B. Giaccone

Pluck a guitar string, and it vibrates — the air around it carries the tremor to your ear. Spacetime vibrates differently: when a gravitational wave passes through, it stretches and squeezes slightly. Spotting such a tremor at frequencies from 10 kilohertz to 100 megahertz is the challenge that new detectors are being built for.

A radio receiver hunting for dark matter is like a bell: it responds to only one note. The trouble is, nobody knows what note dark matter plays, so the bell needs to be retunable. Usually, a metal rod is inserted inside, but it creates extra noise.