Zhoujian Cao

Two giant black holes spiral together and collide — a ripple of spacetime spreads across the Universe. Detectors of gravitational waves catch this ripple. But the signal may hide more than just mass and distance: if the laws of physics differ ever so slightly in different directions, the wave will be distorted.

A figure skater glides on the ice, arms outstretched. If their path is nearly a perfect circle, describing the motion is straightforward. But when they race along a highly flattened oval, they almost freeze at the far edge and then zoom past the near edge at tremendous speed. That's roughly how two stars behave on a very elongated orbit.

The orchestra is playing, but the musicians can't hear each other: each follows their own tempo, while the conductor tries to weave the disparate sounds into a single melody.

A black hole is a place from which nothing can escape. But some theories allow that deep inside, at the quantum level, it might bounce and turn into its opposite — a white hole, which only spews out matter and light. A group of physicists built a computer model of such a transformation.

Two black holes, caught in a dance, spiral closer and closer until they merge into one. This dance is not silent: it shakes spacetime itself, sending gravitational waves rippling across the Universe. To understand what we hear in these waves, we need a precise mathematical model of the dance.