It takes a special kind of personality to argue passionately about the nature of objects that are hundreds of trillions of miles away, impossible to see and impossible even to describe using the known laws of physics. And yet, in the woolly world of modern astrophysics, such personalities are not in short supply. Lately they’ve engaged in a full-on debate about the nature of black holes, with some of the most fundamental notions about these strange objects suddenly under attack. Despite what you saw in the movie Interstellar, black holes may not be black, and they may not be holes, either. Some theorists argue that the event horizon of a black hole — the boundary where light, matter and Matthew McConaughey vanish from our universe — is actually a brilliant, blistering inferno. Others propose that black holes are more properly described as “gray holes” with fuzzy, leaky outer boundaries. And a few agitators argue that the whole debate is off track because nature makes it impossible for black holes to form in the first place.
All of which might seem like so much theoretical navel-gazing, except that the debate over black holes is a proxy in a much grander battle. Right now, physics is split in two: Quantum mechanics describes small, fast phenomena while general relativity describes large, slow ones. But in the extreme conditions around a black hole, time and space get so stretched that the two theories are forced to overlap. Making sense of what happens at that intersection is crucial for developing a “theory of everything”— a unified set of physical laws that describe the entire cosmos, from the Big Bang to a Big Mac.
