Saturday, November 22, 2014

[Sarfatti Commentary #5: The dilemma of the horizons, observer-independent "event" or observer-dependent "apparent"? Stephen Hawking has not only changed his mind about information loss down a black hole now caving in to Lenny Susskind opting for unitarity’s conservation of quantum information, but he has also rejected the existence of event horizons because they are teleological nonlocal in time needing the Wheeler-Feynman-Aharonov back-from-the-future destiny influence. Hawking replaces the event horizon with an apparent horizon-   delicate distinction since they merge into each other eventually and evaporate by Hawking-Unruh radiation. Unitarity requires small non-random deviations from the white noise random thermal equilibrium black hole radiation from the horizons. There is also the firewall problem, which is another conflict between Einstein’s “happiest thought” (the equivalence principle and again that bugaboo unitarity, which is a dragon I am quite willing to slay. The idea of the firewall is that the surface of the black hole is a hot surface that will burn the freely falling observer. Some physicists have gone further to say it’s not a firewall, but fireworks, that because of back-reaction of the inflating negative energy Hawking radiation that neither horizon ever forms. This flies in the face of everything Kip Thorne says in his book and the movie. It is an issue to be debated. Hawking wrote:
Information Preservation and Weather Forecasting for Black Holes∗
S. W. Hawking1
1DAMTP, University of Cambridge, UK
“It has been suggested [1] that the resolution of the information paradox for evaporating black holes is that the holes are surrounded by firewalls, bolts of outgoing radiation that would destroy any infalling observer. Such firewalls would break the CPT invariance of quantum gravity and seem to be ruled out on other grounds. A different 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 effectively be lost, although there would be no loss of unitarity.”

Backreaction of Hawking Radiation on a Gravitationally Collapsing Star I: Black Holes?
Laura Mersini-Houghton
(Submitted on 5 Jun 2014)
Particle creation leading to Hawking radiation is produced by the changing gravitational field of the collapsing star. The two main initial conditions in the far past placed on the quantum field from which particles arise, are the Hartle-Hawking vacuum and the Unruh vacuum. The former leads to a time symmetric thermal bath of radiation, while the latter to a flux of radiation coming out of the collapsing star. The energy of Hawking radiation in the interior of the collapsing star is negative and equal in magnitude to its value at future infinity. This work investigates the backreaction of Hawking radiation on the interior of a gravitationally collapsing star, in a Hartle-Hawking initial vacuum. It shows that due to the negative energy Hawking radiation in the interior, the collapse of the star stops at a finite radius, before the singularity and the event horizon of a black hole have a chance to form. That is, the star bounces instead of collapsing to a black hole. A trapped surface near the last stage of the star's collapse to its minimum size may still exist temporarily. Its formation depends on the details of collapse. Results for the case of Hawking flux of radiation with the Unruh initial state, will be given in a companion paper II.
Back-reaction of the Hawking radiation flux on a gravitationally collapsing star II: Fireworks instead of firewalls
Laura Mersini-Houghton, Harald P. Pfeiffer
(Submitted on 5 Sep 2014)
“A star collapsing gravitationally into a black hole emits a flux of radiation, knowns as Hawking radiation. When the initial state of a quantum field on the background of the star, is placed in the Unruh vacuum in the far past, then Hawking radiation corresponds to a flux of positive energy radiation travelling outwards to future infinity. The evaporation of the collapsing star can be equivalently described as a negative energy flux of radiation travelling radially inwards towards the center of the star. Here, we are interested in the evolution of the star during its collapse. Thus we include the backreaction of the negative energy Hawking flux in the interior geometry of the collapsing star and solve the full 4-dimensional Einstein and hydrodynamical equations numerically. We find that Hawking radiation emitted just before the star passes through its Schwarzschild radius slows down the collapse of the star and substantially reduces its mass thus the star bounces before reaching the horizon. The area radius starts increasing after the bounce. Beyond this point our program breaks down due to shell crossing. We find that the star stops collapsing at a finite radius larger than its horizon, turns around and its core explodes. This study provides a more realistic investigation of the backreaction of Hawking radiation on the collapsing star, that was first presented in [1].]”

Black hole fireworks: quantum-gravity effects outside the horizon spark black to white hole tunneling
Hal M. Haggard∗ and Carlo Rovelli†
Aix-Marseille Universit ́e and Universit ́e de Toulon, CPT-CNRS, Luminy, F-13288 Marseille (Dated: Fourth of July, 2014)
“We show that there is a classical metric satisfying the Einstein equations outside a finite spacetime region where matter collapses into a black hole and then emerges from a white hole. We compute this metric explicitly. We show how quantum theory determines the (long) time for the process to happen. A black hole can thus quantum-tunnel into a white hole. For this to happen, quantum gravity should affect the metric also in a small region outside the horizon: we show that contrary to what is commonly assumed, this is not forbidden by causality or by the semiclassical approximation, because quantum effects can pile up over a long time. This scenario alters radically the discussion on the black hole information puzzle.”
However, this controversy firewalls, or fireworks, event horizon or apparent horizon has no bearing whatsoever on the traversable wormhole stargate which has no horizons and which is not manufactured by collapsing matter. Since the wormhole has no horizons it does not have Hawking radiation. We do have the issue of chronology protection. More on that later.]

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