leaving black holes

On Oct 1, 6:04*pm, Tom Roberts wrote in
sci.physics.relativity:
But yes, just outside the horizon,
if one fired a bullet outward at 0.999 c or so, it would slow down and
essentially halt at distance infinity. But a light beam emitted outward there
would not slow down (as measured locally, anywhere along its trajectory); it
would be greatly redshifted, however.

Honest Roberts do you really believe that nobody knows what "would not
slow down as measured locally" means? Will the bullet slow down as
measured locally? You just know no limits, Honest Roberts.

On 2-Oct-2009, Pentcho Valev wrote:

Honest Roberts do you really believe that nobody knows what "would not
slow down as measured locally" means? Will the bullet slow down as
measured locally? You just know no limits, Honest Roberts.

People talk about spagettification if one got near to a black hole... That
is really crap because it neglects the gyroscopy of the object approaching
the black hole... There has to be a gateway to the center... You can't fall
to the center of the earth and stand at the center of the earth but it is
still possible to stand at the center of the earth by following the
torroidal magnetic lines that lead to the center.

--
Tell it to the Marines.

Dear eric gisse

On Oct 1, 4:37*pm, eric gisse wrote:
dlzc wrote:

[...]

You hyperboilically fly around a black hole within
(I believe) 3M and

Last stable orbit.

No. With the event horizon at 2M (as previously described in this
thread), the closest possible stable orbit for matter is 6M.

Arbitrary acceleration can let you get arbitrarily
close to r = 2M.

You mangled the original newsgroup listing, so Tom's excellent and
thorough response did not make it on the sci.astro branch of this
thread. Please be careful how you apply Occam's razor here...

David A. Smith

wrote in news:ha2lvp$f4d$1
@skeeter.ucdavis.edu:

If she now sticks her hand toward the horizon, she's in trouble. Her
hand needs a huge acceleration to remain at rest, but it doesn't have
a rocket attached; it's accelerating only because it's connected to the
rest of her body, which presumably is in her spacecraft. Bones aren't
strong enough to transmit a near-infinite acceleration; nothing is.

What if the black hole were the size and mass of our universe?




--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

Dear Tom Roberts:

original newsgroup list corrected

On Oct 1, 9:53*pm, Tom Roberts wrote:
N:dlzcD:aol T:com (dlzc) wrote:

"eric gisse" wrote in message
...
dlzcwrote:
You hyperboilically fly around a black
hole within (I believe) 3M and

Last stable orbit.

Photon sphere is 3M. *Last stable orbit for
matter is 6M.

* * * [This is all for a Schwarzschild black hole.
r is the usual Schw. coordinate.]

There is an unstable circular null
geodesic at r=3M that orbits the black
hole, which might be what you are trying
to say, but "photon sphere" does not mean
that to me.

The typical definition is an "Einstein ring" with an infinite number
of "laps".
http://en.wikipedia.org/wiki/Photon_sphere

What I would call the "photon sphere"
is right at the horizon, r=2M -- that is,
outgoing light at the horizon remains at
the horizon (an unstable situation).

Einstein rings and your "salmon swimming upstream" are both unstable,
for a structure that will continue to add or expell contents.

The smallest stable timelike orbit is
indeed at r=6M, and I'm pretty sure it is
true that if an ORBIT goes inside r=6M it
will destabilize and fall in or fly away.

Yes, Eric just was thinking "Schwarzchild radii" rather than tying it
to mass directly, and I was hoping to unconfuse the issue with the OP.

But there are hyperbolic-like timelike
trajectories that come in from far away,
approach between r=3M and r=6M, and then
leave; these are not orbits, and none
come closer than r=3M.

It is also true that any timelike or null
geodesic that comes from far away and gets
below r=3M will enter the horizon (in some
cases it can circle the horizon several
times before entering). But light that is
headed outward and emitted by a timelike
object from 2Mr3M will get away; that's
different from light coming in from far
away.

Arbitrary acceleration can let you get
arbitrarily close to r = 2M.

If you choose a different coordinate
system. *This leaves you still 1M out
from the event horizon.

Not really. The horizon is at r=2M.
Coordinate choice has nothing whatsoever
to do with the locus of the horizon or
the location a given spaceship is able
to hover outside it with a given thrust
[#]. With arbitrarily-high thrust, a
spaceship could hover arbitrarily close
to the horizon at r=2M. This is an
unstable situation if its r is close to
2M.

* * * [#] Coordinate choice only affects
your DESCRIPTION, not the
physical situation.

"A miss is as good as a mile." Eric was selling r_S as 1M. It is off
by a factor of 2. And coordinate choice clarity is necessary:
http://en.wikipedia.org/wiki/Mars_Climate_Orbiter

http://casa.colorado.edu/~ajsh/orbit.html

Hmmm. This page says "The orbit at 2
Schwarzschild radii corresponds to zero kinetic
energy at infinity, so it is possible to fall
freely into this orbit from infinity without
rocket power." -- this is wrong, and it is NOT
possible to enter an orbit at ANY radius
without thrusting, when one starts from
infinity and is free-falling [@]. Here by
"orbit" I mean a trajectory with a permanent
spatial path circling the black hole.

* * This is easy to see, as the spatial path
of any timelike geodesic can be traversed
in the opposite direction, within the
region outside the horizon -- an incoming
* * trajectory that falls into into an orbit,
when reversed, would mean it is not an
orbit.

An elegant argument.

* * *[@] And gravitational radiation is
neglected, as for test particles like
rocket ships compared to stars.

Tom Roberts

Thank you.

David A. Smith

bz wrote:
wrote in news:ha2lvp$f4d$1
@skeeter.ucdavis.edu:

If she now sticks her hand toward the horizon, she's in trouble. Her
hand needs a huge acceleration to remain at rest, but it doesn't have
a rocket attached; it's accelerating only because it's connected to the
rest of her body, which presumably is in her spacecraft. Bones aren't
strong enough to transmit a near-infinite acceleration; nothing is.

What if the black hole were the size and mass of our universe?

Who do you think might stick her hand into an infinite universe?

Bernhard

Bernhard Kuemel wrote in news:4765c$4ac657af$557f726a
:

bz wrote:
wrote in news:ha2lvp$f4d$1
@skeeter.ucdavis.edu:

If she now sticks her hand toward the horizon, she's in trouble. Her
hand needs a huge acceleration to remain at rest, but it doesn't have
a rocket attached; it's accelerating only because it's connected to the
rest of her body, which presumably is in her spacecraft. Bones aren't
strong enough to transmit a near-infinite acceleration; nothing is.

What if the black hole were the size and mass of our universe?

Who do you think might stick her hand into an infinite universe?

Someone that was outside it.
There is no way to prove that it is infinite.

If I remember correctly, "someone" has calculated that the amount of matter
is "close" to the amount that would be needed for a black hole the size of
the known universe.

Perhaps we live inside a black hole.

http://www.mathpages.com/home/kmath339.htm


Bernhard






--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz wrote:

Bernhard Kuemel wrote in news:4765c$4ac657af$557f726a
:

bz wrote:
wrote in news:ha2lvp$f4d$1
@skeeter.ucdavis.edu:

If she now sticks her hand toward the horizon, she's in trouble. Her
hand needs a huge acceleration to remain at rest, but it doesn't have
a rocket attached; it's accelerating only because it's connected to the
rest of her body, which presumably is in her spacecraft. Bones aren't
strong enough to transmit a near-infinite acceleration; nothing is.

What if the black hole were the size and mass of our universe?

Who do you think might stick her hand into an infinite universe?

Someone that was outside it.
There is no way to prove that it is infinite.

If I remember correctly, "someone" has calculated that the amount of
matter is "close" to the amount that would be needed for a black hole the
size of the known universe.

Perhaps we live inside a black hole.

Which direction is the singularity?


http://www.mathpages.com/home/kmath339.htm


Bernhard

Can you say despagettification? I spagettify and despagettify every time I
enter or leave my apartment complex but then again what the hell do I know,
I'm just a schizo. I may be Islam's pi ion but I hopefully have my own pi
ion... or pi ions looking out for my interests without my giving direction.
Nod means no, shake your head means yes, mutiny is not an option.

--
Tell it to the Marines.