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[SOLVED] Hawking in Dublin |
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| Jul2-04, 04:32 AM | #1 |
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[SOLVED] Hawking in Dublin
<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 "[itex]GR-17[/itex]" where I'll also be speaking. I've heard rumors that he believes he's "solved" this problem. Does anyone know what's up? |
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| Jul2-04, 06:09 AM | #2 |
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<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. |
| Jul2-04, 01:57 PM | #3 |
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<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 |
| Jul4-04, 07:39 AM | #4 |
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[SOLVED] Hawking in Dublin
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" |
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| Jul4-04, 09:47 AM | #5 |
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<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. |
| Jul4-04, 09:54 AM | #6 |
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<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@posting.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.com... > 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. |
| Jul6-04, 01:47 PM | #7 |
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<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.or...hep-th/0406260 ------------------------------------------------------------------------ This post submitted through the LaTeX-enabled physicsforums.com To view this post with LaTeX images: http://www.physicsforums.com/showthr...532#post249657 |
| Jul6-04, 01:47 PM | #8 |
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<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.arxi...ant-ph/0207029 [1] http://physicsforums.com/showthread.php?t=25780 |
| Jul9-04, 03:49 AM | #9 |
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<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 [itex]U(1)_em[/itex] 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. |
| Jul9-04, 02:52 PM | #10 |
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<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 [itex]and/or[/itex] 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 [itex]10-11,[/itex] 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. |
| Jul16-04, 08:19 AM | #11 |
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<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 [itex]-0400,[/itex] 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 "[itex]GR-17[/itex]" 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 [itex]/can/[/itex] 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. ;) [itex]=Erk=[/itex] (Eric Baird) : " Trying to construct a theory of gravity using special relativity : is like attempting to build a jellyfish out of Lego. " |
| Jul16-04, 08:21 AM | #12 |
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<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.telenet-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/2004/0407...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/ |
| Jul19-04, 04:13 PM | #13 |
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<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....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. |
| Jul19-04, 04:30 PM | #14 |
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<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....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... |
| Jul22-04, 06:14 AM | #15 |
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<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/%7Ecarro...kingdublin.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 [itex]AdS/CFT[/itex] correspondence is mentioned frequently. Right at the beginning it seems like Hawking is crediting [itex]AdS/CFT[/itex] 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 [itex]AdS/CFT[/itex] 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. :-) |
| Jul22-04, 12:07 PM | #16 |
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<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/%7Ecarro...kingdublin.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 [itex]he _is_[/itex] 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. |
| Jul22-04, 12:12 PM | #17 |
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<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.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\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 [itex]he _is_[/itex] 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/...es/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.arxi...hep-th/9803131 ! |
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