Coronavirus PING!
Too late for a long response.
Masks and the particle scientists have been the subject of controversy for a long time. Many states rebelled against CDC guidance based on lab studies during the 2009 H1N1 pandemic.
The issue is: how many other factors besides penetration of a particle are involved in establishing an infection, and how to universal masks modulate those factors?
If one particle at any velocity arriving at the entrance to the nose caused an infection 100% of the time, then, masks would indeed be useless. This is, however, not the case.
Ordinary surgical or procedure masks are very effective for preventing influenza infections among bedside nurses caring for influenza patients, for example.
COVID has caused a lot of money to be sloshing around, and the particle scientists have not been left out. But their experimental conditions describe a worst case scenario which is not duplicated in the real world.