" there.
> >
> > > That's basically what I think it says, yes.
> >
> >   Well, I think you are wrong.

> Reminds me of that Monty Python sketch:

  Don't belittle me.

  There are two views:

1) Every single text I have read about the subject talks about particles
or objects passing through the event horizon, and how once inside they
cannot get back out. Some texts talk about the problems this imposes
from the point of view of quantum mechanics, as it seems to contradict
the rule that no information about a particle is ever lost, but a particle
entering the EH of a black hole seems to be lost information.
  Also the entire notion of Hawkin radiation is that one half of a split
virtual particle *enters* the event horizon while the other doesn't.
  I don't remember ever reading any text dealing with GR which wouldn't
talk about particles entering the EH without any conditions or problems.

2) You say that nothing ever enters the EH.

  So tell me: Which one should I believe more?

  So I repeat myself: I think you are wrong.

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> clipka wrote:
> >>> Doesn't make sense to me: We get closer to the black hole's center, and when we
> >>> have reached the EH this distance becomes *infinite*?
>
> >> Yes. for the same reason that the diameter of the earth is *greater* than it
> >> should be given its circumference.
> >
> > Don't believe.
>
> Watch. Lay a ruler across the width of a black hole, thru the middle. How
> long does the ruler have to be?
>
> That's what warped spacetime *is* - when euclidean measurements don't work.
> When the angles of a triangle add up to more than 180 degrees, you have a
> mass inside the triangle.

Do believe. Don't believe the *infinity* in your original statement.

> > Although I must confess that the above reasoning indicates that
> > it's something different than zero, and actually greater than the "expected" EH
> > radius.
>
> I think you're confusing circumference and radius and diameter.

I think I thought about them long enough and did enough sorting-out of confusion
to not having confused them in the end...

> > Eddington-Finkelstein metric even has a component called "tortoise coordinate"
>
> Is that Achillese tortoise or A-Tuin tortoise? :-)

Uh... I like to believe that it's the former ;)

(BTW, wasn't that *Great* A-Tuin?)

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Warp <war### [at] tagpovrayorg> wrote:
> > Reminds me of that Monty Python sketch:
>
>   Don't belittle me.

Sorry, no offense intended - I was belittle-ing both of us, so to speak, 'cause
I, too, was running out of arguments and was about to enter that sketch mode.


> 2) You say that nothing ever enters the EH.

Having read more about it, I must correct myself a bit here: Nothing "ever"
enters the EH unless I fall into it myself...

.... which doesn't mean that it "never" enters the EH.

It doesn't seem to happen all throughout *my* eternity, even though it takes
just a few *moments* for the "victim".

Then again, from what I read, it's not so much a question of *when* the "victim"
will cross the EH, but *where*... because the t-coordinate "becomes
space-like"...

*Very* queer beasts, those black holes.

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clipka <nomail@nomail> wrote:
> *Very* queer beasts, those black holes.

  For some reason thinking about neutron stars, they sound even scarier.

  Just imagine: A spherical object which is something like 8 times as
massive as the Sun, but which diameter is just a few kilometers (something
which you could just walk accross in less than a half hour), rotating even
several thousands of times per second.

  I wouldn't want such an object anywhere near me... :P

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:
>   For some reason thinking about neutron stars, they sound even scarier.
>
>   Just imagine: A spherical object which is something like 8 times as
> massive as the Sun, but which diameter is just a few kilometers (something
> which you could just walk accross in less than a half hour), rotating even
> several thousands of times per second.
>
>   I wouldn't want such an object anywhere near me... :P

.... so you'd prefer a thing near you that you can't even *see* that it's there?
:P

But neutron stars are scary enough indeed. Just imagine: The gravitation on
their surface is so strong that although they're incredibly hot, their
atmosphere is just about a meter thick. And you better hold on tight to your
mobile phone, because if you'd accidently drop it, it would *SLAM!* into the
ground at something like 4.3 *MILLION* mph! Now explain *that* to customer care
service, with all those "warranty void if removed" labels not only peeled off,
but probably disintegrated into subatomic particles upon impact...

Scary! Better not go there...

Or think about that spacetime is so warped already that their circumference is
not 2pi r, but something like 4pi r... of which you can see something like 3pi
r at the same time, because the gravitation is so strong that the photons get
the bends... and everything flying away from it at less than something like 33%
the speed of light will ultimately fall back...

And although the light leaving them experiences a *considerable* redshift,
they're so mind-bogglingly hot that most photons reaching us are still in the
X-Ray spectrum...

Yeah, children, heed my advice: Better not go there... so you're right: Who
needs black holes if he can have neutron stars to stay clear of! ;)

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"clipka" <nomail@nomail> wrote:
> Warp <war### [at] tagpovrayorg> wrote:
> >   For some reason thinking about neutron stars, they sound even scarier.
> >
> >   Just imagine: A spherical object which is something like 8 times as
> > massive as the Sun, but which diameter is just a few kilometers (something
> > which you could just walk accross in less than a half hour), rotating even
> > several thousands of times per second.
> >
> >   I wouldn't want such an object anywhere near me... :P
>
> .... so you'd prefer a thing near you that you can't even *see* that it's there?
> :P
>
> But neutron stars are scary enough indeed. Just imagine: The gravitation on
> their surface is so strong that although they're incredibly hot, their
> atmosphere is just about a meter thick. And you better hold on tight to your
> mobile phone, because if you'd accidently drop it, it would *SLAM!* into the
> ground at something like 4.3 *MILLION* mph! Now explain *that* to customer care
> service, with all those "warranty void if removed" labels not only peeled off,
> but probably disintegrated into subatomic particles upon impact...
>
> Scary! Better not go there...
>
> Or think about that spacetime is so warped already that their circumference is
> not 2pi r, but something like 4pi r... of which you can see something like 3pi
> r at the same time, because the gravitation is so strong that the photons get
> the bends... and everything flying away from it at less than something like 33%
> the speed of light will ultimately fall back...
>
> And although the light leaving them experiences a *considerable* redshift,
> they're so mind-bogglingly hot that most photons reaching us are still in the
> X-Ray spectrum...
>
> Yeah, children, heed my advice: Better not go there... so you're right: Who
> needs black holes if he can have neutron stars to stay clear of! ;)

Yes, Neutron Stars are the other freak little brother of blackholes.  If the
immense gravity and pressure isn't enough to impress someone, nor are the small
size and humongous rotation periods, then perhaps the fact that it's not
constituted of any chemical element in existance, but mostly neutrons alone,
should do the trick.

BTW, up until recently the only astronomy site I usually frequently visited was
NASA's famed Astronomy Picture of the Day (APOTD).  This conversation led me to
finally meet the Hubble site:

http://hubblesite.org/

Wonderful.

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clipka wrote:
> Do believe. Don't believe the *infinity* in your original statement.

Oh. I think that's what the equations imply.

Try it this way: take a pole and push it into the black hole until it comes 
out the other side. How much pole do you have to push in before it comes out 
the other side? :-)

>>> Although I must confess that the above reasoning indicates that
>>> it's something different than zero, and actually greater than the "expected" EH
>>> radius.
>> I think you're confusing circumference and radius and diameter.
> 
> I think I thought about them long enough and did enough sorting-out of confusion
> to not having confused them in the end...

I think you're right and I was confusing what the "it" in "it's something 
different from zero" referenced.

> (BTW, wasn't that *Great* A-Tuin?)

There's only one.

-- 
   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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