The question about firewalls is such a good one. In short, physicists identified this problem involving three parts of an evaporating black hole, and all three

The question about firewalls is such a good one. In short, physicists identified this problem involving three parts of an evaporating black hole, and all three seemed to be entangled according to the usual understanding, but that was bad because “entanglement is monogamous”, meaning that a system A can’t be “married” (maximally entangled) to system B and system C at the same time. So it was proposed that maybe spacetime just ends, just inside the event horizon, and so the metaphorical third wheel, system C, is killed off or actually just never existed. It’s not like anyone’s been inside a black hole and then came out to tell us if spacetime ends there. So that’s a firewall, and it was a hypothesis for how to resolve the non-monogamy issue. But it does require a bizarre new phenomenon where spacetime ends suddenly in a region of low curvature where nothing was supposed to happen. So many people did not like this idea. However, there was an alternative idea, which was that C was the “same person” as B, in which case its perfectly legal to be married to B and C at the same time. But B and C are really far apart, so that seemed weird. It would have to be that spacetime was joining these distant systems together via their entanglement. This was called ER=EPR, or roughly speaking the idea that the connectivity of space is defined by entanglement, so that these distantly separated systems B and C were actually connected via a very quantum sort of wormhole and thus were the same thing. This new work on the evaporation paradox, amazingly, makes it clear that at least in some cases, ER=EPR is actually happening in an unexpected but concrete way—in these models, there is the emergence of a spacetime bridge of the distant entangled systems. And that’s what’s so awesome. We always suspected the firewall paradox would prove something about what spacetime is, because it was a very sharp paradox. And now, in this unexpected and un-firewally way, it has!