That's not where we are at right now. Physical systems are insecurely interconnected already. It is likely possible to interact with e.g. the electricity grid t

That's not where we are at right now. Physical systems are insecurely interconnected already. It is likely possible to interact with e.g. the electricity grid through currently publicly unknown exploits. Maybe exploiting this does not lie within the realm of possibilities of humans, but it may lie in the realm of a computer program called AI.