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## Main Question or Discussion Point

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cristo

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The issue is whether unitarity is broken in QG, right ? And they (Ashtekar) can **not** be break unitarity, can they ? Maybe better

__Information is Not Lost in the Evaporation of 2-dimensional Black Holes__

BTW, there has been at least one proposal for a "mechanism for how information might escape from a black hole", but maybe the author did not classify it at as "plausible". Namely, that there are correlations in the supposedly purely thermal radiation emitted by the BH.

BTW, there has been at least one proposal for a "mechanism for how information might escape from a black hole", but maybe the author did not classify it at as "plausible". Namely, that there are correlations in the supposedly purely thermal radiation emitted by the BH.

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marcus

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thanks. I will look for more on that.

I gather it is work by Ashtekar, Taveras, and Varadarajan

on black holes in 2D

and they believe it will generalize to 4D

It says their paper will be published in Physical Review Letters. 20 May 2008

Here

http://arxiv.org/abs/0801.1811

Authors: Abhay Ashtekar, Victor Taveras, Madhavan Varadarajan

(Submitted on 11 Jan 2008)

Abstract: We analyze Hawking evaporation of the Callen-Giddings-Harvey-Strominger (CGHS) black holes from a quantum geometry perspective and show that information is not lost, primarily because the quantum space-time is sufficiently larger than the classical. Using suitable approximations to extract physics from quantum space-times we establish that: i)future null infinity of the quantum space-time is sufficiently long for the the past vacuum to evolve to a pure state in the future; ii) this state has a finite norm in the future Fock space; and iii) all the information comes out at future infinity; there are no remnants.

Comments: 4 pages, 2 figures

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nrqed

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Very interesting. I hope you will stick around and provide more details.

For now, I have a very stupid question. I am confused by one thing. I always hear people saying that quantum mechanics "preserves information" and hence is in conflict with GR because of black holes. But the measurement process in QM is not unitary (at least if we use the Copenhagen interpretation). So why do people always say that QM preserves information?

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Demystifier

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Excellent point!Very interesting. I hope you will stick around and provide more details.

For now, I have a very stupid question. I am confused by one thing. I always hear people saying that quantum mechanics "preserves information" and hence is in conflict with GR because of black holes. But the measurement process in QM is not unitary (at least if we use the Copenhagen interpretation). So why do people always say that QM preserves information?

This is indeed a part of the information-paradox solution proposed in

http://xxx.lanl.gov/abs/0708.0729

See in particular Sec. 3.

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As far as I see it, since QM doesn't model the measurement process in a context where the observer is subject to feedback. It rather models the the expected evolution between measurements relative to this "idealised observer", that as it seems have inifinite memory capacity etc.I am confused by one thing. I always hear people saying that quantum mechanics "preserves information" and hence is in conflict with GR because of black holes. But the measurement process in QM is not unitary (at least if we use the Copenhagen interpretation). So why do people always say that QM preserves information?

So IMO, the unitary evolution of QM, is an expectation only IMO. Sometimes this expectation is very good! and make sense, sometimes not. That's how I personally see it. It's not fundamental to me.

The way I prefer to see this is that "lost/hidden" information may simply be indistinguishable in the general uncertainty. And the complexity of the observer must possible put a bound on the confidence in anything, thus certain things that are indistinguishable _relative to this observer_ (say a black hole) may IMO without contradiction be distinguishable relative to another obsever.

So perhaps, from the point of view of the black hole itself, the radiation is "random", and thus no distiniguishable loss. It then seems to me that by this reasoning one would expect that very small black holes are radiating "less random" than a larger one, as judged by the same observer.

I always thought the origin of alot of mess is the abstraced observer used in QM. There is no constraint HOW MUCH information it makes sense to have at once. Which does not to me, seem physically reasonable in any way. This is why I think the QM formalism needs relaxation.

/Fredrik

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Demystifier

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For an even more explicit (and less technical) discussion of that point see alsoExcellent point!

This is indeed a part of the information-paradox solution proposed in

http://xxx.lanl.gov/abs/0708.0729

See in particular Sec. 3.

arXiv:0805.2555 http://xxx.lanl.gov/abs/0805.2555

to appear tomorrow.

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For example, consider the gastrointestinal tract as a biophysical black hole.

Nutrients enter but are transformed either to useful biological entities or into waste.

Now in total the information is prserved, but in is difficult to piece together the original nutrient from the waste alone or from useful biological entities alone.

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