In 2012, a group of physicists at the University of California, Santa Barbara, proposed that an observer falling into a black hole would be destroyed by a firewall at the event horizon. If such a firewall existed, they argued, it would solve certain inconsistencies in black hole theory, but the idea sparked a heated debate among theoretical physicists: firewalls violate Einstein’s well-established equivalence principle, which says that an observer can’t distinguish between inertial motion and free fall and therefore shouldn’t be able to tell if he has passed the event horizon. This year, two of the original firewall proponents, have rekindled the debate. The authors developed a theoretical model to describe the interior of the black hole, suggesting an in-falling observer would encounter a sea of quanta of arbitrarily high energy, i.e., a “wall of fire.”

Correction (6 January 2014): Because of an editing error, the speed of light in “Light Stopped for One Minute” was written incorrectly.

Correction (7 January 2014): The location of the CDMS experiment in “Dark Matter is Still Obscure” was incorrect.