Will Hawking declare BH info puzzle solved?


by marcus
Tags: declare, hawking, info, puzzle, solved
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#1
Jul2-04, 12:00 PM
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this just appeared at SPR:

John Baez:
-----quote-----
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 "GR17" where I'll also be speaking.

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

Does anyone know what's up?
-----end quote----



davidoff404 replied:

----quote---

Re: Hawking in Dublin

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.

----end quote----
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marcus
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Jul2-04, 12:26 PM
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Here is Baez thread
http://physicsforums.com/showthread....246#post248246

hawking made a surprise annoucement that he would appear at GR17
(the big General Relativity conference this month in Dublin)

here is the webpage for the GR17 conference:
http://www.dcu.ie/~nolanb/gr17.htm

I think it probable that Hawking's decision to announce his solution just now may have something to do with the recent advance by Gambini Porto and Pullin

that is just my hunch----I am guessing that GPP is part of the reason prompting Hawking to go to Dublin and talk BH information loss.
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Jul2-04, 01:56 PM
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Here is the abstract for Hawking's talk

----quote from GR17 program----

Stephen Hawking (Cambridge)


- The information paradox for black holes


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.

---------end quote---------

there always was a connection between Ambjorn and Loll's simplicial approach and Hawking's Euclidean path integral
(for "analytically continued" read Wick rotation)
(for "time slicing" read the causal restriction on triangulation that AJL use)

I think the AJL paper has put some Lorentzian life back into Hawking Euclidean path integral

IMHO I suspect "The way the information gets out seems to be that a true event horizon never forms, just an apparent horizon" is a wild shot in the dark

I think what he is really telling us is that he has made some progress with the Euclidean path integral model for quantum gravity (perhaps inspired by the breakthrough in simplicial gravity)

the close kinship between the path integral and the dynamical triangulation approach was noted by Rovelli in a 1998 survey which is enlightening on the ancestry of the different approaches. I will get a link to that

Yeah, great survey by Rovelli (NOT the LivingReviews article)
http://arxiv.org/gr-qc/9803024
that treats the provenance of every kind of approach tried to QG
and perceptively spotlights their stumblingblocks
"Strings, loops and others: a critical survey of the present approaches to quantum gravity"------this interestingly was Rovelli's talk at GR15

the 15th triennial conference on Gen Rel
just like we have GR17, the 17th triennial, starting 18 July in dublin

jeff
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#4
Jul2-04, 04:19 PM
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Will Hawking declare BH info puzzle solved?


Quote Quote by marcus
Here is the abstract for Hawking's talk

----quote from GR17 program----

Stephen Hawking (Cambridge)


- The information paradox for black holes


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.

---------end quote---------

there always was a connection between Ambjorn and Loll's simplicial approach and Hawking's Euclidean path integral
(for "analytically continued" read Wick rotation)
(for "time slicing" read the causal restriction on triangulation that AJL use)

I think the AJL paper has put some Lorentzian life back into Hawking Euclidean path integral
By this last remark I assume you're referring to AJL's latest paper. Note that hawking points out what I did in the first AJL thread, namely that unitarity requires we integrate over all possible configurations, including those in which there are changes in topology. AJL however include only configurations in which topology is preserved, and no one has explained to me how AJL is unitary nonetheless. Anyway, given this, hawking can't be talking about AJL. I guess we'll just have to see.

Edit: AJL don't integrate over all topologically trivial configurations. Rather, they integrate over all globally hyperbolic configurations. Thus someone still needs to explain to me how AJL is unitary.
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Jul2-04, 07:40 PM
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Quote Quote by marcus
Here is the abstract for Hawking's talk

----quote from GR17 program----

Stephen Hawking (Cambridge)


- The information paradox for black holes


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...

----end quote---
it appears from hawking's summary here that, for him, where there is no topology change (the topologically trivial metrics) the evolution is unitary or can be unitary

I dont think there is much to go on and would rather defer discussion until we know more about his actual talk

however it seems from the summary that there is no reason to assume that including topology change is necessary to have unitarity----one can claim this, and perhaps it is right, but Hawking does not say it here (and indeed may be interpreted to say the contrary)---and so I reckon that this claim requires proof or link to some paper where it is proved.

---------
my feeling is that it is premature extrapolation to be discussing logical details like this (correctly or incorrectly max nix) and the main news that I want to be responding to is simply that Hawking has made a surprise decision to come to GR17 and talk about the BH information puzzle

Another great thing about the Dublin Meeting!

Penrose is scheduled to give a massive public lecture at the Concert Hall at 8PM Friday titled, I now see from the program:

Fashion, Faith, and Fantasy in Theoretical Physics

great title is it not?
Olias
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#6
Jul2-04, 10:08 PM
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The way the information gets out seems to be that a true event horizon never forms, just an apparent horizon.

Could it be because of the initial label of 'Pure Quantum State'?

Marcus the three theorists:Hawking-Thorne-Penrose, who all struck up a 'Bet' about the Blackhole Information Loss paradox all at the conference, my guess there is another ' Bet ' about to be hedged!
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Jul2-04, 10:38 PM
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Quote Quote by marcus
it appears from hawking's summary here that, for him, where there is no topology change (the topologically trivial metrics) the evolution is unitary or can be unitary
But AJL don't integrate over all topologically trivial configurations. Rather, they integrate over all globally hyperbolic configurations (which admit foliation with respect to some discrete time parameter).


Quote Quote by marcus
I dont think there is much to go on and would rather defer discussion until we know more about his actual talk
jgraber
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Jul3-04, 07:19 AM
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Quote Quote by Olias
The way the information gets out seems to be that a true event horizon never forms, just an apparent horizon.

Could it be because of the initial label of 'Pure Quantum State'?

Marcus the three theorists:Hawking-Thorne-Penrose, who all struck up a 'Bet' about the Blackhole Information Loss paradox all at the conference, my guess there is another ' Bet ' about to be hedged!
I believe the third party to the referenced bet is John Preskill, not Roger Penrose.
Best, Jim
Olias
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Jul3-04, 07:35 AM
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Of course!
Many thanks Jim.

I believe Penrose and Hawking just differ with their perspective on :The Nature of Space And Time?
jgraber
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Jul3-04, 09:46 AM
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Quote Quote by Olias
Of course!
Many thanks Jim.

I believe Penrose and Hawking just differ with their perspective on :The Nature of Space And Time?
No doubt this is true.
However, it ismuch too big a topic for me to tackle right now.
Regards, Jim
Entropy
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Jul3-04, 02:20 PM
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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 "GR17" where I'll also be speaking.
:surprise: Whoa dude thats awesome! You're speaking in the same place as Hawking?! Do you know him or ever meet him before?! Man thats almost as cool as meeting Metallica! Maybe cooler!
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Jul3-04, 02:35 PM
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Quote Quote by Entropy
:surprise: Whoa dude thats awesome! You're speaking in the same place as Hawking?! Do you know him or ever meet him before?! Man thats almost as cool as meeting Metallica! Maybe cooler!


Entropy we are all different I guess about who we admire and if I had a chance to chat for 15 or 20 minutes with someone about where physics was going and it is was a choice between Stephen Hawking and John Baez
there is no question in my mind

ranking who I'd personally rather listen to

1. Baez
2. Hawking
3. Metallica
marcus
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Jul6-04, 01:31 PM
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Quote Quote by marcus
...
Another great thing about the Dublin Meeting!

Penrose is scheduled to give a massive public lecture at the Concert Hall at 8PM Friday titled, I now see from the program:

Fashion, Faith, and Fantasy in Theoretical Physics

great title is it not?
someone posting a comment at Woit's blog "Not Even Wrong"
gave a link

http://www.princeton.edu/WebMedia/lectures/

this has three hour-long lectures that Penrose gave at Princeton
last October entitled "Fashion, Faith, and Fantasy"

has anyone else watched them

I thought they were very interesting

he mentioned a book he is writing about the material in the three lectures

the public lecture he is giving at Dublin, with the same title, may well be a condensed and improved version of the series of three talks at princeton
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Jul13-04, 01:25 AM
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I expect suspense is building about Stephen Hawking's talk
will he have found a satisfactory resolution of the Black Hole Information Paradox, within the framework of his own approach to quantum gravity (the Euclidean Path Integral) or not?

His talk is Wednesday in the afternoon, 21 July----a little over 8 days from now.

Curiously enough, I rather think Hawking could prove wrong. I think something more along the lines proposed by Gambini, Porto, and Pullin will might prove correct.
GPP show a fundamental non-unitariness about the passage of time.
Information decays, quantum states become mixed, at a certain rate.
It may be at the heart of what time is
(or what "times are" since physics has no one unique concept of time)


Conventional quantum mechnics is built on an earthquake fault----a classical (and fundamentally unrealistic) time variable T. Unitariness depends on a variable T which corresponds to no observable and to no conceivable clock belonging to the physical universe.

Hawking's abstract suggests that in his treatment of the BH evaporation paradox---essentially a "passage of time" puzzle----he does not break with the ideal classical time variable and he maintains his grip on unitariness.
Intuitively this indicates he could well be wrong.

Eventually the GPP approach and Hawking's will collide and have it out.
It could go either way---just because Hawking has a big reputation doesnt guarantee he's right. IMHO.
Haelfix
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Jul13-04, 04:34 AM
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Yea but Hawking is one of the grandmasters of black hole physics, he's been right about most of those issues for a long time. He is often wrong about other issues, but this is more or less his bread and butter.

One of the reasons everyone always listens to him, is b/c he has a very different way of approaching a problem than most physicists. He doesn't benefit from a pencil and paper, instead he has very powerful mental images and intuitions about things.

I know this is metaphysics mumbo jumbo and name dropping, but I wouldn't be surprised if this particular contribution is indeed something important.
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Jul17-04, 05:14 PM
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Quote Quote by Haelfix
Yea but Hawking is one of the grandmasters of black hole physics, he's been right about most of those issues for a long time. He is often wrong about other issues, but this is more or less his bread and butter.

One of the reasons everyone always listens to him, is b/c he has a very different way of approaching a problem than most physicists. He doesn't benefit from a pencil and paper, instead he has very powerful mental images and intuitions about things.

I know this is metaphysics mumbo jumbo and name dropping, but I wouldn't be surprised if this particular contribution is indeed something important.
Well this thread was started 2 July, two weeks ago.

At that time i had no idea that there would be raised such a lot of talk about Hawking and the GR17 and blackhole Information Paradox. But now there are several threads about it in the Astronomy forum at PF and apparently quite a stew in the media with people interviewing Hawking and so on.

the one clear thing that comes thru (for me) is what Haelfix said in the above post

No matter how cockamamey or even ludicrous it all is, Hawking has been right bigtime in the past and the upcoming could turn out to be quite significant. And there was something curious in what Haelfix said.

Because hawking cant grab a chalk and make pictures on the blackboard he has to daydream more vividly than other people---so his thought is different. I buy that.

I wouldnt have risked saying that myself but it sounds right.

I see hawking's PathIntegral approach to quantizing General Relativity as akin to the Spinfoam approach, which sometimes uses path integral terms. Anyone want to compare them? I gather PathIntegral is not much worked on except by Hawking, but it may have useful similarities to other approaches.
selfAdjoint
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#17
Jul17-04, 07:48 PM
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Baez and company used path integrals in analyzing the simplices in 4D LQG. They corrected some earlier estimates of the mixture of different shaped simplices doing that. Greg Egan, the sf author, wrote some of the software for their calculations and got a coauthorship on the paper.


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