Ultimately, PoW systems have to hit a scarce resource. If power became free, it'd change into a race for chips. If we figured out super cheap ways of making ch

Ultimately, PoW systems have to hit a scarce resource. If power became free, it'd change into a race for chips. If we figured out super cheap ways of making chips, the endless race would move to building factories or repurposing land for the whole system. It has to grow until it hits something hard to grow further. Security of the system depends on using so much resources all the time that an attacker can't waste resources any faster.