Imagine 3 days without internet worldwide. What would happen? Which sectors would be most affected?
If the internet goes down all over the world, first and foremost, you will lose access to your money for 72 hours, except for the cash you already have in your pocket
You will not be able to use your card at POS devices or at ATMs. This means that it will be difficult – at best – for large corporations and governments to access your assets.
In supply chains, stock and shipment status information will also become inaccessible almost everywhere, so the movement of these goods will stop or slow to a near standstill.
Healthcare would proceed at the most primitive level possible. Maybe you can stand in line at the hospital and see the doctor. It would be almost impossible to get an appointment, especially in the big cities, so you might wait until you are writhing in agony. After that, it becomes either impossible or very slow to buy medicines, and even if you get a diagnosis, it becomes impossible or very slow to access treatment.
Public transportation is largely sustainable. especially in train networks, if not 100%, then with secondary systems, with basic capacity. But road transportation becomes very dangerous, both because of difficult access to fuel and because of problems with traffic management systems. Not to mention airplanes. Ships will find their way, of course, but registering the transported goods at the port etc. will remain to be solved.
In this process, all online services have to deal not only with cost management but also with the problems of b2b users. (b2b: business-to-business marketing.)
In universities, the evaluation, experimentation and similar processes of academic studies, especially with computers, stop, and many of these studies that are not properly backed up, especially in cloud systems, may be lost.
Electricity, water and natural gas infrastructures will become inoperable as they will lose their intermediate stations, especially those with new generation systems. The capacities of the backup systems for these cannot reach one hundred percent efficiency again.
If you want to say “what the hell, I’ll read a book” in the midst of all this chaos, by all means do so.
At the end of 72 hours, even if the whole internet is suddenly back on its feet, everything will be slow for at least a few months, as every single job not recorded in that time (goods moved, services rendered, debts, receivables, newborns, relocated people, people who lost their lives, etc.) will be added back into the system.
The longer it takes, the greater the chaos. It doesn’t take much of a clairvoyant to predict this.