{"id":11225,"date":"2013-06-05T10:55:27","date_gmt":"2013-06-05T17:55:27","guid":{"rendered":"http:\/\/www.preposterousuniverse.com\/blog\/?p=11225"},"modified":"2013-06-05T10:55:27","modified_gmt":"2013-06-05T17:55:27","slug":"firewalls-burning-brightly","status":"publish","type":"post","link":"https:\/\/preposterousuniverse.com\/blog\/2013\/06\/05\/firewalls-burning-brightly\/","title":{"rendered":"Firewalls, Burning Brightly"},"content":{"rendered":"

The firewall puzzle<\/a> is the claim that, if information is ultimately conserved as black holes evaporate via Hawking radiation, then an infalling observer sees a ferocious wall of high-energy radiation as they fall through the event horizon. This is contrary to everything we’ve ever believed about black holes based on classical and semi-classical reasoning, so if it’s true it’s kind of a big deal. <\/p>\n

The argument in favor of firewalls is based on everyone’s favorite spooky physical phenomenon, quantum entanglement. Think of a Hawking photon near the event horizon of a very old (mostly-evaporated) black hole, about to sneak out to the outside world. If there is no firewall, the quantum state near the horizon is (pretty close to) the vacuum, which is unique. Therefore, the outgoing photon will be completely entangled with a partner ingoing photon — the negative-energy guy who is ultimately responsible for the black hole losing mass. However, if information is conserved, that outgoing photon must also be entangled with the radiation that left the hole much earlier. This is a problem because quantum entanglement is “monogamous” — one photon can’t be maximally entangled with two other photons at the same time. (Awww.) The simplest way out, so the story goes, is to break the entanglement between the ingoing and outgoing photons, which means the state is not close to the vacuum. Poof: firewall.<\/p>\n

You folks read about this some time ago in a guest post by Joe Polchinski<\/a>, one of the authors (with Ahmed Almheiri, Don Marolf, and James Sully, thus “AMPS”) of the original paper<\/a>. I’m just updating now to let you know: almost a year later, the controversy has not gone away.<\/p>\n

You can read about some of the current state of play in An Apologia for Firewalls<\/a>, by the above authors plus Douglas Stanford. (Those of us with good Catholic educations understand that “apologia” means “defense,” not “apology.”) We also had a physics colloquium by Joe at Caltech last week, where he masterfully explained the basics of the black hole information paradox as well as the recent firewall brouhaha. Caltech is not very good at technology (don’t let the name fool you), so we don’t record our talks, but Joe did agree to put his slides up on the web, which you can now all enjoy. Aimed at physics students, so there might be an equation or two in there.<\/p>\n