Rahul Jain
Jul26-04, 04:41 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"Urs Schreiber" <Urs.Schreiber@uni-essen.de> writes:\n\n> "John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag\n> news:ce0bmc\\$nar\\$1@glue.ucr.edu...\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>\n> Yes. But what\'s puzzling here is that AdS/CFT says that the time evolution\n> of supergravity plus superstring fluctuations must be unitary. Does this\n> imply that pure (super)gravity without the stringy degrees of freedom is\n> unitary by itself?\n\nOK, you (Urs) have already commented (negatively) on my use of\ndecoherence to doubt the validity of Hawking\'s insistence that\nsituations where the black hole did not form somehow contribute to the\nresulting state after a black hole evaporates.\n\nHowever, I don\'t see how unitarity can be assumed if we think that there\nis decoherence. Isn\'t decoherence a non-unitary process? Mixed states\ndecohere to pure(r) states. The states where the black hole did not form\nare removed from the superposition and we must stop contributing the\nforward propagation of the no-black-hole states to the wavefunction of\nthe system. Maybe your definition of "decoherence" is different, but I\nhope it\'s now clear what I mean.\n\nIt\'s possible that this same process that casts doubt on Hawking\'s\nargument is the same one that supports his end result. The standard\n"teleportation" experiment could be occurring with particles that become\nentangled at the event horizon. Of course, this would depend on the\nexact limits of entanglement, as the system could be required to\ndecohere before a particle gets the chance to become entangled at the\nevent horizon. In fact, I got this idea from Hawking\'s mention that\nHawking radiation could be interpreted as tunneling of particles through\nthe event horizon. But I\'m sure most of you will shoot that one down as\nbeing at odds with the geometrical interpretation of GR.\n\nIn any case, shoot away. :)\n\n--\nRahul Jain\nrjain@nyct.net\nProfessional Software Developer, Amateur Quantum Mechanicist\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:
> "John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
> news:ce0bmc$nar$1@glue.ucr.edu...
>> 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?
OK, you (Urs) have already commented (negatively) on my use of
decoherence to doubt the validity of Hawking's insistence that
situations where the black hole did not form somehow contribute to the
resulting state after a black hole evaporates.
However, I don't see how unitarity can be assumed if we think that there
is decoherence. Isn't decoherence a non-unitary process? Mixed states
decohere to pure(r) states. The states where the black hole did not form
are removed from the superposition and we must stop contributing the
forward propagation of the no-black-hole states to the wavefunction of
the system. Maybe your definition of "decoherence" is different, but I
hope it's now clear what I mean.
It's possible that this same process that casts doubt on Hawking's
argument is the same one that supports his end result. The standard
"teleportation" experiment could be occurring with particles that become
entangled at the event horizon. Of course, this would depend on the
exact limits of entanglement, as the system could be required to
decohere before a particle gets the chance to become entangled at the
event horizon. In fact, I got this idea from Hawking's mention that
Hawking radiation could be interpreted as tunneling of particles through
the event horizon. But I'm sure most of you will shoot that one down as
being at odds with the geometrical interpretation of GR.
In any case, shoot away. :)
--
Rahul Jain
rjain@nyct.net
Professional Software Developer, Amateur Quantum Mechanicist
> "John Baez" <baez@galaxy.ucr.edu> schrieb im Newsbeitrag
> news:ce0bmc$nar$1@glue.ucr.edu...
>> 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?
OK, you (Urs) have already commented (negatively) on my use of
decoherence to doubt the validity of Hawking's insistence that
situations where the black hole did not form somehow contribute to the
resulting state after a black hole evaporates.
However, I don't see how unitarity can be assumed if we think that there
is decoherence. Isn't decoherence a non-unitary process? Mixed states
decohere to pure(r) states. The states where the black hole did not form
are removed from the superposition and we must stop contributing the
forward propagation of the no-black-hole states to the wavefunction of
the system. Maybe your definition of "decoherence" is different, but I
hope it's now clear what I mean.
It's possible that this same process that casts doubt on Hawking's
argument is the same one that supports his end result. The standard
"teleportation" experiment could be occurring with particles that become
entangled at the event horizon. Of course, this would depend on the
exact limits of entanglement, as the system could be required to
decohere before a particle gets the chance to become entangled at the
event horizon. In fact, I got this idea from Hawking's mention that
Hawking radiation could be interpreted as tunneling of particles through
the event horizon. But I'm sure most of you will shoot that one down as
being at odds with the geometrical interpretation of GR.
In any case, shoot away. :)
--
Rahul Jain
rjain@nyct.net
Professional Software Developer, Amateur Quantum Mechanicist