Three hundred people are dancing to nothing, and the nothing is the most crowded part of the room. Look closer: the air between the dancers is not empty. It is thick with radio, a lattice of electromagnetic waves pouring from a transmitter, each headset a little copper antenna catching an oscillation that wobbles back and forth roughly a hundred million times per second.
That is what a silent disco actually is. A room flooded to the ceiling with invisible light, at a frequency your eyes happen not to be tuned to.
And the music itself, before it ever became radio, was pressure. A speaker cone shoving air molecules into each other, packing them tight and letting them spring apart, a wave of collisions racing outward at about 340 meters per second. In here that step is skipped. The song travels as pure field, silent until each headset converts it back into a membrane pushing against three tiny bones in the ear, bones we inherited from the jaw hinges of ancient reptiles, now repurposed to translate a pop chorus into a nerve signal.
Watch someone laugh and pull a headset off. Instant silence, and a hundred shuffling feet. Snap it back on: the beat returns, whole, undiminished, because the wave was there the entire time, passing straight through skulls and shoulders and the brick walls, filling the street outside, thinning as it goes but never quite ending.
That song is still traveling. It left the transmitter, leaked past the building, and is climbing away from Earth at the speed of light, a spherical shell of last Friday's dance track expanding forever into the dark.
Somewhere out past the Moon, right now, is the exact moment the bass dropped.