Catching the Shivers: How to Detect Ultra-High-Frequency Gravitational Waves express
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.
The key component is a superconducting radio-frequency cavity — a metallic 'resonator' where an electromagnetic field oscillates with remarkable stability. When a gravitational wave passes through the cavity, it alters the boundaries — by a tiny amount, mere fractions of an atomic nucleus's size. The field responds to this change, and the frequency shift reveals that a wave has arrived. But to catch such a whisper, you need silence: the cavity is cooled to 1.8 kelvin and shielded from seismic vibrations.
Such detectors will be placed at DESY and Fermilab. They will open a window into a range that LIGO and Virgo have never probed. If high-frequency gravitational waves exist, their sources could be exotic events, such as collisions of tiny black holes or processes in the early universe.
At 1.8 kelvin, superconducting cavities lose almost no energy: the field inside can 'ring' billions of times before fading away.
In Carl Sagan's novel 'Contact', an alien signal is caught using a network of radio telescopes; here, humanity tries to hear the very background hum of the universe.