[SOLVED] Hawking in Dublin [Archive]

John Baez

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>\nIn a surprise move, Hawking has decided to give a lecture\non the black hole information problem in Dublin this July,\nat a conference called "GR-17" where I\'ll also be speaking.\n\nI\'ve heard rumors that he believes he\'s "solved" this problem.\n\nDoes anyone know what\'s up?\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 a surprise move, Hawking has decided to give a lecture
on the black hole information problem in Dublin this July,
at a conference called "GR-17" where I'll also be speaking.

I've heard rumors that he believes he's "solved" this problem.

Does anyone know what's up?

davidoff404

Jul2-04, 06:09 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>\nYup. I spoke to one of the organizers of GR17 a few days before this\nwas publicly announced and it seems that Hawking believes that the\ninformation loss question has finally been solved. I\'m unclear as to\nthe details, but I suppose that\'s what the talk is for. I was looking\nforward to GR17 already, but even more so now that he\'s going to\naddress this. I believe the talk is on in the main hall in the RDS at\n1pm on the Wednesday.\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>Yup. I spoke to one of the organizers of GR17 a few days before this
was publicly announced and it seems that Hawking believes that the
information loss question has finally been solved. I'm unclear as to
the details, but I suppose that's what the talk is for. I was looking
forward to GR17 already, but even more so now that he's going to
address this. I believe the talk is on in the main hall in the RDS at
1pm on the Wednesday.

Nicolaas Vroom

Jul2-04, 01:57 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>"davidoff404" <davidoff404@yahoo.com> schreef in bericht\nnews:cc3ffc\\$mj9@odah37.prod.google.com. ..\n>\n> Yup. I spoke to one of the organizers of GR17 a few days before this\n> was publicly announced and it seems that Hawking believes that the\n> information loss question has finally been solved. I\'m unclear as to\n> the details, but I suppose that\'s what the talk is for. I was looking\n> forward to GR17 already, but even more so now that he\'s going to\n> address this. I believe the talk is on in the main hall in the RDS at\n> 1pm on the Wednesday.\n\nFor more information\nhttp://www.gr17.com/\n\nNicolaas Vroom\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>"davidoff404" <davidoff404@yahoo.com> schreef in bericht
news:cc3ffc$mj9@odah37.prod.google.com...
>
> Yup. I spoke to one of the organizers of GR17 a few days before this
> was publicly announced and it seems that Hawking believes that the
> information loss question has finally been solved. I'm unclear as to
> the details, but I suppose that's what the talk is for. I was looking
> forward to GR17 already, but even more so now that he's going to
> address this. I believe the talk is on in the main hall in the RDS at
> 1pm on the Wednesday.

For more information
http://www.gr17.com/

Nicolaas Vroom

marcus

Jul4-04, 07:39 AM

...Yup. I spoke to one of the organizers of GR17 a few days before this was publicly announced
and it seems that Hawking believes that the
information loss question has finally been solved.
I'm unclear as to the details, but I suppose that's what the talk is for.

I was looking forward to GR17 already, but even more so now that he's going to address this. I believe the talk is on in the main hall in the RDS at
1pm on the Wednesday.

Have a look at the May and June 2004 papers by Gambini, Porto, Pullin

http://arxiv.org/hep-th/0406260
"Realistic clocks, universal decoherence and the black hole information paradox"

http://arxiv.org/hep-th/0405183
"No black hole information puzzle in a relational universe"

Thomas Dent

Jul4-04, 09:47 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"Nicolaas Vroom" <nicolaas.vroom@pandora.be> wrote\n\n\n> > Yup. I spoke to one of the organizers of GR17 a few days before this\n> > was publicly announced and it seems that Hawking believes that the\n> > information loss question has finally been solved. I\'m unclear as to\n> > the details, but I suppose that\'s what the talk is for.\n>\n> For more information\n> http://www.gr17.com/\n>\n> Nicolaas Vroom\n\n\nHere\'s the abstract:\n\n"The Euclidean path integral over all topologically trivial metrics\ncan be done by time slicing and so is unitary when analytically\ncontinued to the Lorentzian. On the other hand, the path integral over\nall topologically non-trivial metrics is asymptotically independent of\nthe initial state. Thus the total path integral is unitary and\ninformation is not lost in the formation and evaporation of black\nholes. The way the information gets out seems to be that a true event\nhorizon never forms, just an apparent horizon."\n\nQuite cryptic. Apparently, the existence of a meaningful path integral\nquantization of GR is assumed. That part of it sounds too formal and\ntoo good to be true.\n\nWe knew since Hawking radiation that the Schwarzschild BH is a fiction\nsince real BH\'s are time-dependent and radiate, hence one should\ninclude back-reaction of the radiation (Vaidya metric). Nevertheless,\npeople went on approximating large black holes with Schwarzschild. The\ndifference between the "true event horizon" of the eternal BH and the\n"apparent event horizon" of the real thing is pretty small in most\ncircumstances. Hawking wants to say that this difference can account\nfor the missing information?\n\nI suppose it\'s not beyond the bounds of possibility... We already know\nthat some types of BH have "grey body factors", in plain English that\ntheir spectra are not exactly thermal. With correct time-dependent\nmetric and back-reaction included they could depart further from\nthermality.\n\nPresumably unitarity (along with T symmetry of GR) would imply that\none might take a load of near-thermal radiation, send it in to form an\nexpanding black hole, and suddenly if you had judged it just right the\nthing would decollapse into an expanding neutron star above the\nChandrasekhar limit - or indeed, into anything expanding out of its\nSchwarzschild radius.\n\nOf course the reason why we don\'t see such things happening would be\nnot lack of unitarity but the Second Law. Just as, even in\ntime-reversible Newtonian dynamics, entropy increases most of the\ntime.\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>"Nicolaas Vroom" <nicolaas.vroom@pandora.be> wrote

> > Yup. I spoke to one of the organizers of GR17 a few days before this
> > was publicly announced and it seems that Hawking believes that the
> > information loss question has finally been solved. I'm unclear as to
> > the details, but I suppose that's what the talk is for.
>
> For more information
> http://www.gr17.com/
>
> Nicolaas Vroom

Here's the abstract:

"The Euclidean path integral over all topologically trivial metrics
can be done by time slicing and so is unitary when analytically
continued to the Lorentzian. On the other hand, the path integral over
all topologically non-trivial metrics is asymptotically independent of
the initial state. Thus the total path integral is unitary and
information is not lost in the formation and evaporation of black
holes. The way the information gets out seems to be that a true event
horizon never forms, just an apparent horizon."

Quite cryptic. Apparently, the existence of a meaningful path integral
quantization of GR is assumed. That part of it sounds too formal and
too good to be true.

We knew since Hawking radiation that the Schwarzschild BH is a fiction
since real BH's are time-dependent and radiate, hence one should
include back-reaction of the radiation (Vaidya metric). Nevertheless,
people went on approximating large black holes with Schwarzschild. The
difference between the "true event horizon" of the eternal BH and the
"apparent event horizon" of the real thing is pretty small in most
circumstances. Hawking wants to say that this difference can account
for the missing information?

I suppose it's not beyond the bounds of possibility... We already know
that some types of BH have "grey body factors", in plain English that
their spectra are not exactly thermal. With correct time-dependent
metric and back-reaction included they could depart further from
thermality.

Presumably unitarity (along with T symmetry of GR) would imply that
one might take a load of near-thermal radiation, send it in to form an
expanding black hole, and suddenly if you had judged it just right the
thing would decollapse into an expanding neutron star above the
Chandrasekhar limit - or indeed, into anything expanding out of its
Schwarzschild radius.

Of course the reason why we don't see such things happening would be
not lack of unitarity but the Second Law. Just as, even in
time-reversible Newtonian dynamics, entropy increases most of the
time.

Urs Schreiber

Jul4-04, 09:54 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"Thomas Dent" <tdent@auth.gr> schrieb im Newsbeitrag\nnews:cb504c2c.0407040643.520e396f@pos ting.google.com...\n\n> Presumably unitarity (along with T symmetry of GR) would imply that\n> one might take a load of near-thermal radiation, send it in to form an\n> expanding black hole, and suddenly if you had judged it just right the\n> thing would decollapse into an expanding neutron star above the\n> Chandrasekhar limit - or indeed, into anything expanding out of its\n> Schwarzschild radius.\n>\n> Of course the reason why we don\'t see such things happening would be\n> not lack of unitarity but the Second Law. Just as, even in\n> time-reversible Newtonian dynamics, entropy increases most of the\n> time.\n\nI guess most everyone expects a resolution somwehat along these lines of the\napparent information loss paradox. The big question is if it can be\nunderstood from pure gravity alone - and if the Euclidean path integral\nreally is about quantization of pure gravity.\n\nYears ago Hawking has made other potentially far-reaching deductions from\nformal properties of the Euclidean path integral, concerning the arrow of\ntime. He later claimed this to be the "biggest mistake of his life".\n\nFrom reading the abstract you quoted I am somewhat reminded of the nature of\nthese claims, but I haven\'t looked at the details.\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>"Thomas Dent" <tdent@auth.gr> schrieb im Newsbeitrag
news:cb504c2c.0407040643.520e396f@posting.google.c om...

> Presumably unitarity (along with T symmetry of GR) would imply that
> one might take a load of near-thermal radiation, send it in to form an
> expanding black hole, and suddenly if you had judged it just right the
> thing would decollapse into an expanding neutron star above the
> Chandrasekhar limit - or indeed, into anything expanding out of its
> Schwarzschild radius.
>
> Of course the reason why we don't see such things happening would be
> not lack of unitarity but the Second Law. Just as, even in
> time-reversible Newtonian dynamics, entropy increases most of the
> time.

I guess most everyone expects a resolution somwehat along these lines of the
apparent information loss paradox. The big question is if it can be
understood from pure gravity alone - and if the Euclidean path integral
really is about quantization of pure gravity.

Years ago Hawking has made other potentially far-reaching deductions from
formal properties of the Euclidean path integral, concerning the arrow of
time. He later claimed this to be the "biggest mistake of his life".

From reading the abstract you quoted I am somewhat reminded of the nature of
these claims, but I haven't looked at the details.

marcus

Jul6-04, 01:47 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>\narivero Wrote:\n> http://www.dcu.ie/~nolanb/gr17_plenary.htm#hawking\n>\n>\n> Hmm is there any gossip about causal relationship between these\n> papers and Hawking\'s abstract? decoherence could be a mechanism\n> living also in the apparent horizon he mentions, even if the purpose\n> is contrary.\n\nI have not seen any gossip about that, or any suggestion of a logical\nconnection (indeed as you point out the conclusions are at odds). Both\nHawking\'s announcement and the paper by Gambini, Porto, and Pullin are\nvery recent---public within a week or so---and I was struck by the\ncoincidence in time.\n\nhttp://arxiv.org/hep-th/0406260\n\n------------------------------------------------------------------------\nThis post submitted through the LaTeX-enabled physicsforums.com\nTo view this post with LaTeX images:\nhttp://www.physicsforums.com/showthread.php?t=33532#post249657\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>arivero Wrote:
> http://www.dcu.ie/~nolanb/gr17_plenary.htm#hawking
>
>
> Hmm is there any gossip about causal relationship between these
> papers and Hawking's abstract? decoherence could be a mechanism
> living also in the apparent horizon he mentions, even if the purpose
> is contrary.

I have not seen any gossip about that, or any suggestion of a logical
connection (indeed as you point out the conclusions are at odds). Both
Hawking's announcement and the paper by Gambini, Porto, and Pullin are
very recent---public within a week or so---and I was struck by the
coincidence in time.

http://arxiv.org/http://www.arxiv.org/abs/hep-th/0406260

------------------------------------------------------------------------
This post submitted through the LaTeX-enabled physicsforums.com
To view this post with LaTeX images:
http://www.physicsforums.com/showthread.php?t=33532#post249657

Charlie Stromeyer Jr.

Jul6-04, 01:47 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>\ntdent@auth.gr (Thomas Dent) wrote in message news:\n\n> Presumably unitarity (along with T symmetry of GR) would imply that\n> one might take a load of near-thermal radiation, send it in to form an\n> expanding black hole, and suddenly if you had judged it just right the\n> thing would decollapse into an expanding neutron star above the\n> Chandrasekhar limit - or indeed, into anything expanding out of its\n> Schwarzschild radius.\n>\n> Of course the reason why we don\'t see such things happening would be\n> not lack of unitarity but the Second Law. Just as, even in\n> time-reversible Newtonian dynamics, entropy increases most of the\n> time.\n\nMany papers have been written on both the theory of and the\nexperimental observations of time-reversal symmetry being broken in\nsuperconductors. For new examples of such papers see cond-mat/0404548\nand 0405686. Some other papers have also been written about\nconjectures of phenomena like superconductivity or Cooper pairs\noccurring within neutron stars or other unusual star-like objects.\n\nWhy is it that we should expect the T-symmetry of GR as said above to\napply to black holes? Is it because the high degree of gravitational\ncollapse involved with BHs would overwhelm any somewhat sensitive\nquantum effects like superconductivity?\n\nAdditionally, it might be the case (although perhaps unlikely) that\nBHs don\'t even exist for reasons such as those mentioned in [1]. Also,\nthere is a new paper by N.E. Mavromatos called "CPT violation and\ndecoherence in quantum gravity" [gr-qc/0407005]. However, I have not\nyet looked at this paper nor any of the other papers already mentioned\nwithin this thread. Does anyone know if papers such as these or\nHawking\'s new idea would be compatible with this brief paper which I\nhave read called "Is there more to T?":\n\nhttp://arxiv.org/abs/quant-ph/0207029\n\n\n[1] http://physicsforums.com/showthread.php?t=25780\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>tdent@auth.gr (Thomas Dent) wrote in message news:

> Presumably unitarity (along with T symmetry of GR) would imply that
> one might take a load of near-thermal radiation, send it in to form an
> expanding black hole, and suddenly if you had judged it just right the
> thing would decollapse into an expanding neutron star above the
> Chandrasekhar limit - or indeed, into anything expanding out of its
> Schwarzschild radius.
>
> Of course the reason why we don't see such things happening would be
> not lack of unitarity but the Second Law. Just as, even in
> time-reversible Newtonian dynamics, entropy increases most of the
> time.

Many papers have been written on both the theory of and the
experimental observations of time-reversal symmetry being broken in
superconductors. For new examples of such papers see http://www.arxiv.org/abs/cond-mat/0404548
and 0405686. Some other papers have also been written about
conjectures of phenomena like superconductivity or Cooper pairs
occurring within neutron stars or other unusual star-like objects.

Why is it that we should expect the T-symmetry of GR as said above to
apply to black holes? Is it because the high degree of gravitational
collapse involved with BHs would overwhelm any somewhat sensitive
quantum effects like superconductivity?

Additionally, it might be the case (although perhaps unlikely) that
BHs don't even exist for reasons such as those mentioned in [1]. Also,
there is a new paper by N.E. Mavromatos called "CPT violation and
decoherence in quantum gravity" [http://www.arxiv.org/abs/gr-qc/0407005]. However, I have not
yet looked at this paper nor any of the other papers already mentioned
within this thread. Does anyone know if papers such as these or
Hawking's new idea would be compatible with this brief paper which I
have read called "Is there more to T?":

http://arxiv.org/abs/http://www.arxiv.org/abs/quant-ph/0207029

[1] http://physicsforums.com/showthread.php?t=25780

Thomas Dent

Jul9-04, 03:49 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>\nCharlie Stromeyer Jr. <cstromey@hotmail.com> wrote\n\n> > Presumably unitarity (along with T symmetry of GR) would imply that\n> > one might take a load of near-thermal radiation, send it in to form an\n> > expanding black hole, and suddenly if you had judged it just right the\n> > thing would decollapse into an expanding neutron star above the\n> > Chandrasekhar limit - or indeed, into anything expanding out of its\n> > Schwarzschild radius.\n> >\n> > Of course the reason why we don\'t see such things happening would be\n> > not lack of unitarity but the Second Law. Just as, even in\n> > time-reversible Newtonian dynamics, entropy increases most of the\n> > time.\n>\n> Many papers have been written on both the theory of and the\n> experimental observations of time-reversal symmetry being broken in\n> superconductors. For new examples of such papers see cond-mat/0404548\n> and 0405686.\n\nThis is *spontaneous* breaking by an order parameter. The underlying\nsymmetry is not broken. Just as total electric charge is still\nconserved in superconductors although U(1)_em is spontaneously broken\nby Cooper pair expectation value.\n\n\n> Why is it that we should expect the T-symmetry of GR as said above to\n> apply to black holes? Is it because the high degree of gravitational\n> collapse involved with BHs would overwhelm any somewhat sensitive\n> quantum effects like superconductivity?\n\nNo, because effects like superconductivity are not explicit symmetry\nviolation.\n\nActually, in the Standard Model QFT, there is a small and measurable\neffect of T violation (usually denoted as CP violation). However, it\nonly affects quarks. So it is probably useless to explain anything to\ndo with black holes, since we can imagine black holes even if quarks\ndid not exist.\n\nAlso, the real question in black holes is unitarity, which can be\npreserved even where there is T violation.\n\n\n> there is a new paper by N.E. Mavromatos called "CPT violation and\n> decoherence in quantum gravity" [gr-qc/0407005].\n\nI would think that Hawking works with a theory which is unitary and\nCPT-conserving, so there is no connection. Also, the other paper you\nreferenced relies on Hawking\'s previous contention that there was\ninformation loss, but now that Hawking thinks that there is no\ninformation loss, so there is no connection with that one either.\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>Charlie Stromeyer Jr. <cstromey@hotmail.com> wrote

> > Presumably unitarity (along with T symmetry of GR) would imply that
> > one might take a load of near-thermal radiation, send it in to form an
> > expanding black hole, and suddenly if you had judged it just right the
> > thing would decollapse into an expanding neutron star above the
> > Chandrasekhar limit - or indeed, into anything expanding out of its
> > Schwarzschild radius.
> >
> > Of course the reason why we don't see such things happening would be
> > not lack of unitarity but the Second Law. Just as, even in
> > time-reversible Newtonian dynamics, entropy increases most of the
> > time.
>
> Many papers have been written on both the theory of and the
> experimental observations of time-reversal symmetry being broken in
> superconductors. For new examples of such papers see http://www.arxiv.org/abs/cond-mat/0404548
> and 0405686.

This is *spontaneous* breaking by an order parameter. The underlying
symmetry is not broken. Just as total electric charge is still
conserved in superconductors although U(1)_em is spontaneously broken
by Cooper pair expectation value.

> Why is it that we should expect the T-symmetry of GR as said above to
> apply to black holes? Is it because the high degree of gravitational
> collapse involved with BHs would overwhelm any somewhat sensitive
> quantum effects like superconductivity?

No, because effects like superconductivity are not explicit symmetry
violation.

Actually, in the Standard Model QFT, there is a small and measurable
effect of T violation (usually denoted as CP violation). However, it
only affects quarks. So it is probably useless to explain anything to
do with black holes, since we can imagine black holes even if quarks
did not exist.

Also, the real question in black holes is unitarity, which can be
preserved even where there is T violation.

> there is a new paper by N.E. Mavromatos called "CPT violation and
> decoherence in quantum gravity" [http://www.arxiv.org/abs/gr-qc/0407005].

I would think that Hawking works with a theory which is unitary and
CPT-conserving, so there is no connection. Also, the other paper you
referenced relies on Hawking's previous contention that there was
information loss, but now that Hawking thinks that there is no
information loss, so there is no connection with that one either.

Charlie Stromeyer Jr.

Jul9-04, 02:52 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>\ntdent@auth.gr (Thomas Dent) wrote in message news:\n\n> This is *spontaneous* breaking by an order parameter. The underlying\n> symmetry is not broken.\n\nI am not an expert on this particular topic but what you say is also\nthe impression I have gotten too from reading an article on this topic\nin "Physics Today" and from briefly looking at the two papers I cited,\ni.e. this kind of symmetry "breaking" appears to be only what we might\ncall a surface effect rather than being a more fundamental and\nintrinsic violation of symmetry.\n\n> I would think that Hawking works with a theory which is unitary and\n> CPT-conserving, so there is no connection. Also, the other paper you\n> referenced relies on Hawking\'s previous contention that there was\n> information loss, but now that Hawking thinks that there is no\n> information loss, so there is no connection with that one either.\n\nAh, this is interesting to me because some earlier papers by different\nstring theorists such as [hep-th/9812237, 0008241 and 0108008] have\nimplied that a consideration of the questions about entropy and/or\ninformation for black holes within the context of a theory of quantum\ngravity (e.g., M-theory) might require a modification of the laws of\nQM.\n\nRegarding the last paper I cited, the same two authors examined their\nideas about information and black holes in an earlier paper solely\nabout this question called "Black Hole Evaporation Entails an\nObjective Passage of Time" [quant-ph/0012081]. On pages 10-11, they\nwrite:\n\n"Unless information is somehow retained in the evaporating black\nhole\'s particles, and unless\nthere is an unknown principle that enables these particles to produce\na white hole, our universe\ncannot be a time-reversed one. A single black hole would suffice to\nruin such a reversal. Since\nour universe contains (most probably) numerous black holes, its\nentropy increase in intrinsic,\nregardless of its initial state. [...]\n\nWhether black holes do indeed destroy information is still an open\nquestion. Our proof,\nhowever, holds for any theory or model that invokes indeterminism:\nGiven even a single truly\nrandom interaction, anywhere in the universe, the observed entropy\ngradient cannot be explained\natemporally. There is an objective sense in which low-entropy events\ngive rise to high entropy\nevents, not vice versa. Past begets future, not vice versa.\nCommon sense greets this conclusion with relief, as it rids us from\nthe absurdity of believing\nthat whatever one chooses to do is determined by some incredible\nconspiracy of numerous distant\nparticles in one\'s farthest future.\n\nOur intrinsic time-arrow also accords with the yet unexplained\nCP violation exhibited by neutral kaons, which, by CPT invariance,\nentails a basic T violation\ntoo. "It is hard to believe," says Penrose ([14], p. 583), "that\nNature is not, so to speak, \'trying\nto tell us something\' through the results of this delicate and\nbeautiful experiment." If quantum\ngravity, underlying the dynamics of black holes, indeed produces\ninformation-annihilating effects,\nit might reaffirm Penrose\'s suspicion that time-asymmetry lies at the\nvery foundations of physical law."\n\nBefore trying to understand this issue further, I\'ll wait to see what\nsomeone like John Baez posts about Hawking\'s talk at GR 17.\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>tdent@auth.gr (Thomas Dent) wrote in message news:

> This is *spontaneous* breaking by an order parameter. The underlying
> symmetry is not broken.

I am not an expert on this particular topic but what you say is also
the impression I have gotten too from reading an article on this topic
in "Physics Today" and from briefly looking at the two papers I cited,
i.e. this kind of symmetry "breaking" appears to be only what we might
call a surface effect rather than being a more fundamental and
intrinsic violation of symmetry.

> I would think that Hawking works with a theory which is unitary and
> CPT-conserving, so there is no connection. Also, the other paper you
> referenced relies on Hawking's previous contention that there was
> information loss, but now that Hawking thinks that there is no
> information loss, so there is no connection with that one either.

Ah, this is interesting to me because some earlier papers by different
string theorists such as [http://www.arxiv.org/abs/hep-th/9812237, 0008241 and 0108008] have
implied that a consideration of the questions about entropy and/or
information for black holes within the context of a theory of quantum
gravity (e.g., M-theory) might require a modification of the laws of
QM.

Regarding the last paper I cited, the same two authors examined their
ideas about information and black holes in an earlier paper solely
about this question called "Black Hole Evaporation Entails an
Objective Passage of Time" [http://www.arxiv.org/abs/quant-ph/0012081]. On pages 10-11, they
write:

"Unless information is somehow retained in the evaporating black
hole's particles, and unless
there is an unknown principle that enables these particles to produce
a white hole, our universe
cannot be a time-reversed one. A single black hole would suffice to
ruin such a reversal. Since
our universe contains (most probably) numerous black holes, its
entropy increase in intrinsic,
regardless of its initial state. [...]

Whether black holes do indeed destroy information is still an open
question. Our proof,
however, holds for any theory or model that invokes indeterminism:
Given even a single truly
random interaction, anywhere in the universe, the observed entropy
gradient cannot be explained
atemporally. There is an objective sense in which low-entropy events
give rise to high entropy
events, not vice versa. Past begets future, not vice versa.
Common sense greets this conclusion with relief, as it rids us from
the absurdity of believing
that whatever one chooses to do is determined by some incredible
conspiracy of numerous distant
particles in one's farthest future.

Our intrinsic time-arrow also accords with the yet unexplained
CP violation exhibited by neutral kaons, which, by CPT invariance,
entails a basic T violation
too. "It is hard to believe," says Penrose ([14], p. 583), "that
Nature is not, so to speak, 'trying
to tell us something' through the results of this delicate and
beautiful experiment." If quantum
gravity, underlying the dynamics of black holes, indeed produces
information-annihilating effects,
it might reaffirm Penrose's suspicion that time-asymmetry lies at the
very foundations of physical law."

Before trying to understand this issue further, I'll wait to see what
someone like John Baez posts about Hawking's talk at GR 17.

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 2 Jul 2004 05:32:32 -0400, baez@galaxy.ucr.edu (John Baez) wrote:\n\n>\n>In a surprise move, Hawking has decided to give a lecture\n>on the black hole information problem in Dublin this July,\n>at a conference called "GR-17" where I\'ll also be speaking.\n>\n>I\'ve heard rumors that he believes he\'s "solved" this problem.\n\nI chanced across this in today\'s newspaper, and yes, he\'s reported as\nsaying that he\'s solved it, and as saying that that the information is\nnot lost, and can come back out of the hole at some later time.\n\nI\'d be interested in seeing how he reckons he\'s done it ... if he\'s\nmanaged it without needing a discontinuously-fluctuating underlying\nmetric, then that really would make my ears perk up, because AFAIK,\nyou can\'t recreate indirect radiation through a gravitational horizon\nclassically without changing some of the basic relationships of\nspecial relativity.\nYou /can/ have Hawking radiation classically in a range of "dark star"\n-type models (eg, Visser\'s stuff on the subject), or indirect\ninformation transfer thorugh a sonic horizon in a particulate fluid\n(Unruh) ... and these are very straightforward and easy-to-understand\neffects ... but when you change the energy and momentum relationships\nto those of special relativity, the indirect radiation effect\ndisappears, and you lose duality with quantum mechanics in these sorts\nof situations, and I don\'t /think/ there\'s any way around that\nclassically (although with wierd higher-order acceleraiton effects,\nwho knows).\n\nSo, given that it\'s Hawking, I can\'t help wondering if, just perhaps,\nhe might have taken the "wild" step of not imposing SR-compliance on\nhis model.\n\nBut maybe he\'s not using strictly classical arguments, or perhaps its\nnot immediately clear how the new arguments translate into a physical\ndescription.\n\n\n>\n>Does anyone know what\'s up?\n>\nNope, not me!\n\nI know what he /could/ say, but have no idea if that\'s what he\'s\nactually /going/ to say. ;)\n\n\n=Erk= (Eric Baird)\n: " Trying to construct a theory of gravity using special relativity\n: is like attempting to build a jellyfish out of Lego. "\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 2 Jul 2004 05:32:32 -0400, baez@galaxy.ucr.edu (John Baez) wrote:

>
>In a surprise move, Hawking has decided to give a lecture
>on the black hole information problem in Dublin this July,
>at a conference called "GR-17" where I'll also be speaking.
>
>I've heard rumors that he believes he's "solved" this problem.

I chanced across this in today's newspaper, and yes, he's reported as
saying that he's solved it, and as saying that that the information is
not lost, and can come back out of the hole at some later time.

I'd be interested in seeing how he reckons he's done it ... if he's
managed it without needing a discontinuously-fluctuating underlying
metric, then that really would make my ears perk up, because AFAIK,
you can't recreate indirect radiation through a gravitational horizon
classically without changing some of the basic relationships of
special relativity.
You /can/ have Hawking radiation classically in a range of "dark star"
-type models (eg, Visser's stuff on the subject), or indirect
information transfer thorugh a sonic horizon in a particulate fluid
(Unruh) ... and these are very straightforward and easy-to-understand
effects ... but when you change the energy and momentum relationships
to those of special relativity, the indirect radiation effect
disappears, and you lose duality with quantum mechanics in these sorts
of situations, and I don't /think/ there's any way around that
classically (although with wierd higher-order acceleraiton effects,
who knows).

So, given that it's Hawking, I can't help wondering if, just perhaps,
he might have taken the "wild" step of not imposing SR-compliance on
his model.

But maybe he's not using strictly classical arguments, or perhaps its
not immediately clear how the new arguments translate into a physical
description.

>
>Does anyone know what's up?
>
Nope, not me!

I know what he /could/ say, but have no idea if that's what he's
actually /going/ to say. ;)

=Erk= (Eric Baird)
: " Trying to construct a theory of gravity using special relativity
: is like attempting to build a jellyfish out of Lego. "

Nicolaas Vroom

Jul16-04, 08:21 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"Nicolaas Vroom" <nicolaas.vroom@pandora.be> schreef in bericht\nnews:tdiFc.172447\\$0Y2.8607791@phobos.te lenet-ops.be...\n> "davidoff404" <davidoff404@yahoo.com> schreef in bericht\n> news:cc3ffc\\$mj9@odah37.prod.google.com...\n> >\n> > Yup. I spoke to one of the organizers of GR17 a few days before this\n> > was publicly announced and it seems that Hawking believes that the\n> > information loss question has finally been solved. I\'m unclear as to\n> > the details, but I suppose that\'s what the talk is for. I was looking\n> > forward to GR17 already, but even more so now that he\'s going to\n> > address this. I believe the talk is on in the main hall in the RDS at\n> > 1pm on the Wednesday.\n>\n> For more information\n> http://www.gr17.com/\n>\n> Nicolaas Vroom\n\nThe following document also gives more information:\nhttp://www.nature.com/news/2004/040712/full/040712-12.html\n\nWhat I do not understand is why they use the word information\nin that article when they always mean something physical.\nIn that sense you can not speak in general about any:\n"Information loss question" without specifying what.\n(Specific read the last paragraph "The great Escape")\n\nThey write: " at which point a growing torrent of radiation leaks out"\nshould that not happen with a speed greater than the speed of light\nor is that no issue ?\n\nThey write: "potentially carrying the lost information with it"\nWhat do they mean ?\n\nNicolaas Vroom\nhttp://users.pandora.be/nicvroom/\n\n\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>"Nicolaas Vroom" <nicolaas.vroom@pandora.be> schreef in bericht
news:tdiFc.172447$0Y2.8607791@phobos.telenet-ops.be...
> "davidoff404" <davidoff404@yahoo.com> schreef in bericht
> news:cc3ffc$mj9@odah37.prod.google.com...
> >
> > Yup. I spoke to one of the organizers of GR17 a few days before this
> > was publicly announced and it seems that Hawking believes that the
> > information loss question has finally been solved. I'm unclear as to
> > the details, but I suppose that's what the talk is for. I was looking
> > forward to GR17 already, but even more so now that he's going to
> > address this. I believe the talk is on in the main hall in the RDS at
> > 1pm on the Wednesday.
>
> For more information
> http://www.gr17.com/
>
> Nicolaas Vroom

The following document also gives more information:
http://www.nature.com/news/2004/040712/full/040712-12.html

What I do not understand is why they use the word information
in that article when they always mean something physical.
In that sense you can not speak in general about any:
"Information loss question" without specifying what.
(Specific read the last paragraph "The great Escape")

They write: " at which point a growing torrent of radiation leaks out"
should that not happen with a speed greater than the speed of light
or is that no issue ?

They write: "potentially carrying the lost information with it"
What do they mean ?

Nicolaas Vroom
http://users.pandora.be/nicvroom/

John Baez

Jul19-04, 04:13 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>\nHawking is giving his talk on "the information paradox"\nat GR17 in Dublin on Wednesday July 21st.\n\nThe news media have picked up on it:\n\nhttp://science.newsfactor.com/story.xhtml?story_id=25891\n\nand when I arrived, one of the conference organizers\nwas complaining that the conference has had to hire a\npublic relations firm for 4000 pounds in order to\ncontrol the reporters and other riff-raff who will\ntry to attend Hawking\'s talk. People will be checked\ncarefully to make sure they have their conference badges.\nA certain number of reporters will be allowed to attend,\nbut they will not be allowed to ask questions until the\nconference participants have had time to ask questions.\nThen there will be a time specially for reporters to\nask questions.\n\nI\'ll try to keep you all informed....\n\nOther news:\n\nThere were nice talks today on LISA and on mathematical\nresults in classical GR. Penrose\'s new book will come\nout this Friday in Britain (much later in the US). I\nsaw a draft copy of Rovelli\'s new book on quantum gravity,\nwhich will come out in September. Smolin is giving what\nhe claims to be his last talk on string theory, 10\nminutes from now.\n\n\n\n\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>Hawking is giving his talk on "the information paradox"
at GR17 in Dublin on Wednesday July 21st.

The news media have picked up on it:

http://science.newsfactor.com/story.xhtml?story_id=25891

and when I arrived, one of the conference organizers
was complaining that the conference has had to hire a
public relations firm for 4000 pounds in order to
control the reporters and other riff-raff who will
try to attend Hawking's talk. People will be checked
carefully to make sure they have their conference badges.
A certain number of reporters will be allowed to attend,
but they will not be allowed to ask questions until the
conference participants have had time to ask questions.
Then there will be a time specially for reporters to
ask questions.

I'll try to keep you all informed....

Other news:

There were nice talks today on LISA and on mathematical
results in classical GR. Penrose's new book will come
out this Friday in Britain (much later in the US). I
saw a draft copy of Rovelli's new book on quantum gravity,
which will come out in September. Smolin is giving what
he claims to be his last talk on string theory, 10
minutes from now.

Urs Schreiber

Jul19-04, 04:30 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>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag\nnews:cdgt3o\\$ib8\\$1@glue.ucr.edu... \n>\n> Hawking is giving his talk on "the information paradox"\n> at GR17 in Dublin on Wednesday July 21st.\n>\n> The news media have picked up on it:\n>\n> http://science.newsfactor.com/story.xhtml?story_id=25891\n\nMany thanks for reporting from GR 17!\n\nMaybe you find the time to give some seriously interested science\njournalists a hint that Stephen Hawking is not the only renowned\ntheoretician who has ideas about what is really going on behind the scenes\nof the "black hole information paradox".\n\nOne could cite several people (probably including yourself), but since today\nI heard a talk by him I want to in particular mention Gerard t\'Hooft\'s ideas\nabout what the "paradox" might have to do with holography. I have just\nwritten a little report on that\ntalk, which can be found at\n\nhttp://golem.ph.utexas.edu/string/archives/000400.html\n\nand which I reproduce below:\n\n\nToday Prof. Gerard t\'Hooft gave a talk at University Duisburg-Essen on Black\nHoles in Elementary Particle Physics. Maybe due to the media hype about\nHawking\'s announcement of his new idea about the black hole information\n\'paradox\', t\'Hooft decided to throw his TV set away, and not only his but\nlots of them, in fact enough that they would form a spherical shell\ncollapsing to a black hole.\n\nUsing this picture to emphasize the process in which \'known physics\',\nrepresented by well understood TV sets, passes the horizon and hence a\nborder beyond which all kinds of apparent paradoxes lurk, he talked about\nsome standard facts of high energy physics and then briefly mentioned some\nof his intriguing observations and speculations concerning physics of the\nstretched horizon, the collision of infalling particles with outgoing\nHawking radiation as well as the possibility of a deterministic hidden\nvariable model of quantum theory, which, as he says, he develops as a hobby.\n\nAfter the talk we went to a nearby Biergarten and I had the chance to ask\nsome more detailed questions.\n\nI have to admit that I haven\'t read any of t\'Hooft\'s papers concerning the\nabove mentioned issues, so I learned for the first time about his\ncalculation which indicates that, somehow, the scattering of Hawking\nradiation at infalling matter (one form - even though not the only one\nrelevant I\'d think - of back reaction which is not usually taken into\naccount in related discussions, but which certainly should be) has some\nsurprising resemblance to string scattering amplitudes - well, except for\nthe curious fact that the analogy requires a imaginary string tension.\n\nVery interesting are also his ideas about the foundations of quantum\nmechanics, holography and string theory.\n\nHe says that he expects that there is a deterministic and local (yes, local)\nhidden variable theory behind it all, which would be apparent if only we\nknew the correct degrees of freedom of nature. Since we don\'t, we only see a\nstatistical average of this deterministic process, and this translates in a\nnon-local way to the quantum mechanical wavefunction, roughly.\n\nTo me this philosophy sounded a lot like approaches by Lee Smolin to get\nquantum mechanical dynamics from the classical statistics of ensembles of\nlarge matrices that encode the deterministic interrelation of all particles\n(well, probably, if at all, of all D0 branes) in the universe. But when I\nasked Prof. t\'Hooft about this he said he wasn\'t fully familiar with\nSmolin\'s approach.\n\nAnyway, t\'Hooft\'s idea now is that the full deterministic theory has no\ninformation loss, but that on the \'coarse grained\' level of familiar quantum\ntheory information is lost all the time in virtual black holes that are\nabundant in vacuum fluctuations. The point is that, he says, this way\ninformation about degrees of freedom in the bulk diasappears. The only\ninformation left is that at some holographic boundary! This way, I think, he\ntries to give a \'dynamical\' explanation of holography.\n\nI asked if and how he sees string theory fit into this picture, and he said\nthat he thinks that since in string theory essentially only the S-matrix is\na well defined observable, and since this means that only on-shell\ninformation at the \'boundary\' is available while local physics in the bulk\nis fundamentally out of reach of present day string theory, this fits in\nperfectly with the above picture, where ordinary quantum mechanics is kind\nof an \'effective theory\' on the boundary while the true bulk theory is a\ndeterministic hidden-variable thingy.\n\nI have to say that when first confronted with speculations like this some\nalarm bells go off - but then I realize that when t\'Hooft discovered\nholography a while back this idea must have sounded - before Maldacena came\nalong and gave an explicit relization - just as weird, and now it is widely\naccepted and even standard lore.\n\nSo maybe in this little chat over a glass of beer I was actually shown a\nglimpse of the big physics picture of the future, without my poor mind being\nable to fully grasp it.\n\nOn the other hand, when asked what he thinks about how his ideas about\nstring/gauge duality and holography have come to life in string theory, he\nanswered, humbly and jokingly, that he almost fails to recognize his\noriginal ideas.\n\nThere was much more discussion, but that\'s all I am going to report here. It\nwas a big pleasure to talk to such an outstanding person as t\'Hooft is, and\nI have some things to think about now. First of all, I\'ll toss away my TV\nset...\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>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
news:cdgt3o$ib8$1@glue.ucr.edu...
>
> Hawking is giving his talk on "the information paradox"
> at GR17 in Dublin on Wednesday July 21st.
>
> The news media have picked up on it:
>
> http://science.newsfactor.com/story.xhtml?story_id=25891

Many thanks for reporting from GR 17!

Maybe you find the time to give some seriously interested science
journalists a hint that Stephen Hawking is not the only renowned
theoretician who has ideas about what is really going on behind the scenes
of the "black hole information paradox".

One could cite several people (probably including yourself), but since today
I heard a talk by him I want to in particular mention Gerard t'Hooft's ideas
about what the "paradox" might have to do with holography. I have just
written a little report on that
talk, which can be found at

http://golem.ph.utexas.edu/string/archives/000400.html

and which I reproduce below:

Today Prof. Gerard t'Hooft gave a talk at University Duisburg-Essen on Black
Holes in Elementary Particle Physics. Maybe due to the media hype about
Hawking's announcement of his new idea about the black hole information
'paradox', t'Hooft decided to throw his TV set away, and not only his but
lots of them, in fact enough that they would form a spherical shell
collapsing to a black hole.

Using this picture to emphasize the process in which 'known physics',
represented by well understood TV sets, passes the horizon and hence a
border beyond which all kinds of apparent paradoxes lurk, he talked about
some standard facts of high energy physics and then briefly mentioned some
of his intriguing observations and speculations concerning physics of the
stretched horizon, the collision of infalling particles with outgoing
Hawking radiation as well as the possibility of a deterministic hidden
variable model of quantum theory, which, as he says, he develops as a hobby.

After the talk we went to a nearby Biergarten and I had the chance to ask
some more detailed questions.

I have to admit that I haven't read any of t'Hooft's papers concerning the
above mentioned issues, so I learned for the first time about his
calculation which indicates that, somehow, the scattering of Hawking
radiation at infalling matter (one form - even though not the only one
relevant I'd think - of back reaction which is not usually taken into
account in related discussions, but which certainly should be) has some
surprising resemblance to string scattering amplitudes - well, except for
the curious fact that the analogy requires a imaginary string tension.

Very interesting are also his ideas about the foundations of quantum
mechanics, holography and string theory.

He says that he expects that there is a deterministic and local (yes, local)
hidden variable theory behind it all, which would be apparent if only we
knew the correct degrees of freedom of nature. Since we don't, we only see a
statistical average of this deterministic process, and this translates in a
non-local way to the quantum mechanical wavefunction, roughly.

To me this philosophy sounded a lot like approaches by Lee Smolin to get
quantum mechanical dynamics from the classical statistics of ensembles of
large matrices that encode the deterministic interrelation of all particles
(well, probably, if at all, of all D0 branes) in the universe. But when I
asked Prof. t'Hooft about this he said he wasn't fully familiar with
Smolin's approach.

Anyway, t'Hooft's idea now is that the full deterministic theory has no
information loss, but that on the 'coarse grained' level of familiar quantum
theory information is lost all the time in virtual black holes that are
abundant in vacuum fluctuations. The point is that, he says, this way
information about degrees of freedom in the bulk diasappears. The only
information left is that at some holographic boundary! This way, I think, he
tries to give a 'dynamical' explanation of holography.

I asked if and how he sees string theory fit into this picture, and he said
that he thinks that since in string theory essentially only the S-matrix is
a well defined observable, and since this means that only on-shell
information at the 'boundary' is available while local physics in the bulk
is fundamentally out of reach of present day string theory, this fits in
perfectly with the above picture, where ordinary quantum mechanics is kind
of an 'effective theory' on the boundary while the true bulk theory is a
deterministic hidden-variable thingy.

I have to say that when first confronted with speculations like this some
alarm bells go off - but then I realize that when t'Hooft discovered
holography a while back this idea must have sounded - before Maldacena came
along and gave an explicit relization - just as weird, and now it is widely
accepted and even standard lore.

So maybe in this little chat over a glass of beer I was actually shown a
glimpse of the big physics picture of the future, without my poor mind being
able to fully grasp it.

On the other hand, when asked what he thinks about how his ideas about
string/gauge duality and holography have come to life in string theory, he
answered, humbly and jokingly, that he almost fails to recognize his
original ideas.

There was much more discussion, but that's all I am going to report here. It
was a big pleasure to talk to such an outstanding person as t'Hooft is, and
I have some things to think about now. First of all, I'll toss away my TV
set...

Urs Schreiber

Jul22-04, 06:14 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>A transcript of the talk is now available at\n\nhttp://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt .\n\nMy comment from\n\nhttp://golem.ph.utexas.edu/string/archives/000403.html\n\nis the following:\n\nThe key argument in, well, a nutshell, is that the Euclidean path integral\nfor gravity over topologically trivial manifolds gives an invertible mapping\nfrom initial to final configuration, while that over topologically\nnon-trivial manifolds does not.\n\nHawking concludes from that that the total path integral will be unitary.\n\nI am looking forward for seeing this detailed in a paper, because I am not\nsure what to make of it. Something unitary plus something non-unitary\ncertainly does not give us something unitary, so this cannot be what is\nmeant. I would understand the final claim if we had restricted ourselfs to\nthe path integral over trivial topologies, but is this what is meant?\n\nIn the talk, the AdS/CFT correspondence is mentioned frequently. Right at\nthe beginning it seems like Hawking is crediting AdS/CFT and hence Maldacena\nfor giving the solution to the information paradox and that his talk is\nmerely supposed to elucidate how this happens in detail on the gravity side\nof the duality.\n\nWhat I find puzzling is that AdS/CFT makes the \'gravitational\' path integral\nwell defined by giving it a UV-completion, namely string theory. Hawking on\nthe other hand argues purely from the Euclidea path integral for\nEinstein-Hilbert gravity as well as its canonical quantization. But as far\nas I know the Euclidean path integral is only gradually better behaved than\nthe Lorentzian one, Wick rotation in a scenario where no background metric\nand much less timelike isometries are present is a mystery, really, and\nfinally nobody knows how and even if that canonical Hamiltonian operator of\npure gravity can be defined, which Stephen Hawking argues to generate the\nunitary time evolution.\n\nSome work by Maldacena on 3-dimensional AdS gravity is mentioned which seems\nto support the main claim that information loss and non-unitarity is related\nto nontrivial topologies, but I don\'t know about the details here.\n\nThe last but one part of the talk is concerned with a rough (looks\nhand-waving, indeed, but it is not clear to me which omissions are due to\nthe nature of the talk or actually due to unsolved problems) argument how\none could go about actually calculating a solution which shows the unitary\nformation and evaporation of something that would be a black hole for\npractical purposes.\n\nThe very last part of the talk is about merchandising in theoretical\nphysics. :-)\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>A transcript of the talk is now available at

http://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt .

My comment from

http://golem.ph.utexas.edu/string/archives/000403.html

is the following:

The key argument in, well, a nutshell, is that the Euclidean path integral
for gravity over topologically trivial manifolds gives an invertible mapping
from initial to final configuration, while that over topologically
non-trivial manifolds does not.

Hawking concludes from that that the total path integral will be unitary.

I am looking forward for seeing this detailed in a paper, because I am not
sure what to make of it. Something unitary plus something non-unitary
certainly does not give us something unitary, so this cannot be what is
meant. I would understand the final claim if we had restricted ourselfs to
the path integral over trivial topologies, but is this what is meant?

In the talk, the AdS/CFT correspondence is mentioned frequently. Right at
the beginning it seems like Hawking is crediting AdS/CFT and hence Maldacena
for giving the solution to the information paradox and that his talk is
merely supposed to elucidate how this happens in detail on the gravity side
of the duality.

What I find puzzling is that AdS/CFT makes the 'gravitational' path integral
well defined by giving it a UV-completion, namely string theory. Hawking on
the other hand argues purely from the Euclidea path integral for
Einstein-Hilbert gravity as well as its canonical quantization. But as far
as I know the Euclidean path integral is only gradually better behaved than
the Lorentzian one, Wick rotation in a scenario where no background metric
and much less timelike isometries are present is a mystery, really, and
finally nobody knows how and even if that canonical Hamiltonian operator of
pure gravity can be defined, which Stephen Hawking argues to generate the
unitary time evolution.

Some work by Maldacena on 3-dimensional AdS gravity is mentioned which seems
to support the main claim that information loss and non-unitarity is related
to nontrivial topologies, but I don't know about the details here.

The last but one part of the talk is concerned with a rough (looks
hand-waving, indeed, but it is not clear to me which omissions are due to
the nature of the talk or actually due to unsolved problems) argument how
one could go about actually calculating a solution which shows the unitary
formation and evaporation of something that would be a black hole for
practical purposes.

The very last part of the talk is about merchandising in theoretical
physics. :-)

rof@maths.tcd.ie

Jul22-04, 12:07 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"Urs Schreiber" <Urs.Schreiber@uni-essen.de> writes:\n\n>A transcript of the talk is now available at\n\n>http://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt .\n\n>My comment from\n\n>http://golem.ph.utexas.edu/string/archives/000403.html\n\n>is the following:\n\n>The key argument in, well, a nutshell, is that the Euclidean path integral\n>for gravity over topologically trivial manifolds gives an invertible mapping\n>from initial to final configuration, while that over topologically\n>non-trivial manifolds does not.\n\n>Hawking concludes from that that the total path integral will be unitary.\n\n>I am looking forward for seeing this detailed in a paper, because I am not\n>sure what to make of it. Something unitary plus something non-unitary\n>certainly does not give us something unitary, so this cannot be what is\n>meant. I would understand the final claim if we had restricted ourselfs to\n>the path integral over trivial topologies, but is this what is meant?\n\nI think he _is_ saying that something unitary plus something non-unitary\ngives something unitary, because the contribution of the sum over\nnon-trivial topologies to the sum over all topologies is zero, so the\nevolution that we see is equivalent to summing over the trivial\ntopologies only, at least for the amplitudes that we might be\ninterested in.\n\nMaybe somebody else has some clearer insight? I can\'t really say that\nI understand very it very clearly at the moment.\n\nR.\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" <Urs.Schreiber@uni-essen.de> writes:

>A transcript of the talk is now available at

>http://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt .

>My comment from

>http://golem.ph.utexas.edu/string/archives/000403.html

>is the following:

>The key argument in, well, a nutshell, is that the Euclidean path integral
>for gravity over topologically trivial manifolds gives an invertible mapping
>from initial to final configuration, while that over topologically
>non-trivial manifolds does not.

>Hawking concludes from that that the total path integral will be unitary.

>I am looking forward for seeing this detailed in a paper, because I am not
>sure what to make of it. Something unitary plus something non-unitary
>certainly does not give us something unitary, so this cannot be what is
>meant. I would understand the final claim if we had restricted ourselfs to
>the path integral over trivial topologies, but is this what is meant?

I think he _is_ saying that something unitary plus something non-unitary
gives something unitary, because the contribution of the sum over
non-trivial topologies to the sum over all topologies is zero, so the
evolution that we see is equivalent to summing over the trivial
topologies only, at least for the amplitudes that we might be
interested in.

Maybe somebody else has some clearer insight? I can't really say that
I understand very it very clearly at the moment.

R.

Urs Schreiber

Jul22-04, 12:12 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><rof@maths.tcd.ie> schrieb im Newsbeitrag\nnews:cdoroq\\$tks\\$1@lanczos.maths.t cd.ie...\n\n> I think he _is_ saying that something unitary plus something non-unitary\n> gives something unitary, because the contribution of the sum over\n> non-trivial topologies to the sum over all topologies is zero, so the\n> evolution that we see is equivalent to summing over the trivial\n> topologies only, at least for the amplitudes that we might be\n> interested in.\n\nHave a look at Jacques Distler\'s comment which appeared a minute ago:\n\nhttp://golem.ph.utexas.edu/~distler/blog/archives/000404.html .\n\nHe says that the path integral is _dominated_ (at low temperatures) by the\ntrivial topologies, and that this is indeed an old result - by Edward\nWitten:\n\nhttp://arxiv.org/abs/hep-th/9803131 !\n\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><rof@maths.tcd.ie> schrieb im Newsbeitrag
news:cdoroq$tks$1@lanczos.maths.tcd.ie...

> I think he _is_ saying that something unitary plus something non-unitary
> gives something unitary, because the contribution of the sum over
> non-trivial topologies to the sum over all topologies is zero, so the
> evolution that we see is equivalent to summing over the trivial
> topologies only, at least for the amplitudes that we might be
> interested in.

Have a look at Jacques Distler's comment which appeared a minute ago:

http://golem.ph.utexas.edu/~distler/blog/archives/000404.html .

He says that the path integral is _dominated_ (at low temperatures) by the
trivial topologies, and that this is indeed an old result - by Edward
Witten:

http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/9803131 !

John Baez

Jul25-04, 08:24 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>\nWell, Hawking\'s talk was indeed a media circus, cameras flashing\nand all! It was fairly well orchestrated, with both the other\nparticipants in the famous bet sitting up on stage: Kip Thorne\nand John Preskill. But I think I\'ll save commentary on the\n"media circus" aspect for later - it would be fun in This\nWeek\'s Finds. Right now I\'ll just talk about the technical\naspects.\n\nIn article <40ffa192\\$1@news.sentex.net>,\nUrs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n\n>The key argument in, well, a nutshell, is that the Euclidean path integral\n>for gravity over topologically trivial manifolds gives an invertible mapping\n>from initial to final configuration, while that over topologically\n>non-trivial manifolds does not.\n>\n>Hawking concludes from that that the total path integral will be unitary.\n>\n>I am looking forward for seeing this detailed in a paper, because I am not\n>sure what to make of it. Something unitary plus something non-unitary\n>certainly does not give us something unitary, so this cannot be what is\n>meant. I would understand the final claim if we had restricted ourselfs to\n>the path integral over trivial topologies, but is this what is meant?\n\nI think so!\n\nIt was certainly difficult to figure out what he meant, and\nI spent some time puzzled about the exact same issue you mention\nhere, but *perhaps* he meant something like this:\n\nWe should sum over topologies in our Euclidean path integral,\nwhich is the "only sane way to do nonperturbative quantum gravity"\n(he grinned while his computerized voice said this). For an\neternal black hole the topology of the Euclideanized spacetime\nis nontrivial, but for a black hole that evaporates it is trivial.\nIn the latter case we can foliate the Lorentzian spacetime by\nspacelike slices and compute time evolution using a Hamiltonian,\nwhich implies that time evolution in this case must be unitary.\nSo *if* the black hole evaporates there is no information loss.\n\nAfterwards Rob Mann asked a question about whether there would be\ninformation loss if we kept feeding the black hole to keep it from\nevaporating, and his grad student (the poor chap who had to field\nall the technical questions) seemed to say "yes".\n\nAnother possible interpretation is that we need to sum over\nboth topologies but that the nontrivial topology gives a vanishing\ncontribution to the asymptotics of the n-point functions far\nfrom the black hole. He did mention the phrase "exponentially\ndecaying" a couple of times.\n\nThere were very few details beyond this, except for a sketch of a\ncalculation using the ADS/CFT correspondence, which really went\nno further than the standard claim that via this correspondence\ntime evolution must be unitary.\n\nBtw, on Friday Penrose came out with his blockbuster 1000-page\nbook "The Road to Reality", and gave a talk on "fashion, faith\nand fantasy" in modern physics. You might have fun guessing\nwhich sort of physics he discussed under each category!\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>Well, Hawking's talk was indeed a media circus, cameras flashing
and all! It was fairly well orchestrated, with both the other
participants in the famous bet sitting up on stage: Kip Thorne
and John Preskill. But I think I'll save commentary on the
"media circus" aspect for later - it would be fun in This
Week's Finds. Right now I'll just talk about the technical
aspects.

In article <40ffa192$1@news.sentex.net>,
Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:

>The key argument in, well, a nutshell, is that the Euclidean path integral
>for gravity over topologically trivial manifolds gives an invertible mapping
>from initial to final configuration, while that over topologically
>non-trivial manifolds does not.
>
>Hawking concludes from that that the total path integral will be unitary.
>
>I am looking forward for seeing this detailed in a paper, because I am not
>sure what to make of it. Something unitary plus something non-unitary
>certainly does not give us something unitary, so this cannot be what is
>meant. I would understand the final claim if we had restricted ourselfs to
>the path integral over trivial topologies, but is this what is meant?

I think so!

It was certainly difficult to figure out what he meant, and
I spent some time puzzled about the exact same issue you mention
here, but *perhaps* he meant something like this:

We should sum over topologies in our Euclidean path integral,
which is the "only sane way to do nonperturbative quantum gravity"
(he grinned while his computerized voice said this). For an
eternal black hole the topology of the Euclideanized spacetime
is nontrivial, but for a black hole that evaporates it is trivial.
In the latter case we can foliate the Lorentzian spacetime by
spacelike slices and compute time evolution using a Hamiltonian,
which implies that time evolution in this case must be unitary.
So *if* the black hole evaporates there is no information loss.

Afterwards Rob Mann asked a question about whether there would be
information loss if we kept feeding the black hole to keep it from
evaporating, and his grad student (the poor chap who had to field
all the technical questions) seemed to say "yes".

Another possible interpretation is that we need to sum over
both topologies but that the nontrivial topology gives a vanishing
contribution to the asymptotics of the n-point functions far
from the black hole. He did mention the phrase "exponentially
decaying" a couple of times.

There were very few details beyond this, except for a sketch of a
calculation using the ADS/CFT correspondence, which really went
no further than the standard claim that via this correspondence
time evolution must be unitary.

Btw, on Friday Penrose came out with his blockbuster 1000-page
book "The Road to Reality", and gave a talk on "fashion, faith
and fantasy" in modern physics. You might have fun guessing
which sort of physics he discussed under each category!

Urs Schreiber

Jul25-04, 09:08 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"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag\nnews:ce0bmc\\$nar\\$1@glue.ucr.edu... \n\n> It was certainly difficult to figure out what he meant, and\n> I spent some time puzzled about the exact same issue you mention\n> here, but *perhaps* he meant something like this:\n>\n> We should sum over topologies in our Euclidean path integral,\n> which is the "only sane way to do nonperturbative quantum gravity"\n> (he grinned while his computerized voice said this). For an\n> eternal black hole the topology of the Euclideanized spacetime\n> is nontrivial, but for a black hole that evaporates it is trivial.\n> In the latter case we can foliate the Lorentzian spacetime by\n> spacelike slices and compute time evolution using a Hamiltonian,\n> which implies that time evolution in this case must be unitary.\n> So *if* the black hole evaporates there is no information loss.\n\nI am not sure I understand: We want to compute the amplitude to go from a\nstate which has lots of concentrically infally matter on a slice of\ntopologically trivial space to a state which has outgoing radiation, again\non slice of topologically trivial space.\n\nBoth the initial and the final state have trivial topology. But not all\nspacetimes interpolating between these two spatial slices do.Isn\'t the point\nthat we want to understand why the topologically nontrivial interpolations\ndon\'t contribute? Of course if we just exclude them by hand, then it is\nclear they don\'t contribute. But then we are explucing configurations on\nwhich the path integral has a saddle point and we are loosing contact to the\nclassical theory.\n\nThe fact that Hawking says that the _total_ path integral is well defined\nseems to suggest that he thinks of including the interpolations with\nnontrivial topology, but that he also thinks that somehow they don\'t\ncontribute to the result (due to some "exponential decay", apparently).\n\n> Another possible interpretation is that we need to sum over\n> both topologies but that the nontrivial topology gives a vanishing\n> contribution to the asymptotics of the n-point functions far\n> from the black hole. He did mention the phrase "exponentially\n> decaying" a couple of times.\n\nHm, why do you say "both" topologies? There are lots of topologies appearing\nin the set of all interpolating spacetimes, no?\n\nAs far as I understand it is crucial that we really only think of the\nphysical interpretation of the initial and the final state, and don\'t ever\ntry to physically interpret the spacetimes that are being summed. The\nEudlidean path integral does not allow us to make a bijection between\nEuclidean "spacetimes" and Lorentian ones. If the Euclidean path integral\nmakes any sense at all, then only as a formal trick to compute transition\namplitudes.\n\n> There were very few details beyond this, except for a sketch of a\n> calculation using the ADS/CFT correspondence, which really went\n> no further than the standard claim that via this correspondence\n> time evolution must be unitary.\n\nYes. But what\'s puzzling here is that AdS/CFT says that the time evolution\nof supergravity plus superstring fluctuations must be unitary. Does this\nimply that pure (super)gravity without the stringy degrees of freedom is\nunitary by itself?\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>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
news:ce0bmc$nar$1@glue.ucr.edu...

> It was certainly difficult to figure out what he meant, and
> I spent some time puzzled about the exact same issue you mention
> here, but *perhaps* he meant something like this:
>
> We should sum over topologies in our Euclidean path integral,
> which is the "only sane way to do nonperturbative quantum gravity"
> (he grinned while his computerized voice said this). For an
> eternal black hole the topology of the Euclideanized spacetime
> is nontrivial, but for a black hole that evaporates it is trivial.
> In the latter case we can foliate the Lorentzian spacetime by
> spacelike slices and compute time evolution using a Hamiltonian,
> which implies that time evolution in this case must be unitary.
> So *if* the black hole evaporates there is no information loss.

I am not sure I understand: We want to compute the amplitude to go from a
state which has lots of concentrically infally matter on a slice of
topologically trivial space to a state which has outgoing radiation, again
on slice of topologically trivial space.

Both the initial and the final state have trivial topology. But not all
spacetimes interpolating between these two spatial slices do.Isn't the point
that we want to understand why the topologically nontrivial interpolations
don't contribute? Of course if we just exclude them by hand, then it is
clear they don't contribute. But then we are explucing configurations on
which the path integral has a saddle point and we are loosing contact to the
classical theory.

The fact that Hawking says that the _total_ path integral is well defined
seems to suggest that he thinks of including the interpolations with
nontrivial topology, but that he also thinks that somehow they don't
contribute to the result (due to some "exponential decay", apparently).

> Another possible interpretation is that we need to sum over
> both topologies but that the nontrivial topology gives a vanishing
> contribution to the asymptotics of the n-point functions far
> from the black hole. He did mention the phrase "exponentially
> decaying" a couple of times.

Hm, why do you say "both" topologies? There are lots of topologies appearing
in the set of all interpolating spacetimes, no?

As far as I understand it is crucial that we really only think of the
physical interpretation of the initial and the final state, and don't ever
try to physically interpret the spacetimes that are being summed. The
Eudlidean path integral does not allow us to make a bijection between
Euclidean "spacetimes" and Lorentian ones. If the Euclidean path integral
makes any sense at all, then only as a formal trick to compute transition
amplitudes.

> There were very few details beyond this, except for a sketch of a
> calculation using the ADS/CFT correspondence, which really went
> no further than the standard claim that via this correspondence
> time evolution must be unitary.

Yes. But what's puzzling here is that AdS/CFT says that the time evolution
of supergravity plus superstring fluctuations must be unitary. Does this
imply that pure (super)gravity without the stringy degrees of freedom is
unitary by itself?

Italo Vecchi

Jul26-04, 03:41 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"Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<4103bed0\\$1@news.sentex.net>...\n\n> I am not sure I understand: We want to compute the amplitude to go from a\n> state which has lots of concentrically infally matter on a slice of\n> topologically trivial space to a state which has outgoing radiation, again\n> on slice of topologically trivial space.\n>\n> Both the initial and the final state have trivial topology. But not all\n> spacetimes interpolating between these two spatial slices do.Isn\'t the point\n> that we want to understand why the topologically nontrivial interpolations\n> don\'t contribute?\n\nConsider a dynamics that maps , say, integers into themselves.\nIt results from the averaged sum of two histories. History 1 is\nmultiplication by 2; 0->0, 1->2, 2->4 and so on. It is invertible and so\nit preserves information.\nHistory 2 maps everything into 0. It\'s non-invertible and it destroys all\ninformation. The averaged sum is the identity 1->1, 2->2 which\nis invertible and information-preserving.\n\nNow replace history 1 with the unitary map over trivial toplogies\nand history 2 with the non-unitary map over non-trivial topologies\nin Hawking\'s argument.\nMaybe what he\'s saying is that in the sum the latter doesn\'t\ndestroy the information carried by the former.\n\nRegards,\n\nIV\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" <Urs.Schreiber@uni-essen.de> wrote in message news:<4103bed0$1@news.sentex.net>...

> I am not sure I understand: We want to compute the amplitude to go from a
> state which has lots of concentrically infally matter on a slice of
> topologically trivial space to a state which has outgoing radiation, again
> on slice of topologically trivial space.
>
> Both the initial and the final state have trivial topology. But not all
> spacetimes interpolating between these two spatial slices do.Isn't the point
> that we want to understand why the topologically nontrivial interpolations
> don't contribute?

Consider a dynamics that maps , say, integers into themselves.
It results from the averaged sum of two histories. History 1 is
multiplication by 2; 0->0, 1->2, 2->4 and so on. It is invertible and so
it preserves information.
History 2 maps everything into . It's non-invertible and it destroys all
information. The averaged sum is the identity 1->1, 2->2 which
is invertible and information-preserving.

Now replace history 1 with the unitary map over trivial toplogies
and history 2 with the non-unitary map over non-trivial topologies
in Hawking's argument.
Maybe what he's saying is that in the sum the latter doesn't
destroy the information carried by the former.

Regards,

IV

Serenus Zeitblom

Jul26-04, 03:41 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"Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<40ffa192>\n\n> In the talk, the AdS/CFT correspondence is mentioned frequently. Right at\n> the beginning it seems like Hawking is crediting AdS/CFT and hence Maldacena\n> for giving the solution to the information paradox and that his talk is\n> merely supposed to elucidate how this happens in detail on the gravity side\n> of the duality.\n\nI think you have to read between the lines here. Any experienced\nlecturer knows that the best way to get a good audience\nresponse is to say something nice about their favorite theory.\nWhat is really in H\'s mind, I believe, is that he can do what\nAdS/CFT can do --- only better. Otherwise how do we explain his\nevident belief that *he* has solved the problem? It\'s a bit\nsad really.....by the way, cf J. Distler, I suspect that\nHawking *does* regard the negative cc as a mere technicality.\nRightly or wrongly -- I would say wrongly. And I\'m quite sure\nthat he does not care about the Lambda -> zero limit. Why should\nhe? Either our world *really* somehow-or-other has a negative\ncc, in which case there is nothing to worry about, or it *really*\nhas a positive cc, in which case all this, including the\nAdS/CFT resolution of the paradox, is irrelevant; either way, the\nzero cc limit is of little or no interest. Unless someone knows\nhow to show that the cc is *really* *exactly* zero.......\n\nWick rotation in a scenario where no background metric\n> and much less timelike isometries are present is a mystery, really,\n\nCareful. There are two separate statements here. I agree with\nyou [though H would not] that Wick rotation is pretty dubious\nwhen you don\'t have a background. When you *do*, however, not\nhaving a timelike isometry is not really a problem. In fact,\nit *has* to work for the no-timelike-isometry case in order\nto be internally consistent. By this I mean the following. I guess\nnobody doubts that it is a good idea to Wick rotate AdS, see\nEd Witten\'s great 1998 AdS/CFT paper, which is completely Euclidean.\n\nWhen you do that you get hyperbolic space. But hyperbolic space is\nfoliated by spheres --- that\'s why the boundary CFT is defined\non a sphere. Now when you rotate back to AdS, what happens to\nthose spheres? They have to turn into copies of *dS* --- not\nAdS --- because AdS is [partly] foliated by copies of dS, as\nthe brane-world people know. So for consistency we have to believe\nthat Wick rotating dS makes sense [and that the result is a sphere].\nBut as you know dS has no timelike Killing vectors. [There\nare people who think that "the only physical part of dS is the static\npatch", as I heard somebody say, but this is nonsense of course.] So\nnot having timelike Killing vectors is not a problem for Wick rotation.\n\n>\n> The very last part of the talk is about merchandising in theoretical\n> physics. :-)\n\nI found it painful to read. I was reminded of an episode in the\nlife of Erwin Schroedinger, when he made an analogous media\nsplash over what he thought was a great breakthrough; eventually\npoor S had to admit that the whole thing was a "Schweinerei". And\nthat happened in Dublin, strangely enough...........having said that,\nI am looking at my copy of "Large Scale Structure" and I still marvel\nthat anyone can be that smart; it looks like it was written by Ed. So\nlet\'s bear that in mind before we dis the Man.....\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" <Urs.Schreiber@uni-essen.de> wrote in message news:<40ffa192>

> In the talk, the AdS/CFT correspondence is mentioned frequently. Right at
> the beginning it seems like Hawking is crediting AdS/CFT and hence Maldacena
> for giving the solution to the information paradox and that his talk is
> merely supposed to elucidate how this happens in detail on the gravity side
> of the duality.

I think you have to read between the lines here. Any experienced
lecturer knows that the best way to get a good audience
response is to say something nice about their favorite theory.
What is really in H's mind, I believe, is that he can do what
AdS/CFT can do --- only better. Otherwise how do we explain his
evident belief that *he* has solved the problem? It's a bit
sad really.....by the way, cf J. Distler, I suspect that
Hawking *does* regard the negative cc as a mere technicality.
Rightly or wrongly -- I would say wrongly. And I'm quite sure
that he does not care about the \Lambda -> zero limit. Why should
he? Either our world *really* somehow-or-other has a negative
cc, in which case there is nothing to worry about, or it *really*
has a positive cc, in which case all this, including the
AdS/CFT resolution of the paradox, is irrelevant; either way, the
zero cc limit is of little or no interest. Unless someone knows
how to show that the cc is *really* *exactly* zero.......

Wick rotation in a scenario where no background metric
> and much less timelike isometries are present is a mystery, really,

Careful. There are two separate statements here. I agree with
you [though H would not] that Wick rotation is pretty dubious
when you don't have a background. When you *do*, however, not
having a timelike isometry is not really a problem. In fact,
it *has* to work for the no-timelike-isometry case in order
to be internally consistent. By this I mean the following. I guess
nobody doubts that it is a good idea to Wick rotate AdS, see
Ed Witten's great 1998 AdS/CFT paper, which is completely Euclidean.

When you do that you get hyperbolic space. But hyperbolic space is
foliated by spheres --- that's why the boundary CFT is defined
on a sphere. Now when you rotate back to AdS, what happens to
those spheres? They have to turn into copies of *dS* --- not
AdS --- because AdS is [partly] foliated by copies of dS, as
the brane-world people know. So for consistency we have to believe
that Wick rotating dS makes sense [and that the result is a sphere].
But as you know dS has no timelike Killing vectors. [There
are people who think that "the only physical part of dS is the static
patch", as I heard somebody say, but this is nonsense of course.] So
not having timelike Killing vectors is not a problem for Wick rotation.

>
> The very last part of the talk is about merchandising in theoretical
> physics. :-)

I found it painful to read. I was reminded of an episode in the
life of Erwin Schroedinger, when he made an analogous media
splash over what he thought was a great breakthrough; eventually
poor S had to admit that the whole thing was a "Schweinerei". And
that happened in Dublin, strangely enough...........having said that,
I am looking at my copy of "Large Scale Structure" and I still marvel
that anyone can be that smart; it looks like it was written by Ed. So
let's bear that in mind before we dis the Man.....

Tim S

Jul26-04, 03:41 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 25/07/2004 2:24 pm, John Baez at baez@galaxy.ucr.edu wrote:\n\n[Hawking\'s Dublin talk]\n\n> For an\n> eternal black hole the topology of the Euclideanized spacetime\n> is nontrivial, but for a black hole that evaporates it is trivial.\n\nDid he give any indication why he thought it was trivial? (Or is this\nsomething obvious that I ought to know?) It seems to me that this is simply\nassuming the problem away.\n\nTim\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 25/07/2004 2:24 pm, John Baez at baez@galaxy.ucr.edu wrote:

[Hawking's Dublin talk]

> For an
> eternal black hole the topology of the Euclideanized spacetime
> is nontrivial, but for a black hole that evaporates it is trivial.

Did he give any indication why he thought it was trivial? (Or is this
something obvious that I ought to know?) It seems to me that this is simply
assuming the problem away.

Tim

John Baez

Jul26-04, 06:12 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 <4103bed0\\$1@news.sentex.net>,\nUrs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n\n>The fact that Hawking says that the _total_ path integral is well defined\n>seems to suggest that he thinks of including the interpolations with\n>nontrivial topology, but that he also thinks that somehow they don\'t\n>contribute to the result (due to some "exponential decay", apparently).\n\nYeah, I guess that\'s the most sensible interpretation of these\nfairly cryptic remarks of his:\n\n"So in the end, everyone was right, in a way. Information is lost in\ntopologically non trivial metrics, like the eternal black hole. On the\nother hand, information is preserved in topologically trivial\nmetrics. The confusion and paradox arose because people thought\nclassically, in terms of a single topology for spacetime. It was\neither R^4, or a black hole. But the Feynman sum over histories, allows\nit to be both at once. One can not tell which topology contributed the\nobservation, any more than one can tell which slit the electron went\nthrough, in the two slits experiment. All that observation at infinity\ncan determine, is that there is a unitary mapping from initial states,\nto final, and that information is not lost."\n\nI won\'t try to say more right now, except to clarify a couple\nof things:\n\n>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag\n>news:ce0bmc\\$nar\\$1@glue.ucr.edu.. .\n\n>> Another possible interpretation is that we need to sum over\n>> both topologies but that the nontrivial topology gives a vanishing\n>> contribution to the asymptotics of the n-point functions far\n>> from the black hole. He did mention the phrase "exponentially\n>> decaying" a couple of times.\n\n>Hm, why do you say "both" topologies? There are lots of topologies appearing\n>in the set of all interpolating spacetimes, no?\n\nRight, but he only considered two: the topologically trivial one\nand the one corresponding to a single black hole. The implicit\nassumption is that others don\'t contribute enough to worry about,\neven though there are infinitely many others. He didn\'t try to\njustify this assumption, and there\'s no way to justify it given our\ncurrent limited understanding of 4d Riemannian geometry. But, this\nassumption is no more insane than summing over finitely many Feynman\ndiagrams to get answers in QFT, while ignoring the (divergent!) sum\nover infinitely many others.\n\nHe showed a picture of a cylinder labelled S^1 x S^2, corresponding to\nthe boundary of the Euclidean spacetime - time ranging over the circle\nS^1 because we\'re studying the system at a fixed temperature,\nand spacelike infinity forming the sphere S^2. The picture\nalso indicated two spacetimes having this boundary: the obvious\nboring spacetime S^1 x D^3, and black hole spacetime D^2 x S^2.\n\n(At least I *think* the diagram was labelled this way. If\nnot, it was something essentially the same, but before imposing\nboundary conditions in the time direction.)\n\nSo, I\'m not particularly worried about *this* point - his\nconsideration of just two topologies. I\'m only worried about\neverything else. :-)\n\nOne more thing:\n\n>As far as I understand it is crucial that we really only think of the\n>physical interpretation of the initial and the final state, and don\'t ever\n>try to physically interpret the spacetimes that are being summed.\n\nHmm. You sound a bit like the people who say we should never\ntry to physically interpret individual Feynman diagrams. There\'s\na morality at work here which, while noble, is not shared by the\npractical physicist. :-) And I suspect that the practical physicist\nhas a good reason for wanting to physically interpret individual\nterms in these sums - despite the dangers of doing so!\n\nIt\'s actually a very subtle and interesting issue, giving physical\nmeaning to the individual *terms* that we need to *add up* to get\na physically measurable transition amplitude. If we\'re not careful\nwe\'ll wind up discussing "decoherent histories" and the like...\n\n>The Euclidean path integral does not allow us to make a bijection between\n>Euclidean "spacetimes" and Lorentzian ones. If the Euclidean path integral\n>makes any sense at all, then only as a formal trick to compute transition\n>amplitudes.\n\nWhen people like Hawking calculate of Euclidean path integrals, they\ntypically expand around critical points of the action: Ricci-flat\nRiemannian manifolds. And these often analytically continue to Ricci-flat\nLorentzian manifolds: classical solutions of the vacuum Einstein\nequations. In the case at hand, these two solutions are Minkowski\nspacetime and the Schwarzschild metric. So, it\'s irresistable to\ngive these some physical interpretation when we\'re doing computations\nabout black hole decay - even though it\'s not obvious what that\ninterpretation should be!\n\nIndeed, I think this delicate issue has a lot to do with what Hawking\nwas talking about in the quote above.\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 <4103bed0$1@news.sentex.net>,
Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:

>The fact that Hawking says that the _total_ path integral is well defined
>seems to suggest that he thinks of including the interpolations with
>nontrivial topology, but that he also thinks that somehow they don't
>contribute to the result (due to some "exponential decay", apparently).

Yeah, I guess that's the most sensible interpretation of these
fairly cryptic remarks of his:

"So in the end, everyone was right, in a way. Information is lost in
topologically non trivial metrics, like the eternal black hole. On the
other hand, information is preserved in topologically trivial
metrics. The confusion and paradox arose because people thought
classically, in terms of a single topology for spacetime. It was
either R^4, or a black hole. But the Feynman sum over histories, allows
it to be both at once. One can not tell which topology contributed the
observation, any more than one can tell which slit the electron went
through, in the two slits experiment. All that observation at infinity
can determine, is that there is a unitary mapping from initial states,
to final, and that information is not lost."

I won't try to say more right now, except to clarify a couple
of things:

>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
>news:ce0bmc$nar$1@glue.ucr.edu...

>> Another possible interpretation is that we need to sum over
>> both topologies but that the nontrivial topology gives a vanishing
>> contribution to the asymptotics of the n-point functions far
>> from the black hole. He did mention the phrase "exponentially
>> decaying" a couple of times.

>Hm, why do you say "both" topologies? There are lots of topologies appearing
>in the set of all interpolating spacetimes, no?

Right, but he only considered two: the topologically trivial one
and the one corresponding to a single black hole. The implicit
assumption is that others don't contribute enough to worry about,
even though there are infinitely many others. He didn't try to
justify this assumption, and there's no way to justify it given our
current limited understanding of 4d Riemannian geometry. But, this
assumption is no more insane than summing over finitely many Feynman
diagrams to get answers in QFT, while ignoring the (divergent!) sum
over infinitely many others.

He showed a picture of a cylinder labelled S^1 x S^2, corresponding to
the boundary of the Euclidean spacetime - time ranging over the circle
S^1 because we're studying the system at a fixed temperature,
and spacelike infinity forming the sphere S^2. The picture
also indicated two spacetimes having this boundary: the obvious
boring spacetime S^1 x D^3, and black hole spacetime D^2 x S^2.

(At least I *think* the diagram was labelled this way. If
not, it was something essentially the same, but before imposing
boundary conditions in the time direction.)

So, I'm not particularly worried about *this* point - his
consideration of just two topologies. I'm only worried about
everything else. :-)

One more thing:

>As far as I understand it is crucial that we really only think of the
>physical interpretation of the initial and the final state, and don't ever
>try to physically interpret the spacetimes that are being summed.

Hmm. You sound a bit like the people who say we should never
try to physically interpret individual Feynman diagrams. There's
a morality at work here which, while noble, is not shared by the
practical physicist. :-) And I suspect that the practical physicist
has a good reason for wanting to physically interpret individual
terms in these sums - despite the dangers of doing so!

It's actually a very subtle and interesting issue, giving physical
meaning to the individual *terms* that we need to *add up* to get
a physically measurable transition amplitude. If we're not careful
we'll wind up discussing "decoherent histories" and the like...

>The Euclidean path integral does not allow us to make a bijection between
>Euclidean "spacetimes" and Lorentzian ones. If the Euclidean path integral
>makes any sense at all, then only as a formal trick to compute transition
>amplitudes.

When people like Hawking calculate of Euclidean path integrals, they
typically expand around critical points of the action: Ricci-flat
Riemannian manifolds. And these often analytically continue to Ricci-flat
Lorentzian manifolds: classical solutions of the vacuum Einstein
equations. In the case at hand, these two solutions are Minkowski
spacetime and the Schwarzschild metric. So, it's irresistable to
give these some physical interpretation when we're doing computations
about black hole decay - even though it's not obvious what that
interpretation should be!

Indeed, I think this delicate issue has a lot to do with what Hawking
was talking about in the quote above.

Urs Schreiber

Jul26-04, 07:46 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>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag\nnews:ce2n7h\\$d01\\$1@glue.ucr.edu... \n\n[...]\n\n> Hmm. You sound a bit like the people who say we should never\n> try to physically interpret individual Feynman diagrams.\n\n[...]\n\n> When people like Hawking calculate of Euclidean path integrals, they\n> typically expand around critical points of the action: Ricci-flat\n> Riemannian manifolds. And these often analytically continue to Ricci-flat\n> Lorentzian manifolds: classical solutions of the vacuum Einstein\n> equations.\n\nOk, agreed. I was thinking of doing the full quantum path integral. After\nall, Hawking wants to think of this as a sane way to do _non-perturbative_\nquantum gravity. But as long as we stay close to configurations which have a\nsensible analytic continuation (and I also agree with Serenus Zeitblom that\nthis does not require a timelike isometry) we may and should of course make\nuse of this.\n\nSo the claim is apparently not only that black hole dynamics in pure gravity\nis unitary, but moreover that this can be seen already by making small\nperturbations about classical Euclidean solutions.\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>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
news:ce2n7h$d01$1@glue.ucr.edu...

[...]

> Hmm. You sound a bit like the people who say we should never
> try to physically interpret individual Feynman diagrams.

[...]

> When people like Hawking calculate of Euclidean path integrals, they
> typically expand around critical points of the action: Ricci-flat
> Riemannian manifolds. And these often analytically continue to Ricci-flat
> Lorentzian manifolds: classical solutions of the vacuum Einstein
> equations.

Ok, agreed. I was thinking of doing the full quantum path integral. After
all, Hawking wants to think of this as a sane way to do _non-perturbative_
quantum gravity. But as long as we stay close to configurations which have a
sensible analytic continuation (and I also agree with Serenus Zeitblom that
this does not require a timelike isometry) we may and should of course make
use of this.

So the claim is apparently not only that black hole dynamics in pure gravity
is unitary, but moreover that this can be seen already by making small
perturbations about classical Euclidean solutions.

Creighton Hogg

Jul26-04, 10:32 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>\n\n\n\n\n\n\nOn 26 Jul 2004, Urs Schreiber wrote:\n\n> "John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag\n> news:ce2n7h\\$d01\\$1@glue.ucr.edu...\n>\n> [...]\n>\n> > Hmm. You sound a bit like the people who say we should never\n> > try to physically interpret individual Feynman diagrams.\n>\n> [...]\n>\n> > When people like Hawking calculate of Euclidean path integrals, they\n> > typically expand around critical points of the action: Ricci-flat\n> > Riemannian manifolds. And these often analytically continue to Ricci-flat\n> > Lorentzian manifolds: classical solutions of the vacuum Einstein\n> > equations.\n>\n> Ok, agreed. I was thinking of doing the full quantum path integral. After\n> all, Hawking wants to think of this as a sane way to do _non-perturbative_\n> quantum gravity. But as long as we stay close to configurations which have a\n> sensible analytic continuation (and I also agree with Serenus Zeitblom that\n> this does not require a timelike isometry) we may and should of course make\n> use of this.\n>\n> So the claim is apparently not only that black hole dynamics in pure gravity\n> is unitary, but moreover that this can be seen already by making small\n> perturbations about classical Euclidean solutions.\n\nDumb Question Alert:\n\nSorry, but what do you mean by "black hole dynamics in pure gravity..."?\nDo you mean when including no other interactions but gravity? If that\'s\nwhat you mean, I\'m not sure I understand the qualifier. If black hole\ndynamics is unitary in terms of just gravity, wouldn\'t it be unitary when\nincluding gauge interactions?\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 26 Jul 2004, Urs Schreiber wrote:

> "John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
> news:ce2n7h$d01$1@glue.ucr.edu...
>
> [...]
>
> > Hmm. You sound a bit like the people who say we should never
> > try to physically interpret individual Feynman diagrams.
>
> [...]
>
> > When people like Hawking calculate of Euclidean path integrals, they
> > typically expand around critical points of the action: Ricci-flat
> > Riemannian manifolds. And these often analytically continue to Ricci-flat
> > Lorentzian manifolds: classical solutions of the vacuum Einstein
> > equations.
>
> Ok, agreed. I was thinking of doing the full quantum path integral. After
> all, Hawking wants to think of this as a sane way to do _non-perturbative_
> quantum gravity. But as long as we stay close to configurations which have a
> sensible analytic continuation (and I also agree with Serenus Zeitblom that
> this does not require a timelike isometry) we may and should of course make
> use of this.
>
> So the claim is apparently not only that black hole dynamics in pure gravity
> is unitary, but moreover that this can be seen already by making small
> perturbations about classical Euclidean solutions.

Dumb Question Alert:

Sorry, but what do you mean by "black hole dynamics in pure gravity..."?
Do you mean when including no other interactions but gravity? If that's
what you mean, I'm not sure I understand the qualifier. If black hole
dynamics is unitary in terms of just gravity, wouldn't it be unitary when
including gauge interactions?

Creighton Hogg

Jul26-04, 10:32 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>\n\n\n\n\n\n\nOn 26 Jul 2004, John Baez wrote:\n\n>\n> In article <4103bed0\\$1@news.sentex.net>,\n> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:\n>\n> >The fact that Hawking says that the _total_ path integral is well defined\n> >seems to suggest that he thinks of including the interpolations with\n> >nontrivial topology, but that he also thinks that somehow they don\'t\n> >contribute to the result (due to some "exponential decay", apparently).\n>\n> Yeah, I guess that\'s the most sensible interpretation of these\n> fairly cryptic remarks of his:\n>\n> "So in the end, everyone was right, in a way. Information is lost in\n> topologically non trivial metrics, like the eternal black hole. On the\n> other hand, information is preserved in topologically trivial\n> metrics. The confusion and paradox arose because people thought\n> classically, in terms of a single topology for spacetime. It was\n> either R^4, or a black hole. But the Feynman sum over histories, allows\n> it to be both at once. One can not tell which topology contributed the\n> observation, any more than one can tell which slit the electron went\n> through, in the two slits experiment. All that observation at infinity\n> can determine, is that there is a unitary mapping from initial states,\n> to final, and that information is not lost."\n\nIf you don\'t mind, I\'d like to ask a bit about what the meaning is. I\'m\nrather confused about this idea of including all the possible spacetimes,\nincluding ones that *have* information loss. The only thing I can think\nof that seems close as an analogy would be virtual particle exchange in\nQFT. Here\'s how the analogy looks to me then: in QFT you exchange\nvirtual particles that are not on mass shell and violate the normal\nrelation between particle mass, momentum, and energy; however, at the\nvertices energy and momentum are strictly conserved. I suppose then the\nidea is that you have intermediate spacetimes that are not on "information\nshell" and seem to have a loss, but at the "vertices" of your dynamics\ninformation is strictly conserved.\nThis is the best way I can picture it without seeing the math, I think.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>On 26 Jul 2004, John Baez wrote:

>
> In article <4103bed0$1@news.sentex.net>,
> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote:
>
> >The fact that Hawking says that the _total_ path integral is well defined
> >seems to suggest that he thinks of including the interpolations with
> >nontrivial topology, but that he also thinks that somehow they don't
> >contribute to the result (due to some "exponential decay", apparently).
>
> Yeah, I guess that's the most sensible interpretation of these
> fairly cryptic remarks of his:
>
> "So in the end, everyone was right, in a way. Information is lost in
> topologically non trivial metrics, like the eternal black hole. On the
> other hand, information is preserved in topologically trivial
> metrics. The confusion and paradox arose because people thought
> classically, in terms of a single topology for spacetime. It was
> either R^4, or a black hole. But the Feynman sum over histories, allows
> it to be both at once. One can not tell which topology contributed the
> observation, any more than one can tell which slit the electron went
> through, in the two slits experiment. All that observation at infinity
> can determine, is that there is a unitary mapping from initial states,
> to final, and that information is not lost."

If you don't mind, I'd like to ask a bit about what the meaning is. I'm
rather confused about this idea of including all the possible spacetimes,
including ones that *have* information loss. The only thing I can think
of that seems close as an analogy would be virtual particle exchange in
QFT. Here's how the analogy looks to me then: in QFT you exchange
virtual particles that are not on mass shell and violate the normal
relation between particle mass, momentum, and energy; however, at the
vertices energy and momentum are strictly conserved. I suppose then the
idea is that you have intermediate spacetimes that are not on "information
shell" and seem to have a loss, but at the "vertices" of your dynamics
information is strictly conserved.
This is the best way I can picture it without seeing the math, I think.

Urs Schreiber

Jul26-04, 12:12 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>"Creighton Hogg" <wchogg@hep.wisc.edu> schrieb im Newsbeitrag\nnews:Pine.LNX.4.44.0407260758070.1755 6-100000@erodium.hep.wisc.edu...\n\n> Sorry, but what do you mean by "black hole dynamics in pure gravity..."?\n\nMy apologies for expressing myself so vaguely. All I meant by "pure gravity"\nis a theory of gravity which is neither (necessarily) super nor stringy.\n\n> Do you mean when including no other interactions but gravity? If that\'s\n> what you mean, I\'m not sure I understand the qualifier. If black hole\n> dynamics is unitary in terms of just gravity, wouldn\'t it be unitary when\n> including gauge interactions?\n\nProbably. But who knows?\n\nIf you believe in AdS/CFT then there is precisely one gravitational theory\nwhich is known to be unitary, and that\'s superstrings on an asymptotically\nAdS_5 times S^5 background. Everything else is hidden between the lines of\nHawking\'s talk. ;-)\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>"Creighton Hogg" <wchogg@hep.wisc.edu> schrieb im Newsbeitrag
news:Pine.LNX.4.44.0407260758070.17556-100000@erodium.hep.wisc.edu...

> Sorry, but what do you mean by "black hole dynamics in pure gravity..."?

My apologies for expressing myself so vaguely. All I meant by "pure gravity"
is a theory of gravity which is neither (necessarily) super nor stringy.

> Do you mean when including no other interactions but gravity? If that's
> what you mean, I'm not sure I understand the qualifier. If black hole
> dynamics is unitary in terms of just gravity, wouldn't it be unitary when
> including gauge interactions?

Probably. But who knows?

If you believe in AdS/CFT then there is precisely one gravitational theory
which is known to be unitary, and that's superstrings on an asymptotically
AdS_5 times S^5 background. Everything else is hidden between the lines of
Hawking's talk. ;-)

Torbj?rn Larsson

Jul26-04, 12:22 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>\nbaez@galaxy.ucr.edu (John Baez) wrote in message news:<ce0bmc\\$nar\\$1@glue.ucr.edu>...\n....\n> It was certainly difficult to figure out what he meant, and\n> I spent some time puzzled about the exact same issue you mention\n> here, but *perhaps* he meant something like this:\n....\n> So *if* the black hole evaporates there is no information loss.\n>\n> Afterwards Rob Mann asked a question about whether there would be\n> information loss if we kept feeding the black hole to keep it from\n> evaporating, and his grad student (the poor chap who had to field\n> all the technical questions) seemed to say "yes".\n\n....\nIf this interpretation is the right one, can we find an argument that\nanswer Manns problem? For example, can we feed the black hole\nindefinitely with a realistic process within the assumed universe?\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>baez@galaxy.ucr.edu (John Baez) wrote in message news:<ce0bmc$nar$1@glue.ucr.edu>...
....
> It was certainly difficult to figure out what he meant, and
> I spent some time puzzled about the exact same issue you mention
> here, but *perhaps* he meant something like this:
....
> So *if* the black hole evaporates there is no information loss.
>
> Afterwards Rob Mann asked a question about whether there would be
> information loss if we kept feeding the black hole to keep it from
> evaporating, and his grad student (the poor chap who had to field
> all the technical questions) seemed to say "yes".

....
If this interpretation is the right one, can we find an argument that
answer Manns problem? For example, can we feed the black hole
indefinitely with a realistic process within the assumed universe?

rof@maths.tcd.ie

Jul27-04, 07:52 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\nbaez@galaxy.ucr.edu (John Baez) writes:\n\n>So *if* the black hole evaporates there is no information loss.\n\n>Afterwards Rob Mann asked a question about whether there would be\n>information loss if we kept feeding the black hole to keep it from\n>evaporating, and his grad student (the poor chap who had to field\n>all the technical questions) seemed to say "yes".\n\nHmm. If that actually turns out to be true, then we might conclude from\nthis, plus the idea that information loss is really unacceptable, that\nthe universe must be expanding in such a way as to force all black holes\nto eventually evaporate. That would be slightly bizarre.\n\nR.\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>baez@galaxy.ucr.edu (John Baez) writes:

>So *if* the black hole evaporates there is no information loss.

>Afterwards Rob Mann asked a question about whether there would be
>information loss if we kept feeding the black hole to keep it from
>evaporating, and his grad student (the poor chap who had to field
>all the technical questions) seemed to say "yes".

Hmm. If that actually turns out to be true, then we might conclude from
this, plus the idea that information loss is really unacceptable, that
the universe must be expanding in such a way as to force all black holes
to eventually evaporate. That would be slightly bizarre.

R.

John Baez

Jul27-04, 12:50 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>\n\nIn article <70b38f8b.0407260917.792fc9cd@posting.google.com>, \nTorbj?rn Larsson <070-3993938@comhem.se> wrote:\n\n>baez@galaxy.ucr.edu (John Baez) wrote in message\n>news:<ce0bmc\\$nar\\$1@glue.ucr.edu>...\ n\n>> Afterwards Rob Mann asked a question about whether there would be\n>> information loss if we kept feeding the black hole to keep it from\n>> evaporating, and his grad student (the poor chap who had to field\n>> all the technical questions) seemed to say "yes".\n\n>If this interpretation is the right one, can we find an argument that\n>answer Mann\'s problem?\n\nI think Mann raised it just as a question, not a "problem" in the sense\nof a flaw in Hawking\'s new ideas. Nobody seems to mind information\nloss as long as the black hole doesn\'t evaporate away, because then you\ncan just claim the information is in the black hole. Whether this is\nsensible is another matter, I guess....\n\n>For example, can we feed the black hole indefinitely with a\n>realistic process within the assumed universe?\n\nNot if there\'s a finite amount of matter around, as would\nbe the case in an asymptotically Minkowskian universe. As\nfor a universe like ours, who knows? Right now it seems to\nhold an infinite amount of stuff and to be expanding ever faster\nin an roughly deSitter way. If so, our best bet is that it\nwill eventually be full of black holes, which will however\nthen evaporate away because their Hawking temperature will\nbe higher than the ambient temperature due to the cosmic horizon\n(about 10^{-30} kelvin). For details, see my brief summary of\nthe end of the universe:\n\nhttp://math.ucr.edu/home/baez/end.html\n\nIf so, presumably there will be no information loss in *our*\nuniverse.\n\nHowever, Hawking\'s calculations, insofar as he sketched them, were\nall done in an asymptotically *anti-deSitter* universe, where the\ncosmological constant is the opposite sign from ours. I forget if\nyou can stuff an arbitrary amount of matter in a universe like this,\nbut I guess not.\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 <70b38f8b.0407260917.792fc9cd@posting.google.com>,
Torbj?rn Larsson <070-3993938@comhem.se> wrote:

>baez@galaxy.ucr.edu (John Baez) wrote in message
>news:<ce0bmc$nar$1@glue.ucr.edu>...

>> Afterwards Rob Mann asked a question about whether there would be
>> information loss if we kept feeding the black hole to keep it from
>> evaporating, and his grad student (the poor chap who had to field
>> all the technical questions) seemed to say "yes".

>If this interpretation is the right one, can we find an argument that
>answer Mann's problem?

I think Mann raised it just as a question, not a "problem" in the sense
of a flaw in Hawking's new ideas. Nobody seems to mind information
loss as long as the black hole doesn't evaporate away, because then you
can just claim the information is in the black hole. Whether this is
sensible is another matter, I guess....

>For example, can we feed the black hole indefinitely with a
>realistic process within the assumed universe?

Not if there's a finite amount of matter around, as would
be the case in an asymptotically Minkowskian universe. As
for a universe like ours, who knows? Right now it seems to
hold an infinite amount of stuff and to be expanding ever faster
in an roughly deSitter way. If so, our best bet is that it
will eventually be full of black holes, which will however
then evaporate away because their Hawking temperature will
be higher than the ambient temperature due to the cosmic horizon
(about 10^{-30} kelvin). For details, see my brief summary of
the end of the universe:

http://math.ucr.edu/home/baez/end.html

If so, presumably there will be no information loss in *our*
universe.

However, Hawking's calculations, insofar as he sketched them, were
all done in an asymptotically *anti-deSitter* universe, where the
cosmological constant is the opposite sign from ours. I forget if
you can stuff an arbitrary amount of matter in a universe like this,
but I guess not.

John Baez

Jul27-04, 12:51 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\nIn article <ce3n44\\$dda\\$1@lanczos.maths.tcd.ie>, <rof@maths.tcd.ie> wrote:\n\n>baez@galaxy.ucr.edu (John Baez) writes:\n\n>>So *if* the black hole evaporates there is no information loss.\n\n>>Afterwards Rob Mann asked a question about whether there would be\n>>information loss if we kept feeding the black hole to keep it from\n>>evaporating, and his grad student (the poor chap who had to field\n>>all the technical questions) seemed to say "yes".\n\n>Hmm. If that actually turns out to be true, then we might conclude from\n>this, plus the idea that information loss is really unacceptable, that\n>the universe must be expanding in such a way as to force all black holes\n>to eventually evaporate. That would be slightly bizarre.\n\nI\'m not fond of your argument, because I\'d rather not take "information\nloss is unacceptable" as a *principle* - I\'d rather take whatever theory\nof physics I have and *figure out* if there\'s information loss... as\nHawking just did, for a certain theory.\n\nBut the conclusion you draw seems plausible, namely that the universe is\nexpanding in such a way that all black holes will eventually evaporate.\n\nMore precisely: according to our current best ideas on cosmology,\nonly a black hole with radius larger than the observable universe\nwill have a Hawking temperature lower than that of the limiting\ntemperature of the far-future universe - about 10^{-30} kelvin.\nSo, only enormous black holes like this could last forever and\nnot evaporate away. But, there\'s no reason to think black holes\nthis big can ever form! Maybe one can even show it\'s impossible.\n\nThey would have to be about 10^{22} solar masses or so...\nsee this for details:\n\nhttp://math.ucr.edu/home/baez/end.html\n\nBut anyway, this is not something worth losing much sleep over.\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 <ce3n44$dda$1@lanczos.maths.tcd.ie>, <rof@maths.tcd.ie> wrote:

>baez@galaxy.ucr.edu (John Baez) writes:

>>So *if* the black hole evaporates there is no information loss.

>>Afterwards Rob Mann asked a question about whether there would be
>>information loss if we kept feeding the black hole to keep it from
>>evaporating, and his grad student (the poor chap who had to field
>>all the technical questions) seemed to say "yes".

>Hmm. If that actually turns out to be true, then we might conclude from
>this, plus the idea that information loss is really unacceptable, that
>the universe must be expanding in such a way as to force all black holes
>to eventually evaporate. That would be slightly bizarre.

I'm not fond of your argument, because I'd rather not take "information
loss is unacceptable" as a *principle* - I'd rather take whatever theory
of physics I have and *figure out* if there's information loss... as
Hawking just did, for a certain theory.

But the conclusion you draw seems plausible, namely that the universe is
expanding in such a way that all black holes will eventually evaporate.

More precisely: according to our current best ideas on cosmology,
only a black hole with radius larger than the observable universe
will have a Hawking temperature lower than that of the limiting
temperature of the far-future universe - about 10^{-30} kelvin.
So, only enormous black holes like this could last forever and
not evaporate away. But, there's no reason to think black holes
this big can ever form! Maybe one can even show it's impossible.

They would have to be about 10^{22} solar masses or so...
see this for details:

http://math.ucr.edu/home/baez/end.html

But anyway, this is not something worth losing much sleep over.

Urs Schreiber

Jul27-04, 01:04 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>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag\nnews:ce61d0\\$9fi\\$1@glue.ucr.edu... \n\n> Nobody seems to mind information\n> loss as long as the black hole doesn\'t evaporate away, because then you\n> can just claim the information is in the black hole.\n\nHm, but wouldn\'t you agree that the information loss problem is not that\nsomething may drop behind a horizon. Even with stuff beyond a horizon but in\na total unitary (quantum) theory I still know, given any final state, which\ninitial state it came from. The information will be encoded somehow in the\nmicrostates of the black hole. Otherwise the theory could not be unitary.\n\nThe information "paradox" only arises if we assume that stuff falls in but\nafter a while no trace of it is left, e.g. only thermal radiation is left.\nIf this thermal radiation really has no trace left of the initial stuff, I\ncould not tell from this final state what the initial state looked like.\nThat\'s why we expect it to carry "greybody information" in reality.\n\nI believe the "information paradox" as well as related discussion suffers\nfrom the fact that its participants tend to assume all kinds of\nsemiclacssical and even classical reasoning to apply. From the no-hair\ntheorem one tends to deduce that if something "drops into the hole" its\ninformation is already lost. But that\'s not what happens in a unitary\nquantum theory. The information is rather lost when we ignore the\nmicrostates of the quantum black hole and approximate it by a classical\nblack hole without hair.\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>"John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
news:ce61d0$9fi$1@glue.ucr.edu...

> Nobody seems to mind information
> loss as long as the black hole doesn't evaporate away, because then you
> can just claim the information is in the black hole.

Hm, but wouldn't you agree that the information loss problem is not that
something may drop behind a horizon. Even with stuff beyond a horizon but in
a total unitary (quantum) theory I still know, given any final state, which
initial state it came from. The information will be encoded somehow in the
microstates of the black hole. Otherwise the theory could not be unitary.

The information "paradox" only arises if we assume that stuff falls in but
after a while no trace of it is left, e.g. only thermal radiation is left.
If this thermal radiation really has no trace left of the initial stuff, I
could not tell from this final state what the initial state looked like.
That's why we expect it to carry "greybody information" in reality.

I believe the "information paradox" as well as related discussion suffers
from the fact that its participants tend to assume all kinds of
semiclacssical and even classical reasoning to apply. From the no-hair
theorem one tends to deduce that if something "drops into the hole" its
information is already lost. But that's not what happens in a unitary
quantum theory. The information is rather lost when we ignore the
microstates of the quantum black hole and approximate it by a classical
black hole without hair.

Serenus Zeitblom

Jul28-04, 03:58 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\nbaez@galaxy.ucr.edu (John Baez) wrote in message news:<ce61d0\\$9fi\\$1@glue.ucr.edu>...\n>\n> >For example, can we feed the black hole indefinitely with a\n> >realistic process within the assumed universe?\n>\n> Not if there\'s a finite amount of matter around, as would\n> be the case in an asymptotically Minkowskian universe.\n\nI suppose that you can imagine\nfeeding it with a finite diet in ever-decreasing meals which\nextend for an infinite time; the restaurant at the end\nof the Universe. Oh, he said "realistic". Sorry.\n\n\nAs\n> for a universe like ours, who knows? Right now it seems to\n> hold an infinite amount of stuff\n\nNo, it doesn\'t. Nobody knows whether the Universe is finite,\nthough a surprising number of experts think they do. Ted\nBunn set us straight on this a few months ago. Bottom line:\nwe just don\'t know.\n\n\nand to be expanding ever faster\n> in an roughly deSitter way.\n\nSure. But see http://arxiv.org/abs/astro-ph/0307185\nThere\'s still good reason to doubt that we are going\nto be diluted to death. Again, bottom line: we just\ndon\'t know.\n\n>\n> However, Hawking\'s calculations, insofar as he sketched them, were\n> all done in an asymptotically *anti-deSitter* universe, where the\n> cosmological constant is the opposite sign from ours. I forget if\n> you can stuff an arbitrary amount of matter in a universe like this,\n> but I guess not.\n\nWell, AdS as usually understood has infinitely large spatial sections.\nThey are just hyperbolic spaces. But as you know, if you allow complicated\ntopology these can be made to have finite volume; they can even be made\ncompact. Anyway if we stick to ordinary AdS, in theory we can put in an infinite\namount of matter if we keep it at a low enough density so as not to\ndisturb the AdS geometry too much. But this last bit is the kicker:\nsee http://arxiv.org/abs/hep-th/0406134\n\nSeems that AdS might not survive having even a finite amount of\nstuff crammed into it! I guess the inhabitants of AdS better hope\nthat they can push everything into black holes and thereby somehow\nprevent a total disaster. So maybe the question we are talking\nabout is not as irrelevant as it seems....\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>baez@galaxy.ucr.edu (John Baez) wrote in message news:<ce61d0$9fi$1@glue.ucr.edu>...
>
> >For example, can we feed the black hole indefinitely with a
> >realistic process within the assumed universe?
>
> Not if there's a finite amount of matter around, as would
> be the case in an asymptotically Minkowskian universe.

I suppose that you can imagine
feeding it with a finite diet in ever-decreasing meals which
extend for an infinite time; the restaurant at the end
of the Universe. Oh, he said "realistic". Sorry.

As
> for a universe like ours, who knows? Right now it seems to
> hold an infinite amount of stuff

No, it doesn't. Nobody knows whether the Universe is finite,
though a surprising number of experts think they do. Ted
Bunn set us straight on this a few months ago. Bottom line:
we just don't know.

and to be expanding ever faster
> in an roughly deSitter way.

Sure. But see http://arxiv.org/abs/http://www.arxiv.org/abs/astro-ph/0307185
There's still good reason to doubt that we are going
to be diluted to death. Again, bottom line: we just
don't know.

>
> However, Hawking's calculations, insofar as he sketched them, were
> all done in an asymptotically *anti-deSitter* universe, where the
> cosmological constant is the opposite sign from ours. I forget if
> you can stuff an arbitrary amount of matter in a universe like this,
> but I guess not.

Well, AdS as usually understood has infinitely large spatial sections.
They are just hyperbolic spaces. But as you know, if you allow complicated
topology these can be made to have finite volume; they can even be made
compact. Anyway if we stick to ordinary AdS, in theory we can put in an infinite
amount of matter if we keep it at a low enough density so as not to
disturb the AdS geometry too much. But this last bit is the kicker:
see http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0406134

Seems that AdS might not survive having even a finite amount of
stuff crammed into it! I guess the inhabitants of AdS better hope
that they can push everything into black holes and thereby somehow
prevent a total disaster. So maybe the question we are talking
about is not as irrelevant as it seems....

ebunn@lfa221051.richmond.edu

Jul28-04, 03:59 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\nIn article <ce61d0\\$9fi\\$1@glue.ucr.edu>, John Baez <baez@galaxy.ucr.edu> wrote:\n>\n>\n>In article <70b38f8b.0407260917.792fc9cd@posting.google.com>, \n>Torbj?rn Larsson <070-3993938@comhem.se> wrote:\n\n>>For example, can we feed the black hole indefinitely with a\n>>realistic process within the assumed universe?\n>\n>Not if there\'s a finite amount of matter around, as would\n>be the case in an asymptotically Minkowskian universe.\n\nIs this obvious? Why can\'t you catch the outgoing Hawking radiation\nand feed it back in?\n\n-Ted\n\n--\n[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]\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 <ce61d0$9fi$1@glue.ucr.edu>, John Baez <baez@galaxy.ucr.edu> wrote:
>
>
>In article <70b38f8b.0407260917.792fc9cd@posting.google.com>,
>Torbj?rn Larsson <070-3993938@comhem.se> wrote:

>>For example, can we feed the black hole indefinitely with a
>>realistic process within the assumed universe?
>
>Not if there's a finite amount of matter around, as would
>be the case in an asymptotically Minkowskian universe.

Is this obvious? Why can't you catch the outgoing Hawking radiation
and feed it back in?

-Ted

--
[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]

Italo Vecchi

Jul28-04, 07:28 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\nrof@maths.tcd.ie wrote in message news:<cdoroq\\$tks\\$1@lanczos.maths.tcd.ie>...\n\ n> I think he _is_ saying that something unitary plus something non-unitary\n> gives something unitary, because the contribution of the sum over\n> non-trivial topologies to the sum over all topologies is zero, so the\n> evolution that we see is equivalent to summing over the trivial\n> topologies only, at least for the amplitudes that we might be\n> interested in.\n>\n\nNot necessarily zero, but constant. Something unitary plus something\nnon-unitary may well give us something unitary , like the sum of the\nidentity and a constant map .\n\nWhat Hawking is saying is that paths over non-trivial topologies lose\nALL information (" the path integral over all topologically\nnon-trivial metrics [i.e. over black holes] will be independent of the\nstate on the initial surface."[1], i.e. it\'s a constant map) and so\nthey can\'t do any harm to the information carried by the paths over\ntrivial metrics (which are there because "one can\'t be sure a black\nhole forms"[1]).\n\nBy the way, I just realised that my earlier counterexample [2] was\nalready in your remarks.\n\nIV\n\n\n[1] http://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt\n[2] http://physicsforums.com/showthread.php?t=33532&page=2\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>rof@maths.tcd.ie wrote in message news:<cdoroq$tks$1@lanczos.maths.tcd.ie>...

> I think he _is_ saying that something unitary plus something non-unitary
> gives something unitary, because the contribution of the sum over
> non-trivial topologies to the sum over all topologies is zero, so the
> evolution that we see is equivalent to summing over the trivial
> topologies only, at least for the amplitudes that we might be
> interested in.
>

Not necessarily zero, but constant. Something unitary plus something
non-unitary may well give us something unitary , like the sum of the
identity and a constant map .

What Hawking is saying is that paths over non-trivial topologies lose
ALL information (" the path integral over all topologically
non-trivial metrics [i.e. over black holes] will be independent of the
state on the initial surface."[1], i.e. it's a constant map) and so
they can't do any harm to the information carried by the paths over
trivial metrics (which are there because "one can't be sure a black
hole forms"[1]).

By the way, I just realised that my earlier counterexample [2] was
already in your remarks.

IV

[1] http://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt
[2] http://physicsforums.com/showthread.php?t=33532&page=2

Urs Schreiber

Jul28-04, 07:31 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>"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\nnews:61789046.0407280402.de5540d@post ing.google.com...\n\n> Not necessarily zero, but constant. Something unitary plus something\n> non-unitary may well give us something unitary , like the sum of the\n> identity and a constant map .\n>\n> What Hawking is saying is that paths over non-trivial topologies lose\n> ALL information (" the path integral over all topologically\n> non-trivial metrics [i.e. over black holes] will be independent of the\n> state on the initial surface."[1], i.e. it\'s a constant map) and so\n> they can\'t do any harm to the information carried by the paths over\n> trivial metrics (which are there because "one can\'t be sure a black\n> hole forms"[1]).\n\nSo what if my initial state has nontrivial topology? Am I to deduce that in\nthis case the amplitude to any final state is a constant? This would loose\nme information about the initial state.\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>"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
news:61789046.0407280402.de5540d@posting.google.co m...

> Not necessarily zero, but constant. Something unitary plus something
> non-unitary may well give us something unitary , like the sum of the
> identity and a constant map .
>
> What Hawking is saying is that paths over non-trivial topologies lose
> ALL information (" the path integral over all topologically
> non-trivial metrics [i.e. over black holes] will be independent of the
> state on the initial surface."[1], i.e. it's a constant map) and so
> they can't do any harm to the information carried by the paths over
> trivial metrics (which are there because "one can't be sure a black
> hole forms"[1]).

So what if my initial state has nontrivial topology? Am I to deduce that in
this case the amplitude to any final state is a constant? This would loose
me information about the initial state.

Italo Vecchi

Jul28-04, 02:06 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\n\n"Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<41079ca8\\$1@news.sentex.net>...\n> "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\n> news:61789046.0407280402.de5540d@posting.google.co m...\n....\n> > What Hawking is saying is that paths over non-trivial topologies lose\n> > ALL information (" the path integral over all topologically\n> > non-trivial metrics [i.e. over black holes] will be independent of the\n> > state on the initial surface."[1], i.e. it\'s a constant map) and so\n> > they can\'t do any harm to the information carried by the paths over\n> > trivial metrics (which are there because "one can\'t be sure a black\n> > hole forms"[1]).\n>\n> So what if my initial state has nontrivial topology? Am I to deduce that in\n> this case the amplitude to any final state is a constant? This would loose\n> me information about the initial state.\n\nI am not sure what you mean by "my initial state". If "your" initial\nstate has non-trivial topology you are straddling a black hole . Is\nthis what you mean?\nI don\'t think a human observer can straddle a blackhole, even in\nprinciple. If you fall into a blackhole you may either realise that it\nwasn\'t a blackhole after all and that the topology is trivial and\neverything is unitary or ... . Well , we would miss your posts.\n\nCheers,\n\nIV\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" <Urs.Schreiber@uni-essen.de> wrote in message news:<41079ca8$1@news.sentex.net>...
> "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
> news:61789046.0407280402.de5540d@posting.google.co m...
....
> > What Hawking is saying is that paths over non-trivial topologies lose
> > ALL information (" the path integral over all topologically
> > non-trivial metrics [i.e. over black holes] will be independent of the
> > state on the initial surface."[1], i.e. it's a constant map) and so
> > they can't do any harm to the information carried by the paths over
> > trivial metrics (which are there because "one can't be sure a black
> > hole forms"[1]).
>
> So what if my initial state has nontrivial topology? Am I to deduce that in
> this case the amplitude to any final state is a constant? This would loose
> me information about the initial state.

I am not sure what you mean by "my initial state". If "your" initial
state has non-trivial topology you are straddling a black hole . Is
this what you mean?
I don't think a human observer can straddle a blackhole, even in
principle. If you fall into a blackhole you may either realise that it
wasn't a blackhole after all and that the topology is trivial and
everything is unitary or ... . Well , we would miss your posts.

Cheers,

IV

Urs Schreiber

Jul28-04, 02:14 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"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\nnews:61789046.0407281052.5ea1f95a@pos ting.google.com...\n\n> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message\nnews:<41079ca8\\$1@news.sentex.net>...\n> > "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\n> > news:61789046.0407280402.de5540d@posting.google.co m...\n\n> > So what if my initial state has nontrivial topology? Am I to deduce that\nin\n> > this case the amplitude to any final state is a constant? This would\nloose\n> > me information about the initial state.\n>\n> I am not sure what you mean by "my initial state".\n\nI mean THE initial state.\n\nWe are talking about computing the path integral of gravity with a\nprescribed initial state in the far past and some final state in the far\nfuture as boundary condition. The question is: Is the matrix which is\nobtained by writing the result of this path integral in the entry\ncorresponding to the given initial and final state invertible or not.\n\nHaking argues that all paths=spacetimes between initial and final\nstates=spatial slices which involve a nontrivial topology give vanishing\ncontribution to this entry.\n\nBut if the state in the past has nontrivial spatial topology all spacetimes\nsummed over in the path integral must share this property at least on some\nslice. Therefore by Hawking\'s argument the result should be 0.\n\nThis would mean that the amplitude to go from a black hole in the past to\n_anything_ in the future would be 0.\n\nI am asking if this is what Hawking means, and if not, how he can evade this\nconclusion given his other arguments.\n\n> If "your" initial\n> state has non-trivial topology you are straddling a black hole .\n\nOh, I see. No, I didn\'t mean to include myself as part of the state! :-)\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>"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
news:61789046.0407281052.5ea1f95a@posting.google.c om...

> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message
news:<41079ca8$1@news.sentex.net>...
> > "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
> > news:61789046.0407280402.de5540d@posting.google.co m...

> > So what if my initial state has nontrivial topology? Am I to deduce that
in
> > this case the amplitude to any final state is a constant? This would
loose
> > me information about the initial state.
>
> I am not sure what you mean by "my initial state".

I mean THE initial state.

We are talking about computing the path integral of gravity with a
prescribed initial state in the far past and some final state in the far
future as boundary condition. The question is: Is the matrix which is
obtained by writing the result of this path integral in the entry
corresponding to the given initial and final state invertible or not.

Haking argues that all paths=spacetimes between initial and final
states=spatial slices which involve a nontrivial topology give vanishing
contribution to this entry.

But if the state in the past has nontrivial spatial topology all spacetimes
summed over in the path integral must share this property at least on some
slice. Therefore by Hawking's argument the result should be .

This would mean that the amplitude to go from a black hole in the past to
_anything_ in the future would be .

I am asking if this is what Hawking means, and if not, how he can evade this
conclusion given his other arguments.

> If "your" initial
> state has non-trivial topology you are straddling a black hole .

Oh, I see. No, I didn't mean to include myself as part of the state! :-)

Italo Vecchi

Jul29-04, 07:33 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"Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<4107fb13\\$1@news.sentex.net>...\n\n....\n\n > Haking argues that all paths=spacetimes between initial and final\n> states=spatial slices which involve a nontrivial topology give vanishing\n> contribution to this entry.\n>\n> But if the state in the past has nontrivial spatial topology all spacetimes\n> summed over in the path integral must share this property at least on some\n> slice. Therefore by Hawking\'s argument the result should be 0.\n>\n> This would mean that the amplitude to go from a black hole in the past to\n> _anything_ in the future would be 0.\n>\n\nIf you draw your initial state by hand so that it has ONLY nontrivial\nspatial topologies , yes, but that\'s unphysical. In reality you can\'t\nbe sure there\'s a blackhole in your initial state either.\n\nIV\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" <Urs.Schreiber@uni-essen.de> wrote in message news:<4107fb13$1@news.sentex.net>...

....

> Haking argues that all paths=spacetimes between initial and final
> states=spatial slices which involve a nontrivial topology give vanishing
> contribution to this entry.
>
> But if the state in the past has nontrivial spatial topology all spacetimes
> summed over in the path integral must share this property at least on some
> slice. Therefore by Hawking's argument the result should be .
>
> This would mean that the amplitude to go from a black hole in the past to
> _anything_ in the future would be .
>

If you draw your initial state by hand so that it has ONLY nontrivial
spatial topologies , yes, but that's unphysical. In reality you can't
be sure there's a blackhole in your initial state either.

IV

Urs Schreiber

Jul29-04, 08:14 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>"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\nnews:61789046.0407290334.501fa47e@pos ting.google.com...\n\n> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message\nnews:<4107fb13\\$1@news.sentex.net>...\n\ n> > Haking argues that all paths=spacetimes between initial and final\n> > states=spatial slices which involve a nontrivial topology give vanishing\n> > contribution to this entry.\n> >\n> > But if the state in the past has nontrivial spatial topology all\nspacetimes\n> > summed over in the path integral must share this property at least on\nsome\n> > slice. Therefore by Hawking\'s argument the result should be 0.\n> >\n> > This would mean that the amplitude to go from a black hole in the past\nto\n> > _anything_ in the future would be 0.\n> >\n>\n> If you draw your initial state by hand so that it has ONLY nontrivial\n> spatial topologies , yes, but that\'s unphysical. In reality you can\'t\n> be sure there\'s a blackhole in your initial state either.\n\nTaking superpositions does not help you here. If the S-matrix maps all\nstates with nontrivial topology to 0 then it has "columns" with all entries\n0s and won\'t be invertible. In other words, even if you start with a\nsuperposition of a state with and without trivial topology, as you propose,\nin the end you have always lost part of the information.\n\nAs an illustration, think of a 2x2 matrix M with entry M_11 = 1 and all\nother entries equal to 0. The element [1,0]^T of the vector space that this\nmatrix acts on is analogous to a state with trivial topology. It is\n"unitarily mapped" to a state with trivial topology. The other element\n[0,1]^T is analogous to a state with nontrivial topology. It is send to the\n0-element [0,0]^T no matter what.\n\nNow let v be any superposition of [1,0]^T and [0,1]^T, analogous to an\ninitial state the way you had in mind. It is mapped to the final state Mv\n(application of M on v). But Mv is always of the form [a,0]^T and\nindependent of the second component of v. Therefore the information about\nthis second component is always lost. M is not a unitary "propagation\noperator".\n\nExcept for the fact that we should be thinking of _much_ larger matrices,\nthis is precisely the issue that we are talking about.\n\nAnd it is also confirmed by Hawking himself, when he writes\n\n> One is thus led to the remarkable result that late time amplitudes of the\npath integral > over a topologically non trivial metric, are independent of\nthe initial state. This was\n> noticed by Maldacena in the case of asymptotically anti-deSitter in 3d.\n\nDoes anyone know the precisese reference of this result by Maldacena? Is it\nreally the path integral which is independent of the initial state, or just\nthe correlation functions? As in:\n\n> Maldacena was able to show that topologically trivial metrics\n> have correlation functions that do not decay\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>"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
news:61789046.0407290334.501fa47e@posting.google.c om...

> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message
news:<4107fb13$1@news.sentex.net>...

> > Haking argues that all paths=spacetimes between initial and final
> > states=spatial slices which involve a nontrivial topology give vanishing
> > contribution to this entry.
> >
> > But if the state in the past has nontrivial spatial topology all
spacetimes
> > summed over in the path integral must share this property at least on
some
> > slice. Therefore by Hawking's argument the result should be .
> >
> > This would mean that the amplitude to go from a black hole in the past
to
> > _anything_ in the future would be .
> >
>
> If you draw your initial state by hand so that it has ONLY nontrivial
> spatial topologies , yes, but that's unphysical. In reality you can't
> be sure there's a blackhole in your initial state either.

Taking superpositions does not help you here. If the S-matrix maps all
states with nontrivial topology to then it has "columns" with all entries
0s and won't be invertible. In other words, even if you start with a
superposition of a state with and without trivial topology, as you propose,
in the end you have always lost part of the information.

As an illustration, think of a 2x2 matrix M with entry M_{11} = 1 and all
other entries equal to . The element [1,0]^T of the vector space that this
matrix acts on is analogous to a state with trivial topology. It is
"unitarily mapped" to a state with trivial topology. The other element
[0,1]^T is analogous to a state with nontrivial topology. It is send to the
0-element [0,0]^T no matter what.

Now let v be any superposition of [1,0]^T and [0,1]^T, analogous to an
initial state the way you had in mind. It is mapped to the final state Mv
(application of M on v). But Mv is always of the form [a,0]^T and
independent of the second component of v. Therefore the information about
this second component is always lost. M is not a unitary "propagation
operator".

Except for the fact that we should be thinking of _much_ larger matrices,
this is precisely the issue that we are talking about.

And it is also confirmed by Hawking himself, when he writes

> One is thus led to the remarkable result that late time amplitudes of the
path integral > over a topologically non trivial metric, are independent of
the initial state. This was
> noticed by Maldacena in the case of asymptotically anti-deSitter in 3d.

Does anyone know the precisese reference of this result by Maldacena? Is it
really the path integral which is independent of the initial state, or just
the correlation functions? As in:

> Maldacena was able to show that topologically trivial metrics
> have correlation functions that do not decay

Creighton Hogg

Jul29-04, 08:16 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\nOn 29 Jul 2004, Italo Vecchi wrote:\n>\n> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<4107fb13\\$1@news.sentex.net>...\n> > But if the state in the past has nontrivial spatial topology all spacetimes\n> > summed over in the path integral must share this property at least on some\n> > slice. Therefore by Hawking\'s argument the result should be 0.\n> >\n> > This would mean that the amplitude to go from a black hole in the past to\n> > _anything_ in the future would be 0.\n> >\n>\n> If you draw your initial state by hand so that it has ONLY nontrivial\n> spatial topologies , yes, but that\'s unphysical. In reality you can\'t\n> be sure there\'s a blackhole in your initial state either.\n\nSorry, but can you explain a little more about why that\'s an unphysical\ninitial state assumption? I\'m not quite seeing it.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>On 29 Jul 2004, Italo Vecchi wrote:
>
> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<4107fb13$1@news.sentex.net>...
> > But if the state in the past has nontrivial spatial topology all spacetimes
> > summed over in the path integral must share this property at least on some
> > slice. Therefore by Hawking's argument the result should be .
> >
> > This would mean that the amplitude to go from a black hole in the past to
> > _anything_ in the future would be .
> >
>
> If you draw your initial state by hand so that it has ONLY nontrivial
> spatial topologies , yes, but that's unphysical. In reality you can't
> be sure there's a blackhole in your initial state either.

Sorry, but can you explain a little more about why that's an unphysical
initial state assumption? I'm not quite seeing it.

Creighton Hogg

Jul29-04, 08:41 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 29 Jul 2004, Urs Schreiber wrote:\n\n> "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\n> news:61789046.0407290334.501fa47e@posting.google.c om...\n> >\n> > If you draw your initial state by hand so that it has ONLY nontrivial\n> > spatial topologies , yes, but that\'s unphysical. In reality you can\'t\n> > be sure there\'s a blackhole in your initial state either.\n>\n> Taking superpositions does not help you here. If the S-matrix maps all\n> states with nontrivial topology to 0 then it has "columns" with all entries\n> 0s and won\'t be invertible. In other words, even if you start with a\n> superposition of a state with and without trivial topology, as you propose,\n> in the end you have always lost part of the information.\n<snip>\n> And it is also confirmed by Hawking himself, when he writes\n>\n> > One is thus led to the remarkable result that late time amplitudes of the\n> path integral > over a topologically non trivial metric, are independent of\n> the initial state. This was\n> > noticed by Maldacena in the case of asymptotically anti-deSitter in 3d.\n\nSorry for the questions, but I\'m really struggling here. So this idea\nabove, about independence on the initial state, is where the information\nloss would come in for a spacetime with a blackhole?\nMy problem though is that I\'m not seeing why this should be true for all\ntopologically non-trivial spacetimes. Perhaps I do not understand what\ntopologically non-trivial means in this context. I\'m thinking of it in\nterms of having a non-trivial fundamental group, which even the torus has.\n\n> Does anyone know the precisese reference of this result by Maldacena? Is it\n> really the path integral which is independent of the initial state, or just\n> the correlation functions? As in:\n\n> > Maldacena was able to show that topologically trivial metrics\n> > have correlation functions that do not decay\n\nAgain I am confused, but what does it mean for the correlation functions\nto not decay? Also, the correlation functions of what fields are we\ntalking about?\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 29 Jul 2004, Urs Schreiber wrote:

> "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
> news:61789046.0407290334.501fa47e@posting.google.c om...
> >
> > If you draw your initial state by hand so that it has ONLY nontrivial
> > spatial topologies , yes, but that's unphysical. In reality you can't
> > be sure there's a blackhole in your initial state either.
>
> Taking superpositions does not help you here. If the S-matrix maps all
> states with nontrivial topology to then it has "columns" with all entries
> 0s and won't be invertible. In other words, even if you start with a
> superposition of a state with and without trivial topology, as you propose,
> in the end you have always lost part of the information.
<snip>
> And it is also confirmed by Hawking himself, when he writes
>
> > One is thus led to the remarkable result that late time amplitudes of the
> path integral > over a topologically non trivial metric, are independent of
> the initial state. This was
> > noticed by Maldacena in the case of asymptotically anti-deSitter in 3d.

Sorry for the questions, but I'm really struggling here. So this idea
above, about independence on the initial state, is where the information
loss would come in for a spacetime with a blackhole?
My problem though is that I'm not seeing why this should be true for all
topologically non-trivial spacetimes. Perhaps I do not understand what
topologically non-trivial means in this context. I'm thinking of it in
terms of having a non-trivial fundamental group, which even the torus has.

> Does anyone know the precisese reference of this result by Maldacena? Is it
> really the path integral which is independent of the initial state, or just
> the correlation functions? As in:

> > Maldacena was able to show that topologically trivial metrics
> > have correlation functions that do not decay

Again I am confused, but what does it mean for the correlation functions
to not decay? Also, the correlation functions of what fields are we
talking about?

Urs Schreiber

Jul29-04, 09:06 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"Creighton Hogg" <wchogg@hep.wisc.edu> schrieb im Newsbeitrag\nnews:Pine.LNX.4.44.0407290829150.2139 9-100000@erodium.hep.wisc.edu...\n\n> Sorry for the questions, but I\'m really struggling here. So this idea\n> above, about independence on the initial state, is where the information\n> loss would come in for a spacetime with a blackhole?\n\nOriginally the information loss _seemed_ to come from the fact that when you\nput a quantum field on a spacetime background which is Schwarzschild\ngeometry you see that in the "ground state" quanta of the field are\nradiating away from the black hole. (This can be understood as essentially\nthe Unruh effect, due to the gravitational acceleration produced by the\nhole, felt by a static obsever "at infinity".)\n\nNote that this calculation had only the quantum field on the spacetime\nquantized, not gravity itself.\n\nNow by boldly extrapolating the picture conjured by this result, and\nassuming that we could and would take the back-reaction of the field on the\ngravitational background into account, one could imagine that after a long\nlong while the black hole will have disapeared and only the thermal\nradiation be left.\n\nIf this were the case we\'d have a paradox, because the resulting radiation\non flat background would carry no sign of the matter or whatever which\noriginally formed the black hole. This would then be an example of a\nphysical system where final states don\'t depened on initial states. Such a\nsystem would have lost the information about its past trajectory in\nconfiguration space.\n\n(As Rahul Jain has remarked, such a behaviour is what we expect from\ndissipative systems embedded in an environment. But here it would apply to a\ntotal "closed" system, where it is very strange.)\n\nNow Hawking argues, based on calculations by Maldacena for 3d gravity\napparently, that this supposed information loss is tightly related to the\nfact that the topology of the standard spatial slice of the Schwarzschild\nspacetime is not that of R^3, but that of R^3 with the origin removed (where\nthe singularity is sitting).\n\nHe furthermore argues that those initial states, which do not affect the\nfinal state, i.e. which are "lost" during the evolution, are precisely those\nwith nontrivial spatial topology.\n\nMoreover he says that all these states with nontrivial spatial topology will\nbe mapped to the 0-state by the time evolution (measure by asymptotic time\nin the cases he considers).\n\nAs I have said in a recent message, imagine this in terms of a quantum\nmechanical propagator U(t) = exp(iHt) which maps a subspace of the Hilbert\nspace to 0. As a result the adjoint of U is not invertible and in particular\nnot unitary.\n\n> Again I am confused, but what does it mean for the correlation functions\n> to not decay? Also, the correlation functions of what fields are we\n> talking about?\n\nAs I have said, i would like to see this paper by Maldacena which apparently\ncontains the key idea.\n\nBut as far as I can see we are talking about quantum fields propagating on a\nfixed gravitational background. This could be lineararized excitations of\nthe gravitational field itself, or other fields. Their quantum field\ncorrelation functions apparently in general decrease with Schwarzschild\ntime, which is thought to be due to the fact that parts of the fields\neventually drop behind the horizon.\n\nNow, possibly I don\'t understand yet what Hawking is really saying. But\ncurrently it seems to me that this decays is what he bases the claim that\nthe nontivial topologies don\'t contribute to the gravitational path integral\non. The logic behind this currently escapes me.I\'d appreciate all hints.\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>"Creighton Hogg" <wchogg@hep.wisc.edu> schrieb im Newsbeitrag
news:Pine.LNX.4.44.0407290829150.21399-100000@erodium.hep.wisc.edu...

> Sorry for the questions, but I'm really struggling here. So this idea
> above, about independence on the initial state, is where the information
> loss would come in for a spacetime with a blackhole?

Originally the information loss _seemed_ to come from the fact that when you
put a quantum field on a spacetime background which is Schwarzschild
geometry you see that in the "ground state" quanta of the field are
radiating away from the black hole. (This can be understood as essentially
the Unruh effect, due to the gravitational acceleration produced by the
hole, felt by a static obsever "at infinity".)

Note that this calculation had only the quantum field on the spacetime
quantized, not gravity itself.

Now by boldly extrapolating the picture conjured by this result, and
assuming that we could and would take the back-reaction of the field on the
gravitational background into account, one could imagine that after a long
long while the black hole will have disapeared and only the thermal
radiation be left.

If this were the case we'd have a paradox, because the resulting radiation
on flat background would carry no sign of the matter or whatever which
originally formed the black hole. This would then be an example of a
physical system where final states don't depened on initial states. Such a
system would have lost the information about its past trajectory in
configuration space.

(As Rahul Jain has remarked, such a behaviour is what we expect from
dissipative systems embedded in an environment. But here it would apply to a
total "closed" system, where it is very strange.)

Now Hawking argues, based on calculations by Maldacena for 3d gravity
apparently, that this supposed information loss is tightly related to the
fact that the topology of the standard spatial slice of the Schwarzschild
spacetime is not that of R^3, but that of R^3 with the origin removed (where
the singularity is sitting).

He furthermore argues that those initial states, which do not affect the
final state, i.e. which are "lost" during the evolution, are precisely those
with nontrivial spatial topology.

Moreover he says that all these states with nontrivial spatial topology will
be mapped to the 0-state by the time evolution (measure by asymptotic time
in the cases he considers).

As I have said in a recent message, imagine this in terms of a quantum
mechanical propagator U(t) = \exp(iHt) which maps a subspace of the Hilbert
space to . As a result the adjoint of U is not invertible and in particular
not unitary.

> Again I am confused, but what does it mean for the correlation functions
> to not decay? Also, the correlation functions of what fields are we
> talking about?

As I have said, i would like to see this paper by Maldacena which apparently
contains the key idea.

But as far as I can see we are talking about quantum fields propagating on a
fixed gravitational background. This could be lineararized excitations of
the gravitational field itself, or other fields. Their quantum field
correlation functions apparently in general decrease with Schwarzschild
time, which is thought to be due to the fact that parts of the fields
eventually drop behind the horizon.

Now, possibly I don't understand yet what Hawking is really saying. But
currently it seems to me that this decays is what he bases the claim that
the nontivial topologies don't contribute to the gravitational path integral
on. The logic behind this currently escapes me.I'd appreciate all hints.

Italo Vecchi

Jul29-04, 02:11 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n"Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<4108f82f\\$1@news.sentex.net>...\n\n> Taking superpositions does not help you here. If the S-matrix maps all\n> states with nontrivial topology to 0 then it has "columns" with all entries\n> 0s and won\'t be invertible. In other words, even if you start with a\n> superposition of a state with and without trivial topology, as you propose,\n> in the end you have always lost part of the information.\n>\n\nI don\'t think that the S-matrix maps all states with nontrivial\ntopology to a constant, unless the dynamics is determined by an\nunphysical initial state without trivial topologies. The path\nintegral over trivial topologies defines a unitary map that\npreserves all the information in the initial data. If you start with\na superposition of blackholes and not, you\'ll end up with a\nsuperposition of blackholes and not.\n\nIV\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" <Urs.Schreiber@uni-essen.de> wrote in message news:<4108f82f$1@news.sentex.net>...

> Taking superpositions does not help you here. If the S-matrix maps all
> states with nontrivial topology to then it has "columns" with all entries
> 0s and won't be invertible. In other words, even if you start with a
> superposition of a state with and without trivial topology, as you propose,
> in the end you have always lost part of the information.
>

I don't think that the S-matrix maps all states with nontrivial
topology to a constant, unless the dynamics is determined by an
unphysical initial state without trivial topologies. The path
integral over trivial topologies defines a unitary map that
preserves all the information in the initial data. If you start with
a superposition of blackholes and not, you'll end up with a
superposition of blackholes and not.

IV

Urs Schreiber

Jul29-04, 02:14 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"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\nnews:61789046.0407291108.4ca5098a@pos ting.google.com...\n\n> I don\'t think that the S-matrix maps all states with nontrivial\n> topology to a constant,\n\nI don\'t either (at least not until shown evidence for this claim). But\nHawking does.\n\nHe said:\n\n"One is thus led to the remarkable result that late time amplitudes of the\npath integral over a topologically non trivial metric, are independent of\nthe initial state."\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>"Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
news:61789046.0407291108.4ca5098a@posting.google.c om...

> I don't think that the S-matrix maps all states with nontrivial
> topology to a constant,

I don't either (at least not until shown evidence for this claim). But
Hawking does.

He said:

"One is thus led to the remarkable result that late time amplitudes of the
path integral over a topologically non trivial metric, are independent of
the initial state."

Italo Vecchi

Jul30-04, 07:42 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>\nCreighton Hogg <wchogg@hep.wisc.edu> wrote in message news:<Pine.LNX.4.44.0407290801330.21399-100000@erodium.hep.wisc.edu>...\n> On 29 Jul 2004, Italo Vecchi wrote:\n....\n> > If you draw your initial state by hand so that it has ONLY nontrivial\n> > spatial topologies , yes, but that\'s unphysical. In reality you can\'t\n> > be sure there\'s a blackhole in your initial state either.\n>\n> Sorry, but can you explain a little more about why that\'s an unphysical\n> initial state assumption? I\'m not quite seeing it.\n\nUnphysical= physically meaningless, like "assume we know with\narbitrary precision both the position and the momentum of an electron"\nor , in this case, "assume the initial data have only nontrivial\ntopologies". The key point in Hawking\'s argument in my opinion is:"one\ncan\'t be sure a black hole forms, no matter how certain it might be in\nclassical theory."\n\nTake care,\n\nIV\n\n[1] http://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt\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>Creighton Hogg <wchogg@hep.wisc.edu> wrote in message news:<Pine.LNX.4.44.0407290801330.21399-100000@erodium.hep.wisc.edu>...
> On 29 Jul 2004, Italo Vecchi wrote:
....
> > If you draw your initial state by hand so that it has ONLY nontrivial
> > spatial topologies , yes, but that's unphysical. In reality you can't
> > be sure there's a blackhole in your initial state either.
>
> Sorry, but can you explain a little more about why that's an unphysical
> initial state assumption? I'm not quite seeing it.

Unphysical= physically meaningless, like "assume we know with
arbitrary precision both the position and the momentum of an electron"
or , in this case, "assume the initial data have only nontrivial
topologies". The key point in Hawking's argument in my opinion is:"one
can't be sure a black hole forms, no matter how certain it might be in
classical theory."

Take care,

IV

[1] http://pancake.uchicago.edu/%7Ecarroll/hawkingdublin.txt

Italo Vecchi

Jul30-04, 07:42 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"Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<41094c83\\$1@news.sentex.net>...\n> "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\n> news:61789046.0407291108.4ca5098a@posting.google.c om...\n>\n> > I don\'t think that the S-matrix maps all states with nontrivial\n> > topology to a constant,\n>\n> I don\'t either (at least not until shown evidence for this claim). But\n> Hawking does.\n>\n> He said:\n>\n> "One is thus led to the remarkable result that late time amplitudes of the\n> path integral over a topologically non trivial metric, are independent of\n> the initial state."\n\nThe point here, afaiu, is that the information that reaches the final\nstate travels along paths over nontrivial metrics. The paths over\nnontrivial metrics yield a unitary map that delivers the full\ninformation load, including information about nontrivial metrics in\nthe initial data.\n\nIV\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" <Urs.Schreiber@uni-essen.de> wrote in message news:<41094c83$1@news.sentex.net>...
> "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
> news:61789046.0407291108.4ca5098a@posting.google.c om...
>
> > I don't think that the S-matrix maps all states with nontrivial
> > topology to a constant,
>
> I don't either (at least not until shown evidence for this claim). But
> Hawking does.
>
> He said:
>
> "One is thus led to the remarkable result that late time amplitudes of the
> path integral over a topologically non trivial metric, are independent of
> the initial state."

The point here, afaiu, is that the information that reaches the final
state travels along paths over nontrivial metrics. The paths over
nontrivial metrics yield a unitary map that delivers the full
information load, including information about nontrivial metrics in
the initial data.

IV

Italo Vecchi

Jul31-04, 09:15 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>\nvecchi@weirdtech.com (Italo Vecchi) wrote in message news:<61789046.0407300402.5b8c0ac7@posting.google. com>...\n> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<41094c83\\$1@news.sentex.net>...\n> > "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag\n> > news:61789046.0407291108.4ca5098a@posting.google.c om...\n> >\n> > > I don\'t think that the S-matrix maps all states with nontrivial\n> > > topology to a constant,\n> >\n> > I don\'t either (at least not until shown evidence for this claim). But\n> > Hawking does.\n> >\n> > He said:\n> >\n> > "One is thus led to the remarkable result that late time amplitudes of the\n> > path integral over a topologically non trivial metric, are independent of\n> > the initial state."\n>\n> The point here, afaiu, is that the information that reaches the final\n> state travels along paths over nontrivial metrics. The paths over\n> nontrivial metrics yield a unitary map that delivers the full\n> information load, including information about nontrivial metrics in\n> the initial data.\n>\n> IV\n\n\nSorry, that was a lapsus. It should be replaced by the following:\nThe point here, afaiu, is that the information that reaches the final\nstate travels along paths over TRIVIAL metrics. The paths over\nTRIVIAL metrics yield a unitary map that delivers the full\ninformation load, including information about nontrivial metrics in\nthe initial data.\n\nIV\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>vecchi@weirdtech.com (Italo Vecchi) wrote in message news:<61789046.0407300402.5b8c0ac7@posting.google.com>...
> "Urs Schreiber" <Urs.Schreiber@uni-essen.de> wrote in message news:<41094c83$1@news.sentex.net>...
> > "Italo Vecchi" <vecchi@weirdtech.com> schrieb im Newsbeitrag
> > news:61789046.0407291108.4ca5098a@posting.google.c om...
> >
> > > I don't think that the S-matrix maps all states with nontrivial
> > > topology to a constant,
> >
> > I don't either (at least not until shown evidence for this claim). But
> > Hawking does.
> >
> > He said:
> >
> > "One is thus led to the remarkable result that late time amplitudes of the
> > path integral over a topologically non trivial metric, are independent of
> > the initial state."
>
> The point here, afaiu, is that the information that reaches the final
> state travels along paths over nontrivial metrics. The paths over
> nontrivial metrics yield a unitary map that delivers the full
> information load, including information about nontrivial metrics in
> the initial data.
>
> IV

Sorry, that was a lapsus. It should be replaced by the following:
The point here, afaiu, is that the information that reaches the final
state travels along paths over TRIVIAL metrics. The paths over
TRIVIAL metrics yield a unitary map that delivers the full
information load, including information about nontrivial metrics in
the initial data.

IV

Torbj?rn Larsson

Aug2-04, 06:09 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>ebunn@lfa221051.richmond.edu wrote in message news:<ce68b5\\$gua\\$1@lfa222122.richmond.edu>...\ n> In article <ce61d0\\$9fi\\$1@glue.ucr.edu>, John Baez <baez@galaxy.ucr.edu> wrote:\n> >\n> >\n> >In article <70b38f8b.0407260917.792fc9cd@posting.google.com>, \n> >Torbj?rn Larsson <070-3993938@comhem.se> wrote:\n>\n> >>For example, can we feed the black hole indefinitely with a\n> >>realistic process within the assumed universe?\n\nFirst off, thanks for the subthread answers, it was educational and\nfun (for me)! Now I can sit back and experience the usual exponential\ndecay (of information) in my part of space.\n\n> >Not if there\'s a finite amount of matter around, as would\n> >be the case in an asymptotically Minkowskian universe.\n>\n> Is this obvious? Why can\'t you catch the outgoing Hawking radiation\n> and feed it back in?\n\nAnd since nobody else has gotten around to answer this yet, I may try.\n\nI don\'t think you can do that with 100 % efficiency in a realistic\nprocess; some will leak to the outside of your catcher as thermal\nradiation. You will eventually run out of mass-energy to feed back in.\n\nTo paraphrase Zeitblom (and Heinlein, in "The Moon is a Harsh\nMistress", I think): There Ain\'t No Such Thing As A Free Lunch at the\nRestaurant at the end 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>ebunn@lfa221051.richmond.edu wrote in message news:<ce68b5$gua$1@lfa222122.richmond.edu>...
> In article <ce61d0$9fi$1@glue.ucr.edu>, John Baez <baez@galaxy.ucr.edu> wrote:
> >
> >
> >In article <70b38f8b.0407260917.792fc9cd@posting.google.com>,
> >Torbj?rn Larsson <070-3993938@comhem.se> wrote:
>
> >>For example, can we feed the black hole indefinitely with a
> >>realistic process within the assumed universe?

First off, thanks for the subthread answers, it was educational and
fun (for me)! Now I can sit back and experience the usual exponential
decay (of information) in my part of space.

> >Not if there's a finite amount of matter around, as would
> >be the case in an asymptotically Minkowskian universe.
>
> Is this obvious? Why can't you catch the outgoing Hawking radiation
> and feed it back in?

And since nobody else has gotten around to answer this yet, I may try.

I don't think you can do that with 100 % efficiency in a realistic
process; some will leak to the outside of your catcher as thermal
radiation. You will eventually run out of mass-energy to feed back in.

To paraphrase Zeitblom (and Heinlein, in "The Moon is a Harsh
Mistress", I think): There Ain't No Such Thing As A Free Lunch at the
Restaurant at the end of the Universe.

ebunn@lfa221051.richmond.edu

Aug5-04, 03:24 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>In article <70b38f8b.0408012119.58f633e2@posting.google.com>, \nTorbj?rn Larsson <070-3993938@comhem.se> wrote:\n>ebunn@lfa221051.richmond.edu wrote in message news:<ce68b5\\$gua\\$1@lfa222122.richmond.edu>...\ n>> In article <ce61d0\\$9fi\\$1@glue.ucr.edu>, John Baez <baez@galaxy.ucr.edu> wrote:\n>> >\n>> >\n>> >In article <70b38f8b.0407260917.792fc9cd@posting.google.com>, \n>> >Torbj?rn Larsson <070-3993938@comhem.se> wrote:\n>>\n>> >>For example, can we feed the black hole indefinitely with a\n>> >>realistic process within the assumed universe?\n[...]\n>> >Not if there\'s a finite amount of matter around, as would\n>> >be the case in an asymptotically Minkowskian universe.\n>>\n>> Is this obvious? Why can\'t you catch the outgoing Hawking radiation\n>> and feed it back in?\n[...]\n>I don\'t think you can do that with 100 % efficiency in a realistic\n>process; some will leak to the outside of your catcher as thermal\n>radiation. You will eventually run out of mass-energy to feed back in.\n\nUndoubtedly true, but I didn\'t think "realistic" was a criterion in this\ncontext. That is, I thought of this as very much an "in-principle"\nrather than an "in-practice" sort of question.\n\nIn other words, the purely theoretical question of what happens to an\nindefinitely-fed black hole makes sense as long as there\'s a\nmathematically self-consistent model of such a thing. Maybe there\'s\nnot one in a Universe with a finite amount of matter -- that is, maybe\nthe supposition is impossible in principle rather than merely in\npractice, in this case. But that\'s still not obvious to me.\n\nFor instance, couldn\'t you (in principle) imagine a perfectly\nreflecting spherical shell around the black hole? Or even a black\nhole in a static closed Universe, where the Hawking radiation can\'t\nescape to infinity? In the latter case, I\'d assume you wouldn\'t have\nto go to any trouble to feed the black hole indefnitely: surely the\nlate-time steady-state solution would be a black hole in thermal\nequilibrium with its own Hawking radiation.\n\nIn the latter case, the definition of an event horizon (which, as I\nunderstand it, is expressed in terms of whether stuff can escape to\ninfinity) goes away. Since Hawking\'s claim is all about whether a\ntrue event horizon forms, I guess that makes a difference.\n\nMaybe it\'s true that there\'s no way to formulate the question about\nfeeding a black hole forever in an interesting way without assuming\ninfinite amounts of matter. It\'s not clear to me, but I know\nnext to nothing about this subject.\n\n-Ted\n\n--\n[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]\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 <70b38f8b.0408012119.58f633e2@posting.google.com>,
Torbj?rn Larsson <070-3993938@comhem.se> wrote:
>ebunn@lfa221051.richmond.edu wrote in message news:<ce68b5$gua$1@lfa222122.richmond.edu>...
>> In article <ce61d0$9fi$1@glue.ucr.edu>, John Baez <baez@galaxy.ucr.edu> wrote:
>> >
>> >
>> >In article <70b38f8b.0407260917.792fc9cd@posting.google.com>,
>> >Torbj?rn Larsson <070-3993938@comhem.se> wrote:
>>
>> >>For example, can we feed the black hole indefinitely with a
>> >>realistic process within the assumed universe?
[...]
>> >Not if there's a finite amount of matter around, as would
>> >be the case in an asymptotically Minkowskian universe.
>>
>> Is this obvious? Why can't you catch the outgoing Hawking radiation
>> and feed it back in?
[...]
>I don't think you can do that with 100 % efficiency in a realistic
>process; some will leak to the outside of your catcher as thermal
>radiation. You will eventually run out of mass-energy to feed back in.

Undoubtedly true, but I didn't think "realistic" was a criterion in this
context. That is, I thought of this as very much an "in-principle"
rather than an "in-practice" sort of question.

In other words, the purely theoretical question of what happens to an
indefinitely-fed black hole makes sense as long as there's a
mathematically self-consistent model of such a thing. Maybe there's
not one in a Universe with a finite amount of matter -- that is, maybe
the supposition is impossible in principle rather than merely in
practice, in this case. But that's still not obvious to me.

For instance, couldn't you (in principle) imagine a perfectly
reflecting spherical shell around the black hole? Or even a black
hole in a static closed Universe, where the Hawking radiation can't
escape to infinity? In the latter case, I'd assume you wouldn't have
to go to any trouble to feed the black hole indefnitely: surely the
late-time steady-state solution would be a black hole in thermal
equilibrium with its own Hawking radiation.

In the latter case, the definition of an event horizon (which, as I
understand it, is expressed in terms of whether stuff can escape to
infinity) goes away. Since Hawking's claim is all about whether a
true event horizon forms, I guess that makes a difference.

Maybe it's true that there's no way to formulate the question about
feeding a black hole forever in an interesting way without assuming
infinite amounts of matter. It's not clear to me, but I know
next to nothing about this subject.

-Ted

--
[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]

Torbj?rn Larsson

Aug6-04, 03:05 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> >I don\'t think you can do that with 100 % efficiency in a realistic\n> >process; some will leak to the outside of your catcher as thermal\n> >radiation. You will eventually run out of mass-energy to feed back in.\n>\n> Undoubtedly true, but I didn\'t think "realistic" was a criterion in this\n> context. That is, I thought of this as very much an "in-principle"\n> rather than an "in-practice" sort of question.\n....\n> Maybe it\'s true that there\'s no way to formulate the question about\n> feeding a black hole forever in an interesting way without assuming\n> infinite amounts of matter. It\'s not clear to me, but I know\n> next to nothing about this subject.\n>\nThat makes at least two of us, which is why I was cautious when\nphrasing my question. And I will be more satisfied with an in-practice\nanswer since I sought an answer in the negative.\n\nAlso, in-principle answers may break the rules of Hawkings argument or\nmay introduce unnecessary assumptions. I don\'t know enough to sort\nthat out in this context, so I will leave this as a problem for\nsomeone else.\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>> [...]
> >I don't think you can do that with 100 % efficiency in a realistic
> >process; some will leak to the outside of your catcher as thermal
> >radiation. You will eventually run out of mass-energy to feed back in.
>
> Undoubtedly true, but I didn't think "realistic" was a criterion in this
> context. That is, I thought of this as very much an "in-principle"
> rather than an "in-practice" sort of question.
....
> Maybe it's true that there's no way to formulate the question about
> feeding a black hole forever in an interesting way without assuming
> infinite amounts of matter. It's not clear to me, but I know
> next to nothing about this subject.
>
That makes at least two of us, which is why I was cautious when
phrasing my question. And I will be more satisfied with an in-practice
answer since I sought an answer in the negative.

Also, in-principle answers may break the rules of Hawkings argument or
may introduce unnecessary assumptions. I don't know enough to sort
that out in this context, so I will leave this as a problem for
someone else.

Italo Vecchi

Aug14-04, 06:58 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\n070-3993938@comhem.se (Torbj?rn Larsson) wrote in message news:<70b38f8b.0407260917.792fc9cd@posting.google. com>...\n> baez@galaxy.ucr.edu (John Baez) wrote in message news:<ce0bmc\\$nar\\$1@glue.ucr.edu>...\n> ...\n\n> > Afterwards Rob Mann asked a question about whether there would be\n> > information loss if we kept feeding the black hole to keep it from\n> > evaporating, and his grad student (the poor chap who had to field\n> > all the technical questions) seemed to say "yes".\n>\n> ...\n> If this interpretation is the right one, can we find an argument that\n> answer Manns problem? For example, can we feed the black hole\n> indefinitely with a realistic process within the assumed universe?\n\nBut is this really the point? This seems to imply that information is\n"temporarily locked" inside a blackhole and that stretching that\n"temporary"\nindefinitely entails loss of information . I don\'t think that this is\nwhat Hawking is saying.\n\nAs far as I understand Hawking is saying is that there are no\nblackholes but only supersitions of blackholes and not (" one can\'t be\nsure a black hole forms, no matter how certain it might be in\nclassical theory"). So there is no event horizont but only an apparent\nhorizont (very roughly speaking a superposition of an event horizont\nand not), so all information will find its way to the future through\nthe "non event horizont" amplitude (i.e. through the sum of paths over\ntrivial topologies). There is no "information locking", temporary or\nnot.\n\n\nBtw, If Hawking\'s argument holds for blackholes it must hold for\nwhiteholes too , which means that information pouring out of a\nwhitehole must average out , which is immediately intuitive, but is\nwhat you get from the sum of the path integrals over all nontrivial\ntopologies.\n\nIV\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>070-3993938@comhem.se (Torbj?rn Larsson) wrote in message news:<70b38f8b.0407260917.792fc9cd@posting.google.com>...
> baez@galaxy.ucr.edu (John Baez) wrote in message news:<ce0bmc$nar$1@glue.ucr.edu>...
> ...

> > Afterwards Rob Mann asked a question about whether there would be
> > information loss if we kept feeding the black hole to keep it from
> > evaporating, and his grad student (the poor chap who had to field
> > all the technical questions) seemed to say "yes".
>
> ...
> If this interpretation is the right one, can we find an argument that
> answer Manns problem? For example, can we feed the black hole
> indefinitely with a realistic process within the assumed universe?

But is this really the point? This seems to imply that information is
"temporarily locked" inside a blackhole and that stretching that
"temporary"
indefinitely entails loss of information . I don't think that this is
what Hawking is saying.

As far as I understand Hawking is saying is that there are no
blackholes but only supersitions of blackholes and not (" one can't be
sure a black hole forms, no matter how certain it might be in
classical theory"). So there is no event horizont but only an apparent
horizont (very roughly speaking a superposition of an event horizont
and not), so all information will find its way to the future through
the "non event horizont" amplitude (i.e. through the sum of paths over
trivial topologies). There is no "information locking", temporary or
not.

Btw, If Hawking's argument holds for blackholes it must hold for
whiteholes too , which means that information pouring out of a
whitehole must average out , which is immediately intuitive, but is
what you get from the sum of the path integrals over all nontrivial
topologies.

IV