The very basis of this burning issue is the thing that makes black holes black - the event horizon. In its most basic form, the event horizon of a black hole is the point at which even light cannot escape the gravitational clutches of the massive black hole singularity. If light cannot escape, it stands to reason that it will appear as a black sphere in space. It is a cosmic one-way street: everything goes in, nothing comes out.
An Unlucky Astronaut
In the general relativity universe, for an astronaut who had the misfortune to fall toward a black hole, he or she wouldn't notice anything untoward as they passed across the event horizon. It would be a fairly peaceful event, no drama. "Although later on you're doomed and you'll encounter very strong gravitational forces that will pull you apart," noted Caltech physicist John Preskill at the 2013 Caltech event.
However, the quantum universe contradicts this "no drama" event horizon idea as predicted by general relativity.
In 2012, a group of physicists headed by Joseph Polchinski of the University of California in Santa Barbara revealed their finding that if black holes truly do not destroy information - a standpoint that Hawking himself reluctantly advocates - and that information can escape from the black hole through Hawking radiation, there must be a raging inferno just inside the event horizon they dub the "firewall."