View Full Version : Space elevators and black holes
George, Stuart
Jun12-04, 07:19 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>--=====================_77367437==.ALT\nContent-Type: text/plain; charset="us-ascii"; format=flowed\n\nHi\n\nIs there in principle no objection to lowering a space elevator cable into\na black hole ?\n\nAs I understand it, objects or persons passing the event horizon have no\nknowledge of such a transition, yet where they part of a space elevator\nthey might get cold feet when they see (see ?) what is below and elect to\nreturn via the elevator cable to their home base.\n\nGoodness knows from what the elevator cable might be constructed.\n\nRegards\nGeorge Stuart\n\n\n-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --\n-- -- -- -- --\nCan there be information without an information processor ?\nWhich came first, the information or the processor ?\n-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --\n-- -- -- -- --\nGeorge Lee Stuart\n* Southern Cross University\n* . * School of Multimedia and Information Technology\n* SOMIT\n\nLecturer\nSouthern Cross University\nPO Box 157\nLISMORE NSW 2480\n\nPh: (02) 6620 3704\nFax: (02) 66228098\n\nEmail: gstuart@scu.edu.au\n-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --\n-- -- -- -- --\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>--=====================_77367437==.ALT
Content-Type: text/plain; charset="us-ascii"; format=flowed
Hi
Is there in principle no objection to lowering a space elevator cable into
a black hole ?
As I understand it, objects or persons passing the event horizon have no
knowledge of such a transition, yet where they part of a space elevator
they might get cold feet when they see (see ?) what is below and elect to
return via the elevator cable to their home base.
Goodness knows from what the elevator cable might be constructed.
Regards
George Stuart
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
-- -- -- -- --
Can there be information without an information processor ?
Which came first, the information or the processor ?
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
-- -- -- -- --
George Lee Stuart
* Southern Cross University
* . * School of Multimedia and Information Technology
* SOMIT
Lecturer
Southern Cross University
PO Box 157
LISMORE NSW 2480
Ph: (02) 6620 3704
Fax: (02) 66228098
Email: gstuart@scu.edu.au
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
-- -- -- -- --
Uncle Al
Jun14-04, 03:06 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"George, Stuart" wrote:\n>\n> --=====================_77367437==.ALT\n> Content-Type: text/plain; charset="us-ascii"; format=flowed\n>\n> Hi\n>\n> Is there in principle no objection to lowering a space elevator cable into\n> a black hole ?\n>\n> As I understand it, objects or persons passing the event horizon have no\n> knowledge of such a transition, yet where they part of a space elevator\n> they might get cold feet when they see (see ?) what is below and elect to\n> return via the elevator cable to their home base.\n>\n> Goodness knows from what the elevator cable might be constructed.\n\nLower the unobtainium cable! Lower it at an epsilon short of\nlightspeed if you like. How long will it require for an external\nobserver to see it finally penetrate the event horizon?\n\nYou cannot peform your experiment until you\'ve threaded the event\nhorizon. You cannot thread the event horizon in a finite time\ninterval as viewed by an external reference frame. No conundrums\nobtain.\n\n--\nUncle Al\nhttp://www.mazepath.com/uncleal/qz.pdf\nhttp://www.mazepath.com/uncleal/eotvos.htm\n(The parity Eotvos experiment is queued)\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"George, Stuart" wrote:
>
> --=====================_77367437==.ALT
> Content-Type: text/plain; charset="us-ascii"; format=flowed
>
> Hi
>
> Is there in principle no objection to lowering a space elevator cable into
> a black hole ?
>
> As I understand it, objects or persons passing the event horizon have no
> knowledge of such a transition, yet where they part of a space elevator
> they might get cold feet when they see (see ?) what is below and elect to
> return via the elevator cable to their home base.
>
> Goodness knows from what the elevator cable might be constructed.
Lower the unobtainium cable! Lower it at an \epsilon short of
lightspeed if you like. How long will it require for an external
observer to see it finally penetrate the event horizon?
You cannot peform your experiment until you've threaded the event
horizon. You cannot thread the event horizon in a finite time
interval as viewed by an external reference frame. No conundrums
obtain.
--
Uncle Al
http://www.mazepath.com/uncleal/qz.pdf
http://www.mazepath.com/uncleal/eotvos.htm
(The parity Eotvos experiment is queued)
Jonathan Thornburg
Jun14-04, 03:11 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>George, Stuart <gstuart@scu.edu.au> wrote:\n> Is there in principle no objection to lowering a space elevator cable into\n> a black hole ?\n\n[Throughout my answer I\'m going to assume classical general relativity.\nIf you want a fancier theory of gravity, ... well... good luck, because\nwe don\'t (yet) have any fancier theory which works.]\n\nThere\'s no objection to _lowering_ a cable into a black hole...\nbut if it hasn\'t broken already, the cable will (must) break rather\nshortly thereafter. :(\n\n\n> As I understand it, objects or persons passing the event horizon have no\n> knowledge of such a transition, yet where they part of a space elevator\n> they might get cold feet when they see (see ?) what is below and elect to\n============\n> return via the elevator cable to their home base.\n=========================================== =====\n\nOnce you\'re inside the event horizon,\n* you can\'t get back outside\n* you can\'t send any signal outside\n* you will hit a singularity (a place where the gravitational field\nis infinitely strong) in a finite time\n\n\nThere\'s an excellent discussion of this in the "Black Holes" section\nof the Usenet Physics FAQ, available\nhttp://math.ucr.edu/home/baez/physics/\nand many fine mirror sites.\n\nciao,\n\n--\n-- "Jonathan Thornburg (remove -animal to reply)" <jthorn@aei.mpg-zebra.de>\nMax-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),\nGolm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html\n"Washing one\'s hands of the conflict between the powerful and the\npowerless means to side with the powerful, not to be neutral."\n-- quote by Freire / poster by Oxfam\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>George, Stuart <gstuart@scu.edu.au> wrote:
> Is there in principle no objection to lowering a space elevator cable into
> a black hole ?
[Throughout my answer I'm going to assume classical general relativity.
If you want a fancier theory of gravity, ... well... good luck, because
we don't (yet) have any fancier theory which works.]
There's no objection to _lowering_ a cable into a black hole...
but if it hasn't broken already, the cable will (must) break rather
shortly thereafter. :(
> As I understand it, objects or persons passing the event horizon have no
> knowledge of such a transition, yet where they part of a space elevator
> they might get cold feet when they see (see ?) what is below and elect to
============
> return via the elevator cable to their home base.
================================================
Once you're inside the event horizon,
* you can't get back outside
* you can't send any signal outside
* you will hit a singularity (a place where the gravitational field
is infinitely strong) in a finite time
There's an excellent discussion of this in the "Black Holes" section
of the Usenet Physics FAQ, available
http://math.ucr.edu/home/baez/physics/
and many fine mirror sites.
ciao,
--
-- "Jonathan Thornburg (remove -animal to reply)" <jthorn@aei.mpg-zebra.de>
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"George, Stuart" <gstuart@scu.edu.au> wrote in message news:<5.2.0.9.0.20040609095950.01d55908@popstaff.s cu.edu.au>...\n>\n> Is there in principle no objection to lowering a space elevator cable into\n> a black hole ?\n>\n\nYou can put anything into a black hole. You just can\'t get it back out\nagain. Also, the person inside a closed elevator would know they are\nbeing lowered into a black hole because of the extreme tidal effects.\n\nDavid\n\n[Moderator\'s note: The last statement depends on the size of the black\nhole. The larger the black hole, the weaker the tidal effects at the\nhorizon. -TB]\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"George, Stuart" <gstuart@scu.edu.au> wrote in message news:<5.2.0.9.0.20040609095950.01d55908@popstaff.scu.edu .au>...
>
> Is there in principle no objection to lowering a space elevator cable into
> a black hole ?
>
You can put anything into a black hole. You just can't get it back out
again. Also, the person inside a closed elevator would know they are
being lowered into a black hole because of the extreme tidal effects.
David
[Moderator's note: The last statement depends on the size of the black
hole. The larger the black hole, the weaker the tidal effects at the
horizon. -TB]
tessel@tum.bot
Jun22-04, 04:50 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Sat, 12 Jun 2004, George, Stuart asked:\n\n> Is there in principle no objection to lowering a space elevator cable\n> into a black hole ?\n\nTo be concrete: imagine, in the context of gtr (the current "default"\ngravitation theory), the vacuum region of spacetime around an isolated\nstatic spherically symmetric nonrotating object, hereinafter called the\n"star". IOW, take part of a Schwarzschild exterior vacuum solution. Now\nimagine a very distant static object located far from the star, from which\nis lowered an observer in an "elevator cage" at the end of radially\noriented cable. Assume that the distant object, the cable, and the cage,\nall have mass densities too small to appreciably disturb the ambient\ngravitational field (Schwarzschild vacuum).\n\nIn this situation, assuming the cage is lowered so slowly that it is\nalmost static, the cage tries to fall freely and radially toward the star,\nbut is prevented from so doing by the cable, which pulls it radially\noutward. This pulling results in tension in the cable, which can be\ncalculated subject to the above simplifying assumptions. Just as in\nNewtonian theory, the closer the cage is to the star, the larger the\ntension. Eventually, if the surface gravity of the star is big enough,\nthe cable must break, and the cage thereafter falls freely.\n\nIf the "star" is actually a (Schwarzschild) black hole, then the tension\ndiverges as the cage approaches the event horizon, so the main difference\nbetween a hole and a neutron star is that in the former case, -in\nprinciple- one could be lowered to the surface, but in the latter, the\ncable -must- break before the cage reaches the horizon.\n\n> As I understand it, objects or persons passing the event horizon have no\n> knowledge of such a transition,\n\nYou may have seen a statement like this: " the event horizon of a black\nhole is a global concept; -local- measurements cannot detect whether or\nnot one is near one". Indeed, we could be inside an event horizon right\nnow and not know it! (If this claim intrigues you, see various "Vaidya\nthought experiments" discussed in past posts to this group, or see the\noriginal discussion of this particular Vaidya thought experiment in Frolov\n& Novikov, Black Hole Physics, Kluwer, 1998.)\n\nAlas, in general, the local/global distinction is difficult to explain\nwithout pictures or differential manifolds background. But basically, in\nthe above scenario, the intuition runs something like this:\n\nThe elevator cab can be considered a "lab". Suppose the cable runs right\nthrough the cab and is attached, not at the "roof", but at the "floor".\nSuppose further that the cable has a design flaw so that it is mostly\nlikely to break within the cab itself as the tension increases.\n\nThen, in our "lab", we can measure locally the tension in the cable, and\nif it does eventually break inside the cage, we can confirm that it has\nbroken. But without looking -outside the lab- we couldn\'t say for sure\nwhat was causing the tension in the cable, just that the increasing\ntension eventually caused it to break. A more alarming observation which\nwe would no doubt make (by "local observation") immediately after the\ncable breaks is that suddenly we are "weightless".\n\n> Goodness knows from what the elevator cable might be constructed.\n\nAs you probably know, nanotech buckycables or whatever may eventually be\nstrong enough to support a hypothetical space elevator reaching from a\ngeostationary satellite to the surface of the Earth, but AFAIK no\ncurrently envisaged material holds promise for a similar setup near an\nastrophysical neutron star.\n\n"T. Essel" (hiding somewhere in cyberspace)\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Sat, 12 Jun 2004, George, Stuart asked:
> Is there in principle no objection to lowering a space elevator cable
> into a black hole ?
To be concrete: imagine, in the context of gtr (the current "default"
gravitation theory), the vacuum region of spacetime around an isolated
static spherically symmetric nonrotating object, hereinafter called the
"star". IOW, take part of a Schwarzschild exterior vacuum solution. Now
imagine a very distant static object located far from the star, from which
is lowered an observer in an "elevator cage" at the end of radially
oriented cable. Assume that the distant object, the cable, and the cage,
all have mass densities too small to appreciably disturb the ambient
gravitational field (Schwarzschild vacuum).
In this situation, assuming the cage is lowered so slowly that it is
almost static, the cage tries to fall freely and radially toward the star,
but is prevented from so doing by the cable, which pulls it radially
outward. This pulling results in tension in the cable, which can be
calculated subject to the above simplifying assumptions. Just as in
Newtonian theory, the closer the cage is to the star, the larger the
tension. Eventually, if the surface gravity of the star is big enough,
the cable must break, and the cage thereafter falls freely.
If the "star" is actually a (Schwarzschild) black hole, then the tension
diverges as the cage approaches the event horizon, so the main difference
between a hole and a neutron star is that in the former case, -in
principle- one could be lowered to the surface, but in the latter, the
cable -must- break before the cage reaches the horizon.
> As I understand it, objects or persons passing the event horizon have no
> knowledge of such a transition,
You may have seen a statement like this: " the event horizon of a black
hole is a global concept; -local- measurements cannot detect whether or
not one is near one". Indeed, we could be inside an event horizon right
now and not know it! (If this claim intrigues you, see various "Vaidya
thought experiments" discussed in past posts to this group, or see the
original discussion of this particular Vaidya thought experiment in Frolov
& Novikov, Black Hole Physics, Kluwer, 1998.)
Alas, in general, the local/global distinction is difficult to explain
without pictures or differential manifolds background. But basically, in
the above scenario, the intuition runs something like this:
The elevator cab can be considered a "lab". Suppose the cable runs right
through the cab and is attached, not at the "roof", but at the "floor".
Suppose further that the cable has a design flaw so that it is mostly
likely to break within the cab itself as the tension increases.
Then, in our "lab", we can measure locally the tension in the cable, and
if it does eventually break inside the cage, we can confirm that it has
broken. But without looking -outside the lab- we couldn't say for sure
what was causing the tension in the cable, just that the increasing
tension eventually caused it to break. A more alarming observation which
we would no doubt make (by "local observation") immediately after the
cable breaks is that suddenly we are "weightless".
> Goodness knows from what the elevator cable might be constructed.
As you probably know, nanotech buckycables or whatever may eventually be
strong enough to support a hypothetical space elevator reaching from a
geostationary satellite to the surface of the Earth, but AFAIK no
currently envisaged material holds promise for a similar setup near an
astrophysical neutron star.
"T. Essel" (hiding somewhere in cyberspace)
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