Black holes break theories. These sites of extremely large masses in extremely small spaces invoke both of the behemoths of modern physics—general relativity (which rules over large masses) and quantum mechanics (which reigns in small spaces). But the two theories do not get along, and they break down in situations where both apply. For physicists, this is a good thing—it means black holes have revealed a flaw in our existing view of the universe, and offer fertile grounds to look for a solution.
The latest development in the quest for a better theory introduced firewalls—theoretical borders around black holes made of walls of high-energy particles. Firewalls are a radical departure from conventional thinking, which held that the borders of black holes—their so-called event horizons—were nothing special; simply continuous space where an invisible boundary marked the point of no return. Someone passing through one would have noticed nothing amiss. But if event horizons contain firewalls, space would not be continuous. It may, in fact, end altogether at the wall. And that hapless observer, rather than passing through unawares, would disintegrate immediately upon contact with the firewall.
One of the authors of the firewall idea, theoretical physicist Joseph Polchinski of the University of California, Santa Barbara, describes the concept thoroughly in Scientific American’s April cover story. Polchinski also took the time to chat with me and answer reader questions about firewalls in a recent Google Hangout video, here: