Regulars from Cosmic Variance will be well acquainted with the idea of “firewalls” around black holes, from reading Joe Polchinski’s guest post on the subject. And then you heard more about them from John Preskill’s post at Quantum Frontiers. Or maybe George Musser’s post at Scientific American. Long story short: there is a believable claim on the market that, if you believe that information is preserved in the evaporation of black holes via Hawking radiation, an infalling observer should be incinerated by a wall of high-energy radiation when they cross the event horizon, in dramatic contradiction to everything classical general relativity would lead you to believe. Important stuff, if true. (“True” might mean “the argument is valid but one of the underlying assumptions is wrong, therefore teaching us something important about quantum gravity.)

Word is now finally leaking out into the more popular press, courtesy of my lovely wife Jennifer Ouellette’s article at Simons Science News, a new initiative from the Simons Foundation. It’s a great article, which I would say even if we were not notoriously nepotistic back-scratchers.

Here’s my attempt to squeeze the firewall argument down to its essence, for people who know a little quantum mechanics. If information escapes from a black hole, the radiation emitted at late times must share quantum entanglement with radiation that escaped at early times, in order to describe a pure quantum state (from which the black hole presumably formed). At the same time, to an observer near the event horizon, the local conditions are supposed to look almost like empty space — the quantum vacuum. But within that vacuum are virtual particles, some of which will eventually escape in the form of radiation and some of which will eventually fall into the black hole. In order for the state near the horizon to look like the vacuum, that outgoing radiation and the ingoing radiation must also be entangled. Therefore, it appears that the outgoing radiation is both entangled with the ingoing radiation, and with the radiation that escaped at earlier times. But that’s impossible; quantum mechanics won’t let degrees of freedom be separately (maximally) entangled with two different other sets of degrees of freedom. Entanglement is monogamous. A simple — but unpalatable — way out is to suggest that the state near the horizon is not a quiet state of maximal entanglement, but a noisy thermal state of high-energy radiation — a firewall.

It’s a slightly tricky business, as you expect it to be when we’re mixing up quantum mechanics with things happening in spacetime, in the absence of a once-and-for-all theory of quantum gravity. Probably most people who have thought about the issue don’t believe firewalls really exist (although some do), but in that either there’s a secret flaw in the argument, or one of our fundamental assumptions is out of whack. Maybe information is not conserved, or maybe it’s transferred faster than light, or maybe quantum mechanics doesn’t work quite the way we thought. The story should continue to be interesting no matter what happens.

Here’s the video from a talk I gave at Skepticon V last month. It’s basically a superposition of a Higgs-boson talk with the From Particles to People talk. How is such a feat even possible, you may ask? Well, it wasn’t easy.

Fortunately, this talk is only 50 minutes long; it’s not like sitting through 15 hours of Moving Naturalism Forward videos.

This is the talk, by the way, from which the little picture of me at the top right corner of the blog was taken. I like it because it appears that I am looking at each new blog post with skeptical bemusement.

Also, at one point I said “light years” when I meant “miles” (talking about Voyager). They may take my scientist card away for that one.

I’ll take this opportunity to offer one of my occasional plugs for Caltech’s Quantum Frontiers blog. They publish posts by various members of the Institute for Quantum Information and Matter. Remarkably, the posts manage to exhibit considerable personality, rather than being perfunctory mentions of recent papers or talks. Much credit should go to Spiros Michalakis for getting the thing off the ground.

A lot of credit should also go to John Preskill, who is very well-known for his work in particle physics and quantum field theory as well as his second career as a quantum information. Who knew there was an entertaining blogger lurking inside the facade of a respectable scientist? (Third career?) John’s posts invariably manage to be enjoyable as well as informative. Now he’s put up a couple of hour-long videos, lectures that he gave at the 12th Canadian Summer School on Quantum Information. Two hours is a good length: enough time to actually convey useful information, without demanding the commitment of a full-semester course.

That’s the first video; click over for the second. And for an entertaining story about noisy hotel rooms and the exciting, thrill-a-minute life of the academic lecturer.