Before this COVID-19 pandemic began, most people weren't concerned about the differences between "aerosols" and "droplets." Through those first few months (even before things got bad), we were told to wash our hands a lot, passing around plentiful memes of songs to sing to fill the 20 second recommended washing time. That was when it was largely believed that COVID spread through droplets which only tend to travel up to six feet before falling to the ground. Aerosols on the other hand, can linger in the air — which means handwashing won't help, and they stay around longer, though they be dispersed with the right ventilation.
This eventually turned out to be a life-or-death distinction, as well as a hugely embarrassing scientific SNAFU. Over at Wired, Megan Molteni has the fantastically reported story of how, exactly, so many scientists got this wrong, and what it took to change their minds. It has nothing to do with conspiracies, or corruption, or frankly, even scientists being bad at their jobs. It all goes back to a small, simple human error: learning things in school, and taking them for granted.
In this case, it all went back to some 1940s research into the spread of tuberculosis, and an early experiment that mistakenly drew the line between aerosols and droplets at 5 microns. By the 80s, the same person who had proposed this measurement had recognized that further research had proved him wrong, and that the threshold was probably more like 100 microns. But by that point, it was too late: somehow, the "5-micron myth" had taken hold in the minds of certain people, mostly in the field of public health, who had accepted it as a given fact and used it as a guiding principle for years.
And no one ever stopped to take a second look at the source of this factoid until the COVID-19 pandemic was already underway.
My summary doesn't do the whole story justice. It's worth reading it for yourself, to see just how deadly one small, sloppy human assumption can be.
The 60-Year-Old Scientific Screwup That Helped Covid Kill [Megan Molteni / Wired]
Image: Song Tang / Wikimedia Commons (CC-BY-SA 4.0)