Colliding Black Holes

It's notoriously difficult to model black holes on a computer. Computer simulations don't much like infinities, and black holes are defined by their infinite density. What's more, the flow of time literally stops at the event horizon—the point of no return surrounding the black hole—and computer simulations have trouble dealing with time that doesn't flow. (Don't we all?) Even getting the math into the machines in the first place is a challenge, since Einstein's equations use mathematical objects called tensors that don't easily translate into computer code. But scientists at the NASA Goddard Space Flight Center have found a way around these problems—unfortunately, the press release doesn't detail exactly how—and created a simulation of two black holes merging that doesn't crash their supercomputers. It also makes for a wicked-cool video. —Michael Moyer