Is Stephen Hawking messing with our heads? The famed astrophysicist has shaken up the world of popular science with his newest study about the basic nature of black holes, but is his theory truly as radical as it sounds in its attempts to solve a paradox surrounding the fundamental building blocks of how the universe works? Some scientists aren't convinced. Hawking's new study — entitled "Information Preservation and Weather Forecasting for Black Holes" — was published Jan. 22 through the preprint journal arXiv.org and has not yet undergone the standard peer review vetting process for academic papers.
"Hawking's paper is short and does not have a lot of detail, so it is not clear what his precise picture is, or what the justification is," Joseph Polchinski of the Kavli Institute wrote in an email to SPACE.com. [The Strangest Black Holes in the Universe].
A couple of years ago, Polchinski and colleagues at the Kavli Institute for Theoretical Physics, in Santa Barbara, California, used quantum mechanics to analyze the event horizon, and realized that quantum effects first described by Hawking himself back in the 1970s would make the event horizon anything but invisible: “The event horizon would literally be a ring of fire that burns anyone falling through,” Polchinski told Nature in a 2012 interview. it would instead be a seething sheet of energy, dubbed “the firewall."
So the event horizon is undetectable—or it’s a firewall—but it can’t be both. In his new paper, Hawking proposed a solution to this paradox by proposing that black holes don’t have event horizons. Instead they have apparent horizons that don’t require a firewall to obey thermodynamics.
However, counters Brian Koberlain Why Hawking in Wrong About Black Holes, "the firewall paradox only arises if Hawking radiation is in a pure state, and a paper last month by Sabine Hossenfelder shows that Hawking radiation is not in a pure state. In her paper, Hossenfelder shows that instead of being due to a pair of entangled particles, Hawking radiation is due to two pairs of entangled particles. One entangled pair gets trapped by the black hole, while the other entangled pair escapes. The process is similar to Hawking’s original proposal, but the Hawking particles are not in a pure state.
"So there’s no paradox," concludes Koberlain, " Black holes can radiate in a way that agrees with thermodynamics, and the region near the event horizon doesn’t have a firewall, just as general relativity requires. So Hawking’s proposal is "a solution to a problem that doesn’t exist."
"It's not possible to have both of those things, to have no drama at the apparent horizon and to have the information come out," Bousso told SPACE.com. "Stephen just doesn't discuss this argument, so it's unclear how he means to address it."
"I do not think that eliminating event horizons by itself solves the firewall problem, which is a subtle problem," wrote Don Page, physicist at the University of Alberta in Canada, in an email. And an event horizon-free black hole isn't a new proposal, either, Page added.
"The idea that a black hole does not truly have an event horizon goes back more than a third of a century, and I would not be surprised if someone could trace it back even many years earlier," Page told SPACE.com via email.
For a more detailed overview of the debate check out astrophysicist and NASA columnist Ethan Seigel’s post on his blog Starts With a Bang! as well as Sabine Hossenfelder, Assistant Professor for High Energy Physics at Nordita in Stockholm, Sweden on her blog, Back Reaction, where she talks about the issue and her Arvix paper on this. No paywall. Disentangling the Black Hole Vacuum.
The image at the top of the page shows what happens when a cloud of gas passes close by a supermassive black hole. In 2011, a small cloud of interstellar gas, named G2 by the discoverers, was found using the Very Large Telescope observatory of the European Science Organization. The rapid motion of G2 is clearly apparent in the figure above, where the blue image marks G2's position in 2006, the green in 2010, and the red in 2013. Located less than a few light-days from Sagittarius A**, the Milky Way's 4 million-solar mass supermassive black hole, G2 has a mass about three times that of the Earth, and is on a near-collision course with Sagittarius A*.
Read Hawking's full study, called "Information Preservation and Weather Forecasting for Black Holes," on arXiv.org: http://arxiv.org/abs/1401.5761
The Daily Galaxy via http://www.universetoday.com/108870/why-hawking-is-wrong-about-black-holes/, Space.com and Christain Science Monitor