Hongwei Tan

A bathtub full of water is a simple thing. You fill it, the level holds, and then it slowly drains away. Entropy, the measure of disorder, behaves much the same way in a living organism over the course of a lifetime. First, in childhood and youth, the body puts things in order: cells divide, organs grow, entropy falls. In maturity, order holds on a plateau, like water sitting in the tub.

Gravitational waves from a tiny body falling into a black hole work like an X-ray image. Only instead of a bone, they illuminate the curved spacetime itself.