Warp escreveu:
> clipka <nomail@nomail> wrote:
>> From an outside observer's frame of reference, the victim not only *appears* to
>> be "hanging out there", he still physically *is*.
> 
>   How is he "physically" there? The external observer can't touch him nor
> communicate with him.

If he could, he'd be in the very same spacetime region and thus subject 
to the same effects.

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Warp escreveu:
>   The victim was not "hanging out" anywhere. There were simply some
> leftover photons there, going out (with asymptotically lessening frequency).
> 
>   When the event horizon recedes, these leftover photons will be in a
> less strong gravity field and will thus get a boostup. The photons which
> were almost touching the EH will now be farther away, and will get out
> in less time.


I thought you said, the speed of time is constant.  How can it slow down 
or boost up?

If we take it instead that near a humongous gravitational field 
spacetime is dilated, then light should have a hard time (bad pun) 
getting out of it, either because space expands near it or time slows 
down (which is about the same thing given space and time 
interchangeability)...

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nemesis wrote:
> Darren New escreveu:
>> clipka wrote:
>>> Maybe what we see isn't the "big bang" after all, but the "big crunch"?
>>
>> My favorite personal random idea is ... what if we really *are* at the 
>> center of the universe, and everything really *is* moving away from *us*?
> 
> Shouldn't then we not see them above the peak? 

Uh, 4D curvature. What if it isn't "everything is moving away from 
everything else" but really "everything is moving away from the Milky Way"?

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

Post a reply to this message

Darren New escreveu:
> What if it isn't "everything is moving away from 
> everything else" but really "everything is moving away from the Milky Way"?

They know we're baddass mofos. :D

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nemesis <nam### [at] gmailcom> wrote:
> I thought you said, the speed of time is constant.  How can it slow down 
> or boost up?

  It's not the speed of the photons which changes, but their timeframe.

  (No, I don't fully understand this myself. Don't ask for specifics.
I'm just blindly repeating what I have read. And it's perfectly possible
that I have misunderstood what I have read.)

-- 
                                                          - Warp

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Warp escreveu:
>   (No, I don't fully understand this myself. Don't ask for specifics.
> I'm just blindly repeating what I have read. And it's perfectly possible
> that I have misunderstood what I have read.)

we're all laymen, even the scientists. :)

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Warp <war### [at] tagpovrayorg> wrote:
> clipka <nomail@nomail> wrote:
> > From an outside observer's frame of reference, the victim not only *appears* to
> > be "hanging out there", he still physically *is*.
>
>   How is he "physically" there? The external observer can't touch him nor
> communicate with him.

He can: He can send light pulses to him. And the poor victim can send light
pulses back. After all, he has not passed the EH yet.

Doing so, the observer will easily be able to convince himself that the victim
is still there. He's a bit slow of speech, but still responding. And the victim
will find it hard to understand the observer because he's speaking a bit fast,
but... well, from a theoretical point of view, they'll have no trouble still
communicating :)

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Darren New <dne### [at] sanrrcom> wrote:
> I saw a great line:  "Of *course* God put the Earth in the center of the
> universe. That's why all the stars shine *towards us*!"

LOL - that's a good one :)

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Darren New <dne### [at] sanrrcom> wrote:
> It's like waves, I guess. No matter how hard you try, you can't combine
> sin(t) and -sin(t) and wind up with a wave. It's not a matter of squeezing
> them real hard - they just cancel out.

Stupid bastards! We'll *make* them combine! :)

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Darren New <dne### [at] sanrrcom> wrote:
> > So if there's no EH, you can just zip straight through the singularity?
>
> I think it's more that you can see things coming out of the singularity.

If that is so, then where do they come from? Must have fallen in there, don't
they? So *they* sort of zipped right through, right? ;)

> > I think I recall remember having heard that spinning black holes would actually
> > not have a point-shaped singularity at all, but a loop, because their drag on
> > spacetime is that extreme.
>
> Yep. And if you fly through the hole, you wind up ... somewhere else.

Ah... could that be a variation of that "fly into it - happen to most probably
be not there at all but someplace else" effect I suggested?

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nemesis <nam### [at] gmailcom> wrote:
> >> Perhaps only Phil Connor would know. :P
> >
> > Maybe - I don't know *him*... should I?
>
> Ever seen "Groundhog Day" with Bill Murray?  A classic. :)

Aaah! Of course, yes - that rings a bell. Great movie, liked it a lot!

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nemesis <nam### [at] gmailcom> wrote:
> Well, it's all relative to the observer, so from our point of view the
> universe indeed revolves around us.  Actually, to the common man in the
> streets -- whose view at nights is occluded by both smog polution and
> city lights so he doesn't really take the time to look up the few
> blinking stars so far away and so static -- the universe revolves around
> mundane job, bills and society's many rituals. :P

Yeah, and for too many of them, the world actually revolves around *them* :)

BTW, as a child I pictured that as of course the world is round, then whenever
we would be driving around, the world would revolve below us... and, by the
way, of course mountains would be the places where the earth was "bent" :)

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"clipka" <nomail@nomail> wrote:
> nemesis <nam### [at] gmailcom> wrote:
> > blinking stars so far away and so static -- the universe revolves around
> > mundane job, bills and society's many rituals. :P
>
> Yeah, and for too many of them, the world actually revolves around *them* :)

That's the worst. ;)

> BTW, as a child I pictured that as of course the world is round, then whenever
> we would be driving around, the world would revolve below us... and, by the
> way, of course mountains would be the places where the earth was "bent" :)

hah!

BTW, has any of you guys ever witnessed the Milky Way by your own eyes?  I did
as a pre-teen, one of the most amazing moments in my life, no doubt.  My family
went in vacation to some rural place of sorts and I was roaming around in my
bike until dark at night.  I looked up at the sky and couldn't believe the
sheer amount of stars just above my head!  There were so many that they
gathered in thick luminous regions, which at first I thought were clouds, but
then remembered the sky was clean in the afternoon and looking more closely, it
could be seen very faint flickering in said clouds... quite a moment!  You feel
right in space, in the full glory of a 180% view of the universe... I recommend
any of you at least once to take refuge from noisy and bright cityscapes just to
marvel at this true natural beauty.

It's why I'm so full of passion for astronomic topics... :)

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clipka <nomail@nomail> wrote:
> [-- text/plain, encoding 8bit, charset: iso-8859-1, 19 lines --]

> Warp <war### [at] tagpovrayorg> wrote:
> > clipka <nomail@nomail> wrote:
> > > From an outside observer's frame of reference, the victim not only *appears* to
> > > be "hanging out there", he still physically *is*.
> >
> >   How is he "physically" there? The external observer can't touch him nor
> > communicate with him.

> He can: He can send light pulses to him. And the poor victim can send light
> pulses back.

  No he can't. The light pulses sent by the external observer won't ever
reach the falling object, from the external observer's point of view, for
the exact same reason that it looks to him like the falling object never
crosses the EH.

  The falling object won't be able to send anything back because he is
inside the EH.

> After all, he has not passed the EH yet.

  Of course he has.

-- 
                                                          - Warp

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"nemesis" <nam### [at] gmailcom> wrote:
> BTW, has any of you guys ever witnessed the Milky Way by your own eyes?  I did
> as a pre-teen, one of the most amazing moments in my life, no doubt.

I fancy I did when I was a child - although I can't remember being able to make
out any stars, just a blurry band. Maybe that was because I've been
short-sighted ever since I can remember.

I grew up in a rather small town in a hilly region, spread across multiple
valleys, in a smaller side valley not too close to the town centers, so the air
was very clean, and not too many light sources nearby late at night. Occasionaly
our dad (a teacher) would take us out on a night barbecue with his pupils in an
even more remote spot in the woods around. We also did a few camping vacations
in different European contries (UK, France and Italy), and later took trips
once or twice a year to sparsely populated seaside regions, where we'd often go
for walks after dark.

I loved the stars, and particularly the moon, and looking up at the night sky. I
still enjoy looking up on a clear night when I'm far from the big city I live
in, and marvel in some kind of surprise once again how clear a starry night can
be!

(Unfortunately, nothing so clear though as to identify the milky way as a mass
of stars. Or maybe my glasses just aren't good enough for that.)

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Warp <war### [at] tagpovrayorg> wrote:
> > He can: He can send light pulses to him. And the poor victim can send light
> > pulses back.
>
>   No he can't. The light pulses sent by the external observer won't ever
> reach the falling object, from the external observer's point of view, for
> the exact same reason that it looks to him like the falling object never
> crosses the EH.

Just believe me (or figure out for yourselves): He can...

>   The falling object won't be able to send anything back because he is
> inside the EH.

.... because he isn't.

I'll draw a picture today, to illustrate what's going on with that warped
spacetime. I thought you should know about that, if only for the sake of your
nick ;)

The key to understanding is that a second is not a second. Delta-t is not
universal (just like distance isn't), but rather depends on the frame of
reference.

Likening some time dilation effects to "after-image" effects may make them more
"digestible" to laymen than having them try to imagine how a second cannot be a
second, but it's not *precisely* what's going on.

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clipka <nomail@nomail> wrote:
> >   The falling object won't be able to send anything back because he is
> > inside the EH.

> .... because he isn't.

  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.

  Great, you have solved the information loss problem. No information
is ever lost to a BH because nothing can enter it. Everything will just
hover endlessly asymptotically close to the EH, and can in fact be
interacted with.

  What are the quantum mechanists complaining about?

-- 
                                                          - Warp

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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.

>   Great, you have solved the information loss problem. No information
> is ever lost to a BH because nothing can enter it. Everything will just
> hover endlessly asymptotically close to the EH, and can in fact be
> interacted with.
>
>   What are the quantum mechanists complaining about?

I have no idea. Ask them :)


BTW, I after having so far worked only with what I picked up and remembered and
imagined, but finding that drawing a proper image based on this information is
not so trivial, I did have a closer look at the Schwarzschild metric details,
finding this on Wikipedia:

----------------------------------------
In Schwarzschild Coordinates, the Schwarzschild metric has the form:

c^2 dT^2 = (1 - r[s]/r) c^2 dt^2 - ... - ...

where

T is the proper time (time measured by a clock moving with the particle) ...
t is the time coordinate (measured by a stationary clock at infinity) ...,
r is the radial coordinate ...
r[s] is the Schwarzschild radius (in meters) of the massive body
....
----------------------------------------
(Note that dT and dt denote time intervals. I stripped the other terms because
they're not easy to represent in ASCII, and are independent of time, so they
can be considered constant for the sake of my arguments.)

There are a few interesting things to note here:

(1) As we approach r = r[s] (the radius of the EH), we'll find that the factor
of the dt^2 term diminishes zero. That means not only that "victim time" slows
down with respect to the "observer time", but that it actually slows down to
zero (or, seen the other way round, "observer time" speeds up to infinity) at
the EH.

Thus, in the observer's reference frame (I'm deliberately avoiding the phrase
"as seen from the observer", because the formula doesn't say anything about
perception, but plain hard facts), as soon as the "victim" would hit the EH,
its time would come to a standstill, so it couldn't move *any* distance in
finite time. (Note however that time slows down so dramatically already very
close to the EH that the "victim" will not even *reach* EH in finite time.)

However, in the "victim's" reference frame, as soon as the "victim" would hit
the EH, the observer's time would speed up to infinity. Again, note that the
speedup would already have reached dramatic values very close to the EH.


(2) Note that the formula is given "in Schwarzschild Coordinates"...
(Uh-huh?!)... Well, this is what Wikipedia has to say about those (emphasis
added):

"The defining characteristic of Schwarzschild chart is that the radial
coordinate possesses a natural geometric interpretation in terms of the SURFACE
AREA and Gaussian curvature of each sphere. However, RADIAL DISTANCES and angles
are NOT ACCURATELY REPRESENTED."

So, the equation does *not* state that the EH has a radius of r[s] = 2GM/c^2
after all. Instead, it states that it has a *surface* of 4 pi (2GM/c^2)^2.

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...


(Again, I find my theory of "EH=singularity" supported - it will mark a paradigm
shift in the understanding of black holes, and I'm going to be a world-famous
nobel prize winner, named along with Einstein, Hawking and Feinman! GR and QM
will at last be proven false, and MY theory will TAKE OVER THE WORLD... no, THE
*UNIVERSE*! *MUAHAHAHAHA*!)

(Good enough to quality for a world-class crackpot this time, huh? =B))

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"clipka" <nomail@nomail> wrote:
> Another BTW: With contemporary German orthography, "Schwartzschild" would lose
> the "t" in his name... like "Rothschild" (which is "Redshield") would lose the
> "h"...

Duh... sorry folks for misinforming you on this important subject: Looks like
Schwarzschild's "t" *already* got lost in some black hole... must have been
redundant information after all...

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clipka wrote:
> Thus, in the observer's reference frame (I'm deliberately avoiding the phrase
> "as seen from the observer", because the formula doesn't say anything about
> perception, but plain hard facts), as soon as the "victim" would hit the EH,
> its time would come to a standstill, so it couldn't move *any* distance in
> finite time.

I'm not sure that follows. Photons move as fast as possible, and in their 
own reference frame, time has come to a standstill. Why does the victim's 
clock influence the velocity of the victim in the observer's timeframe?

This is like saying I stick a giant engine on a spaceship, turn it on, and 
just go, and after a while you see me slowing down, because my clock is 
getting asymptotically close to stopped from your reference frame.

> (Note however that time slows down so dramatically already very
> close to the EH that the "victim" will not even *reach* EH in finite time.)

*That* is why I think the victim will not find himself inside the EH - the 
universe (including himself) will have decayed to nothingness or some such 
before he gets there.

> So, the equation does *not* state that the EH has a radius of r[s] = 2GM/c^2
> after all. Instead, it states that it has a *surface* of 4 pi (2GM/c^2)^2.

That difference is exactly the warped space. It happens with the sun and the 
earth, too, because of their gravity.

IIRC, I read where the circumference of the (ideal) earth is something like 
a cm shorter than what it should be given the radius, and the sun is a 
kilometer or ten kilometers or some such different.

> 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.

> (Good enough to quality for a world-class crackpot this time, huh? =B))

I don't think real crackpots go "Mwa ha ha ha!"

-- 
   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:

> 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...
>
>
> (Again, I find my theory of "EH=singularity" supported - it will mark a paradigm
> shift in the understanding of black holes, and I'm going to be a world-famous
> nobel prize winner, named along with Einstein, Hawking and Feinman! GR and QM
> will at last be proven false, and MY theory will TAKE OVER THE WORLD... no, THE
> *UNIVERSE*! *MUAHAHAHAHA*!)

Then why are the problems with the metric at the Schwarzschild radius removable
with a coordinate substitution, e.g. Eddington-Finklestein coordinates?  If

r* = r+2m ln( r/2m - 1 ),
u = t-r*,
v = t+r*

Then you work out the details, and - voila - the problems disappear, except at
the center.  Just sayin' is all...  Oh, but don't let that stop your plans for
universe domination.

 - Ricky

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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.

-- 
                                                          - Warp

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"clipka" <nomail@nomail> wrote:
> (Unfortunately, nothing so clear though as to identify the milky way as a mass
> of stars. Or maybe my glasses just aren't good enough for that.)

It's like this: even in the big city, if you look up the sky and begin counting
the stars nearby you soon realize you can't, because looking further next to
the bright ones you can also see lots of smaller, faint flickering dots.  They
are everywhere even though when you first felt venturous enough to try to count
the stars, they didn't seem too many.

I don't know if people on glasses have difficult to distinguish the smaller
stars, but once you start counting by the brightest ones, you inevitably become
more aware of the area closer to it and can distinguish a myriad of smaller
stars next to it...

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"clipka" <nomail@nomail> wrote:
> "clipka" <nomail@nomail> wrote:
> > Another BTW: With contemporary German orthography, "Schwartzschild" would lose
> > the "t" in his name... like "Rothschild" (which is "Redshield") would lose the
> > "h"...
>
> Duh... sorry folks for misinforming you on this important subject: Looks like
> Schwarzschild's "t" *already* got lost in some black hole... must have been
> redundant information after all...

Thanks.  I'm getting many useful tips in this thread, even though might some
conflict like either accelerating towards a blackhole or keeping where you are
curled up in fetal position... :D

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> > Thus, in the observer's reference frame (I'm deliberately avoiding the phrase
> > "as seen from the observer", because the formula doesn't say anything about
> > perception, but plain hard facts), as soon as the "victim" would hit the EH,
> > its time would come to a standstill, so it couldn't move *any* distance in
> > finite time.
>
> I'm not sure that follows. Photons move as fast as possible, and in their
> own reference frame, time has come to a standstill. Why does the victim's
> clock influence the velocity of the victim in the observer's timeframe?

That's a misconception here: Time for photons has not come to a standstill in
their *own* frame of reference, but at their location in the *observer's* frame
of reference (i.e. in the spacetime co-ordinate system where the observer is not
moving in space, and time flows at "normal speed" at his location).

Time is not universal, even in a single frame of reference.

> This is like saying I stick a giant engine on a spaceship, turn it on, and
> just go, and after a while you see me slowing down, because my clock is
> getting asymptotically close to stopped from your reference frame.

It's a bit different here I guess, because this is not about GR, but just about
SR, with a different underlying mechanism for time dilation.

In SR, which ignores gravitation and acceleration and just deals with constant
relative motion, all time dilation effects are just due to a change in frame of
reference, and can in fact be applied *mutually*: If you zoom by me at near
lightspeed, it seems to me that *your* clock is slower, while at the same time
it seems to you that *my* clock is slower. These are really just illusions due
to the peculiar nature of the question what "now" and "here" actually is.

This apparent paradoxon, however, only leads to problems when we meet once
again, which can only happen if at least one of us accelerates. Enter GR, which
deals with accelerated motion and gravitation; here, *real* time delation
effects happen, that are independent of the frame of reference, with the only
difference that in the "here" frame of reference, time "over there" slows down,
while in the "over there" frame of reference, it is time "here" that speeds up.
The relative effect is the same: Time "over there" runs slower than "here"

> > (Note however that time slows down so dramatically already very
> > close to the EH that the "victim" will not even *reach* EH in finite time.)
>
> *That* is why I think the victim will not find himself inside the EH - the
> universe (including himself) will have decayed to nothingness or some such
> before he gets there.

Yesss!

> > So, the equation does *not* state that the EH has a radius of r[s] = 2GM/c^2
> > after all. Instead, it states that it has a *surface* of 4 pi (2GM/c^2)^2.
>
> That difference is exactly the warped space. It happens with the sun and the
> earth, too, because of their gravity.
>
> IIRC, I read where the circumference of the (ideal) earth is something like
> a cm shorter than what it should be given the radius, and the sun is a
> kilometer or ten kilometers or some such different.

The order of magnitude is right, but someone messed up the sign; see
http://www.johnstonsarchive.net/relativity/stcurve.pdf (emphasis added):

"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"

(Duh - took quite a while to google that one up. Looks like this is a topic not
so frequently tackled.)


> > 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*?

Now *that* would be *really* warped spacetime! :)


> > (Good enough to quality for a world-class crackpot this time, huh? =B))
>
> I don't think real crackpots go "Mwa ha ha ha!"

Darn. Lost again, hm?

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"triple_r" <nomail@nomail> wrote:
> Then why are the problems with the metric at the Schwarzschild radius removable
> with a coordinate substitution, e.g. Eddington-Finklestein coordinates?  If
>
> r* = r+2m ln( r/2m - 1 ),
> u = t-r*,
> v = t+r*
>
> Then you work out the details, and - voila - the problems disappear, except at
> the center.  Just sayin' is all...  Oh, but don't let that stop your plans for
> universe domination.

Spoil-sport :P

Don't know, haven't looked at these. At the moment I fancy the're... well,
dunno, maybe just plain wrong? =B)

They look a bit... weird to me in any case. I know UV co-ordinates, but these
don't seem to fit any mesh :P

(Hey, nothing like a bit of ridiculing some (probably) well-established formulae
that can't seem to be argued against; gotta make a few crackpot points after
all...)

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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"
"..."

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"nemesis" <nam### [at] gmailcom> wrote:
> Thanks.  I'm getting many useful tips in this thread, even though might some
> conflict like either accelerating towards a blackhole or keeping where you are
> curled up in fetal position... :D

Practical applied science, yes :)

Post a reply to this message

clipka 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. :-)

>> IIRC, I read where the circumference of the (ideal) earth is something like
>> a cm shorter than what it should be given the radius, and the sun is a
>> kilometer or ten kilometers or some such different.
> 
> The order of magnitude is right, but someone messed up the sign; see
> http://www.johnstonsarchive.net/relativity/stcurve.pdf (emphasis added):
> 
> "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?

>>> 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.

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

Post a reply to this message

"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

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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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Darren New wrote:
>> (BTW, wasn't that *Great* A-Tuin?)
> There's only one.

Well, unless you believe in the Big Bang theory, at least.

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

"Dragon's Egg" by Robert Forward. Very cool book.

Always neat to read sci-fi set in exotic locations (like in orbit around a 
neutron star) written by someone who actually understands the physics of it.

-- 
   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:
> 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? :-)

Sure, but if you push *two* poles in, from opposing sides - how much pole do you
have to push in before they meet?

I think it's a tricky one.

> > (BTW, wasn't that *Great* A-Tuin?)
>
> There's only one.

In one of the stories there were little baby ones. (Or was it just one baby?
Don't recall.)

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nemesis <nam### [at] gmailcom> wrote:
> 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.

  Not only does the core of a neutron star consist (most probably) of
mostly neutrons, but the neutrons are in fact so packed together that
there's no empty space between them (like there is between atoms). The
whole core consists entirely and thoroughly of neutron matter, with no
empty space at all, so the density of the core is the same as the density
of one single neutron, which is *humongous*.

-- 
                                                          - Warp

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clipka wrote:
> Sure, but if you push *two* poles in, from opposing sides - how much pole do you
> have to push in before they meet?

How do you know if they meet?

> I think it's a tricky one.

Indeed.

> In one of the stories there were little baby ones. (Or was it just one baby?
> Don't recall.)

No, all the planets hatched.

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

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> >   I wouldn't want such an object anywhere near me... :P

> "Dragon's Egg" by Robert Forward. Very cool book.

> Always neat to read sci-fi set in exotic locations (like in orbit around a 
> neutron star) written by someone who actually understands the physics of it.

  Assuming a neutron star of something like 2 times the mass of the Sun,
with no accretion disc and radio-quiet (ie. it's not a pulsar), would it
be considerably different from orbiting a regular star?

  Of course another question is whether such a "peaceful" neutron star
can form in practice...

-- 
                                                          - Warp

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Warp wrote:
> whole core consists entirely and thoroughly of neutron matter, with no
> empty space at all, so the density of the core is the same as the density
> of one single neutron, which is *humongous*.

I'm really curious what QM says about this. As I understand it, "density" 
doesn't really work that way for elementary particles. Like, in a 
"Bose-Einstein Condensate", the "density" of a single particle could be such 
that it fills an entire room.

Not that I'm disagreeing with what you're saying. I'm just saying it's one 
of those areas where the QM and the GR come together to do something 
curious. It's not a big bowl of neurons - it's more a neuron soup. :-)

-- 
   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:
>   Assuming a neutron star of something like 2 times the mass of the Sun,
> with no accretion disc and radio-quiet (ie. it's not a pulsar), would it
> be considerably different from orbiting a regular star?

Yes, because you'd be orbiting it several times a second, and the tides 
would rip you apart as you try to get into orbit.

That's not the point of the book. It's just cool to read the aside about how 
they make it work and such, and how they need another set of masses orbiting 
at right angles to their own orbit to counteract the tides and such. The 
description of dealing with the neutron star's gravity takes up about as 
much as the explanations of the technology on Star Trek do, but it's cool 
when it's written by someone who has (for example) actually invented 
technology for measuring gravity waves, so you can have a decent idea it 
really is how things work.

It would be like reading a cyberpunk book by Alan Turing.

>   Of course another question is whether such a "peaceful" neutron star
> can form in practice...

That too. The book, being Sci-Fi, of course, goes far past that simple 
postulate. :-)  I won't spoil it, tho.

-- 
   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:
> Warp wrote:
> >   Assuming a neutron star of something like 2 times the mass of the Sun,
> > with no accretion disc and radio-quiet (ie. it's not a pulsar), would it
> > be considerably different from orbiting a regular star?

> Yes, because you'd be orbiting it several times a second, and the tides 
> would rip you apart as you try to get into orbit.

  Why would you do that? The density of the star doesn't change its mass,
and consequently doesn't change the orbits around it.

  The only thing I can think of that would make orbiting a neutron star
not very viable is that neutron stars emit humongous amounts of X rays.
Those are not very healthy.

-- 
                                                          - Warp

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Warp wrote:
>   Why would you do that?

If I recall the story, they were looking for a synchronous orbit.  Fiction, 
remember? :-)

-- 
   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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