http://arxiv.org/pdf/1401.5761v1.pdf
这里是地址////感觉很厉害的样子！！

Information Preservation and Weather Forecasting for Black
Holes
S. W. Hawking1
1DAMTP, University of Cambridge, UK
Abstract
It has been suggested [1] that the resolution of the information paradox for evaporating black
holes is that the holes are surrounded by rewalls, bolts of outgoing radiation that would destroy
any infalling observer. Such rewalls would break the CPT invariance of quantum gravity and seem
to be ruled out on other grounds. A dierent resolution of the paradox is proposed, namely that
gravitational collapse produces apparent horizons but no event horizons behind which information is
lost. This proposal is supported by ADS-CFT and is the only resolution of the paradox compatible
with CPT. The collapse to form a black hole will in general be chaotic and the dual CFT on the
boundary of ADS will be turbulent. Thus, like weather forecasting on Earth, information will
eectively be lost, although there would be no loss of unitarity.
Talk given at the fuzz or re workshop, The Kavli Institute for Theoretical Physics, Santa Barbara, August
2013

Some time ago [2] I wrote a paper that started a controversy that has lasted until the
present day. In the paper I pointed out that if there were an event horizon, the outgoing
state would be mixed. If the black hole evaporated completely without leaving a remnant,
as most people believe and would be required by CPT, one would have a transition from
an initial pure state to a mixed nal state and a loss of unitarity. On the other hand, the
ADS-CFT correspondence indicates that the 7evaporating black hole is dual to a unitary
conformal eld theory on the boundary of ADS. This is the information paradox.
Recently there has been renewed interest in the information paradox [1]. The authors
of [1] suggested that the most conservative resolution of the information paradox would be
that an infalling observer would encounter a rewall of outgoing radiation at the horizon.
There are several objections to the rewall proposal. First, if the rewall were located
at the event horizon, the position of the event horizon is not locally determined but is a
function of the future of the spacetime.
Another objection is that calculations of the regularized energy momentum tensor of
matter elds are regular on the extended Schwarzschild background in the Hartle-Hawking
state [3, 4]. The outgoing radiating Unruh state diers from the Hartle-Hawking state
in that it has no incoming radiation at innity. To get the energy momentum tensor in
the Unruh state one therefore has to subtract the energy momentum tensor of the ingoing
radiation from the energy momentum in the Hartle-Hawking state. The energy momentum
tensor of the ingoing radiation is singular on the past horizon but is regular on the future
horizon. Thus the energy momentum tensor is regular on the horizon in the Unruh state.
So no rewalls.
For a third objection to rewalls I shall assume that if rewalls form around black holes
in asymptotically
at space, then they should also form around black holes in asymptotically
anti deSitter space for very small lambda. One would expect that quantum gravity should
be CPT invariant. Consider a gedanken experiment in which Lorentzian asymptotically anti
deSitter space has matter elds excited in certain modes. This is like the old discussions
of a black hole in a box [5]. Non-linearities in the coupled matter and gravitational eld
equations will lead to the formation of a black hole [6]. If the mass of the asymptotically anti
deSitter space is above the Hawking-Page mass [7], a black hole with radiation will be the
most common conguration. If the space is below that mass the most likely conguration
is pure radiation.

Whether or not the mass of the anti deSitter space is above the Hawking-Page mass
the space will occasionally change to the other conguration, that is the black hole above
the Hawking-Page mass will occasionally evaporate to pure radiation, or pure radiation will
condense into a black hole. By CPT the time reverse will be the CP conjugate. This shows
that, in this situation, the evaporation of a black hole is the time reverse of its formation
(modulo CP), though the conventional descriptions are very dierent. Thus if one assume
quantum gravity is CPT invariant, one rules out remnants, event horizons, and rewalls.
Further evidence against rewalls comes from considering asymptotically anti deSitter to
the metrics that t in an S1 cross S2 boundary at innity. There are two such metrics: periodically identied anti deSitter space, and Schwarzschild anti deSitter. Only periodically
identied anti deSitter space contributes to the boundary to boundary correlation functions because the correlation functions from the Schwarzschild anti deSitter metric decay
exponentially with real time [8, 9]. I take this as indicating that the topologically trivial
periodically identied anti deSitter metric is the metric that interpolates between collapse
to a black hole and evaporation. There would be no event horizons and no rewalls.
The absence of event horizons mean that there are no black holes - in the sense of regimes
from which light can't escape to innity. There are however apparent horizons which persist
for a period of time. This suggests that black holes should be redened as metastable bound
states of the gravitational eld. It will also mean that the CFT on the boundary of anti
deSitter space will be dual to the whole anti deSitter space, and not merely the region
outside the horizon.
The no hair theorems imply that in a gravitational collapse the space outside the event
horizon will approach the metric of a Kerr solution. However inside the event horizon, the
metric and matter elds will be classically chaotic. It is the approximation of this chaotic
metric by a smooth Kerr metric that is responsible for the information loss in gravitational
collapse. The chaotic collapsed object will radiate deterministically but chaotically. It will
be like weather forecasting on Earth. That is unitary, but chaotic, so there is eective
information loss. One can't predict the weather more than a few days in advance.

1] A. Almheiri, D. Marolf, J. Polchinski, J. Sully, Black Holes: Complementarity or Firewalls?,
J. High Energy Phys. 2, 062 (2013)
[2] S. W. Hawking, Breakdown of Predicatability in Gravitational Collapse, Phys. Rev. D 14, 2460
(1976)
[3] M. S. Fawcett, The Energy-Momentum Tensor near a Black Hole Commun. Math. Phys. 89,
103-115 (1983)
[4] K. W. Howard, P. Candelas, Quantum Stress Tensor in Schwarzschild Space-Time, Physical
Review Letters 53, 5 (1984)
[5] S. W. Hawking, Black holes and Thermodynamics, Phys. Rev. D 13, 2 (1976)
[6] P. Bizon, A. Rostworowski, Weakly Turbulent Instability of Anti-de Sitter Space, Phys. Rev.
Lett. 107, 031102 (2011)
[7] S. W. Hawking, D. N. Page, Thermodynamics of Black Holes in Anti-de Sitter Space, Commun.
Math. Phys. 87, 577-588 (1983)
[8] J. Maldacena, Eternal black holes in anti-de Sitter, J. High Energy Phys. 04, 21 (2003)
[9] S. W. Hawking, Information Loss in Black Holes, Phys. Rev. D 72, 084013 (2005)

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