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"nemesis" <nam### [at] gmail com> 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."
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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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