The fight between QM and GR is heating up.http://www.nature.com/news/astrophysics-fire-in-the-hole-1.12726
Quantum Mechanics describes the very small and General Relativity the very large but unfortunately they don't get along very well. To make matters worse, they meet each other all the time on their common playground; black holes.
TL;DR - Either firewalls exist and general relativity falls apart, or information is lost in black holes and QM is off.> Incineration instead of spaghettification?
In March 2012, Joseph Polchinski began to contemplate suicide — at least in mathematical form. He was pondering what would happen to an astronaut who dived into a black hole. Obviously, he would die. But how? According to the then-accepted account, he wouldn’t feel anything special at first, even when his fall took him through the black hole’s event horizon: the invisible boundary beyond which nothing can escape. But eventually he would begin to notice that gravity was tugging at his feet more strongly than at his head. As his plunge carried him inexorably downwards, the difference in forces would quickly increase and rip him apart, before finally crushing his remnants into the black hole’s infinitely dense core.
But Polchinski’s calculations, carried out with two of his students — Ahmed Almheiri and James Sully — and fellow string theorist Donald Marolf at the University of California, Santa Barbara (UCSB), were telling a different story. In their account, quantum effects would turn the event horizon into a seething maelstrom of particles. Anyone who fell into it would hit a wall of fire and be burned to a crisp in an instant.> Hawking radiation
The roots of the current firewall crisis go back to 1974, when physicist Stephen Hawking at the University of Cambridge, UK, showed that quantum effects cause black holes to run a temperature. Left in isolation, the holes will slowly spew out thermal radiation — photons and other particles — and gradually lose mass until they evaporate away entirely.
Hawking’s argument basically comes down to the observation that in the quantum realm, ‘empty’ space isn’t empty. Down at this sub-sub-microscopic level, it is in constant turmoil, with pairs of particles and their corresponding antiparticles continually popping into existence before rapidly recombining and vanishing. Only in very delicate laboratory experiments does this submicroscopic frenzy have any observable consequences. But when a particle–antiparticle pair appears just outside a black hole’s event horizon, Hawking realized, one member could fall in before the two recombined, leaving the surviving partner to fly outwards as radiation. The doomed particle would balance the positive energy of the outgoing particle by carrying negative energy inwards — something allowed by quantum rules. That negative energy would then get subtracted from the black hole’s mass, causing the hole to shrink.
Hawking’s original analysis has since been refined and extended by many researchers, and his conclusion is now accepted almost universally. But with it came the disturbing realization that black-hole radiation leads to a paradox that challenges quantum theory.> The black-hole information paradox
Quantum mechanics says that information cannot be destroyed. In principle, it should be possible to recover everything there is to know about the objects that fell in a black hole by measuring the quantum state of the radiation coming out. But Hawking showed that it was not that simple: the radiation coming out is random. Toss in a kilogram of rock or a kilogram of computer chips and the result will be the same. Watch the black hole even until it dies, and there would still be no way to tell how it was formed or what fell in it.
This problem divided physicists into two camps. Some argued that the information truly vanishes when the black hole dies. If that contradicted quantum laws, then better laws needed to be found. Others stuck by quantum mechanics.> Holography to the rescue
The holographic principle states that any three-dimensional region of our universe can be described by information encoded on its two-dimensional boundary, in much the same way that laser light can encode a 3D scene on a 2D hologram. Juan Maldacena, a physicist then at Harvard University in Cambridge built on this work and came up with a concrete mathematical formulation of the hologram idea that made use of ideas from superstring theory. His model envisages a 3D universe containing strings and black holes that are governed only by gravity, bounded by a 2D surface on which elementary particles and fields obey ordinary quantum laws without gravity.
A few years later, Marolf showed that every model of quantum gravity will obey the same rules, whether or not it is built from string theory.
This meant that even 3D black-hole evaporation could be described in the 2D world, where there is no gravity, where quantum laws reign supreme and where information can never be lost. And if information is preserved there, then it must also be preserved in the 3D world. Somehow, information must be escaping from the black holes."> A wall of fire
Such was the strength of Maldacena’s discovery that most physicists believed that the paradox had been settled — even though nobody had yet explained how Hawking radiation smuggles information out of the black hole. “I guess we just all assumed there would be a straightforward answer,” says Polchinski.
There wasn’t. When Polchinski and his team set themselves the task of clearing up that loose end in early 2012, they soon stumbled on yet another paradox — the one that eventually led them to the fatal firewall.
Hawking had shown that the quantum state of any one particle escaping from the black hole is random, so the particle cannot be carrying any useful information. But in the mid-1990s, Susskind and others realized that information could be encoded in the quantum state of the radiation as a whole if the particles could somehow have their states ‘entangled’ — intertwined in such a way that measurements carried out on one will immediately influence its partner, no matter how far apart they are.
But how could that be, wondered the Polchinski’s team? For a particle to be emitted at all, it has to be entangled with the twin that is sacrificed to the black hole. And if Susskind and others were right, it also had to be entangled with all the Hawking radiation emitted before it. Yet a rigorous result of quantum mechanics dubbed ‘the monogamy of entanglement’ says that one quantum system cannot be fully entangled with two independent systems at once.
To escape this paradox, Polchinski and his co-workers realized, one of the entanglement relationships had to be severed. Reluctant to abandon the one required to encode information in the Hawking radiation, they decided to snip the link binding an escaping Hawking particle to its infalling twin. But there was a cost. “It’s a violent process, like breaking the bonds of a molecule, and it releases energy,” says Polchinski. The energy generated by severing lots of twins would be enormous. “The event horizon would literally be a ring of fire that burns anyone falling through,” he says. And that, in turn, violates the equivalence principle and its assertion that free-fall should feel the same as floating in empty space — impossible when the former ends in incineration. So they posted a paper on the preprint server, arXiv, presenting physicists with a stark choice: either accept that firewalls exist and that general relativity breaks down, or accept that information is lost in black holes and quantum mechanics is wrong. “For us, firewalls seem like the least crazy option, given that choice,” says Marolf.
Such firewalls would violate a foundational tenet of physics that was first articulated almost a century ago by Albert Einstein, who used it as the basis of general relativity, his theory of gravity. Known as the equivalence principle, it states in part that an observer falling in a gravitational field — even the powerful one inside a black hole — will see exactly the same phenomena as an observer floating in empty space. Without this principle, Einstein’s framework crumbles.
Polchinski admits that he thought they could have made a silly mistake. So he turned to Susskind, one of the fathers of holography, to find it. “My first reaction was that they were wrong,” says Susskind. He posted a paper stating as much, before quickly retracting it, after further thought. “My second reaction was that they were right, my third was that they were wrong again, my fourth was that they were right,” he laughs. “It’s earned me the nickname, ‘the yo-yo,’ but my reaction is pretty much the same as most physicists’.” Since then, more than 40 papers have been posted on the topic in arXiv, but as yet, nobody has found a flaw in the team’s logic. It’s a really beautiful argument proving that there’s something inconsistent in our thinking about black holes.http://www.nature.com/news/astrophysics-fire-in-the-hole-1.12726
Paper; http://arxiv.org/abs/1207.3123 #ScienceSunday