Saturday, December 22, 2012

Notes from the Firewall

Perhaps you?ve been hearing rumblings in the ether about physicists wrangling over black holes and something called a firewall: namely, that we should question our longstanding assumption that someone who crosses the event horizon of a black hole won?t notice anything amiss until they near the singularity ? at which point they will experience what Caltech physicist Kip Thorne once dubbed ?spaghettification.?

So if we aren?t going to be spaghettified when we fall into the black hole, what will happen instead? How about being burned alive in a wall of fire right at the moment we start to cross? My fellow SciAm blogger George Musser already reported on a recent talk by string theorist Joe Polchinski at New York University in which he made the argument for just that scenario. Polchinski is one of four co-authors (known by the acronym AMPS) behind this controversial proposal. And now I?ve got an article (on both Scientific American and the fledgling Simons Science News site, a new venture by the Simons Foundation) breaking down what?s at stake.

Dr. John A. Zoidberg of Futurama falling into a black hole. Image Source:

This is physics-in-progress, since physicists are still debating how best to resolve what?s turned out to be a pretty intriguing paradox. You can peruse the linked references at the bottom of this post for more technical discussions (both in blog posts and original papers). It?ll be fun to watch how this whole thing shakes out, since even if the firewalls scenario turns out to be wrong? ? and plenty of physicists think this will be the case ? it?ll likely be wrong in an interesting way.

Working on this story nearly broke my brain. It meant grappling with the nuances of some very big ideas, just to illuminate my own ignorance, before casting about for a means of communicating the essential elements. (There was at least one evening when the Time Lord came home to find me pacing around the living room, muttering, ?Fucking firewalls?.? I?m sure several physicists feel the same way.)

One of the toughest challenges for a science writer is conveying this kind of advanced abstract topic to a general reader who has never heard of things like AdS/CFT duality, Hawking radiation, the Page time, complementarity, monogamous quantum entanglement, the information paradox, black hole entropy, nonlocality, effective field theory, or even Einstein?s equivalence principle ? all concepts central to the firewall debate.

Entangled particles at the event horizon of a black hole. Credit: Joe Polchinski

That?s not even counting more exotic notions like mirror black holes, fuzzballs, gray bodies, Planck-sized remnants, and baby universes, all of which get bandied about whenever physicists gather to debate firewalls.

Most people never have the chance to observe and interact with physicists in their natural habitat, which is a shame, because there?s no better way to get a sense for what the field is all about. Thanks to the generosity of Leonard Susskind, I had the privilege of sitting in on a special workshop (really more of a brainstorming session) at Stanford University, and watching 50 or so physicists haggle over the details as Susskind played referee.

There were moments of frustration, and rueful laughter ? eg, John Preskill stopping in the middle of his remarks to address a colleague (?You don?t look happy. Well, I don?t care that you?re unhappy?), before continuing. Things occasionally got heated ? ?I think it?s wonderful that somebody actually drew a singularity coming out of? black hole in a spacelike manner!? one physicist griped ?? but never uncivil, because everyone there was united in their passion to resolve the paradox, or at least to better delineate the issues.

When energies were flagging towards the end of the first day, a positively effervescent Yasunori Nomura brought everyone back to life with a lively, fast-paced exchange with Polchinski, in particular. Overall, the participants seemed to be really enjoying themselves. And why shouldn?t they?

It?s early days yet: while there are those who think they?ve solved the conundrum, and their arguments might well prevail in the end, there isn?t yet a strong consensus, so the matter remains unsettled. There are rumors of a conference on firewalls in April, and perhaps by then the field will be coalescing toward a solution. That?s part of the excitement of following physics-in-progress.

By necessity, given the target audience, the resulting article presents the firewall paradox painted in the broadest of strokes. I focused on three core issues outlined in the AMPS paper, delineating the most basic, stripped-down logical argument to show why there is a paradox in the first place ? and hopefully capture some of the flavor of how physicists think and approach their work. They?re not just making up crazy ideas to mess with our heads, people! These are rigorous, nuanced arguments with a long history, backed up by lots of math. Lots and lots and lots of math, plus the occasional scrawled diagram.

To include every last detail, the piece would have had to be a good 6000 words long, and frankly, very few general readers would care to slog through all the gory details. So why even bother to try, if one can?t be comprehensive? Because FIREWALLS! That?s why! Seriously, how cool is this concept? There?s nothing more crowd-pleasing than death by black hole ? just ask Neil de Grasse Tyson ? and now there could be more than one way to die. Spaghetiffication, or incineration? Take your pick.

Image: NASA Goddard Space Flight Center. Public Domain.

All joking aside, it?s the kind of challenge that makes me love my job even more, because I learn so much in the process ? which means I can keep getting better at my job. Sure, I could play it safe and shy away from tackling tough subjects like black hole firewalls, but where?s the adventure in that? It?s better to push the boundaries occasionally and risk failure than to never try at all. That?s how science advances, and it?s how science writers like me learn and grow professionally.

Of course, in order to achieve this, I am beholden to the kindness and patience of physicists like Susskind, Polchinski, Raphael Bousso, Preskill, Nomura, and yes, the Time Lord? ? read his bloggy take here ? all of whom took the time to break certain things down for me, thereby saving my sanity and making for a much more coherent article.

This is the reality: there will always be something lost in translation, because the gap between the top levels of theoretical physics and cosmology, and even a somewhat scientifically literate reader is pretty large. Information rarely seeps out from the black hole of theoretical physics in such a way that a general observer can make sense of it. It takes the combined efforts of scientists, science writers, and dedicated readers to bridge that gap. That?s the essence of science communication.

Is the end result imperfect and incomplete? Yes. So is an imperfect article still worth all that collective effort to bridge the gap? Yes. Just because communication is hard, doesn?t mean it?s not worth doing. Quite the opposite.

I found myself pondering Stephen Hawking?s predicament during the Stanford workshop, since his information paradox and the Hawking radiation proved so central to the discussion. In Hawking?s case, you?ve got a brilliant mind with all manner of useful insights trapped behind a metaphorical event horizon by the nature of Lou Gehrig?s disease. Yet Hawking has always managed to find a way for the information to leak out. It has become increasingly difficult for him to communicate in recent years, but he?s still doing it. And physics is the better for it. So, too, for science communication.

Speaking of bridging the gap between two cultures: Physicists sometimes talk about the event horizon of a black hole as a kind of membrane, and Jen-Luc Piquant serendipitously stumbled upon visual artist Aaron Sherwood?s stunning exhibit? (created in collaboration with Michael Allison) called ?Firewall,? which uses an interactive fabric surface ? a kind of membrane.? Per Colossal: ?different ?modes? of light are projected onto a taut membrane of spandex which then reacts kinetically in response to touch.? It?s a kinder, gentler version of a firewall, set to evocative music in the video below.


Almheiri, Ahmedl Marolf, Donald; Polchinski, Joseph; and Sully, James. (2012) ?Black Holes: Complementarity or Firewalls??

Einstein, A., Podolsky, B., and Rosen, N. (1935) ?Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?? Physical Review 47, 777-780.

Bousso, Raphael. ?Complementarity Is Not Enough,?

Hawking S. (1975) ?Particle Creation by Black Holes,? Communications in Mathematical Physics 43(3): 199-220.

Maldacena, J.M. (2003) ?Eternal black holes in anti-de Sitter,? JHEP 0304, 021.

Nomura, Y., Varela, J., and Weinberg S.J. (2012) ?Complementarity Endures: No Firewall for an Infalling Observer,? arXiv:1207.6626

Page, Don. (1980) ?Is Black Hole Evaporation Predictable?? Physical Review Letters 44: 301?304.

Polchinski, Joseph. ?Guest Post: Black Holes, Complementarity, and Firewalls,? Cosmic Variance, September 27, 2012.

Preskill, John. ?Is Alice Burning? The Black Hole Firewall Controversy,? Quantum Frontiers, December 3, 2012.

Susskind, L., Thorlacius, L., Uglum, J. (1993) ?The Stretched Horizon and Black Hole Complementarity,? Physical Review D 48: 3743-3761.

Susskind, Leonard. (2012) ?Singularities, Firewalls, and Complementarity,?



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