Professor Stephen Hawking gave this very interesting and fun lecture at the University of Southern California College of Letters, Arts and Sciences in which he gives us a brief history of black holes and a way in which we might be theoretically able to travel through them. “If you feel you are in a black hole, don’t give up,” says Professor Hawking. Black holes are the remains of stars that have collapsed under their own gravity, producing gravitational forces so strong that even light can’t escape. Anything that falls inside is thought to be ripped apart by the massive gravity, never to been seen or heard from again. What you may not know is that physicists have been arguing for 40 years about what happens to the information about the physical state of those objects once they fall in. Quantum mechanics says that this information cannot be destroyed, but general relativity says it must be – that’s why this argument is known as the information paradox. Now Hawking says this information never makes it inside the black hole in the first place. “I propose that the information is stored not in the interior of the black hole as one might expect, but on its boundary, the event horizon,” The event horizon is the sphere around a black hole from inside which nothing can escape its clutches. Hawking is suggesting that the information about particles passing through is translated into a kind of hologram – a 2D description of a 3D object – that sits on the surface of the event horizon. “The idea is the super translations are a hologram of the ingoing particles,” he said. “Thus they contain all the information that would otherwise be lost.” In the 1970s Hawking introduced the concept of Hawking radiation – photons emitted by black holes due to quantum fluctuations. Originally he said that this radiation carried no information from inside the black hole, but in 2004 changed his mind and said it could be possible for information to get out. Just how that works is still a mystery, but Hawking now thinks he’s cracked it. His new theory is that Hawking radiation can pick up some of the information stored on the event horizon as it is emitted, providing a way for it to get out. But don’t expect to get a message from within, he said. “The information about incoming particles is returned, but in a chaotic and useless form. This resolves the information paradox. For all practical purposes, the information is lost.” Last year Hawking made headlines for saying “there are no black holes” – although what he actually meant was a little more complicated, as he proposed replacing the event horizon with a related concept, an apparent horizon. “The message of this lecture is that black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought,” Hawking said. “Things can get out of a black hole both on the outside and possibly come out in another universe.”