Bowen Fan

A doctor prescribes a pill for the heart and a pill for blood pressure. Individually, each helps, but together they can scramble signals in the blood and cause harm. These unwanted encounters between drugs are called interactions, and testing every pair in the lab is impossible: there are millions of them.

A tiny black hole flies through a hydrogen cloud and stretches atoms like taffy. That is what a superconductor looks like when it traps a persistent current: a material in which electricity flows without losses turns into a miniature permanent magnet.