Sorry for belated delay. Other stuff going on.
Been digging through the literature and the physics of physical distancing. Looks like it only might made a small difference in interactions with family / close friends. Otherwise no basis in science.
First normal physical distancing during social interactions. With strangers > 1.2M. Acquaintances, 0.9M. Family / close friends 0.6M. This comes from studies of physicals distancing depending on culture and country.
SARs-CoV 2 has exactly the same infection transmission characteristics as Influenza A Virus. So IAV research applies to SARs CoV 2 transmission.
All research regarding airborne transmission seems to use airborne droplet density. Droplets with active viruses. Not qualified by active virus density per droplet. The generally accepted density of active droplet exposure of the upper respiratory system before there is a 50% probability of detectable infection is 10^3 droplets. Which equates to an air density of 10^4 droplets / m^3 in 10 mins. Or 10^5 in 1 min. Assuming typical respiratory intake rate of 10L per min.
Although a sneeze can generate 10^4 droplets, cough’s only around 10^2, when respiratory source aerosols are tested in real world environments somewhere between 80% and 95% seem to be from tidal respiration. Simple breathing. Not sneezes or coughs.
People with active infections can produce from 0 to 10^6 active droplets per min during normal respiration. But the median is around 10^2. Very small number of the 10^6 people. But they are the super-spreaders. Seems to be no correlation between strength of infection and number of active infectious droplets produced. Super-spreaders can only be identified post-facto.
The fall off of density of airborne repository droplets is around 70% at 1M and 80% and 2M. In still air. Add normal air circulation in any typically ventilated room or outdoor space and the difference is statistically meaningless.
So given that normal physical distancing between strangers is already more than 1M all officially “social distancing” policies are statistically meaningless. Zero effect for huge disruption.
If the R0 actually was 3 or 4 rather than 1.5 then crowded trains, buses, etc might be a problem. But public transit was not shut down in 2009 and there is no reason why it should be now.
In crowed situations surgical mask / cloth face masks give zero protection against airborne infectious droplets. Their purpose is to deflect the velocity out outgoing droplets. N95 or N99 masks do give meaningful protection. N95 good, N99 almost total if fitted correctly.
So for most people going about their day to day life if they actually want to reduce exposure in a meaningful way they should not bother with wearing a mask in public but should wear a N95 mask or better around friends and family. Thats the only form of social distancing that has any actual scientific basis. But given the actual risk profile opening the window or door or turning on a fan would have a far far bigger positive risk reduction effect…