Read this sentence aloud: With every passing word, an expanding blast of spittle spews from your mouth—the more emphatic the speech, the greater the spray.

This mouth-made mist is the subject of a great debate about how the coronavirus hitches a ride from person to person. Virus-riddled globs can be inhaled, or even land in the eyes, potentially sparking infections in others. But for respiratory diseases like coronavirus, it’s long been thought these droplets are so large they will fall rapidly to the ground, inspiring public health recommendations such as cleaning surfaces and keeping six feet of social distance.

Other scientists, however, have become increasingly concerned that the novel coronavirus spreads through a more insidious route—as an airborne pathogen. Every sneeze, cough,