Last April, in the midst of the pandemic's first wave, the jazz pianist Dan Tepfer was on a call with his friend Ben Wendel, a jazz saxophonist. Wendel had flown to Maui just before the lockdown, and now he was stuck there--not so terrible, except that he was desperate to play music with friends back in New York. He asked Tepfer, a self-taught coder, whether any technology existed that would let him play in real time with someone so far away. Tepfer, who lives in Brooklyn, did a quick calculation: Wendel was forty-nine hundred miles from New York; a flawless signal, travelling at the speed of light from Maui, would take twenty-six milliseconds to arrive. Studies showed that faster rhythms couldn't be coherently sustained with time lags longer than twenty milliseconds or so.