1. Physicist Claims Black Holes Mathematically Don't Exist (Henry Baker) http://beta.slashdot.org/story/207637

Black holes, the stellar phenomena that continue to capture the imagination of scientists and science fiction authors, may not actually exist. According to a paper published by physics professor Laura Mersini-Houghton at the University of North Carolina and Mathematics Professor Harald Pfeiffer of the University of Toronto, as a collapsing star emits Hawking radiation, it also sheds mass at a rate that suggests it no longer has the density necessary to become a black hole ? the singularity and event horizon never form. While the arXiv paper with the exact solution has not yet been peer reviewed, the preceding paper by Mersini-Houghton with the approximate solutions was published in Physics Letters B.

"I'm still not over the shock," said Mersini-Houghton. "We've been studying this problem for a more than 50 years and this solution gives us a lot to think about... Physicists have been trying to merge these two theories ? Einstein's theory of gravity and quantum mechanics ? for decades, but this scenario brings these two theories together, into harmony." ------------------ http://arxiv.org/abs/1409.1837

Back-reaction of the Hawking radiation flux on a gravitationally collapsing star II: Fireworks instead of firewalls

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 reach ing 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].

--Classically a collapsing star takes a finite amount of time according to clocks on the star surface, to turn into a black hole. But according to external observer, the star's surface never falls inside the event horizon in any finite time, albeit it gets exponentially close to it. In view of this, if we regard the Hawking evaporation as taking some large but finite time as viewed by external observer, it will happen before the black hole forms, hence it never forms, as perceived by external observer. But since it gets "exponentially close to forming" in view of same external observer, it sure looks black for a long time! Meanwhile, the co-collapsing observer thinks he has hit singularity & died in finite time. But he has no way to communicate this experience to external observer. So... all that reasoning has been around for ages, and certainly I have been =awre of it for at least 20 years. So I don't see what is wrong with the view proposed by http://arxiv.org/abs/1409.1837 that "the black hole never forms" and the collapse "bounces." It is just a very long wait before the bounce... during which the non-black-hole bears a very great resemblance to a true black hole. And their numerical work can be viewed as providing further evidence for this picture. But I'm not sure how seriously we should regard this numerical result because as they admit, their numerical methods stop working after a "shell crossing" and cannot follow most or all of the outward bounce. (What do they mean by "shell crossing"? They explain: "The inner layers of the star pick up a larger positive velocity than the outer layers, resulting in shell crossing.") As they remark: "The star never crosses its horizon, so neither unitarity nor causality are violated, thereby solving the longstanding information loss paradox." Also no "firewall paradox." Also no singularity and no horizon form. However. What about this OTHER PARADOX: the infalling observer thinks he has hit a singularity and died in finite time by his own clock. Is this still true within their computer simulation? The paradox would be: we have two observers who think a singularity exists, and who think a singularity never exists. They do not explicitly raise or answer this question. But I think they intended the answer to be: "really, the infalling observer perceives a massive blast of outgoing Hawking radiation just before he hits the horizon. This kills him before hitting that horizon. He never really enters a horizon and never really hits any singularity, and the singularity never forms in his view because of a big influx of negative energy toward where it would have been."