How the Black Hole Firewall Paradox Was Resolved

Stephen Hawking's recent comments about the nature of black holes have bred uncertainty about physics concepts that were relatively well understood. This article from astrophysicist Ethan Siegel explains that yes, black holes still exist, and how a group of three academic papers answered the black hole 'firewall' paradox. Quoting: "... And so what these three papers, in tandem, have done, is demonstrate that there is no firewall and that the resolution to the firewall paradox is that the first assumption, that Hawking radiation is in a pure state, is the one that's flawed. You won't read about this in the popular write-ups because it doesn't have a catchy headline, it's complex, and it's not work by someone that's already very famous for other work. But it's right. Hawking radiation is not in a pure state, and without that pure state, there's no firewall, and no paradox. There is still an incredible amount to learn and understand about black holes, event horizons, and the behavior of quantum systems in strongly curved spacetime, to be sure, and there's lots of very interesting research ahead. These findings arguably raise more questions than they answer, although at least we know that black holes won't fry you when you fall in; it will still be death by spaghettification, not by incineration!"

Comments

Complementarity

[Maritz]

It all depends where you're observing from.

If you're alice, falling through the black hole horizon, you see no horizon, and no firewall. It's a harmless point of no return. In a particularly large black hole say with a horizon the size of the solar system (this would have to be a super-galactic beastie) you could potentially live out your life in there before getting crushed by tidal forces.

If you're bob on the outside, it looks like alice slows down and gets increasingly red shifted. Alice moves asymptotically towards the horizon but never quite reaches it. Just getting slower and redder. Of course the reverse is also true, if alice looked back at bob she'd see him all sped up like keystone cops.

Because the light coming to you from the regime around alice is so red shifted, you conclude that it must be incredibly high energy/frequency down where alice is (the firewall)

The funny part is, if you send photons at alice hoping to reflect them back to yourself (to see if she's alright) - the photons have to be so energetic to make the return trip that you end up vapourising alice just as the firewall would have done.

This is the impression I get from reading Leonard Susskind's stuff, broadly taken to be black hole complementarity. Neither view is objectively more 'correct' than the other. We've accepted wave/particle duality so I don't really see how we can't have two pictures of what happens in a black hole.