Interesting article. I remember very well the days that followed 911 during which all non-military aircraft over the continental US were ordered grounded. At the time, I was working as a commercial pilot, and I had returned home from a 7-day rotation on Sept 10th...
Where I reside in southern CT, there is a large volume of jet traffic high overhead - with arrivals/departures in/out of Boston and the New York Metroplex - and the silence that defined those already surreal days following 911 could only be described as eerie. I will never forget it, especially the silence at night.
What I found most interesting, was that nobody recognized or noticed this silence consciously, but if we were sitting around outside at night and I mentioned it, everybody would suddenly say, "Yeahhhh", as if their 'ears' were opened for the very first time.
Now, there is a new noise that can be occasionally heard from the skies - in the form of drones. Is this bad? It doesn't physically hurt the ears, but maybe it can ruin a quiet moment in a natural setting while sightseeing. I wonder though, will there ever come a day when the absence of that drone sound could only be described as eerie? I say yes, this technology has only just begun, and it is unstoppable, the direction it is going.