Two mathematicians have proved that a straightforward question—how hard is it to untie a knot?—has a complicated answer.

By constructing these so-called Einstein-Rosen caterpillar wormholes, researchers offer a tangible way to imagine what the inside of a typical black hole might look like. Rather than being smooth or ...

For obvious reasons, we do not know what the inside of a black hole looks like. But thanks to theoretical physics, we can ask ...