Yannis K. Semertzidis

A metal resonator, chilled to near absolute zero, listens to the radio noise of the universe. Amid the chaos of thermal fluctuations and electronics, a faint peak might emerge — the trace of an axion, a particle that could make up dark matter.

In the basement of the laboratory, an 8 tesla magnet hums. Inside it, like a bell in a bell tower, hangs a hollow copper cylinder tuned to a single note. If an axion, a dark matter particle, flies by, the cylinder responds with a faint ring. The trouble is that ordinary copper muffles this ring: at high frequencies, current flows only through a thin skin of the metal, and losses grow.

Picture a radio receiver with a single tuning knob that moves all of its internal coils at once, like one living organism. That is exactly how a new instrument for the search for the axion works, a particle that may fill galaxies with invisible mass. Inside a copper cylinder the height of a coffee can sit rods of aluminum oxide.

Picture yourself listening to a radio in the dead of night, hoping to catch the whisper of some distant station. Instead, all you get is the hiss of the ether. That is roughly how physicists listened for a signal from dark photons: 36 hours of silence, but that silence turned out to be worth more than any amount of noise. Dark photons are hypothetical particles thought to be possible constituents of dark matter.

An orchestra of a hundred violins plays in a vast hall. The conductor stands before them but cannot get the instruments to sound in unison: every bow moves at its own tempo, and the music crumbles into noise. The axion search problem looks much the same. These dark matter particles, thought to stream through us every second, turn into microwave photons only when the conditions line up with extreme precision.