View Full Version : information loss in black holes
alistair
Jun22-04, 05:02 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>If I burned a book the information in it would be lost forever with\nrespect to all possible observers.This is because the burning of the\nbook is about as irreversible a process as can be imagined.Processes\nin which information is retrieved depend on the idea of reversibility:\nI can put information on a hard disc of a computer and take it off; I\ncan put a book on a shelf and take it off the shelf etc.So if\ninformation which has gone into a black hole is to be retrieved the\nprocess by which the information went into the black hole must have\nsomething inherently reversible about it.Suppose a book fell into a\nblack hole.I could not physically intervene to get it out again - as I\ncould in the case of a book on a shelf - I could not grab the book and\nreverse the path it has taken. And just as I wouldn\'t expect a book on\na shelf to spontaneously jump off the shelf into my hands, I wouldn\'t\nexpect the black hole to spontaneously yield the information in the\nbook in the form of radiation.\nBut all my ideas of the likelihood of processes occurring is based on\nmy experience of living outside a black hole.If I could live inside a\nblack hole\n( where there is no three space) would I reach the same conclusion\nabout the loss of information - would I conclude that information that\ncomes into the hole is destroyed irreversibly?\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>If I burned a book the information in it would be lost forever with
respect to all possible observers.This is because the burning of the
book is about as irreversible a process as can be imagined.Processes
in which information is retrieved depend on the idea of reversibility:
I can put information on a hard disc of a computer and take it off; I
can put a book on a shelf and take it off the shelf etc.So if
information which has gone into a black hole is to be retrieved the
process by which the information went into the black hole must have
something inherently reversible about it.Suppose a book fell into a
black hole.I could not physically intervene to get it out again - as I
could in the case of a book on a shelf - I could not grab the book and
reverse the path it has taken. And just as I wouldn't expect a book on
a shelf to spontaneously jump off the shelf into my hands, I wouldn't
expect the black hole to spontaneously yield the information in the
book in the form of radiation.
But all my ideas of the likelihood of processes occurring is based on
my experience of living outside a black hole.If I could live inside a
black hole
( where there is no three space) would I reach the same conclusion
about the loss of information - would I conclude that information that
comes into the hole is destroyed irreversibly?
alistair
Jun24-04, 06:31 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>\nBlack holes can have angular momentum, mass and charge.It is often\npointed out that these three variables on their own cannot reflect the\nlarge number of ways in which a large number of unique black holes\ncould be made.\nBut how do we know that black holes are made in lots of different\nways?\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>Black holes can have angular momentum, mass and charge.It is often
pointed out that these three variables on their own cannot reflect the
large number of ways in which a large number of unique black holes
could be made.
But how do we know that black holes are made in lots of different
ways?
tessel@tum.bot
Jun24-04, 06:31 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>On Tue, 22 Jun 2004, alistair wrote:\n\n> But all my ideas of the likelihood of processes occurring is based on my\n> experience of living outside a black hole. If I could live inside a\n> black hole (where there is no three space)\n\nI don\'t know what you mean by this, but it sounds like a misconception.\n\nHere is some information which may help to clarify the situation:\n\n1. Conventional Lorentzian spacetimes M are everywhere four dimensional,\nwhich means that it in each local neighborhood U of an event P (think of a\nsmall four dimensional "box" containing P--- if you like, you can now\ndistort the "box" diffeomorphically without moving P, and call the result\na new neighborhood U\' of P), we can find an infinite variety of\n"slicings". Such a slicing consists of a family of three dimensional\nspacelike "hypersurfaces" which fill up the "box", such that no two\nhypersurfaces intersect one another. IOW: the hypersurfaces are the level\nsurfaces of an appropriate function f:U-->R.\n\n2. A spacetime containing an isolated black hole has (with some additional\nassumptions which need not concern us) "interior" and "exterior"\nregions. These are four dimensional pieces, separated by the "event\nhorizon". (Describing the "dimension" of the horizon itself, or rather\nits "world sheet", gets us into further technical issues which I\'ll ignore\nhere).\n\n3. In particular, events P in the interior region admit infinitely many\nthree dimensional spacelike hypersurfaces containing P. In a small enough\nneighborhood of P, each of these corresponds (many-one), approximately, to\na "local Lorentz frame" at P.\n\n4. Physically, this means that any observer in the interior region will\nexperience three dimensional space just like we do, they will just observe\nsome pretty extreme physics like large tidal stresses, weird optical\neffects, etc.\n\n"T. Essel" (hiding somewhere in cyberspace)\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 Tue, 22 Jun 2004, alistair wrote:
> But all my ideas of the likelihood of processes occurring is based on my
> experience of living outside a black hole. If I could live inside a
> black hole (where there is no three space)
I don't know what you mean by this, but it sounds like a misconception.
Here is some information which may help to clarify the situation:
1. Conventional Lorentzian spacetimes M are everywhere four dimensional,
which means that it in each local neighborhood U of an event P (think of a
small four dimensional "box" containing P--- if you like, you can now
distort the "box" diffeomorphically without moving P, and call the result
a new neighborhood U' of P), we can find an infinite variety of
"slicings". Such a slicing consists of a family of three dimensional
spacelike "hypersurfaces" which fill up the "box", such that no two
hypersurfaces intersect one another. IOW: the hypersurfaces are the level
surfaces of an appropriate function f:U-->R.
2. A spacetime containing an isolated black hole has (with some additional
assumptions which need not concern us) "interior" and "exterior"
regions. These are four dimensional pieces, separated by the "event
horizon". (Describing the "dimension" of the horizon itself, or rather
its "world sheet", gets us into further technical issues which I'll ignore
here).
3. In particular, events P in the interior region admit infinitely many
three dimensional spacelike hypersurfaces containing P. In a small enough
neighborhood of P, each of these corresponds (many-one), approximately, to
a "local Lorentz frame" at P.
4. Physically, this means that any observer in the interior region will
experience three dimensional space just like we do, they will just observe
some pretty extreme physics like large tidal stresses, weird optical
effects, etc.
"T. Essel" (hiding somewhere in cyberspace)
alistair
Jun24-04, 09:32 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>\nTESSEL@TUM.BOT replied to ALISTAIR with respect to the loss of\ninformation in black holes:\n\n>any observer in the interior region will\n>experience three dimensional space just like we do, they will just\nobserve\n>some pretty extreme physics like large tidal stresses, weird optical\n>effects, etc.\n\nALISTAIR writes:\n\nIf I put a sheet of paper in my hands with writing on it, and\npulled it until it ripped, is this what tidal forces inside a black\nhole\'s event horizon would do to the sheet of paper? Pulling a sheet\nof paper apart with my hands\nwill irreversibly destroy information on the sheet so if a black\nhole\'s tidal forces tears the sheet apart then surely this means\ninformation is lost forever in a black hole?\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>TESSEL@TUM.BOT replied to ALISTAIR with respect to the loss of
information in black holes:
>any observer in the interior region will
>experience three dimensional space just like we do, they will just
observe
>some pretty extreme physics like large tidal stresses, weird optical
>effects, etc.
ALISTAIR writes:
If I put a sheet of paper in my hands with writing on it, and
pulled it until it ripped, is this what tidal forces inside a black
hole's event horizon would do to the sheet of paper? Pulling a sheet
of paper apart with my hands
will irreversibly destroy information on the sheet so if a black
hole's tidal forces tears the sheet apart then surely this means
information is lost forever in a black hole?
tessel@tum.bot
Jun28-04, 12:10 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>Alistair asked about information loss; his post included the dubious claim\n\n> If I could live inside a black hole (where there is no three space)\n\nI replied only to correct this apparent misconception, saying in part:\n\n> >any observer in the interior region will experience three dimensional\n> >space just like we do, they will just observe some pretty extreme\n> >physics like large tidal stresses, weird optical effects, etc.\n>\n> ALISTAIR writes:\n>\n> If I put a sheet of paper in my hands with writing on it, and\n> pulled it until it ripped, is this what tidal forces inside a black\n> hole\'s event horizon would do to the sheet of paper?\n\nSome relevant points:\n\n1. In gtr--- and in any other theory which has a chance of comparing\nfairly well with observation/experiment, including good old Newtonian\ngravitation--- any gravitational field will produce tidal forces on\ninfalling objects (even free falling objects). Indeed, in gtr, one could\neven say that describing the tidal forces experienced by arbitrarily\nfalling small objects is exactly the same thing as describing "the\ngravitational field".\n\n2. Small falling objects near a -compact massive object- will experience\ntidal forces having a "Coulomb character". This means that they will be\n-stretched- along the direction of fastest increase of the strength of the\nfield (i.e. the direction pointing toward the compact object) and also\n-compressed- transversely. In particular, a sheet of paper falling\nthrough a Coulomb tidal force field will torn apart most efficiently if it\nis oriented so that a diagonal drawn on the sheet points in the direction\nof fastest increase of the magnitude of the field (i.e. points toward the\ncompact object). The nature of this tearing is not much different from\nwhat you will observe if you hold a piece of paper by the tips and pull\nvery hard. As a little experimentation quickly suggests, if you could\nobserve a sheet of paper falling in a really strong Coulomb tidal force\nfield, you would expect to see "transverse crumpling" long before you see\n"radial tearing"!\n\n3. It doesn\'t matter all that much precisely how your object is "falling",\ne.g. an -orbiting- object will also experience tidal forces with a Coulomb\ncharacter similar to those experienced by a -radially infalling- object,\nalthough the details may differ slightly, at least in relativistic\ngravitation theories like gtr. (In past posts, I\'ve compared in detail\nthe tidal forces for small objects in stable circular orbits around a\nSchwarzschild hole with the tidal forces on small objects which are\nradially and freely falling into the hole.)\n\n4. In any reasonable gravitation theory--- including good old Newtonian\ngravitation--- of two equally massive objects, the more compact one will\nallow for stronger fields in its -exterior- simply because falling objects\ncan approach more closely before reaching the "surface" (if any). So in a\nsense, the strong gravitational fields experienced (according to gtr) near\na neutron star are due to the fact that one can approach much more closely\nto a stellar mass object without running into anything than one can for an\nordinary star. Similarly, of course, for stellar mass black holes---\nwhich are not that much more compact than neutron stars, incidentally! So\nnone of this depends upon whether your compact massive object is "made\nof", in particular, whether it is some kind of star or black hole, or even\nupon which gravitation theory you are using to model the situation, as\nlong as your theory has the correct Newtonian limit.\n\n5. Tidal forces are -local-; they can be measured within a small idealized\n"laboratory" without "looking out the window". For example, in (2), in\nprinciple one can determine the "direction of fastest increase of\nmagnitude of tidal forces" without looking out the window, so this is a\nlocal concept. Contrast this with the "direction pointing at the massive\ncompact object which is the source of the field"--- determining this\ndirection presumably requires looking out the window! In this case, these\nphrases describe two (not entirely well-defined) methods (one local and\none not) for determining a certain spatial direction somewhere outside a\nSchwarzschild hole. But I am certainly not claiming that every local\nconcept can be alternatively expressed in nonlocal terms, or vice versa.\nIn particular, "event horizon" is a -global- concept which we should not\nexpect to be expressible in local terms. (If this seems confusing, the\nreason is probably that the "local/global distinction" is difficult to\nreally explain without first explaining certain concepts from manifold\ntheory.)\n\n6. Since "tidal force" is a -local- concept, but "event horizon" is a\n-global- concept, the nature of tidal forces must be identical on either\nside of any horizon. This is not invalidated by the fact that deep inside\nthe horizon of some black hole solutions admitted by the EFE (Einstein\nfield equation), the tidal forces measured by at least some observers may\nassume a "non-Coulomb character".\n\n7. I see now I missed another possible objection to the phrase quoted\nabove--- you can "live" inside a Schwarzschild hole for only a limited\ntime, since (according to gtr) you cannot possibly avoid falling further\nin, and in fact there is a specific upper bound to your remaining proper\nlifetime. It is true that for more exotic black hole solutions of the\nEFE, it is in principle possible for at least some observers to avoid\nstriking a "strong scalar curvature singularity", but this may be an\nartifact of assuming too much symmetry or of neglecting the effect of\ninfalling radiation and "stuff". (This question is a whole \'nother can of\nworms, however--- the true nature of the interior of "generic" black hole\nsolutions in gtr remains very vexed, and this problem is the focus of a\ngood deal of current research. In various previous posts I have said much\nmore about this.)\n\n8. All the above concerns purely classical gravitation physics; no\nstatistical, thermodynamical, or quantum mechanical ideas are involved\n(although I did make some modest nongravitational assumptions concerning\nhow material like paper responds to tensile and compressive forces). The\n"black hole information loss problem", however, concerns quantum field\ntheory as well as gravitation physics, in (apparently) an essential way.\nFurthermore, the (apparently) relevant notions of "information/entropy"\nemploy thermodynamical or statistical concepts.\n\n> Pulling a sheet of paper apart with my hands will irreversibly destroy\n> information on the sheet so if a black hole\'s tidal forces tears the\n> sheet apart then surely this means information is lost forever in a\n> black hole?\n\nYou are trying to invoke an alleged "destruction" of some kind of\n"information" which you think should happen when you shred paper, but even\nif you can invent precise mathematical definitions which capture this\nintuition, I doubt your notion of "shredable information" will turn out to\nbe readily comparable with the kind(s) of "information" physicists have in\nmind when they discuss the "information loss problem".\n\nBut again, I\'ll leave it to others to discuss the "information loss\nproblem" itself; I have only been attempting to correct various apparent\nmisconceptions concerning classical gravitation physics.\n\n"T. Essel" (hiding somewhere in cyberspace)\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>Alistair asked about information loss; his post included the dubious claim
> If I could live inside a black hole (where there is no three space)
I replied only to correct this apparent misconception, saying in part:
> >any observer in the interior region will experience three dimensional
> >space just like we do, they will just observe some pretty extreme
> >physics like large tidal stresses, weird optical effects, etc.
>
> ALISTAIR writes:
>
> If I put a sheet of paper in my hands with writing on it, and
> pulled it until it ripped, is this what tidal forces inside a black
> hole's event horizon would do to the sheet of paper?
Some relevant points:
1. In gtr--- and in any other theory which has a chance of comparing
fairly well with observation/experiment, including good old Newtonian
gravitation--- any gravitational field will produce tidal forces on
infalling objects (even free falling objects). Indeed, in gtr, one could
even say that describing the tidal forces experienced by arbitrarily
falling small objects is exactly the same thing as describing "the
gravitational field".
2. Small falling objects near a -compact massive object- will experience
tidal forces having a "Coulomb character". This means that they will be
-stretched- along the direction of fastest increase of the strength of the
field (i.e. the direction pointing toward the compact object) and also
-compressed- transversely. In particular, a sheet of paper falling
through a Coulomb tidal force field will torn apart most efficiently if it
is oriented so that a diagonal drawn on the sheet points in the direction
of fastest increase of the magnitude of the field (i.e. points toward the
compact object). The nature of this tearing is not much different from
what you will observe if you hold a piece of paper by the tips and pull
very hard. As a little experimentation quickly suggests, if you could
observe a sheet of paper falling in a really strong Coulomb tidal force
field, you would expect to see "transverse crumpling" long before you see
"radial tearing"!
3. It doesn't matter all that much precisely how your object is "falling",
e.g. an -orbiting- object will also experience tidal forces with a Coulomb
character similar to those experienced by a -radially infalling- object,
although the details may differ slightly, at least in relativistic
gravitation theories like gtr. (In past posts, I've compared in detail
the tidal forces for small objects in stable circular orbits around a
Schwarzschild hole with the tidal forces on small objects which are
radially and freely falling into the hole.)
4. In any reasonable gravitation theory--- including good old Newtonian
gravitation--- of two equally massive objects, the more compact one will
allow for stronger fields in its -exterior- simply because falling objects
can approach more closely before reaching the "surface" (if any). So in a
sense, the strong gravitational fields experienced (according to gtr) near
a neutron star are due to the fact that one can approach much more closely
to a stellar mass object without running into anything than one can for an
ordinary star. Similarly, of course, for stellar mass black holes---
which are not that much more compact than neutron stars, incidentally! So
none of this depends upon whether your compact massive object is "made
of", in particular, whether it is some kind of star or black hole, or even
upon which gravitation theory you are using to model the situation, as
long as your theory has the correct Newtonian limit.
5. Tidal forces are -local-; they can be measured within a small idealized
"laboratory" without "looking out the window". For example, in (2), in
principle one can determine the "direction of fastest increase of
magnitude of tidal forces" without looking out the window, so this is a
local concept. Contrast this with the "direction pointing at the massive
compact object which is the source of the field"--- determining this
direction presumably requires looking out the window! In this case, these
phrases describe two (not entirely well-defined) methods (one local and
one not) for determining a certain spatial direction somewhere outside a
Schwarzschild hole. But I am certainly not claiming that every local
concept can be alternatively expressed in nonlocal terms, or vice versa.
In particular, "event horizon" is a -global- concept which we should not
expect to be expressible in local terms. (If this seems confusing, the
reason is probably that the "local/global distinction" is difficult to
really explain without first explaining certain concepts from manifold
theory.)
6. Since "tidal force" is a -local- concept, but "event horizon" is a
-global- concept, the nature of tidal forces must be identical on either
side of any horizon. This is not invalidated by the fact that deep inside
the horizon of some black hole solutions admitted by the EFE (Einstein
field equation), the tidal forces measured by at least some observers may
assume a "non-Coulomb character".
7. I see now I missed another possible objection to the phrase quoted
above--- you can "live" inside a Schwarzschild hole for only a limited
time, since (according to gtr) you cannot possibly avoid falling further
in, and in fact there is a specific upper bound to your remaining proper
lifetime. It is true that for more exotic black hole solutions of the
EFE, it is in principle possible for at least some observers to avoid
striking a "strong scalar curvature singularity", but this may be an
artifact of assuming too much symmetry or of neglecting the effect of
infalling radiation and "stuff". (This question is a whole 'nother can of
worms, however--- the true nature of the interior of "generic" black hole
solutions in gtr remains very vexed, and this problem is the focus of a
good deal of current research. In various previous posts I have said much
more about this.)
8. All the above concerns purely classical gravitation physics; no
statistical, thermodynamical, or quantum mechanical ideas are involved
(although I did make some modest nongravitational assumptions concerning
how material like paper responds to tensile and compressive forces). The
"black hole information loss problem", however, concerns quantum field
theory as well as gravitation physics, in (apparently) an essential way.
Furthermore, the (apparently) relevant notions of "information/entropy"
employ thermodynamical or statistical concepts.
> Pulling a sheet of paper apart with my hands will irreversibly destroy
> information on the sheet so if a black hole's tidal forces tears the
> sheet apart then surely this means information is lost forever in a
> black hole?
You are trying to invoke an alleged "destruction" of some kind of
"information" which you think should happen when you shred paper, but even
if you can invent precise mathematical definitions which capture this
intuition, I doubt your notion of "shredable information" will turn out to
be readily comparable with the kind(s) of "information" physicists have in
mind when they discuss the "information loss problem".
But again, I'll leave it to others to discuss the "information loss
problem" itself; I have only been attempting to correct various apparent
misconceptions concerning classical gravitation physics.
"T. Essel" (hiding somewhere in cyberspace)
<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>\n\n\n\nalistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0406240621.244067b7@posting.google. com>...\n> TESSEL@TUM.BOT replied to ALISTAIR with respect to the loss of\n> information in black holes:\n>\n> >any observer in the interior region will\n> >experience three dimensional space just like we do, they will just\n> observe\n> >some pretty extreme physics like large tidal stresses, weird optical\n> >effects, etc.\n>\n> ALISTAIR writes:\n>\n> If I put a sheet of paper in my hands with writing on it, and\n> pulled it until it ripped, is this what tidal forces inside a black\n> hole\'s event horizon would do to the sheet of paper? Pulling a sheet\n> of paper apart with my hands\n> will irreversibly destroy information on the sheet so if a black\n> hole\'s tidal forces tears the sheet apart then surely this means\n> information is lost forever in a black hole?\n\n\nWhen people talk about information loss in a black hole, they are\nreferring to the fact that someone outside the event horizon would\nhave no way of knowing what is written on the piece of paper.\n\nDavid\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>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0406240621.244067b7@posting.google.com>...
> TESSEL@TUM.BOT replied to ALISTAIR with respect to the loss of
> information in black holes:
>
> >any observer in the interior region will
> >experience three dimensional space just like we do, they will just
> observe
> >some pretty extreme physics like large tidal stresses, weird optical
> >effects, etc.
>
> ALISTAIR writes:
>
> If I put a sheet of paper in my hands with writing on it, and
> pulled it until it ripped, is this what tidal forces inside a black
> hole's event horizon would do to the sheet of paper? Pulling a sheet
> of paper apart with my hands
> will irreversibly destroy information on the sheet so if a black
> hole's tidal forces tears the sheet apart then surely this means
> information is lost forever in a black hole?
When people talk about information loss in a black hole, they are
referring to the fact that someone outside the event horizon would
have no way of knowing what is written on the piece of paper.
David
Urs Schreiber
Jun29-04, 04:29 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>"alistair" <alistair@goforit64.fsnet.co.uk> schrieb im Newsbeitrag\nnews:861c1b21.0406240621.244067b7@pos ting.google.com...\n\n> ALISTAIR writes:\n>\n> If I put a sheet of paper in my hands with writing on it, and\n> pulled it until it ripped, is this what tidal forces inside a black\n> hole\'s event horizon would do to the sheet of paper? Pulling a sheet\n> of paper apart with my hands\n> will irreversibly destroy information on the sheet so if a black\n> hole\'s tidal forces tears the sheet apart then surely this means\n> information is lost forever in a black hole?\n\nNo, this is not the "information loss problem" of black holes. Pulling stuff\napart doesn\'t have anything in particular to do with black holes, obviously,\nand is not related to information loss (non-unitarity). The apparent problem\nwith black holes is rather that stuff "falls inside" and after a long-long\ntime thermal Hawking radiation escapes. There would be a problem if in this\n(possibly overly naive) scenario the Hawking radiation carried no signature\nof the original stuff that fell into the black hole, roughly.\n\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>"alistair" <alistair@goforit64.fsnet.co.uk> schrieb im Newsbeitrag
news:861c1b21.0406240621.244067b7@posting.google.c om...
> ALISTAIR writes:
>
> If I put a sheet of paper in my hands with writing on it, and
> pulled it until it ripped, is this what tidal forces inside a black
> hole's event horizon would do to the sheet of paper? Pulling a sheet
> of paper apart with my hands
> will irreversibly destroy information on the sheet so if a black
> hole's tidal forces tears the sheet apart then surely this means
> information is lost forever in a black hole?
No, this is not the "information loss problem" of black holes. Pulling stuff
apart doesn't have anything in particular to do with black holes, obviously,
and is not related to information loss (non-unitarity). The apparent problem
with black holes is rather that stuff "falls inside" and after a long-long
time thermal Hawking radiation escapes. There would be a problem if in this
(possibly overly naive) scenario the Hawking radiation carried no signature
of the original stuff that fell into the black hole, roughly.
alistair
Jun29-04, 04:32 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>In classical thermodynamics the final state of a system is independent\nof the path taken to get to that state.And nobody thinks that there is\na problem with information loss. So, when black holes, made in\ndifferent ways, end up with the same spin, mass and charge, why is it\nbelieved that information is lost?\nOne can say " information disppears from the universe into a black\nhole" but isn\'t the black hole part of the universe?\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>In classical thermodynamics the final state of a system is independent
of the path taken to get to that state.And nobody thinks that there is
a problem with information loss. So, when black holes, made in
different ways, end up with the same spin, mass and charge, why is it
believed that information is lost?
One can say " information disppears from the universe into a black
hole" but isn't the black hole part of the universe?
chronon
Jun29-04, 04:34 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>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0406220844.2054bbdc@posting.google. com>...\n> If I burned a book the information in it would be lost forever with\n> respect to all possible observers.This is because the burning of the\n> book is about as irreversible a process as can be imagined.\n\nExcept that an all knowing Laplace\'s demon could look at the state of\nthe universe at a later stage, then reconstruct the book using the\nreversibility of the laws of physics. The question is whether\ndropping something into a black hole is more of an irreversible\nprocess than the rest of physics.\n\nThe paradox here is that although we think of the second law of\nthermodynamics as causing decay and information loss, at the\nmicroscopic scale the law rests on the fact that information is never\ntruly lost - if a Maxwell\'s demon could lose information (say by\ndropping it into a black hole) then he would be able to overcome the\nsecond law.\n\nStephen Lee\nwww.chronon.org\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>alistair@goforit64.fsnet.co.uk (alistair) wrote in message news:<861c1b21.0406220844.2054bbdc@posting.google.com>...
> If I burned a book the information in it would be lost forever with
> respect to all possible observers.This is because the burning of the
> book is about as irreversible a process as can be imagined.
Except that an all knowing Laplace's demon could look at the state of
the universe at a later stage, then reconstruct the book using the
reversibility of the laws of physics. The question is whether
dropping something into a black hole is more of an irreversible
process than the rest of physics.
The paradox here is that although we think of the second law of
thermodynamics as causing decay and information loss, at the
microscopic scale the law rests on the fact that information is never
truly lost - if a Maxwell's demon could lose information (say by
dropping it into a black hole) then he would be able to overcome the
second law.
Stephen Lee
www.chronon.org
alistair
Jun29-04, 04:40 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>When information is erased entropy increases (e.g. book burning).\nSo if the area of the event horizon of a black hole ( which gets\nbigger with increasing entropy) increases when a book falls into the\nblack hole, does this mean that the information in the book has been\nerased?\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>When information is erased entropy increases (e.g. book burning).
So if the area of the event horizon of a black hole ( which gets
bigger with increasing entropy) increases when a book falls into the
black hole, does this mean that the information in the book has been
erased?
alistair
Jun29-04, 05:50 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>TESSEL@TUM.BOT said:\n\n>The "black hole information loss problem", however, concerns quantum\nfield\n>theory as well as gravitation physics, in (apparently) an essential\nway.\n\nALISTAIR writes:\n\nIsn\'t Quantum field theory invoked because of the possibility that\ninformation\n"leaks" out of the black hole in the hawking radiation?\n\nALISTAIR says in addition:\n\nA blank sheet of paper would increase the area of the event horizon\nand the increase in area would be associated with an increase in the\nentropy\nof the black hole.If I cut away bits of a heavier sheet to write some\nsentences,and the cut sheet had the same mass as before, the increase\nin area of the event horizon would be the same as before,and would not\nreflect the fact that the sheet carried information.\nI would have to conclude that, in fact, the area of the horizon does\nnot say anything about the information that went into a black hole and\nthat as far as black holes are concerned, entropy and information are\nnot linked.\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>TESSEL@TUM.BOT said:
>The "black hole information loss problem", however, concerns quantum
field
>theory as well as gravitation physics, in (apparently) an essential
way.
ALISTAIR writes:
Isn't Quantum field theory invoked because of the possibility that
information
"leaks" out of the black hole in the hawking radiation?
ALISTAIR says in addition:
A blank sheet of paper would increase the area of the event horizon
and the increase in area would be associated with an increase in the
entropy
of the black hole.If I cut away bits of a heavier sheet to write some
sentences,and the cut sheet had the same mass as before, the increase
in area of the event horizon would be the same as before,and would not
reflect the fact that the sheet carried information.
I would have to conclude that, in fact, the area of the horizon does
not say anything about the information that went into a black hole and
that as far as black holes are concerned, entropy and information are
not linked.
Daniel Elander
Jun29-04, 05:54 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>> When people talk about information loss in a black hole, they are\n> referring to the fact that someone outside the event horizon would\n> have no way of knowing what is written on the piece of paper.\n\nBut for the outside observer it takes an infinite amount of time for\nthe paper to fall into the black hole. So it would seem the paradox\nnever happens. Or am I wrong?\n\nDaniel\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>> When people talk about information loss in a black hole, they are
> referring to the fact that someone outside the event horizon would
> have no way of knowing what is written on the piece of paper.
But for the outside observer it takes an infinite amount of time for
the paper to fall into the black hole. So it would seem the paradox
never happens. Or am I wrong?
Daniel
alistair
Jun29-04, 06:04 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>Urs Schreiber said:\n\n>The apparent problem\n>with black holes is rather that stuff "falls inside" and after a\nlong-long\n>time thermal Hawking radiation escapes. There would be a problem if\nin this\n>(possibly overly naive) scenario the Hawking radiation carried no\nsignature\n<of the original stuff that fell into the black hole, roughly.\n\nAlistair writes:\n\nAs a black hole evaporates it will emit Hawking radiation and increase\nits temperature.A higher temperature is associated with a greater\nentropy.The entropy of the universe (of which the black hole is a\npart)thus increases\nwith time in keeping with the second law of thermodynamics.The black\nhole is under no further obligation to do more than this - it does not\nhave to leave a trace of the information contained in the masses it\nhas taken in.\n\nChronon:\n\n>if a Maxwell\'s demon could lose information (say by\n>dropping it into a black hole) then he would be able to overcome the\n>second law.\n\n\nAlistair says:\n\n\nThe demon would have to expend energy to lose the information and this\nwould increase the entropy of the universe, so the second law would\nnot be broken.\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>Urs Schreiber said:
>The apparent problem
>with black holes is rather that stuff "falls inside" and after a
long-long
>time thermal Hawking radiation escapes. There would be a problem if
in this
>(possibly overly naive) scenario the Hawking radiation carried no
signature
<of the original stuff that fell into the black hole, roughly.
Alistair writes:
As a black hole evaporates it will emit Hawking radiation and increase
its temperature.A higher temperature is associated with a greater
entropy.The entropy of the universe (of which the black hole is a
part)thus increases
with time in keeping with the second law of thermodynamics.The black
hole is under no further obligation to do more than this - it does not
have to leave a trace of the information contained in the masses it
has taken in.
Chronon:
>if a Maxwell's demon could lose information (say by
>dropping it into a black hole) then he would be able to overcome the
>second law.
Alistair says:
The demon would have to expend energy to lose the information and this
would increase the entropy of the universe, so the second law would
not be broken.
Greg Egan
Jun30-04, 05:39 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>In article <37d84b42.0406290104.3402b89f@posting.google.com>, \ndaniel@elit.net (Daniel Elander) wrote:\n\n> > When people talk about information loss in a black hole, they are\n> > referring to the fact that someone outside the event horizon would\n> > have no way of knowing what is written on the piece of paper.\n>\n> But for the outside observer it takes an infinite amount of time for\n> the paper to fall into the black hole. So it would seem the paradox\n> never happens. Or am I wrong?\n>\n> Daniel\n\nThe statement "for the outside observer it takes an infinite amount of\ntime" for something to fall into a black hole is true in two senses, but\nyou have to look very carefully at what those statements are to see what\nthey tell you about information accessibility.\n\n(1) The first sense in which "for the outside observer it takes an\ninfinite amount of time" is purely a statement about coordinate systems.\nIn the Schwarzschild coordinates, t, r, phi and theta -- which become\nasymptotically close to ordinary polar coordinates in flat spacetime far\nfrom the black hole, and so in a sense might qualify as appropriate\ncoordinates for "an outside observer" -- the spacelike hypersurfaces of\nconstant t which begin anywhere outside the event horizon never actually\ncross it.\n\nFigure 9 in this article:\n\nhttp://gregegan.customer.netspace.net.au/FOUNDATIONS/03/found03.html#s8\n\nshows curves of constant t in a 2-d slice through the spacetime. These\ncurves never cross the horizon (r=2M), so by increasing the value of t\nyou can get closer to the horizon, but you can never actually pass\nthrough it.\n\nOK, but I can construct coordinates that do the same absurd thing in flat\nspacetime, so this doesn\'t really tell us much about the physics of black\nholes. I can make up coordinates which are sensible close to me, but\nhave the property that all the spacelike hypersurfaces that intersect my\nworld line never cross an arbitrary barrier, say 1 metre away from me.\nAnd as Figure 9 shows, it\'s not hard to find another sensible coordinate,\nt*, such that the hypersurfaces of constant t* do cross the black hole\'s\nhorizon.\n\n(2) The second sense in which "for the outside observer it takes an\ninfinite amount of time" for something to fall across the event horizon\nis that if you drop a flashing beacon into a black hole, and watch from a\nfixed distance away from the event horizon, there is no upper bound on\nhow long (according to your own watch) you continue to receive *some*\nlight from the beacon. Classically at least, the light becomes dimmed\nand red-shifted in an exponential decay, but it never strictly hits zero.\n\nHowever, note that:\n\n(a) if you count the flashes of the falling beacon, there is a finite\nnumber assigned to the last flash you will ever see from it. That last\nflash (assuming the beacon is "on" rather than "off" as it crosses the\nhorizon) reaches you over an unbounded time, but you still only ever get\nto see a finite portion of the beacon\'s history.\n\n(b) after you drop the beacon from a Schwarzschild coordinate of r, there\nis a finite time *for you*, T(r), after which it becomes physically\nimpossible for you to chase after the beacon and retrieve it (even if you\ncan tolerate arbitrarily large accelerations), or even to illuminate it\nwith a light source of your own. Once T(r) has elapsed, it doesn\'t\nmatter what you do, and it doesn\'t matter that you can still see the\nbeacon; for all practical purposes, it\'s lost to you.\n\nThe fact that you\'re receiving ever-dimmer light from the beacon for all\neternity just tells you that the last light from it as it crossed the\nhorizon is reaching you in a strange, drawn-out fashion.\n\nGreg Egan\n\nEmail address (remove name of animal and add standard punctuation):\ngregegan netspace zebra net au\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>In article <37d84b42.0406290104.3402b89f@posting.google.com>,
daniel@elit.net (Daniel Elander) wrote:
> > When people talk about information loss in a black hole, they are
> > referring to the fact that someone outside the event horizon would
> > have no way of knowing what is written on the piece of paper.
>
> But for the outside observer it takes an infinite amount of time for
> the paper to fall into the black hole. So it would seem the paradox
> never happens. Or am I wrong?
>
> Daniel
The statement "for the outside observer it takes an infinite amount of
time" for something to fall into a black hole is true in two senses, but
you have to look very carefully at what those statements are to see what
they tell you about information accessibility.
(1) The first sense in which "for the outside observer it takes an
infinite amount of time" is purely a statement about coordinate systems.
In the Schwarzschild coordinates, t, r, \phi and \theta -- which become
asymptotically close to ordinary polar coordinates in flat spacetime far
from the black hole, and so in a sense might qualify as appropriate
coordinates for "an outside observer" -- the spacelike hypersurfaces of
constant t which begin anywhere outside the event horizon never actually
cross it.
Figure 9 in this article:
http://gregegan.customer.netspace.net.au/FOUNDATIONS/03/found03.html#s8
shows curves of constant t in a 2-d slice through the spacetime. These
curves never cross the horizon (r=2M), so by increasing the value of t
you can get closer to the horizon, but you can never actually pass
through it.
OK, but I can construct coordinates that do the same absurd thing in flat
spacetime, so this doesn't really tell us much about the physics of black
holes. I can make up coordinates which are sensible close to me, but
have the property that all the spacelike hypersurfaces that intersect my
world line never cross an arbitrary barrier, say 1 metre away from me.
And as Figure 9 shows, it's not hard to find another sensible coordinate,
t*, such that the hypersurfaces of constant t* do cross the black hole's
horizon.
(2) The second sense in which "for the outside observer it takes an
infinite amount of time" for something to fall across the event horizon
is that if you drop a flashing beacon into a black hole, and watch from a
fixed distance away from the event horizon, there is no upper bound on
how long (according to your own watch) you continue to receive *some*
light from the beacon. Classically at least, the light becomes dimmed
and red-shifted in an exponential decay, but it never strictly hits zero.
However, note that:
(a) if you count the flashes of the falling beacon, there is a finite
number assigned to the last flash you will ever see from it. That last
flash (assuming the beacon is "on" rather than "off" as it crosses the
horizon) reaches you over an unbounded time, but you still only ever get
to see a finite portion of the beacon's history.
(b) after you drop the beacon from a Schwarzschild coordinate of r, there
is a finite time *for you*, T(r), after which it becomes physically
impossible for you to chase after the beacon and retrieve it (even if you
can tolerate arbitrarily large accelerations), or even to illuminate it
with a light source of your own. Once T(r) has elapsed, it doesn't
matter what you do, and it doesn't matter that you can still see the
beacon; for all practical purposes, it's lost to you.
The fact that you're receiving ever-dimmer light from the beacon for all
eternity just tells you that the last light from it as it crossed the
horizon is reaching you in a strange, drawn-out fashion.
Greg Egan
Email address (remove name of animal and add standard punctuation):
gregegan netspace zebra net au
Bob Day
Jun30-04, 05:41 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>"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\nnews:861c1b21.0406240841.3f5890b0@posting .google.com...\n> In classical thermodynamics the final state of a system is independent\n> of the path taken to get to that state.And nobody thinks that there is\n> a problem with information loss. So, when black holes, made in\n> different ways, end up with the same spin, mass and charge, why is it\n> believed that information is lost?\n> One can say " information disppears from the universe into a black\n> hole" but isn\'t the black hole part of the universe?\n>\n\nI don\'t understand this. I tear out a page from Nature, and\nput it into my super-duper CIA designed paper shredder that\nshreds paper into atoms! Are you saying that I, theoretically,\ncould reconstruct that page?\n\n-- Bob Day\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>"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
news:861c1b21.0406240841.3f5890b0@posting.google.c om...
> In classical thermodynamics the final state of a system is independent
> of the path taken to get to that state.And nobody thinks that there is
> a problem with information loss. So, when black holes, made in
> different ways, end up with the same spin, mass and charge, why is it
> believed that information is lost?
> One can say " information disppears from the universe into a black
> hole" but isn't the black hole part of the universe?
>
I don't understand this. I tear out a page from Nature, and
put it into my super-duper CIA designed paper shredder that
shreds paper into atoms! Are you saying that I, theoretically,
could reconstruct that page?
-- Bob Day
alistair
Jul1-04, 04:46 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>The correct theory of quantum gravity is expected to show that\nsingularities do not exist inside black holes.So how could this affect\nthe information loss problem associated with black holes? Would the\nsingularity become a small region of space into which a particle\ncannot fall? If nothing can get into this region,it would have zero\nentropy.Since the outer part of a black hole, the event horizon, has\nentropy, perhaps entropy for a black hole would increase,per unit\narea, as we move from the centre towards the horizon.\nSome particles just on the edge of the small region of space at the\ncentre of a black hole,could not move from their position unless more\nparticles\n(cosmic microwave background photons for example)replaced them to keep\nthe entropy in that area the same as it was before (else the second\nlaw of thermodynamics would be broken).Would this mean that Hawking\nradiation could not be emitted from the black hole without an influx\nof particles from outside\nit? Since Hawking radiation is postulated to carry information out of\nthe hole, this would mean that the outflow of information can only\noccur if there is an inflow of other information.Or can someone think\nof an argument against this idea?\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>The correct theory of quantum gravity is expected to show that
singularities do not exist inside black holes.So how could this affect
the information loss problem associated with black holes? Would the
singularity become a small region of space into which a particle
cannot fall? If nothing can get into this region,it would have zero
entropy.Since the outer part of a black hole, the event horizon, has
entropy, perhaps entropy for a black hole would increase,per unit
area, as we move from the centre towards the horizon.
Some particles just on the edge of the small region of space at the
centre of a black hole,could not move from their position unless more
particles
(cosmic microwave background photons for example)replaced them to keep
the entropy in that area the same as it was before (else the second
law of thermodynamics would be broken).Would this mean that Hawking
radiation could not be emitted from the black hole without an influx
of particles from outside
it? Since Hawking radiation is postulated to carry information out of
the hole, this would mean that the outflow of information can only
occur if there is an inflow of other information.Or can someone think
of an argument against this idea?
Frank Hellmann
Jul1-04, 04:48 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>"Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message news:<GdBEc.27680\\$Av3.13513@nwrdny01.gnilink.net >...\n> "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\n> news:861c1b21.0406240841.3f5890b0@posting.google.c om...\n> > In classical thermodynamics the final state of a system is independent\n> > of the path taken to get to that state.And nobody thinks that there is\n> > a problem with information loss. So, when black holes, made in\n> > different ways, end up with the same spin, mass and charge, why is it\n> > believed that information is lost?\n> > One can say " information disppears from the universe into a black\n> > hole" but isn\'t the black hole part of the universe?\n> >\n>\n> I don\'t understand this. I tear out a page from Nature, and\n> put it into my super-duper CIA designed paper shredder that\n> shreds paper into atoms! Are you saying that I, theoretically,\n> could reconstruct that page?\n>\n> -- Bob Day\n\nOf course. Take every atom, including yours and the shredders one,\ninvert their momentum precisely replace matter with anti matter and\nthe paper will reassemble.\nIt just happens to be that these are arbitrarily unlikely initial\nconditions to encounter.\n\n---\n\nfrank\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>"Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message news:<GdBEc.27680$Av3.13513@nwrdny01.gnilink.net>...
> "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
> news:861c1b21.0406240841.3f5890b0@posting.google.c om...
> > In classical thermodynamics the final state of a system is independent
> > of the path taken to get to that state.And nobody thinks that there is
> > a problem with information loss. So, when black holes, made in
> > different ways, end up with the same spin, mass and charge, why is it
> > believed that information is lost?
> > One can say " information disppears from the universe into a black
> > hole" but isn't the black hole part of the universe?
> >
>
> I don't understand this. I tear out a page from Nature, and
> put it into my super-duper CIA designed paper shredder that
> shreds paper into atoms! Are you saying that I, theoretically,
> could reconstruct that page?
>
> -- Bob Day
Of course. Take every atom, including yours and the shredders one,
invert their momentum precisely replace matter with anti matter and
the paper will reassemble.
It just happens to be that these are arbitrarily unlikely initial
conditions to encounter.
---
frank
<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>\nGreg Egan <gregegan@netspace.zebra.net.au> writes\n>\n>The statement "for the outside observer it takes an infinite amount of\n>time" for something to fall into a black hole is true in two senses, but\n>you have to look very carefully at what those statements are to see what\n>they tell you about information accessibility.\n>\n>However, note that:\n>\n>(a) if you count the flashes of the falling beacon, there is a finite\n>number assigned to the last flash you will ever see from it. That last\n>flash (assuming the beacon is "on" rather than "off" as it crosses the\n>horizon) reaches you over an unbounded time, but you still only ever get\n>to see a finite portion of the beacon\'s history.\n\nThat\'s a really useful bit of information that nobody ever mentions.\nIts a different statement from \'an infalling observer will hit the\nsingularity in a finite time\', although clearly very closely related.\n\nIts altered how I see a BH, possibly significantly.\n\nThank you for that.\n\nJust for completeness, can you give an expression for the \'infalling\nobserver number of flashes\' as seen by an external observer at infinity?\n\n--\nOz\nThis post is worth absolutely nothing and is probably fallacious.\n\nBTOPENWORLD address about to cease. DEMON address no longer in use.\n>>Use oz@farmeroz.port995.com (whitelist check on first posting)<<\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>Greg Egan <gregegan@netspace.zebra.net.au> writes
>
>The statement "for the outside observer it takes an infinite amount of
>time" for something to fall into a black hole is true in two senses, but
>you have to look very carefully at what those statements are to see what
>they tell you about information accessibility.
>
>However, note that:
>
>(a) if you count the flashes of the falling beacon, there is a finite
>number assigned to the last flash you will ever see from it. That last
>flash (assuming the beacon is "on" rather than "off" as it crosses the
>horizon) reaches you over an unbounded time, but you still only ever get
>to see a finite portion of the beacon's history.
That's a really useful bit of information that nobody ever mentions.
Its a different statement from 'an infalling observer will hit the
singularity in a finite time', although clearly very closely related.
Its altered how I see a BH, possibly significantly.
Thank you for that.
Just for completeness, can you give an expression for the 'infalling
observer number of flashes' as seen by an external observer at infinity?
--
Oz
This post is worth absolutely nothing and is probably fallacious.
BTOPENWORLD address about to cease. DEMON address no longer in use.
>>Use oz@farmeroz.port995.com (whitelist check on first posting)<<
Jerzy Karczmarczuk
Jul2-04, 04:32 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>\nUrs Schreiber wrote:\n> ... The apparent problem\n> with black holes is rather that stuff "falls inside" and after a long-l=\nong\n> time thermal Hawking radiation escapes. There would be a problem if in =\nthis\n> (possibly overly naive) scenario the Hawking radiation carried no signa=\nture\n> of the original stuff that fell into the black hole, roughly.\n\nCould you elaborate please on "after a long-long time"?\nI had the impression that the Hawking radiation "escapes" independently o=\nf the\nfalling stuff. If we take the model of virtual pairs which form around th=\ne\nhorizon, the negative-energy part falls-in, not respecting any internatio=\nnal\nlaws *before* the falling ordinary matter, which will glue to the horizon=\n\nforever, from the distant frame viewpoint. So, it is hardly conceivable t=\nhat\nthe falling matter could transmit some \'signature\' to the outgoing fragme=\nnts\nof those virtual pairs.\n\nNow, I am sure I am pretty na=EFve. Correct me please.\n\nSomehow I cannot free myself from the impression that all this stuff of\n\'information loss\' is a well painted red herring. What does it *really* m=\nean,\nin view of the fact that the word *really* is ambiguous; for a distant ob=\nserver\nthe falling matter NEVER crosses the event horizon. For the falling obser=\nver\nit is the *external* world which is "lost", since when he is in, the "out=\nside"\npatch of the universe had already passed through the Eternity, and the go=\nd\nShiva had burnt it...\n\nAnyway, I repeat once more the question I posed several weeks ago, and no=\nbody\ncared to answer:\n\nHow, from the perspective of the observer who falls in a black hole and i=\ns\nalready inside, the Hawking radiation looks like?\n\n\n\nJerzy Karczmarczuk\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>Urs Schreiber wrote:
> ... The apparent problem
> with black holes is rather that stuff "falls inside" and after a long-l=
ong
> time thermal Hawking radiation escapes. There would be a problem if in =
this
> (possibly overly naive) scenario the Hawking radiation carried no signa=
ture
> of the original stuff that fell into the black hole, roughly.
Could you elaborate please on "after a long-long time"?
I had the impression that the Hawking radiation "escapes" independently o=
f the
falling stuff. If we take the model of virtual pairs which form around th=
e
horizon, the negative-energy part falls-in, not respecting any internatio=
nal
laws *before* the falling ordinary matter, which will glue to the horizon=
forever, from the distant frame viewpoint. So, it is hardly conceivable t=
hat
the falling matter could transmit some 'signature' to the outgoing fragme=
nts
of those virtual pairs.
Now, I am sure I am pretty na=EFve. Correct me please.
Somehow I cannot free myself from the impression that all this stuff of
'information loss' is a well painted red herring. What does it *really* m=
ean,
in view of the fact that the word *really* is ambiguous; for a distant ob=
server
the falling matter NEVER crosses the event horizon. For the falling obser=
ver
it is the *external* world which is "lost", since when he is in, the "out=
side"
patch of the universe had already passed through the Eternity, and the go=
d
Shiva had burnt it...
Anyway, I repeat once more the question I posed several weeks ago, and no=
body
cared to answer:
How, from the perspective of the observer who falls in a black hole and i=
s
already inside, the Hawking radiation looks like?
Jerzy Karczmarczuk
carlip@no-physics-spam.ucdavis.edu
Jul2-04, 04:32 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>\nalistair <alistair@goforit64.fsnet.co.uk> wrote:\n\n[...]\n> Pulling a sheet of paper apart with my hands will irreversibly\n> destroy information on the sheet\n\nNo, it won\'t -- a person with some tape and enough time will\nbe able to reconstruct the information. More generally, any\nordinary means of ``destroying\'\' information will just mess\nit up in a way that makes it hard to reconstruct. Even if\nyou burn the paper, the photons coming out plus the motion\nof the molecules of heated air plus the remaining ash contain,\nin principle, all the information you started with.\n\n> so if a black\n> hole\'s tidal forces tears the sheet apart then surely this means\n> information is lost forever in a black hole?\n\nYou need to be careful about the distinction between information\nbeing made difficult to recover and information that is genuinely\nlost. When a sheet of paper falls into a black hole, classically\nthe information is lost *in principle*, not just as a practical\nmatter. If Hawking radiation is genuinely exactly thermal and the\nblack hole evaporates completely, this is true quantum mechanically\nas well -- it remains impossible even in principle to reconstruct\nthe information that has fallen in.\n\nThe technical statement is that the quantum evolution of an object\noutside a black hole is unitary, while -- again, assuming Hawking\nradiation is exactly thermal and the black hole evaporates completely\n-- the quantum evolution of an object falling into a black hole and\ncoming out as Hawking radiation is nonunitary. This is a hard problem,\nand it\'s not going to be solved with vague analogies.\n\nSteve Carlip\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>alistair <alistair@goforit64.fsnet.co.uk> wrote:
[...]
> Pulling a sheet of paper apart with my hands will irreversibly
> destroy information on the sheet
No, it won't -- a person with some tape and enough time will
be able to reconstruct the information. More generally, any
ordinary means of ``destroying'' information will just mess
it up in a way that makes it hard to reconstruct. Even if
you burn the paper, the photons coming out plus the motion
of the molecules of heated air plus the remaining ash contain,
in principle, all the information you started with.
> so if a black
> hole's tidal forces tears the sheet apart then surely this means
> information is lost forever in a black hole?
You need to be careful about the distinction between information
being made difficult to recover and information that is genuinely
lost. When a sheet of paper falls into a black hole, classically
the information is lost *in principle*, not just as a practical
matter. If Hawking radiation is genuinely exactly thermal and the
black hole evaporates completely, this is true quantum mechanically
as well -- it remains impossible even in principle to reconstruct
the information that has fallen in.
The technical statement is that the quantum evolution of an object
outside a black hole is unitary, while -- again, assuming Hawking
radiation is exactly thermal and the black hole evaporates completely
-- the quantum evolution of an object falling into a black hole and
coming out as Hawking radiation is nonunitary. This is a hard problem,
and it's not going to be solved with vague analogies.
Steve Carlip
<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>\n"Frank Hellmann" <Certhas@gmail.com> wrote in message\nnews:e2b39847.0407010718.4ddaa5ae@posting .google.com...\n> "Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message\nnews:<GdBEc.27680\\$Av3.13513@nwrdny01.gn ilink.net>...\n> > "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\n> > news:861c1b21.0406240841.3f5890b0@posting.google.c om...\n> > > In classical thermodynamics the final state of a system is independent\n> > > of the path taken to get to that state.And nobody thinks that there is\n> > > a problem with information loss. So, when black holes, made in\n> > > different ways, end up with the same spin, mass and charge, why is it\n> > > believed that information is lost?\n> > > One can say " information disppears from the universe into a black\n> > > hole" but isn\'t the black hole part of the universe?\n> > >\n> >\n> > I don\'t understand this. I tear out a page from Nature, and\n> > put it into my super-duper CIA designed paper shredder that\n> > shreds paper into atoms! Are you saying that I, theoretically,\n> > could reconstruct that page?\n> >\n> > -- Bob Day\n>\n> Of course. Take every atom, including yours and the shredders one,\n> invert their momentum precisely replace matter with anti matter and\n> the paper will reassemble.\n\nBut if the combination of position and momentum of each of the atoms\nis fundamentally uncertain, how can that be done?\n\n-- Bob Day\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>"Frank Hellmann" <Certhas@gmail.com> wrote in message
news:e2b39847.0407010718.4ddaa5ae@posting.google.c om...
> "Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message
news:<GdBEc.27680$Av3.13513@nwrdny01.gnilink.net>...
> > "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
> > news:861c1b21.0406240841.3f5890b0@posting.google.c om...
> > > In classical thermodynamics the final state of a system is independent
> > > of the path taken to get to that state.And nobody thinks that there is
> > > a problem with information loss. So, when black holes, made in
> > > different ways, end up with the same spin, mass and charge, why is it
> > > believed that information is lost?
> > > One can say " information disppears from the universe into a black
> > > hole" but isn't the black hole part of the universe?
> > >
> >
> > I don't understand this. I tear out a page from Nature, and
> > put it into my super-duper CIA designed paper shredder that
> > shreds paper into atoms! Are you saying that I, theoretically,
> > could reconstruct that page?
> >
> > -- Bob Day
>
> Of course. Take every atom, including yours and the shredders one,
> invert their momentum precisely replace matter with anti matter and
> the paper will reassemble.
But if the combination of position and momentum of each of the atoms
is fundamentally uncertain, how can that be done?
-- Bob Day
Greg Egan
Jul4-04, 07:39 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>\nIn article <A8lP3WG9n+4AFw4a@farmeroz.port995.com>, Oz\n<oz@farmeroz.port995.com> wrote:\n\n> Greg Egan <gregegan@netspace.zebra.net.au> writes\n> >\n> >(a) if you count the flashes of the falling beacon, there is a finite\n> >number assigned to the last flash you will ever see from it.\n>\n> Just for completeness, can you give an expression for the \'infalling\n> observer number of flashes\' as seen by an external observer at infinity?\n\nAn object free-falling radially into a black hole, starting from a\nSchwarzschild r-coordinate of R, obeys the parametric equations:\n\nr = (R/2) (1 + cos eta)\ntau = (R/2) sqrt(R/2M) (eta + sin eta)\n\nwhere r is the Schwarzschild r-coordinate, tau is elapsed proper time for\nthe falling object, M is the mass of the black hole, and everything is\nmeasured in geometrical units. The parameter eta ranges from 0 (r=R) to\npi (r=0).\n\n[Source: Gravitation, by Misner, Thorne & Wheeler, page 663]\n\nThe solution for tau in terms of r is:\n\ntau(r) = sqrt(R/2M) [ R arctan(sqrt(R/r-1)) + sqrt(r(R-r))]\n\n>From this, we can find the elapsed proper time before the object hits the\nsingularity, r=0:\n\ntau_S = sqrt(R/2M) R (pi/2)\n\nand the elapsed proper time before the object crosses the event horizon,\nr=2M:\n\ntau_H = sqrt(R) [ R/sqrt(2M) arctan(sqrt(R/2M - 1)) + sqrt(R-2M) ]\n\nThis time, tau_H, tells us how much of the history of the infalling\nobject can ever be visible from outside the black hole. After tau_H, no\nlight from the object can escape the hole, so light emitted up to tau_H\ngets stretched out indefinitely in the view from outside the hole.\n\nGreg Egan\n\nEmail address (remove name of animal and add standard punctuation):\ngregegan netspace zebra net au\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>In article <A8lP3WG9n+4AFw4a@farmeroz.port995.com>, Oz
<oz@farmeroz.port995.com> wrote:
> Greg Egan <gregegan@netspace.zebra.net.au> writes
> >
> >(a) if you count the flashes of the falling beacon, there is a finite
> >number assigned to the last flash you will ever see from it.
>
> Just for completeness, can you give an expression for the 'infalling
> observer number of flashes' as seen by an external observer at infinity?
An object free-falling radially into a black hole, starting from a
Schwarzschild r-coordinate of R, obeys the parametric equations:
r = (R/2) (1 + cos \eta)\tau = (R/2) \sqrt(R/2M) (\eta + sin \eta)
where r is the Schwarzschild r-coordinate, \tau is elapsed proper time for
the falling object, M is the mass of the black hole, and everything is
measured in geometrical units. The parameter \eta ranges from (r=R) to
\pi (r=0).
[Source: Gravitation, by Misner, Thorne & Wheeler, page 663]
The solution for \tau in terms of r is:
\tau(r) = \sqrt(R/2M) [ R arctan(\sqrt(R/r-1)) + \sqrt(r(R-r))]
>From this, we can find the elapsed proper time before the object hits the
singularity, r=0:\tau_S = \sqrt(R/2M) R (\pi/2)
and the elapsed proper time before the object crosses the event horizon,
r=2M:\tau_H = \sqrt(R) [ R/\sqrt(2M) arctan(\sqrt(R/2M - 1)) + \sqrt(R-2M) ]
This time, \tau_H, tells us how much of the history of the infalling
object can ever be visible from outside the black hole. After \tau_H, no
light from the object can escape the hole, so light emitted up to \tau_H
gets stretched out indefinitely in the view from outside the hole.
Greg Egan
Email address (remove name of animal and add standard punctuation):
gregegan netspace zebra net au
Frank Hellmann
Jul6-04, 01:38 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>\n\n"Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message news:<jmfFc.652\\$zn2.59@nwrdny03.gnilink.net>...\ n> "Frank Hellmann" <Certhas@gmail.com> wrote in message\n> news:e2b39847.0407010718.4ddaa5ae@posting.google.c om...\n> > "Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message\n> news:<GdBEc.27680\\$Av3.13513@nwrdny01.gnilink.net >...\n> > > "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\n> > > news:861c1b21.0406240841.3f5890b0@posting.google.c om...\n> > > > In classical thermodynamics the final state of a system is independent\n> > > > of the path taken to get to that state.And nobody thinks that there is\n> > > > a problem with information loss. So, when black holes, made in\n> > > > different ways, end up with the same spin, mass and charge, why is it\n> > > > believed that information is lost?\n> > > > One can say " information disppears from the universe into a black\n> > > > hole" but isn\'t the black hole part of the universe?\n> > > >\n> > >\n> > > I don\'t understand this. I tear out a page from Nature, and\n> > > put it into my super-duper CIA designed paper shredder that\n> > > shreds paper into atoms! Are you saying that I, theoretically,\n> > > could reconstruct that page?\n> > >\n> > > -- Bob Day\n> >\n> > Of course. Take every atom, including yours and the shredders one,\n> > invert their momentum precisely replace matter with anti matter and\n> > the paper will reassemble.\n>\n> But if the combination of position and momentum of each of the atoms\n> is fundamentally uncertain, how can that be done?\n>\n> -- Bob Day\n\nSimilar if you grant me the ability to create a wavefunction of any\nshape. The same symmetry is valid for QM so if you operate with CP on\nthe initial state you will get a negative time evolution.\nAnother way to look at it is that QM is unitary. the time evolution is\ngoverend by exp(iHt) and if H is a valid hamiltonian so is -H so you\ncan undo exp(iHt) by multiplying with exp(-iHt) from the left.\nEven if that would not be physically valid (which, to my\nunderstanding, it is) you still don\'t have any information lost during\nyour QM shredding since in principle you could take the final state of\nyour shredded thing and make a numerical simulation of sufficient\npower (we are gedankenexperimenting here after all) with an exp(-iHt)\nevolution.\nNow to get the final state you have to meassure it of course, and\nmeassurement is (unless proven otherwise) non unitary and information\nis indeed lost. But that\'s the meassurement problem and unrelated(??!)\nto the black hole information loss problem.\n\n----\nfrank\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>"Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message news:<jmfFc.652$zn2.59@nwrdny03.gnilink.net>...
> "Frank Hellmann" <Certhas@gmail.com> wrote in message
> news:e2b39847.0407010718.4ddaa5ae@posting.google.c om...
> > "Bob Day" <xxxxxxx@yyyyyyy.com> wrote in message
> news:<GdBEc.27680$Av3.13513@nwrdny01.gnilink.net>...
> > > "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
> > > news:861c1b21.0406240841.3f5890b0@posting.google.c om...
> > > > In classical thermodynamics the final state of a system is independent
> > > > of the path taken to get to that state.And nobody thinks that there is
> > > > a problem with information loss. So, when black holes, made in
> > > > different ways, end up with the same spin, mass and charge, why is it
> > > > believed that information is lost?
> > > > One can say " information disppears from the universe into a black
> > > > hole" but isn't the black hole part of the universe?
> > > >
> > >
> > > I don't understand this. I tear out a page from Nature, and
> > > put it into my super-duper CIA designed paper shredder that
> > > shreds paper into atoms! Are you saying that I, theoretically,
> > > could reconstruct that page?
> > >
> > > -- Bob Day
> >
> > Of course. Take every atom, including yours and the shredders one,
> > invert their momentum precisely replace matter with anti matter and
> > the paper will reassemble.
>
> But if the combination of position and momentum of each of the atoms
> is fundamentally uncertain, how can that be done?
>
> -- Bob Day
Similar if you grant me the ability to create a wavefunction of any
shape. The same symmetry is valid for QM so if you operate with CP on
the initial state you will get a negative time evolution.
Another way to look at it is that QM is unitary. the time evolution is
goverend by \exp(iHt) and if H is a valid hamiltonian so is -H so you
can undo \exp(iHt) by multiplying with \exp(-iHt) from the left.
Even if that would not be physically valid (which, to my
understanding, it is) you still don't have any information lost during
your QM shredding since in principle you could take the final state of
your shredded thing and make a numerical simulation of sufficient
power (we are gedankenexperimenting here after all) with an \exp(-iHt)
evolution.
Now to get the final state you have to meassure it of course, and
meassurement is (unless proven otherwise) non unitary and information
is indeed lost. But that's the meassurement problem and unrelated(??!)
to the black hole information loss problem.
----
frank
Eric Baird
Jul16-04, 08:19 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>\n\nOn Tue, 29 Jun 2004 22:54:04 +0000 (UTC), daniel@elit.net (Daniel\nElander) wrote:\n\n>> When people talk about information loss in a black hole, they are\n>> referring to the fact that someone outside the event horizon would\n>> have no way of knowing what is written on the piece of paper.\n>\n>But for the outside observer it takes an infinite amount of time for\n>the paper to fall into the black hole. So it would seem the paradox\n>never happens. Or am I wrong?\n\nWell, in a simple classical model, the infalling object does (in a\nmathematical sense) seem to take forever to reach the horizon, but you\nalso have to remember that it radiates a finite and fixed amount of\nradiation during the last few momewnts, and that tiny little bit of\nlight, with limited detail, might mathematically have to last the\noutside observer an infinite amount of time.\nThere\'s going to be all sorts of information embedded in that lost\nobject that won\'t be encoded in its "fossil light". It\'s like ... if\nyou take a photograph of an ocean liner, and then drop it into a black\nhole, then sure, you can still "see" the information recorded in the\nphotograph, but you can\'t interact with the photo, or peer inside it,\nor bounce light off the object pictured to see how it responds, or\nbounce radar off it.\n\nReal information would seem to be lost. If the grainy photo of the\nocean liner didn\'t happen to reveal who was in berth 1A or what was\nbeing served for breakfast, it\'s too late to find out.\n\n\nOne possible potential workaround that was suggested was to say that\nperhaps all the information is trapped at the horizon and imprinted on\nit in some way as a sort of skin, and perhaps the patterns embedded in\nthat surface then condition the form of radiation emitted from the\nhole by QM processes.\nIn that scenario, the pattern of radiation from the hole might in some\nway reflect the internal structure of the missing ocean liner, if you\nhad some way of collecting and collating it all.\n\nThe most extreme interpretation of this idea would be if the surface\ncould spit out mangled versions of the previously infallen material.\nI suppose that while the suibject is still a bit vague, we might even\nstill be allowed to suggest that if we aimed a spaceship through the\nedge of a black hole, equipped with a suitable warp drive, we /might/\nbe allowed to see a somewhat singed spaceship emerge some time later,\nwith a more advanced clock reading and with what appears to be a\ndigitised recording of a journey through the horizon sitting in its\nmemory banks ... and say that no, the spaceship didn\'t really enter\nand then escape the horizon, the ship that exited was a recreation of\nthe original ship, with its data convolved with the other information\nembedded in the horizon (containing a record of everything else that\never fell in) , extrapolated forwards mechanically and\ndeterministically inside the horizon, and the distortion caused by the\nwarp engines set off a delayed reaction "bounce" provoked the horizon\nto burp out an more aged version of the ship, complete with a record\nof its apparent adventures inside the surface, at a later time (with\nall that ship informaiton removed from the surface as the ship\nappeared).\n\nBut at that point, it starts to get a bit silly, because by then we\nhave lost any justification for saying that the ship didn\'t /really/\nenter and exit the hole by firing up its warp engines, which would be\nimpossible according to GR circa 1970-2000.\n\nSo we really need to work out /exactly/ how far QM modifies GR, and\nwhat the /exact/ relationship is between emitted radiation and\npreviously infallen material. If there\'s no relationship at all, then\nwe lose all sorts of nice ideas about causality. Many people would not\nbe happy with a science that said that sometimes things just happened\nfor no reason at all.\nAt the other end of the spectrum, if there\'s complete 1:1 mapping,\nthen the idea of a conventional GR horizon begins to look a bit silly\n- I could equally claim that my bedroom door is a one-way surface that\ndoes not allow information to escape, and that when you see me walkign\nin and out of the rtoom, you are seeing quantum constructions of the\noriginal data being stored and ejected at the doorway surface.\nIt becomes a slightly pointless theory.\n\nAnd in the middle, I guess we have a mess of possible intermediate\nideas, which at the moment still seem slightly grungey.\n\n\nSo it\'s an important point in physics history. We lose general\nrelativity in its current form, or we lose causality, or we get some\nnew thing that we don\'t fully understand yet.\nThose seem to be the choices.\nAnd although it would seem that we might be able to patch together a\nnew general theory of relativity that does agree with QM and allow\ninformation (and matter) to leak out, the only plan of attack that I\nknow for /that/ involves deleting special relativity and rebuilding\nour gravitational theory from scratch without the SR layer, and some\npeople would regard losing SR as being an even bigger disaster.\n\nSo it\'s a biggie. Like the bit in the movie where everyone knows that\nthere\'s a bomb on the bus, and the bus can\'t stop, and they realise\nthat its heading for a section of motorway that hasn\'t been built yet\n....\n\n=Erk= (Eric Baird)\n"You\'re fired! Everybody\'s f***in\' fired!"\n- Speed (1994)\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 Tue, 29 Jun 2004 22:54:04 +0000 (UTC), daniel@elit.net (Daniel
Elander) wrote:
>> When people talk about information loss in a black hole, they are
>> referring to the fact that someone outside the event horizon would
>> have no way of knowing what is written on the piece of paper.
>
>But for the outside observer it takes an infinite amount of time for
>the paper to fall into the black hole. So it would seem the paradox
>never happens. Or am I wrong?
Well, in a simple classical model, the infalling object does (in a
mathematical sense) seem to take forever to reach the horizon, but you
also have to remember that it radiates a finite and fixed amount of
radiation during the last few momewnts, and that tiny little bit of
light, with limited detail, might mathematically have to last the
outside observer an infinite amount of time.
There's going to be all sorts of information embedded in that lost
object that won't be encoded in its "fossil light". It's like ... if
you take a photograph of an ocean liner, and then drop it into a black
hole, then sure, you can still "see" the information recorded in the
photograph, but you can't interact with the photo, or peer inside it,
or bounce light off the object pictured to see how it responds, or
bounce radar off it.
Real information would seem to be lost. If the grainy photo of the
ocean liner didn't happen to reveal who was in berth 1A or what was
being served for breakfast, it's too late to find out.
One possible potential workaround that was suggested was to say that
perhaps all the information is trapped at the horizon and imprinted on
it in some way as a sort of skin, and perhaps the patterns embedded in
that surface then condition the form of radiation emitted from the
hole by QM processes.
In that scenario, the pattern of radiation from the hole might in some
way reflect the internal structure of the missing ocean liner, if you
had some way of collecting and collating it all.
The most extreme interpretation of this idea would be if the surface
could spit out mangled versions of the previously infallen material.
I suppose that while the suibject is still a bit vague, we might even
still be allowed to suggest that if we aimed a spaceship through the
edge of a black hole, equipped with a suitable warp drive, we /might/
be allowed to see a somewhat singed spaceship emerge some time later,
with a more advanced clock reading and with what appears to be a
digitised recording of a journey through the horizon sitting in its
memory banks ... and say that no, the spaceship didn't really enter
and then escape the horizon, the ship that exited was a recreation of
the original ship, with its data convolved with the other information
embedded in the horizon (containing a record of everything else that
ever fell in) , extrapolated forwards mechanically and
deterministically inside the horizon, and the distortion caused by the
warp engines set off a delayed reaction "bounce" provoked the horizon
to burp out an more aged version of the ship, complete with a record
of its apparent adventures inside the surface, at a later time (with
all that ship informaiton removed from the surface as the ship
appeared).
But at that point, it starts to get a bit silly, because by then we
have lost any justification for saying that the ship didn't /really/
enter and exit the hole by firing up its warp engines, which would be
impossible according to GR circa 1970-2000.
So we really need to work out /exactly/ how far QM modifies GR, and
what the /exact/ relationship is between emitted radiation and
previously infallen material. If there's no relationship at all, then
we lose all sorts of nice ideas about causality. Many people would not
be happy with a science that said that sometimes things just happened
for no reason at all.
At the other end of the spectrum, if there's complete 1:1 mapping,
then the idea of a conventional GR horizon begins to look a bit silly
- I could equally claim that my bedroom door is a one-way surface that
does not allow information to escape, and that when you see me walkign
in and out of the rtoom, you are seeing quantum constructions of the
original data being stored and ejected at the doorway surface.
It becomes a slightly pointless theory.
And in the middle, I guess we have a mess of possible intermediate
ideas, which at the moment still seem slightly grungey.
So it's an important point in physics history. We lose general
relativity in its current form, or we lose causality, or we get some
new thing that we don't fully understand yet.
Those seem to be the choices.
And although it would seem that we might be able to patch together a
new general theory of relativity that does agree with QM and allow
information (and matter) to leak out, the only plan of attack that I
know for /that/ involves deleting special relativity and rebuilding
our gravitational theory from scratch without the SR layer, and some
people would regard losing SR as being an even bigger disaster.
So it's a biggie. Like the bit in the movie where everyone knows that
there's a bomb on the bus, and the bus can't stop, and they realise
that its heading for a section of motorway that hasn't been built yet
....
=Erk= (Eric Baird)
"You're fired! Everybody's f***in' fired!"
- Speed (1994)
Thomas Dent
Jul19-04, 03:09 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>\n\n\n\ndaniel@elit.net (Daniel Elander) wrote in message news:<37d84b42.0406290104.3402b89f@posting.google. com>...\n> > When people talk about information loss in a black hole, they are\n> > referring to the fact that someone outside the event horizon would\n> > have no way of knowing what is written on the piece of paper.\n>\n> But for the outside observer it takes an infinite amount of time for\n> the paper to fall into the black hole. So it would seem the paradox\n> never happens. Or am I wrong?\n>\n> Daniel\n\nSee "Hawking changes his mind about black holes":\n\nhttp://www.nature.com/news/2004/040712/full/040712-12.html\n\n`The view seems to be forming in his mind that there isn\'t a black\nhole in the absolute sense, there\'s just a region where things take a\nvery long time to escape," says Gibbons. This suggests that black\nholes do not actually narrow to a singularity at all.\'\n\nIf black holes were actually eternal Schwarzschild solutions there\nwould definitely be a problem. But they evolve over time and\neventually evaporate away. The phrase "event horizon" is strictly only\nmeaningful for a black hole that lives for ever, but actually they all\nhave finite lifetimes, so there is only an apparent event horizon.\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>daniel@elit.net (Daniel Elander) wrote in message news:<37d84b42.0406290104.3402b89f@posting.google.com>...
> > When people talk about information loss in a black hole, they are
> > referring to the fact that someone outside the event horizon would
> > have no way of knowing what is written on the piece of paper.
>
> But for the outside observer it takes an infinite amount of time for
> the paper to fall into the black hole. So it would seem the paradox
> never happens. Or am I wrong?
>
> Daniel
See "Hawking changes his mind about black holes":
http://www.nature.com/news/2004/040712/full/040712-12.html
`The view seems to be forming in his mind that there isn't a black
hole in the absolute sense, there's just a region where things take a
very long time to escape," says Gibbons. This suggests that black
holes do not actually narrow to a singularity at all.'
If black holes were actually eternal Schwarzschild solutions there
would definitely be a problem. But they evolve over time and
eventually evaporate away. The phrase "event horizon" is strictly only
meaningful for a black hole that lives for ever, but actually they all
have finite lifetimes, so there is only an apparent event horizon.
Daniel Elander
Jul19-04, 05:14 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>\n\n> >But for the outside observer it takes an infinite amount of time for\n> >the paper to fall into the black hole. So it would seem the paradox\n> >never happens. Or am I wrong?\n>\n> Well, in a simple classical model, the infalling object does (in a\n> mathematical sense) seem to take forever to reach the horizon, but you\n> also have to remember that it radiates a finite and fixed amount of\n> radiation during the last few momewnts, and that tiny little bit of\n> light, with limited detail, might mathematically have to last the\n> outside observer an infinite amount of time.\n> There\'s going to be all sorts of information embedded in that lost\n> object that won\'t be encoded in its "fossil light". It\'s like ... if\n> you take a photograph of an ocean liner, and then drop it into a black\n> hole, then sure, you can still "see" the information recorded in the\n> photograph, but you can\'t interact with the photo, or peer inside it,\n> or bounce light off the object pictured to see how it responds, or\n> bounce radar off it.\n\nWell, this happens in any gravitational field, not just that of a\nblack hole, and has nothing to do with the event horizon. It seems to\nme that it is a matter of not being able to retrieve information in\npractice, rather than that the complete wave function does not contain\ninformation about the past object.\n\n> One possible potential workaround that was suggested was to say that\n> perhaps all the information is trapped at the horizon and imprinted on\n> it in some way as a sort of skin, and perhaps the patterns embedded in\n> that surface then condition the form of radiation emitted from the\n> hole by QM processes.\n\nIt\'s a suggestive idea since the entropy is proportional to the area\nof the event horizon, yes.\n\n> So we really need to work out /exactly/ how far QM modifies GR, and\n> what the /exact/ relationship is between emitted radiation and\n> previously infallen material. If there\'s no relationship at all, then\n> we lose all sorts of nice ideas about causality. Many people would not\n> be happy with a science that said that sometimes things just happened\n> for no reason at all.\n\nI guess what I wonder is if there are any problem with just saying\nthat to an outsider observer, since it takes an infinite amount of\ntime to get into the black hole, there is no information lost, and to\nan observer travelling into a black hole, everything looks normal\n(relatively speaking!). To both observers, information would be\npreserved - it\'s just different information.\nI mean, to speak of the evolution of the wavefunction of the universe,\nas it seems to be implicit that we do when we ask qustions such as if\ninformation is lost, we have to pick a time coordinate, perhaps\nsomeone\'s proper time. Is it then not enough to say that no matter how\nyou pick the time coordinate, information will be conserved? What is\nactually the stronger claim that Hawking wants to/has proved?\n\nDaniel\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>>But for the outside observer it takes an infinite amount of time for
> >the paper to fall into the black hole. So it would seem the paradox
> >never happens. Or am I wrong?
>
> Well, in a simple classical model, the infalling object does (in a
> mathematical sense) seem to take forever to reach the horizon, but you
> also have to remember that it radiates a finite and fixed amount of
> radiation during the last few momewnts, and that tiny little bit of
> light, with limited detail, might mathematically have to last the
> outside observer an infinite amount of time.
> There's going to be all sorts of information embedded in that lost
> object that won't be encoded in its "fossil light". It's like ... if
> you take a photograph of an ocean liner, and then drop it into a black
> hole, then sure, you can still "see" the information recorded in the
> photograph, but you can't interact with the photo, or peer inside it,
> or bounce light off the object pictured to see how it responds, or
> bounce radar off it.
Well, this happens in any gravitational field, not just that of a
black hole, and has nothing to do with the event horizon. It seems to
me that it is a matter of not being able to retrieve information in
practice, rather than that the complete wave function does not contain
information about the past object.
> One possible potential workaround that was suggested was to say that
> perhaps all the information is trapped at the horizon and imprinted on
> it in some way as a sort of skin, and perhaps the patterns embedded in
> that surface then condition the form of radiation emitted from the
> hole by QM processes.
It's a suggestive idea since the entropy is proportional to the area
of the event horizon, yes.
> So we really need to work out /exactly/ how far QM modifies GR, and
> what the /exact/ relationship is between emitted radiation and
> previously infallen material. If there's no relationship at all, then
> we lose all sorts of nice ideas about causality. Many people would not
> be happy with a science that said that sometimes things just happened
> for no reason at all.
I guess what I wonder is if there are any problem with just saying
that to an outsider observer, since it takes an infinite amount of
time to get into the black hole, there is no information lost, and to
an observer travelling into a black hole, everything looks normal
(relatively speaking!). To both observers, information would be
preserved - it's just different information.
I mean, to speak of the evolution of the wavefunction of the universe,
as it seems to be implicit that we do when we ask qustions such as if
information is lost, we have to pick a time coordinate, perhaps
someone's proper time. Is it then not enough to say that no matter how
you pick the time coordinate, information will be conserved? What is
actually the stronger claim that Hawking wants to/has proved?
Daniel
<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>Frank Hellmann <Certhas@gmail.com> writes\n>Of course. Take every atom, including yours and the shredders one,\n>invert their momentum precisely replace matter with anti matter and\n>the paper will reassemble.\n>It just happens to be that these are arbitrarily unlikely initial\n>conditions to encounter.\n\nI have a problem with this quantum mechanically.\n\nClassically (although describing atoms and photons classically is moot)\nit might be possible, but surely uncertainty wipes out the reverse path\nwhenever a mildly chaotic system is under discussion.\n\nI am prepared to believe for the moment that information (in a technical\nsense) is preserved. That strikes me as a lesser requirement. For\nexample a gas contains all the information required to generate it. In\nthis case typically rather small amounts of information. Number of\nmolecules, their internal configuration, temp and volume is pretty well\nall that is needed: a handful of numbers. The precise configuration at\nany moment in time requires a godzillion numbers.\n\nI haven\'t really ever gone into information theory, but I get the\ngeneral impression that a body with n parts has information roughly\nscaling as ln(n). Since very many physical systems also have forms\nscaling as ln(n) (or exp(n)) the tie between these and information\nstrikes me as very strong.\n\nI have a vague gut feeling that entropy and information should be\nrelated. That somehow entropy and information loss is related.\n\nThe classic image I have is the simple one of a drop of liquid dropped\ninto a sealed hot box. The drop evaporates and produces a gas. I do not\nbelieve that, given the precise (as theoretically possible) energy and\npath of every atom in the box and the gas, you could time-reverse them\nto give a hot box and a cold drop of liquid at the precise time the\nliquid was introduced. The system is so chaotic, and the accuracy\nrequired so vastly less than the uncertainty principle permits, that\nthis is undoable, even in theory.\n\n--\nOz\nThis post is worth absolutely nothing and is probably fallacious.\n\nBTOPENWORLD address about to cease. DEMON address no longer in use.\n>>Use oz@farmeroz.port995.com<<\nozacoohdb@despammed.com still functions.\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>Frank Hellmann <Certhas@gmail.com> writes
>Of course. Take every atom, including yours and the shredders one,
>invert their momentum precisely replace matter with anti matter and
>the paper will reassemble.
>It just happens to be that these are arbitrarily unlikely initial
>conditions to encounter.
I have a problem with this quantum mechanically.
Classically (although describing atoms and photons classically is moot)
it might be possible, but surely uncertainty wipes out the reverse path
whenever a mildly chaotic system is under discussion.
I am prepared to believe for the moment that information (in a technical
sense) is preserved. That strikes me as a lesser requirement. For
example a gas contains all the information required to generate it. In
this case typically rather small amounts of information. Number of
molecules, their internal configuration, temp and volume is pretty well
all that is needed: a handful of numbers. The precise configuration at
any moment in time requires a godzillion numbers.
I haven't really ever gone into information theory, but I get the
general impression that a body with n parts has information roughly
scaling as ln(n). Since very many physical systems also have forms
scaling as ln(n) (or \exp(n)) the tie between these and information
strikes me as very strong.
I have a vague gut feeling that entropy and information should be
related. That somehow entropy and information loss is related.
The classic image I have is the simple one of a drop of liquid dropped
into a sealed hot box. The drop evaporates and produces a gas. I do not
believe that, given the precise (as theoretically possible) energy and
path of every atom in the box and the gas, you could time-reverse them
to give a hot box and a cold drop of liquid at the precise time the
liquid was introduced. The system is so chaotic, and the accuracy
required so vastly less than the uncertainty principle permits, that
this is undoable, even in theory.
--
Oz
This post is worth absolutely nothing and is probably fallacious.
BTOPENWORLD address about to cease. DEMON address no longer in use.
>>Use oz@farmeroz.port995.com<<
ozacoohdb@despammed.com still functions.
Frank Hellmann
Aug6-04, 03:03 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>We are not talking practical limitations here we are talking about the\nmathematical nature of our project. QM introduces the uncertainty\nrelationship but even that doesn\'t matter. The state of a system in QM\ndoes neither have a precise momentum nor a precise location ascociated\nwith it but it is still a single identical state.\nOf course then specifying momentum and location of every particle is\nnot what you need, you need to give the precise QM state of the system\nwhich can not in general be known to inhabitants of the system (that\'s\nwhat the uncertainty relation is about, it\'s about observables not\nstates) but that is inconsequential for the question.\nTime evolution is governed by operating with exp(iHt) on our state. We\ncan take the final state operate with exp(-iHt) on it and recover the\ninitial state (assume you have infinitely many systems undergoing the\ntime evolution that allow you to actually know the final state\nprecisely and use and infiniotely strong computer to simulate the\nexp(-iHt) evolution if you like to). of course (CP)T is stronger then\njust conservation of information as in the above, as it says that this\nsecond operation is actually physically viable as well. But if you\ngoogle the CPT theorem (which i do not understand) you will see that\nactually every QFT has to be CPT invariant, and QFTs are the strongest\nand best modells we have.\n\nAs to your information vs entropy, I don\'t know much about it but you\nare spot on. Entropy is the opposite of shannon information. However\nwe are not talking about shannon information and entropy here which\nare macroscopic we are talking on a more fundamental microscopic\nlevel.\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>We are not talking practical limitations here we are talking about the
mathematical nature of our project. QM introduces the uncertainty
relationship but even that doesn't matter. The state of a system in QM
does neither have a precise momentum nor a precise location ascociated
with it but it is still a single identical state.
Of course then specifying momentum and location of every particle is
not what you need, you need to give the precise QM state of the system
which can not in general be known to inhabitants of the system (that's
what the uncertainty relation is about, it's about observables not
states) but that is inconsequential for the question.
Time evolution is governed by operating with \exp(iHt) on our state. We
can take the final state operate with \exp(-iHt) on it and recover the
initial state (assume you have infinitely many systems undergoing the
time evolution that allow you to actually know the final state
precisely and use and infiniotely strong computer to simulate the
\exp(-iHt) evolution if you like to). of course (CP)T is stronger then
just conservation of information as in the above, as it says that this
second operation is actually physically viable as well. But if you
google the CPT theorem (which i do not understand) you will see that
actually every QFT has to be CPT invariant, and QFTs are the strongest
and best modells we have.
As to your information vs entropy, I don't know much about it but you
are spot on. Entropy is the opposite of shannon information. However
we are not talking about shannon information and entropy here which
are macroscopic we are talking on a more fundamental microscopic
level.
<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>Frank Hellmann <Certhas@gmail.com> writes\n>We are not talking practical limitations here we are talking about the\n>mathematical nature of our project. QM introduces the uncertainty\n>relationship but even that doesn\'t matter. The state of a system in QM\n>does neither have a precise momentum nor a precise location ascociated\n>with it but it is still a single identical state.\n\nOK, although I am not convinced.\n\n>Of course then specifying momentum and location of every particle is\n>not what you need, you need to give the precise QM state of the system\n>which can not in general be known to inhabitants of the system (that\'s\n>what the uncertainty relation is about, it\'s about observables not\n>states) but that is inconsequential for the question.\n\nOk so you are claiming that the state \'TV infalling\' contains all the\n*information* on \'TV infalling\'.\n\nSo you are saying that in:\n\n\'TV\' (at infinity) + BH -> BH having absorbed TV\n\nShould both contain the same amount of information.\n\nI now throw in another identical TV. Surely the amount of information\nthat the black hole needs to contain is only one bit larger.\n\nThat is BH + (1) TV -> BH + (2) TV doesn\'t requite much extra\ninformation.\n\nAssuming quite a few TV\'s of various types have found their way into the\nBH, pretty much the whole description of the TV itself could be already\nin there. This chip here and that resistor there etc etc.\n\nIn effect the BH is just a big .jpg of what fell in.\n\nSo we shouldn\'t expect to retrieve the full information of everything\nthat went in, but just enough information to be able to say what it was\nthat went in.\n\nNow we have a further problem.\n\nThings don\'t just fall into a BH intact. In fact I suspect its very hard\nto get a TV into a BH. I would imagine that it would invariably have\nbeen reduced to ionised atoms some distance from the horizon. Since this\ncan be observed by external observers it means that the BH actually just\ningests a thermal soup.\n\nHmm, that\'s not quite accurate for big BH\'s though. But then their\nboundary is vast and can encode for a godzillion incoming states.\n\n>As to your information vs entropy, I don\'t know much about it but you\n>are spot on. Entropy is the opposite of shannon information. However\n>we are not talking about shannon information and entropy here which\n>are macroscopic we are talking on a more fundamental microscopic\n>level.\n\nI can see no reason why these should be different in principle.\n\n--\nOz\nThis post is worth absolutely nothing and is probably fallacious.\n\nBTOPENWORLD address about to cease. DEMON address no longer in use.\n>>Use oz@farmeroz.port995.com<<\nozacoohdb@despammed.com still functions.\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>Frank Hellmann <Certhas@gmail.com> writes
>We are not talking practical limitations here we are talking about the
>mathematical nature of our project. QM introduces the uncertainty
>relationship but even that doesn't matter. The state of a system in QM
>does neither have a precise momentum nor a precise location ascociated
>with it but it is still a single identical state.
OK, although I am not convinced.
>Of course then specifying momentum and location of every particle is
>not what you need, you need to give the precise QM state of the system
>which can not in general be known to inhabitants of the system (that's
>what the uncertainty relation is about, it's about observables not
>states) but that is inconsequential for the question.
Ok so you are claiming that the state 'TV infalling' contains all the
*information* on 'TV infalling'.
So you are saying that in:
'TV' (at infinity) + BH -> BH having absorbed TV
Should both contain the same amount of information.
I now throw in another identical TV. Surely the amount of information
that the black hole needs to contain is only one bit larger.
That is BH + (1) TV -> BH + (2) TV doesn't requite much extra
information.
Assuming quite a few TV's of various types have found their way into the
BH, pretty much the whole description of the TV itself could be already
in there. This chip here and that resistor there etc etc.
In effect the BH is just a big .jpg of what fell in.
So we shouldn't expect to retrieve the full information of everything
that went in, but just enough information to be able to say what it was
that went in.
Now we have a further problem.
Things don't just fall into a BH intact. In fact I suspect its very hard
to get a TV into a BH. I would imagine that it would invariably have
been reduced to ionised atoms some distance from the horizon. Since this
can be observed by external observers it means that the BH actually just
ingests a thermal soup.
Hmm, that's not quite accurate for big BH's though. But then their
boundary is vast and can encode for a godzillion incoming states.
>As to your information vs entropy, I don't know much about it but you
>are spot on. Entropy is the opposite of shannon information. However
>we are not talking about shannon information and entropy here which
>are macroscopic we are talking on a more fundamental microscopic
>level.
I can see no reason why these should be different in principle.
--
Oz
This post is worth absolutely nothing and is probably fallacious.
BTOPENWORLD address about to cease. DEMON address no longer in use.
>>Use oz@farmeroz.port995.com<<
ozacoohdb@despammed.com still functions.
Frank Hellmann
Aug12-04, 08:29 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>\n\n\n\n> \'TV\' (at infinity) + BH -> BH having absorbed TV\n>\n> Should both contain the same amount of information.\n\nWell... Now you are talking Black Holes I wasn\'t talking about the\nBlack Hole information paradox, I was just talking about the general\nstage.\nQM is of the nature described above, always the same information.\nClassical GR kind of is, though the information within the Black Hole\nis inaccesible to people outside it it still exists. Now if a\nblackhole evaporates in finite time via perfectly thermal hawking\nradiation that information is gone forever. That would violate\nunitarity in QM which basically says that there always exists a good\ninverse operator with which one can undo the time evolution (not\nneccesarily we, but Descartes Demon could)\n\n>\n> I now throw in another identical TV. Surely the amount of information\n> that the black hole needs to contain is only one bit larger.\n>\n> That is BH + (1) TV -> BH + (2) TV doesn\'t requite much extra\n> information.\n>\n\nYou are massively confusing macroscopic information as in shannon\ninformation or even just colloquial naive information and the\ninformation meant in the Black Hole Information Paradox, the kind of\ninformation preserved by unitarity.\nThe macroscopic information can be lost due to thermodynamics while\nthe microscopic one stays intact. You have a gas of N particles\nseperated in one of two boxes, with this you can encode one bit of\nmacroscopical information, the gas is in one box, the gas is in the\nother box. You bring them in contact, entropy does it\'s work the\nencoded information is lost. However microscopicaly you still have N\nparticles with N wavefunctions. The same amount of information.\n\nThere is no comprression of this kind of microscopic information as in\nsaying "2 TVs".\n\nAlso this is all NOT about what information is accesible to us outside\nof the black hole. if the information is inside, and we are outside\nand can\'t get at it, it\'s still preserved. There is nothing that says\nthat information reachable by us should be preserved.\n\n> >As to your information vs entropy, I don\'t know much about it but you\n> >are spot on. Entropy is the opposite of shannon information. However\n> >we are not talking about shannon information and entropy here which\n> >are macroscopic we are talking on a more fundamental microscopic\n> >level.\n>\n> I can see no reason why these should be different in principle.\n\nInformation like anything in an exact science like physics needs to be\ncarefully defined. Especially for Information this is tricky. There is\nshannons definition which ties it closely to entropy and\nthermodynamics. This is not the information people talk about in the\nBHIP! You can\'t just assume your intuition wrt information is valid to\nuse here, far from it!\n\nWhen talking about microscopical information we are really talking\nabout the nature of the time evolution. Specifically if it is\ninvertible.\n\nc\nfrank\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>'TV' (at infinity) + BH -> BH having absorbed TV
>
> Should both contain the same amount of information.
Well... Now you are talking Black Holes I wasn't talking about the
Black Hole information paradox, I was just talking about the general
stage.
QM is of the nature described above, always the same information.
Classical GR kind of is, though the information within the Black Hole
is inaccesible to people outside it it still exists. Now if a
blackhole evaporates in finite time via perfectly thermal hawking
radiation that information is gone forever. That would violate
unitarity in QM which basically says that there always exists a good
inverse operator with which one can undo the time evolution (not
neccesarily we, but Descartes Demon could)
>
> I now throw in another identical TV. Surely the amount of information
> that the black hole needs to contain is only one bit larger.
>
> That is BH + (1) TV -> BH + (2) TV doesn't requite much extra
> information.
>
You are massively confusing macroscopic information as in shannon
information or even just colloquial naive information and the
information meant in the Black Hole Information Paradox, the kind of
information preserved by unitarity.
The macroscopic information can be lost due to thermodynamics while
the microscopic one stays intact. You have a gas of N particles
seperated in one of two boxes, with this you can encode one bit of
macroscopical information, the gas is in one box, the gas is in the
other box. You bring them in contact, entropy does it's work the
encoded information is lost. However microscopicaly you still have N
particles with N wavefunctions. The same amount of information.
There is no comprression of this kind of microscopic information as in
saying "2 TVs".
Also this is all NOT about what information is accesible to us outside
of the black hole. if the information is inside, and we are outside
and can't get at it, it's still preserved. There is nothing that says
that information reachable by us should be preserved.
> >As to your information vs entropy, I don't know much about it but you
> >are spot on. Entropy is the opposite of shannon information. However
> >we are not talking about shannon information and entropy here which
> >are macroscopic we are talking on a more fundamental microscopic
> >level.
>
> I can see no reason why these should be different in principle.
Information like anything in an exact science like physics needs to be
carefully defined. Especially for Information this is tricky. There is
shannons definition which ties it closely to entropy and
thermodynamics. This is not the information people talk about in the
BHIP! You can't just assume your intuition wrt information is valid to
use here, far from it!
When talking about microscopical information we are really talking
about the nature of the time evolution. Specifically if it is
invertible.
c
frank
<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>\n\n\nFrank Hellmann <Certhas@gmail.com> writes\n>\n>\n>\n>\n>> \'TV\' (at infinity) + BH -> BH having absorbed TV\n>>\n>> Should both contain the same amount of information.\n>\n>Well... Now you are talking Black Holes I wasn\'t talking about the\n>Black Hole information paradox, I was just talking about the general\n>stage.\n\nOK.\n\n>QM is of the nature described above, always the same information.\n>Classical GR kind of is, though the information within the Black Hole\n>is inaccesible to people outside it it still exists. Now if a\n>blackhole evaporates in finite time via perfectly thermal hawking\n>radiation that information is gone forever. That would violate\n>unitarity in QM which basically says that there always exists a good\n>inverse operator with which one can undo the time evolution (not\n>neccesarily we, but Descartes Demon could)\n\nIs this actually so? Is this what unitarity really means?\n\nThis is very interesting.\n\nThis in effect states that given some state, one can always time-reverse\nit to an earlier state(s). I am assuming full 4D description here, time\nis immutable both backwards and forwards.\n\nI don\'t believe that. QM systems are inherently statistical. There is a\ndeep theoretical uncertainty built into the entire theory. Chaos theory\nenforces different evolutionary paths for arbitrarily close states in\nthe appropriate situation so it seems inevitable to me that time\nreversing any given complex state can produce a range of possible\nresults.\n\nThere will be ONE inverse operator which will precisely reverse any\nstate, under any conditions, but this will be one of (typically) a\nmyriad allowable inverse states that each produce a different result.\n\nSo I can give you an inverse operator that removes a TV from the BH, it\nwill likely contain all the information required to make the TV in the\nfirst place. It will be one of a myriad inverse operators that can\nremove anything you want from a black hole. Just they are terribly\nimprobable compared to thermal radiation.\n\nIf QM as currently formulated insists that the waveform of a complex\nparticle defines its temporal evolution for all time when observed by an\noutside observer then it is flawed. That implies all waveforms in the\nuniverse are forever pre determined which implies that a better theory\ncould predict the future and the uncertainty of QM is a sham.\n\n>When talking about microscopical information we are really talking\n>about the nature of the time evolution. Specifically if it is\n>invertible.\n\nIndeed. I have discussed this in various \'antiparticles are particles\ntravelling back in time\' threads. The discussion seems to peter out\npretty fast so I haven\'t been able to properly thrash it out and see why\nI am wrong.\n\nHowever I currently think antiparticles ARE particles travelling\nbackwards in time and they give an uncertainty in reverse time\nevolution. That is antiparticles (and that would include virtual\nantiparticles) CAN alter the past, and time-evolve \'backwards\' in the\nsame way as particles. These are of course very short range particles\n(so the effect is short range in time) or very rare (so having very\nlittle statistical effect) in the perceived forward timeflow of\nmacroscopic bodies. That is I do not believe that a given state now will\nuniquely and precisely predict its state in the past nor its state in\nthe future. To achieve a close approximation of that we need a detector\nthat has two states involving many particles that has two states\n(\'detected\' and \'undetected\') that have very few paths between them and\na highly improbable reverse path.\n\nWe see an immutable forward progress of time because the possible\nreverse paths of a macroscopic body are totally dominated by the\nclassical paths and so any alternative is totally improbable for the\ngroup. Paths where an electron is *here* rather than *there* have no\nobservable effect (detectors excluded).\n\nHmm, in a way its just feynman in qed writ large.\n\nSo no, I don;t agree with your statement of unitarity. There are reverse\nfunctions that will precisely reverse time, but outside the simplest\nsystems these will be one of many that reverse to a slightly different\nstate. Who is to say this other state isn\'t the one we started off with?\n\n--\nOz\nThis post is worth absolutely nothing and is probably fallacious.\n\nBTOPENWORLD address about to cease. DEMON address no longer in use.\n>>Use oz@farmeroz.port995.com<<\nozacoohdb@despammed.com still functions.\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>Frank Hellmann <Certhas@gmail.com> writes
>
>
>
>
>> 'TV' (at infinity) + BH -> BH having absorbed TV
>>
>> Should both contain the same amount of information.
>
>Well... Now you are talking Black Holes I wasn't talking about the
>Black Hole information paradox, I was just talking about the general
>stage.
OK.
>QM is of the nature described above, always the same information.
>Classical GR kind of is, though the information within the Black Hole
>is inaccesible to people outside it it still exists. Now if a
>blackhole evaporates in finite time via perfectly thermal hawking
>radiation that information is gone forever. That would violate
>unitarity in QM which basically says that there always exists a good
>inverse operator with which one can undo the time evolution (not
>neccesarily we, but Descartes Demon could)
Is this actually so? Is this what unitarity really means?
This is very interesting.
This in effect states that given some state, one can always time-reverse
it to an earlier state(s). I am assuming full 4D description here, time
is immutable both backwards and forwards.
I don't believe that. QM systems are inherently statistical. There is a
deep theoretical uncertainty built into the entire theory. Chaos theory
enforces different evolutionary paths for arbitrarily close states in
the appropriate situation so it seems inevitable to me that time
reversing any given complex state can produce a range of possible
results.
There will be ONE inverse operator which will precisely reverse any
state, under any conditions, but this will be one of (typically) a
myriad allowable inverse states that each produce a different result.
So I can give you an inverse operator that removes a TV from the BH, it
will likely contain all the information required to make the TV in the
first place. It will be one of a myriad inverse operators that can
remove anything you want from a black hole. Just they are terribly
improbable compared to thermal radiation.
If QM as currently formulated insists that the waveform of a complex
particle defines its temporal evolution for all time when observed by an
outside observer then it is flawed. That implies all waveforms in the
universe are forever pre determined which implies that a better theory
could predict the future and the uncertainty of QM is a sham.
>When talking about microscopical information we are really talking
>about the nature of the time evolution. Specifically if it is
>invertible.
Indeed. I have discussed this in various 'antiparticles are particles
travelling back in time' threads. The discussion seems to peter out
pretty fast so I haven't been able to properly thrash it out and see why
I am wrong.
However I currently think antiparticles ARE particles travelling
backwards in time and they give an uncertainty in reverse time
evolution. That is antiparticles (and that would include virtual
antiparticles) CAN alter the past, and time-evolve 'backwards' in the
same way as particles. These are of course very short range particles
(so the effect is short range in time) or very rare (so having very
little statistical effect) in the perceived forward timeflow of
macroscopic bodies. That is I do not believe that a given state now will
uniquely and precisely predict its state in the past nor its state in
the future. To achieve a close approximation of that we need a detector
that has two states involving many particles that has two states
('detected' and 'undetected') that have very few paths between them and
a highly improbable reverse path.
We see an immutable forward progress of time because the possible
reverse paths of a macroscopic body are totally dominated by the
classical paths and so any alternative is totally improbable for the
group. Paths where an electron is *here* rather than *there* have no
observable effect (detectors excluded).
Hmm, in a way its just feynman in qed writ large.
So no, I don;t agree with your statement of unitarity. There are reverse
functions that will precisely reverse time, but outside the simplest
systems these will be one of many that reverse to a slightly different
state. Who is to say this other state isn't the one we started off with?
--
Oz
This post is worth absolutely nothing and is probably fallacious.
BTOPENWORLD address about to cease. DEMON address no longer in use.
>>Use oz@farmeroz.port995.com<<
ozacoohdb@despammed.com still functions.
John Baez
Aug13-04, 07:36 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>\nIn article <20040630011102.7605542CC9@mail.netspace.net.au>,\ nGreg Egan <gregegan@netspace.zebra.net.au> wrote:\n\n>In article <37d84b42.0406290104.3402b89f@posting.google.com>, \n>daniel@elit.net (Daniel Elander) wrote:\n\n>> Someone wrote:\n\n>> > When people talk about information loss in a black hole, they are\n>> > referring to the fact that someone outside the event horizon would\n>> > have no way of knowing what is written on the piece of paper.\n\nMaybe, but this isn\'t what had physicists like Hawking worried.\n\n>> But for the outside observer it takes an infinite amount of time for\n>> the paper to fall into the black hole. So it would seem the paradox\n>> never happens.\n\nThere isn\'t really a "paradox", by the way - just some puzzles.\n\n>>Or am I wrong?\n\n>The statement "for the outside observer it takes an infinite amount of\n>time" for something to fall into a black hole is true in two senses, but\n>you have to look very carefully at what those statements are to see what\n>they tell you about information accessibility.\n\nOne certainly must get this stuff straight to appreciate what\'s\ngoing on, so it\'s good you explained that stuff!\n\nbut there\'s also other stuff one must get straight, which nobody\ncompletely understands yet - and *that\'s* why this problem is famous.\n\nThe stuff you explained is all about classical general relativity,\nnot taking quantum theory into account. Stuff falls into black holes;\nwe can argue about whether it ever gets completely in, but we can\nstraighten out the semantics of this issue and then there\'s no problem.\nThe main thing is that classically, if I drop a rock into a black hole,\nit never comes back out.\n\nSo, we lose information about the rock, or at least lose *access* to it -\na semantic fine point not worth worrying about. But, this is no big deal.\nThe rock fell into a black hole, so what do you expect? OF COURSE you\nyou lose information about it. If you want, you can say the information\nabout it is stuck inside the black hole. But there\'s no paradox, and\nnot even much of a puzzle.\n\nThe "information loss problem" starts when we try to take quantum\ntheory into account. Now it seems that black holes radiate, lose\nenergy, shrink, and eventually disappear. This leads to some\ninteresting puzzles.\n\nFor example:\n\nIf we drop a rock in, does it actually fall in before the hole evaporates?\n\nWhere, if anywhere, does the information about this rock go after\nthe black is gone? Is it lost, or does it come out in the radiation\nsomehow?\n\nNow Hawking says it comes out in the radiation.\n\nI guess some of you have already read Paul Ginsparg\'s article\nabout this:\n\nhttp://www.arxiv.org/abs/physics/0408033\n\nIf you haven\'t, you should. He\'s not convinced.\n\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>In article <20040630011102.7605542CC9@mail.netspace.net.au>,
Greg Egan <gregegan@netspace.zebra.net.au> wrote:
>In article <37d84b42.0406290104.3402b89f@posting.google.com>,
>daniel@elit.net (Daniel Elander) wrote:
>> Someone wrote:
>> > When people talk about information loss in a black hole, they are
>> > referring to the fact that someone outside the event horizon would
>> > have no way of knowing what is written on the piece of paper.
Maybe, but this isn't what had physicists like Hawking worried.
>> But for the outside observer it takes an infinite amount of time for
>> the paper to fall into the black hole. So it would seem the paradox
>> never happens.
There isn't really a "paradox", by the way - just some puzzles.
>>Or am I wrong?
>The statement "for the outside observer it takes an infinite amount of
>time" for something to fall into a black hole is true in two senses, but
>you have to look very carefully at what those statements are to see what
>they tell you about information accessibility.
One certainly must get this stuff straight to appreciate what's
going on, so it's good you explained that stuff!
but there's also other stuff one must get straight, which nobody
completely understands yet - and *that's* why this problem is famous.
The stuff you explained is all about classical general relativity,
not taking quantum theory into account. Stuff falls into black holes;
we can argue about whether it ever gets completely in, but we can
straighten out the semantics of this issue and then there's no problem.
The main thing is that classically, if I drop a rock into a black hole,
it never comes back out.
So, we lose information about the rock, or at least lose *access* to it -
a semantic fine point not worth worrying about. But, this is no big deal.
The rock fell into a black hole, so what do you expect? OF COURSE you
you lose information about it. If you want, you can say the information
about it is stuck inside the black hole. But there's no paradox, and
not even much of a puzzle.
The "information loss problem" starts when we try to take quantum
theory into account. Now it seems that black holes radiate, lose
energy, shrink, and eventually disappear. This leads to some
interesting puzzles.
For example:
If we drop a rock in, does it actually fall in before the hole evaporates?
Where, if anywhere, does the information about this rock go after
the black is gone? Is it lost, or does it come out in the radiation
somehow?
Now Hawking says it comes out in the radiation.
I guess some of you have already read Paul Ginsparg's article
about this:
http://www.arxiv.org/abs/http://www.arxiv.org/abs/physics/0408033
If you haven't, you should. He's not convinced.
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